Numerical study on two-phase flow and heat transfer characteristics of the ionic liquid compressor for hydrogen refuelling stations

The ionic liquid compressor has emerged as a highly promising technology for hydrogen refuelling stations. It offers the potential to improve compressor efficiency by integrating the liquid piston and the free piston with the conventional reciprocating compressor. However, the investigation is lacking on the characteristics of the two-phase flow and heat transfer between the liquid piston with hydrogen during one compression cycle, which imposes restrictions on the development of the ionic liquid compressor. A 3D CFD model for the ionic liquid compressor was established in this paper to investigate the two-phase flow and heat transfer of hydrogen and the liquid piston during a compression cycle at various frequencies. The results show that the interaction between hydrogen with the ionic liquid was intensified due to the inlet shock and piston reciprocation, leading to the destabilization and fragmentation of the phase interface and generating numerous hydrogen bubbles and ionic liquid droplets. The two-phase heat transfer area and relative velocity were both greatly increased by this two-phase distribution, resulting in an obvious enhancement of heat transfer. At the recommended frequency of 5 Hz, the hydrogen temperature rise of the compression stage was 55.69 K and the polytropic index was 1.114, which was significantly close to the isothermal process.