Atipoang Nuntaphan

Heat transfer prediction for a direct contact ice thermal energy storage

This research work studies the heat transfer characteristics of a direct contact evaporator. A cold two phase refrigerant (R12 or R22) is injected into water kept in a storage tank to exchange heat with the water directly. The water temperature is reduced to the freezing point, and ice could be formed. The lump model is used to predict the water temperature, and it is found that this model can predict the water temperature quite well. A correlation that relates the dimensionless parameters, such as Stanton number, Stephan number, Prandtl number and pressure ratio, is also developed.

Thermal Performance Enhancement of Thermosyphon Heat Pipe with Binary Working Fluids

Thermal performance of a thermosyphon heat pipe using ethanol-water and TEG-water with variations of parameters such as the mixture content, the pipe diameter, and the working temperature have been studied in this research work. From the experiments, it is found that at low temperature of heat source (less than 80oC), the ethanol-water mixture has a higher heat transfer rate than that of water and close to that of pure ethanol. In the case of TEG-water mixture, the heat transfer rate of the thermosyphon varies with the content of TEG in the mixture, and it is found that TEG in the mixture can increase the critical heat flux due to the flooding limit in a small thermosyphon. The boiling equation of Rohsenow and the condensation equation of Nusselt are modified to predict the heat transfer coefficients inside the thermosyphon. For the mixtures, the weighted average of the heat transfer coefficient of each component can be used to predict the total heat transfer coefficient. Furthermore, it is found that Fag...Thermal performance of a thermosyphon heat pipe using ethanol-water and TEG-water with variations of parameters such as the mixture content, the pipe diameter, and the working temperature have been studied in this research work. From the experiments, it is found that at low temperature of heat source (less than 80oC), the ethanol-water mixture has a higher heat transfer rate than that of water and close to that of pure ethanol. In the case of TEG-water mixture, the heat transfer rate of the thermosyphon varies with the content of TEG in the mixture, and it is found that TEG in the mixture can increase the critical heat flux due to the flooding limit in a small thermosyphon. The boiling equation of Rohsenow and the condensation equation of Nusselt are modified to predict the heat transfer coefficients inside the thermosyphon. For the mixtures, the weighted average of the heat transfer coefficient of each component can be used to predict the total heat transfer coefficient. Furthermore, it is found that Faghris equation can be used to predict the critical heat flux due to the flooding limit of the thermosyphon with the binary mixtures.

Comparison of Conventional Flat-Plate Solar Collector and Solar Boosted Heat Pump Using Unglazed Collector for Hot Water Production in Small Slaughterhouse

This study presents simulated results of solar water heating systems in a small slaughterhouse using two techniques. The first one is a normal solar water heating system using a flat-plate solar collector and the second one uses a solar-boosted heat pump system having a corrugated metal sheet roof as a solar collector. The number of solar collector units is between 1 and 5, and the volume of water in a storage tank is 300–1200 L. The heat pump in this work uses refrigerant mixture R22:R124:R152a of 20%:57%:23% as the working fluid. The weather conditions of Chiang Mai, Thailand, are taken as the input data. In the case of the normal solar water heating system, the shortest payback periods for 300, 600, 900, and 1200 L water are 3.63, 3.12, 2.95, and 2.82 yr, respectively. The suitable number of collectors for 300 L water is 1 unit with 600–900 L water storage; 2 units of collectors is suitable in the case of 1200 L water, and 3 units of collectors gives the shortest payback period. However, in the case of a solar heat pump system, the suitable payback periods for 300, 600, 900, and 1200 L water are 2.74, 1.79, 1.83, and 1.88 yr, respectively. In our case, 1 unit of this collector gives the shortest payback period.

Performance improvement of thermosyphon heat exchangers by using two kinds of working fluids

In this study, the concept of introducing two-fluid thermosyphons is examined. Calculations were performed for both low and high temperature ranges with parallel and counter-flow arrangements. For lower-temperature application, 125°C > T hi > 75°C, use of ammonia in some rows and water in the rest of the thermosyphon can slightly improve the associated heat transfer performance for balanced counter-flow arrangement. However, for balanced parallel-flow arrangement in both low-and high-temperature applications, the concept of using two-fluid thermosyphons may not be feasible. The use of two-fluid thermosyphons is especially advantageous for high-temperature applications. For instance, in the range of 375°C > T hi > 350°C, the two-fluid thermosyphons (Dowtherm A-water) shows a 15-99% increase of heat transfer performance relative to Dowtherm A alone.In this study, the concept of introducing two-fluid thermosyphons is examined. Calculations were performed for both low and high temperature ranges with parallel and counter-flow arrangements. For lower-temperature application, 125°C > T hi > 75°C, use of ammonia in some rows and water in the rest of the thermosyphon can slightly improve the associated heat transfer performance for balanced counter-flow arrangement. However, for balanced parallel-flow arrangement in both lowand high-temperature applications, the concept of using two-fluid thermosyphons may not be feasible. The use of two-fluid thermosyphons is especially advantageous for high-temperature applications. For instance, in the range of 375°C > T hi > 350°C, the two-fluid thermosyphons (Dowtherm A-water) shows a 15-99% increase of heat transfer performance relative to Dowtherm A alone.

Air-Side Performance Analysis of a Wire-on-Tube Heat Exchanger With an Oscillating Heat Pipe as an Extended Surface Under Natural Convection Conditions

This study investigates the performance of a wire-on-tube heat exchanger that uses an oscillating heat pipe as an extended surface under natural convection. The results have been compared with those of a conventional wire-on-tube unit. The heat exchanger exchanges heat between hot water flowing inside the tube, which is varied from 50 to 85°C, and the surrounding ambient air, which is kept constant at 25°C. The tested unit is installed in the horizontal and vertical directions, and the effects of tube diameter and tube and wire pitches on thermal performance are considered. The results show that the performance of the heat exchanger with an oscillating heat pipe is slightly higher than that of the conventional wire-on-tube heat exchanger. It was also found that the air-side performance of the heat exchanger is directly proportional to the tube diameter and tube and wire pitches. Moreover, when the heat exchanger is installed horizontally, its performance is approximately 15–20% higher than that of the unit in the vertical installation. A heat transfer model for evaluating the heat exchanger performance is also developed, and the results agree well with the experimental data.

Performance Analysis of a Modular Adsorption Cooling System with Sonic Vibration at the Evaporator

The experimental study of a single-effect modular adsorption cooling system with an activated carbon-methanol working pair is presented in this paper. The test unit is comprised of an adsorber, a condenser, and an evaporator in vertical alignment. Heating and cooling at the adsorber is by hot water at 70–90°C, whereas heating at the evaporator is performed by water at the ambient temperature. At the evaporator, a sonic wave generator enhances heat transfer for the boiling of methanol during the adsorption process. The system performance by considering the coefficient of performance (COP), specific cooling power (SCP), and volumetric cold production (VCP) is evaluated, and the sonic wave is demonstrated to reduce the evaporation time of methanol, which results in better system performances compared with the results in literature. The highest COP and SCP obtained from this system are 0.718 and 248.90  W/kg, respectively.

Performance Analysis of a Modular Adsorption Cooling System with Sonic Vibration in the Adsorber

This article presents a performance evaluation of an adsorption cooling system using activated carbon–methanol as the working pair. The desorption process was enhanced by a sonic-wave generator attached to the center of the side of the adsorber. The results show that the sonic-wave activation reduced the cycle time of the heating–condensation process and improved the system performance in terms of coefficient of performance, specific cooling power, and volumetric capacity power, of which the highest achieved for this system were 0.619, 229.15 W/kg, and 17.61 cm3/W, respectively.