Improved Equivalent Simple Model of Complicated Bypass Leakages in Scroll Compressors

In the previous study for an equivalent simple model to calculate the bypass leakage mass flow rate along the tip seal in scroll compressors, presented in the previous 2016 Purdue Compressor Engineering Conference, it was supposed that the leakage loss through the tangential slot under the tip seal, with a comparatively large cross-section, must be so small that its effect upon the pressure loss can be ignored. However, many studies continued after that showed that the assumption was wrong. That’s why the present study was carefully carried out to present an improved equivalent simple model to calculate the complicated bypass leakages, taking the ignored pressure loss into exact consideration. In the first place, a bypass leakage test model was precisely developed to be compatible with a practical scroll compressor with large cooling capacity, and then detailed tests of pressure decay in a pressurized vessel due to the bypass leakages were conducted with dry refrigerant gas R410A. Secondly, the measured pressure decay characteristics were theoretically simulated using the very simple Darcy-Weisbach equation with an empirical friction factor determined in our previous study for the leakage flow through axial clearances, where the complicated flow patterns through bypass clearances were decomposed into two thin representative rectangular cross-section leakage passes: one with the effective mean width for the leakage flows from the radial flow over the scroll rap, to the axial flow in front of the tip seal, to the tangential through the tip seal slot, and then to the axial and radial flows; and another with the effective mean length for the tangential leakage over the scroll rap. Thirdly, empirical values of the effective pass width and length were determined so that the measured pressure decays are well predicted by the calculations. As a result, it was evidently shown that the complicated bypass leakage flow rate along the tip seal in scroll compressors can be calculated by a very simple scheme introducing the parallel leakage passes with a thin rectangular cross-section. Fourthly, the calculated leakage mass flow rates were shown to examine the contribution level of two representative leakage passes upon the resultant. Finally, the effective pass width and length for the parallel leakage passes with a thin rectangular cross-section were reduced to a non-dimensional form to examine the key factor dominating the complicated leakages