Tanongkiat Kiatsiriroat

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.

Effect of the Electrode Arrangements in a Tube Bank on the Characteristic of Electrohydrodynamic Heat Transfer Enhancement: Low Reynolds Number

Enhancement in heat transfer using the electrohydrodynamic (EHD) technique is numerically examined in laminar forced convection across a tube bank with six different wire electrode arrangements. The electric field is generated by the wire electrodes charged with high DC voltages ranging from 7.5 to 17.5 kV. The Reynolds number corresponding to the flow considered is between 100 and 1,500. The numerical modeling of the laminar forced convection includes the interactions among the electric field, the flow field, and the temperature field. It is found that the heat transfer is significantly enhanced by the EHD at a low Reynolds number, and the short distance between the wire electrodes and the tube surface from which different electrode arrangements are reported for aligned and staggered tube configurations. The value Nu/Nu 0 of an aligned configuration increases from row to row and appears to be similar with that of a staggered configuration.

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.

Performance analyses of an automobile air-conditioning system with R22/R124/R152A refrigerant

In this research work, the performance of the vapour compression system of an automobile with R22/R124/R152a refrigerant mixture is studied. A mathematical model of each component is developed and used to simulate the system performance. The vehicle has an engine of 1300 cc capacity and the heat exchanges at the evaporator and the condenser are undertaken with water streams at different temperatures. The simulated results agree well with those of the experiments. Performance of the system is also simulated at different working conditions. It was found that as the mass fraction of R22 decreased the system COP and EER increase and when the mass fraction was less then 30% the performance slightly increased.

Enhancement of heat transport in thermosyphon air preheater at high temperature with binary working fluid: A case study of TEG–water

Abstract In this research, the critical heat flux (CHF) due to flooding limit of thermosyphon heat pipe using triethylene glycol (TEG)–water mixture has been investigated. From the experiment it is found that, use of TEG–water mixture can extend the heat transport limitation compared with pure water and higher heat transfer is obtained compared with pure TEG at high temperature applications. Moreover it is found that ESDU equation is appropriate to predict the CHF of the thermosyphon in case of TEG–water mixture. For thermosyphon air preheater at high temperature applications, it is found that with selected mixture content of TEG–water in each row of the thermosyphon the performance of the system could be increased approximately 30–80% compared with pure TEG for parallel flow and 60–115% for counter flow configurations. The performances also increase approximately 80–160% for parallel flow and 140–220% for counter flow compared with those of pure dowtherm A which is the common working fluid at high temperature applications.

Performance Analysis of Flat-Plate Solar Collector Having Silver Nanofluid as a Working Fluid

A study on water solar collector performance having silver nanofluid as working fluid was carried out. In this study, 20-nm silver particles mixed with water at the concentrations of 1,000 and 10,000 ppm were undertaken in 3 small identical closed-loop flat-plate solar collectors, each with an area of 0.15 m × 1.0 m. The mass flux of the working fluid varied between 0.8 and 1.2 L/min-m2 and the inlet temperatures were controlled in the range of 35–65°C. The tests were performed outdoor under a steady-state condition. The experimental results showed that at the same Reynolds number, the convective heat transfer coefficient of the nanofluid inside the solar absorber tube at 1,000 ppm was slightly higher than that of water, and at 10,000 ppm, the heat transfer coefficient was about 2 times that of water. This meant that the overall heat loss coefficient of the solar collector with nanofluid could be reduced and more solar heat gain could be obtained, especially with a high inlet temperature of the working fluid. In our experiments, for 10,000 ppm concentration of silver nanoparticles, the optical characteristic and the thermal loss characteristic of the solar collector, under steady-state condition with a mass flux of 1.2 kg/min-m2, were 0.691 and 4.869 W/m2-K, compared with 0.684 and 7.178 W/m2-K, respectively for 1,000 ppm concentration and 0.702 and 8.318 W/m2-K for water. When the flow rate was different from the standard value, the solar thermal characteristics were also improved with the nanofluid.

Performance analysis of thermosyphon heat exchanger under electric field

Abstract This paper presents a numerical method to analyze the thermosyphon heat exchanger with and without the presence of electrohydrodynamics (EHD). The proposed model is capable of handling both balanced and unbalanced thermosyphon heat exchangers. For the balanced thermosyphon heat exchanger, the calculated results of heat transfer rate for water and R-134a agree well with experimental data. For the unbalanced thermosyphon heat exchangers, it is found that the performance improvement increases with the ratio of m e / m c when EHD is applied at the condenser alone. Conversely, the performance improvement decreases with the ratio of m e / m c when EHD is applied at the evaporator alone.

Air-Cooling Enhancement with Delta Winglet Vortex Generators in Entrance Region of In-Line Array Electronic Modules

The objective of this study is to experimentally investigate the heat transfer enhancement by delta winglet vortex generators for air cooling in the entrance region of an in-line array of electronic modules. The study has been carried out when the winglet pairs are placed in front of all modules with attack angles of 10, 15 and 20 degrees. Each module has dimensions of 1.8 cm × 5.8 cm × 0.6 cm and generates heat at 5 W. The adiabatic heat transfer coefficients and the thermal wake functions for the modules with and without the generators are considered at different values of Reynolds number. It could be seen that the vortex generators could enhance the adiabatic heat transfer coefficients and reduce the thermal wake function and the module temperature significantly. Moreover, the correlations to predict the heat transfer data when the vortex generators are integrated have been developed. The temperatures of the modules in each row could be predicted from these correlations, and the results agree very well with the experimental data.

Performance analysis of a direct-contact thermal energy storage-solidification

Performance of a direct-contact latent heat energy storage during discharging process has been investigated. The storage medium used is sodium thiosulphate pentahydrate of which the melting temperature is 48°C and the heat exchanging fluid is heat transfer oil. An empirical expression to evaluate the volumetric heat transfer coefficient has been carried out. A lumped analysis is also found to be quite suitable to analyze the temperature of the storage medium and its solid fraction including the temperature of the oil leaving the storage. The results agree well with those of the experiments.

Performance analysis of a refrigeration cycle using a direct contact evaporator

This research work studies an ice thermal energy storage having an injection of R12 refrigerant into the water to exchange heat directly. The water temperature decreases to the freezing point and ice is formed. The ice is used for creating chilled water for an air-conditioning purpose. The system consists of a compressor, a condenser, an expansion valve and a direct contact evaporator. This system has a capacity of approximately 2 tons of refrigeration. The system simulation created from the mathematical model of each component has been carried out. It was found that the performance of the system depends on two factors, the compressor speed and the mass flow rate of the refrigerant. The suitable conditions are 8–10 rps for the compressor speed and 0.04–0.06 kgs−1 for the mass flow rate. The coefficient of performance is about 3·4–3·6 which is higher than that of the conventional system.