CH-95-23-1 -- Predicting Refrigerant Inventory of R134a in Air-Cooled Condensers PDF

Currently, the refrigerant inventory for vapour-compression systems is determined using a costly trial-and-error procedure. An accurate computer model that predicts the amount of refrigerant in a system would reduce the time and expense of this process. 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 in order to separate the three regions of the coil - desuperheating, condensing, and subcooling - 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 (1983), Hughmark (1962), Premoli et al. (1971), and Tandon et al. (1985) 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 circulating refrigerant is R134a. The model is exercised to illustrate the effects of different operating conditions and void fraction correlations on the refrigerant inventory in condensers. The results indicate that the prediction of refrigerant inventory is heavily influenced by both the selection of the void fraction correlation and the predicted length of the subcooling section in the condenser. This length is determined by the simulation program and is dependent on the correlations used to determine the heat transfer coefficients and pressure drop. It is as important for the condenser simulation to properly predict the outlet conditions as it is to predict the overall capacity of the coil. Inventory comparisons are provided using the refrigerant two-phase heat transfer correlation that most accurately predicts the condenser outlet conditions. Future work includes experimental validation of the inventory model.

KEYWORDS: year 1995, calculating, refrigerants, R134a, air cooled condensers, computer programs, content, accuracy, heat flow, coils, voids, cross flow heat exchangers, unit air conditioners, operations, accuracy, subcooling