• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.6
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• pp.570-580
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• 2000

The performance simulation of refrigeration system for the automotive vehicles was peformed, in which the refrigerant was HFC-l34a as an alternative to CFC-12. The coefficient of performance of the system for HFC-l34a was lower than that for CFC-12 operated in the same operating and design conditions. The optimal design conditions were obtained as a function of optimum capacity ratios of condenser and evaporator.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.11
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• pp.1044-1050
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• 2004

The present study has been conducted to develop a heat pipe heat exchanger for middle-high temperature ranged from 300 to $600^{\circ}C$. Heat transfer rate, overall heat transfer coefficient and temperature effectiveness were investigated using a heat pipe heat exchanger with Dowtherm A as working fluid. Theoretical analysis was also conducted, and the followings were obtained: (1) Heat exchange rate increased as waste gas temperature supplied to evaporator and frontal velocity in condenser increased, (2) Overall heat transfer coefficient increased by $3{\sim}7\%$ as frontal velocity in evaporator and condenser increased, (3) Temperature effectiveness was about $30\%$ in evaporator and was about $40\%$ in condenser, (4) Heat recovery rate was about $38\%$, (5) Pressure drop did not exceed $8\;mmH_{2}O$ under the running condition of $1{\sim}3Nm/s$, (6) Simulation results were corresponded with experimental results.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.6
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• pp.592-598
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• 2015

In this study, we experimentally investigate the performance characteristics of a high-performance summer-cooling heat pump for an R410A by applying an air-cooled-type vapor-injection (VI) cycle. The devices used for the experiment consist of a VI compressor, condenser, oil separator, plate-type heat-exchanger, economizer, evaporator, and re-cooler. The experimental conditions employed for the cooling performance were divided into three cycles. First, in Cycle A, we apply a VI cycle and with no heat exchange between the evaporator outlet refrigerant and the VI cycle suction refrigerant in the re-cooler. For Cycle B, there is heat exchange, and for Cycle C, there is neither a VI cycle nor heat exchange between the evaporator outlet refrigerant and the VI cycle suction refrigerant. From the analysis results, we observe that the performance was highest in the VI cycle with heat exchange between the evaporator outlet refrigerant and the VI cycle suction refrigerant (Cycle B), while it was lowest in Cycle C without application of the VI cycle. Moreover, the cooling coefficient of Performance ($COP_C$) averaged 3.5 in Cycle B, which was 8.6% higher than the corresponding value in Cycle A, and 33% higher than that in Cycle C.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2291-2296
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• 2007

Thermal transport from vertical heated surface to falling liquid film in a channel has been investigated experimentally. Air-flow is introduced into channel to make a counter flow against falling liquid film. This problem is of particular interest in the design of direct contact heat exchange system, such as cooling tower, evaporative cooling system, absorption cooling system, and distillation system. The effects of channel width and air flow rate on the heat transfer to falling liquid film are studied in detail. The results obtained indicate that heat transfer rate is gradually decreased with an increase in the channel width without air flow as well as with air flow in a channel. It is also found that heat transfer rate of air-flow is increased while heat transfer rate of falling liquid film is decreased with an increase in the air flow rate at a given channel width. However, total heat transfer rate form the heated surface is increased as the air flow rate is increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.5
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• pp.335-341
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• 2008

Thermal transport from vertical heated surface to falling liquid film in a channel has been investigated experimentally. Air-flow is introduced into channel to make a counter flow against falling liquid film. This problem is of particular interest in the design of direct contact heat exchange system, such as cooling tower, evaporative cooling system, absorption cooling system, and distillation system. The effects of channel width and air flow rate on the heat transfer to falling liquid film are studied in detail. The results obtained indicate that heat transfer rate is gradually decreased with an increase in the channel width without air flow as well as with air flow in a channel. It is also found that heat transfer rate of air-flow is increased while heat transfer rate of falling liquid film is decreased with an increase in the air flow rate at a given channel width. However, total heat transfer rate from the heated surface is increased as the air flow rate is increased.

• Journal of Biosystems Engineering
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• v.27 no.3
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• pp.235-240
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• 2002

Performance of the heat pump with attaching an air heat exchanger was investigated in the heating condition when the air heat exchanger was worked in the ambient air temperature of -5 to 11$\^{C}$ and air flow rate of 542 to 747 ㎡/h. Performance tests for heating condition were conducted in an experimental room equipped with heat pump. The performance tests were performed in a ambient temperature of -4 ∼ 11$\^{C}$, and room temperature of 4∼22$\^{C}$ respectively. Measured data(temperature, capacity of heat transfer and consumption of electronic power) were analyzed to the efficiency of HEEVA(Heat Exchanger fur the Evaporator), overall heat transfer coefficient and COP of heat pump. The results of inlet temperature for evaporator increased that the temperature was 2 ∼6$\^{C}$, and inlet temperature for condenser decreased that the temperature was 3 ∼ 8$\^{C}$. The results of comparing efficiency of HEEVA for the ratio of heat exchange between hot air and cold air showed that efficiency were considered to 91% because of the ratio of 83∼98%. The results of comparing of COP for the heat pump increased that improvement COP was approximately 0.3∼7.5 than HEEVA had not been operated.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.1
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• pp.48-56
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• 2021

In this study, the heat transfer process around the finned channel tubes is numerically examined. Serially arranged tubes of an evaporator were used for heat exchange. The numerical analysis results confirmed that the vortex generated at the rear of the channel pipe was caused by the fin. Furthermore, it was also confirmed that the temperature difference was large between the inlet and outlet ends of the fin. The temperature of the location where the fin was attached to the channel pipe was found to be close to the surface temperature of the channel wall. However, the temperature rose rapidly closer to the ambient air temperature of 350 K towards the fin end, located at a distance of 0.035 m; it was found to have a significant influence on the heat transfer around the fin-attached channel tube. The wider the vertical flow path, the lower the total heat transfer coefficient. However, the overall heat transfer coefficient increased as the horizontal flow path narrowed. The increment is attributed to an increase in the heat transfer amount due to increased heat transfer surface.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.209-215
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• 2007

This study presents the air side heat transfer and friction characteristics of fin-tube heat exchangers. Variations of heat transfer performance in each row are investigated in the present work. Experiments were performed for the Louver fin-tube heat exchangers using air-enthalpy type calorimeter, which is based on air-enthalpy method described in ASHRAE standards. The air velocity was varied from 0.7 to 2.5 m/s with 0.3 m/s interval. The results are plotted in terms of Colburn j-factor and friction factor of with respect to Reynolds number in the range of 200 to 1100.

• Journal of Fisheries and Marine Sciences Education
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• v.19 no.3
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• pp.383-389
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• 2007

To evaluate the performance of heat exchanger with rotating porous plates, the experimental investigation was carried out under various conditions. With an equal interval of 18 mm inside the heat exchanger, the rotating porous plates are mounted. The hot and cold airs enter at opposite ends of heat exchanger and exchange heat each other. In order to measure the temperature distribution of the hot air side inside heat exchanger, the thermocouples are inserted between the plates. The first location of thermocouple is 10 mm downstream from the inlet of heat exchanger, and succeeding ten locations are aligned at an equal interval of 18 mm. As a result of the measurement, the temperature distribution inside heat exchanger was constant as the hot air temperature of inlet is low. It was found that the heat transfer rate does not depend on the variation of RPM at the lower temperature of inlet. The heat transfer rate at the higher temperature of inlet increased a little with the increase in RPM.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.8
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• pp.720-729
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• 2001

The effect of vapor flow direction on falling film heat transfer was experimentally investigated by using water. Parallel flow (both water and vapor downwards) showed higher heat exchange performance than counterflow(downward water and upward vapor). The difference became significant as the vapor flow rate was increased. It is supposed that the uprising vapor disturbs the solution film flow and heat transfer is reduced by uneven distribution or detachment of water film.