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ACRC Technical Report 143PDF


Title:Development of a Transient System Model of Mobile Air-Conditioning Systems
Author(s):Hemami, T.L.
Contributor(s):Dunn, W.E.
Subject(s):mobile air conditioning systems
Abstract: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.
Issue Date:1998-09
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center TR-143
Genre:Technical Report
Sponsor:Air Conditioning and Refrigeration Project 78
Date Available in IDEALS:2009-05-22
Identifier in Online Catalog:4136298

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