MICROTHERMOCOUPLE ANEMOMETRY VERSUS LASER DOPPLER ANEMOMETRY FOR EXPERIMENTAL VELOCITY MEASUREMENT IN AIR JET

摘要

This article compares two different methods for the velocity profiles measurement of an air jet at the outlet of a circular tube: the microthermocouple anemometry (μTA) and the Laser Doppler Anemometry (LDA). The microthermocouple anemometer consists of two type K (Chromel/Alumel) microthermocouples (25.4 μm diameter) used in an electronic oscillator. One is placed in the system and the other takes place in a reference volume. During a half period the two microthermocouples are heated to a suitable temperature above ambient. During the next half period, when the supply of current is interrupted, the microthermocouple placed in the system measures the flow while the other compensates for the ambient temperature changes. Cooling caused by experimental conditions under variable flow results in a change in the oscillator frequency. The sensor measure flows and temperatures simultaneously. The second method uses a classical Laser Doppler Anemometry to extract the velocity profiles and to be considered as reference measurements. Results of the two methods are globally in good agreements. The flow measurements are in the range 0 to 5 m.s~(-1).