TRANSIENT ANALYSIS OF REFRIGERATION SYSTEM

The vapor compression refrigeration system consists of the basic components--compressor, condenser, expansion device and evaporator. For low temperature applications, an accumulator is also included between the evaporator and the compressor shell. The mathematical modelling of a refrigeration system involves developing of equations which predict the movement of refrigerant in the system and the change of state of refrigerant in the system components with time. The refrigeration system is a complex physical system with all its intricacies such as two phase refrigerant flow phenomena, foaming of oil-vapor refrigerant mixture, oil transportation, etc. Unlike steady state analysis, the influence of various metal masses on the system response have also to be taken into account. Development of a computer program which is to be used as a design tool requires that the computational time be a minimum for the computer program to be economical. This was achieved for the complex physical phenomena associated with the refrigeration system by combining basic engineering principles with empirical parameters for system intricacies like heat transfer coefficients, oil transportation, oil-refrigerant foaming, etc., which need to be evaluated experimentally. The continuous physical process occurring in the system has been represented as a sequence of discrete small steps taken one at a time. System components have been represented by discrete control volumes. Heat exchanger control volumes are further divided into sub-control volumes which keep track of vapor and liquid refrigerant regions. Oil in the compressor shell has been treated as source/sink of refrigerant. The developed mathematical model was applied to an existing unitary room air conditioner. The computer program was run for various system and environmental conditions. The general trend of the predicted results agrees with how the actual system would respond, as experienced by the sponsor\u27s staff and other engineers knowledgeable in this field