Comparative experimental analysis of the effect of lubricant viscosity on the performance of a single-screw expander with different structures

Abstract

Compressed air energy storage (CAES) is considered a promising energy storage technology because it promotes global energy saving, emission reduction, and the development of renewable energy. Improvement in the expander performance is a major concern in CAES systems. The addition of lubricant is beneficial for reducing leakage and friction losses, which can improve the expander performance and the CAES system efficiency. To clarify the influence of lubricant on the expander performance, a comparative experimental study was conducted. A single-screw expander (SSE) with different internal volume ratios and clearances was analyzed under different operating conditions with six different lubricant viscosities (viscosity from small to large: 10#, 22#, 32#, 46#, 68#, and 80#). The results show that increasing the kinematic viscosity of lubricant can effectively improve the volumetric efficiency. The volumetric efficiency of an SSE with a small clearance and a small internal volume ratio is higher, and it can approach 100% with 68# and 80# lubricants when the intake pressure is 0.5 MPa. Increasing the kinematic viscosity of the lubricant reduces the shaft power. The shaft power of an SSE with a large clearance and a small internal volume ratio is larger, and the maximum shaft power with 10# lubricant is 5.78 kW at 0.9 MPa and 3000 rpm. The kinematic viscosity of the lubricant significantly influences the shaft power of the SSE under high-speed conditions, and with the maximum variation being 11.9%. The shaft efficiency of an SSE with a small clearance and a small internal volume ratio is higher, and the gas consumption rate is lower. A low-viscosity lubricant should be used to avoid over-expansion when the intake pressure is lower than 0.6 MPa. The SSE with 46# lubricant has good comprehensive performance, where the maximum shaft efficiency and the minimum gas consumption rate obtained experimentally are 49.29% and 61.23 kg/(kW·h), respectively.