Microthermocouples Sensors for Velocity and Temperature Measurements in Gas Flow

This paper presents the development of two classes of sensors based on microthermocouples with different wire diameters (from 7.6 μm to 25.4 μm). The first one uses the pulsed-wire technique for the couple velocity/temperature measurement. These sensors are used with three different techniques we developed in our laboratory: the time of flight method, the oscillation frequency method and the phase method. Because the purpose of this kind of sensor is to be introduced in different microdevices, it is realized with two thermocouple wires and does not use the micromachining technologies. Its working principle is close to that of the hot wire anemometer and it presents the same advantages such as very small dimensions and weak response time. The sensor is developed in order to measure flows and temperatures in microsystems like small channels (width < 500 μm), microtubes (diameter < 53 μm) and small structures (volume < 100 μm³). The second class of sensors are based on the multi-wire thermocouple technique. In this paper we present a probe using two wires of same nature but different in diameter located close together at the measurement point. This probe is used to measure simultaneously the temperature and the velocity of flowing gas. Results will focus on oscillating flows of gas.