Caractérisation et modélisation d'un microdébitmètre thermique à thermocouple bifilaire

Realization and dynamic characterization of a microthermocouple thermal flowmeter

Centre de Recherche sur les Ecoulements les Surfaces et les Transferts, CNRS UMR 6000

Abstract

This article deals with the realization and the dynamic characterization of a thermal flowmeter designed to measure flows in microsystems. This device uses a microthermocouple placed in the flow and submitted to two successive phases of heating by Joule effect and cooling by natural convection. Convective cooling caused by experimental conditions under variable gas flow rate results in a change in the oscillator frequency. In the same time, at the end of the cooling period, the sensor gives the temperature of the gas flow. From the two temperatures and flow informations the mass flow is determined using the perfect gas hypothesis. Experiments with thermocouple diameters from 12.7 to 127 µm have demonstrated good sensitivity for mass flows less than 10 mL.min^-1.