Thermal performance of low melting point metal-based heat sinks for high-power airborne equipment

Abstract

Low melting point metals (LMPMs) have greater potential to address the cooling difficulties of high-power airborne equipment than conventional phase change materials (PCMs). However, the heating power in existing LMPM-based heat sinks is generally low. Here, a bismuth-based alloy, Bi44.7Pb22.6In19.1Sn8.3Cd5.3, is adopted. Experiments were conducted in a pin fin heat sink (PFHS) and an empty heat sink (EHS) under 50–1500 W. Experimental results on the effect of PCMs indicate that heat sinks filled with LMPMs outperform n-dodecane. The heating wall temperature is decreased, and the holding time is prolonged significantly. The EHS and PFHS remain below 50 °C from 847 and 1268 s to 2209 and 2302 s at 50 W, respectively. Experimental data illustrate that for LMPM-based heat sinks, the heating wall temperature and holding time are improved by applying pin fins. The EHS and PFHS remain below 50 °C for 143 and 183 s at 500 W, respectively. However, the difference between the holding time below 70 °C for EHS and PFHS is reduced to ±3%. Experimental results reveal that increasing the heating power results in rising heating wall temperature and falling holding time. The holding time of the LMPM-based PFHS decreases from 2302 s at 50 W to 61 s at 1500 W, and the heating power effect weakens from approximately 50% at 100–200 W to approximately 10% at 900–1500 W. Moreover, the Nusselt number (Nu) decreases with increasing dimensionless time, but the decrease is increasingly smaller. A higher Rayleigh number correlated with a larger heating power leads to a higher Nu due to the intensive effect of natural convection. New dimensionless correlations of Nu are developed, yielding mean absolute deviations of 3.5% and 2.7% for the LMPM-based PFHS and EHS, respectively.