Experimental investigation on thermal behavior of paraffin in a vertical shell and spiral fin tube latent heat thermal energy storage unit

Abstract

Abstract Aided by the phase change material (PCM) with high thermal storage density, latent heat thermal energy storage (LHTES) technology may provide a solution to the energy supply-demand dilemma, e.g. LHTES in solar energy utilization and waste heat recovery. This paper presents an experimental investigation on the thermal performance of a LHTES unit equipped with vertical multitube shell and spiral-finned tube. Using paraffin as PCM and water as heat transfer fluid (HTF), the thermal charging and discharging characteristics of the LHTES unit can be evaluated. The thermophysical properties of latent heat and phase change temperature of PCM were characterized by the differential scanning calorimeter (DSC). Tests were conducted under different inlet temperatures and flow rates of HTF, during which the temperature variation of PCM, heat stored/released, mean charging/discharging power, total charging/discharging time and instantaneous effectiveness were acquired. Experimental results indicate that the natural convection of melted paraffin impacts substantially on the phase-change rate of paraffin. Once melt completes, the natural convection intensity surges temporarily. Moreover, the increase of inlet HTF temperature and flow rate during charging can dramatically improve the heat transfer between HTF and PCM, which in turn shortens the total charging time. The HTF flow rate was found to play little role on the heat transfer during discharging since the thermal resistance of the solidified PCM increases considerably.