Geometric measurement and characterization of a microchannel heat exchanger for performance validation

Abstract

With substantial size and performance advantages, microchannel heat exchangers have been attracting increasing attention for various energy recovery and conversion processes. While much research and recent studies focus on their applications and performance, few studies have been devoted to the measurement and dimensional accuracy of actual microchannels in use. In this study, in-depth geometric characterization of a microchannel heat exchanger manufactured using standard photochemical etching and diffusion bonding processes is carried out. The measured channel dimensions are then compared with the design values, which can help better interpret experiment data of the heat exchanger for model validation. Two nondestructive methods were developed to measure cross-sectional areas and perimeters of the microchannels. The first method uses a stereoscopic microscope to take images of the exhaust channels at one end of the microchannel heat exchanger. An image processing routine was developed in MATLAB to measure the exhaust channel dimensions. For the second method, an optical profilometer was used to scan both the exhaust and oil channels from sample shims. Two additional MATLAB routines were developed to process the obtained 3D shim images with the capability of accounting for the bow in the shims. As results, both methods have close agreement on the measured channel dimensions. On average, the cross-sectional areas of the exhaust channels vary more significantly between individual shims due to the nature of the batch photochemical etching process; and the produced exhaust and oil channels are 11% and 8% smaller than the design values. These findings help explain the emerged discrepancy between modeling and experimental data.