Summary

Refrigeration compressors adopt valves that automatically open due to the pressure difference between the compression and suction/discharge chambers. The specification of such valves is one of the most important steps in the design of a high efficiency compressor. For instance, if the sealing of the valve is not complete due to surface irregularity or misalignment, gas leakage will occur and significantly reduce the compressor performance. This thesis reports a simulation model developed to predict gas leakage in compressor valves. The lubricating oil in compressors acts also as a sealing element for valves. However, since very little information is available about the amount of oil that is actually present between the valve and its seat, the presence of oil has been neglected in the model. The pressure difference between the compression and suction/discharge chambers is the driving force of gas leakage through valves. The model developed in the present work assumes a one-dimensional flow through the micro channel formed between the reed valve and its seat, considering the effects of viscous friction, compressibility, gas rarefaction and valve bending into the port due to pressure load. Computations are carried out for a wide range of pressure differences that prevail in the valve clearances during the complete compression cycle of a small reciprocating compressor designed for household refrigeration. Results show that gas leakage in the suction and discharge valves significantly affect the compressor volumetric and isentropic efficiencies and that valve bending and gas rarefaction are very important parameters of the analysis.

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