Enhancing the melting of phase change materials via convective flows and container geometry

Three strategies for enhancing the melting rate of phase change materials (PCMs) are analyzed numerically: natural convection, thermocapillary convection, and variations in container geometry motivated by the natural shape of the advancing solid/liquid front. An enthalpy-porosity formulation of the Navier-Stokes equations is used to model the melting process, where the organic PCM n-octadecane is considered as a single phase whose physical properties depend on the local temperature. The phase change is driven by subjecting the material to a constant temperature T H = T M + Δ T , where T M is the melting temperature, at one of its lateral boundaries of length l H ; the remaining boundaries are assumed adiabatic. Melting dynamics are described for both individual and combined enhancement strategies, using as reference the melting process in a rectangular container purely driven by conduction. The efficacy of each strategy is compared using the time τ required to melt 90% of the given PCM volume V ; the inverse ratio of this time to that of the reference case, G = τ 0 / τ , defines the enhancement factor. Comparisons are made for small and large values of Δ T and l H . Increasing Δ T drives stronger convective flow and increases the associated enhancement factor. The isothermal length l H has opposite effects on each type of convection, favoring the enhancement of natural convection or thermocapillary flows at large and small values, with rates of G ∈ 5 12 and G ∈ 12 33 , respectively. The optimal container geometry is characterized by a type of aspect ratio Γ = l c / h c that compares its characteristic length and height. For pure conduction or with natural convection, Γ ∼ 0.5 , while with thermocapillary convection, Γ ∼ 2.5 − 5 . • Analysis of heat transport enhancement strategies for PCM melting. • Melting dynamics are described for both individual and combined strategies. • Increasing thermal forcing drives stronger convective flow and enhances performance. • The isothermal length enhances natural/thermocapillary flows at large/small values.