Melt front visualization and flow prediction in dynamic phase change materials on finned heat sinks

Abstract

Dynamic phase change materials (dynPCMs) offer high heat transfer rates over extended times due to a force applied to the PCM that pumps away melted liquid and maintains a thin melt layer. The melt layer dynamics governs the system behavior; however, little is known about how the melt layer forms and flows, especially when the heat source has a complex three-dimensional shape. This study investigates heat transfer and fluid flow during dynPCM cooling of heated finned copper heat sinks. Melt flow is visualized using computer vision, and these results are coupled with thermal measurements and simulations to gain a fundamental understanding of the flow physics. By measuring the shape of the liquid–solid interface, we resolve the coupling between the heat transfer and melt flow. Four extended surface designs are investigated consisting of fins with varying tip shapes and spacings. Experiments show a reduction in thermal resistance up to 36% with sharp-tip fins compared with rectangular fins, with the thinnest melt layer forming at the fin tips. Using experimental observations as inputs, a three-dimensional simulation investigates heat transfer and fluid flow in the liquid PCM. Simulations show that liquid drainage is a key limitation to dynPCM performance and that the melt layer is thinnest in the center of the heat sink, growing as the melted PCM flows out. The results demonstrate that dynPCM heat transfer is governed by the interplay of surface area, fin geometry, and liquid drainage. The outcomes presented here may be used to design higher-performing dynPCM systems.