Autonomous flow-rate regulators using pressure-adaptive parallel membrane valves

Abstract

In this thesis, autonomous flow-rate regulators using pressure-adaptive parallel membrane valves, capable of maintaining a constant flow-rate at varying inlet pressure supplied from micropumps, has been proposed. The previous flow-rate regulators are difficult to be integrated with micropumps, because of not only the complex multi-layer structures, but also the high threshold inlet pressure required for flow-rate regulation. The present autonomous flow-rate regulators achieve flow-rate regulation function at the minimum threshold inlet pressure as low as 15 kPa with simple structure formed by a single mask process. The pressure-adaptive parallel membrane valves in the autonomous flow-rate regulators are designed to adjust flow resistance according to the inlet pressure, thus maintaining a constant flow-rate independent of the inlet pressure variation. Total 6 different prototypes of W4, W10, W20, W30, W40, and W50, having different gaps between parallel membranes of 4, 10, 20, 30, 40 and 50 μm, respectively, has been designed and fabricated by polymer molding process using PDMS (PolyDiMethylSiloxane) with different base and curing agent mixing ratios (10 : 1 and 20 : 1). In the experimental study, flow-rate characteristics of the fabricated autonomous flow-rate regulators for both static and dynamic inlet pressures was measured. The prototype W20 fabricated by 10 : 1 PDMS achieved the constant flow-rate of 6.09 ± 0.32 μl/s over an inlet pressure of 20 kPa. The prototype fabricated by 20 : 1 PDMS, having lower Young``s Modulus than 10 : 1 PDMS, showed a lower threshold inlet pressure for regulation, and higher flow-rate than prototypes fabricated by 10 : 1 PDMS. The measured flow-rates from the combination of 6 different prototypes and 2 different material properties, were ranged from 32.83 nl/s (W4, 10 : 1 PDMS) to 24.32μl/s (W50, 20 : 1 PDMS), thus achieving 800\% of ratio. For a dynamic inlet pressure, we had applied the inlet pressure switched between 2...