Comparative investigation of charging performance in shell and tube device containing molten salt based phase change materials for thermal energy storage

This work concerns the melting performance enhancement in a finned shell and tube thermal energy storage device containing salt based phase change materials. Two storage materials of a pure nitrate salt and a nitrate salt based composite that made of nitrate salt, vermiculite and graphite were employed and comparatively investigated. A two-dimensional mathematical model was established to predict the heat transfer occurred in the salts by considering the combined impacts of natural convection and thermal conduction. A set of simulation data from literature was used to verify the modelling code for the pure salt and an experiment was built to validate the numerical model for the salt composite. The effects of fin amount, arrangement, length and thickness as well as operating condition on the device melting behaviour were detailedly evaluated. The results indicated the benefit of employment fins in accelerating the salt melting rate. The use of salt based composite combined with enhanced fins led to a more remarkable improvement on the device melting process, and the adjustment of fin length and thickness as well as composite ingredients composition achieved further intensification. For a given fin amounts over 0–8 with the same neighbour angle, the melting process in the device containing salt composite is respectively shortened around 79% and 56% compared to the device containing pure salt, indicating the utilization of composite is a better choice than the pure salt for the performance enhancement in finned shell and tube thermal energy storage device.