Investigation of heat transfer from thin wires in air and a new method for temperature correction of hot-wire anemometers
Hans Lundström
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.