Teerapat Chompookham - Academia.edu (original) (raw)

Papers by Teerapat Chompookham

Asia-Pacific Journal of Science and Technology, Apr 13, 2017

Journal of Engineering Thermophysics, Jul 1, 2015

An experimental study was undertaken for investigating the heat transfer enhancement in a channel... more An experimental study was undertaken for investigating the heat transfer enhancement in a channel with baffle turbulators mounted on the lower wall. The baffles with rectangular, triangular, and trapezoidal upper edges were examined. The experiments were conducted in the rectangular channel with aspect ratio AR = 10 and height H = 30 mm, using air as the working fluid for Reynolds numbers between 5100 and 22,500. The effect of a baffle height to channel height ratio (y/H = 0.2, 0.3, and 0.4) on the heat transfer, pressure drop, and thermal enhancement factor characteristics was also investigated. The uniform heat flux condition was applied to the external surface of the lower wall of the channel. The results revealed that the baffles with rectangular upper edges gave a higher Nusselt number and friction factor than the ones with triangular and trapezoidal upper edges. Nusselt number increased while thermal performance factor decreased as a baffle to channel height ratio (y/H) and Reynolds number increased. For the range determined, the maximum thermal performance factor was achieved by using the baffles with trapezoidal upper edges at the smallest baffle to channel height ratio and the lowest Reynolds number, due to the best tradeoff between the increases of heat transfer and friction loss.

Advanced Materials Research, May 1, 2014

The experimental study on heat transfer enhancement in a tubular heat exchanger fitted with 60o w... more The experimental study on heat transfer enhancement in a tubular heat exchanger fitted with 60o winglet pairs is carried out by varying airflow velocity in turbulent region in the test section having a constant wall heat-flux. Effects of three blockage ratios (BR=e/D= 0.1, 0.15 and 0.2) and three pitch ratios (PR=P/D= 1, 1.5 and 2) of the winglet pairs on heat transfer rates in the terms of Nusselt number (Nu) and pressure loss in the form of friction factor (f) are examined. The experimental results illustrated that the tube with winglet pair insert provides the heat transfer rate higher than the smooth tube around 1.7 to 2.6 times, depending upon operating conditions. The thermal enhancement factor for using the winglet-pair turbulator is in a range of 1.03 - 1.31.

International Journal of Thermal Sciences, 2022

The application of wire coil as a turbulent generator to enhance the heat transfer in heat exchan... more The application of wire coil as a turbulent generator to enhance the heat transfer in heat exchangers is constantly being studied and presented. In this work, a novel wire coil turbulator was developed to have characteristics that are different from those previously proposed. It is based on the concept of a combination of a coiled wire structure with a continuous V-shaped rib turbulator, which was referred to as a serrated wire coil (SWC). In the paper, the turbulent air flow behavior and heat transfer characteristics in a tube heat exchanger with SWC insert was investigated experimentally under isothermal-flux condition. Ambient air was used as a working fluid in a turbulent flow regime with Reynolds numbers (Re) ranging from 5114 to 14,752. The SWCs were inserted into test tubes with three different coil diameters (D C) of 34.4, 41.2 and 47.9 mm (or diameter ratio, D R = D C /D T = 0.68, 0.81 and 0.94) and four different pitch lengths (P C) of 10, 20, 30 and 40 mm (or pitch ratio, P R =P C /D T = 0.1969, 0.3937, 0.5906 and 0.7874). The experimental results of heat transfer and friction loss were presented as dimensionless parameters, Nusselt number (Nu) and friction factors (f), respectively. It was observed that the Nu increased with a decrease in pitch length and an increase in coil diameter. While the f decreased with an increase in both pitch length and coil diameter. Under the scope of this study, it was found that the insertion of the coils increased the Nu and f above the smooth tubes by approximately 1.75-2.46 times and 3.31-8.16 times, respectively. The empirical correlations of Nu and f for tubular heat exchanger inserted with SWC under the scope of this study were developed and showed error within ±4 % for Nu and ±12 % for f. The maximum thermal performance enhancement factor (η) for this work was about 1.41 for the SWC with D C = 47.9 mm and P C = 10 mm at Re = 5114. In addition, the Nu, f and η obtained in the optimal conditions of this work were compared with previous work.

วารสารวิทยาศาสตร์และเทคโนโลยี มหาวิทยาลัยมหาสารคาม (Journal of Science and Technology Mahasarakham University), 2014

This research aims to study the effect of inclination angle on the heat transfer performance of a... more This research aims to study the effect of inclination angle on the heat transfer performance of a Closed-Loop Oscillating Heat-Pipe with Check Valve (CLOHP/CV) with fi ns on the tube wall. The heat pipe was made from a copper pipe, and the capillary tube had a 5.0 mm inside diameter. There were 24 meandering turns with two check valves. The lengths of the evaporator section and condenser section were 200 mm and the adiabatic section was 100 mm. The working fl uid used was water with a fi lling ratio of 50% of the total volume of the tube. The temperatures for the evaporator section were 60, 70 and 80 o C. Inclination angles were 0, 20, 40, 45, 60, 80 and 90 degrees from the horizontal axis were established. It was found that when the variable temperature increased from 60, 70 to 80 o C heat fl ux and thermal effi ciency increased. In addition, when the inclination angle increased from 0, 20, 40, 45, 60, 80 and 90 degrees heat fl ux and thermal effi ciency increased. Therefore, this research concluded, from the experiment that the heat pipe was a CLOHP/CV. The maximum specifi c heat fl ux equaled 1,926.97 W/m 2 and the maximum thermal effectiveness equaled 0.44, the operating temperature was 80 °C and an angle of inclination to the horizontal axis was 90 o

Social Science Research Network, 2023

Sustainability

This study aimed to enhance the thermal characteristics of rice husk biomass through torrefaction... more This study aimed to enhance the thermal characteristics of rice husk biomass through torrefaction conducted in a fixed-bed reactor. A novel approach was employed by circulating the gas produced within the system, instead of using traditional nitrogen. The torrefaction process took place at temperatures ranging from 200 to 320 °C, with different residence times of 10, 20, and 30 min for heat exchange. Quantitative analysis of the torrefied biomass revealed several notable improvements. The higher heating value of the biomass increased significantly, reaching 23.69 MJ/kg at a temperature of 320 °C and a residence time of 30 min. This enhancement indicates the effectiveness of torrefaction in increasing the energy content of the biomass. Furthermore, the torrefied biomass exhibited a remarkable reduction in hygroscopicity, with reduction by as much as 92 wt% compared to raw rice husk biomass. This reduction implies that the torrefied biomass is more resistant to moisture absorption, ma...

Case Studies in Thermal Engineering

International Journal of Renewable Energy Development

The helical oscillating heat pipe (HOHP) is a high heat transfer heat exchanger with high flexibi... more The helical oscillating heat pipe (HOHP) is a high heat transfer heat exchanger with high flexibility in its installation and can therefore be used in a wide variety of applications. In this study, the effect of various parameters on the heat transfer rates of HOHP were used to establish a correlation equation for use in the heat flux prediction, the dimensionless parameters studied were rv/rl, Bo, Nu, We, Ja, Pr, Fr, Co, Ga, Bi, Wo, Oh, and Ku. Experiments were conducted to find out their effects on the heat transfer rates of copper HOHP with internal diameters were 2.03, 3.5, and 4.5 mm. The lengths of evaporator and condenser sections were equal at 1500, 2000, and 2500 mm. The pitch coils were 10, 15, and 20 mm. The working fluids used were R134a, ethanol, and water with the filling ratios were 30%, 50%, and 80% of the total internal volume. The temperature of evaporator section were varied between 60, 70, and 80°C within normal operating conditions in a vertical position. The r...

This research study aims to investigate the effect of working uids on thermal performance in a th... more This research study aims to investigate the effect of working uids on thermal performance in a thermosyphon heat exchanger with and without annular ns. The thermosyphon heat exchangers were formed from the evaporator, adiabatic and condenser sections in which the lengths were 20, 10 and 20 cm respectively, made from steel, the tube had an outside diameter of 20 mm and a thickness of 3 mm. Distilled water, ethanol and R134a were used as the working uids with a lling ratio of 50% by total volume of the evaporator section. The temperature of the hot air in the evaporator section was controlled at 60 70 and 80 ° C The results show that when the variable temperature increased from 60, 70 to 80°C the heat transfer rate and thermal effectiveness also increased. In addition, it was found that at all operating temperatures, the highest heat transfer rate and thermal effectiveness were with R134a as the working uid. Moreover, the thermosyphon heat exchanger with annular ns had a higher heat transfer rate and thermal effectiveness than the thermosyphon heat exchanger without ns under all variables.

Asia-Pacific Journal of Science and Technology, 2017

The paper presents an experimental study on turbulent flow and heat transfer characteristics in a... more The paper presents an experimental study on turbulent flow and heat transfer characteristics in a square duct fitted diagonally with double V-ribbed tapes. The tested duct has uniform heat-fluxed walls and the flow rate of air used as the test fluid is presented in terms of Reynolds number (Re) from 4,000 to 25,000 . The insertion of the ribbed tape is performed with three blocked ratios of rib-to-duct height ( b/H , BR ) = 0.10, 0.15 and 0.20, two pitch ratios of rib pitch to duct height ( P/H , PR = 1 and 2), attack angle ( a ) = 45 o , pointing upstream of the flow with respect to the main flow direction. Influences of blocked ratios and pitch ratios on thermal and flow friction characteristics of the inserted duct are investigated. The experimental result of heat transfer in the form of Nusselt number and pressure drop in term of friction factor are compared between the duct mounted with double V-ribbed tapes and the smooth duct. The experimental result shows that at...

The paper presents a study of heat transfer in a heat exchanger square channel inserted with 20,... more The paper presents a study of heat transfer in a heat exchanger square channel inserted with 20, 30 and 45 angled, U-shaped ribs. The test channel has a square section with uniform wall heat flux conditions. The fluid flow and heat transfer characteristics are presented for Reynolds numbers based on the hydraulic diameter of the channel ranging from 4000 to 25,000. The U-Shaped ribs with axial pitch equal to three times of channel height and two rib-to-channel height ratios e/H = 0.1 and 0.2 are introduced. The experimental result of heat transfer in terms of Nusselt number and pressure loss in terms of friction factor are compared between the inserted channel and the smooth channel. The Ushaped rib with the attack angle of 45 gives higher heat transfer and friction factor than the one with the attack angle of 30, 20 and the smooth channel. It is worth noting that the heat transfer and pressure loss for the rib with e/H = 0.2 provides higher Nusselt number and friction factor ...

International Journal of Thermal Sciences, 2022

The application of wire coil as a turbulent generator to enhance the heat transfer in heat exchan... more The application of wire coil as a turbulent generator to enhance the heat transfer in heat exchangers is constantly being studied and presented. In this work, a novel wire coil turbulator was developed to have characteristics that are different from those previously proposed. It is based on the concept of a combination of a coiled wire structure with a continuous V-shaped rib turbulator, which was referred to as a serrated wire coil (SWC). In the paper, the turbulent air flow behavior and heat transfer characteristics in a tube heat exchanger with SWC insert was investigated experimentally under isothermal-flux condition. Ambient air was used as a working fluid in a turbulent flow regime with Reynolds numbers (Re) ranging from 5114 to 14,752. The SWCs were inserted into test tubes with three different coil diameters (D C) of 34.4, 41.2 and 47.9 mm (or diameter ratio, D R = D C /D T = 0.68, 0.81 and 0.94) and four different pitch lengths (P C) of 10, 20, 30 and 40 mm (or pitch ratio, P R =P C /D T = 0.1969, 0.3937, 0.5906 and 0.7874). The experimental results of heat transfer and friction loss were presented as dimensionless parameters, Nusselt number (Nu) and friction factors (f), respectively. It was observed that the Nu increased with a decrease in pitch length and an increase in coil diameter. While the f decreased with an increase in both pitch length and coil diameter. Under the scope of this study, it was found that the insertion of the coils increased the Nu and f above the smooth tubes by approximately 1.75-2.46 times and 3.31-8.16 times, respectively. The empirical correlations of Nu and f for tubular heat exchanger inserted with SWC under the scope of this study were developed and showed error within ±4 % for Nu and ±12 % for f. The maximum thermal performance enhancement factor (η) for this work was about 1.41 for the SWC with D C = 47.9 mm and P C = 10 mm at Re = 5114. In addition, the Nu, f and η obtained in the optimal conditions of this work were compared with previous work.

Journal of Engineering Thermophysics, 2015

An experimental study was undertaken for investigating the heat transfer enhancement in a channel... more An experimental study was undertaken for investigating the heat transfer enhancement in a channel with baffle turbulators mounted on the lower wall. The baffles with rectangular, triangular, and trapezoidal upper edges were examined. The experiments were conducted in the rectangular channel with aspect ratio AR = 10 and height H = 30 mm, using air as the working fluid for Reynolds numbers between 5100 and 22,500. The effect of a baffle height to channel height ratio (y/H = 0.2, 0.3, and 0.4) on the heat transfer, pressure drop, and thermal enhancement factor characteristics was also investigated. The uniform heat flux condition was applied to the external surface of the lower wall of the channel. The results revealed that the baffles with rectangular upper edges gave a higher Nusselt number and friction factor than the ones with triangular and trapezoidal upper edges. Nusselt number increased while thermal performance factor decreased as a baffle to channel height ratio (y/H) and Reynolds number increased. For the range determined, the maximum thermal performance factor was achieved by using the baffles with trapezoidal upper edges at the smallest baffle to channel height ratio and the lowest Reynolds number, due to the best tradeoff between the increases of heat transfer and friction loss.

Advanced Materials Research, 2014

The experimental study on heat transfer enhancement in a tubular heat exchanger fitted with 60o w... more The experimental study on heat transfer enhancement in a tubular heat exchanger fitted with 60o winglet pairs is carried out by varying airflow velocity in turbulent region in the test section having a constant wall heat-flux. Effects of three blockage ratios (BR=e/D= 0.1, 0.15 and 0.2) and three pitch ratios (PR=P/D= 1, 1.5 and 2) of the winglet pairs on heat transfer rates in the terms of Nusselt number (Nu) and pressure loss in the form of friction factor (f) are examined. The experimental results illustrated that the tube with winglet pair insert provides the heat transfer rate higher than the smooth tube around 1.7 to 2.6 times, depending upon operating conditions. The thermal enhancement factor for using the winglet-pair turbulator is in a range of 1.03 - 1.31.

Energy Conversion and Management, 2010

Effects of combined ribs and winglet type vortex generators (WVGs) on forced convection heat tran... more Effects of combined ribs and winglet type vortex generators (WVGs) on forced convection heat transfer and friction loss behaviors for turbulent airflow through a constant heat flux channel are experimentally investigated in the present work. The cross-section of the ribs placed inside the opposite channel walls to create a reverse flow is an isosceles triangle shape. Two rib arrangements, namely, in-line and staggered arrays, are introduced. Also, two pairs of the WVGs with various attack angles (a) of 60°, 45°and 30°are mounted on the test duct entrance to create a longitudinal vortex flow through the test channel. Measurements are carried out for a rectangular duct of aspect ratio, AR = 10 and height, H = 30 mm with a single rib height, e/H = 0.13 and rib pitch, P/H = 1.33. The flow rate is in terms of Reynolds numbers based on the inlet hydraulic diameter of the channel ranging from 5000 to 22,000. The experimental results show a significant effect of the presence of the rib turbulator and the WVGs on the heat transfer rate and friction loss over the smooth wall channel. The values of Nusselt number and friction factor for utilizing both the rib and the WVGs are found to be considerably higher than those for using the rib or the WVGs alone. The larger the attack angle value leads to higher heat transfer and friction loss than the lower one. The in-line rib together with the WVGs provides higher heat transfer and friction loss than the staggered one for similar operating conditions. In common with the WVGs, the in-line rib yields the highest increase in both the Nusselt number and the friction factor but the rib with staggered array shows better thermal performance than the others.

Journal of Mechanical Science and Technology, Jul 1, 2017

The transient temperature profiles of a Helical oscillating heat pipe (HOHP), the heat transfer p... more The transient temperature profiles of a Helical oscillating heat pipe (HOHP), the heat transfer profiles of the HOHP, and the heat transfer profiles of a HOHP heat exchanger during start-up operation from a numerical model and from an experiment were studied. This article presents the details of a calculation for the HOHP, in which the HOHP has a domain consisting of a pipe wall and a vapor core. The governing equation at the pipe wall and the vapor core of the HOHP was solved by a numerical method. The numerical solution for the transient model in this study was obtained using a finite difference method, and the finite difference method used in this study was the Clank-Nicolson method. The temperature at the pipe wall of the HOHP, the heat transfer of the HOHP, and the heat transfer of the HOHP heat exchanger were plotted as functions of time. The results show that the transient temperature distributions at the pipe wall of the HOHP from the numerical model were successfully compared with the results from the experimental data, which utilizes the concept of temperature distributions during transient operation. The steady state temperature profiles were obtained as a steady temperature was input into the outer wall at the evaporator section of the HOHP. This study also found that the transient heat transfer profiles of the HOHP from the numerical model were successfully compared with the results from the experimental data, which utilizes the concept of heat transfer increments in the HOHP during transient operation. Moreover, it was also found that the transient heat transfer profiles of the HOHP heat exchanger from the numerical model were successfully compared with the results from the experimental data. Therefore, it can be concluded that the numerically validated temperature distributions of the HOHP, the heat transfer of the HOHP, and the heat transfer of the HOHP heat exchanger were successfully simulated in this model.

Asia-Pacific Journal of Science and Technology, Apr 13, 2017

Journal of Engineering Thermophysics, Jul 1, 2015

An experimental study was undertaken for investigating the heat transfer enhancement in a channel... more An experimental study was undertaken for investigating the heat transfer enhancement in a channel with baffle turbulators mounted on the lower wall. The baffles with rectangular, triangular, and trapezoidal upper edges were examined. The experiments were conducted in the rectangular channel with aspect ratio AR = 10 and height H = 30 mm, using air as the working fluid for Reynolds numbers between 5100 and 22,500. The effect of a baffle height to channel height ratio (y/H = 0.2, 0.3, and 0.4) on the heat transfer, pressure drop, and thermal enhancement factor characteristics was also investigated. The uniform heat flux condition was applied to the external surface of the lower wall of the channel. The results revealed that the baffles with rectangular upper edges gave a higher Nusselt number and friction factor than the ones with triangular and trapezoidal upper edges. Nusselt number increased while thermal performance factor decreased as a baffle to channel height ratio (y/H) and Reynolds number increased. For the range determined, the maximum thermal performance factor was achieved by using the baffles with trapezoidal upper edges at the smallest baffle to channel height ratio and the lowest Reynolds number, due to the best tradeoff between the increases of heat transfer and friction loss.

Advanced Materials Research, May 1, 2014

The experimental study on heat transfer enhancement in a tubular heat exchanger fitted with 60o w... more The experimental study on heat transfer enhancement in a tubular heat exchanger fitted with 60o winglet pairs is carried out by varying airflow velocity in turbulent region in the test section having a constant wall heat-flux. Effects of three blockage ratios (BR=e/D= 0.1, 0.15 and 0.2) and three pitch ratios (PR=P/D= 1, 1.5 and 2) of the winglet pairs on heat transfer rates in the terms of Nusselt number (Nu) and pressure loss in the form of friction factor (f) are examined. The experimental results illustrated that the tube with winglet pair insert provides the heat transfer rate higher than the smooth tube around 1.7 to 2.6 times, depending upon operating conditions. The thermal enhancement factor for using the winglet-pair turbulator is in a range of 1.03 - 1.31.

International Journal of Thermal Sciences, 2022

The application of wire coil as a turbulent generator to enhance the heat transfer in heat exchan... more The application of wire coil as a turbulent generator to enhance the heat transfer in heat exchangers is constantly being studied and presented. In this work, a novel wire coil turbulator was developed to have characteristics that are different from those previously proposed. It is based on the concept of a combination of a coiled wire structure with a continuous V-shaped rib turbulator, which was referred to as a serrated wire coil (SWC). In the paper, the turbulent air flow behavior and heat transfer characteristics in a tube heat exchanger with SWC insert was investigated experimentally under isothermal-flux condition. Ambient air was used as a working fluid in a turbulent flow regime with Reynolds numbers (Re) ranging from 5114 to 14,752. The SWCs were inserted into test tubes with three different coil diameters (D C) of 34.4, 41.2 and 47.9 mm (or diameter ratio, D R = D C /D T = 0.68, 0.81 and 0.94) and four different pitch lengths (P C) of 10, 20, 30 and 40 mm (or pitch ratio, P R =P C /D T = 0.1969, 0.3937, 0.5906 and 0.7874). The experimental results of heat transfer and friction loss were presented as dimensionless parameters, Nusselt number (Nu) and friction factors (f), respectively. It was observed that the Nu increased with a decrease in pitch length and an increase in coil diameter. While the f decreased with an increase in both pitch length and coil diameter. Under the scope of this study, it was found that the insertion of the coils increased the Nu and f above the smooth tubes by approximately 1.75-2.46 times and 3.31-8.16 times, respectively. The empirical correlations of Nu and f for tubular heat exchanger inserted with SWC under the scope of this study were developed and showed error within ±4 % for Nu and ±12 % for f. The maximum thermal performance enhancement factor (η) for this work was about 1.41 for the SWC with D C = 47.9 mm and P C = 10 mm at Re = 5114. In addition, the Nu, f and η obtained in the optimal conditions of this work were compared with previous work.

วารสารวิทยาศาสตร์และเทคโนโลยี มหาวิทยาลัยมหาสารคาม (Journal of Science and Technology Mahasarakham University), 2014

This research aims to study the effect of inclination angle on the heat transfer performance of a... more This research aims to study the effect of inclination angle on the heat transfer performance of a Closed-Loop Oscillating Heat-Pipe with Check Valve (CLOHP/CV) with fi ns on the tube wall. The heat pipe was made from a copper pipe, and the capillary tube had a 5.0 mm inside diameter. There were 24 meandering turns with two check valves. The lengths of the evaporator section and condenser section were 200 mm and the adiabatic section was 100 mm. The working fl uid used was water with a fi lling ratio of 50% of the total volume of the tube. The temperatures for the evaporator section were 60, 70 and 80 o C. Inclination angles were 0, 20, 40, 45, 60, 80 and 90 degrees from the horizontal axis were established. It was found that when the variable temperature increased from 60, 70 to 80 o C heat fl ux and thermal effi ciency increased. In addition, when the inclination angle increased from 0, 20, 40, 45, 60, 80 and 90 degrees heat fl ux and thermal effi ciency increased. Therefore, this research concluded, from the experiment that the heat pipe was a CLOHP/CV. The maximum specifi c heat fl ux equaled 1,926.97 W/m 2 and the maximum thermal effectiveness equaled 0.44, the operating temperature was 80 °C and an angle of inclination to the horizontal axis was 90 o

Social Science Research Network, 2023

Sustainability

This study aimed to enhance the thermal characteristics of rice husk biomass through torrefaction... more This study aimed to enhance the thermal characteristics of rice husk biomass through torrefaction conducted in a fixed-bed reactor. A novel approach was employed by circulating the gas produced within the system, instead of using traditional nitrogen. The torrefaction process took place at temperatures ranging from 200 to 320 °C, with different residence times of 10, 20, and 30 min for heat exchange. Quantitative analysis of the torrefied biomass revealed several notable improvements. The higher heating value of the biomass increased significantly, reaching 23.69 MJ/kg at a temperature of 320 °C and a residence time of 30 min. This enhancement indicates the effectiveness of torrefaction in increasing the energy content of the biomass. Furthermore, the torrefied biomass exhibited a remarkable reduction in hygroscopicity, with reduction by as much as 92 wt% compared to raw rice husk biomass. This reduction implies that the torrefied biomass is more resistant to moisture absorption, ma...

Case Studies in Thermal Engineering

International Journal of Renewable Energy Development

The helical oscillating heat pipe (HOHP) is a high heat transfer heat exchanger with high flexibi... more The helical oscillating heat pipe (HOHP) is a high heat transfer heat exchanger with high flexibility in its installation and can therefore be used in a wide variety of applications. In this study, the effect of various parameters on the heat transfer rates of HOHP were used to establish a correlation equation for use in the heat flux prediction, the dimensionless parameters studied were rv/rl, Bo, Nu, We, Ja, Pr, Fr, Co, Ga, Bi, Wo, Oh, and Ku. Experiments were conducted to find out their effects on the heat transfer rates of copper HOHP with internal diameters were 2.03, 3.5, and 4.5 mm. The lengths of evaporator and condenser sections were equal at 1500, 2000, and 2500 mm. The pitch coils were 10, 15, and 20 mm. The working fluids used were R134a, ethanol, and water with the filling ratios were 30%, 50%, and 80% of the total internal volume. The temperature of evaporator section were varied between 60, 70, and 80°C within normal operating conditions in a vertical position. The r...

This research study aims to investigate the effect of working uids on thermal performance in a th... more This research study aims to investigate the effect of working uids on thermal performance in a thermosyphon heat exchanger with and without annular ns. The thermosyphon heat exchangers were formed from the evaporator, adiabatic and condenser sections in which the lengths were 20, 10 and 20 cm respectively, made from steel, the tube had an outside diameter of 20 mm and a thickness of 3 mm. Distilled water, ethanol and R134a were used as the working uids with a lling ratio of 50% by total volume of the evaporator section. The temperature of the hot air in the evaporator section was controlled at 60 70 and 80 ° C The results show that when the variable temperature increased from 60, 70 to 80°C the heat transfer rate and thermal effectiveness also increased. In addition, it was found that at all operating temperatures, the highest heat transfer rate and thermal effectiveness were with R134a as the working uid. Moreover, the thermosyphon heat exchanger with annular ns had a higher heat transfer rate and thermal effectiveness than the thermosyphon heat exchanger without ns under all variables.

Asia-Pacific Journal of Science and Technology, 2017

The paper presents an experimental study on turbulent flow and heat transfer characteristics in a... more The paper presents an experimental study on turbulent flow and heat transfer characteristics in a square duct fitted diagonally with double V-ribbed tapes. The tested duct has uniform heat-fluxed walls and the flow rate of air used as the test fluid is presented in terms of Reynolds number (Re) from 4,000 to 25,000 . The insertion of the ribbed tape is performed with three blocked ratios of rib-to-duct height ( b/H , BR ) = 0.10, 0.15 and 0.20, two pitch ratios of rib pitch to duct height ( P/H , PR = 1 and 2), attack angle ( a ) = 45 o , pointing upstream of the flow with respect to the main flow direction. Influences of blocked ratios and pitch ratios on thermal and flow friction characteristics of the inserted duct are investigated. The experimental result of heat transfer in the form of Nusselt number and pressure drop in term of friction factor are compared between the duct mounted with double V-ribbed tapes and the smooth duct. The experimental result shows that at...

The paper presents a study of heat transfer in a heat exchanger square channel inserted with 20,... more The paper presents a study of heat transfer in a heat exchanger square channel inserted with 20, 30 and 45 angled, U-shaped ribs. The test channel has a square section with uniform wall heat flux conditions. The fluid flow and heat transfer characteristics are presented for Reynolds numbers based on the hydraulic diameter of the channel ranging from 4000 to 25,000. The U-Shaped ribs with axial pitch equal to three times of channel height and two rib-to-channel height ratios e/H = 0.1 and 0.2 are introduced. The experimental result of heat transfer in terms of Nusselt number and pressure loss in terms of friction factor are compared between the inserted channel and the smooth channel. The Ushaped rib with the attack angle of 45 gives higher heat transfer and friction factor than the one with the attack angle of 30, 20 and the smooth channel. It is worth noting that the heat transfer and pressure loss for the rib with e/H = 0.2 provides higher Nusselt number and friction factor ...

International Journal of Thermal Sciences, 2022

The application of wire coil as a turbulent generator to enhance the heat transfer in heat exchan... more The application of wire coil as a turbulent generator to enhance the heat transfer in heat exchangers is constantly being studied and presented. In this work, a novel wire coil turbulator was developed to have characteristics that are different from those previously proposed. It is based on the concept of a combination of a coiled wire structure with a continuous V-shaped rib turbulator, which was referred to as a serrated wire coil (SWC). In the paper, the turbulent air flow behavior and heat transfer characteristics in a tube heat exchanger with SWC insert was investigated experimentally under isothermal-flux condition. Ambient air was used as a working fluid in a turbulent flow regime with Reynolds numbers (Re) ranging from 5114 to 14,752. The SWCs were inserted into test tubes with three different coil diameters (D C) of 34.4, 41.2 and 47.9 mm (or diameter ratio, D R = D C /D T = 0.68, 0.81 and 0.94) and four different pitch lengths (P C) of 10, 20, 30 and 40 mm (or pitch ratio, P R =P C /D T = 0.1969, 0.3937, 0.5906 and 0.7874). The experimental results of heat transfer and friction loss were presented as dimensionless parameters, Nusselt number (Nu) and friction factors (f), respectively. It was observed that the Nu increased with a decrease in pitch length and an increase in coil diameter. While the f decreased with an increase in both pitch length and coil diameter. Under the scope of this study, it was found that the insertion of the coils increased the Nu and f above the smooth tubes by approximately 1.75-2.46 times and 3.31-8.16 times, respectively. The empirical correlations of Nu and f for tubular heat exchanger inserted with SWC under the scope of this study were developed and showed error within ±4 % for Nu and ±12 % for f. The maximum thermal performance enhancement factor (η) for this work was about 1.41 for the SWC with D C = 47.9 mm and P C = 10 mm at Re = 5114. In addition, the Nu, f and η obtained in the optimal conditions of this work were compared with previous work.

Journal of Engineering Thermophysics, 2015

An experimental study was undertaken for investigating the heat transfer enhancement in a channel... more An experimental study was undertaken for investigating the heat transfer enhancement in a channel with baffle turbulators mounted on the lower wall. The baffles with rectangular, triangular, and trapezoidal upper edges were examined. The experiments were conducted in the rectangular channel with aspect ratio AR = 10 and height H = 30 mm, using air as the working fluid for Reynolds numbers between 5100 and 22,500. The effect of a baffle height to channel height ratio (y/H = 0.2, 0.3, and 0.4) on the heat transfer, pressure drop, and thermal enhancement factor characteristics was also investigated. The uniform heat flux condition was applied to the external surface of the lower wall of the channel. The results revealed that the baffles with rectangular upper edges gave a higher Nusselt number and friction factor than the ones with triangular and trapezoidal upper edges. Nusselt number increased while thermal performance factor decreased as a baffle to channel height ratio (y/H) and Reynolds number increased. For the range determined, the maximum thermal performance factor was achieved by using the baffles with trapezoidal upper edges at the smallest baffle to channel height ratio and the lowest Reynolds number, due to the best tradeoff between the increases of heat transfer and friction loss.

Advanced Materials Research, 2014

The experimental study on heat transfer enhancement in a tubular heat exchanger fitted with 60o w... more The experimental study on heat transfer enhancement in a tubular heat exchanger fitted with 60o winglet pairs is carried out by varying airflow velocity in turbulent region in the test section having a constant wall heat-flux. Effects of three blockage ratios (BR=e/D= 0.1, 0.15 and 0.2) and three pitch ratios (PR=P/D= 1, 1.5 and 2) of the winglet pairs on heat transfer rates in the terms of Nusselt number (Nu) and pressure loss in the form of friction factor (f) are examined. The experimental results illustrated that the tube with winglet pair insert provides the heat transfer rate higher than the smooth tube around 1.7 to 2.6 times, depending upon operating conditions. The thermal enhancement factor for using the winglet-pair turbulator is in a range of 1.03 - 1.31.

Energy Conversion and Management, 2010

Effects of combined ribs and winglet type vortex generators (WVGs) on forced convection heat tran... more Effects of combined ribs and winglet type vortex generators (WVGs) on forced convection heat transfer and friction loss behaviors for turbulent airflow through a constant heat flux channel are experimentally investigated in the present work. The cross-section of the ribs placed inside the opposite channel walls to create a reverse flow is an isosceles triangle shape. Two rib arrangements, namely, in-line and staggered arrays, are introduced. Also, two pairs of the WVGs with various attack angles (a) of 60°, 45°and 30°are mounted on the test duct entrance to create a longitudinal vortex flow through the test channel. Measurements are carried out for a rectangular duct of aspect ratio, AR = 10 and height, H = 30 mm with a single rib height, e/H = 0.13 and rib pitch, P/H = 1.33. The flow rate is in terms of Reynolds numbers based on the inlet hydraulic diameter of the channel ranging from 5000 to 22,000. The experimental results show a significant effect of the presence of the rib turbulator and the WVGs on the heat transfer rate and friction loss over the smooth wall channel. The values of Nusselt number and friction factor for utilizing both the rib and the WVGs are found to be considerably higher than those for using the rib or the WVGs alone. The larger the attack angle value leads to higher heat transfer and friction loss than the lower one. The in-line rib together with the WVGs provides higher heat transfer and friction loss than the staggered one for similar operating conditions. In common with the WVGs, the in-line rib yields the highest increase in both the Nusselt number and the friction factor but the rib with staggered array shows better thermal performance than the others.

Journal of Mechanical Science and Technology, Jul 1, 2017

The transient temperature profiles of a Helical oscillating heat pipe (HOHP), the heat transfer p... more The transient temperature profiles of a Helical oscillating heat pipe (HOHP), the heat transfer profiles of the HOHP, and the heat transfer profiles of a HOHP heat exchanger during start-up operation from a numerical model and from an experiment were studied. This article presents the details of a calculation for the HOHP, in which the HOHP has a domain consisting of a pipe wall and a vapor core. The governing equation at the pipe wall and the vapor core of the HOHP was solved by a numerical method. The numerical solution for the transient model in this study was obtained using a finite difference method, and the finite difference method used in this study was the Clank-Nicolson method. The temperature at the pipe wall of the HOHP, the heat transfer of the HOHP, and the heat transfer of the HOHP heat exchanger were plotted as functions of time. The results show that the transient temperature distributions at the pipe wall of the HOHP from the numerical model were successfully compared with the results from the experimental data, which utilizes the concept of temperature distributions during transient operation. The steady state temperature profiles were obtained as a steady temperature was input into the outer wall at the evaporator section of the HOHP. This study also found that the transient heat transfer profiles of the HOHP from the numerical model were successfully compared with the results from the experimental data, which utilizes the concept of heat transfer increments in the HOHP during transient operation. Moreover, it was also found that the transient heat transfer profiles of the HOHP heat exchanger from the numerical model were successfully compared with the results from the experimental data. Therefore, it can be concluded that the numerically validated temperature distributions of the HOHP, the heat transfer of the HOHP, and the heat transfer of the HOHP heat exchanger were successfully simulated in this model.