Numerical Investigations of Thermal Performance of Cooling Pipes for an Ionic Liquid-Piston Compressor*

          Inside a cylindrical chamber, the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate compressed hydrogen gas from 220 bar to 752.3 bar, raising its temperature from 298.15 K to 394.2 K within approximately 6 seconds. A three-dimensional liquid-piston compressor model was developed and validated with experimental data. Two-phase flow simulations were performed using the finite volume method and volume of fluid model in ANSYS Fluent software. Various cooling scenarios were investigated to improve compression and thermal performance, focusing on parameters such as the number of pipes, their cross-sectional shape, diameter, and temperature. To achieve the desired pressure ratio, employing four cooling circular pipes reduced the hydrogen temperature from 394.2 K to 355 K, resulting in a significant 40.8% improvement in thermal efficiency. Furthermore, compression performance reached 95.8% with a power density of 3221.4 kW·m^-3, compared to 90.9% and 4550.6 kW·m^-3 without cooling. This work is crucial as it expands the repertoire of cooling methods for gas in liquid-piston compressors. The findings provide deeper insights into flow dynamics and heat transfer mechanisms within the chamber, while also demonstrating heat transfer enhancement and compression efficiency using cooling tubes. Moreover, these results could potentially promote the development of fuel cell electric vehicles, particularly benefiting the automotive sector overall.