Double sided Kapton heat flux gauges which are used routinely by the Ohio State University Gas Turbine Laboratory are driven by two main calibrations, the sensors temperature as a function of resistance and the material properties of Kapton. The material properties separate into those that govern the steady-state response of the gauge and those that influence the transient response. The steady-state response, as it forms the key to data processing, will be the topic of this investigation and is based on the thermal conductivity divided by the thickness (k/d).
Calibration accuracies for the heat flux gauge sensors reached levels on the order of +-.05 °C and were well within the target accuracy of +- 0.1 °C over a 100 °C calibration range. Time degradation of the gauges did occur and for these cases and a single point calibration method is introduced that maintains the accuracy to ±0.4 °C instead of the ± 3 °C that would have resulted from the resistance shift due to erosion. This method will allow for longer use of the gauges in the turbines.
Various calibration methods for k/d were investigated and performed. Of the three methods presented, a hot air method provided the best results of a single value. For 1 mil Kapton k/d was calculated to be between 8520 - 8882, or a k = 0.2164 - 0.2256 W/mK (a 4% variation). Different gauge thicknesses were calibrated using a variety of methods resulting in similar values of thermal conductivity, although each method had different limitations on its accuracy.