Slip Flow Analyses of a Capacitive Pressure-Based Micro Flow Sensor

Abstract

We present gas flow measurements and slip flow analyses considering velocity slip at the wall in a capacitive pressure-based micro flow sensor. The sensor consists of a pair of capacitors for measuring pressure difference between the inlet and outlet and absolute pressure at the outlet, inlet/outlet reservoirs, and the main microchannel. The main microchannel is 128.0μm wide, 4.64μm deep, and 5680μm long, where the outlet Knudsen number is 0.0137. The sensor was fabricated using wet etching, ultrasonic drilling, Deep Reactive Ion Etching (RIE) and anodic bonding. The capacitance change of the sensor and the mass flow rate of nitrogen were measured as the inlet to outlet pressure ration increased up to 1.24. With the increasing pressure difference, the capacitance change of the differential pressure sensor increases. The TMAC for the channel whose sides are made of silicon dioxide and Pyrex #7740 glass was extracted for nitrogen. The friction factor was also measured and compared with a previous simulation result.