Valve-less diffuser micropumps

Abstract: Today there is growing interest in research on microfluidicsystems, e.g., for chemical analysis systems and microdosagesystems. One of the basic components in microfluidic systems ismicropumps. During recent years several different micropumpshave been presented based on different pump principles andusing different actuation principles. In this thesis the firstmicromachined versions of pumps based on the new valve-lessdiffuser pump principle are presented.The key element in the diffuser pump is the diffuserelement. A diffuser is a gradually expanding flow channelintended to raise the static pressure. The largest pressurerise is achieved for small opening angles. The diffuser elementis a diffuser with a rounded inlet and a sharp outlet. It ischaracterized by a lower flow resistance in the diffuserdirection than in the opposite direction, the nozzledirection.In the valve-less diffuser pump diffuser elements are usedas flow directing elements. One diffuser element is directedfrom the inlet chamber to the pump chamber and the otherdiffuser element from the pump chamber to the outlet chamber. Amoving boundary of the pump chamber forces the fluid throughthe two diffuser elements. The result is a net transport offluid from the inlet side to the outlet side due to thedifference in the flow resistances in the diffuser and nozzledirections.Pumps of different sizes for both liquids and gases havebeen fabricated in different materials using both conventionalfabrication methods and micromachining technology. Extensivemeasurements have been made to investigate the performance ofthe diffuser pumps. These results have been used together withnumerical simulations and classical fluid mechanics in order tounderstand the working principle of the diffuser pump and tofurther improve the design. Based on the empirical results andsimulations using a lumped-mass model improved designs aresuggested.All the tested pumps show good performance. The pump withthe best test result is fabricated in silicon using deepreactive ion etching (DRIE) which allows any arbitrary planardesign of the pump. A glass wafer is bonded to the pump cavityside of the silicon wafer. The pump diaphragms are excitedusing piezoelectric discs. The diffuser "throat" cross-sectionis 80×80 µm and the pump chamber diameter is 6 mm.The entire pump chip has a size of 15×17×1 mm. Forwater a maximum pressure head of 74 kPa was reached and amaximum volume flow of 2.3 ml/min was obtained.Keywords:micropump, valve-less pump, diffuser pump,diffuser elements, fluid, liquid, gas, microfluid system,KOH-etching, isotropic etching, deep reactive ion etching,micromachining, anodic bonding, bulk micromachining,Computational Fluid Dynamics, CFD, lumped-mass model.