An Investigation on the Bearing Design and Friction Characteristics of a Hermetic Reciprocating Compressor

The most important design parameters for hermetically sealed compressors used in domestic refrigerators are the Coefficient of Performance (COP); low manufacturing and operating costs; long operating life, low noise and vibration levels and to achieve environmentally friendly constructions. Positive displacement piston type compressors are used in refrigerators today due to their high capacity/volume ratios. Hence, the bearings of the hermetic compressors must also satisfy these design conditions. Investigation and optimization of crank shaft bearings in hermetic compressor applications are the main objectives of this study . The effect of crank shaft geometry, bearing clearance, lubricant viscosity, surface roughness and bearing location along the shaft on the friction losses were investigated and the new journal bearing designs were developed. Detailed parametric numerical simulations were performed using commercial software. According to the results of the simulations number of compressors were assembled with the selected design parameters and performance measurements were carried out. The results of the numerical analysis have shown that the numerically calculated mechanical loss level is similar to the performance results measured in a calorimeter test system. Results of the simulations and experiments were evaluated with six sigma (6?) techniques. Measurement of the efficiency of the compressor with the improved bearing design showed 1.3 % increase in the coefficient of performance (COP) with respect to the compressor with previous bearing design. This study shows that the mechanical loss characteristics are significantly influenced by the length of the bearings, clearance between the crankshaft journal and its bearing, kinematic viscosity and operating conditions. Bearing analysis results help to characterize the optimum journal bearing parameters which lead to improved mechanical efficiency of the compressor