Experimental Studies on Temperature Effects of Freestream and Hot Wire Sensors on the Calibration Curves and Velocity Measurements

In this paper, the effects of two important parameters on characteristic curves and the calibration of hot films and hot wires are studied experimentally. One of them is the freestream temperature and the other is the probe temperature or probe overheat ratio. The results show that increasing the wind tunnel (freestream) temperature decreases the voltage of the Wetston's bridge in the Constant Temperature Anemometry (CTA) circuit. It must be noted that, the decreasing rate depends on the physical properties of sensors, the flow velocity, and the overheat ratio. Temperature correction factors can be used for modification of these errors. Also, consideration of probe temperature shows that the calibration curves of a probe, in different overheat ratios, can be matched using a suitable correction factor, i.e. if the calibration curves of a probe were available only for two different overheat ratios, the other calibration curves for any arbitrary one can be obtained.