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The phase change materials (PCM) are widely used in several applications, especially in the latent heat thermal energy storage system (LHTESS). Due to the very low thermal conductivity of PCMs. A small mass fraction of hybrid nanoparticles TiO2-CuO (50%-50%) is dispersed in PCM with five mass concentrations of 0%, 0.25%, 0.5%, 0.75% and 1 mass % to improve its thermal conductivity. This article is focused on thermal performance of the hybrid nano-PCM (HNPCM) used for the LHTESS. A numerical model based on the enthalpy-porosity technique is developed to solve the Navier-Stocks and energy equations. The computations were conducted for the melting and solidification processes of the HNPCM in a shell and tube latent heat storage (LHS). The developed numerical model was validated successfully with experimental data from the literature. The results showed that the dispersed hybrid nanoparticles improved the effective thermal conductivity and density of the HNPCM. Accordingly, when the mass fraction of a HNPCM increases by 0.25%, 0.5%, 0.75% and 1 mass %, the average charging time improves by 12.04 %, 19.9 %, 23.55%, and 27.33 %, respectively. Besides, the stored energy is reduced by 0.83%, 1.67%, 2.83% and 3.88%, respectively. Moreover, the discharging time was shortened by 18.47%, 26.91%, 27.71%, and 30.52%, respectively. [ABSTRACT FROM AUTHOR]

A detailed numerical investigation has been carried out here about a heat storage system inclination effect on the phase change material (PCM) melting process in order to comprehend the natural convection mechanism inside a shell and tube thermal energy storage (TES) unit. This unit is filled by Rubitherm organic material (RT35) which has a low storage density. Distilled water is used as heat transfer fluid (HTF,) that circulates downwardly inside the tube to melt the PCM which contributes to acquire a storable thermal energy. Based on the enthalpy method, two dimensional numerical method has been employed to analyze this process which has shown a good numerical predictions against the experimental results. 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. [ABSTRACT FROM AUTHOR]

In this paper, we have studied numerically thermo-convective characteristics between a heat transfer fluid (HTF) and phase change material (PCM) in shell and tube thermal energy storage (TES) unit. The paraffin wax is considered as a PCM, filled in a shell which is thermally isolated with the external environment, while the water plays a role of a HTF and flows inside the tube at the moment of charging and discharging cycle. The heat transfer between HTF and PCM is performed by conduction and forced convection, this transfer allows to change the physical state of PCM solid-liquid to obtain a quantity of storable heat in order to create a thermal battery. Enthalpy formulation is used to analyze the heat transfer during melting and solidification process. A good agreement was found between our numerical predictions and the results of the literature. On the other hand, we have investigated the effect of geometrical parameters (tube length and shell diameter) and Reynolds number on the charging and discharging cycles. The obtained results reveal that the tube length and the shell diameter are the most influential parameters on the time of storage system. Similarly, the Reynolds number has much impact on the HTF outlet temperature and the time of solidification and melting process. Furthermore, we have proposed a new thermal storage unit containing the Paraffin wax and RT60 that it gives us a good rate and time of storage compared to the first unit that has only the paraffin wax. [ABSTRACT FROM AUTHOR]