Summary

Heat transfer has a major role in the efficiency and reliability of reciprocating compressors adopted in household refrigeration. The objective of this study is to evaluate the heat transfer in several components of the compressor during thermal transients that occurs in the usual on/off operating condition of refrigeration systems. In fact, this is an important aspect since virtually all analyzes consider the condition of thermal equilibrium. Measurements of temperatures in the lubricating oil and in the refrigerant at different locations inside the compressor are also performed to allow the evaluation of local heat transfer coefficients. The investigation revealed the presence of different time scales associated with the heat transfer process in each component during the thermal transient. It has also been observed that the flow of refrigerant and lubricating oil induced by the crankshaft mechanism greatly affect the heat transfer process in different regions of the compressor. As far as the thermal transient is concerned, the heat flux in some regions was seen to be significantly affected by the cyclic operating condition. For instance, mean heat flux on the surface of the suction muffler in the cyclic condition is approximately 70% of that obtained in the thermal equilibrium condition. Moreover, the temperatures of both the lubricating oil and the electric motor in the cyclic condition are significantly smaller than those achieved in the thermal equilibrium condition.

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