Abstract
The melting of a coconut oil–CuO phase change material (PCM) embedded in an engineered nonuniform copper foam was theoretically analyzed to reduce the charging time of a thermal energy storage unit. A nonuniform metal foam could improve the effective thermal conductivity of a porous medium at regions with dominant conduction heat transfer by increasing local porosity. Moreover, the increase in porosity contributes to flow circulation in the natural convection-dominant regimes and adds a positive impact to the heat transfer rate, but it reduces the conduction heat transfer and overall heat transfer. The Taguchi optimization method was used to minimize the charging time of a shell-and-tube thermal energy storage (TES) unit by optimizing the porosity gradient, volume fractions of nanoparticles, average porosity, and porous pore sizes. The results showed that porosity is the most significant factor and lower porosity has a faster charging rate. A nonuniform porosity reduces the charging time of TES. The size of porous pores induces a negligible impact on the charging time. Lastly, the increase in volume fractions of nanoparticles reduces the charging time, but it has a minimal impact on the TES unit’s charging power.
Highlights
The present study investigates the melting process of a phase change material (PCM) embedded in a nonuniform metal foam
The charging process of a thermal energy storage (TES) unit filled with a nonuniform metal foam was studied
The metal foam was saturated with coconut oil–CuO NEPCM, and the porosity was linearly changed from bottom to top
Summary
Zhao et al [14] compared the advantages of using fins with those of using metal foams in reducing the melting time of a PCM in a shell-and-tube shape TES unit. They found an optimum design for the fins. The literature studies showed that the natural convection effects and the thermal conductivity of composite PCMs could significantly influence a TES unit’s phase change behavior. The study addressed the following research questions: (1) Does a nonuniform porosity reduce the melt of 18 ing time for a fixed amount of metal foam?
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