Multi-criteria decision-making techniques based optimum selection of phase change material and its implementation in a solar crop dryer for agricultural products

Abstract

The energy storage in solar thermal systems is crucial as the fluctuations in solar energy and its unavailability in the night periods adversely affects the system effectiveness. The proper selection of phase change material (PCM) for energy storage in a particular application is vital important as it directly affects the overall performance of the system. The selection of an optimum PCM for a specific application is a complex problem, requiring consideration of multiple criteria involving thermal, economic, environmental and physical aspects. The present study aims to select the optimum PCM for energy storage in a solar crop dryer, while being sustainable and cost-effective. The organic PCM alternatives with their melting temperature in the range suitable for crop drying application are selected for the study. Six widely recognized multi-criteria decision-making (MCDM) methods viz. EDAS, MOOSRA, TOPSIS, PROMETHEE, MOORA and CODAS have been employed to identify the most suitable PCM from the available alternatives. The criteria weights for optimization are determined using AHP, CRITIC and ENTROPY techniques, and their combinations. All MCDM techniques gives paraffin wax as the optimum PCM to be used as energy storage material in solar dryer. The average scores such as TOPSIS: 0.75, EDAS: 0.82, MOOSRA: 0.94, MOORA: 0.36, CODAS: 0.13 and PROMETHEE: 0.094 are obtained for paraffin wax, and are found to be highest compared with other alternatives. The sensitivity analysis carried out with weight variation method ensures the robustness and reliability of applied methods. Further, a simplified iterative computational procedure is developed to compute the required quantity of PCM and its container dimension to maintain the drying temperature for a specific duration during off-sun shine hours. The computational procedure also selects paraffin wax as the best PCM, as its required quantity is less and thus container size is small. The experimental investigation on the solar dryer, incorporating paraffin wax as the thermal storage material exhibits good agreement with the computational procedure, thereby substantiating the effectiveness of the PCM selection methodology. The paraffin wax in its optimum quantity could deliver the heat at a constant temperature of nearly 60 °C for six hours, during sun down hours and night (from 3.00 pm to 9.00 pm), which supports the PCM selection using MCDM techniques and agrees with findings of computational procedure. The absorber temperature is also able to be maintained above 50 °C for an extended period of six hours. The average air temperature of 45 °C is maintained in the dryer during the sun-down period (3.00 pm to 9.00 pm), using paraffin wax as energy storage material. With the highest benefit-cost ratio of 8.17, paraffin wax also emerged as the most cost-effective option among the PCM alternatives. © 2025 Elsevier Ltd