Switched cavity: An approach to micromass-flow sensors

A method is proposed for measuring and/or controlling the mass-flow rate of gases. A small cavity is connected in series to a conduit via two valves that are alternately opened and closed. When the upstream valve is open and the downstream one is closed, the gas in the cavity is compressed to the upstream pressure. In the next phase, the cavity is switched downstream, i.e., the upstream valve is closed, the downstream valve is opened, and the gas in the cavity is rarefied to the downstream pressure. Thus, a small volume of gas is conveyed via the cavity from the upstream to the downstream in each switching cycle. The average mass-flow rate per unit time is proportional to the valve switching frequency, the pressure difference between the upstream and downstream regions, the inverse of the gas temperature, and the capacity of the cavity. The mass-flow rate can be determined from the pressure difference and gas temperature, provided that the cavity is switched at a fixed frequency. In addition, the mass-flow rate can be controlled by changing the frequency of the switching. An experimental device that employed piezoelectric bimorph actuators as switching valves and a cavity of capacity 1.33×10 −6 m 3 was constructed and experiments were performed with mass-flow rates ranging from 0.2×10 −4 to 2.7×10 −4 g/s . The results verified the applicability of the proposed method as a micromass-flow sensor/controller.