Pressure loss in constriction microchannels

Constriction devices contain elements inserted into the fluid stream, which change the local streamwise flow area. One such element is the orifice-like obstruction with sharp corners, a back-to-back abrupt contraction and expansion, which could trigger flow separation. A series of microchannels, 40 μm × 1 μm × 4000 μm in nominal dimensions, with constriction elements at the centers of the channels has been fabricated using standard micromachining techniques. The channel widths at the constriction sections varied from 10 μm to 34 μm, with pressure sensors integrated in each channel. Nitrogen gas was passed through the microdevices under inlet pressure up to 50 psi. The mass flow rates were measured for all the devices as a function of the pressure drop. A monotonic decrease of the flow rate with decreasing constriction-gap width was observed. The pressure distribution along the microchannel with the smallest constriction gap showed a pressure drop across the constriction element. Both mass flow rate and pressure measurements indicate that flow separation from the constriction sharp corners could occur.