Heat transfer, reciprocating compressor, cylinder, CFD, empirical correlations
Heat transfer inside the cylinder of reciprocating compressor causes decrease of volumetric efficiency. The reason is superheating of the working fluid from the cylinder walls, which are heated up by the compression process itself. Decreasing gas superheating is favorable not just for efficiency, but also for reliability of a compressor. Understanding heat transfer phenomenon inside the cylinder is necessary step for that. Nowadays there are several empirical correlation available in the literature, which are often used in simulation tools due to their easy-to-use properties and capability of providing fast results with solid accuracy compared to more complex numerical models for heat transfer modeling. Nevertheless there is a problem with verifying these empirical correlations. Experimental measurements are troublesome to perform because of fast phenomenon changes inside the cylinder and long thermal inertia of test bench components. Another problem is positioning of heat flux sensors inside the cylinder. Therefore it is necessary to verify these methods alternatively. Good opportunity could be found in CFD simulation tools. This paper presents the CFD analysis of heat transfer in order to compare heat fluxes calculated by numerical tools with those obtained by empirical correlations from literature. The valves are significantly influencing the flow field inside the compressor and therefore the heat transfer between the cylinder walls and working gas, what is also covered in the paper. The analysis was done on simplified 3D geometry, including the movement of valves and remeshing through the simulation to guarantee mesh quality. Based on the results of numerical analysis, empirical correlations were adjusted to increase their accuracy.