Summary Melting rate enhancement inside an accumulator unit for a phase change material (PCM) has been numerically investigated in a shell‐and‐tube (S‐T) arrangement that incorporates the circular type of fins, considering a fixed total volume of fins. The number of fins was chosen as the design parameter. The heat transfer fluid (HTF) was chosen as water that flows through the selected accumulator unit during the process of melting. The computational fluid dynamics (CFD) technique has been utilized for the simulation of the accumulator using ANSYS FLUENT software by considering a two‐dimensional axisymmetric cylindrical accumulator in a vertical direction. During the melting process, two heat transfer mechanisms were considered, namely, conduction and convection. The HTF flow was 5 L/min with a flow temperature of 358 K for charging. The predicted complete melting time of the PCM decreased by 53.125%, 65.625%, 71.875%, and 71.875% for fins numbering 6, 18, 30, and 36, respectively, compared with the S‐T without fins where it took approximately 480 minutes to melt completely. The optimal fin parameters are recommended in this study as follows: number of fins N = 30, thickness t/d = 0.01858, interval d/L = 0.03227, and aspect ratio t/h = 0.015. These recommended values maximize the thermal performance of the selected accumulator unit. The effects of changing the flow rate of the heat transfer fluid and its inlet temperature have been found to be significant on the PCM melting rate. The total melting time of the PCM is found to be reduced by about 57% when the inlet flow temperature is increased from 343 to 358 K. Moreover, the total melting time reduces by about 70.5% with an increase in the heat transfer fluid mass flow rate from 0.15 to 5 L/min. Furthermore, increasing the HTF flow rate from 0.15 to 5 L/min leads to a reduction of about 61.1% in the predicted total time that is required for solidification. The temperature differences for low flow rates are greater than those for high flow rates. The novelty of this study is in investigating the performance at a fixed total volume of fins.

Many renewable energy sources are not available at any time in nature so the development of energy storage technologies is very important to conserve the available energy and improve its utilization. Thermal energy storage by using Phase Change Materials (PCM) is considered one of the promising technology to store thermal energy. The numerical study of the shell and tube storage unit is carried out. Paraffin wax was filled in the shell side and the Heat Transfer Fluid (HTF) flowed inside the tube. The validation among numerical and experimental results was conducted. It is found that the effect of natural convection is important and should be taken to perform the model of the heat storage unit.

The use of a phase change materials (PCMs) is a very promising technology for thermal energy storage where it can absorb and release a large amount of latent heat during the phase transition process. The issues that have restricted the use of latent heat storage include the thermal stability of the storage materials and the limitation of the container size. The study of the influence of thermal cycling on the properties of PCMs, such as melting temperature and latent heat, is important. It is found that the paraffin wax and fatty acids (e.g., lauric acid, myristic acid, palmitic acid, and stearic acid) have good thermal stability and can be used for solar thermal energy storage applications. However, Calcium chloride hexahydrate (CaCl2. 6H2O) is a good PCM in building applications.

Selection of a suitable phase change material (PCM) for thermal energy storage systems is important. There are an enormous number of available PCM and hence choosing a particular PCM for a certain application is difficult. Many researchers rely on their expertise or the material available to use PCM for a specific application. The purpose of the selection of a certain PCM is to choose the best material from the commercially available PCM for a given application. An effective evaluation approach is essential to enhance the quality of the decisions. The issue of choosing a material for different applications can be managed as a multi-criteria decision-making issue. In this paper, the Analytic Hierarchy Process (AHP) method is used to select between five PCM for solar heating systems considering both the technical specification and the criteria of the materials. The selected materials have a melting temperature in the required working temperature range. Seven criteria are used in this study and these include the latent heat of fusion, thermal conductivity of the material, specific heat, density, thermal stability, cost, and corrosion. The results show that the paraffin is the best material from the selected PCM using the AHP method for this solar heating system using all known thermo-physical properties and the weights of these criteria to achieve the objective.

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