Numerical Study of an Isothermal Compressor for Isothermal Compressed Air Energy Storage System

Abstract

Combining compressed air energy storage (CAES) with renewable energy generation can make energy generation stable and continuous. Isothermal compressed air energy storage(I-CAES) has high efficiency, and can improve the power destiny. Spraying low-temperature liquid droplets into the compression cylinder is an effective method to reduce the air temperature rise to realize isothermal. The challenge is to master the flow-heat transfer coupling mechanism between droplets and air to improve the efficiency of isothermal compression. In this paper, a spraying isothermal piston compressor model is established by applying dynamic mesh to simulate the motion of the piston, and Discrete Phase Model (DPM) is utilized to simulate the droplet spray. The temperature, pressure distribution and air flow in the isothermal compressor cylinder as well as the distribution and flow characteristics of the liquid droplets are obtained. The results show that vortex occurs inside the compressor cylinder in the working process resulting in uneven distribution of droplet concentration in space, which leads to uneven temperature distribution. Compared with the adiabatic process, the sprayed droplets effectively mitigated the compression temperature rise by 89.52% and reduces the compression work by about 54.99 kJ/kg (about 19.59%). The high liquid-air ratio and small droplet diameter facilitate the realization of the isothermal process.

Keywords: Compressed air energy storage, Isothermal compressor, Water droplets injection, heat transfer, Fluid-thermal coupling