This document discusses heat transfer and thermal transport in lithium-ion battery cells. The key points are:
1) Thermal conduction within lithium-ion battery cells is dominated by the thermal contact resistance between the cathode and separator, which accounts for around 88% of the total thermal resistance.
2) Measured values of the thermal contact resistance between the cathode and separator agree with theoretical models that account for weak adhesion between the materials.
3) Chemically bridging the cathode-separator interface using an amine reduces the thermal contact resistance by 4 times without negatively impacting electrochemical performance, resulting in an expected 3-fold increase in effective thermal conductivity and 60% reduction in peak temperature rise.
This document summarizes an experiment to measure the out-of-plane thermal conductivity of flexible substrate materials like polyethylene naphthalate (PEN) and polyethylene teraphthalate (PET). A steady-state method is used where a heat flux is applied through one copper block in contact with the substrate, and the temperature difference across the substrate is measured. Thermal conductivity values are determined from the temperature differences and heat fluxes for substrates of varying thicknesses. The results indicate low thermal conductivity for flexible substrates, which could challenge thermal management in flexible electronics due to limited heat spreading and lack of active cooling options.
This document discusses waste heat recovery using thermoelectric generators. It begins by introducing the Seebeck effect which allows heat to be directly converted to electricity via a temperature gradient across conductors. The key factors for good thermoelectric materials - high Seebeck coefficient, electrical conductivity and low thermal conductivity - are discussed. Lead telluride is identified as a suitable high performance material for recovering waste heat between 200-600°C. A thermoelectric couple model is analyzed using ANSYS software, showing a voltage of 0.074806V, current of 19.083A and power of 1.4275W can be generated. The summary concludes the analysis demonstrates the potential of thermoelectric generation to recover low grade waste heat as
Performance Evaluation of Thermoelectric Materials: A Case Study of Orthorhom...inventionjournals
Designers often face the predicament of non-standardized and poor performing materials for thermoelectric module manufacturing. Other than analytical means, the only method to evaluate the performance of thermoelectric materials would be through experimental means. This work studies the experimental approach employed in performance investigation of thermoelectric materials using Orthorhombic SnSe crystals as a case study. The result obtained reveals the high thermoelectric conversion efficiency of orthorhombic crystals, and that they can operate as both low and high temperature thermoelectric material.
This study uses computational fluid dynamics software to model heat transfer in a water pipe as the fluid reaches supercritical conditions. The model considers both conductive heat transfer through the pipe walls and convective heat transfer from the fluid flow. Validation is performed against existing literature on supercritical water heat transfer in pipes. The results show that downward flow has the best heat transfer, while upward flow performance deteriorates and recovers over the length of the pipe due to buoyancy effects. Both improvement and deterioration of heat transfer are observed under different conditions.
Performance of water and diluted ethylene glycol as coolants for electronic c...IJERA Editor
As the number of transistors increases with new generation of microprocessor chips, the power draw and heat load to dissipate during operation increases. As a result of increasing the heat loads and heat fluxes the Conventional cooling technologies such as fan, heat sinks are unable to absorb and heat transfer excess heat dissipated by these new microprocessor. So, new technologies are needed to improve the heat removal capacity. In the present work single phase liquid cooling system with mini channel is analyzed and experimentally investigated. Mini channels are chosen as to provide higher heat transfer co-efficient than conventional channel. Copper pipes of 0.36 mm diameter are taken to fabricate heat sink and heat exchanger. A pump is used to circulate the fluid through heat sink and heat exchanger. A solid heated aluminium block to simulate heat generated electronic component is used and electrical input is supplied to the heated aluminium block and cooling system is placed over the heated block. The performance of the cooling system is analyzed from the experimental data obtained. It is experimentally observed that the mini channel liquid cooling system with water as a coolant has better performance than diluted ethylene glycol as coolant at different flow rates. The surface temperature of the heated aluminium block with convective heat transfer co-efficient is observed
Electric motor thermal analysis trade studyDon Blanchet
A thermal analysis was performed on a large 10 HP electric motor to estimate the maximum case temperature during operation at 70% efficiency. The analysis accounted for heat transfer through natural convection from exposed surfaces to the dirty ambient air environment, and conduction through the motor mounting plate. The results showed that using an aluminum housing instead of the baseline steel housing provided a considerable cooling advantage and lower operating temperatures.
The overall convection heat transfer coefficients for long horizontal rectangular fin
arrays are low because the surfaces in the inner region are poorly ventilated. In this
study, perforations through the fin base are introduced to improve ventilation with
cold air from below the fin base. Aluminum fin arrays with length L= 380mm, fin
height H = 38mm, fin thickness tf = 1mm, and fin spacing S = 10mm are analyzed
experimentally and numerically using ANSYS 14.0 so as to obtain the temperature
distribution along the fin height and fin length. In this work the fin array
configurations are tested experimentally with two different heater input as 50W and
65W. The heat transfer coefficient for fin array with perforations in fin base increased
by the enhancement factor of 1.49 and
1.42 as compared to fin array without perforation with 50W and 65W heater input
respectively. The heat transfer coefficient for the same fin configuration is also
increased with increase in heater input from 50W to 65W. Experimental and
numerical results for the temperature distribution show a difference of 5-9%. The
distribution of heat flux obtained with ANSYS 14.0 quantitatively follows the trend of
the same reported in the literature review.
This document summarizes a numerical study of heat transfer characteristics inside a bottom-heated square enclosure. Simulations were conducted for air and Al2O3-water nanofluid inside the enclosure as the conducting medium. Results showed that heat transfer rate, as measured by Nusselt number, increased with increasing hot wall temperature. For air, heat transfer occurred through bulk fluid motion, while for nanofluid it occurred through local interactions. However, nanofluids also exhibited bulk motion at higher temperatures. Isotherm and streamline patterns revealed higher heat transfer and more organized flow for nanofluids compared to air.
This document summarizes an experiment to measure the out-of-plane thermal conductivity of flexible substrate materials like polyethylene naphthalate (PEN) and polyethylene teraphthalate (PET). A steady-state method is used where a heat flux is applied through one copper block in contact with the substrate, and the temperature difference across the substrate is measured. Thermal conductivity values are determined from the temperature differences and heat fluxes for substrates of varying thicknesses. The results indicate low thermal conductivity for flexible substrates, which could challenge thermal management in flexible electronics due to limited heat spreading and lack of active cooling options.
This document discusses waste heat recovery using thermoelectric generators. It begins by introducing the Seebeck effect which allows heat to be directly converted to electricity via a temperature gradient across conductors. The key factors for good thermoelectric materials - high Seebeck coefficient, electrical conductivity and low thermal conductivity - are discussed. Lead telluride is identified as a suitable high performance material for recovering waste heat between 200-600°C. A thermoelectric couple model is analyzed using ANSYS software, showing a voltage of 0.074806V, current of 19.083A and power of 1.4275W can be generated. The summary concludes the analysis demonstrates the potential of thermoelectric generation to recover low grade waste heat as
Performance Evaluation of Thermoelectric Materials: A Case Study of Orthorhom...inventionjournals
Designers often face the predicament of non-standardized and poor performing materials for thermoelectric module manufacturing. Other than analytical means, the only method to evaluate the performance of thermoelectric materials would be through experimental means. This work studies the experimental approach employed in performance investigation of thermoelectric materials using Orthorhombic SnSe crystals as a case study. The result obtained reveals the high thermoelectric conversion efficiency of orthorhombic crystals, and that they can operate as both low and high temperature thermoelectric material.
This study uses computational fluid dynamics software to model heat transfer in a water pipe as the fluid reaches supercritical conditions. The model considers both conductive heat transfer through the pipe walls and convective heat transfer from the fluid flow. Validation is performed against existing literature on supercritical water heat transfer in pipes. The results show that downward flow has the best heat transfer, while upward flow performance deteriorates and recovers over the length of the pipe due to buoyancy effects. Both improvement and deterioration of heat transfer are observed under different conditions.
Performance of water and diluted ethylene glycol as coolants for electronic c...IJERA Editor
As the number of transistors increases with new generation of microprocessor chips, the power draw and heat load to dissipate during operation increases. As a result of increasing the heat loads and heat fluxes the Conventional cooling technologies such as fan, heat sinks are unable to absorb and heat transfer excess heat dissipated by these new microprocessor. So, new technologies are needed to improve the heat removal capacity. In the present work single phase liquid cooling system with mini channel is analyzed and experimentally investigated. Mini channels are chosen as to provide higher heat transfer co-efficient than conventional channel. Copper pipes of 0.36 mm diameter are taken to fabricate heat sink and heat exchanger. A pump is used to circulate the fluid through heat sink and heat exchanger. A solid heated aluminium block to simulate heat generated electronic component is used and electrical input is supplied to the heated aluminium block and cooling system is placed over the heated block. The performance of the cooling system is analyzed from the experimental data obtained. It is experimentally observed that the mini channel liquid cooling system with water as a coolant has better performance than diluted ethylene glycol as coolant at different flow rates. The surface temperature of the heated aluminium block with convective heat transfer co-efficient is observed
Electric motor thermal analysis trade studyDon Blanchet
A thermal analysis was performed on a large 10 HP electric motor to estimate the maximum case temperature during operation at 70% efficiency. The analysis accounted for heat transfer through natural convection from exposed surfaces to the dirty ambient air environment, and conduction through the motor mounting plate. The results showed that using an aluminum housing instead of the baseline steel housing provided a considerable cooling advantage and lower operating temperatures.
The overall convection heat transfer coefficients for long horizontal rectangular fin
arrays are low because the surfaces in the inner region are poorly ventilated. In this
study, perforations through the fin base are introduced to improve ventilation with
cold air from below the fin base. Aluminum fin arrays with length L= 380mm, fin
height H = 38mm, fin thickness tf = 1mm, and fin spacing S = 10mm are analyzed
experimentally and numerically using ANSYS 14.0 so as to obtain the temperature
distribution along the fin height and fin length. In this work the fin array
configurations are tested experimentally with two different heater input as 50W and
65W. The heat transfer coefficient for fin array with perforations in fin base increased
by the enhancement factor of 1.49 and
1.42 as compared to fin array without perforation with 50W and 65W heater input
respectively. The heat transfer coefficient for the same fin configuration is also
increased with increase in heater input from 50W to 65W. Experimental and
numerical results for the temperature distribution show a difference of 5-9%. The
distribution of heat flux obtained with ANSYS 14.0 quantitatively follows the trend of
the same reported in the literature review.
This document summarizes a numerical study of heat transfer characteristics inside a bottom-heated square enclosure. Simulations were conducted for air and Al2O3-water nanofluid inside the enclosure as the conducting medium. Results showed that heat transfer rate, as measured by Nusselt number, increased with increasing hot wall temperature. For air, heat transfer occurred through bulk fluid motion, while for nanofluid it occurred through local interactions. However, nanofluids also exhibited bulk motion at higher temperatures. Isotherm and streamline patterns revealed higher heat transfer and more organized flow for nanofluids compared to air.
Mr. Sankalp Kulshrestha is the guide for Dalvir Singh's M.Tech thesis on developing high ZT thermoelectric materials and modules. The objectives are: 1) Developing n-type Bi2Te3 and p-type Sb2Te3 materials for low temperature applications with high ZT values. 2) Demonstrating thermoelectric effect by combining the n-type and p-type materials. Bi2Te3 is synthesized using a solvothermal route and Sb2Te3 is also synthesized using solvothermal. ZT values are improved through nanostructuring approaches like adding BiTe to Bi2Te3 and PbTe to Sb2Te3
Thermal Simulations of an Electronic System using Ansys IcepakIJERA Editor
Present electronics industry component sizes are efficiently reducing to meet the product requirement with
compact size with greater performance in compact size products resulting in different problems from thermal
prospective to bring product better performance electrically and mechanically.
In this paper we will study how to overcome the thermal problem for a product which includes components
reliability and PCB performance by using CFD thermal simulation tool (Ansys Icepak).
Review on Thermoelectric materials and applicationsijsrd.com
In this paper thermoelectric materials are theoretically analyzed. The thermoelectric cooler device proposed here uses semiconductor material and uses current to transport energy (i.e., heat) from a cold source to a hot source via n- and p-type carriers. This device is fabricated by combining the standard n- and p-channel solid-state thermoelectric cooler with a two-element device inserted into each of the two channels to eliminate the solid-state thermal conductivity. The heat removed from the cold source is the energy difference, because of field emitted electrons from the n-type and p-type semiconductors. The cooling efficiency is operationally defined as where V is the anode bias voltage The cooling device here is shown to have an energy transport (i.e., heat) per electron of about500 me V depending on concentration and field while, in good thermoelectric coolers, it is about 50-60 me V at room temperature.
IRJET- Analysis of Solar Water Heating SystemIRJET Journal
This document summarizes a study that used computational fluid dynamics (CFD) software to analyze the thermal performance of flat plate solar water collectors with internal fins on riser pipes compared to collectors without fins. The CFD model simulated collectors from 10am to 3:30pm over half hour intervals at flow rates of 0.4, 0.5, and 0.6 kg/min. Results showed collectors with fins had higher heat transfer and 10-15% greater efficiency than plain tubes, with maximum efficiency at 0.4 kg/min flow rate. Experimental data validated the CFD results, showing temperature increases of 6-9°C for experiments and 7-11°C for CFD with fins, along with 9-
Experimental Investigations and Analysis of Thermoelectric Refrigerator with ...ijtsrd
As the conventional refrigeration system are large in size and consumes a lot of electrical energy which in terns leads to releases of more green house gases for production of electricity which is major environmental concern nowadays. Thermo electric refrigerators are compact and consume less electrical energy which supports use of renewable energy resources such as solar, tidal, wind power, etc. major applications of thermo electric refrigerator are in medical storage systems, blood tissue transfer and as a portable refrigerator. Harvind Yadav | Durgesh Srivastav | Gaurav Kumar | Amit Kumar Yadav | Akshay Goswami ""Experimental Investigations and Analysis of Thermoelectric Refrigerator with Multiple Peltier Modules"" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-3 , April 2019, URL: https://www.ijtsrd.com/papers/ijtsrd23332.pdf
Paper URL: https://www.ijtsrd.com/engineering/mechanical-engineering/23332/experimental-investigations-and-analysis-of-thermoelectric-refrigerator-with-multiple-peltier-modules/harvind-yadav
The Effects of Heat on Electronic ComponentsIJERA Editor
Regardless of the cause of overheating, the general and primary effect of overheating on an electronic component is damage. In this paper, the effects of excessive levels heat on different types of electronic components are explored and discussed. Take note that included in this discussion are the causes of overheating to better understand and appreciate the overheating phenomenon as it applies to electronic components, as well as electronic assemblies and electronic devices. Through a review of literature, especially studies and engineering reference materials, this paper found out that at the micro-level, overheating causes material degradation on or in a specific electronic component. This degradation is further caused by cracks, expansion, and other structural deformation. Note that this degradation is also caused by different changes in the physical and chemical properties of a specific material due to exposure to high levels of heat. At macro-level, the effects of overheating center on systems failure due to degradation of different constituents and components, causeeffect loop, and neighboring-effect. Both micro-level and macro-level effects of overheating on electronic components increase the health and safety risk of an entire electronic assembly and electronic device. Hence, through a review of literature, this paper also discusses the techniques or processes for preventing overheating or reducing the negative effects of excessive levels of heat.
The effect of magnetic field direction on thermoelectric and thermomagnetic c...Muhammid Al-Baghdadi
This document investigates the effect of magnetic field direction on thermoelectric and thermomagnetic coefficients of undoped single crystalline InSb at room temperature. It describes how samples of InSb were tested under varying magnetic fields and temperature gradients to measure the Seebeck and Nernst coefficients. The results showed that the Seebeck coefficient depended only on the temperature gradient, while the Nernst coefficient depended on both the temperature gradient and magnetic field. However, the values of the thermoelectric and thermomagnetic coefficients were found to be independent of the direction of the applied magnetic field with respect to the InSb sample surface.
This document summarizes research on cooling systems for high heat flux electronics. It discusses direct and indirect liquid cooling systems using single or two-phase flow. Direct systems use coolants like dielectric fluids in contact with chips, while indirect systems use a liquid loop and secondary refrigeration loop. Two-phase microchannel and spray cooling can remove over 800 W/cm2. Refrigeration systems maintain low chip temperatures below 125°C even at over 1000 W/cm2. Flow instabilities are a challenge, and active control methods are needed for transient applications. Advanced modeling and control strategies may enable effective cooling of future high-power electronics.
This document presents a heat response model for a phase layered topology in a photovoltaic thermal (PVT) system. The PVT system is constructed to maximize electrical energy generation through fast removal of heat from PV modules. A new phase layered topology uses combinations of aluminum plates and heatsinks to transfer heat from PV modules to a thermal container. The heat transfer through each layer is investigated with and without water as a coolant. Experimental results show the PV temperature is reduced by around 10 degrees Celsius with this system, which is critical for improving PV performance by reducing wasted thermal energy and increasing electrical energy conversion efficiency.
Design and optimization of cost-effective coldproof portable enclosures for p...IJECEIAES
Based on the International Electrotechnical Commission standards, the electronic devices in the industrial class (e.g., integrated circuits or batteries) can only operate at the ambient temperature between -40°C and 85°C. For the human-involved regions in Alaska, Northern Canada, and Antarctica, extreme cold condition as low as -55°C might affect sensing electronic devices utilized in the scientific or industrial applications. In this paper, we propose a design and optimization methodology for the selfheating portable enclosures, which can warm up the inner space from -55°C for encasing the low-cost industrial-class electronic devices instead of expensive military-class ones to work reliably within their allowed operating temperature limit. Among the other options, ceramic thermal resistors are selected as the heating elements inside the enclosure. The placement of the thermal resistors is studied with the aid of thermal modelling for the single heating device by using the curve fitting technique to achieve uniform temperature distribution within the enclosure. To maintain the inner temperature above -40°C but with the least power consumption from the thermal resistors, we have developed a control system based on the fuzzy logic controller. For validation, we have utilized COMSOL Multiphysics software and then one prototyped enclosure along with the fuzzy control system. Our experimental measurement exhibits its efficacy compared to the other design options.
This Application Note illustrates the use and advantages of dielectric heating, which as the name implies, is used for materials that are non-conducting. The essential advantage of dielectric heating is that the heat is generated within the material to be heated. In comparison with more conventional heating techniques (hot air, infrared, et cetera) in which the material is heated via the outer surface, dielectric heating is much more rapid. This is because electrical insulating materials, i.e. the domain of dielectric heating, are usually also poor conductors of heat.
Other interesting characteristics of radio frequency and microwave heating are the high power density and the potential for selectively heating materials. However, dielectric heating is a very expensive technique that cannot usually compete in cost terms with techniques such as resistance or infrared heating.
HEAT TRANSFER CO EFFICIENT VS HEAT FLOW RATE BY FORCED CONVECTIONTajammul Kamal
This document is a project report submitted by a student for their diploma in petrochemical engineering. It investigates heat transfer coefficients and heat flow rates through forced convection. Specifically, it looks at optimizing the design of heat sinks by considering factors like fin shape, thickness, spacing, and their effects on thermal resistance and heat dissipation. It provides background on previous related studies and the importance of heat transfer in applications like electronics cooling. The goal is to develop equations to determine the optimum specifications of fins in a heat sink based on parameters like the Biot number, heat transfer coefficient, and fin shape.
This document discusses electrical heating and its various applications. It begins with defining electrical heating as any process where electrical energy is converted to heat energy, based on the principle of Joule heating. Some key points made include:
- Electrical heating has domestic applications like room heaters, water heaters, and industrial uses like melting metals and plastic molding.
- Advantages over other heating methods include being clean, allowing for accurate temperature control, and having high efficiency.
- Heat transfer occurs via conduction, convection, or radiation.
- Classification includes power frequency heating, high frequency heating, and resistance heating both direct and indirect.
- Dielectric heating involves generating heat in non-conducting
Electric heating works by converting electrical energy to heat energy using the principle of Joule heating. When an electric current passes through a resistor, it produces heat due to I2R losses. There are various domestic and industrial applications of electric heating, including water heaters, ovens, welding, and heat treatment processes. Electric heating has advantages over other heating methods like being clean, allowing for accurate temperature control, and providing uniform heating. Resistance heating and dielectric heating are two common methods for electric heating. Resistance heating directly or indirectly heats an object by passing a current through it or a nearby resistive element. Dielectric heating generates heat in non-conductive materials using electromagnetic fields.
This document summarizes research on the electrical conductivity of wafer-bonded structures made of n-type InP and n-type GaAs with miscut substrates. It was found that increasing the relative misorientation between bonded substrate surfaces led to more non-ohmic behavior and higher interface resistance. Interfaces containing InP generally showed lower sensitivity to misorientation. The potential barrier height at the interface, as determined by a theoretical model, increased with greater relative misorientation. However, lattice mismatch between InP and GaAs did not significantly impact interface resistance. Further studies on bond resistance with respect to doping, pretreatment, and substrate miscut could help optimize the bond resistance for applications like wafer-bonded tandem solar cells.
1) Spherical ceria nanoparticles 18-25 nm in size were synthesized and dispersed in propylene glycol via ultrasonication to create stable ceria-propylene glycol nanofluids.
2) Thermal conductivity of the nanofluids increased with ceria concentration and temperature, showing up to an 18.8% enhancement over propylene glycol.
3) Viscosity of the 0.5 and 1 vol% nanofluids was lower than propylene glycol at temperatures below 80°C. Heat absorption of the nanofluids increased with ceria concentration in transient natural convection experiments.
This application note illustrates the use and advantages of dielectric heating, which as the name implies, is used for materials that are non-conducting. The essential advantage of dielectric heating is that the heat is generated within the material to be heated. In comparison with more conventional heating techniques (hot air, infrared, et cetera) in which the material is heated via the outer surface, dielectric heating is much more rapid. This is because electrical insulating materials, i.e. the domain of dielectric heating, are usually also poor conductors of heat.
Other interesting characteristics of radio frequency and microwave heating are the high power density and the potential for selectively heating materials. However, dielectric heating is an expensive technique and its application is generally limited to the heating of products with high added value, or to products that cannot be heated by other means.
Organic thermoelectric generators are a promising alternative to traditional inorganic thermoelectric materials. They offer advantages such as abundance, low weight, flexibility, low-cost solution processing and the potential for high thermoelectric figures of merit. Research has achieved a maximum figure of merit (ZT) of 0.42 for p-type and 0.2 for n-type organic materials. However, major challenges remain in reducing the large contact resistance between organic thermoelectric materials and device electrodes, which hinders power output. Further optimization of materials processing and device design is needed to realize the commercial potential of organic thermoelectric generators.
This document summarizes a research paper that analyzes the heat transfer characteristics of an induction furnace using finite element analysis. It begins with an introduction to induction heating processes and describes the basic components of an induction furnace. The researchers aim to computationally validate the modified composite wall thickness of an induction furnace using heat transfer analysis. The document reviews several other studies on induction heating simulations and experimental validations. It then outlines the thermal modeling approach using the heat diffusion equation and describes the boundary conditions for the finite element analysis.
Germanium-tin alloys were grown by molecular beam epitaxy and characterized. The tin content ranged from 4-20% atomic percent, lowering the bandgap energy by about 10 meV per percent tin. A sample with 12% tin exhibited a direct bandgap of 0.623 eV at 100K. Heterojunction diodes of p-GeSn/n-Ge showed nearly ideal rectifying characteristics with low turn-on voltage but increasing reverse dark current with higher tin content and temperature, attributed to the decreasing bandgap. The results indicate GeSn alloys have potential for future electronic and optoelectronic devices.
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive functioning. Exercise causes chemical changes in the brain that may help protect against mental illness and improve symptoms.
Mr. Sankalp Kulshrestha is the guide for Dalvir Singh's M.Tech thesis on developing high ZT thermoelectric materials and modules. The objectives are: 1) Developing n-type Bi2Te3 and p-type Sb2Te3 materials for low temperature applications with high ZT values. 2) Demonstrating thermoelectric effect by combining the n-type and p-type materials. Bi2Te3 is synthesized using a solvothermal route and Sb2Te3 is also synthesized using solvothermal. ZT values are improved through nanostructuring approaches like adding BiTe to Bi2Te3 and PbTe to Sb2Te3
Thermal Simulations of an Electronic System using Ansys IcepakIJERA Editor
Present electronics industry component sizes are efficiently reducing to meet the product requirement with
compact size with greater performance in compact size products resulting in different problems from thermal
prospective to bring product better performance electrically and mechanically.
In this paper we will study how to overcome the thermal problem for a product which includes components
reliability and PCB performance by using CFD thermal simulation tool (Ansys Icepak).
Review on Thermoelectric materials and applicationsijsrd.com
In this paper thermoelectric materials are theoretically analyzed. The thermoelectric cooler device proposed here uses semiconductor material and uses current to transport energy (i.e., heat) from a cold source to a hot source via n- and p-type carriers. This device is fabricated by combining the standard n- and p-channel solid-state thermoelectric cooler with a two-element device inserted into each of the two channels to eliminate the solid-state thermal conductivity. The heat removed from the cold source is the energy difference, because of field emitted electrons from the n-type and p-type semiconductors. The cooling efficiency is operationally defined as where V is the anode bias voltage The cooling device here is shown to have an energy transport (i.e., heat) per electron of about500 me V depending on concentration and field while, in good thermoelectric coolers, it is about 50-60 me V at room temperature.
IRJET- Analysis of Solar Water Heating SystemIRJET Journal
This document summarizes a study that used computational fluid dynamics (CFD) software to analyze the thermal performance of flat plate solar water collectors with internal fins on riser pipes compared to collectors without fins. The CFD model simulated collectors from 10am to 3:30pm over half hour intervals at flow rates of 0.4, 0.5, and 0.6 kg/min. Results showed collectors with fins had higher heat transfer and 10-15% greater efficiency than plain tubes, with maximum efficiency at 0.4 kg/min flow rate. Experimental data validated the CFD results, showing temperature increases of 6-9°C for experiments and 7-11°C for CFD with fins, along with 9-
Experimental Investigations and Analysis of Thermoelectric Refrigerator with ...ijtsrd
As the conventional refrigeration system are large in size and consumes a lot of electrical energy which in terns leads to releases of more green house gases for production of electricity which is major environmental concern nowadays. Thermo electric refrigerators are compact and consume less electrical energy which supports use of renewable energy resources such as solar, tidal, wind power, etc. major applications of thermo electric refrigerator are in medical storage systems, blood tissue transfer and as a portable refrigerator. Harvind Yadav | Durgesh Srivastav | Gaurav Kumar | Amit Kumar Yadav | Akshay Goswami ""Experimental Investigations and Analysis of Thermoelectric Refrigerator with Multiple Peltier Modules"" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-3 , April 2019, URL: https://www.ijtsrd.com/papers/ijtsrd23332.pdf
Paper URL: https://www.ijtsrd.com/engineering/mechanical-engineering/23332/experimental-investigations-and-analysis-of-thermoelectric-refrigerator-with-multiple-peltier-modules/harvind-yadav
The Effects of Heat on Electronic ComponentsIJERA Editor
Regardless of the cause of overheating, the general and primary effect of overheating on an electronic component is damage. In this paper, the effects of excessive levels heat on different types of electronic components are explored and discussed. Take note that included in this discussion are the causes of overheating to better understand and appreciate the overheating phenomenon as it applies to electronic components, as well as electronic assemblies and electronic devices. Through a review of literature, especially studies and engineering reference materials, this paper found out that at the micro-level, overheating causes material degradation on or in a specific electronic component. This degradation is further caused by cracks, expansion, and other structural deformation. Note that this degradation is also caused by different changes in the physical and chemical properties of a specific material due to exposure to high levels of heat. At macro-level, the effects of overheating center on systems failure due to degradation of different constituents and components, causeeffect loop, and neighboring-effect. Both micro-level and macro-level effects of overheating on electronic components increase the health and safety risk of an entire electronic assembly and electronic device. Hence, through a review of literature, this paper also discusses the techniques or processes for preventing overheating or reducing the negative effects of excessive levels of heat.
The effect of magnetic field direction on thermoelectric and thermomagnetic c...Muhammid Al-Baghdadi
This document investigates the effect of magnetic field direction on thermoelectric and thermomagnetic coefficients of undoped single crystalline InSb at room temperature. It describes how samples of InSb were tested under varying magnetic fields and temperature gradients to measure the Seebeck and Nernst coefficients. The results showed that the Seebeck coefficient depended only on the temperature gradient, while the Nernst coefficient depended on both the temperature gradient and magnetic field. However, the values of the thermoelectric and thermomagnetic coefficients were found to be independent of the direction of the applied magnetic field with respect to the InSb sample surface.
This document summarizes research on cooling systems for high heat flux electronics. It discusses direct and indirect liquid cooling systems using single or two-phase flow. Direct systems use coolants like dielectric fluids in contact with chips, while indirect systems use a liquid loop and secondary refrigeration loop. Two-phase microchannel and spray cooling can remove over 800 W/cm2. Refrigeration systems maintain low chip temperatures below 125°C even at over 1000 W/cm2. Flow instabilities are a challenge, and active control methods are needed for transient applications. Advanced modeling and control strategies may enable effective cooling of future high-power electronics.
This document presents a heat response model for a phase layered topology in a photovoltaic thermal (PVT) system. The PVT system is constructed to maximize electrical energy generation through fast removal of heat from PV modules. A new phase layered topology uses combinations of aluminum plates and heatsinks to transfer heat from PV modules to a thermal container. The heat transfer through each layer is investigated with and without water as a coolant. Experimental results show the PV temperature is reduced by around 10 degrees Celsius with this system, which is critical for improving PV performance by reducing wasted thermal energy and increasing electrical energy conversion efficiency.
Design and optimization of cost-effective coldproof portable enclosures for p...IJECEIAES
Based on the International Electrotechnical Commission standards, the electronic devices in the industrial class (e.g., integrated circuits or batteries) can only operate at the ambient temperature between -40°C and 85°C. For the human-involved regions in Alaska, Northern Canada, and Antarctica, extreme cold condition as low as -55°C might affect sensing electronic devices utilized in the scientific or industrial applications. In this paper, we propose a design and optimization methodology for the selfheating portable enclosures, which can warm up the inner space from -55°C for encasing the low-cost industrial-class electronic devices instead of expensive military-class ones to work reliably within their allowed operating temperature limit. Among the other options, ceramic thermal resistors are selected as the heating elements inside the enclosure. The placement of the thermal resistors is studied with the aid of thermal modelling for the single heating device by using the curve fitting technique to achieve uniform temperature distribution within the enclosure. To maintain the inner temperature above -40°C but with the least power consumption from the thermal resistors, we have developed a control system based on the fuzzy logic controller. For validation, we have utilized COMSOL Multiphysics software and then one prototyped enclosure along with the fuzzy control system. Our experimental measurement exhibits its efficacy compared to the other design options.
This Application Note illustrates the use and advantages of dielectric heating, which as the name implies, is used for materials that are non-conducting. The essential advantage of dielectric heating is that the heat is generated within the material to be heated. In comparison with more conventional heating techniques (hot air, infrared, et cetera) in which the material is heated via the outer surface, dielectric heating is much more rapid. This is because electrical insulating materials, i.e. the domain of dielectric heating, are usually also poor conductors of heat.
Other interesting characteristics of radio frequency and microwave heating are the high power density and the potential for selectively heating materials. However, dielectric heating is a very expensive technique that cannot usually compete in cost terms with techniques such as resistance or infrared heating.
HEAT TRANSFER CO EFFICIENT VS HEAT FLOW RATE BY FORCED CONVECTIONTajammul Kamal
This document is a project report submitted by a student for their diploma in petrochemical engineering. It investigates heat transfer coefficients and heat flow rates through forced convection. Specifically, it looks at optimizing the design of heat sinks by considering factors like fin shape, thickness, spacing, and their effects on thermal resistance and heat dissipation. It provides background on previous related studies and the importance of heat transfer in applications like electronics cooling. The goal is to develop equations to determine the optimum specifications of fins in a heat sink based on parameters like the Biot number, heat transfer coefficient, and fin shape.
This document discusses electrical heating and its various applications. It begins with defining electrical heating as any process where electrical energy is converted to heat energy, based on the principle of Joule heating. Some key points made include:
- Electrical heating has domestic applications like room heaters, water heaters, and industrial uses like melting metals and plastic molding.
- Advantages over other heating methods include being clean, allowing for accurate temperature control, and having high efficiency.
- Heat transfer occurs via conduction, convection, or radiation.
- Classification includes power frequency heating, high frequency heating, and resistance heating both direct and indirect.
- Dielectric heating involves generating heat in non-conducting
Electric heating works by converting electrical energy to heat energy using the principle of Joule heating. When an electric current passes through a resistor, it produces heat due to I2R losses. There are various domestic and industrial applications of electric heating, including water heaters, ovens, welding, and heat treatment processes. Electric heating has advantages over other heating methods like being clean, allowing for accurate temperature control, and providing uniform heating. Resistance heating and dielectric heating are two common methods for electric heating. Resistance heating directly or indirectly heats an object by passing a current through it or a nearby resistive element. Dielectric heating generates heat in non-conductive materials using electromagnetic fields.
This document summarizes research on the electrical conductivity of wafer-bonded structures made of n-type InP and n-type GaAs with miscut substrates. It was found that increasing the relative misorientation between bonded substrate surfaces led to more non-ohmic behavior and higher interface resistance. Interfaces containing InP generally showed lower sensitivity to misorientation. The potential barrier height at the interface, as determined by a theoretical model, increased with greater relative misorientation. However, lattice mismatch between InP and GaAs did not significantly impact interface resistance. Further studies on bond resistance with respect to doping, pretreatment, and substrate miscut could help optimize the bond resistance for applications like wafer-bonded tandem solar cells.
1) Spherical ceria nanoparticles 18-25 nm in size were synthesized and dispersed in propylene glycol via ultrasonication to create stable ceria-propylene glycol nanofluids.
2) Thermal conductivity of the nanofluids increased with ceria concentration and temperature, showing up to an 18.8% enhancement over propylene glycol.
3) Viscosity of the 0.5 and 1 vol% nanofluids was lower than propylene glycol at temperatures below 80°C. Heat absorption of the nanofluids increased with ceria concentration in transient natural convection experiments.
This application note illustrates the use and advantages of dielectric heating, which as the name implies, is used for materials that are non-conducting. The essential advantage of dielectric heating is that the heat is generated within the material to be heated. In comparison with more conventional heating techniques (hot air, infrared, et cetera) in which the material is heated via the outer surface, dielectric heating is much more rapid. This is because electrical insulating materials, i.e. the domain of dielectric heating, are usually also poor conductors of heat.
Other interesting characteristics of radio frequency and microwave heating are the high power density and the potential for selectively heating materials. However, dielectric heating is an expensive technique and its application is generally limited to the heating of products with high added value, or to products that cannot be heated by other means.
Organic thermoelectric generators are a promising alternative to traditional inorganic thermoelectric materials. They offer advantages such as abundance, low weight, flexibility, low-cost solution processing and the potential for high thermoelectric figures of merit. Research has achieved a maximum figure of merit (ZT) of 0.42 for p-type and 0.2 for n-type organic materials. However, major challenges remain in reducing the large contact resistance between organic thermoelectric materials and device electrodes, which hinders power output. Further optimization of materials processing and device design is needed to realize the commercial potential of organic thermoelectric generators.
This document summarizes a research paper that analyzes the heat transfer characteristics of an induction furnace using finite element analysis. It begins with an introduction to induction heating processes and describes the basic components of an induction furnace. The researchers aim to computationally validate the modified composite wall thickness of an induction furnace using heat transfer analysis. The document reviews several other studies on induction heating simulations and experimental validations. It then outlines the thermal modeling approach using the heat diffusion equation and describes the boundary conditions for the finite element analysis.
Germanium-tin alloys were grown by molecular beam epitaxy and characterized. The tin content ranged from 4-20% atomic percent, lowering the bandgap energy by about 10 meV per percent tin. A sample with 12% tin exhibited a direct bandgap of 0.623 eV at 100K. Heterojunction diodes of p-GeSn/n-Ge showed nearly ideal rectifying characteristics with low turn-on voltage but increasing reverse dark current with higher tin content and temperature, attributed to the decreasing bandgap. The results indicate GeSn alloys have potential for future electronic and optoelectronic devices.
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive functioning. Exercise causes chemical changes in the brain that may help protect against mental illness and improve symptoms.
Colorado Living and 1 day bath Berger PPT TemplateMatthew Colligan
Speed is the key to disruption according to the document. It discusses that the speed of iteration beats the quality of iteration, and that spending time optimizing processes and growing quickly is important. It also emphasizes that speeding up contact with customers, iterations of products and services, time to market for new offerings, and speed of customer service delivery are critical to being disruptive.
GMW_PowerPoint_Tracy Kearey_GC, ADL and PerthTracy Kearey
Tracy Kearey, a home loan broker, shares her positive experience participating in Global Money Week, an annual event that promotes financial literacy. She was inspired to get involved to help others avoid financial struggles. During her presentations to over 300 students, the students were engaged and asked insightful questions. The experience reinforced the importance of financial education and created positive awareness for her business through increased profile and connections in the community. Kearey encourages other brokers to get involved, as it positions them as socially responsible leaders while benefiting their business and communities.
Researchers generally see quantitative methods as very different to qualitative methods. However with modern analytics and the advent of ‘big data’ our insight approaches are undergoing a shift.
The numbers of data points and activity measured in a typical digital product is growing, providing increasingly rich and complete sets of insightful data. This gives us the information we need to understand what people are doing and more importantly, why they are doing it.
However researchers are not typically asked to get involved with the design of analytics measures. Digital teams are lacking skills on how to extract qualitative meaning from analytics, opting for traditional qualitative research approaches that are not fully integrated with their existing user-base.
We took the challenge on and built our first Big Data System bringing Quant and Qual together.
The document lists various building material products available from NBChino including Chino nano-PVC sheets with embossed, cross grain, and rose patterns. It also lists color glossy PVC sheets, narrow color glossy PVC, aluminum and wood corners, rigid PVC extrude profiles, and rigid PVC pipes. Each product is listed along with available colors and product codes.
This Facebook assignment proposes 5 creative advertising ideas for Tide detergent: 1) an "Imaginary Messes" campaign, 2) a series of "Tide Apologies" ads, 3) a campaign tying Tide To Go pens to the popularity of Pokemon Go, 4) an ad campaign upcycling empty Tide bottles into "Tide Keepsies" kettlebells, and 5) a "#TideTips" campaign sharing stain removal advice for outdoor activities.
The philosophy of co-founder profoundly relevant the growth, and always inspiring any stakeholders. You can see the case, Apple CEO, Steve Jobs is also no exceptional influencer. After the WWⅡ, highly sophisticated entreprenuers evolved, moreover founded Japanese fundamental. Whether we’ll be going or not, all in anybody’s hand with their death.
Omar Kamal Banat is an electrical engineer from Amman, Jordan with over 5 years of experience as an electrical technical and site engineer for projects such as the Saraya's W-Amman Hotel and Tower. He has a B.Sc. in Electrical Engineering from Hashemite University with honors and is proficient in AutoCAD, Ecodial, and Microsoft Office.
The document discusses research on suburbs and their built environments over time. It covers using historic business directories and maps to analyze how the structure and use of space in suburbs has changed. The talk will also discuss challenges in categorizing aspects of suburbs, like post offices, and how community maps can complement other research methods. The overall goals are to better understand the role of suburbs and inform policies by addressing gaps and encouraging cross-disciplinary discussions.
Functionality of Legal Litigation Team of Religare Finvest Ltd (NBFC) vis-a-v...Sahil Sharma
Religare Finvest Ltd is a non-banking financial company and subsidiary of Religare Enterprises Ltd. It provides loans to small and medium enterprises. The internship report discusses Religare Finvest's history and operations. It was originally incorporated in 1995 and provides loans for property, securities, corporate needs, commercial assets and SMEs. The report also summarizes information on Religare Enterprises Ltd, Religare Housing Development Finance Corporation Ltd and arbitration law in India.
Rundown de Programa de TV- Clase Taller AvanzadoMaria Perez
El documento presenta el guión de un programa de televisión de una hora que consta de 5 segmentos. El primer segmento incluye la apertura, introducción y un paquete sobre memes. Los segmentos 2 al 5 consisten en entrevistas, reportajes y cierres. El cronograma detalla la duración y fuentes de cada parte del programa.
From Mobile to Content First EngagementJustin Kirby
My presentation at FIPP London yesterday as part of their mobile strand that was billed as follows:
From Mobile to Content First Engagement: strategies for and examples of the best content-first, mobile-focused marketing campaigns in the world today
With a decline in advertising revenues and fears about the 'adblocalypse’ abound, branded content is being increasingly seen as a possible survival strategy by publishers. But is editorial-style content and its delivery through native advertising formats for brands enough to compete for consumers’ attention? We now live an increasingly skippable on demand world where mobile is becoming the first screen, particularly for the millennial audience who are consuming more video content than ever before. That’s why brands are looking at more innovative ways to engage audiences. Justin will explain how all marketing is now based around content and the different directions driving this - presenting inspiring examples and insights from global experts about how strategies are becoming content first and the role publishers can play in helping deliver this.
Dokumen tersebut memberikan informasi mengenai program-program jaminan sosial yang diselenggarakan oleh BPJS Ketenagakerjaan untuk pekerja penerima upah (PU) dan bukan penerima upah (BPU), meliputi Program Jaminan Kecelakaan Kerja (JKK), Jaminan Hari Tua (JHT), Jaminan Kematian (JKM), dan Jaminan Pensiun (JP). Dokumen juga menjelaskan manfaat, besaran iuran, dan ketentuan untuk masing-m
UX - From the tactical to the strategic. UX Brighton 2014Jason Ryan
This document discusses the importance of user experience (UX) strategy and its relationship to customer experience (CX). It provides guidance on developing a UX strategy, including:
1) Understanding customers and their journeys across all touchpoints of a brand from consideration to advocacy.
2) Using UX and CX methods strategically to align business goals with desired customer experiences.
3) Measuring the impact of UX initiatives on key metrics like engagement, advocacy, and customer lifetime value.
4) Developing a UX strategy is imperative now as customer expectations rise and digital transformation increases in all industries.
2011 _charge discharge simulation of an all-solid-state thin-film batteryMarshallSc1
The document describes a mathematical model of an all-solid-state thin-film lithium microbattery. The model is one-dimensional and considers lithium ion diffusion in the solid electrolyte and electrodes, as well as charge transfer kinetics at the interfaces. Model parameters are determined from experimental techniques like GITT and EIS for a commercial Li/LiPON/LiCoO2 microbattery. Simulation results agree well with charge/discharge curves, validating the model. The model can then be used to optimize design and predict performance under different conditions.
The present trend in the electronic packaging industry is to reduce the size and increase the performance of the equipment. As the power of these systems increases and the volume allowed diminishes, heat flux or density is spiraled. The cooling of modern electronic components is one of the prime areas for the application of thermal control techniques. Of the many thermal-cooling techniques, forced air-cooling being one such extensively used technique due to its simple design and easy availability of air. The present study is to design an air cooled high power electronic system to dissipate heat from selected electronic components.
Recent Trends in Bimetallic Oxides and Their Composites as Electrode Material...T Maiyalagan
This document summarizes recent progress in the development of bimetallic oxide materials for supercapacitor electrode applications. Bimetallic oxides have shown improved electrochemical performance compared to single metal oxides by combining the properties of two different metals in a single crystal structure. The performance of supercapacitor electrodes depends on factors such as the electrochemical behavior of the materials, electrolyte choice, and device potential window. Researchers are working to develop new nanomaterials with low cost, high stability, excellent electrochemical properties, and mechanical performance to enhance supercapacitor capacitance, power density, energy density and cycling life for applications such as electric vehicles.
Recent Trends in Bimetallic Oxides and Their Composites as Electrode Material...MaiyalaganT
There is a growing interest in supercapacitors as energy storage
systems due to their high specific power, fast charge/discharge
rates, and long cycling stability. Researchers have focused
recently on developing nanomaterials to enhance the capacitive
performance of supercapacitors. The inclusion of electroactive
components, such as transition metal oxides (TMOs), carbonbased
materials, and conducting polymers (CPs), is believed to
play an important role in improving the electrochemical
behavior of the electrode materials. Nevertheless, supercapacitors
containing TMOs, carbon-based materials, and CPs commonly
suffer from inferior ion-transport kinetics and poor
electronic conductivity, which can affect the rate capability and
cycling stability of the electrodes. Therefore, the development
of TMO/CP and TMO/carbon-based electrode materials has
gained widespread attention because they synergistically
combine the advantages of both materials, enabling revolutionary
applications in the electrochemical field. In general,
TMOs have given good performance as electrodes for supercapacitors
by further increasing the performance of the
electrode when two metal cations are introduced into a single
crystal structure. This Review describes and highlights recent
progress in the development of bimetallic oxides regarding
their design approach, configurations, and electrochemical
properties for supercapacitor applications, at the same time
providing new opportunities for future energy storage technologies.
In this paper, new thermal techniques for silicon-based thermoelectric materials were revealed as well as the characterisation processes involved in the manufacturing of silicon-based thermoelectric (TE) materials. The functionality of the silicon-based thermoelectric materials was emphasized in the course of writing this paper. The background, improvement & the physics of thermoelectric materials were examined.
Thermoelectric Refrigeration System Running On Solar Energypaperpublications3
Abstract: The global increasing demand for refrigeration in field of refrigeration, food preservation, storages, medical services, and cooling of electronic devices, led to production of more electricity and consequently more release of CO2 all over the world which it is contributing factor of global warming on climate change. With the increase awareness towards environmental degradation due to the production, use and disposal of Chloro Fluoro Carbons (CFCs) and Hydro Chlorofluorocarbons (HCFCs) as heat carrier fluids in conventional refrigeration and air conditioning systems. Thermoelectric refrigeration is new alternative because it can convert waste electricity into useful cooling, is expected to play an important role in today's energy challenges. It does not require working fluids or any moving parts, which is friendly to the environment and it simply uses electrons rather than refrigerants as a heat carrier. Continuous efforts are given by researchers for development of thermo electric materials with increase figure of merit may provide a potential commercial use of thermoelectric refrigeration system.
In this work it has been identified that there is enormous scope to develop TER system running on solar energy and its performance evaluation along with mathematical modeling. Mathematical results can be correlate by performing experimental test set up. Present paper especially focuses on evaluation of numbers of thermoelectric cooling module; heat sink fan assembly for each module which is used to increase heat dissipation rate and time required for attaining the cooling of heat sink fan assembly after a solar power is applied.
In tech polymer-based_nanodielectric_compositesMohsen Fayik
The document discusses polymer-based nanodielectric composites for applications requiring high energy density and high temperature dielectric materials. It describes how nanodielectric composites aim to leverage the high breakdown strength of polymers and high permittivity of ceramic fillers. The challenges of maintaining breakdown strength in multi-phase systems are discussed. Well-dispersed, low defect fillers and good particle-polymer interfaces are needed to prevent localized breakdowns. High-K ceramic or ferroelectric fillers could increase permittivity but require optimization to avoid decreasing breakdown strength.
The author and his students have investigated anomalous heat generation during carbon arcing done under saline water solutions using carbon electrodes. Energy balance calculations, indicate a marginal excess energy of up to 50 % with MS electrodes while with carbon electrodes output to input energy ratios are found to be as high as a factor of eight indicating excess heat up to 700%. We think that the anomalous excess energy could be due to some type of Low Energy Nuclear Reactions (LENR) but the nature of these reactions have not been studied by us so far. The carbon-electrode arc results on heat-accounting corroborate the mass-spectroscopic findings reported by BARC, Texas A & M University and other groups.
The document summarizes research on supercapacitor technology conducted by YUNASKO. It finds that:
1) The inner resistance and RC-constant of carbon-carbon supercapacitors can be reduced to a limit of 0.05 seconds through design improvements, allowing for power densities up to 200 kW/kg.
2) Operating temperatures up to 100°C and voltages up to 3V are achievable through new electrolyte formulations but limits energy density to 6-7 Wh/kg.
3) Hybrid devices combining battery and supercapacitor electrodes can substantially increase energy density to 50-60 Wh/kg while maintaining high power, though limiting cycle life to around 10,000 cycles.
An understanding of the electronic bipolar resistance switching behavior in C...IJRES Journal
In this study, TiO2 films and devices were prepared by sol-gel method. The bipolar resistive switching
phenomena was observed in the Cu/TiO2/ITO device. The conduction mechanism of devices were analyzed. It was
found that the conduction mechanism is dominated by space charge limited current in high resistance state, and
Schottky emission in low resistance state.
This paper presents the comparison temperature of thermoelectric (Tec1-12708) between the series circuit and parallel circuit by adjusting of water flow rate pump and electrical supplying to thermoelectric, The electrical voltage at 8,10 and 12 V, water flow rate in reservoir was 0.015 kg/s and 0.025 kg/s. Experiments perform were 6 hours. The result from the researches, thermoelectric with parallel circuit high temperature more than thermoelectric with series circuit. The parallel circuit of thermoelectric can work better than the series circuit in hot side. The different temperature hot side of parallel circuit with the electrical voltage at 8, 10 and 12 V water flow rate in reservoir was 0.015 kg/s temperature average is 22.44 oC, 22.90 oC, 29.86 oC, and water flow rate in reservoir was 0.025 kg/s temperature average is 20.67 oC, 26.66 oC, 27.69 oC. Thermoelectric with parallel circuit makes the higher temperature more than thermoelectric with series circuit about 33%, 37%, 44% water flow rate in reservoir was 0.015 kg/s and 30%, 40%, 41% water flow rate in reservoir was 0.025 kg/s.
The document discusses various characterization techniques used to analyze battery materials, including X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). XRD is used to verify crystal structure by analyzing diffraction patterns. TGA analyzes weight changes with temperature to measure thermal stability and composition. SEM provides high-resolution images of morphology and composition through backscattered electrons and EDX. These techniques are applied to characterize the synthesized sodium titanium phosphate (NaTi2(PO4)3) battery anode material.
This document discusses experiments on conduction and breakdown mechanisms in transformer oil. For conduction experiments, three stages were identified prior to breakdown for highly nonuniform fields: 1) a resistive current at low fields, 2) a "tunneling" mechanism leading to rapid current rise as field increases, and 3) current reaching space charge saturation at high fields, with an apparent mobility of 3 x 10-3 cm2 V s. Breakdown shows polarity dependence. Negative needle/plane breakdown voltage reduces 50% at hundreds of mtorr pressure, while positive needle reduces only 10%, indicating the breakdown mechanism does not have a strong gaseous component. Shadowgraphy and electrical measurements support a gas bubble model for cathode-initiated breakdown.
Potential enhancement of thermoelectric energy conversion in cobaltite superl...Anastasios Englezos
This document is a master's thesis submitted by Tasos Englezos investigating the potential enhancement of thermoelectric energy conversion in cobaltite oxide superlattices. The thesis aims to grow superlattices composed of alternating layers of NaxCoO3 and Ca3Co4O9 using pulsed laser deposition, as both materials show promise for thermoelectric applications but also have limitations. Characterization of the superlattices shows the structures maintain crystalline coherence while electrical and thermal properties are preserved at a good level. Further measurements of thermal conductivity are needed to determine if the superlattice approach reduces thermal conductivity and thereby improves thermoelectric efficiency in these cobaltite oxides.
This document provides an overview of thermoelectric cooling, including:
- Why thermoelectric coolers are used for applications requiring precise temperature control and no moving parts.
- The basic principles of the Peltier effect and semiconductor doping to create N-type and P-type materials.
- Key factors that determine thermoelectric performance like thermal and electrical conductivity.
- Common thermoelectric materials like Bi2Te3 and design considerations and methods.
- Applications of thermoelectric cooling in electronics, medical, aerospace and other industries.
Design and development of cooling system of battery in an electric two wheelerIRJET Journal
This document discusses the design and development of a cooling system for the battery in an electric two-wheeler. It begins with an introduction to electric vehicles and lithium-ion batteries, explaining that proper thermal management is needed to control the battery's temperature and maximize its performance and lifespan. The authors then describe their design process, which includes selecting appropriate materials, performing heat transfer calculations, and using CAD software to model fins on the battery casing. Finally, they analyze the battery casing both with and without fins using ANSYS Icepak software to evaluate the fins' ability to improve heat dissipation from the battery.
Modifying of li ni0.8co0.2o2 cathode material by chemical vapor deposition co...Alexander Decker
The document summarizes research on modifying the cathode material LiNi0.8Co0.2O2 by depositing thin ceramic oxide coatings via chemical vapor deposition to improve its thermal stability. Al2O3 and ZnO coatings were deposited. X-ray diffraction analysis showed the Al2O3 coating did not significantly change the material's structure, while the ZnO coating resulted in a new phase, likely a nickel-zinc compound. Electrochemical testing found the Al2O3-coated material had lower specific capacity in the first cycle but better capacity retention over subsequent cycles compared to the uncoated material. Differential scanning calorimetry also showed the Al2O3 coating reduced the exothermic reaction
Experimental Studies on Pool Boiling Heat Transfer Using Alumina and Graphene...IRJET Journal
This document presents an experimental study on pool boiling heat transfer using alumina and graphene oxide nanofluids. The study tested different concentrations of alumina and graphene oxide nanofluids to determine their effect on critical heat flux during pool boiling. Scanning electron microscope images showed that higher concentrations resulted in a porous nanoparticle layer forming on the heating surface, which significantly improved critical heat flux. Alumina nanofluids achieved up to 56.27% higher critical heat flux than distilled water, while graphene oxide nanofluids achieved up to 51% higher critical heat flux. The experimental results indicate that nanofluids have potential to enhance pool boiling heat transfer and critical heat flux.
Kill Cancer Tumour Cells using Radio-Frequency AblationIRJET Journal
This document summarizes a study on using radiofrequency ablation to kill cancer tumor cells. Radiofrequency ablation involves inserting an electrode rod into the tumor site and applying an electric current to generate heat. This causes temperatures above 45°C-50°C which is sufficient to kill tumor cells. The study uses computer modeling to analyze the electric potential, temperature distribution, and extent of killed tumor cells (necrotic tissue) generated over time by a cylindrical electrode rod placed in liver tissue. The results show that temperatures over 100°C can be achieved within 60 seconds, killing cancer cells within a radius of about 12mm from the electrode within 10 minutes of treatment. This minimally invasive technique shows promise for treating inoperable tumors.
2. high (for example, around 4 W for a 26650 cell undergoing 6C
discharge [6]), its poor thermal conductivity [7] results in large
temperature rise and thermal gradients within the cell [8,9],
leading, in extreme cases, to a thermal runaway situation [3,10]. In
order to maintain the cell temperature within safe limits, perfor-
mance is often sacrificed by operating the cell less aggressively than
it could be, overdesigning the battery pack and providing an elab-
orate external cooling system [5,11]. Each of these measures results
in reduced performance and reliability, and does not address the
root cause of inefficient thermal dissipation within the cell.
Despite the importance of thermal transport in Li-ion cells, a
fundamental understanding of underlying mechanisms is lacking.
While materials in a Li-ion cell are reasonably well-optimized for
electrochemical performance [12e14], relatively lesser research has
been carried out to measure, understand and optimize thermal
transport within the Li-ion cell materials. Our recent work showed
that thermal conduction within the cell is the dominant mechanism
in determining the overall thermal performance of the cell, as
opposed to heat transfer from outer surface of the cell [8,9]. Our
recent measurements on Li-ion cells indicated strong anisotropy in
thermal conduction, and a poor thermal conductivity of
0.15e0.20 W/mK in the direction normal to the electrodes [7]. This
value is as poor as that of typical polymers [15]. It is clearly impor-
tant to understand and improve the material-level origin of this
poor thermal conductivity. Thermal conductivity of typical elec-
trode and separator materials has been reported to be 2e5 W/m-K
[16e18] and 0.5e1.0 W/m-K [19e21] respectively. Other compo-
nents such as current collectors (copper or aluminum) and anode
(graphite) have even higher thermal conductivity. Using a simple
series resistance model that accounts for only material thermal
conductivities, the effective thermal conductivity of the thermal
unit cell in the direction normal to electrode surface is found to be
around 1.76 W/mK, about 8 times higher than the experimentally
measured cell-level thermal conductivity of 18650 and 26650 Li-ion
cells [7]. This suggests that thermal transport in a Li-ion cell may be
dominated by interface thermal resistance between materials rather
than thermal resistance of the materials themselves. This may be
occurring in a Li-ion cell because separator and electrodes are
merely pressed on to each other during cell manufacturing, which is
likely to result in poor surface adhesion and hence large thermal
contact resistance [22]. Dominance of thermal conduction processes
by interfacial thermal resistance is encountered in other micro-
systems as well, including microelectronics and micro-
electromechanical systems (MEMS) [23e25].
Fig. 1A shows a cut-out of a typical Li-ion cell, indicating the
spirally wound stack of electrodes, separator and current collectors.
While in-plane heat flow can occur along high thermal conductivity
materials, such as current collectors, heat flow in the out-of-plane
direction of the stack must conduct through each of these mate-
rials as well as through their interfaces before it can be convected
away from the outer surface of the cell. The thermal unit cell that
repeats itself in the direction normal to the electrode surface is
shown in Fig. 1B. The unit cell comprises multiple layers of anode,
cathode, separator and current collectors, and offers various mate-
rial and interfacial thermal resistances associated with these mate-
rials. Note that the anode/cathode materials are coated on both sides
of the current collectors. In order to improve cell-level thermal
performance, it is critical to measure the thermal resistances in this
unit cell, and identify and improve the dominant, rate-limiting steps
in the thermal conduction process in this unit cell.
In this paper, we show that thermal conduction within this
thermal unit cell is dominated by a large thermal contact resistance
(TCR) at the separator-cathode interface, contributing around 88%
of total thermal resistance and temperature rise. On the other hand,
TCR at the anode-separator interface is negligible. Our measured
TCR agrees with the recently reported [7] poor cell-level thermal
conductivity of Li-ion cells despite the large thermal conductivities
of constituent materials. We show that the large TCR is caused by
weak adhesion between the separator and cathode materials.
Dominance of the TCR shows that improving thermal conductivity
of electrode or separator is unlikely to result in significant
enhancement in overall thermal performance. We demonstrate 4X
improvement in TCR by chemically bridging the interface with
amine chemistry [23,26,27] without affecting electrochemical
performance of the cell. This improvement is expected to result in
more than 3X improvement in cell-level thermal conductivity and
60% reduction in peak temperature rise during cell operation at 7C
discharge rate. By identifying and alleviating the rate-limiting
process in thermal conduction in a Li-ion cell, this work provides
the technological basis for significantly reducing the overheating
problem in Li-ion cells, resulting in improved performance, safety
and reliability.
2. Experimental methods
2.1. Electrode and separator sample preparation
Positive electrode (LiCoO2) and separator are extracted from
26650 commercial Li-ion batteries. The cell is first discharged
completely. The metal casing enclosing the spirally-wound elec-
trodes and separator is opened in a laminar flow fume hood.
Separator and positive electrode are peeled off carefully from the
separatoreelectrode stack. All experiments are carried out on these
materials extracted from a 26650 cell, and not on the 26650 cell
Fig. 1. Thermal transport in the spiral geometry of a Li-ion cell: (A) Image of the spiral geometry of the electrode-separator roll extracted from a prismatic Li-ion cell; (B) Basic
thermal unit cell that repeats itself in the direction normal to the electrode surface, and comprises of various material and interfacial thermal resistances; (C) Thermal resistances in
the cathode-side half-cell considered in this work.
V. Vishwakarma et al. / Journal of Power Sources 300 (2015) 123e131124
3. itself.
2.2. Thermal measurements
Total thermal resistance across a material stack is determined by
sandwiching the stack between two identical copper blocks [28].
Fig. 2 shows a schematic of the experimental setup. A picture is also
shown in the inset in Fig. 3. The faces of the copper blocks are
polished, first with a 120 grit sandpaper belt on a LECO BG-30
polisher, and then with a 1200 grit sandpaper embedded with
0.05 mm alumina microparticles on LECO Vp-150 polisher. In one of
the blocks, heat is generated using a thin Kapton heater affixed on
one of the faces. Heat is removed from the other block using cooling
water from a chiller passing through a 1 mm diameter through-
hole drilled close to one of the faces. Temperature measurement
is carried out using T-type thermocouples inserted in seven holes of
1.0 mm diameter in each block. The holes are spaced closer to each
other near the surfaces contacting the material stack for greater
accuracy near the stack. Holes are drilled in the horizontal plane,
which minimizes heat loss down the thermocouple wires. High
temperature thermal cement is used to ensure good thermal con-
tact between thermocouple tips and the copper block. The copper
blocks are then insulated on all faces except the ones contacting the
material stack to minimize stray heat losses. Kapton heater
attached to the top block is electrically heated using a power
source. Since the electrical resistance of the heater does not vary
appreciably in the temperature range of interest, it serves as a
source of constant heat flux throughout the experiment. A Keithley
2100 digital multimeter is used to monitor voltage across the
heater. Thermocouple temperature measurements are recorded
using a National Instruments 9213 DAQ and LabView software with
1 Hz frequency. The experiment continues until steady state is
reached. Steady-state temperature measurements from embedded
thermocouples are extrapolated to determine the temperature
drop across the sample. Heat flux passing through the blocks is
determined from the slope of the temperature curve in the copper
blocks. Total thermal resistance of the material stack is determined
from the ratio of temperature drop and heat flux.
2.3. Electrochemical testing
A split flat cell with active area of 2.54 cm2
from MTI Corp. is
employed for electrochemical testing. The baseline and surface-
modified cathodes, together with commercial Celgard 2500 sepa-
rators extracted from a 26650 cell as described in Section 2.1 and
standard lithium anodes are used as cell components. During as-
sembly of the cell in a controlled atmosphere glove box, additional
home-made 1.0 M LiPF6 in mixed solvents of ethylene carbonate
(EC)-dimethyl carbonate (DMC) (1:1 by volume) is added to
compensate for electrolyte loss. After being kept at rest for 24 h, the
cell is first charged at 1.5 mA (roughly corresponding to a rate of
0.33C) until the voltage reached 4.0 V, then was held at a constant
voltage of 4.0 V for 30 min, followed by a second period of rest for
20 min. After that, the cell is discharged at 1.5 mA until the voltage
dropped below 2.5 V. EIS experiments are conducted over a fre-
quency range from 0.1 mHz to 100 MHz at open circuit with an
amplitude of 10 mV while the cells are fully discharged. Both bat-
tery performance and EIS tests are performed on a Parstat 2273
potentiostat/galvanostat.
Fig. 2. Schematics of three steady state temperature gradient based experiments. A (a) separator-electrode stack (Experiment 1), (b) single separator (Experiment 2), and (c) single
cathode foil (Experiment 3) was placed between two copper blocks to determine various material and interface thermal resistances through measurement of total thermal
resistance.
Fig. 3. Measured temperature data from various thermocouples embedded in the
copper blocks for Experiment 1. Extrapolated temperature difference determines
temperature drop across the sample under test, and slope of the plot determines the
heat flux. This results in measurement of total thermal resistance.
V. Vishwakarma et al. / Journal of Power Sources 300 (2015) 123e131 125
4. 2.4. Surface modification
In order to enhance interfacial thermal conductance, surface
modification is carried out on both cathode and separator surfaces.
The separator is subjected to oxygen plasma in Micro-RIE Series
800 Plasma System for 5e10 min at 30mTorr. Surface modification
of cathode is carried out using amine chemistry [27]. Extracted
cathode sample, after wash and dry is immersed into a 2% v/v so-
lution of (3-Aminopropyl)triethoxysilane in ethanol, and left for
incubation for 30 min in room temperature. This forms an amine
self-assembled amine monolayer (SAM).
3. Theoretical modeling for electrode-separator TCR
Multiple features of the cathode-separator interface must be
accounted for in determining the interfacial thermal contact
resistance: a) Large acoustic mismatch between cathode and
separator, b) Weak adhesion between cathode and separator, c)
Large porosity of separator resulting in reduction in effective area of
contact, and, d) Further reduction in area of contact [29], due to the
fibrous nature of the separator (~1 mm fiber diameter) [30]. The
baseline contact conductance per unit area (g) between two ma-
terial surfaces is given by [31].
g ¼ G$
c$v
2
(1)
where G is the integrated phonon transmissivity, c the specific heat
for polyethylene and v is the speed of phonons in polyethylene.
Since the phonon speed is smaller in polyethylene, conductance
must be calculated from the polyethyelene side, wherein G is in-
tegrated till the critical angle. The conductance shown in equation
(1) is valid only for interface between two flat substrates. This
conductance is scaled to account for porosity and non-flat nature of
the substrate. The effective thermal contact conductance is thus
given by
g ¼
a
R
$f$G$
c$v
2
(2)
where f is the porosity, a is the contact width and R is the radius of
the fiber. a is computed using the well-known Johnson-Kendall-
Roberts adhesion mechanics model [32] for cylinders [33]. R is
assumed to be 1 mm in these calculations (typical radius of fibers in
the separator [34]). Porosity is assumed to be 50%.
Note that critical angle of refraction for LiCoO2 and Polyethylene
interface is very low due to large mismatch in phonon speed, which
is expected to result in very high interface resistance. On the other
hand, the critical angle between graphite (anode) and polyethylene
is much larger as the phonon speeds are much closer. Therefore, the
contact conductance is expected to be much higher for this inter-
face compared to LiCoO2/Polyethylene interface.
4. Results and discussion
4.1. TCR measurement
The thermal unit cell shown in Fig. 1B comprises of two half-
cells, one each on the anode and cathode sides. The material
thermal resistances in the two half-cells are expected to be similar
to each other, due to the relatively similar values of thermal con-
ductivity of anode and cathode materials [16e18,35]. However,
theoretical modeling results discussed in section 4.2 show that
thermal contact resistance between anode and separator, Rsep-anode
is two orders of magnitude lower than thermal contact resistance
between cathode and separator, Rsep-cathode. As a result, the overall
thermal conductivity of the entire unit cell is expected to be
dominated by the thermal resistance of the cathode-side half-cell.
Consequently, we focus on measurement and reduction of total
thermal resistance of the cathode half-cell, shown in Fig. 1B. The
total thermal resistance of the cathode half-cell is given by
Rtotal ¼
Lsep
ksep
þ 2$RsepÀcathode þ
Lcathode
kcathode
þ
Lcc
kcc
þ 2$RcathodeÀcc (3)
where subscripts sep and cc refer to the separator and current
collector respectively, L and k are thickness and thermal conduc-
tivity respectively. Rsep-cathode and Rcathode-cc refer to the thermal
contact resistances at the separator-cathode and cathode-current
collector interfaces respectively. Note that Rsep-cathode must be
considered twice due to two cathode-separator interfaces in the
unit cell.
We have neglected the contribution of the electrolyte to thermal
transport. To verify this assumption, we carried out cell-level mea-
surements on commercial 18650 and 26650 Li-ion cells [7], which
included electrolyte inside the cell. Our cell level thermal conduc-
tivity with electrolyte matched closely with thermal conductivity
determined from material-level measurements reported here.
Within the various thermal resistances shown in equation (3),
Lcc/kcc is expected to be very small (estimated 0.05e0.1 mKm2
/W)
due to the large thermal conductivity of current collector e typi-
cally made of copper or aluminum. Further, since the cathode
material is coated directly on to the current collector foil, therefore,
the two are in intimate thermal contact, with negligible thermal
contact resistance compared to the interface between separator
and cathode, which are merely pressed on to each other during cell
manufacturing. As a result, the three dominant thermal resistances
in this half-cell are expected to be the material resistance through
cathode, material resistance through separator, and thermal con-
tact resistance between cathode and separator (Fig. 1C).
We carry out a series of measurements based on one-
dimensional, steady-state, out-of-plane thermal conduction to
determine these thermal resistances. In experiment 1, a separator-
electrode stack is sandwiched between two copper blocks (Fig. 2A).
One of the blocks is heated using a Kapton heater, and the other is
cooled using water flow, resulting in the setting up of linear one-
dimensional heat flow through the sandwiched material. Fig. 3
shows the steady-state temperature distribution measured using
thermocouples for Experiment 1. Supplementary Figure S1 shows
temperature measurement from one of the thermocouples as a
function of time. Only steady-state measurements are used here,
since at steady-state, all of the heat passing through the top copper
block conducts across the sample. Total thermal resistance, Rtotal
through the separator-electrode stack is determined by extrapo-
lating these temperature measurements and dividing by the heat
flux flowing through the stack. In this case, the total thermal
resistance is given by
Rtotal ¼ RCuÀsep þ
Lsep
ksep
þ RCuÀcathode þ
Lcathode
kcathode
þ RsepÀcathode (4)
where, as noted prior, thermal resistance through the current col-
lector and the cathode-current collector interface is negligibly
small.
Thermal conductivities of cathode and separator materials have
been measured in the past [16e19]. Based on a value of 0.5 W/mK
for the separator thermal conductivity reported by two of the co-
authors [19], the material thermal resistance for the separator is
found to be Lsep/ksep ¼ 50 mKm2
/W. Based on thermal measure-
ments on various cathode materials [16e18], the cathode thermal
conductivity is assumed to be 5.4 W/mK. As a result, the material
V. Vishwakarma et al. / Journal of Power Sources 300 (2015) 123e131126
5. thermal resistance of the cathode is around 11 mKm2
/W, which is
even lower than the thermal resistance of the separator.
In contrast to material thermal resistances, the thermal contact
resistances appearing in equation (4) are largely unknown. While
RCu-sep and RCu-cathode occur due to the experimental setup, Rsep-
cathode is intrinsic to the Li-ion material stack. We carry out two sets
of experiments, shown in Fig. 2B and C to determine these thermal
contact resistances.
In order to determine, RCu-sep, the contact resistance between
copper block and separator, the total thermal resistance across a
single separator sample sandwiched between copper blocks is
measured (Experiment 2, shown in Fig. 2B). Since there are two
interfaces between copper and separator, the total resistance in this
case is given by
Rtotal ¼ 2RCuÀsep þ
Lsep
ksep
(5)
Measurement of Rtotal, together with the material thermal
resistance of the separator based on prior measurements, results in
RCu-sep ¼ 625 mKm2
/W from equation (5).
In Experiment 3, a cathode sample coated on both sides of a
current collector is sandwiched between the copper blocks
(Fig. 2C). In this case, the total thermal resistance is given by
Rtotal ¼ 2$RCuÀcathode þ
Lcathode
kcathode
(6)
where, similar to Experiment 1, we neglect the thermal resistance
due to the current collector and the thermal contact resistance
between cathode and current collector.
Using recently reported values for thermal conductivity of the
cathode [16e18] together with measurement of Rtotal for Experi-
ment 3, we determine the thermal contact resistance RCu-cathode to
be 345 mKm2
/W.
Experiments 2 and 3 provide two of the thermal contact re-
sistances appearing in equation (4), leaving only the thermal con-
tact resistance between separator and cathode as an unknown.
Thus, a measurement of the total thermal resistance of the
separator-cathode stack in Experiment 1 can be used to determine
Rsep-cathode. This value is found to be 420 mKm2
/W, which is much
larger than the material resistances due to separator and cathode.
These experiments provide measurements of all thermal re-
sistances involved in the cathode-side half-cell shown in Fig. 1B.
Left side of Fig. 4 summarizes the contributions of these thermal
resistance terms to total thermal resistance, as well as the effective
thermal conductivity of the unit cell. Note that the interface ther-
mal resistance Rsep-cathode must be accounted for twice since there
are two separator-cathode interfaces in the unit cell. In addition,
the unit cell also comprises two separator layers. Our measure-
ments indicate that thermal contact resistance between separator
and cathode dominates the thermal conduction process, account-
ing for around 88% of the total thermal resistance of the unit cell.
Consequently, material-level optimization of thermal transport in a
Li-ion cell must focus on this rate-limiting process by improving
thermal contact between these two materials. Merely improving
material thermal conductivities of separator and/or electrodes
without addressing conduction through the interface [37] is un-
likely to result in significantly improved overall thermal perfor-
mance. For example, doubling the separator or cathode thermal
conductivity results in only 4.4% and 0.5% reduction in total thermal
resistance respectively. It is imperative, instead, to improve the
thermal contact resistance between cathode and separator.
4.2. Theoretical modeling results
Material properties used for the calculation of thermal contact
resistance are listed in Table 1. The baseline thermal contact resis-
tance calculated using Acoustic Mismatch Model (AMM) [36] based
on properties of the cathode and separator is 1.1 mKm2
/W. We ac-
count for the other effects listed in section 3 through the following
analysis: we assume that the separator is in contact with the
cathode through weak van der Waals adhesion due to the two
being merely pressed against each other during the Li-ion cell
manufacturing process. One of the co-authors has shown [31] that
weak adhesion leads to dramatic reduction in transmissivity of
phonons at the interface leading to high interface resistance. For
van der Waals adhesion, the adhesion energy is around 50 mJ/m2
[34]. The transmissivity of phonons for this adhesion energy is
10e20 times lower than that of AMM [32] computed for a strongly
bonded interface. Accounting for this effect results in thermal
contact resistance in the range of 11e22 mKm2
/W. Furthermore,
assuming 50% porous separator [12], the expected thermal contact
resistance increases to 22e44 mKm2
/W. Finally, since the separator
is made of polymer fibers only the deformed part of the fiber due to
adhesive forces participates in heat transfer [29]. This deformed
part effectively creates a nano-constriction through which heat
must conduct. The area of the deformed part is calculated using
Johnson-Kendall-Roberts theory [32] for cylinders [33]. Based on
the properties of polypropylene, the ratio of width of this
constriction and radius of the fiber is 0.084, i.e. the effective contact
Fig. 4. Summary of material-level thermal resistances in thermal unit cell of a Li-ion cell in baseline (Experiment A) and enhanced experiments (Experiment D). Colorbars show
relative magnitudes of various resistances. Note that resistances due to the separator-cathode interface and separator must be counted twice in determining the total thermal
resistance of the unit cell. keff refers to the effective thermal conductivity of the unit cell, including interface thermal resistances. The materials and surface modifications for
Experiments A and D are discussed in Fig. 5. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
V. Vishwakarma et al. / Journal of Power Sources 300 (2015) 123e131 127
6. resistance increases by a factor of 1/0.084 ¼ 11.85. Using this
number, the thermal contact resistance between cathode and
separator is found to be in the range of 260e520 mKm2
/W which
agrees well with experimental measurements discussed in section
4.1. On the other hand, due to much larger critical angle between
anode and separator compared to the cathode-separator interface,
the thermal contact resistance between anode and separator is
found to be in the range of 2e4 mKm2
/W, which represents around
two orders of magnitude lower thermal contact ‘resistance’ than
the cathodeeseparator interface. This shows that the anode-
separator interface plays an insignificant role in determining
overall thermal performance of the unit cell.
4.3. TCR enhancement
In order to improve thermal dissipation in a Li-ion cell by
reducing the dominant thermal contact resistance, we carry out
experiments to investigate improved thermal adhesion between
the separator and cathode through surface treatment. This is
motivated by past work by one of the co-authors [23] in which
improved adhesion between surfaces using chemical surface
modification led to significant decrease in thermal contact resis-
tance [23]. It is well known that thermal contact resistance is
correlated with surface adhesion energy [22,23], which is the
lowest for van der Waals based adhesion, and can be improved
through chemically bridging the interface. Three experiments are
carried out as illustrated in Fig. 5. Our experiments are based on a
self-assembled monolayer of amine groups on the cathode surface,
and plasma treatment of the separator. Amine groups are
commonly used for functionalizing glass surfaces with DNA and
other biomolecules [26,27]. Plasma treatment of the separator is
motivated by well-known enhancement of surface adhesion of
polymers and other materials caused by plasma treatment [38,39].
Four experiments that combine surface modification with plasma
treatment, as shown schematically in Fig. 5 are carried out.
Experiment A is the baseline case. In Experiments B and C, surface
modification of cathode and plasma treatment of separator are
carried out, respectively. In Experiment D, both are carried out. In
each case, we measure the resulting thermal contact resistance
between the separator and cathode using the technique described
in section 2.2. Fig. 6 plots the steady-state temperature measure-
ments from each thermocouple in the experimental setup for Ex-
periments A-D. For each case, temperature drop across the
separator-electrode sample, and hence total thermal resistance is
obtained by extrapolation of data shown in Fig. 6. Starting from the
imposition of Joule heating on the experimental setup, temperature
drop across the sample increases with time, and eventually reaches
a steady-state, as shown in Supplementary Figure S2. Only the
steady-state temperature difference is considered, since heat is
being stored in the copper blocks prior to steady state, due to which
the temperature difference across the sample does not accurately
reflect its thermal resistance. Data presented in Fig. 6 show sig-
nificant reduction in total thermal contact resistance due to surface
modification. When the material resistances and contact re-
sistances with the copper blocks are subtracted out, similar to
section 4.1, Rsep-cathode was found to reduce by 26%, 41% and 78%
compared to baseline measurements for experiments B, C and D
respectively. The largest reduction is found when both separator
and cathode surfaces are treated (Experiment D), in which case, the
measured TCR of 90 mKm2
/W is 4Â lower than the baseline case, as
shown on the right side of Fig. 4. The total thermal resistance of the
unit cell reduces from 951 mKm2
/W to 291 mKm2
/W. This extent of
TCR reduction is consistent with 4X and 6X reduction reported by
O'Brien et al. [22] and Kaur et al. [23] respectively, using an organic
Table 1
Thermal and mechanical properties for various materials for theoretical calculation of thermal contact resistance Note that since the calculation of thermal contact resistance
was done from the Polyethylene side, only the heat capacity of Polyethylene is needed.
Material Effective speed of sound (m/s) Mass density (g/cm3
) Heat capacity (J/m3
C) Young's modulus (GPa) Poisson's ratio
LiCoO2 [18] 5020 5.06 174 0.38
Polyethylene [40] 672 0.95 1824000 0.7 0.42
Graphite [35] 1940 2.26 33 0.33
Fig. 5. Schematic showing the baseline experiment and various surface chemistry modifications explored for understanding the effect on thermal contact resistance between
cathode and separator.
V. Vishwakarma et al. / Journal of Power Sources 300 (2015) 123e131128
7. bonding layer across Cu/SiO2 interface, and amine-terminated
carbon nanotubes respectively.
By reducing the thermal resistance responsible for the largest
contribution to overall thermal conduction in the Li-ion cell, the
surface modification results in improved overall thermal conduc-
tivity of the thermal unit cell, as summarized on the right side of
Fig. 4.
In order to investigate the effect of surface modification of the
cathode on battery performance, electrochemical tests are per-
formed in a split flat cell. Fig. 7A shows the complete charge-rest-
discharge curves for the baseline (Experiment A) and modified
(Experiment D) electrodes. The charging potential is about 32 mV
lower than the baseline, and the discharge potential is about 37 mV
higher than the baseline, indicating more available energy and
higher round trip energy efficiency. This may be due to lower
interfacial impedance. The voltage efficiency, evaluated by the ratio
of plateau potentials during discharge and charge, is improved by
around 2%. To determine the cell internal resistance, electro-
chemical impedance spectroscopy (EIS) is conducted at fully
discharged condition. Fig. 7B shows that the internal resistance of
the cell with modified cathode is reduced by about 3 Ohms, while
the charge transfer resistance (diameter of the high-frequency
semi-circle) does not change significantly. This indicates that the
improved cell performance and reduced internal resistance may be
due to enhanced surface contact between the modified cathode and
separator.
Further work must be carried out to fully optimize the specific
nature of the chemical bridge for both thermal and electrochemical
performance. Long-term stability of the chemical bridge in an
electrochemically active environment needs to be further analyzed
by evaluating electrochemical stability of the chemical species in
the full electrochemical potential window of operation, and po-
tential side reactions with chemical species present in the cell.
4.4. Influence on cell-level thermal performance
Our material-level measurements are consistent with cell-level
thermal conductivity measurements [7]. The thermal conductivity
of the thermal unit cell, accounting for the measured value of the
thermal contact resistance between cathode and separator, is found
to be 0.24 W/mK, which is very close to cell-level measurements of
0.15e0.20 W/mK for 26650 and 18650 Li-ion cells [7]. If the thermal
contact resistance measured here is not accounted for, and only
material thermal resistances are considered, then the effective cell-
level thermal conductivity is found to be 1.76 W/mK, which is much
higher than cell-level measurements [7]. This shows that interface
contact resistance is important and must be accounted for.
Fig. 8 plots the expected overall cell-level thermal conductivity
as a function of thermal contact resistance between cathode and
separator. Baseline (Experiment A) and improved (Experiment D)
values of the thermal contact resistance are also shown on the x-
axis. Fig. 8 indicates an improvement in overall thermal conduc-
tivity from 0.24 W/mK (baseline) to 0.76 W/mK (experiment D).
There is potential for even steeper improvement in overall thermal
conductivity by reducing TCR more through further optimization of
the separator-electrode interface. If the TCR can be eliminated
completely, the cell-level thermal conductivity can be improved up
to 1.76 W/mK.
Fig. 8 also plots the peak temperature rise in a 26650 Li-ion cell
operating at 7C discharge rate in ambient conditions as a function
of TCR. The peak temperature rise is computed using our recently
reported cell-level thermal model that solves the governing energy
equations to predict the temperature distribution in a Li-ion cell as
a function of its thermophysical properties [8]. Fig. 8 shows a sig-
nificant reduction in peak temperature rise due to TCR reduction
Fig. 6. Comparison of the steady-state temperature response of baseline and three
surface-modified separator-cathode stacks showing reduction in Rtotal. Note that the
same heat flux is applied in each case. Once thermal contact resistance to copper
blocks is subtracted out, the reduction in Rsep-cathode due to surface treatment is even
more significant.
Fig. 7. Electrochemical evaluation of the baseline and thermally enhanced cathodes in a half-coin cell format with a Lithium counter electrode: (A) chargeedischarge performance
at 1.5 mA, and (B) Electrochemical Impedance Spectroscopy (EIS) spectra taken at fully discharge state. A split flat cell with active area of 2.54 cm2
was assembled using Lithium
anodes.
V. Vishwakarma et al. / Journal of Power Sources 300 (2015) 123e131 129
8. and the consequent improvement in thermal conduction within
the cell. An additional benefit of TCR reduction demonstrated here
is a reduction in temperature gradients within the cell, which is
very desirable for balanced and safe cell operation [3]. Temperature
gradient within the cell is expected to reduce from 23 C to 9.5 C
between the baseline TCR and enhanced TCR e a reduction of over
58%. This is made possible by more effective heat removal from the
core of the cell, which is a significant challenge at present due to
poor cell thermal conductivity. Reductions in both peak tempera-
ture and temperature gradient are expected to result in reduced
risk of failure, improved reliability and enhanced performance [3].
For example, the thermal head made available by the reduced cell
temperature could be made use of by allowing the cell to operate at
a higher discharge rate than present, thereby improving perfor-
mance. This may also reduce the number of cells needed in a bat-
tery pack for a certain power output, thereby reducing cost and
weight.
Our material-level approach addresses the thermal manage-
ment problem in Li-ion cells at its fundamental root cause, as
opposed to other external approaches, such as cold plate cooling,
external liquid cooling, embedded phase change cooling, etc. [3,11].
External cooling approaches are likely to have very limited benefits
if the inherent cause of the poor thermal conduction within the cell
is not addressed. In addition, our work shows the dominance of
thermal contact resistance over material resistances within the Li-
ion material stack.
The key results presented here e the dominance of TCR as well
as reduction in TCR due to surface modification e are both largely
insensitive to the thermal conductivities of electrode and separator.
Figure S3 in Supplementary Information shows plots of measured
baseline and enhanced thermal contact resistances (experiments A
and D) over a range of ksep and kelec respectively. Figure S3 shows
that results from our measurements do not change significantly
with changes in the material thermal conductivities within the
range of values reported in the recent past [16e19].
Our results also indicate key trade-offs in thermal and electro-
chemical performance of a Li-ion cell. Much effort has focused on
increasing the porosity and pore size in separators to facilitate ionic
transport through the separator [12]. Our results indicate that do-
ing so may actually be detrimental to thermal performance, since
the rate-limiting thermal transport at the separator-electrode
interface depends critically on good thermal contact between the
two.
5. Conclusions
This paper identifies interfacial thermal conduction between
cathode and separator as the rate-limiting material-level compo-
nent of heat transfer within a Li-ion cell, contributing around 88% of
overall thermal resistance of the cell. Results also indicate dramatic
reduction in this thermal resistance without affecting electro-
chemical resistance based on surface modification. Experimental
measurements of the interfacial thermal contact resistance are in
good agreement with predictions based on the acoustic mismatch
model. These measurements also correctly predict cell-level
thermal properties of a Li-ion cell. Results indicate the possibility
of significant improvement in cell-level thermal conductivity and
reduction in operating temperature rise as a result of surface
modification.
Future research should further investigate the effect of material
properties on the separator-cathode contact, for example by
changing the size and nature of separator polymer strands, etc.
Various possible mechanisms for chemically bridging the interface
must be evaluated experimentally and theoretically, for optimizing
thermal and electrochemical effects, as well as for longer-term
stability. Due to the closely coupled, multiphysics nature of a Li-
ion cell, thermal transport must be evaluated in the context of
the fundamental electrochemical processes within the cell. For
inclusion in commercially manufactured batteries, integration of
the surface modification process in the manufacturing flow must be
considered and optimized.
Acknowledgments
A.J. and V.V. would like to acknowledge support from Provost's
Office and Department of Mechanical and Aerospace Engineering,
The University of Texas at Arlington. F.L. would like to acknowledge
support from National Science Foundation (ECCS-1125588).
Research at Oak Ridge National Laboratory, managed by UT Battelle,
LLC, for the U.S. Department of Energy (DOE) under contract DE-
AC05-00OR22725, utilized the DOE Battery Manufacturing RD
Facility at ORNL sponsored by the Office of Energy Efficiency and
Renewable Energy's Vehicle Technologies Office.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jpowsour.2015.09.028.
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