On the temperature dependence of constant temperature hotwire probes with small wire aspect ratio

An experimental investigation of the temperature dependence of small aspect ratio hotwire probes operated at constant temperatures has been carried out. Measurements of the wire properties have resolved the experimental uncertainties reported by Davies and Fisher (1964). Data evaluation was carried out using both constant velocity and constant overheat ratio methods. A considerable velocity dependence of the nonlinear temperature term was established. The temperature dependence of the slope parameter B in a constant exponent power law approximation was found at high velocity to be of opposite sign to the low velocity results of Collis and Williams (1959). Good approximation of the measured calibration data by a constant exponent power law was obtained when the value of the exponent n was set equal to 0.45 at low velocity and to 0.42 at high velocity.