Abstract
Variations in fluid temperature are the most important error source in hot-wire anemometer measurements and must sometimes be compensated for. Although many temperature compensation schemes have been proposed over the years, no consensus seems to be reached regarding correction methods. In this paper new precision measurements on heat transfer from heated wires have confirmed that, provided the fluid properties are evaluated at the mean temperature between the air and sensor temperatures, the Nusselt number is a consistent function of the Reynolds number without any further corrections. Based on this knowledge a new calibration function which accounts for temperature dependencies in fluid properties is proposed. The aim has been to come up with a calibration function that is useful in practical anemometry. The only parameters in the function are air- and sensor temperatures. Velocity calibration is only necessary at one air temperature because temperature dependencies on conductivity and viscosity are incorporated in the calibration function.
Highlights
IntroductionThe sensor is heated by means of Joule heating
The sensor is heated by means of Joule heating. It is usually operated in constant temperature mode, which means that electric current through the sensor is controlled by means of electronic control circuitry, so that the temperature of the sensor wire is kept at a constant value irrespective of the surrounding velocity- and temperature- fields
If the anemometer is calibrated at the air temperature TAcal and a correlation is made between E2 and U, measurements may be performed at the air temperature TA, different from TAcal, if the output is modified using Eq (14)
Summary
The sensor is heated by means of Joule heating It is usually operated in constant temperature mode, which means that electric current through the sensor is controlled by means of electronic control circuitry, so that the temperature of the sensor wire is kept at a constant value irrespective of the surrounding velocity- and temperature- fields. Ignoring heat losses through radiation and end conduction, the electrical power delivered to the sensor to maintain its temperature is a measure of the heat transfer from the sensor to the air and can be related to velocity. This is achieved through calibration to known air velocities
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