Numerical and experimental studies of flat-walled diffuser elements for valve-less micropumps

An investigation of flat-walled diffuser elements for valve-less micropumps is presented. The diffuser element is a small angle flow channel with a ro unded inlet and a preferably sharp outlet. The diverging-wall direction is the positive flow direction. The flow-directing capability under steady flo w conditions was determined experimentally for several different diffuser e lements. The flow-pressure characteristic was studied in detail for one of them. The result is compared with previously published results on pump perf ormance. Numerical simulations were done using the Computational Fluid Dyna mics program ANSYS/Flotran. The simulations show the flow-directing capabil ity of the diffuser elements and predict the flow-pressure characteristics well for Reynolds numbers below 300-400. For higher Reynolds numbers, the s imulations show the flow-directing capability, but there is a larger discre pancy between simulations and measurements. Simulations were also done for a nozzle element, a wide-angle flow channel with sharp inlet and outlets us ed in the micropump with dynamic passive-valves. A nozzle element has the c onverging-wall direction as positive flow direction. The simulations show d ifferences in the flow patterns for diffuser elements and nozzle elements t hat explain the opposite positive flow directions. The diffuser element has an ordered flow and takes advantage of the pressure recovery in the diverg ing-wall direction. The nozzle element has gross flow separation in the div erging-wall direction and there is a "vena-contracta" effect instead of pre ssure recovery. The effective cross-sectional area is smaller in the diverg ing-wall direction than in the converging-wall direction. (C) 2000 Elsevier Science B.V. All rights reserved.