Controlled Atmosphere Brazing of Compact Heat Exchangers for Mini-Cooling Systems

This paper addresses various aspects related to fabrication of novel compact heat exchangers designed for mini-cooling systems. For example, open cell metal foams can be used in a wide range of applications such as light weight structure material, energy absorber, liquid/gas separators and filters, owing to its excellent strength to weight ratio and highly porous structure. Recent attentions have also been paid on using metal foams, especially aluminum and copper foams, as heat transfer enhancement in thermal management applications, apparently due to the large surface area to volume ratio. Therefore, it is important to develop reliable joining techniques to bond the metal foams with similar or dissimilar metal surfaces. Controlled atmosphere brazing technology has been proved to be a proper choice for bonding numerous foam ligaments simultaneously to a substrate surface. The objectives of this paper are: (1) further exploring options for brazing foam structures in terms of materials selection and process feasibility; (2) studying proper brazing conditions for small scale heat exchangers with complicated geometries. The integrities of brazed joints are metallurgically examined.  Selected brazing processes are applied to fabrication of microchannel heat exchanger prototypes using open cell foam as air side fin structure. Thermal performances of the brazed heat exchangers are discussed as well.