Summary

In this work, the refrigerant gas leakage through the radial clearance  in a rolling piston compressor has been modeled taking into account the pure oil as well as the oil-refrigerant mixture as the leakage fluids. In this way, six flow models considering both steady and unsteady state flows have been developed. Starting with the simplest model involving only the steady state flow of pure oil, which has been frequently used by other authors so far, time changing of both compression pressure and rolling piston tangential velocity has been taken into account. For that, it has been necessary to model the refrigerant gas compression process and rolling piston dynamics, turning the flow unsteady. The influence of the dissolved gas in the oil has been analyzed by means of the single-phase homogenous and heterogeneous flow models of the oil- refrigerant mixture. Finally, the refrigerant gas bubble formation has been introduced into the two-phase homogenous flow model of the mixture. Attempts have also been made to introduce foam generation. The proposed models have been solved by finite-volume and Runge-Kutta numerical methods, although only the steady state flow model of the pure oil could be experimentally validated. Results show the importance of dissolved refrigerant gas in calculating the mixture physical properties as well as gas bubble formation along the flow. Furthermore, the need of including the inertial terms in the momentum transport equation, for high flow rate, has been highlighted. In addition, radial clearance changes, due to pump setting must be considered in the unsteady state models and foam formation at the channel exit can significantly influence the flow results. Two-phase homogenous flow model is recommended in this work in order to calculate the refrigerant gas leakage through radial clearance. However, the importance of this leakage in the volumetric efficiency of the compressor has not been confirmed yet.

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