A Stefan-Type Problem with Void Formation and its Explicit Solution

For most materials, the densities of the solid and liquid phasesare different. For some materials being considered as potentiallatent heat thermal energy storage materials, this density changeis large. When the solid phase is more dense than the liquid,solidification may result in the formation of vapour bubblesor voids. We have formulated a problem, representing a phasechange process with such a void, that has an explicit solution.We examine the solution to gain a further understanding of thethermal and phase change performance of a material in whichsuch voids form. We use the solution to analyse an example probleminvolving freezing lithium fluoride, a candidate phase-changematerial with a density change on freezing of about 25 per cent.