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Development Of A Refrigerant Distribution Header Applied To Microchannel Heat Exchangers, Tomoki Hirokawa, Kouju Yamada, Yoshio Oritani, Hirokazu Fujino
Development Of A Refrigerant Distribution Header Applied To Microchannel Heat Exchangers, Tomoki Hirokawa, Kouju Yamada, Yoshio Oritani, Hirokazu Fujino
International Refrigeration and Air Conditioning Conference
A microchannel heat exchanger applied to air conditioners has advantages because of its high heat transfer performance. However, there are some challenges to utilize its maximum performance. One of the most important challenges is refrigerant maldistribution resulting in heat transfer deterioration when it is used as an evaporator. The authors proposed a refrigerant distribution header that can be applied to variable capacity air conditioners, named “Refrigerant loop header.” In this paper, the “Refrigerant loop header”, which enables to equally distribute in a wide range of capacity, is introduced. In addition, high distribution performance is experimentally confirmed at different refrigerant mass …
Effect Of Flow Regime Before Distributor On Two-Phase Flow Distribution, Yufang Yao, Pega Hrnjak
Effect Of Flow Regime Before Distributor On Two-Phase Flow Distribution, Yufang Yao, Pega Hrnjak
International Refrigeration and Air Conditioning Conference
Conical refrigerant distributors are usually used to improve the distribution of two-phase flow to each circuit of the DX evaporators. A nozzle is commonly added before a cone to homogenize two-phase flow and that way unify distribution among channels. However, when the nozzle is not properly sized or, in some cases, there is no nozzle, the distributor performance is much affected by the flow regimes at the distributor inlet. This paper presents the effect of the flow regime at the distributor inlet on the uniformity of two-phase flow distribution. In this case, the flow regime is determined by mass flux, …
Oil Effects On Performance Of Automobile A/C System, Xuan Liu, Pega Hrnjak
Oil Effects On Performance Of Automobile A/C System, Xuan Liu, Pega Hrnjak
International Refrigeration and Air Conditioning Conference
This paper presents the effect of lubricant on automotive A/C system based on a series experiments in a real MAC system at two SAE conditions. The lubricant effect on heat transfer, pressure drop, refrigerant distribution, available enthalpy difference across evaporator, mass flow rate, capacity, compressor work and system COP are investigated and presented. It is found that the system capacity decreases with increase of OCR, but COP achieves a highest value when OCR is around 2-3% for constant compressor speed (capacity drops). Â
Oil Effects On Distribution Of Refrigerant In Mac Heat Exchangers, Xuan Liu, Pega Hrnjak
Oil Effects On Distribution Of Refrigerant In Mac Heat Exchangers, Xuan Liu, Pega Hrnjak
International Refrigeration and Air Conditioning Conference
This paper presents results of investigation of lubricant effects on refrigeration distribution by conducting a series experiments in a real MAC system at two SAE conditions. Infrared images of evaporator and condensers are taken and compared with two previous publications. It is found that the lubricant effect on evaporator largely depends on geometry and structure of evaporator, such as the inlet position and orientation. For condenser, the inlet header acts as an oil separator, which results in the oil accumulation at the bottom of the first pass of condenser.
Refrigerant And Lubricant Charge In Ac Heat Exchangers: Experimentally Validated Model, Shenghan Jin, Predrag S. Hrnjak
Refrigerant And Lubricant Charge In Ac Heat Exchangers: Experimentally Validated Model, Shenghan Jin, Predrag S. Hrnjak
International Refrigeration and Air Conditioning Conference
The paper presents a semi-empirical model to predict refrigerant and lubricant inventory in both microchannel condenser and plate-and-fin evaporator of an air conditioning system. In the model, heat exchanger is discretized into finite volumes. Temperature, pressure and mass inventory are calculated by applying heat transfer, pressure drop and void fraction correlations to these volumes respectively. Refrigerant and lubricant are treated as a zeotropic mixture with a temperature glide. As refrigerant evaporates or condenses, thermophysical properties are evaluated accordingly with the change of lubricant concentration. Oil is assumed to be retained in refrigerant oil mixture at concentration that is changing during …
Refrigerant Distribution Effects On The Performance Of Microchannel Evaporators, Chad D. Bowers, Helena Mai, Stefan Elbel, Predrag S. Hrnjak
Refrigerant Distribution Effects On The Performance Of Microchannel Evaporators, Chad D. Bowers, Helena Mai, Stefan Elbel, Predrag S. Hrnjak
International Refrigeration and Air Conditioning Conference
The performance of air to refrigerant heat exchangers can be affected greatly by both refrigerant and air flow distribution. Maldistribution of either fluid stream can lead to reduced heat transfer effectiveness of the heat exchanger and thus lower system efficiency and capacity. Microchannel evaporators are especially susceptible to refrigerant maldistribution as they typically have many parallel channels fed by a common header or manifold. This paper outlines general trends in refrigerant flow distribution in such evaporators taking into account various heat exchanger orientations. In addition, links between heat exchanger performance and refrigerant flow distribution characteristics in microchannel evaporators are made …