Effect of heat transfer through an interface on convective melting dynamics of phase change materials

Abstract

The presence of thermocapillary (Marangoni) convection in microgravity may help to enhance the heat transfer rate of phase change materials (PCMs) in space applications. We present a three-dimensional numerical investigation of the nonlinear dynamics of a melting PCM placed in a cylindrical container filled with n-octadecane and surrounded by passive air. The heat exchange between the PCM and ambient air is characterized in terms of the Biot number, when the air temperature has a linear profile. The effect of thermocapillary convection on heat transfer and the topology of the melting front is studied by varying the applied temperature difference between the circular supports and the heat transfer through the interface. The evolution of Marangoni convection during the PCM melting leads to the appearance of hydrothermal instabilities. A new mathematical approach for the nonlinear analysis of emerging hydrothermal waves (HTWs) is suggested. Being applied for the first time to the examination of PCMs, this procedure allows us to explore the nature of the coupling between HTWs and heat gain/loss through the interface, and how it changes over time. We observe a variety of dynamics, including standing and travelling waves, and determine their dominant and secondary azimuthal wavenumbers. Coexistence of multiple travelling waves with different wavenumbers, rotating in the same or opposite directions, is among the most fascinating observations.

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

“…The melting of a PCM in the presence of thermocapillary convection can be seen as a fluid dynamics problem with an evolving boundary since both the volume fraction and the shape of the liquid domain change continually over time. This changing liquid domain tends to induce transitions among different thermocapillary modes as the effective forcing (Marangoni number) and aspect ratio (domain shape) change [31,37]. The corresponding instabilities not only alter the fluid dynamics but any measurable quantity that is influenced by them, like the heat transfer rate.…”

“…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].…”