Volume 54

Design and performance characterization of aqueous sodium hydroxide based thermochemical storage systems: Experimental and thermodynamic comparative analysis among various heat exchanger designs and working pairs Sai Yagnamurthy, Steven Metcalf, Robert Critoph

Abstract

Absorption thermal storage technology has emerged as a viable option for both long and short term energy storage applications. Aqueous sodium hydroxide (NaOH) water pair has shown potential for high storage density and long-term storage. The present study experimentally investigates the impact of various design and operating conditions on the absorption performance of an aqueous sodium hydroxide storage system. The heat and mass transfer characteristics are further analysed and compared for two finned heat exchangers with various aspect ratios along with their energy and exergy performance characteristics. It has been observed that the solution depth is more critical to the system
performance over the heat exchanger surface area, with a storage density reduction of up to 41.2% for the heat exchanger with higher fin height. Higher exergy efficiency is also observed for the heat exchanger with lower fin height owing to its better absorption characteristics. The performance of NaOH-H2O based heat exchangers is finally compared with that of the LiBrH2O pair over a microchannel membrane heat exchanger design from the literature. It is seen that the LiBr-H2O pair offers a lower storage density by around 55% compared to the NaOH-H2O pair. The findings of the present study suggest significant potential for the NaOHH2O pair and can assist in identifying better heat exchanger designs for thermal storage applications.

Keywords absorption storage, thermal storage technologies, NaOH, LiBr, exergy, microchannel