Investigation on in-cylinder and in-intercooler thermodynamic properties of miniature multi-stage reciprocating compressor with insufficient inter-stage volumes

Miniature multi-stage reciprocating compressor is the core component in the on-board continuous high-pressure gas supply system. Intercoolers play an important role in determining the thermodynamic performance of multi-stage reciprocating compressor. However, adequate inter-stage volume cannot be provided to miniature multi-stage reciprocating compressor due to the restriction of compacted dimension. Understanding the thermodynamic performance with insufficient inter-stage volume is the key issue for design and application of miniature multi-stage reciprocating compressor. However, the previous work focused on the thermodynamic process in single-stage cylinder, the proposed model cannot predict the real-time thermodynamic process in intercoolers. In this paper, stage-in-series thermodynamic model has been established by connecting the multi-stage cylinders through the intercoolers and the internal transient heat transfer was emphasized. The in-cylinder and in-intercooler thermodynamic properties have been numerically analyzed under insufficient inter-stage volumes. Experimental investigation on compressor performance has been carried out by varying the intercooler channel diameter. The results show that insufficient inter-stage volumes bring about the abnormal movement of suction and discharge valves. Pressure peak in former-stage cylinders increases when the inter-stage volume decreases, which results in obvious increase in frictional loss and power consumption. This study provides significant references for design optimization of miniature multi-stage reciprocating compressor. Furthermore, the proposed methods can be applied to large-scale reciprocating compressor for improving efficiency and reducing power consumption.