Thermodynamic and exergy analysis of salt cavern compressed air energy storage reservoirs incorporating internal gas flow dynamics

High-frequency cyclic operations in salt cavern compressed air energy storage (CAES) systems induce complex transient thermodynamic responses that dictate plant efficiency. Based on empirical data from the Mao-8 well in Jintan, China, this study employs COMSOL Multiphysics to simulate 30 continuous charge-discharge cycles. We systematically investigate the spatiotemporal thermo-pneumatic evolution under varying mass flow rates, phase durations, operating pressures, and cavern volumes. Through statistical normalization, we quantify individual parameter contributions to temperature fluctuations and formulate empirical equations correlating volumetric convergence with internal thermal dynamics. The principal findings reveal: (1) Net working gas mass fluctuation fundamentally drives the cavern's transient thermodynamic state. (2) The cavern roof endures extreme aerodynamic velocities and temperature oscillations, emerging as the primary zone susceptible to localized thermomechanical fatigue. (3) Thermal penetration depth into the surrounding rock expands nonlinearly over repeated cycles, with steeper internal thermal gradients accelerating conjugate heat dissipation. (4) Critically, cavern convergence imposes a nonlinear penalty on generation capacity; a 30% viscoplastic shrinkage in volume triggers a disproportionate 41.5% depletion in available exergy. These quantitative insights and predictive models provide a robust theoretical framework for optimizing injection-withdrawal strategies and conducting lifecycle techno-economic assessments of utility-scale CAES facilities.