The Role of Radiation in Mixed Convection Heat Transfer from a Rectangular Fin Heat Sink: Experimental Investigation

Abstract

Nowadays, effective thermal management is essential to prevent overheating in high-power devices. The utilization of high-emissivity materials plays a crucial role in enhancing heat transfer efficiency in both natural and mixed convection systems. This study presents an experimental investigation of a rectangular fin heat sink’s thermal performance, exploring the effect of mixed convection and radiation heat transfer on two symmetrical fins with an aspect ratio of S*= 0.4 and 0.8. The experiment was carried out in a laboratory-scale wind tunnel, where the inlet fluid velocity was maintained at a constant value of u = 0.3 m/s across a range of Richardson number (0.6–5) and Rayleigh number (1.09–9.15 ×105), corresponding to the variation of heat loads 18–100 W. High-emissivity paint (ε = 0.85) was applied to the heat sink fins and compared to a low-emissivity paint (ε = 0.05) to assess the effect of performance. The results reveal that the high emissivity fin dissipated heat more effectively, with radiation and convection contributing approximately 25% and 75%, respectively, at the highest Rayleigh number. The study also revealed that increased fin spacing enhanced the view factor, although radiation heat transfer was higher for lower fin spacing due to a greater number of fins. Additionally, fin effectiveness was influenced more by fin spacing compared to surface emissivity, with effectiveness decreasing at higher Rayleigh numbers across all conditions. Infrared (IR) imaging confirmed that the high-emissivity coating allowed the heat sink to dissipate up to 30 °C from the heated surface, underscoring the substantial impact of high-emissivity materials in thermal management applications.