Summary

The present dissertation considers a comparative analysis between the thermodynamic performances of reciprocating and rolling piston compressors for application in heat pumps with 1,4kW of heating capacity. Both compressors adopt R134a as the refrigerant fluid and evaporating and condensing temperatures equal to 10°C and 55°C, respectively. The aim of this study is to identify the advantages and disadvantages of each compressor based on estimates of the main effects that influence their volumetric and isentropic efficiencies. The effect of increasing the speed of each compressor for the purpose of miniaturization at this heating capacity is also investigated with emphasis on their thermodynamic performances. The mathematical models used to simulate the compression processes of both compressors are based on integral formulations of the conservation equations of mass and energy, allowing the prediction of density and temperature of the gas throughout the compression cycle. The coupling to an external library allowed estimates of other thermodynamic properties, such as the pressure in the compression chamber. The valve dynamics was solved by using a single-degree-of-freedom mass-spring-damper model. Pressure pulsation in the suction and discharge systems of the reciprocating compressor was estimated via a one-dimensional formulation for the compressible flow, which was numerically solved with the finite volume method. Leakage and superheating of refrigerant were also taken into account in the modeling of both compressors. In order to guarantee a meaningful analysis, each compressor was previously optimized for the operating conditions established for the comparison. The study shows that the rolling piston compressor performs better than the reciprocating compressor in the specified operating conditions and it is better suited for miniaturization purpose. The major limitations encountered in the reciprocating compressors are related to the inefficiencies caused by both the clearance volume and the suction and discharge processes. On the other hand, gas superheating and backflow in the suction orifice are the phenomena that most compromise the performance of the rolling piston compressor.

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