Comparative study of analytical and numerical solutions for the thermodynamic processes of compressed air energy storage reservoirs in abandoned mines

Efficient utilization of renewable energy demands strategies to manage fluctuations in generation and demand mismatches. Compressed air energy storage (CAES) offers a promising solution by compressing excess energy into air for storage and releasing it during peak demand. This study compares analytical and numerical solutions for thermodynamic processes in CAES reservoirs repurposed from abandoned mine tunnels. Using COMSOL finite element software, the thermodynamic behavior of compressed air was modeled under three heat transfer boundary conditions: adiabatic, constant temperature, and variable temperature walls. Results reveal substantial discrepancies in temperature and pressure distributions, with numerical simulations capturing pronounced non-uniformity and steep longitudinal gradients. Maximum temperatures from numerical solutions exceed analytical predictions, underscoring the risk of underestimating thermal variations with analytical methods alone. The analytical model demonstrates a critical failure in predicting local temperature hotspots in elongated geometries, fundamentally masking extreme thermal safety risks. These insights emphasize the need for numerical approaches in designing elongated reservoirs to accurately evaluate thermodynamic properties and material needs, optimizing CAES systems through abandoned mine repurposing.