Flow Characteristics of Micro Diffuser/Nozzles for a Valveless Micropump

In this study, the flow characteristics have been experimentally investigated for various shapes of the diffuser/nozzles, and the results are compared with the numerical simulation. Three chambers (inlet, exit, and middle) and two identical diffuser/nozzles are fabricated on a silicon wafer. The inlet and middle chamber is connected by one diffuser/nozzle; and the middle and exit chamber is connected by another diffuser/nozzle. The experiments are performed in a pump mode in which pressure is applied to the middle chamber and a supply mode in which pressure is supplied to the inlet and exit chamber. The net flow rate is determined by the flow difference between the pump and supply mode. The important parameters considered in this study are the throat width (30–12μm) and the taper angle (3.15–25.2°). For the taper angle and the throat width, it is found that there exists an optimum at which the net flow rate is the greatest. The optimal taper angle is in the range of 10–20° for all the pressure differences; and the throat width indicates an optimal value near 90μm for the case of 35kPa pressure difference. This tendency has been verified by the numerical simulation. From the numerical simulation, it is also found that the net flow rate is influenced by the size of the middle chamber. With decreasing chamber size, the net flow rate is reduced because of the interference between two streams flowing into the middle chamber.