Experimental study of PCM melting in triplex tube thermal energy storage for liquid desiccant air conditioning system

Thermal energy storage such as latent heat thermal energy storage can reduce the energy supply–demand discrepancy and improve the efficiency of solar energy systems because of its high thermal energy density (per unit mass and per unit volume). The present work investigates the application of a triplex tube heat exchanger with a phase-change material (PCM) (paraffin wax RT 82) in the middle tube to power a liquid-desiccant air-conditioning system. The experiment examined the effects of mass flow rates and heating methods selected on PCM melting. Three techniques were investigated: heating the inside tube, heating the outside tube, and heating both sides tube. The PCM temperature gradients in the radial, angular, and axial directions were analyzed. Results indicated that the third case (i.e., heating both sides) achieved complete PCM melting within a short time and used a lower inlet heat transfer fluid temperature compared with the other cases. No significant temperature variation in the axial direction was indicated. The heat transfer phenomena in the radial and angular directions can be predicted in melted PCM.

► Three heat methods were investigated to reduce the time required for PCM melting.
► The turbulent flow behaviors on the thermal diffusion for the first case were studied.
► The temperatures distributions in axial, angular, and radial direction were analyzed.