| A transient model was developed to predict the behavior of the vapor compression cycle of a mobile air-conditioning system. Mobile air-conditioning systems operate in a transient mode due to variations in compressor speed, variations in condenser air flow rate, and the controls strategy such as clutch-cycling. We developed a model to simulate start-up transients, clutch cycling transients, city-driving transients, and shut-down transients including the following charge redistribution.; Our transient model treats the components in a vapor compression refrigeration system including the compressor, condenser, orifice tube, evaporator, and accumulator. The heat exchangers are divided into a series of constant-volume cells. The conservation of mass, conservation of energy, and conservation of momentum equations are applied to each cell. The number of cells and/or the volume of the cells can be changed between simulations in order to change the resolution of the model. The accumulator model is a modification of the heat exchanger model which constrains the outlet to always be vapor. The orifice tube model and the compressor model are semi-empirical.; The model is validated with steady-state and transient data obtained from a test facility specifically designed to simulate mobile air-conditioners. The steady-state model predicts most of the system parameters to within +/-15%. The transient model predicted the behavior of the city driving cycle, compressor shut-down, compressor start-up, and clutch-cycling simulations well.; An important part of the system model is calculating the refrigerant properties correctly. We developed refrigerant property routines to the calculate equilibrium thermodynamic properties in the liquid, vapor, two-phase liquid-vapor, and supercritical region using the Modified-Benedict-Webb-Rubin equation of state. Our property routines accurately solve for a given output property for applicable combinations of input properties. They also accurately predict whether the refrigerant is in the single-phase or two-phase region. The property routines agree extremely well with the experimental data found in the literature. |
