• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.12
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• pp.1167-1174
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• 2004

The method to consider gravity effect on the performance of a condenser is developed, and a simple condenser having 'nU' type two circuits is analyzed. Each circuit has the same length and inlet air-side operational conditions. The only difference between two circuits is the direction of refrigerant flow, which is exactly opposite each other between the upper 'n' type circuit and the lower 'U' type circuit. It is shown that the gravity makes the distribution of refrigerant flow uneven in the two circuits at lower refrigerant flow rates; heat transfer rate also becomes uneven. Moreover, much of the refrigerant exists as liquid state in the circuit having low refrigerant flow rate, which will make the cycle balance unstable in the refrigeration cycle system like a heat pump.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.12
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• pp.1043-1048
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• 2003

An experimental investigation was executed to determine the capacity degradation due to non-uniform refrigerant distribution in a multi-path evaporator. In addition, the possibility of recovering the capacity reduction by controlling the refrigerant distribution among refrigerant paths was assessed. 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 30%, even when the overall evaporator superheat was kept at a target value of 5.6$^{\circ}C$. It may indicate that the internal heat transfer within the evaporator assembly caused the partial capacity drop. For the evaporator having air mal-distributions, the maximum capacity reduction was found to be 8.7%. A 4.5% capacity recovery was obtained by controlling refrigerant distribution to obtain the target superheat at the outlet of each path.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.371-375
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• 2009

The distribution control of refrigerant flow is one of the basic technique to enhance system efficiency. However, if engineers forget to control the refrigerant flow speed in all operation range, refrigerant flow mal distribution becomes a noise source. The refrigerant flow noise should be checked and controlled at the lowest air flow mode which is the most silent mode and frequently used in night time.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.5
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• pp.444-450
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• 2013

The distribution performance of refrigerant distributors in air conditioner evaporators was examined numerically and experimentally. Internal flow analysis of the distributor by CFD found that the distance from the socket to the cone, the angle of the cone and the base area of the cone were the most important factors affecting refrigerant distribution ability and vortex creation. To enhance distribution performance, two distributors with improved internal structures were designed. To test these new structures, distribution performance was also analyzed by CFD and an empirical experiment was carried out using the water-nitrogen. Experimental results on the distribution fraction of each distributor hole showed a good agreement with the results of the CFD analysis. Thus, the new design of the distributors enhanced distribution performance of the refrigerant distributors.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.9
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• pp.491-496
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• 2015

Generally, the phase of the refrigerants that circulate in air-conditioning systems is repeatedly changed from liquid to gas and from gas to liquid. In vapor-compression refrigeration, the refrigerant at the inlet of the evaporator is in a gas-liquid two-phase state; therefore, to enhance the heat-transfer performance of the evaporator, the even distribution of the refrigerant across multiple passages of the evaporator is essential. Unlike the distribution of a single-phase refrigerant, multi-phase distribution requires further considerations. It is known that the multi-phase distribution at the outlet of the distributor is affected by factors such as the operating condition, the distributor's shape, and the insertion depth of the outlet pipes; here, the insertion depth of the outlet pipes is especially significant. In this study, for a cylindrical distributor with a 90-degree bend entrance and three outlet pipes, the flow uniformity at the outlet pipes was numerically tested in relation to variations of the insertion depth of the outlet pipes.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.221-226
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• 2008

A microchannel condenser as a part of a R410A residential air-conditioning system was examined experimentally and numerically in this study. The system was operated in separate environmental chambers and its performance was measured in ARI A, B, and C conditions. A numerical model for the microchannel condenser was developed and its results were compared with the experimental results. The model simulated the condenser with the assumption of the uniform air and refrigerant distribution, and with the consideration of the non-uniform air distribution at the face of the condenser and refrigerant distribution in the headers. In order to consider the non-uniform air distribution, air velocity contours were generated from the measured local air velocities at the face of the condenser. The simulation results showed that the effect of the air and refrigerant distribution was not a significant parameter in predicting the capacity of the microchannel condenser which was experimentally examined in this study. The comparison of the calculated and experimental results showed that the condenser capacity could be predicted well for every test condition. However, the prediction of refrigerant pressure drop deviated significantly from the measured values.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3546-3552
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• 2009

In this study, an analysis code was created for a 190*650*25-mm (W*H*D) parallel-flow evaporator, and research was done on how to increase the heat transfer rate of aluminum PF heat exchanger for application in IDU. After varying the R410A refrigerant up-down flow to two and three passes and the distribution ratio to 1:1:1 and 1:2:2, it was determined that the two-pass flow has a 30% higher partial heat transfer rate and a 25% lower heat transfer coefficient compared to the three-pass flow. As for the distribution ratios of the three-pass flow, 1:1:1 was found to have a lower refrigerant pressure loss than 1:2:2 distribution. It was assumed, though, that the refrigerant distribution had a uniform flow and that its value was thus overestimated in the actual case of maldistribution in each pass.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.1
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• pp.49-56
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• 2008

When the outdoor air temperature decreased less than the freezing temperature, frost forms at the surface of heat exchangers and it makes the performance degradation of a heat pump system. In this study, a heat pump system has been developed which has a refrigerant heating device as an auxiliarly heating equipment. To reduce power consumptions of the system, a liquid pump, rather than a compressor, was used to drive refrigerant in the heat pump cycle. Ratio of refrigerant mass flow between a refrigerant heating heat exchanger(GHX) and a outdoor plate heat exchanger(PHX) was varied and the system performance was measured and analyzed. As results, when the refrigerant flow rate to the GHX was decreased, the system performance is decreased due to heat absorption capability restriction of the GHX and small variation of the power consumption in the compressor. The effect on the evaporating and condensing pressure by the distribution ratio of the refrigerant to the each heat exchanger is small compare to the effect by the frequency change in the compressor. When the compressor was replaced by the liquid pump, the capacity of the system decreased a little, however the power consumption decrease approximately 80% compare with the power used in the compressor.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.340-345
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• 2008

A computer program, which simulates the parall flow evaporator was developed. The program was having used to simulate the sample $650\;mm{\times}190\;mm$ frontal area, 25 mm flow depth and 3.0 mm fin pitch. It was shown that the cooling capacity of 3kW could be available from the sample. The present model, however, does not consider refrigerant mal-distribution in each pass, which is known to reduce the cooling capacity of the parallel flow heat exchanger.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.4
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• pp.262-270
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• 2001

This paper deals with a prediction method for the condensation of ternary refrigerant mixture inside a horizontal smooth tube. Based on some reliable assumptions, the governing equations for the local heat and mass transfer characteristics are derived, and the prediction for the condensation of ternary zeotropic refrigerant mixtures composed of HFC32/HFC125/HFC134a, including R407C, is carried out. The local values of vapor quality, thermodynamic states at bulk vapor, vapor-liquid interface and bulk liquid, mass flux etc. are obtained for a constant wall temperature and a constant wall heat flux conditions, and the effects of the composition of HFC32/HFC125/HFC134a on heat transfer characteristics are examined. The prediction result is also compared with experimental data for condensation of ternary refrigerant mixtures. The predicted wall temperature distribution has a similar trend with experimental data but the predicted local heat transfer coefficients are 20-30% higher than the experimental data.