Leakage research on supercritical carbon dioxide fluid in rolling piston expander

The leakage research on supercritical carbon dioxide fluid in rolling piston expander was investigated experimentally. Using expander instead of throttle valve is an important way to improve the efficiency of carbon dioxide refrigeration system. However, the supercritical fluid leakage in expander is serious and is the main factor affecting the expander's efficiency. This paper presented and compared four classic leakage models. The analysis indicated that laminar leakage model is suitable in leakage simulation of expander. A leakage test system, including the leakage test part which has two types of leakage specimens with different gaps ranging from 5 to 15 mu m, was established. The experimental results indicated that lubricant film played an important role. When the leakage clearance of cylindrical specimen was 5 mu m, the mass flow rate of leakage was about 0.88 g s(-1). The data was 3.638 g s(-1) with leakage clearance being 10 mu m and 7.11g s(-1) with leakage clearance being 15 mu m. A modified leakage model was developed, whose average deviation was within 10% compared with the experimental data. At last, this paper simulated the leakage in rolling piston expander presented by Tian et al. (2010). The leakage between rolling piston and cylinder was the most serious part with the value up to 0.04 kg s(-1).