Microscale crossflow heat exchanger fabricated by laser-based xurography

Abstract

Commercial applications of microfluidic systems have been expanding exponentially over the last decade. Most commercial systems are fabricated using silicon processing; however, development costs remain high. For fundamental process development, a less expensive alternative is desirable. Xurography is an inexpensive rapid prototyping technology for microfluidic systems that is becoming more prevalent in research labs. In this technology, patterns are cut in double-sided adhesive polyimide tape, which is then sandwiched between two substrates. Traditionally, a cutting tool forms the patterns, which are relatively imprecise and subject to defects. To improve the cutting process, a laser has been implemented in this work. Due to the laser energy input, features are found to be more precise, but subject to soot production and melting. Laser-based xurography has been used to create five multilayer heat exchangers to explore the feasibility of thermal processing in devices sealed with the polyimide tape. The crossflow and counterflow heat exchangers were tested under a wide range of conditions; however, turbulent flow was not achieved due to pressure drop limitations. The devices performed leak free at temperatures up to 75 °C and pressures as high as 2520 kPa. Heat exchanger effectiveness matched theoretical predictions within experimental uncertainties. Using an exergy analysis, it was determined that the heat exchangers performed most efficiently at low Reynolds number. This work represents the first time laser-based xurography has been used to develop multilayer microfluidic devices