Metal foams as novel materials for air-cooling heat exchangers

Metal foams;Heat exchangers;Pressure drop;Heat transfer coefficient;condensate drainage;Frost formation

Nawaz, Kashif ; Jacobi ; Anthony M.

关键词: Metal foams;    Heat exchangers;    Pressure drop;    Heat transfer coefficient;    condensate drainage;    Frost formation;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/29424/Nawaz_Kashif.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

High-porosity metal foams have thermal, mechanical, electrical, and acoustic properties making them attractive for various engineering applications. Due to their large surface-area-to-volume ratio, tortuous flow path, and relatively high thermal conductivity they are being considered for a range of heat transfer applications. In this experimental study, open-cell aluminum metal foam is considered as a replacement for conventional louvered fins in brazed-aluminum heat exchangers. Closed-loop wind tunnel experiments are conducted to measure the pressure drop and heat transfer performance of metal-foam heat exchangers. In addition to characterizing the air-side pressure-drop and heat transfer performance, issues related to condensate drainage and frost formation are considered. The main performance obstacle for the application of metal foams is the relatively high pressure drop occurring for velocities typical to air-cooling applications. This high pressure drop results in larger air-side fan power requirements if metal foams are used as a “drop-in replacement” for louver fins. On the other hand, the heat transfer performance of the metal foams far surpasses that of conventional louvered fins, reaching two to three times the heat transfer coefficient of conventional fins. Smaller pore sizes provide larger surface area per unit volume and enhanced mixing, resulting in higher heat transfer. This excellent heat transfer performance means that alternate deployments of the metal foam are possible to manage fan power, while achieving comparable thermal performance. The experimental data are presented in terms of friction factors and Colburn j factors, and design correlations are developed to predict heat exchanger performance. Under wet-surface conditions, water retention can be an important problem for louvered-fin operation. Surprisingly, metal foams have water drainage behavior superior to that of conventional fins.The effects of geometry, porosity, surface treatment, and orientation on water drainage have been analyzed.