This work reports the convection calibration of Schmidt-Boelter heat flux gages in shear and stagnation air flow. The gages were provided by Sandia National Laboratories and included two one-inch diameter and two one-and-one-half-inch diameter Schmidt-Boelter heat flux gages. In order to calibrate the sensors a convection calibration facility has been designed, including a shear test stand, a stagnation test stand, an air heater and a data acquisition system. The current physical model for a combined radiation and convection heat transfer environment uses an additional thermal resistance around the heat flux gage. This model clearly predicts a non-linear dependency of the gage sensitivity over a range of heat transfer coefficients. A major scope of this work was to experimentally verify the relation found by the model assumptions. Since the actual heat sink temperature is not known and cannot be measured, three different cases have been examined resulting in three different sensitivities for one pressure value, which is the gage sensitivity for the not cooled case and the gage sensitivity for the cooled case, based on the plate temperature or on the cooling water temperature. All of the measured sensitivities for shear as well as for stagnation flow fit well in the theory and show the non-linear decay for increasing heat transfer coefficient values. However, the obtained data shows an offset in the intersection with the sensitivity at zero heat transfer coefficient. This offset might arise from different radiation calibration techniques and different surface coatings of test gage and reference standard. / Master of Science

Heat flux gages are important in applications where measurement of the transfer of energy is more important than measurement of the temperature itself. There is a need for a heat flux sensor that can perform reliably for long periods of time in high temperature and high heat flux environment. The primary objective is to design and build a heat flux sensor that is capable of operating for extended periods of time in a high heat flux and high temperature environment. A High Temperature Heat Flux Sensor (HTHFS) was made by connecting 10 brass and steel thermocouple junctions in a thermopile circuit. This gage does not have a separate thermal resistance layer making it easier to fabricate. The HTHFS was calibrated in a custom-made convection calibration facility using a commercial Heat Flux Microsensor (HFM) as the calibration standard. The measured sensitivity of the HTHFS was 20.4 ±2.0ìV/(W/cm2). The measured sensitivity value matched with the theoretically calculated value of 20.5 ìV/(W/cm2). The average sensitivity of the HTHFS prototype was one-fifth of the sensitivity of a commercially available HFM. Better ways of mounting the HTHFS in the calibration stand have been recommended for future tests on the HTHFS for better testing. The HTHFS has the potential to be made into a microsensor with thousands of junctions added together in a thermopile circuit. This could lead to a heat flux sensor that could generate large signals (~few mV) and also be capable of operating in high heat flux and high temperature conditions. / Master of Science