Design, Fabrication and Testing of Fixed-Valve Micro-Pumps

Abstract

Abstract Micro-fluidic systems rely on positive displacement pumps to move fluid due to the low Reynolds numbers encountered at flow rates that are typically in a range around 100 μl/min. These pumps are usually reciprocating devices due to limitations of rotating machinery at small scales. Valves for micro-pumps are not necessarily scaled-down macro-valve designs. Existing designs range from passive membranes to complex thermally-controlled active devices. A simpler idea and one that may be more applicable to particulate-laden fluids is a valve that is fixed in shape. Such a valve operates solely by the differential pressure characteristics in each flow direction, which are caused by the flow through it. Such fixed or no-moving-parts (NMP) valves are attractive due to their simplicity of fabrication but have not been studied in enough detail to determine optimal designs. We present design and testing techniques for use in developing efficient NMP valves and for comparing various designs. These techniques were applied to diffuser and valvular conduit designs etched on silicon. Valve performance was characterized by flow resistance and by diodicity, which is the ratio of pressure losses in the reverse to forward direction. Techniques for measuring diodicity in steady and transient flow were developed, and both viscous and dynamic loss contributions to valve performance were analyzed. Computational techniques were used to demonstrate their use in the design of efficient valves.