scroll compressor, slug, two-phases flow CFD
Slug test is used to simulate a real application work condition in lab. During operation, a compressor eventually gets to endure dynamic slugging which is characterized by the arrival of a liquid refrigerant at the suction side when the compressor is already running. Because of this dynamic, the liquid is able to reach the compression side. The presence of incompressible liquid in the scrolls (volumetric compression) involves mechanical strength quickly becoming unbearable for the compressor involute breakage or Oldham coupling breakage are the consequences suffered by the compressor following a severe slugging. In this paper, a prediction method of slug limit is introduced which is based on simulation result numerical fitting to experimental result. In laboratory, engineers use dynamometer to monitor the image of compressor current intensity which shows a steep peak when more and more liquid refrigerant injected. Once the current peak ratio exceeds our goals, we would take the corresponding liquid quantity as slug limit of the compressor. And this liquid injection process is transient simulated by CFD method using two-phases flow model – Eulerian multiphases model which allows for the modeling of multiple separate yet interacting phases. The phases can be liquids, gases, or solids in nearly any combination. Liquid refrigerant is thought as granular phase and calculated. Mass flow rate of each phase at outlets is recorded during calculation process and divided by normal mass flow rate (only gas suction). The maximum ratio of mass flow rate is used to predict slug limit comparing to experimental criterion. Using this method, it’s easier to comparing with different parts structure which one is better for slug performance and which one is worse, saving time and cost and more and more helpful for engineering design.