Spray enhanced heat transfer in multi-machine compensable pumped hydro compressed air energy storage system

In a multi-machine compensable pumped hydro-compressed air energy storage (MMC-PHCAES) system, the air-water heat transfer performance is weak, resulting in a low round-trip efficiency. To address this limitation, spray equipment was introduced into the MMC-PHCAES system. A mathematical model considering the interplay of spray flow rate, droplet size, and pressure was established, the optimal design of the spray flow rate was realized, and the effect of spray heat transfer enhancement measures on the thermodynamic, energy, and exergy performance was characterized. When a spray device was used in Tanks 1/2 during charging, the thermodynamic performance in Tanks 1/2 were enhanced. With an increase in the spray flow rate under the operating conditions of Tank 1 charging, Tank 1 discharging, Tank 2 charging, or Tank 2 discharging, the round-trip and exergy efficiencies of the system first increased and then decreased. After enhanced heat transfer, the amplitude of air temperature variation in Tanks 1 and 2 can be reduced by approximately 78.1 % and 77.3 %, respectively. The application of spray devices in both tanks increased the round-trip efficiency by 6.0 % and the exergy efficiency by 5.8 %. In Case 3, the equipment optimization priorities achieved by the energy and exergy analyses differed; the energy analysis prioritized Tanks 1 and 2 (TKS), and the exergy analysis prioritized the pumped storage unit (PSU). This study improves the operational performance of an MMC-PHCAES system and promotes its engineering applications.