Investigation on the characteristics of oil supply system for a hermetic variable speed rotary compressor

Abstract A hermetic variable speed rotary compressor has a substantially vertically oriented drive shaft, by which the oil is driven upwards and delivered to the lubricating components. To avoid oil starvation or excessive oil supply over a wide range of working speed, it is essential to understand the flow characteristics in such a centrifugal oil pump. In this study, a novel test rig has been built to perform the measurements of oil flow rate under various operating conditions. Several key design parameters in relation to the flow rate such as oil inlet diameter, oil viscosity and oil level height in oil sump have been discussed in detail. The results indicate that the oil flow rate increases up to the speed at which the flow stagnation appears and then starts to slightly decrease with the speed. The stagnation speed decreases with the oil inlet diameter but increases with an augment in oil level height. The oil viscosity does not considerably affect the stagnation speed. Based on the simulated results, it is found that the gas region at oil inlet expands and the effective oil flow area reduces when the rotational speed is high enough. Such behavior of oil flow could be one potential explanation to the occurrence of flow rate stagnation.