Summary

The efficiency of reciprocating compressors adopted for refrigeration purpose is significantly affected by gas superheating that takes place as the refrigerant flows through the suction system and enters the cylinder. Therefore, it is quite important to correctly predict heat transfer between the cylinder walls and the refrigerant in order to optimize the compressor performance, by increasing its volumetric and isentropic efficiencies. This dissertation considers the numerical modeling of the heat transfer process within the cylinder of reciprocating compressors used for household refrigeration, taking into account contributions of the compression, discharge, expansion and suction processes. The mode is tested for two-dimensional and three-dimensional formulations and numerically solved via the finite volume method. Three different turbulence models (SST, Realizable k-å and RNG k-å) have been adopted to solve the associated compressible, turbulent flow in the presence of heat transfer. The dynamics of both valves is described with a single degree-of-freedom model. The results show that high-speed flow that occurs in the initial opening stages of the suction and discharge valves gives rise to high rates of heat transfer in the cylinder. On the other hand, the analysis reveals that the inclination of the suction orifice, commonly adopted in actual compressors, affects the heat flux distribution on the cylinder lateral wall. Nevertheless, the overall heat transfer over a complete cycle is virtually insensitive to such geometric feature. It was also observed that estimates for in-cylinder heat flux given by correlations available in the literature are not in agreement with the numerical results obtained in the present study. A new correlation is proposed and tested for different compressor operating conditions, showing satisfactory results.

Material for download