• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.7
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• pp.645-651
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• 2004

Fin-tube evaporator for carbon dioxide has been investigated both by experiment and simulation. Inside refrigerant heat transfer and outside heat and mass transfer of a wet surface heat exchanger were modeled using appropriate correlations. The results estimated by the calculation were in good agreement with the experimental results. The simulation errors were less than 7.9% for estimating capacity, 0.6$^{\circ}C$ for air exit temperature, 1.2% for air exit humidity and 17% for $CO_2$ exit pressure. The simulation program was used to study the effect of air flow direction, number of rows and refrigerant circuits. For a 2-row evaporator, parallel flow showed better performance for low air velocity but for high air velocity, counter-flow was better. Refrigerant circuits, however, showed insignificant effect on the performance.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.1107-1112
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• 2006

The purpose of this study is a heat transfer coefficient test of evaporator tube in shell and tube heat exchanger by shapes, using R-404A. The experimental apparatus is designed to simulate the real heat transfer rate in one shell and tube heat exchanger. The test section is formed four type tubes that are Inner ridged tube, Corrugated tube, Turbo-C tube, Inner fin tube and shell type is formed by electrical heater. All tests were performed at a fixed refrigerant evaporator temperature at $1.5^{\circ}C,\;-3^{\circ}C$ and with mass fluxes of 29, 25 kg/hr. Heat transfer rate is calculated a enthalpy difference in test section. In experiment, heat transfer coefficient measured one by one and electrical heaters are supplemented by evaporator.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.4
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• pp.388-398
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• 1994

Computer simulation model for predicting more accurately the heat transfer performance of the evaporator and condenser which have significantly affected on the performance of air-conditioner has been suggested. In this model oil and micro-fin tube used in a actual unit are considered to simulate the more realistic case. The effects of oil and micro-fin tube on the performance of an air-conditioner have been investigated. It is found that the present model requires higher pressure than the existing model due to the characteristics of the tube considered. However, it turns out that the present model is very close to an actual cycle. As the amount of oil inside the tube increases, condensation heat transfer coefficient shows a linear decrease irrespective of a kind of oil, while evaporation heat transfer coefficient increases slightly in the oil with low viscosity and decreases exponentially in the oil with high viscosity. Pressure drop in both evaporator and condenser increases linearly irrespective of a kind of oil. It is also found that the effect of the variation of oil concentration on the magnitude of two-phase region is negligible.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.4
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• pp.100-105
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• 2004

Fin-tube type(Fin-type) heat exchanger has been tested in order to replace the heat exchanger of parallel flow type(P.F -type) which is now widly used in automobile air conditioning system The following conclusions are drawn by the comparison of the characteristics of the heat exchangers. Evaporator and condenser capacities and COP(Coefficience of performance) were varied as with the compressor speed, outdoor air temperature and air flow rate changed, which much influenced on the characteristics of the air conditioning system Evaporator and condenser capacities were increased with increasing compressor speed and outdoor air temperature. Evaporator and condenser pressures of Fin-type were decreased by 7% and 5% respectively compared with those of P.F-type. The COP of Fin-type was decreased with increasing outdoor air temperature and compressor speed. The COP of P.F-type was decreased by 14% compared with that of Fin-type.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.30 no.1
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• pp.33-44
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• 1994

This work studies for boiling and condensation heat transfer performance of trapezoidally shaped integral-fin tubes having fin densities from 748fpm to 1654fpm. For comparison, tests are made using a plain tube having the same inside and outside diameter as that of the root of fins of finned tubes. Hahne's theoretical model and Webb's theoretical model are used to predict the R-11 boiling heat transfer coefficient and condensing heat transfer coefficient respectively for plain tube and all integral-fin tubes. Experiments are carried out using R-11 as working fluid. This work is limited to film-wise condensation and pool boiling on the outside surface of plain tube and 4 low integral-fin tubes. In case of condensation, the refrigerant condenses at saturation state of 32$^{\circ}C$ on the outside tube surface cooled by coolant and in case of boiling. the refrigerant evaporates at saturation state of 1bar on the outside tube surface. The amount of non-con-densable gases in the test loop is reduced to a negligible value by repeated purging. The actual boiling and condensing processes occur on the outside tube surfaces. Hence the nature of this surface geometry affects the heat transfer performances of condenser and evaporator in refrigerating system. The condensation heat transfer coefficient of integral-fin tube is enhanced by both extended tube surface area and surface tension. The ratio of the condensation heat transfer coefficients of finned to plain tubes is greater than that of surface area of finned to plain tubes, while ratio of the boiling heat transfer coefficient of finned to plain tubes shows reverse result. As a result, low integral-fin tube can be used in condenser more effectively than used in evaporator.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.105-112
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• 2011

The objective of this study is to predict the heat-transfer performance of a spirally coiled circular fin-tube evaporator in which either R134a or R600a was used; this heat-transfer performance was predicted by varying the mass flow rate, inlet air temperature, air flow rate, and tube thickness. Mean deviation for the analytical model from the measured data was ${\pm}8.3%$. Simulation results revealed that at a given mass flow rate, the heat-transfer rate of the evaporator using R600a was higher than that usingR134a because the enthalpy of the former is higher than that of the latter at the given conditions. The heat-transfer rate of both refrigerants increased with an increase in the air flow rate and inlet air temperature but decreased with an increase in the tube thickness.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2358-2372
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• 1993

In this study, the computer modeling for prediction of the performance of fin-tube heat exchanger using alternative refrigerant, HFC-134a was developed and the computer program for calculating the various properties of HFC-134a and the existing refrigerant CFC-12 and HCFC-22 was made. The heat exchanger modeling is based on a tube-by-tube approach, which is capable of analysis for the complex coil array. Performance of each tube is analyzed separately by considering the cross-flow heat transfer with external airstream and the appropriate heat and mass transfer relationships. A performance comparison according to the different refrigerants is provided using this developed model. As the result of this study, total heat transfer rate of evaporator and condenser using HFC-134a were found higher than that of using CFC-12 for the same operating conditions. When the mass flow rate of HFC-134a was less than CFC-12 about 18. 16%, the cooling capacities of evaporator were found to be the same.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.3
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• pp.216-222
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• 2005

An experimental investigation was executed to determine the capacity degradation due to fin conduction and non-uniform refrigerant distribution in a multi-path evaporator with cross-counter flow. The finned-tube evaporator, which had a three-path and three-depth-row, was tested by controlling inlet quality, exit pressure, and exit superheat for each refrigerant path. The capacity reduction due to superheat unbalance between each path was as much as $25\%$ for non-cutting evaporator, even when the overall evaporator superheat was kept at a target value of $5.6^{\circ}C$. It indicates that the internal heat transfer within the evaporator assembly causes the partial capacity drop. The capacity of cutting-evaporator with respect to non-cutting evaporator was enhanced according to the increment of air flow rate when superheat or superheat unbalance increased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.9
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• pp.516-521
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• 2013

In the present study, the performances of a fin-tube evaporator and three PF evaporators for a heat pump dryer were experimentally investigated. Among the tested evaporators, the PF3 type evaporator showed the highest values of heat transfer capacity and dehumidification performance, while the fin-tube evaporator had the lowest values. PF3 showed better performance compared to PF1 and PF2, due to the large pin pitch, which leads to more draining for dehumidified water. Also, the $45^{\circ}$ inclined PF evaporator presented better performance than that of the $90^{\circ}$ inclined PF evaporator, owing to its easier draining characteristics. The effect of air velocity was revealed to be quite large. When the air velocity increased by 20%, the heat transfer capacity and dehumidification performance increased 43%/11%, 48%/13% and 54%/23% for PF1, PF2 and PF3, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.6
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• pp.476-486
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• 2012

A simulation program was developed to evaluate the heat transfer performance of a multi-pass fin-tube evaporator, considering the pressure drop in the distributor and capillary tubes. The effect of capillary tube length for each pass was analyzed with various inlet air flow types and distributions. The appropriate capillary tube length distribution and correlation were determined for various inlet air flow types and distributions. The correlated results agreed well with the simulation, with an average error of less than 7%. By applying an optimal capillary tube length distribution, the heat transfer rate was increased by 4~5% compared to cases with uniform tubelength distributions, for each of the inlet air flow types and distributions considered in this study.