Abstract

Scroll compressors are becoming popular in refrigeration applications where high pressure ratio operation is required. To achieve competitive efficiency and minimize discharge temperature, a discharge valve is often mandatory in these applications. However, the discharge valve brings with it its own reliability risk. Operation of the valve in scroll compressors in many ways is similar to rotary or reciprocating compressors, but there are specific features of the scroll compression process requiring special consideration in scroll wrap design.

This paper addresses a risk with scroll compressor discharge valve reeds in the form of sudden backflow at the time of porting which occurs at the end of discharge process. The mechanisms responsible for valve impact are evaluated and ways to minimize and to even virtually eliminate them are presented. Computer simulation results quantify the effect of design and application variables on valve impact. Two levels of analysis are presented, first a more rigorous but computationally involved approach, then a simplified method more applicable for a quick estimate or evaluation of trends. A comparison between the two analyses is presented. Effects of clearance volume, discharge pressure, suction pressure, and scroll wrap geometry on valve impact are considered. It is shown that discharge pressure and volumetric flow rate at porting have the greatest effect on the valve impact velocity against the scat. Design tradeoffs for minimizing valve impact also presented.

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