Gas flow in microchannels with bends

Bends or curves are unavoidable features in fluidic systems due to design or technology constraints. These fluidic elements in a macrochannel always induce secondary flows, which result in pressure loss in addition to frictional loss. In this paper, this phenomenon is investigated on a microscale where flow separation is not expected to develop. A set of microchannels, with the dimensions 20 × 1 × 5810 μm³, with a 90° turn at the channel centre, has been fabricated using standard micromachining techniques. Three bend configurations have been tested: miter, curved and double-turn. All the microchannels were integrated with pressure microsensors. Argon gas was passed through the microdevices under an inlet pressure of up to 50 psi, and the mass flow rate was measured for all the devices as a function of the driving pressure drop. The flow rate through the channel with the miter bend, a single sharp turn at a right angle, was found to be the lowest. Pressure distributions along the microchannels were recorded, showing an additional pressure drop across the bends. The largest drop was found in the miter bend with the lowest flow rate. The mass flow rate and pressure measurements indicate that secondary flow could develop in microchannels also due to a bend, contrary to expectations.