Experimental and numerical evaluations of geometry and structure effects on passive cooling efficiency in metal foam finned heat sinks

Abstract

This study investigates the thermal performance of metal foam–based finned heat sinks under natural convection using both experimental and numerical approaches. The numerical analysis was performed in ANSYS Fluent using the Local Thermal Non-Equilibrium (LTNE) model. Experiments were carried out for four pore densities (5, 10, 15, and 20 PPI) and porosities ranging from 95% to 71%. Four types of metal foams—aluminum, copper, nickel, and titanium—were tested, with air as the working fluid and heat inputs varying from 4 to 30 W. The experimental setup included six aluminum foam fins (100 × 100 × 10 mm³) mounted on an aluminum base plate (100 × 100 × 3.5 mm³), with an 8 mm spacing between fins. Aluminum foam fins with a pore density of 10 PPI and 91% porosity were tested in both covered and uncovered configurations, with the heat sink oriented vertically and horizontally. Results showed that the optimal porosity and pore density were 0.79 and 5 PPI, respectively. Consequently, reducing the porosity from 95% to 79% results in a 16.7% decrease in the base temperature difference, while the Nusselt number (Nu) improves by 21.3%. Additionally, the 5 PPI foam exhibits a 12% higher reduction in average temperature and a slight increase in heat transfer, 1.92% relative to the 20 PPI sample. The horizontal orientation provided better thermal performance than other positions. Using copper instead of aluminum improved the base-to-ambient temperature difference by 3.3%. Conversely, aluminum performed 22% and 3% better than titanium and nickel, respectively. The best ratio of cover height to fin height was found to be 0.8. Accordingly, the convergent rate of results is approximately 98.8% between the heat sink with a cover height ratio of 0.8 and the uncovered heat sink. Additionally, a correlation equation was developed linking the Nusselt number with porosity and Rayleigh number. Overall, the findings highlight the strong potential of metal foam heat sinks, particularly in horizontal configurations, for enhancing natural convection cooling performance in compact electronic and thermal systems.