Abstract
A latent heat thermal energy storage (LHTES) unit can store a notable amount of heat in a compact volume. However, the charging time could be tediously long due to weak heat transfer. Thus, an improvement of heat transfer and a reduction in charging time is an essential task. The present research aims to improve the thermal charging of a conical shell-tube LHTES unit by optimizing the shell-shape and fin-inclination angle in the presence of nanoadditives. The governing equations for the natural convection heat transfer and phase change heat transfer are written as partial differential equations. The finite element method is applied to solve the equations numerically. The Taguchi optimization approach is then invoked to optimize the fin-inclination angle, shell aspect ratio, and the type and volume fraction of nanoparticles. The results showed that the shell-aspect ratio and fin inclination angle are the most important design parameters influencing the charging time. The charging time could be changed by 40% by variation of design parameters. Interestingly a conical shell with a small radius at the bottom and a large radius at the top (small aspect ratio) is the best shell design. However, a too-small aspect ratio could entrap the liquid-PCM between fins and increase the charging time. An optimum volume fraction of 4% is found for nanoparticle concentration.
Highlights
The latent heat thermal energy storage (LHTES) units are compact storage systems, benefiting the latent heat energy of phase change materials (PCMs)
The results showed that an aluminum foam with a high porosity of 97% is adequate for heat transfer improvement since the heating loads were smooth
The design of an LHTES is a complex task as the internal hydrodynamic and convection heat transfer is under the influence of Molecules 2021, 26, 1605 the molten PCM
Summary
The latent heat thermal energy storage (LHTES) units are compact storage systems, benefiting the latent heat energy of phase change materials (PCMs). Nie et al [23] utilized copper foams in a shell-tube shape LHTES unit They modified the typical shell’s cylindrical shape to a conical shape to allow better natural convection circulation and improve the heat transfer rate. The design of an LHTES is a complex task as the internal hydrodynamic and convection heat transfer is under the influence of Molecules 2021, 26, 1605 the molten PCM In such systems, the conduction-dominant heat transfer mechanisms should be identified and improved in the initial charging stages, while the free convection mechanism in liquid PCM regions should be supported. The present study aims to design a shell-tube LHTES unit with a conical shape shell and inclined fins to improve the conduction mechanism in the early stage of melting heat transfer but allow adequate space to benefit from later natural convection flows. The Taguchi method, is used to find an optimum design for the LHTES unit systematically
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