Dynamics of PCM melting driven by a constant heat flux at the free surface in microgravity

Abstract

In this work, we analyze the thermocapillary-enhanced melting of n-octadecane driven by a constant heat flux, applied at the free surface, in microgravity. The material is enclosed in an open rectangular container of dimensions 2L×H, and its solid-to-liquid transition is described using an enthalpy-porosity formulation of the Navier–Stokes equations, assuming laminar and incompressible flow. We study the influence of key governing parameters, including the effect of the heated length l̂ϕ∈(0,1], the applied flux ϕ̂∈(0,8], and the container aspect ratio Γ∈[1.5,22.8]. Heat transport is analyzed by comparing the thermocapillary-enhanced process with that driven solely by conduction, and quantified by the enhancement ratio G, which simply compares melting times in each scenario. We find that G increases with ϕ̂ and Γ, and is maximum at an optimal heated length l̂ϕ≃0.5. Compared to previous works on the melting of n-octadecane in microgravity, the associated enhancement G is more moderate in this system, and oscillatory thermocapillary convection is not observed over the range of parameters explored.