Eric Gavignet

Visualization of flow instabilities in supersonic ejectors using Large Eddy Simulation

Graphical Abstract

Évolution des techniques de micromesures thermiques au travers de quelques applications

Abstract The thermoelectric sensors made at present in our laboratory have junction dimensions from a few micrometers to 0.5 μm. Two techniques are used: welding of ultra-thin wires and vacuum deposition (PVD). Two applications related to the first one will be presented: the detection of periodic field of temperature for photothermal microscopy and acoustic resonator characterization. In the latter, the comparison of simultaneous pressure and temperature will lead us to improve the knowledge of thermoacoustic phenomena. The deposition technique allows us to create either simple thermoelectric couples, multiple as thermopiles; or heat (and light) flow sensors. Our work is presented in that field, with the development of a laser light sensor designed to image its light profile for large emission bandwidth and power densities. Finally, the description followed by an example of application is shown in the case of the heat flow measurement between a laminar gaseous flow and a wall. By comparison, we show that the use of such sensors could be worthwhile to replace the usual temperature sensors in the estimation of the heat transfer coefficient at the gas-wall boundary.

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.Copyright