Effects of Thermocapillary and Natural Convection During the Melting of PCMs with a Liquid Bridge Geometry

Abstract

The results of a numerical investigation of the melting of a PCM occupying an axisymmetric volume in the presence of gravity are presented. The PCM is held between two circular supports maintained at different temperatures. The melting process, which is analyzed for n-octadecane, is affected by a combination of thermocapillary and natural convection. If the PCM is heated from above, the convective motion driven by the thermocapillary force is opposed by the buoyant force, which reduces the heat transfer rate. If the PCM is heated from below, natural convection acts in the same sense as thermocapillary convection and the heat transfer rate is increased. The volume $$\mathcal {V}$$ V of the PCM relative to an ideal cylinder, which selects the shape of the PCM/air interface, is found to play an important role. The overall effect of natural convection on heat transfer is characterized by the ratio of the melting time in microgravity to that of the same system with gravity. This gain factor is greater (less) than unity when heating from below (above) and depends strongly on $$\mathcal {V}$$ V , particularly for smaller PCM volumes.

Three-Dimensional Effects During Thermocapillary-Driven Melting of Pcms in Cuboidal Containers in Microgravity

“…The central row of Fig. 4 shows the time dependence of the total liquid fraction X L for all 3D and 2D simulations, while the lower part complements this with its rate of change, which more clearly reveals certain features like the decrease in melting rate when the S/L front arrives at the cold boundary [27,41].…”

“…The efficacy of thermocapillary convection and complementary strategies like nanoparticles for improving PCM performance in microgravity environments will be directly evaluated by the "Effect of Marangoni Convection on Heat Transfer in Phase Change Materials" (MarPCM) project, which is planned for implementation by the European Space Agency (ESA) on the International Space Station (ISS) [38,39]. A range of numerical investigations have recently been conducted in support of this anticipated experiment and the questions it addresses, including an analysis of dynamical modes and their effect on heat transport [18][19][20]31], melting with combined gravitational and thermocapillary convection [40,41], PCM melting in a liquid bridge configuration in microgravity [27,28,37,42,43], the influence of surface heat exchange [30,44,37], the effect of nanoparticles [45], and the coupling between thermocapillary flows and sloshing [46][47][48][49][50].…”