Minor Losses in Rectangular Xurographic Microchannels

Abstract

Xurography is a novel manufacturing process for microfluidic systems, providing rapid prototyping capability at low cost compared to traditional microfabrication technologies. An experimental study of flow characteristics in rectangular xurographic microchannels is reported. Mean microchannel depth, defined by the thickness of the double-sided adhesive kapton tape that forms the channel pattern, is 105–110 μm. The microchannels are capped with glass and mechanically reinforced to withstand the high operating pressures that accompany high Reynolds number Re flow (250–3500). Channel aspect ratios range from 0.45 to 0.074. Width and length measurements are performed using optical microscopy. Microchannel height is measured using a unique nondestructive laser interferometry technique, capable of accurate measurement of the enclosed, compressed microchannels. Data are reported for friction factor, critical Reynolds number, and minor losses in expansions, contractions, and 90° miter bends. Expansion and contraction area ratios are 2, 3, and 5. The experimental Poissuille number in laminar flow for all aspect ratios is in good agreement with theoretical values. Critical Reynolds number ranges from 1800 to 2300, and is found to be dependent on channel defects, such as adhesive droplets and edge imperfections, inherent to xurography. Expansion and contraction losses decrease gradually with increasing Re in the range 250–4000 and increase for decreasing area ratio. Loss coefficients in the 90° miter bends increase with modified aspect ratio and are nearly invariant for 1200 < Re < 2100. Loss coefficients increase nearly linearly with Re for Re < 1200 and decrease significantly for Re greater than the critical Reynolds number.