Abstract: As a critical component of compressed air energy storage systems, underground gas storage exhibits complex internal thermodynamic characteristics that directly affect the energy storage efficiency, structural safety, and engineering economy of the storage system. In this study, based on extensive investigation of the global literature, the research progress on the thermodynamic characteristics of constant-volume underground gas storage is systematically reviewed. The core thermodynamic evaluation indicators of gas storage caverns are clarified, the applicability and limitations of three mainstream thermodynamic analysis methods currently in use are assessed, the temporal and spatial evolution patterns and engineering significance of key thermodynamic parameters are summarized, and the technical performance and economic efficiency of existing temperature control measures are discussed. The results indicate the following information: (1) Pressure, temperature, relative humidity, density, and exergy constitute the core indicators for evaluating gas storage performance, with internal pressure exhibiting a generally linear variation, the temperature field showing pronounced spatial heterogeneity, humidity accumulation inducing condensate formation and latent heat effects, and pressure exergy playing a dominant role in the energy storage. (2) Among the thermodynamic analysis methods, the theoretical analytical approach is suitable for the preliminary design of gas storage projects, numerical simulation effectively reveals the complex flow field and local high-temperature mechanisms inside the cavern, and experimental modeling serves as an essential foundation for verifying theoretical findings and ensuring engineering safety. (3) Regarding temperature control technologies, active heat-exchange measures suffer from poor economic viability, whereas passive heat-exchange measures based on flow-field optimization, such as multipoint air injection and inlet structure optimization, are more compatible with practical engineering applications. Future research should focus on five key directions: (1) high-precision model development, (2) efficient local analytical methods, (3) engineering verification of nonheat-exchange temperature control technologies, (4) establishment of standardized evaluation systems, and (5) multiobjective collaborative optimization design. The coordinated advancement of these directions is expected to facilitate the transition from theoretical simulation to practical engineering application.

Key words: compressed air energy storage, underground gas storage caverns, thermodynamic characteristics, pressure, temperature