Effects of Materials on Temperature Distribution of a Compressor

To evaluate the effects of the thermal properties of components on the overall temperature distribution of a compressor, a heat transfer model employing the lumped thermal conductance approach has been formulated. The model has been verified with extensive measurements and the overall discrepancy of less than 7% is obtained. The discrepancies in the prediction are mainly the results of assumptions made in assigning various heat transfer convection correlations, and simplification made in distributing the various components of the compressor into discrete parts. The model has been used to predict the effects on overall temperature distribution of a compressor when introducing new materials for some of the compressor components. Results are shown and discussed. INTRODUCTION Literature shows that limited research work has been carried out to provide heat transfer information on refrigeration compressors, let alone the temperature distribution of the whole compressors. Literature also showed that most of the heat transfer studies were mainly focused on convection heat transfer in the cylinder. However, in 1992 Padhy [I] employed the lumped capacitance model to predict temperature distributions of a rolling piston compressor. Using the same approach, Ooi and Ng [2] attempted to predict temperature distribution of a reciprocating compressors. The results showed that the lumped conductance approach is economical and efficient The knowledge on the temperature of the compressor components plays an important role in designing a reliable and high efficiency compressor. With the advent in the materials technology, many new materials with good thermal and physical properties have been introduced. A good understanding of the temperature distribution of a compressor helps in selecting suitable materials with better thermal and physical properties for the compressor design. This paper shows that the application of the heat transfer model [2] in an attempt to predict temperatures of the components in the compressor. This information is particularly important when assessing the performance and the reliability of the compressor by introducing newly available materials. HEAT TRANSFER MODEL In this study, the thermal conduction approach has been employed to study the temperature distribution of the complete reciprocating compressor. In the formulation [2], the complete hermetic refrigeration compressor unit has been divided into 46 discrete elements of simple shape, see Table 1. Each element is assumed to be at a uniform temperature. The lumped and isothermal elements are selected such that most of these elements conform with the natural geometric boundaries. The boundaries of the elements include solid parts, fluid flow paths and interfaces between solid parts and fluid. However, the actual parts in the compressor are usually made in intricate shapes which resulted in flow conditions which are too complicated to be modelled directly. Assumptions and simplifications have been introduced and these intricate parts have been made into simpler elements in order to allow the heat transfer