Validation of Manufacturing Process Designs for Stamped Microchannel Recuperators

Microchannel recuperators can achieve high-efficiency power cycles and chemical reactions by recovering waste heat from hot turbine exhaust and chemical reaction streams. However, the industrial application of microchannel recuperators are restricted by the high cost of patterning and bonding. The objective of this study was thus to investigate new methods for producing microchannel recuperators for emerging markets. Based on greenfield cost estimates, process designs based on stamping, laser welding and vacuum brazing of 316L stainless steel laminae were found to be more economical than conventional photochemical machining and diffusion bonding. Subsequently, validation experiments were conducted to produce stamped microchannel components using cost model parameters. At a mass flow rate of 0.99 g/s, the test article made with laser welding was found to provide higher effectiveness than the test article produced using vacuum brazing. Preliminary investigations showed that residual stresses during laser welding of the laminae led to significant warpage, collapsing channels and making lamina-to-lamina fit up challenging. In contrast, the test article produced by vacuum brazing of stamped laminae showed no clogging and 4.6% and 10.5% channel height standard deviation for the cold and hot channels, respectively. Channel variation in the vacuum brazing sample was determined to be caused by misregistration of laminae during brazing. In future work, efforts are needed to choose cheaper, more ductile brazing foils as well as design a brazing fixture to improve lamina-to-lamina registration.