Experimental and numerical investigation of PCM-based cylindrical heat sinks with radially oriented fins under transient high-power loads

Abstract

Phase change material (PCM)-based heat sinks buffer intermittent thermal loads, but the heating-to-solidification response of cylindrical heat sinks with radially oriented fins remains insufficiently quantified. This response was characterized experimentally, while validated simulations resolved melting. An experimentally derived transient Nusselt number correlation was developed. An aluminum heat sink containing 20 radially oriented fins and n-eicosane was heated at 10–140 W until its average near-center temperature rose from 28°C to 50°C. It was then passively cooled in quiescent air, and PCM-filled and unfilled configurations were compared at 30 W. A three-dimensional model coupling the volume-of-fluid and enthalpy–porosity methods was validated against measured temperatures. At 30 W, PCM increased the time to 50°C from 7.1 to 13.1 min (84%), reduced the near-center temperature by 10.3°C when the unfilled heat sink reached 50°C, and extended the subsequent 50–35°C cooling time from 32.8 to 86.0 min (162%). Increasing power from 10 to 140 W shortened the time to 50°C from 62.0 to 1.9 min (96.9%). Simulations revealed upward buoyancy-driven melt transport and a marked melting-rate decrease above a melt fraction of approximately 0.98. The apparent degree of supercooling, recalescence amplitude, and time from liquidus passage to apparent completion of solidification were 1.5–1.7°C, 0.18–0.31°C, and 47.2–49.0 min, respectively, without systematic dependence on preceding heating power. Correlations developed for three-side-heated rectangular cavities inadequately represented the experimental data, whereas the proposed correlation yielded a coefficient of determination of 0.98 and a root-mean-square error of 1.98 for the modified Nusselt number.