Effect of design parameters on the performance of a closed loop pulsating

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  • 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 306 EFFECT OF DESIGN PARAMETERS ON THE PERFORMANCE OF A CLOSED LOOP PULSATING HEAT PIPE Ch. Sreenivasa Rao1 , Avssks Gupta2 , K. Rama Narasimha3 1 Department of Mechanical Engineering, Madanapalle Institute of Technology and Science, Madanapalle , India.-517325 2 Department of Mechanical Engineering, JNTU college of Engineering, Hyderabad-500085, India 3 Centre for Emerging Technologies, Jain University, Bangalore-562112, India. ABSTRACT Pulsating heat pipes (PHP) have emerged as very promising passive devices for heat transfer applications especially suited for thermal management of electronics. A closed loop PHP made of brass with 1.5 mm ID and 2.5 mm OD with a single loop is tested in the present work at atmospheric conditions. This paper attempts to describe the effect of working fluid, heat input, orientation and fill ratio as primary design parameters on the performance of PHP. The transient and steady state experiments are conducted for various heat loads, fill ratio and working fluids. Acetone and Propanol are used as working fluids during the experimentation. The performance quantities of PHP like thermal resistance and heat transfer coefficients are evaluated. The results showed that Acetone exhibits better heat transfer characteristics of PHP compared to Propanol. The PHP is tested for horizontal, 300 and 600 orientations. The results indicate that the performance of PHP changes with different fill ratio, orientation and heat load. Better heat transfer performance is obtained for zero and 300 orientations and at a fill ratio of 80%. Keywords: electronic cooling, closed loop pulsating heat pipe, pressure pulsations, design parameters and thermal performance. 1. INTRODUCTION Thermal management of modern electronics is the challenge of the day in the wake of component miniaturization and attracted the attention of researchers to develop efficient INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 4, Issue 3, May - June (2013), pp. 306-317 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2013): 5.7731 (Calculated by GISI) www.jifactor.com IJMET © I A E M E
  • 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 307 cooling systems. Several cooling methods are employed to cool the electronic devices. The oscillating or pulsating heat pipe (OHP/PHP) is a promising two-phase heat transfer device for applications like electronic cabinet cooling. It is simple in structure with a coil of capillary dimensions filled with certain working fluid in it and extended from the heat source to sink. PHP does not contain wick structure to return the condensate back to the evaporator section unlike a conventional heat pipe. Instead, PHP works on the principle of fluid pressure oscillations that are created by means of differential pressure across vapor plugs from evaporator to condenser and back. The vapor formed at the evaporator is pushed towards the condenser in the form of discrete vapor bubbles amidst packets of fluid. The vapor gets condensed at the condenser releasing the latent heat of vaporization and returns to the evaporator to complete the cycle. The thermal performance of an actual PHP depends upon the temperature gradient exists between the evaporator and the condenser section. PHP was first proposed and patented by Akachi[1] as a passive cooling device and gains the attention of many investigators. Although a plethora of heat pipe technology is established, the open literature available on PHPs is limited. The numerical studies on PHPs reported in the literature are limited to estimate the complex behavior of thermo-fluidic transport phenomena. More over the mathematical models proposed in the literature on PHPs needs experimental verification [2, 3, and 11]. Characterization of thermal performance in multi-loop PHPs has been reported in few experimental investigations.[4,5,6,7,8]. Results on thermal performance of single loop PHP are also reported in some literatures [9, 10]. Experimental results mainly focused on flow visualization studies and the measurement of temperature variation pattern. The effect of working fluid, heat input, tube material, orientation and fill ratio are identified as primary design parameters affecting the performance of PHP which requires detailed investigation [12]. Lee et al. (1999) conducted few performance tests on a multi loop PHP made of brass using Ethanol as working fluid. The PHP was tested for different orientations (30°-90°). Most active oscillations caused by the formation or estimation of bubbles are observed in bottom heating with fill ratio of 40-60%. Khandekar (2003) demonstrated the existence of multiple quasi-steady state in a PHP by developing an experimental set up of PHP made of copper tubes of inner diameter 2mm and outer diameter 3mm.Experiments were conducted for the heat input range of 10-20 W with Ethanol as the working fluid at 60% fill ratio. The data was recorded for 12 hrs continuously. The multiple quasi steady states observed were named as steady state 1, 2&3. The flow in steady state 1 was unidirectional with alternate fluid movement and stop over due to which intermittent heat transfer was happened. In steady state-2, a tendency of liquid hold- up was observed in the condenser section which made the evaporator zone becomes drier. Poor thermal performance was reported in the steady state-2. In steady state-3, unidirectional continuous flow pattern with no stop-over was observed leading to least thermal resistance. It was showed that churn flow takes place in the evaporator and slug flow in the condenser zone. Rama Narasimha et.al (2010) presented the experimental results for a single loop PHP made of copper. Lower thermal resistance was found at atmospheric pressure when compared to Vacuum pressure levels maintained inside the PHP [19]. The performance characteristics such as thermal resistance and heat transfer coefficient are estimated and analyzed for different heat inputs, working fluids and evacuation levels.
  • 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May Y.Zhang et al (2011) explained that the thermal performance of many PHPs degraded as the Inclination angle is varied and some may not operate at all. If the inner diameter of PHP is sufficiently smaller that aids the PHP to perform at low inclination angles. (The orientation is considered to be 0° for horizontal heat mode, +90° bottom heat mode and 90° top heat mode operation). Thus from the literature study, it is understood that not many experimental investigations were reported on single loop PHP and needs further research progress in this area. More over the scope of the suitability of Propanol as fluid is not verified. The experimental results available so far are only related to copper or aluminium PHP. There are no experimental results available related to PHP when it is made of other materials. Hence in the prese experimental study. Acetone and Propanol are considered as the working fluids for PHP operation. The transient experiments are conducted for various heat inputs. The thermal resistance and heat transfer coefficient are evaluated. 2. EXPERIMENTATION 2.1 Instrumentation Made With Fig. 1 Photograph of PHP Experimental setup Fig. 1 shows the pictorial view of the experimental setup. In this setup, the basic components used in PHP are brass tube, borosilicate glass tube, silicon rubber tube, a non return valve, a tape heater and thermocouples. Brass is an alloy and would be free f the action of continuous interaction with working fluid flowing through it. More over the fouled surfaces make the fluid gets clogged and affects the thermal performance of PHP severely. Under these circumstances Brass can be used as a good conductor of heat. The ID of the brass tube selected is 1.5mm and the OD is 2.5mm. The glass tube attached between the U section which was specified earlier (by khandekar et.al,2 transparent surface, it permits to capture the flow visual effects. The glass tube is made of borosilicate, which can resist temperature up to 1200° C. Silicon rubber tubes of 2mm inner diameter and 4mm outer diameter ar connectors between glass and copper tubes. They are thermal insulators and can resist temperatures up to 400°C. They are leak proof and expand at higher temperatures. ional Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 308 Y.Zhang et al (2011) explained that the thermal performance of many PHPs degraded on angle is varied and some may not operate at all. If the inner diameter of PHP is sufficiently smaller that aids the PHP to perform at low inclination angles. (The orientation is considered to be 0° for horizontal heat mode, +90° bottom heat mode and Thus from the literature study, it is understood that not many experimental investigations were reported on single loop PHP and needs further research progress in this area. More over the scope of the suitability of Propanol as a promising thermal dissipation fluid is not verified. The experimental results available so far are only related to copper or aluminium PHP. There are no experimental results available related to PHP when it is made of other materials. Hence in the present work, a single loop brass PHP is considered for the experimental study. Acetone and Propanol are considered as the working fluids for PHP operation. The transient experiments are conducted for various heat inputs. The thermal r coefficient are evaluated. Instrumentation Made With the Experimental Setup Photograph of PHP Experimental setup 1 shows the pictorial view of the experimental setup. In this setup, the basic components used in PHP are brass tube, borosilicate glass tube, silicon rubber tube, a non return valve, a tape heater and thermocouples. Brass is an alloy and would be free from fouling effects unlike the pure copper under the action of continuous interaction with working fluid flowing through it. More over the fouled surfaces make the fluid gets clogged and affects the thermal performance of PHP ances Brass can be used as a good conductor of heat. The ID of the brass tube selected is 1.5mm and the OD is 2.5mm. The glass tube attached between the U-turn Brass tube is considered as adiabatic section which was specified earlier (by khandekar et.al,2004) in the literature. Having the transparent surface, it permits to capture the flow visual effects. The glass tube is made of borosilicate, which can resist temperature up to 1200° C. Silicon rubber tubes of 2mm inner diameter and 4mm outer diameter ar connectors between glass and copper tubes. They are thermal insulators and can resist temperatures up to 400°C. They are leak proof and expand at higher temperatures. ional Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – June (2013) © IAEME Y.Zhang et al (2011) explained that the thermal performance of many PHPs degraded on angle is varied and some may not operate at all. If the inner diameter of PHP is sufficiently smaller that aids the PHP to perform at low inclination angles. (The orientation is considered to be 0° for horizontal heat mode, +90° bottom heat mode and - Thus from the literature study, it is understood that not many experimental investigations were reported on single loop PHP and needs further research progress in this a promising thermal dissipation fluid is not verified. The experimental results available so far are only related to copper or aluminium PHP. There are no experimental results available related to PHP when it is made nt work, a single loop brass PHP is considered for the experimental study. Acetone and Propanol are considered as the working fluids for PHP operation. The transient experiments are conducted for various heat inputs. The thermal 1 shows the pictorial view of the experimental setup. In this setup, the basic components used in PHP are brass tube, borosilicate glass tube, silicon rubber tube, a non rom fouling effects unlike the pure copper under the action of continuous interaction with working fluid flowing through it. More over the fouled surfaces make the fluid gets clogged and affects the thermal performance of PHP ances Brass can be used as a good conductor of heat. The ID turn Brass tube is considered as adiabatic 004) in the literature. Having the transparent surface, it permits to capture the flow visual effects. The glass tube is made of Silicon rubber tubes of 2mm inner diameter and 4mm outer diameter are used as the connectors between glass and copper tubes. They are thermal insulators and can resist temperatures up to 400°C. They are leak proof and expand at higher temperatures.
  • 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May In order to maintain unidirectional fluid flow; a non return valve is used made of stainless steel and has inner diameter of 5mm. The ball and seating arrangement is used with a ball diameter of 4mm. A tape heater of heating capacity 0 as the source of heat input. Six K-type thermocouples are connected for temperature measurements, four in the evaporator section and two in the condenser section. The wire diameter of thermocouples is 1mm and can measure temperature up to 1000° c with a maximum error of ± 0.1° C. T temperature values are recorded at a frequency of 1Hz. The experiment is performed with three working fluids viz. Propanol, distilled water and acetone. The working fluid is injected into the heat pipe using a syringe. 2.2 Experimental Procedure The experimental test facility as shown in figure 1 is setup to characterize the pulsating heat pipe thermal performance and the following procedure is adopted during the experiment: 1. Before filling the fluid in the PHP it is ensured that no traces of working previous cycle of experimentation is available. 2. The required amount of working fluid is then filled through the filling valve using a syringe by opening the one end of the non the evaporator section. It is reported in the literature (Khandekar, 2004) that the PHP develops true pulsating motion when the fill ratio is between 20% stated that 50% is the optimum fill ratio. Hence, in the present work, experiments are conducted for fill ratios ranging from 50% to 80%, 3. Now the air is filled through the filling valve provided on the brass tube using another syringe. This is done to ensure simultaneous formation of liquid slug and vapor bubbles. 4. The display unit is ON and required w present experimentation, heat input is varied from 7w to 12w in steps of 1w. 5. The cooling water is allowed to the condenser section of PHP from the constant head water bath. 6. .In the present work, the heat tr angles of 0°, 30° and 60°. 7. The transient experiments are conducted and the temperatures at various locations of the PHP are recorded from the temperature data logger. The experiments are continued till steady state is reached. The measurement has inherent uncertainties. The thermo couple-temperature display system has uncertainty of ±2% of full scale. 3. RESULTS AND DISCUSSION The performance effectiveness and understanding of the he of closed loop pulsating heat pipe is evaluated by measuring wall temperature at different points of the CLPHP. The uncertainty in condenser and evaporator temperature Uc and Ue are evaluated respectively using the relations of % Ue = ional Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 309 In order to maintain unidirectional fluid flow; a non return valve is used made of stainless steel and has inner diameter of 5mm. The ball and seating arrangement is used with a ball diameter of 4mm. A tape heater of heating capacity 0-50 W is attached to the evaporator section and acts type thermocouples are connected for temperature measurements, four in the evaporator section and two in the condenser section. The wire diameter of thermocouples is 1mm and can measure temperature up to 1000° c with a maximum error of ± 0.1° C. T temperature values are recorded at a frequency of 1Hz. The experiment is performed with three working fluids viz. Propanol, distilled water and acetone. The working fluid is injected into the heat pipe using a syringe. experimental test facility as shown in figure 1 is setup to characterize the pulsating heat pipe thermal performance and the following procedure is adopted during the Before filling the fluid in the PHP it is ensured that no traces of working previous cycle of experimentation is available. The required amount of working fluid is then filled through the filling valve using a syringe by opening the one end of the non-return valve such that the fluid directly enters ction. It is reported in the literature (Khandekar, 2004) that the PHP develops true pulsating motion when the fill ratio is between 20% - 80% and it is also stated that 50% is the optimum fill ratio. Hence, in the present work, experiments are or fill ratios ranging from 50% to 80%, Now the air is filled through the filling valve provided on the brass tube using another syringe. This is done to ensure simultaneous formation of liquid slug and vapor bubbles. The display unit is ON and required wattage is set using the power supply unit. In the present experimentation, heat input is varied from 7w to 12w in steps of 1w. The cooling water is allowed to the condenser section of PHP from the constant head .In the present work, the heat transfer behavior of PHP is analyzed for the inclination The transient experiments are conducted and the temperatures at various locations of the PHP are recorded from the temperature data logger. The experiments are continued steady state is reached. The measurement has inherent uncertainties. The thermo temperature display system has uncertainty of ±2% of full scale. 3. RESULTS AND DISCUSSION The performance effectiveness and understanding of the heat transfer characteristics of closed loop pulsating heat pipe is evaluated by measuring wall temperature at different points of the CLPHP. The uncertainty in condenser and evaporator temperature Uc and Ue are evaluated respectively using the relations of Kline et al. (1953). Accordingly ional Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – June (2013) © IAEME In order to maintain unidirectional fluid flow; a non return valve is used. The valve is made of stainless steel and has inner diameter of 5mm. The ball and seating arrangement is 50 W is attached to the evaporator section and acts type thermocouples are connected for temperature measurements, four in the evaporator section and two in the condenser section. The wire diameter of thermocouples is 1mm and can measure temperature up to 1000° c with a maximum error of ± 0.1° C. The The experiment is performed with three working fluids viz. Propanol, distilled water experimental test facility as shown in figure 1 is setup to characterize the pulsating heat pipe thermal performance and the following procedure is adopted during the Before filling the fluid in the PHP it is ensured that no traces of working fluid used in The required amount of working fluid is then filled through the filling valve using a return valve such that the fluid directly enters ction. It is reported in the literature (Khandekar, 2004) that the PHP 80% and it is also stated that 50% is the optimum fill ratio. Hence, in the present work, experiments are Now the air is filled through the filling valve provided on the brass tube using another syringe. This is done to ensure simultaneous formation of liquid slug and vapor bubbles. attage is set using the power supply unit. In the present experimentation, heat input is varied from 7w to 12w in steps of 1w. The cooling water is allowed to the condenser section of PHP from the constant head ansfer behavior of PHP is analyzed for the inclination The transient experiments are conducted and the temperatures at various locations of the PHP are recorded from the temperature data logger. The experiments are continued steady state is reached. The measurement has inherent uncertainties. The thermo at transfer characteristics of closed loop pulsating heat pipe is evaluated by measuring wall temperature at different points of the CLPHP. The uncertainty in condenser and evaporator temperature Uc and Ue Kline et al. (1953). Accordingly
  • 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May % Uc = The maximum temperature uncertainty found from the equations is about 6%. 3.1. Effect of Heat Input Fig.2 Variation of Evaporator Temperature with time at different heat load for Propanol at a fill ratio of 60% Fig.2 shows the variation of evaporator wall temperature with time for fill ratio of 60%. It can be seen from the fig.2 with respect to time is periodic in nature at steady state. As there is a continuous pressure pulsation during the flow in a PHP, the evaporator temperature versus time curve is periodic in nature. It is also clear that the pressure pulsati consequently the evaporator temperature rises at lower heat load of 8 the system takes more time to reach the steady state at lower heat input of 8 Fig.3 Variation of Condenser Te Fig.3 shows the variation of condenser wa different heat inputs for Propano condenser wall temperature is less at lower heat load of 8 This is because of very slow and intermittent motion of the working fluid at lower heat load. As the movements of the working fluid is slow at lower heat input due to levels, the hot fluid takes more time to reach the condenser from evaporator sectio 50 55 60 65 70 0 100 EvaparatorTemperatureTe 0 C 25 26 27 28 29 30 31 32 33 0 100 CondenserTemperatureTc 0 C ional Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 310 The maximum temperature uncertainty found from the equations is about 6%. Evaporator Temperature with time at different heat load for Propanol at a fill ratio of 60% Fig.2 shows the variation of evaporator wall temperature with time for . It can be seen from the fig.2 that the variation of evaporator temperature with respect to time is periodic in nature at steady state. As there is a continuous pressure pulsation during the flow in a PHP, the evaporator temperature versus time curve is periodic in nature. It is also clear that the pressure pulsating effect is less at lower heat load and consequently the evaporator temperature rises at lower heat load of 8 W. It is also clear that the system takes more time to reach the steady state at lower heat input of 8 W. Fig.3 Variation of Condenser Temperature with time at different heat load for Propanol at a fill ratio of 60% Fig.3 shows the variation of condenser wall temperature with respect different heat inputs for Propanol at a fill ratio of 60%. It is clear from figure denser wall temperature is less at lower heat load of 8 W compared to higher heat inputs. This is because of very slow and intermittent motion of the working fluid at lower heat load. As the movements of the working fluid is slow at lower heat input due to levels, the hot fluid takes more time to reach the condenser from evaporator sectio Effect of heat input on evaparator 200 300 400 500 600 700 800 900 1000 Time t (s) 12 W 11 W 10 W 9 W 8 W Effect of heat input on Condensor 200 300 400 500 600 700 800 900 1000 Time t (s) 12 W 11 W 10 W 9 W 8 W ional Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – June (2013) © IAEME Evaporator Temperature with time at different heat load for Fig.2 shows the variation of evaporator wall temperature with time for Propanol at a tor temperature with respect to time is periodic in nature at steady state. As there is a continuous pressure pulsation during the flow in a PHP, the evaporator temperature versus time curve is periodic ng effect is less at lower heat load and . It is also clear that mperature with time at different heat load for Propanol espect to time at io of 60%. It is clear from figure 3 that the compared to higher heat inputs. This is because of very slow and intermittent motion of the working fluid at lower heat load. lower energy levels, the hot fluid takes more time to reach the condenser from evaporator section.
  • 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 311 3.2. Effect of Fill ratio Fig.4 Variation of Evaporator Temperature with time at different fill ratio for Acetone at a heat load of 10 W Fig. 4 shows the variation of evaporator wall temperature with time at different fill ratios for Acetone at a heat load of 10 W. It is understood from the figure that the minimum evaporator temperature is recorded at 80% fill ratio. At higher fill ratio less vapor bubbles exists in the tube with consequent decrease in the evaporator temperature. The thermal performance of PHP can be studied by its thermal resistance and heat transfer coefficient. The thermal resistance of PHP is given by Q TT R ce − = (K/W) (3.1) Fig. 5 Effect of Thermal Resistance on heat load at different Fill ratio for Acetone Fig. 5 shows the variation of thermal resistance with heat load for Acetone at different fill ratios. From the figure it is clear that the thermal resistance decreases with increase in heat load at all fill ratios considered. The fill ratio of 80% exhibits the lower values of thermal resistance compared to lower fill ratios considered. As the temperature difference between evaporator and condenser is less at higher fill ratio of 80%, the magnitude of thermal resistance is also less. On the other hand at lower fill ratio, the pressure pulse oscillation is decreased in overcoming the flow friction between the fluid and the valve and hence the rate of heat transferred also decreases. Consequently the overall thermal resistance is increased as a result of increase in temperature difference. Effect of heat input on evaporator 50 52 54 56 58 60 62 64 66 68 0 100 200 300 400 500 600 700 800 900 1000 Time t (s) EvaporatorTemperatureTe 0 C 80% 70% 60% 50% 2 2.5 3 3.5 4 4.5 7 8 9 10 11 12 13 Heat Input, Q (W) ThermmalResistance,R(K/W) 50% 60% 70% 80%
  • 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 312 The convective heat transfer coefficient of PHP is given by )( ce TTA Q h − = (W/m2 K) (3.2) Fig. 6 Effect of Heat Transfer coefficient on heat load at different Fill ratio for Acetone Fig 6 shows the variation of Heat transfer coefficient with varying heat loads for Acetone at different fill ratios. From the figure, it is seen that the Heat transfer coefficient increases with increase in heat load at all fill ratios considered. Higher values of heat transfer coefficient can be seen at higher fill ratio of 80% which indicates better performance of brass PHP. 3.3. Effect of Working Fluid Fig. 7 Variation of Evaporator Temperature with time for different working Fluids at a heat load of 12 W and a fill ratio of 60% The variation of evaporator wall temperature with respect to time for different working fluids at a fill ratio of 60% and at a heat input of 12 W is shown in Fig 7. From the figure it is clear that the evaporator wall temperature is higher in case of Propanol and lower in the case of Acetone. It is also observed that the system takes more time to reach the steady state in case of Propanol when compared to Acetone. More random motion of the fluid is observed in case of Propanol due to higher perturbations during the flow. Effect of heat input on Thermal Resistance for Accetone 600 800 1000 1200 1400 1600 1800 7 8 9 10 11 12 13 Heat Input, Q (W) HeatTransferCo-efficient,h(W/m2K) 50% 60% 70% 80% 40 45 50 55 60 65 0 100 200 300 400 500 600 700 800 900 1000 Time t (s) EvaporatorTemperatureTe0 C ACCETONE 2-PROPANOL
  • 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 313 Fig. 8 Variation of Temperature difference with time for different working Fluids at a heat load of 12 W and a fill ratio of 60% Fig. 8 shows the variation of temperature difference between evaporator and condenser with time for different working fluids at a fill ratio of 60% and at a heat input of 12 W. It is seen that the temperature difference between the evaporator and condenser is less for Acetone and more for Propanol. This shows that Acetone can transfer heat with less temperature difference compared to Propanol. The temperature difference between evaporator and condenser for Acetone is found to be around 210 C and for Propanol it is around 310 C. Fig. 9 Effect of Thermal Resistance on heat load for different working fluids at a fill ratio of 60% Fig.9 shows the variation of thermal resistance with heat input for different working fluids at 60% fill ratio. The figure indicates that the thermal resistance decreases with increase in heat input in case of both the working fluids considered .Further it is seen that Acetone exhibits lower values of thermal resistance compared to Propanol. This is due to lower value of temperature difference between evaporator and condenser in case of Acetone. The lower values of thermal resistance of Acetone indicate that Acetone has better heat transport capability compared to Propanol. Effect of working fluid on temperature 20 22 24 26 28 30 32 34 36 38 40 0 100 200 300 400 500 600 700 800 900 1000 Time t (s) TemperatureDifferenceTe-Tc0 C ACCETONE 2-PROPANOL Effect of working fluid on Thermal Resistance 1.25 1.75 2.25 2.75 3.25 3.75 4.25 7 8 9 10 11 12 13 Time t (s) ThermmalResistance,R(K/W) ACCETONE 2-PROPANOL
  • 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 314 Fig. 10 Effect of Heat Transfer coefficient on heat load for different working fluids at a fill ratio of 60% The variation of Heat transfer coefficient with respect to heat input for different working fluids at a fill ratio of 60% is shown in Fig.10. It is seen that the Heat transfer coefficient increases with increase in heat input for the working fluids considered. Acetone shows higher heat transfer coefficient values compared to Propanol. This is due to the lower values of temperature difference between evaporator and condenser for Acetone. 3.4 Effect of Orientation Fig.11 Variation of Evaporator Temperature with time for different orientation at a heat load of 10W and a fill ratio of 60% The orientation of PHP plays a very important role in its thermal performance. In the present work, experiments are conducted at zero, 30 and 60 degree orientations of PHP with respect to horizontal. Fig. 11 shows the variation of evaporator temperature with time for different orientations considered. From the figure, it is seen that the evaporator wall temperature is less at an orientation of zero and 30 degree compared to 60 degree. Effect of working fluid on Heat Transfer Co-Effiecient 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 7 8 9 10 11 12 13 Time t (s) HeatTransferCo-efficient,h(W/m2K) ACCETONE 2-PROPANOL 40 45 50 55 60 65 70 75 0 100 200 300 400 500 600 700 800 900 1000 Time t (s) EvaparatorTemperatureTe0C zero degrees 30 Degrees 60 Degrees
  • 10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 315 Fig.12 Variation of Temperature Difference with time for different orientation at a heat load of 10W and a fill ratio of 60% Fig. 12 shows the variation of temperature difference between evaporator and condenser with time for different orientations considered. From the figure, it is seen that the temperature difference between evaporator and condenser is less at an orientation of zero and 30 degree compared to 60 degree. This shows that the PHP is desired to be operated at zero or 30 degree compared to 60 degree orientation. Fig. 13 Variation of Thermal Resistance with heat load for different orientation at a fill ratio of 60% for Acetone Fig. 13 shows the variation of thermal resistance with Heat input at various orientations considered for Acetone at a fill ratio of 60%. It is observed from the figure that the thermal resistance decreases with increase in heat load at all orientations considered. It is also observed that the thermal resistance is less at zero and 30 degree orientations compared to 60 degree. As the fluid should overcome the effects of gravity more at 60 degree orientation, there is more resistance for heat transfer and flow at this orientation. Hence, it is desirable to operate the PHP at zero or 30 degree orientations to achieve better heat transfer characteristics. 10 15 20 25 30 35 40 45 0 100 200 300 400 500 600 700 800 900 1000 Time t (s) TemperatureDifferenceTe-Tc 0 C zero degrees 30 Degrees 60 Degrees 0 0.5 1 1.5 2 2.5 3 3.5 7 8 9 10 11 12 13 Time t (s) ThermmalResistance,R(K/W) zero degrees 30 Degrees 60 Degrees
  • 11. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 316 Fig. 14 Variation of Heat Transfer coefficient with heat load for different orientation at a fill ratio of 60% for Acetone Fig. 14 shows the variation of heat transfer coefficient with Heat input at various orientations considered for Acetone at a fill ratio of 60%. It is observed from the figure that the heat transfer coefficient increases with increase in heat load at all orientations considered. It is also observed that the heat transfer coefficient is more at zero and 30 degree orientations compared to 60 degree showing better heat transfer capability of PHP operation at zero and 30 degree orientations. 4. CONCLUSIONS Experimental studies are conducted on a single closed loop brass PHP in the present work and the thermal performances of the PHP are studied. The following conclusions can be drawn from the present work: 1. Brass PHP showed intermittent flow of the working fluid with perturbations at lower heat loads. 2. The PHP showed better heat transfer performance at a fill ratio of 80%. 3. Acetone is found to be the better working fluid compared to Propanol in terms of its lower thermal resistance and higher heat transfer coefficient. 4. PHP should be operated at zero and 30 degree orientations for its better thermal performance. REFERENCES [1] Akachi, H. “Structure Of Heat Pipe”, US patent, 4921041, 1990 [2] Shafii, B. M., Faghri, A., Zhang, Y., “Thermal modeling of unlooped pulsating heat pipes, Journal of Heat Transfer” Vol. 123, No. 6, 2001, pp. 1159-1172. [3] Zhang, Y., Faghri, A., “Heat Transfer in a pulsating heat pipe with open end, International Journal of Heat Mass Transfer”, Vol. 45, No. 4, 2002, pp. 755-764. [4] Cai, Q., Chung-lung Chen, Julie F. Asfia, “Operating Characteristic Investigations in Pulsating Heat Pipe”, journal of heat transfer, vol. 128, 2006, pp.1329-1334. Effect of orientarion on Heat Transfer Co-Effiecient 0 500 1000 1500 2000 2500 3000 3500 7 8 9 10 11 12 13 Time t (s) HeatTransferCo-efficient,h(W/m2K) zero degrees 30 Degrees 60 Degrees
  • 12. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 3, May - June (2013) © IAEME 317 [5] Charoensawan, P., Khandekar, S., Groll, M. and Terdtoon, P. “Closed loop pulsating heat pipes”, part-A; Parametric experimental investigations”, Applied Thermal engineering, Vol.23 No.6, 2001, pp.2009-2020. [6] Khandekar, S., “Multiple Quasi- Steady States in a Closed Loop Pulsating Heat Pipe”, NTUS-IITK 2nd joint workshop in mechanical, Aerospace and Industrial Engineering, April 5-6, 2008, IIT, Kanpur, India. [7] Khandekar, S., “Thermo Hydrodynamics of Pulsating Heat Pipes”, Ph.D Dissertation, University of Stuttgart, Germany, 2004. [8] Meena, P., Rittidech, S., Tammasaeng, P, “Effect of inner Diameter and inclination angles on operation limit of closed-loop Oscillating heat pipes with check valves”, American journal of Applied Sciences, vol. 1, No.2,2008,pp.100-103. [9] Rama Narasimha, K., “Studies on Pulsating Heat pipes” Ph.D. Dissertation, Visveswaraya Technological University, India, 2009 [10] Rama Narasimha, K., Rajagopal, M.S., Sridhara, S.N., “Influence of Heat Input, Working Fluid and Evacuation Level on the Performance of a Pulsating Heat Pipe” Journal of Applied Fluid Mechanics, Vol. 5, No. 2, Issue 10, 2012, Accepted for Publication. [11] Rama Narasimha, K., Rajagopal, M.S., Sridhara, S.N., Seetharamu, K. N., “Parametric studies on Pulsating Heat Pipes”, International Journal for Numerical Methods for Heat and Fluid Flow, Vol. 20, Issue 4, 2010.pp. 392-415. [12] Nagvase S.Y., Pachghare P.R., “Parameters affecting the function of closed loop pulsating heat pipe: A Review”, Research Journal of Engineering Sciences, Vol 2(1), 2013, pp. 35-39. [13] M.M. Shete and Prof.Dr.A.D.Desai, “Design and Development of Test-Rig to Evaluate Performance of Heat Pipes in Different Orientations for Mould Cooling Application”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 360 - 365, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [14] M.N.Khan, Utkarsh Gupta, Shubhansh Sinha, Shubhendu Prakash Singh and Sandeep Pathak, “Parametric Study of the Performance of Heat Pipe – A Review”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 1, 2013, pp. 173 - 184, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359.