Numerical Simulation of a Reciprocating Compressor For Household Refrigerators

This paper presents a method for the numerical simulation of reciprocating compressors for household refrigeration. The compressor is regarded as a set of volumes and one-dimensional, variable-area ducts connected together. The model describes all relevant features of the compressor, including suction and discharge mufflers and automatic valves. The equations governing the unsteady flow of a real gas in the ducts are numerically solved with a high order accurate discontinuous Galerkin method. The model accounts for the interaction between the gas flow and the automatic valves motion by solving the governing equations in a strictly coupled fashion. The method has been validated by comparing the numerical results obtained in the simulation of a compressor for household refrigeration with experimental data. The results show the potentialities offered by the proposed approach. INTRODUCTION In this paper . ye present a new numerical procedure for the simulation of the hermetic reciprocating compressor used in the households appliances. The method can simulate accurately the unsteady flow of a real gas through the compressor (including the flow in the cylinder leakage) and can handle the interaction between the fluid flow and the automatic valves motion. Moreover, the effects of friction and heat exchange between gas and solid walls can be taken into account by means of appropriate correlations. The space discretization of the flow equations is based on a recently developed Discontinuous Galerkin (DG) method [1] that has proved to be very accurate and numerically robust. For the application presented in this paper we have used a one-dimensional (in space) version of the code. However, work has been planned to employ multidimensional spatial discretizations to compute the fluid flow in those components which greatly influence the fluid dynamic b~havior of the whole compressor. In the following we present and discuss the governing equations of the flow in the compressor components; then we briefly outline the DG solution procedure; finally we present the numerical results of an unsteady simulation, that takes into account fluid flow, heat exchanges, fluid structure interaction with the automatic valves, cylinder leakage, and compare the results with available experimental measurements. GOVERNING EQUATIONS This section briefly describes 1) the equations governing the gas flow through ducts and volumes, 2) the equations governing the heat flux among the various components of the compressor and 3) the equations governing the suction and discharge valve motion. We first begin with the fluid dynamic model of the compressor, which is constructed using two basic building blocks called "ducts" and "volumes". Ducts are used to model the regions of the compressor where the flow displays a prevailing velocity direction. Volumes are instead used to model more complex regions where the onedimensional flow hypothesis does not apply. The various chambers inside the suction and discharge mufflers and the compressor cylinder are for example modeled as volumes, while the ducts connecting the various chambers are modeled as ducts. The equations governing the gas flow through ducts with cross sectional areaS can be written as Fifteenth International Compressor Engineering Conference at Purdue University, West Lafayette, IN, USAJuly 25-28, 2000 97