Influence of end conduction on the sensitivity to stream temperature fluctuations of a hot-wire anemometer

Abstract

The influence of end conduction on the sensitivity to stream temperature fluctuations of a constant current hot-wire anemometer operated at low overheat has been investigated using a newly developed dynamic, cross-correlation calibration technique. A lumped parameter heat-transfer model of the wire and support system consistent with the experimental data is presented. Results show that for commonly used tungsten and platinum wires, a frequency dependent sensitivity to stream temperature fluctuations is obtained in air flows at low subsonic velocities. For measurements with an accuracy of approximately 5% under non-isothermal flow conditions, use of a wire of low thermal conductivity such as Pt 10% Rh with a length-to-diameter ratio of at least 400, irrespective of wire diameter, is recommended compared with 800 for equivalent accuracy with tungsten wire. The relevance of the results to velocity measurements with constant temperature hot-wire anemometers in non-isothermal flows is also discussed.