Experimental and numerical investigation on the flow and heat transfer behaviors during a compression–cooling–expansion cycle using a liquid piston for compressed air energy storage

This paper investigates flow patterns and heat transfer characteristics inside the Liquid Piston (LP) column during a complete compression–cooling–expansion (CCE) cycle. The phenomena associated to this cycle have not been yet well-documented but are essential to understand the transfer mechanisms for piston geometry optimization. A 3D CFD model based on VOF method and the Particle Image Velocimetry (PIV) technique have been used to study the CCE cycle. Different air flow patterns and transition as well as the temperature field at different stages of the cycle have been visualized, analyzed, compared and discussed. During the expansion stage, a fast establishment of an axisymmetric flow structure, its evolution and disruption to a totally chaotic one can be identified. Under the tested piston speed (0.033 m s−1) and compression/expansion ratio (CR = ER = 4.8), a close-to-isothermal cycle could be realized by the LP, with high compression, expansion and overall efficiencies (up to ηc=91.2%, ηe=94.7% and ηcycle=86.3%), confirming the interests of LP in realizing Isothermal–CAES systems. Results of a numerical parametric study show that a lower wall temperature could slightly enhance both the compression and expansion efficiencies while a slow piston speed is rather beneficial for a high overall efficiency.