Etude thermo hydraulique d’un écoulement à moyenne température

Abstract

This work focuses on the thermal energy storage utilization using latent heat transfer mode, different thermo physical characteristics of phase change materials (PCMs) have been discussed by their applications. A heat transfer evaluation of a shell and tube thermal energy storage (TES) unit has been carried out numerically. This devise is filled by organic material (paraffin wax) which is considered as a phase change material (PCM). Distilled water plays a role of heat transfer fluid (HTF) that flows inside the tube by constant inlet temperatures at melting and solidification moment of PCM. All the system storage is thermally isolated with the external environment. The enthalpy formulation is used to analyze the heat transfer inside 2D planar physical model during phase change process. As a result, a good agreement is found compared to the experimental results of the literature. First, the effect of geometrical parameters (tube length and shell diameter) and Reynolds number on the charging and discharging time in terms of HTF outlet temperature are investigated. The obtained results reveal that the tube length and the shell diameter are among the most influential geometrical parameters on the melting and solidification time, similarly the Reynolds number has too much effect to speed up the charging cycle. Moreover, an improved thermal storage unit is proposed which contains two phase change materials (PCMs), separated longitudinally inward the shell space and have a close melting point and different thermal characteristics. This configuration is more stable and speeds up the charging and discharging processes compared to the first unit. In addition to that, several unit positions were examined to interpret physically the thermal demeanor of the fusion process in terms of; heat transfer modes estimation, PCM melting rate, axial and radial temperatures distribution. The obtained results clarify that the TES unit inclination according to the range angles [0-90°] makes an imbalance of the natural convection in the PCM liquid fraction which contributes to create an instability and diminution of the heat transfer during the melting process. Moreover, the vertical unit state was the favorite position to the heat transfer recirculation inward the PCM.