Thermal Performance of a Heat Storage Module Using PCM’s With Different Melting Temperatures: Mathematical Modeling

TLDR

Earlier models neglected radial temperature gradients in cylindrical capsules, limiting their applicability to small‑diameter units. The authors developed a cylindrical‑coordinate heat‑conduction model for both solid and melt phases, using radial temperature profiles to compute surface heat flux and determine the air exit temperature via a simple heat balance. The model permits efficient computation by evaluating every few rows, and simulations show that using PCMs with different melting temperatures markedly enhances heat‑transfer rates, with air flow direction reversed between charging and discharging.

Abstract

In the present study, the performance of a heat storage unit consisting of number of vertical cylindrical capsules filled with phase change materials, with air flowing across them for heat exchange has been analyzed. Earlier theoretical models did not consider temperature distribution in the radial direction within the capsules, an assumption that limits their applications for small diameter capsules. The mathematical model developed in this work is based on solving the heat conduction equation in both melt and solid phases in cylindrical coordinates, taking into account the radial temperature distribution in both phases. Heat flux was then evaluated at the surface of the first row of the capsules to determine the temperature of the air leaving that row by a simple heat balance. It was found that such computation may be carried out for every few rows rather than for a single row to minimize computer time. The simulation study showed a significant improvement in the rate of heat transfer during heat charge and discharge when phase change materials with different melting temperatures were used. Air must flow in the direction of decreasing melting temperature during heat charge, while it must be reversed during heat discharge.