Numerical Study of a Quasi-isothermal Expander by Spraying Water

Abstract

Compressed air energy storage (CAES) technology is considered as a promising method to improve the reliability and efficiency of the electricity transmission and distribution, especially with high penetration of renewable energy. The expander is a vital component of CAES system. The specific work generation through an expander can be improved through an isothermal expander compared with an adiabatic expansion process. And the temperature is almost constant, which enables the expander operate with high pressure ratio. A specific reciprocating expander with high pressure ratio is developed and its adiabatic expansion process is measured. A numerical modelling is constructed to mimic the adiabatic expansion, and it is validated by the experimental results. Furthermore, a quasi-isothermal expansion is proposed by using water injection into the cylinder based on the studied expander. The modelling is further developed by introducing water-air direct heat change equations to simulate the quasi-isothermal process. The simulated results of the quasi-isothermal expander when spraying tiny water droplets into the cylinder indicate that the specific work generation is improved by 11.57% compared with that of the adiabatic expansion under the same air inlet condition. The temperature difference is only about 10% of that of the adiabatic process.