Pressure losses in microchannels with bends

Bends in fluidic systems are necessary features due to design or technology constraints. Bends or curves in a duct always induce flow separation at the walls, which results in additional pressure loss. In this work, this phenomenon is investigated on a microscale. A set of microchannels, 20μm×1.1μm×5810μm in dimensions, with a 90°-bend at the channel center 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 inlet pressure up to 50 psi, and the mass flow rate was measured for all the devices as a function of the 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 this microdevice were recorded, showing a pressure jump across the miter bend. The mass flow rate and pressure measurements indicate the existence of flow separation in the microchannels.