Energy efficiency and power density analysis of a tube array liquid piston air compressor/expander for compressed air energy storage

To improve the power density and efficiency of compressed air energy storage (CAES), this paper adopts an array-based compression/expansion (C/E) chamber structure, coupling a liquid piston with a tubular heat exchanger to form a new compressor/expander. By providing a heat exchange chamber outside the arrayed C/E chamber, natural convection heat transfer is utilized and heat is absorbed during compression and released during expansion, constituting an advanced isothermal CAES system. For low-pressure (0.8 MPa to 5 MPa) and high-pressure (5 MPa to 31.25 MPa) stages, the effects of tube diameter and flow rate variations on C/E pressure, temperature, power density, and efficiency were analyzed. Results show that by keeping the tube diameter constant and the power density increasing one order of magnitude, the efficiency decreases about 9 %. Keeping the power density constant and reducing the tube diameter to 1/7 increases the efficiency of the low and high-pressure sections by about 16 % and 6.4 % respectively, or keeping the efficiency at 93.4 % and 83.9 %, increasing the power density all by about 50 times. This study provides a new way to improve the efficiency and power density of C/E by reducing the tube diameter of the array chamber for high-pressure and high-efficiency CAES.