Energy and exergy analysis of an experimentally examined latent heat thermal energy storage system

In this study, an experimental investigation is carried out on a Latent Heat Thermal Energy Storage system (LHTES). All the experimental data are optimized using thermodynamic principles in which exergy analysis is conducted to examine the system's performance at different time constants. The proposed system uses paraffin wax RT35 as Phase Change Material (PCM) and water as Heat Transfer Fluid (HTF). The water enters the successive helical rounds of the tube and the melting process initiates from locations around the tube and propagates throughout the shell. In recent years, surface enhancement through using spiral and helical configurations of the tube is preferred by scientists to overcome the problem of slow charging in the outermost positions of the subdomain filled with PCM. Hence, the effect of the change in the coil number of the heat exchanger is investigated by choosing three different helical coil diameters which are 50, 70 and 90 mm, respectively. It is aimed to find the most efficient case capable of storing the maximum energy possible as well as higher exergy efficiencies in minimum melting duration through the phase change process. Parameters such as the transferred heat from HTF to PCM, PCM average temperature, melting front growth, Nusselt number, exergy efficiency, and the entropy generation number are investigated meticulously. Results showed that for the highest used helical diameter (90 mm) compared to the lowest one (50 mm), better melting performance is observed in which the melting time is reduced by 72.6%. Moreover, although some cases may achieve higher exergy efficiencies at their full melting time, they are not offered as best choices due to the limitations in heat storage time duration. (c) 2019 Elsevier Ltd. All rights reserved.