Artificial roughness is an efficient way for increasing the heat transfer rate in solar air heater with the
corresponding improvement in its thermal performance. A viscous sub-layer is responsible for the low heat
transfer coefficient between absorber plate and flowing air. Repeated ribs in form of artificial roughness are an
effective way to increase the heat transfer rate and improving the performance of solar air heater. Artificial
roughness of the absorber plate is much economical and effective way to improve the thermal performance of
solar air heater. Several investigators have done various investigations to improve heat transfer coefficient with
little penalty of friction factor. They have also developed different correlation for heat transfer coefficient and
friction factor. The correlations developed for heat transfer and friction factor by various investigators have been
reviewed and presented.
Analysis of Heat Generation in Double Pipe Heat Exchanger: An Experimental Ev...IRJET Journal
This document summarizes research on analyzing heat generation in a double pipe heat exchanger with an elliptical fin surface contact. An experiment was conducted to compare the heat transfer rate of an elliptical fin to other fin types (tube-tube, rectangular, annular, spiral rod). The results showed the elliptical fin had a higher heat transfer rate. The document reviews several other studies analyzing different fin geometries, heat transfer optimization techniques, and computational fluid dynamics simulations of heat exchangers. It provides background on analyzing heat exchangers using methods like logarithmic mean temperature difference and effectiveness-NTU and discusses prior work optimizing dimensions, materials, and flow conditions to improve heat transfer performance.
A Review on Comparative Study of Thermal Performance of Artificially Roughene...IRJAES
This document reviews research on enhancing heat transfer in solar air heaters through the use of artificial surface roughness. It summarizes findings from several studies that have experimentally analyzed heat transfer performance for different roughness configurations and geometries. The highest average Nusselt numbers were found for a multi V-rib roughness configuration experimentally, while analytical models predicted higher values for end-of-side roughened collectors. A roughness Reynolds number of around 24 was found to give optimal thermal-hydraulic performance across a range of studies.
This document summarizes a study on improving the cooling efficiency of fins in a two-stage reciprocating compressor through finite element analysis and dimensional modification. The existing annular fins are made of aluminum alloy. A finite element model of the fins is created in ANSYS to analyze temperature distribution over time under natural convection conditions. The results show the fins reach room temperature in 30 minutes. The fins are then modified by increasing the number of fins from 11 to 13. Finite element analysis of the modified fins shows cooling time is reduced to 22 minutes. In conclusion, modifying the fin geometry through additional fins improves the cooling rate of the reciprocating compressor.
Effect of artificial roughness on Thermal and Thermohydraulic efficiency in R...IJMER
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
International Journal of Modern Engineering Research (IJMER) covers all the fields of engineering and science: Electrical Engineering, Mechanical Engineering, Civil Engineering, Chemical Engineering, Computer Engineering, Agricultural Engineering, Aerospace Engineering, Thermodynamics, Structural Engineering, Control Engineering, Robotics, Mechatronics, Fluid Mechanics, Nanotechnology, Simulators, Web-based Learning, Remote Laboratories, Engineering Design Methods, Education Research, Students' Satisfaction and Motivation, Global Projects, and Assessment…. And many more.
The Effect of insertion of different geometries on heat transfer performance ...IJMER
Abstract: Under turbulent flow conditions, the increase in heat transfer rate is more significant than that under laminar flow conditions. The turbulent effects become a dominant factor over secondary flow at higher Reynolds number. The turbulent flow can be produced by inserting different geometries in the circular pipe. This study focuses on the various methods or geometries used to produce turbulent geometries and its effect on the heat transfer. The turbulent generators with different geometrical
configurations have been used as one of the passive heat transfer enhancement techniques and are the most widely used in tubes in several heat transfer applications. Insertion of such geometries may lead to increase the friction factor and pressure drop which directly enhances the heat transfer characteristics.
This document summarizes an experimental study on heat transfer enhancement from surface roughness at laminar flow. Specifically, it examines using circular and oval dimples on an aluminum plate to increase heat transfer from the plate to air flowing over it at Reynolds numbers from 600 to 2000. The study finds that both circular and oval dimples enhance heat transfer compared to a flat plate, while maintaining equivalent or lower pressure drops. The experimental results are validated by comparing the measured Nusselt numbers to theoretical values for a plain vertical plate under laminar flow conditions. In general, the dimpled surfaces increase thermal performance without significantly increasing pressure drops compared to a smooth surface.
Experimental Analysis Of Heat Transfer From Square Perforated Fins In Stagger...IJERA Editor
This project gives the experimental analysis of heat transfer over a flat surface equipped with Square perforated
pin fins in staggered arrangement in a rectangular channel. The Fin dimensions are 100mm in height & 25mm in
width. The range of Reynolds number is fixed & about 13,500– 42,000, the clearance ratio (C/H) 0, 0.33 and 1,
the inter-fin spacing ratio (Sy /D) 1.208, 1.524, 1.944 and 3.417. Sy i.e. stream wise distance is varies and Sx i.e.
span wise distance is constant. The friction factor, enhancement efficiency and heat transfer correlate in
equations with each other. Here we are comparing Square pin fins with cylindrical pin fins. Staggered
arrangement and perforation will enhance the heat transfer rate. Clearance ratio and inter-fin spacing ratio affect
on Enhancement efficiency. Both lower clearance ratio and lower inter-fin spacing ratio and comparatively lower
Reynolds number give higher thermal performance. Friction factor & Nusselt number are Key parameter which
relates with efficiency enhancement and heat transfer rate.
Review of Convective Heat Transfer from Plate Fins Under Natural and Mixed Co...IRJET Journal
This document reviews research on convective heat transfer from plate fins under natural and mixed convection conditions. It summarizes several previous studies that investigated the effects of fin geometry (such as fin length, height, width, spacing, thickness) and operating parameters (such as heat supplied, temperature difference) on heat transfer. The studies found that convective heat transfer increases with fin spacing until an optimal spacing is reached, beyond which further increases in spacing decrease heat transfer. Inclination angle and mixed convection were also found to impact heat transfer. The document provides background on using fins to dissipate heat from electronic devices and explores parameters that most affect natural convective heat transfer within constrained heat sink dimensions.
Analysis of Heat Generation in Double Pipe Heat Exchanger: An Experimental Ev...IRJET Journal
This document summarizes research on analyzing heat generation in a double pipe heat exchanger with an elliptical fin surface contact. An experiment was conducted to compare the heat transfer rate of an elliptical fin to other fin types (tube-tube, rectangular, annular, spiral rod). The results showed the elliptical fin had a higher heat transfer rate. The document reviews several other studies analyzing different fin geometries, heat transfer optimization techniques, and computational fluid dynamics simulations of heat exchangers. It provides background on analyzing heat exchangers using methods like logarithmic mean temperature difference and effectiveness-NTU and discusses prior work optimizing dimensions, materials, and flow conditions to improve heat transfer performance.
A Review on Comparative Study of Thermal Performance of Artificially Roughene...IRJAES
This document reviews research on enhancing heat transfer in solar air heaters through the use of artificial surface roughness. It summarizes findings from several studies that have experimentally analyzed heat transfer performance for different roughness configurations and geometries. The highest average Nusselt numbers were found for a multi V-rib roughness configuration experimentally, while analytical models predicted higher values for end-of-side roughened collectors. A roughness Reynolds number of around 24 was found to give optimal thermal-hydraulic performance across a range of studies.
This document summarizes a study on improving the cooling efficiency of fins in a two-stage reciprocating compressor through finite element analysis and dimensional modification. The existing annular fins are made of aluminum alloy. A finite element model of the fins is created in ANSYS to analyze temperature distribution over time under natural convection conditions. The results show the fins reach room temperature in 30 minutes. The fins are then modified by increasing the number of fins from 11 to 13. Finite element analysis of the modified fins shows cooling time is reduced to 22 minutes. In conclusion, modifying the fin geometry through additional fins improves the cooling rate of the reciprocating compressor.
Effect of artificial roughness on Thermal and Thermohydraulic efficiency in R...IJMER
International Journal of Modern Engineering Research (IJMER) is Peer reviewed, online Journal. It serves as an international archival forum of scholarly research related to engineering and science education.
International Journal of Modern Engineering Research (IJMER) covers all the fields of engineering and science: Electrical Engineering, Mechanical Engineering, Civil Engineering, Chemical Engineering, Computer Engineering, Agricultural Engineering, Aerospace Engineering, Thermodynamics, Structural Engineering, Control Engineering, Robotics, Mechatronics, Fluid Mechanics, Nanotechnology, Simulators, Web-based Learning, Remote Laboratories, Engineering Design Methods, Education Research, Students' Satisfaction and Motivation, Global Projects, and Assessment…. And many more.
The Effect of insertion of different geometries on heat transfer performance ...IJMER
Abstract: Under turbulent flow conditions, the increase in heat transfer rate is more significant than that under laminar flow conditions. The turbulent effects become a dominant factor over secondary flow at higher Reynolds number. The turbulent flow can be produced by inserting different geometries in the circular pipe. This study focuses on the various methods or geometries used to produce turbulent geometries and its effect on the heat transfer. The turbulent generators with different geometrical
configurations have been used as one of the passive heat transfer enhancement techniques and are the most widely used in tubes in several heat transfer applications. Insertion of such geometries may lead to increase the friction factor and pressure drop which directly enhances the heat transfer characteristics.
This document summarizes an experimental study on heat transfer enhancement from surface roughness at laminar flow. Specifically, it examines using circular and oval dimples on an aluminum plate to increase heat transfer from the plate to air flowing over it at Reynolds numbers from 600 to 2000. The study finds that both circular and oval dimples enhance heat transfer compared to a flat plate, while maintaining equivalent or lower pressure drops. The experimental results are validated by comparing the measured Nusselt numbers to theoretical values for a plain vertical plate under laminar flow conditions. In general, the dimpled surfaces increase thermal performance without significantly increasing pressure drops compared to a smooth surface.
Experimental Analysis Of Heat Transfer From Square Perforated Fins In Stagger...IJERA Editor
This project gives the experimental analysis of heat transfer over a flat surface equipped with Square perforated
pin fins in staggered arrangement in a rectangular channel. The Fin dimensions are 100mm in height & 25mm in
width. The range of Reynolds number is fixed & about 13,500– 42,000, the clearance ratio (C/H) 0, 0.33 and 1,
the inter-fin spacing ratio (Sy /D) 1.208, 1.524, 1.944 and 3.417. Sy i.e. stream wise distance is varies and Sx i.e.
span wise distance is constant. The friction factor, enhancement efficiency and heat transfer correlate in
equations with each other. Here we are comparing Square pin fins with cylindrical pin fins. Staggered
arrangement and perforation will enhance the heat transfer rate. Clearance ratio and inter-fin spacing ratio affect
on Enhancement efficiency. Both lower clearance ratio and lower inter-fin spacing ratio and comparatively lower
Reynolds number give higher thermal performance. Friction factor & Nusselt number are Key parameter which
relates with efficiency enhancement and heat transfer rate.
Review of Convective Heat Transfer from Plate Fins Under Natural and Mixed Co...IRJET Journal
This document reviews research on convective heat transfer from plate fins under natural and mixed convection conditions. It summarizes several previous studies that investigated the effects of fin geometry (such as fin length, height, width, spacing, thickness) and operating parameters (such as heat supplied, temperature difference) on heat transfer. The studies found that convective heat transfer increases with fin spacing until an optimal spacing is reached, beyond which further increases in spacing decrease heat transfer. Inclination angle and mixed convection were also found to impact heat transfer. The document provides background on using fins to dissipate heat from electronic devices and explores parameters that most affect natural convective heat transfer within constrained heat sink dimensions.
EXPERIMENTATION ON COPPER TUBE WITH INTERNAL THREADING FOR A HEAT EXCHANGER P...Journal For Research
Experimental model has been carried out to study the effect of heat transfer, thermal enhancement factor and friction factor in a smooth copper tube and different test copper tube having internal threads of pitch ( p=3.5mm), with water as a working fluid media. For such experimentation purpose Reynolds number were varied in the range of 4000 to 8000. The copper tube (OD=38mm, ID=25mm, t=6.5mm) was subjected to constant and uniform heat flux. The experimental data obtained from test tube having different surface geometry i.e. by internal threading of different pitch (p=3.5mm) were compared with smooth circular copper tube. The effect of different surface geometry of inside copper tube i.e. by threading with varying pitch on thermal enhancement factor, heat transfer and friction factor were presented. In that experimental we also calculate Nusselt number, Prandtl number, pitch like heat transfer parameter. The heat transfer rate for copper tubes having internal threads was found to be much higher than smooth circular copper tube for a given value Reynolds number. So simply by changing the internal surface geometry the performance of circular section copper tube is improved.
CIRCULAR FINS WITH SLANTED BLADES: UNIFORM HEAT FLUX AND ISOTHERMAL PROCESSES IAEME Publication
This paper investigates experimentally the heat transfer enhancement process over external surface of copper pipe with circular fins attached on the outer surface (heat exchanger) in rectangular channel with air cross-flow. Four types of circular fins were used in the experiments with 32 mm in. I.D., 92 mm. O.D and 1 mm. thick attached on copper pipe. Each type has five (5) circular fins. 1st type has five (5) fins without slanted blades, 2nd type has five (5) slanted blades per one fin, 3rd type has seven (7) slanted blades per one fin and 4th type has nine (9) slanted blades per one fin.
Effect of artificial roughness on heat transfer and friction factor charIAEME Publication
1) The study examines the effect of adding transverse ribs to the absorber plate of a double pass solar air heater on heat transfer and friction factor characteristics.
2) Maximum heat transfer and friction factor occurred at a relative roughness pitch of 10, with heat transfer enhanced 1.6 times over a smooth plate.
3) Artificial roughness is used to increase turbulence and break the laminar sub-layer on the absorber plate, improving heat transfer and thermal efficiency.
The document presents an experimental study on enhancing heat transfer from copper pipes using circular fins with slanted blades. Four types of fins were tested: 1) without blades, 2) with 5 blades per fin, 3) with 7 blades per fin, and 4) with 9 blades per fin. Results showed that Nusselt number increased by 11.8% for the second type, 20.25% for the third type, and 27.5% for the fourth type compared to the first type. The fourth type also significantly reduced thermal resistance and improved fin performance compared to the first type. Increasing the number of slanted blades was more effective at enhancing heat transfer.
IRJET- Numerical Analysis for Effect of Different Length Combination of Turbu...IRJET Journal
This document describes a numerical analysis of the effect of different length combinations of twisted tape and wire coil turbulators on heat transfer, pressure drop, and friction factor in a double pipe heat exchanger. Five combinations of twisted tape and wire coil lengths were analyzed (25-75%, 30-70%, 35-65%, 40-60%, 45-55%) using computational fluid dynamics software. The results were compared to existing studies on enhancing heat transfer using twisted tape and wire coil inserts in heat exchanger pipes. Key findings included increased heat transfer coefficients and Nusselt numbers but also higher friction factors compared to a plain pipe.
A Study on Various Heat Transfer Enhancement TechniquesIRJET Journal
This document summarizes research on various heat transfer enhancement techniques, including wavy fins, louvered fins, and different tube shapes. It discusses how constructal theory can be used to optimize the configuration of wavy and louvered fins to improve thermal performance. Several studies that analyzed parameters like fin pitch and louver angle are summarized. The results showed that an optimal design using constructal theory can improve heat transfer by 14-32% while maintaining pressure drop. For wavy fins, an amplitude ratio of around 0.7 performed well. The document also analyzes different tube shapes, finding that a circular cross-section performed most efficiently, with lower turbulence than elliptical or oval shapes.
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
Heat transfer enhancement and friction factor analysis in tube using conical ...eSAT Journals
Abstract Role of the conical spring array for the heat transfer enhancement and pressure drop change in a pipe with constant heat flux boundary condition was investigated. Three different arrangements of conical spring array inserts were used in the experimental setup. Conical spring inserts with diverging conical spring, converging-diverging conical spring and converging conical spring array inserts arrangements were used. Water was used as a working fluid in the experimental setup. It was found that use of conical spring array inserts arrangement leads to enhancement in heat transfer. Higher heat transfer rate was achieved in the divergent spring array arrangement than the converging-diverging and converging arrangement. However, maximum friction factor is achieved in the diverging spring array insert arrangement. By increasing the Reynolds Number for different turbulator arrangement, the significant increase in Nusselt number was obtained. The enhancement in Nusselt Number for the diverging, converging-diverging, converging conical spring array arrangement was 645% ,431% and 259% respectively. The heat transfer enhancement efficiency can be evaluated based on the power consumption per unit mass of fluid. Heat transfer enhancement efficiencies were found for the divergent spring array arrangement up to 277% and for the convergent-divergent spring arrangement up to 212% and for the convergent spring array arrangement up to 153%. Keywords— Heat exchanger, Heat transfer enhancement, Friction factor, Conical spring turbulator, Heat transfer enhancement efficiency
FLUID FLOW ANALYSIS IN AIR DUCT FLOW WITH AND WITHOUT INTERNAL THREADS USING ...IAEME Publication
Computational heat transfer flow modeling is one of the great challenges in the classical sciences. As with most problems in engineering, the interest in the heat transfer augmentation is increasing due to its extreme importance in various industrial applications. This paper deals with the analysis of heat transfer for fluid flowing through the pipe with and without internal threads using CFD. Using CFD codes for modeling the heat and fluid flow is an efficient tool for predicting equipment performance. CFD offers a convenient means to study the detailed flows and heat exchange processes, which take place inside the tube. Simulations were carried out using commercial CFD software ANSYS Fluent version 14.5. Friction factor and Nusselt number for air flowing through the specified tube (internal diameter = 0.005 m, length = 0.1 m) were obtained first for the plain tube and then for the tube with internal threads with pitch 5mm in the Reynolds number range of 2000 to 5000. Finally results will be compared to available experimental and analytical calculations. The data obtained by simulation are matching with the literature value for a plain tube with the discrepancy of less than plus or minus 5% for Nusselt number and for the friction factor.
Enhanced heat transfer for the tube with internal threads has been observed. Heat flux is more uniform all along the tube and decreases uniformly towards the center.
IRJET- Thermal Analysis on Solar Air Heater DuctIRJET Journal
This document summarizes a numerical study on the effects of transverse rectangular ribs on heat transfer properties in a solar air heater duct. Computational fluid dynamics (CFD) simulations were performed to analyze thin and square ribs arranged in single, staggered, and inline patterns. The simulations found that introducing ribs significantly increased heat transfer compared to a smooth duct. Thin ribs performed better than square ribs. Inline thin ribs produced a 1.83 times higher heat transfer coefficient than the smooth duct. Reynolds number increases led to higher Nusselt numbers for all cases. Staggered ribs had lower heat transfer than inline ribs. The study provides conclusions on rib effects and turbulence model selection for predicting solar air heater performance.
REVIEW PAPER- ON ENHANCEMENT OF HEAT TRANSFER USING RIBSIaetsd Iaetsd
This document reviews research on enhancing heat transfer using ribs mounted inside ducts. Various studies investigated ribs of different shapes, pitches, heights and angles. Continuous ribs, transverse ribs, angled ribs, and other rib configurations were examined. Most studies found that ribs increased turbulence and heat transfer compared to smooth ducts. Some key findings included V-shaped ribs providing better performance than other shapes, and certain rib pitches and angles performing better depending on parameters like Reynolds number. In general, ribs were found to effectively enhance heat transfer through boundary layer disruption and increased turbulence compared to smooth ducts.
CFD Analysis of Concentric Tube Heat Exchanger Using Twisted TapesIJARIIT
In this paper, the three dimensional CFD modeling studies on heat transfer, friction factor and thermal performance
of concentric tube heat exchanger using twisted tapes (Plain, V-cut, , Jagged V-cut) with different twist ratios (y=2.0, 4.0) are
used. Twisted tapes are used to augment the heat transfer by creating turbulence in the fluid flow. Various methods are applied
to increase thermal performance of heat transfer devices such as treated surfaces, rough surfaces, swirling flow devices, coiled
tubes, and surface tension devices. Out of these twisted tape method is used to increase the thermal performance. Twisted tape
inserts on effectiveness of heat exchanger has analyzed for different Reynolds Number. The maximum thermal performance
factor was obtained by the Jagged V-cut twisted tape (H=50) insert compare to other twisted tapes. Simultaneously the friction
factor has been analyzed
IRJET- Experimental Analysis of Convective Heat Transfer Augmentation of Bi-M...IRJET Journal
This document provides a literature review of research on bi-metallic plate heat exchangers to enhance convective heat transfer. It discusses 8 studies that experimentally analyzed heat transfer coefficients and pressure drops of different combinations of bi-metallic plates under forced convection. The goal of improving heat transfer efficiency while minimizing pressure losses is important for industries using such heat exchangers like power plants, refrigeration, and chemical processes. The document focuses on reviewing work done to optimize the design of bi-metallic heat exchangers.
This document summarizes an experimental study on heat transfer characteristics of a shell and tube heat exchanger using hiTRAN wire matrix turbulators as tube inserts. The study found that using the hiTRAN inserts increased turbulence in the tube side flow, reducing the boundary layer and increasing heat transfer coefficients by 120-130% compared to a plain tube. While the inserts increased pressure drop, the significant increase in heat transfer outweighed this effect. The main applications of hiTRAN inserts are in laminar and transitional flow regimes where they are most effective at enhancing heat transfer, but they can also provide benefits in turbulent flow regimes.
IRJET- Study of Heat Transfer Characteristics for the Flow of Air over a Heat...IRJET Journal
This document summarizes a study that used computational fluid dynamics (CFD) to analyze heat transfer from circular and diamond-shaped tubes. The study found that the diamond shape performed better than the circular shape. Specifically:
1) Temperature distribution results showed higher surface temperatures on the circular tube compared to the diamond tube. Higher Reynolds numbers also reduced surface temperatures for both shapes.
2) Nusselt number, a measure of heat transfer, increased with Reynolds number for both shapes. However, the diamond shape had higher Nusselt numbers, indicating better heat transfer performance compared to the circular shape.
3) Tube shape was found to significantly impact heat transfer characteristics, with the diamond shape offering better heat
A Review on Experimental and CFD Analysis for Heat Transfer Enhancement in He...IRJET Journal
This document reviews experimental and computational fluid dynamics (CFD) analyses that have evaluated methods to enhance heat transfer in heat exchanger tubes. Specifically, it focuses on the use of drilled twisted tape inserts of various geometries within the tubes. It provides background on heat exchangers and heat transfer enhancement techniques, including passive techniques like twisted tape inserts. The literature review summarizes several studies that have examined twisted tape inserts computationally or experimentally, finding that inserts can increase turbulence and heat transfer but also pressure drop. The present study aims to contribute additional CFD and experimental analysis of drilled twisted tape inserts of different dimensions to further understand their impact on heat transfer and fluid friction characteristics in heat exchanger tubes.
A Review- Comparative Study of Thermal and Hydrostatic Performance Analysis O...IRJET Journal
This document summarizes research comparing the thermal and hydrostatic performance of helical coil heat exchangers and straight tube heat exchangers. It first provides background on heat exchangers and discusses how helical coils offer advantages over straight tubes, including higher heat transfer coefficients and more compact designs. It then reviews several previous studies that have found helical coils provide higher heat transfer rates compared to straight tubes. Specifically, one study found heat transfer increased up to 3.955 times with corrugated tubes compared to smooth tubes. Another study found Nusselt numbers and friction factors increased up to 117% and 254% respectively when both inner and outer tubes were corrugated compared to only the inner tube being corrugated.
HEAT TRANSFER AUGMENTATION OF LAMINAR NANOFLUID FLOW IN HORIZONTAL TUBE INSER...IAEME Publication
In this paper, an experimental study on the heat transfer enhancement and friction factor characteristics for fully developed laminar CuO/distilled-water (DI-water) nanofluid flow through horizontal tube inserted with different geometries of twisted tapes under constant heat flux condition ranged from 4483 to 10000 W/m^2. φ=0.08% and 0.35% volume concentrations of CuO nanoparticles are suspending in distilled water to prepare nanofluid. Twisted types made from copper material with twist ratios Y=2.6 and 5.3 twist ratios, thickness t=1 and 2mm and with semicircular and triangular cuts shape were used to study their effect on twisted tape performance. Results showed that both convective heat transfer in terms of average Nusselt number (Nu) ̅ and friction factor have significantly increasing with inserting twisted tape with nanofluids as working fluid comparing with nanofluids or DI-water in smooth tube case and this enhancement increases as both Reynold number and volume concentration increases.
IRJET-Enhancing the Performance of Hybrid Microgrid using non Isolated Single...IRJET Journal
This document analyzes heat transfer in a light passenger car radiator with various geometrical configurations using computational fluid dynamics (CFD). It studies a staggered fin-and-tube radiator with circular and oval tubes. The radiator is modeled and analyzed in FLUENT to obtain velocity, temperature, and pressure contours. Oval tubes are found to improve heat transfer compared to circular tubes. Specifically, oval tube configurations reduce temperature differences between the tubes and air, indicating more efficient heat absorption. While circular tubes show higher temperatures, oval tube designs enhance convection and lower outlet temperatures. In conclusion, varying the tube shape geometrically through oval designs improves the radiator's thermal performance.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
STUDY OF HEAT TRANSFER ON BROKEN ARC ROUGHNESS ELEMENTS ON THE ABSORBER PLATE...IAEME Publication
Performance of solar air heater can be enhanced by adding roughness to the inner periphery. The present study on the effect of various shape parameters for broken arc roughness elements of heat transfer and friction factor characteristics of rectangular duct. The duct has Reynolds number (Re) range of 3000-22300, respective roughness height (e/D) values is 0.045, arc angle (α) is 60˚ and roughness width (W/w) is 5 and relatively roughness pitch is 8.
Heat Transfer and Friction Factor Characteristics in a Discrete Rib Roughened...IRJET Journal
This document reviews studies on using discrete rib roughness elements to enhance heat transfer in channels with minimal increase in friction. Different types of discrete ribs are discussed, including transverse and inclined discrete ribs. Several studies investigated the effects of discrete rib geometry parameters like rib angle, number of ribs, and presence of gaps on heat transfer and friction characteristics. In general, discrete rib arrangements were found to increase heat transfer more than continuous ribs due to increased secondary flows and local turbulence, though friction is also increased. The document provides context on rib-roughened channel heat transfer and summarizes key findings and parameters investigated in different studies on discrete rib geometries.
EXPERIMENTATION ON COPPER TUBE WITH INTERNAL THREADING FOR A HEAT EXCHANGER P...Journal For Research
Experimental model has been carried out to study the effect of heat transfer, thermal enhancement factor and friction factor in a smooth copper tube and different test copper tube having internal threads of pitch ( p=3.5mm), with water as a working fluid media. For such experimentation purpose Reynolds number were varied in the range of 4000 to 8000. The copper tube (OD=38mm, ID=25mm, t=6.5mm) was subjected to constant and uniform heat flux. The experimental data obtained from test tube having different surface geometry i.e. by internal threading of different pitch (p=3.5mm) were compared with smooth circular copper tube. The effect of different surface geometry of inside copper tube i.e. by threading with varying pitch on thermal enhancement factor, heat transfer and friction factor were presented. In that experimental we also calculate Nusselt number, Prandtl number, pitch like heat transfer parameter. The heat transfer rate for copper tubes having internal threads was found to be much higher than smooth circular copper tube for a given value Reynolds number. So simply by changing the internal surface geometry the performance of circular section copper tube is improved.
CIRCULAR FINS WITH SLANTED BLADES: UNIFORM HEAT FLUX AND ISOTHERMAL PROCESSES IAEME Publication
This paper investigates experimentally the heat transfer enhancement process over external surface of copper pipe with circular fins attached on the outer surface (heat exchanger) in rectangular channel with air cross-flow. Four types of circular fins were used in the experiments with 32 mm in. I.D., 92 mm. O.D and 1 mm. thick attached on copper pipe. Each type has five (5) circular fins. 1st type has five (5) fins without slanted blades, 2nd type has five (5) slanted blades per one fin, 3rd type has seven (7) slanted blades per one fin and 4th type has nine (9) slanted blades per one fin.
Effect of artificial roughness on heat transfer and friction factor charIAEME Publication
1) The study examines the effect of adding transverse ribs to the absorber plate of a double pass solar air heater on heat transfer and friction factor characteristics.
2) Maximum heat transfer and friction factor occurred at a relative roughness pitch of 10, with heat transfer enhanced 1.6 times over a smooth plate.
3) Artificial roughness is used to increase turbulence and break the laminar sub-layer on the absorber plate, improving heat transfer and thermal efficiency.
The document presents an experimental study on enhancing heat transfer from copper pipes using circular fins with slanted blades. Four types of fins were tested: 1) without blades, 2) with 5 blades per fin, 3) with 7 blades per fin, and 4) with 9 blades per fin. Results showed that Nusselt number increased by 11.8% for the second type, 20.25% for the third type, and 27.5% for the fourth type compared to the first type. The fourth type also significantly reduced thermal resistance and improved fin performance compared to the first type. Increasing the number of slanted blades was more effective at enhancing heat transfer.
IRJET- Numerical Analysis for Effect of Different Length Combination of Turbu...IRJET Journal
This document describes a numerical analysis of the effect of different length combinations of twisted tape and wire coil turbulators on heat transfer, pressure drop, and friction factor in a double pipe heat exchanger. Five combinations of twisted tape and wire coil lengths were analyzed (25-75%, 30-70%, 35-65%, 40-60%, 45-55%) using computational fluid dynamics software. The results were compared to existing studies on enhancing heat transfer using twisted tape and wire coil inserts in heat exchanger pipes. Key findings included increased heat transfer coefficients and Nusselt numbers but also higher friction factors compared to a plain pipe.
A Study on Various Heat Transfer Enhancement TechniquesIRJET Journal
This document summarizes research on various heat transfer enhancement techniques, including wavy fins, louvered fins, and different tube shapes. It discusses how constructal theory can be used to optimize the configuration of wavy and louvered fins to improve thermal performance. Several studies that analyzed parameters like fin pitch and louver angle are summarized. The results showed that an optimal design using constructal theory can improve heat transfer by 14-32% while maintaining pressure drop. For wavy fins, an amplitude ratio of around 0.7 performed well. The document also analyzes different tube shapes, finding that a circular cross-section performed most efficiently, with lower turbulence than elliptical or oval shapes.
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
Heat transfer enhancement and friction factor analysis in tube using conical ...eSAT Journals
Abstract Role of the conical spring array for the heat transfer enhancement and pressure drop change in a pipe with constant heat flux boundary condition was investigated. Three different arrangements of conical spring array inserts were used in the experimental setup. Conical spring inserts with diverging conical spring, converging-diverging conical spring and converging conical spring array inserts arrangements were used. Water was used as a working fluid in the experimental setup. It was found that use of conical spring array inserts arrangement leads to enhancement in heat transfer. Higher heat transfer rate was achieved in the divergent spring array arrangement than the converging-diverging and converging arrangement. However, maximum friction factor is achieved in the diverging spring array insert arrangement. By increasing the Reynolds Number for different turbulator arrangement, the significant increase in Nusselt number was obtained. The enhancement in Nusselt Number for the diverging, converging-diverging, converging conical spring array arrangement was 645% ,431% and 259% respectively. The heat transfer enhancement efficiency can be evaluated based on the power consumption per unit mass of fluid. Heat transfer enhancement efficiencies were found for the divergent spring array arrangement up to 277% and for the convergent-divergent spring arrangement up to 212% and for the convergent spring array arrangement up to 153%. Keywords— Heat exchanger, Heat transfer enhancement, Friction factor, Conical spring turbulator, Heat transfer enhancement efficiency
FLUID FLOW ANALYSIS IN AIR DUCT FLOW WITH AND WITHOUT INTERNAL THREADS USING ...IAEME Publication
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International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
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Under turbulent flow conditions, the increase in heat transfer rate is more significant than
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circular pipe. This study focuses on the various methods or geometries used to produce turbulent
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It is well known fact that the heat transfer coefficient between the absorber surface of solar air collector & flowing fluid i.e. air can be improved by providing artificial roughness geometry on heat transfer surface (absorber surface).In this way the Thermal efficiency is increased. But at the same time due to roughness geometry pumping power of solar air collector in increased due to fictional losses in duct. So it necessary to examine the shape, size & flow pattern of various roughness elements to get maximum efficiency with minimum frictional losses. Therefore the selection of roughness geometry has to be based on the parameter that takes into account both Thermal & Hydraulic (friction) performance i.e. Thermo-hydraulic Performance of Solar air collector. Number of roughness elements has been investigated on heat transfer & friction characteristics of solar air collectors. In this paper, reviews of various artificial roughness elements used as passive heat transfer techniques, in order to improve Thermo-hydraulic performance of solar air collectors is reviewed & presented. Correlations developed by various researchers with the help of experimental results for heat transfer & friction factor for solar air collector by taking different roughness geometries are given & these correlations are useful to predict the Thermo-hydraulic performance of solar air collector having roughened ducts. The objective of this paper is also the awareness of effect of various types’ roughness geometries on heat
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Experimental Investigation of Heat Transfer through Rectangular and Trapezoid...IRJET Journal
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Assessment of Performance Characteristic of Solar Air Heater with Assorted Geometries - A Review
1. Alok Kumar Rohit Int. Journal of Engineering Research and Applications www.ijera.com
ISSN: 2248-9622, Vol. 6, Issue 1, (Part - 4) January 2016, pp.40-48
www.ijera.com 40|P a g e
Assessment of Performance Characteristic of Solar Air Heater
with Assorted Geometries - A Review
Alok Kumar Rohit1
, A.M. Lanjewar2
1
PhD Scholar, Department of Mechanical Engineering AISECT University Bhopal, India
2
Assistant Professor Maulana Azad National Institute of Technology, Bhopal, India
Abstract
Artificial roughness is an efficient way for increasing the heat transfer rate in solar air heater with the
corresponding improvement in its thermal performance. A viscous sub-layer is responsible for the low heat
transfer coefficient between absorber plate and flowing air. Repeated ribs in form of artificial roughness are an
effective way to increase the heat transfer rate and improving the performance of solar air heater. Artificial
roughness of the absorber plate is much economical and effective way to improve the thermal performance of
solar air heater. Several investigators have done various investigations to improve heat transfer coefficient with
little penalty of friction factor. They have also developed different correlation for heat transfer coefficient and
friction factor. The correlations developed for heat transfer and friction factor by various investigators have been
reviewed and presented.
Keywords: Solar air heater, Absorber plate, Artificial roughness, Review
I. INTRODUCTION
In current scenario everyone turn towards the
non-conventional energy because it is abundant in
nature. For the better economic process and industrial
growth it is necessary to turn towards solar energy.
Efficiency of solar air heater is generally low due to
low heat transfer capability as compare to solar water
heaters. So it is necessary to enhance heat transfer
coefficient for increasing the efficiency of solar air
heater. It may be possible to use two criterions for
improving the heat transfer coefficient. First to
increase the surface area of the material with the help
of corrugated surfaces or extended surfaces called
fins. The second method is to increase the heat
transfer coefficient with the help of artificial
turbulence at the heat-transferring surface. This
turbulence can be achieved by applying artificial
roughness on the underside of absorber plate. Various
investigators have worked on several designs for
enhancing the heat transfer coefficient with minimum
penalty of friction.
II. ARTIFICIAL ROUGHNESS
Roughness converts the laminar sub layer into
local turbulence at heat transferring surface. Several
investigators have investigated on different roughness
geometry in order to enhance the heat transfer rate
with minimum friction losses. For reducing the
friction losses it is necessary to reduce roughness
height as compare to duct dimension. The roughness
element height (e) and pitch (p) are the important
parameters that stabilize the arrangement and shape
of the roughness. The parameter of
artificial roughness can be expressed in terms of
dimensionless parameters like relative roughness
height (e/D), relative gap width, chamfer angle,
relative roughness pitch (p/e), relative gap position
(d/W), relative gap width (g/e) . The roughness
element can be V-shaped continuous or broken,
discrete elements, transverse or angled ribs. It may be
noted that square ribs are the most commonly used
geometry but chamfered, circular, semi-circular and
grooved sections have been investigated in order to
get most beneficial arrangement from thermo-
hydraulic analysis.
III. FLOW PATTERN
Different types of artificial roughness have
different shapes, orientation and rib arrangements.
Enhancement of heat transfer totally depends upon
resulting flow pattern.
3.1 Effect of rib
In case of air flow the rib is responsible for the
generation of two flow separation regimes, one on
each side of the rib. Rib vortices generated are
responsible for the creation of turbulence at the
vicinity of rib arrangement. Friction losses also take
place but enhancement of heat transfer becomes the
core criterion.
3.2 Effect of rib height and pitch
Fig. 1 and 2 shows reattachment point that is
responsible for the enhancement of heat transfer rate
and it also shows the flow pattern downstream
corresponding to as the pitch is changed. With
relative roughness pitch ratio (p/e) less than about 8
reattachment of shear layer does not occur. The
reattachment will not occur for relative roughness
RESEARCH ARTICLE OPEN ACCESS
2. Alok Kumar Rohit Int. Journal of Engineering Research and Applications www.ijera.com
ISSN: 2248-9622, Vol. 6, Issue 1, (Part - 4) January 2016, pp.40-48
www.ijera.com 41|P a g e
pitch considerably less than about 8 resulting in the
decrease of heat transfer enhancement. A similar
effect can be produce by increasing the relative
roughness pitch (p/e) for a fixed relative roughness
height (e/D). Decrease in enhancement of heat
transfer rate occurs due to increase in relative
roughness pitch beyond about 10. After investigation
optimum combination of pitch and height necessary
for maximum enhancement of heat transfer rate can
be evaluated.
Fig. 1. Flow pattern as a function of relative
roughness pitch
Fig. 2. Flow pattern as a function of relative
roughness height
IV. DEVELOPMENT OF ARTIFICIAL
ROUGHNESS IN SOLAR AIR
HEATER
4.1. Transverse ribs
4.1.1 Transverse continuous ribs
Varun et al. [1] carried out an experimental study on
heat transfer and friction characteristics by using a
combination of transverse and inclined ribs on the
heated plate of solar air heater duct. Small diameter
transverse roughness was introduced by Prasad and
Mullick [2].The study parameters of Prasad and
Mullick [2] were relative roughness pitch as 12.7 and
relative roughness height as 0.019. They reported that
the application of protruding wires led to
improvement in plate efficiency factor from 0.63 to
0.72.
Parameters such as relative roughness pitch as 10-40,
relative roughness height as 0.01-0.03, roughness
Reynolds number as 8-42 and Reynolds number as
5000– 20,000 were used by Verma and Prasad [3].
They reported that corresponding to Reynolds
number of 24 the thermo-hydraulic performance was
calculated as 71%.
Prasad and Saini [4] investigated using small
thickness diameter wire as artificial roughness in
solar air collector. They used relative roughness
height of 0.020–0.033 and relative roughness pitch of
10–20 for the investigation of heat transfer rate and
friction factor. Correspond to relative roughness
pitch of 10 the maximum value of Nusselt number
and friction factor were reported as 2.38 and 4.25
respectively. The shape of roughness geometry is
shown in “Fig. 3”.
Gupta et al. [5] used transverse wire in solar air
heater for alteration of rough flow regime. They used
aspect ratio (W/H) as 6.8–11.5, relative roughness
height as 0.018–0.052, relative roughness pitch as 10
and Reynolds number varied from 3000-18000. They
concluded that Stanton number increases with
increase in Reynolds number and Stanton number
achieved maximum value for Reynolds number of
12,000.
4.1.2 Transverse broken ribs
This type of geometry is investigated by Sahu and
Bhagoria [6]. They used transverse broken ribs as
shown in “Fig. 4”. Investigated parameters are aspect
ratio 8, roughness pitch as 10–30 mm, rib height as
1.5 mm and Reynolds number as 3000–12000. For
the pitch value as 20 mm the maximum Nusselt
number has been observed. Under the similar
operating condition the roughened absorber plate
increased heat transfer coefficient by 1.25–1.4 times
as compare to smooth duct.
Fig. 3. Transverse small diameter wire
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Fig. 4. Transverse broken ribs
4.2. Inclined ribs
4.2.1 Continuous inclined ribs
Gupta et al. [7] investigated inclined ribs as
compared to transverse ribs and concluded that
inclined ribs give increased effect of heat transfer
coefficient and friction factor. They investigated
inclined circular ribs as artificial roughness by taking
the Reynolds number of 3000-18000, duct aspect
ratio as 6.8–11.5, relative roughness height as 0.018–
0.052 for relative roughness pitch of 10. The
enhancement of thermal efficiency was reported as
1.16–1.25 as compared to smooth plate in range of
parameters investigated. The roughness geometry is
shown in “Fig. 5”.
Fig. 5. Inclined continuous ribs
4.2.2 Broken inclined ribs
Aharwal et al. [8] introduced a criterion of secondary
flow and main flow through the gap thereby creating
local turbulence in inclined ribs. The “Fig. 6”. shows
roughness geometry. Range of parameters during
investigation are aspect ratio 5.84, Reynolds number
range as 3000–18,000, relative roughness height as
0.0377, relative roughness pitch and angle of attack
of 60o
. Gap position (d/W) and gap width (g/e) were
in the range of 0.5–2 and 0.1667–0.667 respectively.
As compare to smooth duct the roughened plate has
maximum enhancement in Nusselt number and
friction factor being reported as 2.59 and 2.87.
Maximum thermo-hydraulic performance was
reported corresponding for relative gap width of 1.0
and for relative gap position of 0.25.
Fig. 6. Inclined ribs with gap
4.3. Wire mesh
4.3.1 Expanded metal mesh
This type of roughness geometry is introduced
by Saini et al. [9]. They studied the effect of relative
long way length of mesh (l/e) and relative short way
length of mesh (s/e) on heat transfer and friction
factor. The optimum parameters reported are angle of
attack of 61.9o
and 72o
respectively for enhanced heat
transfer rate and friction factor. Enhancement of heat
transfer coefficient and friction factor is reported of
order of 4 and 5 times as compare to smooth duct.
The geometry of artificial roughness is shown in
“Fig. 7”.
Fig. 7. Expanded metal mesh
4.3.2 Discretized metal mesh
Metal mesh geometry further discretized by Karmare
and Tikekar [10]. They investigated heat transfer and
friction factor for metal grit ribs as shown in “Fig. 8”.
Parameters used for investigation were p/e as 12.5–
36, e/Dh as 0.035–0.044, l/s as 1.72–01 and Reynolds
numbers as 4000–17000. The optimum performance
was reported for discretized metal mesh
corresponding to l/s as 1.72, e/Dh 0.044 and p/e as
17.5 showed optimum performance.
Fig. 8. Metal grit ribs
4.4. Chamfered ribs
Chamfered rib artificial roughness was investigated
by Karwa et al. [11] as shown in “Fig. 9”.
Investigation showed two and three times increase in
Stanton number and friction factor respectively. With
the chamfer angle of 15o
both Stanton number and
friction factor were reported to be highest. The
various parameters of investigation were chamfer
angle (ɸ) as 15o
to 18o
, duct aspect ratio as 4.8–12,
relative roughness height as 0.014–0.0328, Reynolds
number as 3000–20,000 and relative roughness pitch
as 4.5–8.5. The heat transfer increases with
increasing of aspect ratio from 4.65 to 9.66 and the
roughness function decreases with the increase in
aspect ratio from 4.65 to 7.75. Investigation showed
increase in thermal efficiency about 10 to 40% with
enhancement of Nusselt number in order of 50 to
120%.
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Fig. 9. Integral chamfered ribs
4.5. Wedge ribs
Bhagoria et al. [12] proposed the enhancement of
heat transfer rate using wedge shaped transverse
integral ribs as shown in “Fig. 10”. On the
experimental analysis basis it is concluded that
enhancement of Nusselt number is 2.4 times while of
friction factor as 5.3 times as compare to smooth duct
in range of parameters investigated. They also
investigated the effect of relative roughness height,
relative roughness pitch and wedge angle on heat
transfer rate and friction factor. They concluded
relative roughness pitch of 7.57 was better for
maximum heat transfer rate corresponding to wedge
angle of 10.
Fig. 10. Wedge shaped transverse integral ribs
4.6. V-shaped rib
4.6.1 Continuous V-ribs
Momin et al. [13] investigated the effect of
continuous ribs on heat transfer rate and friction
factor. They concluded that inclined rib give better
result as compare to transverse ribs due to increase in
secondary vortices. V-shaping of angled rib gives
maximum secondary vortices. V-shaped rib
roughness geometry is shown in “Fig. 11”. Necessary
parameters of investigation were relative roughness
height as 0.02-0.034, angle of attack of flow (α) as
30o
– 90o
and Reynolds number of 2500–18,000.
Maximum enhancement of heat transfer coefficient
and friction factor was reported as 2.30 and 2.83
times as compare to smooth duct for angle of attack
of 60o
.
Fig. 11. V-shaped ribs
Fig. 12. Discretized V-ribs
V discontinuous rib
V- discrete rib
Fig. 13. V-shaped rib of different configurations.
4.6.2 Discrete V-ribs
Muluwork et al. [14] worked on transverse staggered
discrete ribs and compared it with staggered discrete
V-apex up and V-down ribs and evaluated thermal
performance. The roughness geometry is shown in
“Fig. 12”. They reported maximum enhancement of
Stanton number, was in case of V-down discrete ribs
as compare to corresponding V-up and transverse
ribs.
Karwa et al. [15] investigated V-discontinuous and
V-discrete rib with range ofparameters of relative
roughness length (B/S) as 3 and 6, relative roughness
pitch as 10.63, angle of attack as 45o
and 60o
and
Reynolds number as 2850–15,500. They concluded
that angle of attack of 60o
perform better as compare
to 45o
and also discrete ribs give better performance
as compare to discontinuous ribs. This type of
roughness geometry is shown in “Fig. 13”.
Singh et al. [16] investigated discrete V-down ribs
roughness geometry as shown in “Fig. 14”.The range
of investigated parameters are relative roughness
pitch as 4–12, relative gap width (g/e) as 0.5–2.0 and
relative gap position (d/w) as 0.20–0.80 respectively,
relative roughness height as 0.015– 0.043 and
Reynolds number from 3000 to 15,000. Maximum
increase in Nusselt number and friction factor are
3.04 and 3.11 times respectively as compare to
smooth duct. For maximum increase in Nusselt
number and friction factor the parameters used are
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e/Dh as 0.043, d/w as 0.65, p/e as 10, g/e as 1.0 and α
as 60o
.
Fig. 14. Discrete V-down ribs
Fig. 15. W-shaped rib roughness
Fig. 16. Discrete W-shaped ribs
4.7. W-shaped ribs
4.7.1 Continuous W-ribs
Lanjewar et al. [17] used concept of increased
secondary cell responsible for the enhancement of
heat transfer rate. The roughness geometry is shown
in “Fig. 15”. After investigation they concluded that
maximum enhancement of Nusselt number and
friction factor observed was 2.36 and 2.01. They also
reported that W-down arrangement with angle of
attack of 60o
give optimum thermo-hydraulic
performance. The different range of parameters were
relative roughness height as 0.018–0.03375, relative
roughness pitch as 10 and angle of attack as 30o
–
75o
.
4.7.2 Discrete W-ribs
Kumar et al. [18] investigated discrete W-shaped rib.
The roughness geometry is shown in “Fig. 16”. The
range of parameters used are relative roughness
height as 0.0168–0.0338, relative roughness pitch as
10 and angle of attack as 30o
–75o
and Reynolds
number as 3000 to 15,000. They reported that
maximum enhancement of Nusselt number and
friction factor was 2.16 and 2.75 times as compare to
smooth duct with angle of attack as 60o
.
4.8. Multiple V-ribs
4.8.1 Multiple continuous V-ribs
Hans et al. [19] introduced a phenomenon of
secondary flow cells in multiple V-ribs and also
investigated with such geometry. After investigation
they concluded that the maximum enhancement of
Nusselt number and friction factor was 6 and 5 times
respectively as compare to smooth duct for range of
parameters investigated and also angle of attack of
60o
is responsible for maximum enhancement of heat
transfer and friction factor. There roughness
geometry is shown in “Fig. 17”. The experiment
conducted on the basis of several important
parameters such as Reynolds number from 2000 to
20,000, relative roughness pitch as 6-12, relative
roughness height as 0.019–0.043, relative roughness
width (W/w) range as 1–10 and angle of attack as
30o
–75o
.
Fig. 17. Multiple V-ribs
Fig. 18. Multi V-shaped ribs with gap.
4.8.2 Multiple V-rib with gap
Kumar at al. [20] introduced a phenomenon of local
turbulence and acceleration of flow by putting gap.
After completion of experimental analysis they
concluded that maximum enhancement of Nusselt
number and friction factor was 6.32 and 6.12 times
respectively as compare to smooth duct for range of
parameters investigated. During investigation they
used different parameters such as relative roughness
height as 0.043, relative gap width as 0.5–1.5,
relative gap distance ratio as 0.24 – 0.8, Reynolds
number from 2000 to 20,000, angle of attack as 60o
and relative width ratio as 6. Roughness geometry is
shown in “Fig. 18”.
4.9. Roughness element combination
4.9.1 Transverse and inclined ribs combination
Varun at al. [1] introduced concept of combination
roughness of inclined ribs and transverse ribs. The
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roughness geometry is shown in “Fig. 19”. They
concluded that roughened collector with roughness
pitch of 8 gave better result as compare to smooth
one. The range of parameters used is Reynolds
number from 2000 to 14,000, relative roughness
height as 0.030, relative roughness pitch in between
3–8.
Fig. 19. Transverse and inclined ribs
Fig. 20. Rib groove roughness
Fig. 21. Integral transverse chamfered rib
groove roughness
4.9.2 Transverse rib groove combination
Jaurker et al. [21] proposed transverse rib roughness
by incorporating groove between two transverse ribs.
They investigated rib grooved artificial roughness
and the geometry is shown in “Fig. 20”. After
investigation they concluded that maximum heat
transfer occurs at relative roughness pitch of 6 and
optimum heat transfer was registered for groove
position to pitch ratio of 0.4.
4.9.3 Chamfered rib groove combination
Layek et al. [22] used chamfered rib roughness
geometry for the enhancement of heat transfer rate
and friction characteristic of repeated integral
transverse chamfered rib groove roughness as shown
in “Fig. 21”. Parameters used during investigation are
Reynolds number range from 3000–21,000, relative
roughness pitch as 4.5 – 10, relative groove position
as 0.3–0.6, chamfered angle as 5–30 and relative
roughness height as 0.022– 0.04. They reported that
Nusselt number and friction factor increased by 3.24
and 3.78 times respectively as compared to smooth
duct. With relative groove position of 0.4 maximum
enhancements of Nusselt number and friction factor
were observed.
4.10. Arc shaped ribs
Saini et al. [23] proposed arc shaped rib roughness
geometry. Parameters studied were relative
roughness height as 0.0213–0.0422, duct aspect ratio
12, Reynolds number as 2000–17,000, relative
roughness pitch 10 and relative angle of attack 0.33–
0.66. The roughness geometry is shown in “Fig. 22”.
After investigation they reported maximum
enhancement in Nusselt number as 3.80 times
corresponding to relative arc angle (α/90) of 0.33 at
relative roughness height of 0.0422 and
corresponding increase in friction factor was 1.75
times only.
Fig. 22. Arc shaped wire roughness
4.11. Dimple surfaces
4.11.1 Transverse dimple roughness
Saini et al. [24] used dimple shaped artificial
roughness in place of transverse ribs. The roughness
geometry is shown in “Fig. 23”. Range of parameters
used are Reynolds number from 2000 to 12,000,
relative roughness pitch as 8–12, and relative
roughness height as 0.018–0.037. They reported the
maximum value of Nusselt number for relative
roughness height of 0.0379 and relative roughness
pitch of 10 and minimum value of friction factor
observed for relative roughness height of 0.0289 and
relative roughness pitch of 10.
Fig. 23. Dimple shaped artificial roughness
4.11.2 Staggered dimple roughness
Bhushan et al. [25] investigated staggered dimple
roughness in place of transverse dimple roughness.
The staggered dimple roughness geometry is shown
in “Fig. 24”. Maximum enhancement in heat transfer
coefficient was observed for relative long way length
(L/e) of 31.25, relative short-way length (S/e) of
31.25 and relative print diameter (d/D) of 0.294. The
maximum enhancement of Nusselt number and
friction factor was 3.8 and 2.2 times respectively as
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compared to smooth duct surface. The range of
parameters for study were Reynolds number as 4000–
20,000, relative roughness height as 0.03, relative
long way length (L/e) as 25.00 – 37.50, relative short
way length (S/e) as 18.75 –37.50 and relative print
diameter (d/D) as 0.0147 – 0.367.
Fig. 24. Staggered dimple roughness
4.11.3 Arc shaped dimple roughness 1
Yadav et al. [26] investigated dimple shaped
roughness in arc shaped manner. Maximum
enhancement of heat transfer and friction factor was
observed at relative roughness pitch of 12, relative
roughness height of 0.03 and corresponding arc angle
of 60o
. The roughness geometry is show in “Fig. 25”.
The range of parameters used during investigation are
relative roughness pitch as 12 –24, relative roughness
height as 0.015 to 0.03, arc angle of protrusion
manner as 45–75 and Reynolds number in between
the range of 3600 to 18,100.
Fig. 25. Dimple roughness in arc manner
4.11.4 Arc shaped dimple roughness 2
Sethi et al. [27] investigated again dimple shaped
roughness with different set of parameters.
Roughness geometry is same as shown in “Fig. 25”.
After investigation they concluded that maximum
value of Nusselt number observed corresponded to
relative roughness pitch of 10, relative roughness
height of 0.036 and arc angle of 60o
. The investigated
range of parameters are relative roughness height as
0.021–0.036, relative roughness pitch as 10–20, duct
aspect ratio 11, Reynolds number in between 3600–
18,000 and arc angle from 45o
–75o
.
Fig. 26. Double arc rib roughness with up and
down orientation
Lanjewar et al. [28] investigated on double arc
shaped roughness geometry. They investigated the
effect of orientation of double arc shaped roughness
on thermo-hydraulic performance of solar air heater.
Roughness geometry is shown in “Fig. 26”. After
investigation on double arc down, double arc up and
single arc rib they concluded double arc down gives
maximum enhancement of Nusselt number as
102.57-162.45%. Enhancement of Nusselt number
for double arc-up and single arc rib roughness were
66.99-115.24% and 45.55-169.61%. They also found
double arc-up rib perform better as compare to single
arc till Reynolds number 8000 beyond that Nusselt
number of double arc-up rib is lower than single arc.
The experimentation involved relative roughness
pitch 10, angle of attack of 45, relative roughness
height 0.029, relative angle of attack (α/90), duct
aspect ratio 8 and Reynolds number from 4000 to
14000. Investigation showed double arc down has
higher Nusselt number as compare to double arc up
and single arc roughness over the entire range of
Reynolds number.
V. CONCLUSIONS
This review paper reveals various artificial
roughness geometry to enhance heat transfer
coefficient in solar air heater. Several investigators
have carried out research to investigate the effect of
artificial roughness of different shapes and size on
heat transfer and friction factor and also have
developed correlation for heat transfer coefficient and
friction factor. These correlations can be used to
predict the thermal as well as thermo-hydraulic
performance of solar air heater having roughened
duct. Substantial enhancement of heat transfer
coefficient can be achieved with little penalty of
friction factor using artificial roughness.
NOMENCLATURES
Ap Area of absorber plate, m2
B half length of V-rib element (m)
D, Dh hydraulic diameter of duct (m)
d dimple diameter
e rib height (m)
g groove position (m)
H duct height (m)
l longway length of mesh
p pitch (p)
s shortway length of mesh
S length of main segment of rib (m)
W duct width (m)
Dimensionless parameters
B/S relative roughness length ratio
d/D relative print diameter
d/W relative gap position
e/Dh relative roughness height
fr friction factor for roughened duct
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fs friction factor for smooth duct
g/e relative gap width
g/p groove position to pitch ratio
l/e relative longway length of mesh
l/s relative length of metal grid
m Mass flow rate of air
Nur Nusselt number of roughened duct
Nus Nusselt number of smooth duct
p/e relative roughness pitch
p՛ /p relative roughness staggering ratio
s/e relative shortway length of mesh
S՛ /S relative roughness segment ratio
W/H duct aspect ratio
W/w relative roughness width
ε enhancement factor
Greek symbols
α angle of attack (o
)
ɸ wedge angle (o
)
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