Multi-objective optimization of acetone droplet impingement on phase change material in direct-contact discharge method

Abstract

Improving the discharge process of phase change materials (PCMs) is of great importance and can be effective for thermal energy storage (TES) systems. In this research, the direct-contact method for acetone droplet on molten paraffin is optimized to enhance the efficiency of the discharge process of PCMs and TES systems working with intermediate boiling fluid (IBF). In order to improve the storage rate and increase the freezing rate in the system, the NSGA-II algorithm is used. When the acetone droplet hits, owing to its low boiling point relative to the temperature of molten paraffin, the acetone evaporates, causing the creation of solidified paraffin area. The main goal of the current investigation is to maximize the solid volume, which depends on two parameters: the Weber acetone droplet and the temperature of the molten paraffin. Furthermore, maximizing this volume is equivalent to increasing the freezing rate and decreasing the melting rate. For better discernibility, the relative sensitivities of solidified paraffin area and maximum crater depth to the variations in the dimensionless parameters of paraffin surface temperature and Weber number are obtained. In this regard, the experimental results are fitted by exponential functions. Two-objective optimization with the solidified paraffin area and maximum crater depth as cost functions are performed to be maximized. Moreover, uncertainties and tolerances are considered through performing a robust triple optimization. By using final decision makings (FDMs), the results are achieved from Pareto front through two methods, LINMAP (We = 1699.428, θ = 1.188) and TOPSIS (We = 1699.325, θ = 1.202). Based on the results, the solidified paraffin areas obtained by LINMAP and TOPSIS methods are 168.616 mm2 and 155.101 mm2, respectively.