Abstract:

A dynamic calibration technique for evaluating the thermal product values of different scratched temperature sensors is presented. These sensors have renewable junction, fast response time and it can be used for transient heat transfer measurements in hypersonic vehicles. Two types of scratch were used, mainly abrasive papers with different grit sizes and scalpel blades with different thicknesses to form the sensor junction. The effect of scratch technique on the sensor's thermal product is investigated. The sensors were tested in shock tube facility at different operating conditions. It was observed that the thermal product of a particular sensor depends on the Mach number, surface junction scratch technique, junction location as well as on the enthalpy conditions. It was also noticed that using scalpel blade technique with a particular blade size gives consistent thermal product values. Thus, it does not require an individual calibration. However, for sensors whose junction created using abrasive paper technique with different grit sizes, a calibration for each sensor is likely to be needed. The present results have provided useful and practical data for thermal product values for different scratched temperature sensors. These data are beneficial to the experimentalists in the field and it can be used for accurate transient heat transfer rate determination. Furthermore, the present calibration technique has shown that the response time of these sensors is on the order of microseconds (less than 50 μs) and it has a rise time less than 0.3 μs. A numerical technique was used in the calculation of the heat transfer rate by developing a MATLAB routine to obtain the transient heat flux history from the measured surface temperatures history.