Experimental study on output characteristics of valved linear compressor under different regulating valve openings

Abstract

The valved linear compressor (VLC) plays a critical role in Joule-Thomson (JT) cryocoolers in liquid helium temperatures, with its performance influenced by various loads. To improve output characteristics, it is essential to study the relationship between the VLC and the load. In deep space applications, the JT orifice load is fixed, and takes time to achieve in low temperature. This paper presents a closed platform with a regulating valve to simulate JT loads in room temperature. Experiments are carried out to study the effects of stroke and frequency on the output characteristics of a single-stage VLC with different valve openings. The results show that increasing the valve opening reduces the load, increases mass flow rate and exergy efficiency, slightly decreases pressure ratio, and alters motor efficiency. Either increasing frequency or stroke enhances both the mass flow rate and pressure ratio. Under a load of 2-turn opening(Φ=1E-4 m), the stroke length increases from 0.002 m to 0.008 m, thereby causing the pressure ratio to exceed the reciprocal of the critical pressure ratio (1/λ*=2.04), suppressing growth rate of the mass flow rate from 44.7 % to 2.2 %. This suppression means the rest of the stroke can't play more functions, and it is attributed to choked state of the working medium, which can be identified by comparing experimental and theoretical mass flux values of the VLC. It also suggests that there exists a matching relationship between the compressor and the JT load, offering a basis for the compressor design and the match with JT orifice.