Hotwire anemometry

A two channel hotwire anemometer (DANTEC) was used for the present investigation. Hotwire anemometry (HWA) is based on the principle of compensation of the rate of heat loss of a small heated metallic wire exposed to flow. The probe responds primarily to the magnitude of the velocity vector. The anemometer output voltage then undergoes signal conditioning to filter out noise and improve the signal-to-noise ratio. The operating temperature of the hotwire is usually much higher than the room temperature, typically 150 in air flow measurements. In the present experiments, the probe operated at a temperature of around ; this minimized mixed convection and radiation errors, without appreciable loss of sensitivity. Higher temperatures enhance the sensitivity of wire but make the wire fragile. Additionally, to avoid oxidization it is essential that the wire temperature at any point along the wire element is kept well below 350⁰C.To illustrate these points, consider a typical hotwire probe (DANTEC 55P11) for which the electrical properties are For an overheat ratio of 1.5, the operational resistance of the wire will be The corresponding mean wire temperature can be evaluated from the equation

as being equal to about which is well below the oxidation temperature. On the front panel of the anemometer, the parameter fixed is the operating resistance of the wire.