Summary

One of the main sources of thermodynamic inefficiency in compressors is associated with heat transfer that takes place as the gas flows throughout the suction system and enters the compression chamber. This process is usually referred to as superheating and its main effect is the decrease of both the volumetric efficiency, due to the reduction of the gas density, and the isentropic efficiency, since the specific work of compression becomes greater as the gas temperature is increased. For a suitable analysis of gas superheating and proposals to reduce its negative effects, one must be able to verify the compressor temperature distribution according to different design alternatives. However, the temperature of each one of the compressor components is affected by several phenomena that act simultaneously, making the temperature distribution particularly difficult to predict. This work presents a simulation model for thermal analysis of reciprocating compressors formed by combining a lumped formulation for heat convection in fluid flow regions and a three-dimensional differential formulation for heat conduction in the solid components. Convective heat transfer coefficients were evaluated from correlations available in the literature so as to avoid calibration based on experimental data. Because some complex flow geometries in the solution domain have no correlation available, a sensitivity analysis was carried out via DoE to identify those coefficients that require more attention. The model was applied to a reciprocating compressor under three operating conditions and predictions for temperature distribution and heat transfer were seen to be in good agreement with measurements.

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