Study of effect of heat transfer in an air storage vessel on performance of a pumped hydro compressed air energy storage system

Abstract

Pumped Hydro Compressed Air (PHCA) energy storage is a new technology which offers high energy storage performance. In this paper, the effect of dynamic flow and heat transfer in a cylindrical air storage vessel on the performance of a PHCA system is investigated using multiphase Volume of Fluid (VOF) and turbulence k−ε models. The numerical simulation is validated using experimental data available in the literature. The influence of governing parameters including the pre-set pressure, storage pressure, charging and discharging flow rates on heat transfer and performance of the PHCA system is investigated. The results show that heat transfer between air and water in the storage vessel has a large effect on compression and expansion processes. The polytropic index during the compression/expansion process ranges between 1.05 and 1.3 under the studied conditions. It increases with increasing pre-set initial pressure, lowering of the storage pressure, or with increasing charging/discharging flow rates. Consequently, the required work input increases and the generated work output decreases. Further analyses show that as the charging/discharging flow rate increases, the compression/expansion efficiency decreases with reducing heat transfer between air and water. The results also show that the stored energy level in an actual process lies in between those of isothermal and isentropic processes.