Numerical investigations of heat transfer enhancement in ionic liquid-piston compressor using cooling pipes

Abstract

In a cylindrical chamber, the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate was used to compress gaseous hydrogen from 220 to 752.3 bar, concurrently raising its temperature from 298.15 to 394.2 K over approximately six seconds. A three-dimensional liquid-piston compressor model was established and validated against the experimental data. Two-phase flow was simulated using the finite volume method and the volume of fluid model in ANSYS Fluent software. A novel heat transfer enhancement technique using cooling pipes was investigated inside a liquid-piston compressor to achieve near-isothermal compression. Multiple cooling scenarios were explored to enhance the compression and thermal performance, considering the number of pipes, cross-sectional shape, diameter, and pipe temperature. This approach provided a more comprehensive understanding of the flow regimes and heat transfer behaviors of working fluids throughout the compression process. To achieve the desired pressure ratio, using four circular pipes reduced the hydrogen temperature from 394.2 to 355 K, marking 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.

Graphic Abstract