Heat transfer of a shell and tube sodium acetate trihydrate heat storage tank

Abstract

Heat storage is the key factor in future energy systems with a large share of renewable energies. A shell and tube heat storage tank capable of both long and short term heat storage has been developed by utilizing stable supercooling of sodium acetate trihydrate. Theoretical and experimental investigations were carried out to determine power, heat exchange capacity rate (HXCR), and stored energy of the heat storage tank during the charge and discharge. Theoretically, a multiphase computational fluid dynamics (CFD) model of the storage was developed. The CFD model was validated against the measurement. The heat transfer mechanisms of the heat storage were investigated. The results show that the multiphase model can satisfactorily predict thermal behaviour of the heat storage under different operation conditions. The CFD model shows that 21.15 kWh of heat was charged into the heat storage unit within 7.5 h, compared to 21.16 ± 0.85 kWh in the measurement. During discharge, 14.05 kWh of sensible heat was discharged as short term heat storage, and 7.65 kWh of latent heat can be released on-demand as long term heat storage. The measured sensible heat and latent heat during discharge are 13.57 ± 0.54 kWh and 7.56 ± 0.30 kWh, respectively, corresponding to a relative difference of 1.2–3.7 % compared to the CFD model. There is a strong natural convection flow in some of the tubes, which significantly increases the heat transfer rate. The energy-weighted heat exchange capacity rates are 850 W/K and 795 W/K during charge and discharge of the heat storage, respectively. The findings of the paper give a good reference for designers and manufacturers of latent heat/cold storage.