Predicting Refrigerant Inventory of HFC 134a in Air Cooled Condensers

Abstract

Currently, the refrigerant inventory for vapor compression systems is determined using a costly trial and error procedure. An accurate computer model of the refrigerant in a system would reduce the time and expense of this process. This paper presents a computer model that has the capability to predict the amount of refrigerant in air cooled condensers. For accurate prediction of refrigerant inventory two important steps are required. The first step is to model the heat transfer of the coil. This is needed to separate the three regions of the coil, de superheating, condensing, and sub cooling and then to further divide the condensing region into increments of quality. The second step is to predict the void fraction (ratio of area occupied by gas to liquid) throughout the condensing region. Void fraction correlations by Domanski and Didion[ll], Hughmark[14], Premoli et al.[12], and Tandon et al. [10] are included in the model. The simulation is used to model a cross flow heat exchanger, with parallel refrigerant paths, used in mobile air conditioning systems. The model is exercised to illustrate the effects of different operating conditions and void fraction correlations on the refrigerant inventory in condensers. A condenser used in mobile air conditioning applications is modeled. Future work includes experimental validation of the model.