In this study, the method for predicting the performance of multi-pass type evaporators for automobile air conditioners is developed. The study is based on the previous studies of the flow boiling heat transfer and two phase pressure drop in small diameter tubes. The heat transfer rate, distribution of air/refrigerant temperature, pressure, vapor quality and void fraction are calculated on the various conditions of evaporator's specification, refrigerant flow and air flow. The effect of various calculation conditions on the heat transfer rate and refrigerant pressure drop in evaporator are also examined. It is found that the evaporator size can be reduced keeping almost the same outlet air temperature when the optimum specification of evaporator is selected. conclusions are, Pressure drop is extremely large when the number of turns is increased from four to six, in the case of the same refrigerant flow rate and the same number of tubes per row. Increasing the number of turns above 6 makes a large pressure drop in the case of using R134a. In the case of using R744 (CO2), it is found that pressure drop does not become a large problem. Heat transfer rate is almost kept constant when the number of tubes is decreased from 30 to 24. Therefore, the evaporator can be miniaturized from the viewpoint of heat transfer rate. If the inlet vapor quality of R744 is around 0.3, there are some conditions that heat transfer rate of R744 becomes almost the same as that of R134a. Decreasing evaporator size and refrigerant flow rate, there are some conditions that air temperature at the outlet of evaporator is almost kept constant. Therefore, the evaporator can be miniaturized from the viewpoint of outlet air temperature for R134a.
Numerical study on the performance of the evaporator for car air-conditioners
Numerische Untersuchung der Eigenschaften des Verdampfers für Fahrzeug-Klimaanlagen
2006
8 Seiten, 7 Bilder, 3 Tabellen, 4 Quellen
Conference paper
English
British Library Online Contents | 2009
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