Gas flow in constriction microdevices

Constriction devices contain an element inserted into the fluid stream, which either changes the local streamwise distribution of flow area or applied frictional resistance to the flow. Two such devices: a micro orifice plate and a micro Venturi tube have been successfully fabricated for the study of fundamental flow phenomena in microdomains. Each device was integrated with a set of pressure sensors, and fabricated using standard micromachining techniques. Nitrogen gas was passed through the microdevices under inlet pressure up to 50 psi. Mass flow rate was first measured as a function of the overall pressure drop, and compared with results for a straight microchannel. Then, the detailed pressure distribution along each device was measured to understand the flow pattern around the flow obstruction. The results demonstrate that flow separation may occur in a microchannel flow with a very small Reynolds number. It is very possible that a micro vortex, on the order of 10 μm in size, can develop upstream and downstream of the obstruction.