Heat transfer with phase change in a shell and tube latent heat storage unit

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

Concerning thermal energy storage, latent heat thermal energy storage is particularly attractive technique because it provides a high energy storage density. The development of a latent heat thermal energy storage system therefore involves first the understanding of heat transfer in the phase change materials (PCM) when they undergo solid-to-liquid phase transition in the required operating temperature range, and second, the design of the container for holding the PCM and the formulation of the phase change problem. The paper presents a study on the heat transfer mode of a PCM stored in a horizontal cylindrical shell and tube heat exchanger, being the PCM placed inside the tubes. For this purpose, an experimental bench has been developed to test the heat transfer process, coupled with a Ground-Source Heat Pump (GSHP), controlled by a computer program developed to manage the coupled GSHP+PCM system. The aim is to compute the heat transfer of the installation during the loading, storage and downloading energy processes. More precisely, the interest is to check experimentally to what extent some common hypothesis used for heat transfer calculations are valid or not. In particular: (i) Comparison between the radial and the axial heat transfer through the wall of the PCM tube; (ii) The temperature distribution of the heat transfer fluid in the central and peripheral locations; (iii) The heat transfer rate between the container and the ambient temperature. Results indicate that density gradients could occur during energy exchange between the heat transfer fluid and the PCM when melting or solidification are taking place, leading to modification of central flow with respect to peripheral flow. Also, the temperature gradients recorded in the axial direction during the change of phase were very small compared with those of that of the radial direction, indicating essentially a two-dimensional heat transfer mode.