Fluid flow characteristics in xurographic microchannels

An experimental study to evaluate fluid flow characteristics in xurographic microchannels was conducted. Microfluidic systems created with xurography are inexpensive compared to those manufactured using other traditional microfabrication technologies. Xurography is a rapid-prototyping technology, making it an ideal tool for microfluidic system development in the laboratory. Flows of water in microchannels with rectangular cross section and channel height on the order of 100 |im in the Reynolds number range from 250 to 3500 were studied. Static pressure measurements were made in the fully developed flow region to obtain the pressure drop at different flow rates. For the microchannel systems with two 90° miter bends, the bend separation distance was more than the re-establishment length following the first bend. Microchannels were characterized using optical microscopy and laser interferometry, which was capable of measuring depths of approximately 100 |um in enclosed microchannels with a relative uncertainty of less than 0.2%. Data for frictional pressure drop in straight sections, critical Reynolds number, and minor losses associated with 90° miter bends were generated. The average Poissuille numbers in fully-developed laminar flow were in excellent agreement with Stokes flow theory for all thirteen microchannels. The critical Reynolds number was in the range of 2250 and 2600 for channels with smooth sidewalls. An early transition to turbulence was evident for the microchannels with flow tripping elements such as adhesive droplets on the sidewalls. The dependence of the laminar Poissuille number on aspect ratio was equivalent to macroscale theory, within the uncertainty of the data. The minor loss coefficients for 90° bends were found to increase with increasing modified aspect ratio. The loss coefficients for every channel were nearly invariant with Reynolds number in the range from 1200 to 2100. A steep increase and a sudden decrease in minor losses was observed for Reynolds numbers less than 1200 and Reynolds numbers greater than the critical Reynolds number, respectively. No microscale effects were evident in the xurographic microchannels.