(8.1)VACUUM FURNACE BRAZING OPEN CELL RETICULATEDFOAM TO STAINLESS STEEL TUBING

摘要

A heat exchanging device for separating hydrogen isotopes was designed using open cellrnreticulated copper foam that was brazed to stainless steel tubing. It is anticipated that the copperrnfoam in the annular space of a tube-in-tube (TnT) style heat exchanger would improve thernthermal efficiency; it is further anticipated that brazing the foam to the inner tube that isrnalternately filled with heating and cooling fluid, would further improve the thermal efficiency ofrnthe process.rnThe development included alloy and process development. Two series of alloys were developedrnusing electro-brush plating to apply the braze materials. The processing temperatures were eitherrnhigh, approximately 980°C, or low temperature, approximately 550°C. High temperature brazesrnwere comprised of copper-gold alloys and low temperature alloys of gold-indium. The heatingrnrate and furnace environments were examined to ensure acceptable braze conditions. Additionalrndevelopment activities included foam internal diameter sizing, foam and tube assembly, andrnfoam and brazement mechanical property characterization.rnThis paper describes the intended application and development effort required to braze therncopper foam to the stainless steel tubing. Challenges, such as differences in thermal expansion,rnloss of high temperature strength, and excess braze material will be discussed.