HTCC Heat Flux Sensor using Printed Type-K Thermocouples

Schmidt-Boelter heat flux gauges are commonly used in aerospace testing to measure heat transfer at the surface of a test article, which is essential for the safety and performance of various components in in-flight systems. This gauge is often employed in testing and analyzing thermal protection systems, heat exchangers, and other areas where precise temperature readings are vital during dynamic operating conditions, such as ascent, re-entry, or extreme environments. Schmidt-Boelter gauges are essential in aerospace engineering, offering precision and responsiveness for maintaining the integrity and functionality of aircraft and spacecraft components.  Due to their current manufacturing limitations, small size, and intricate nature, these sensors are handcrafted one at a time, limiting their size, sensor-to-sensor accuracy and repeatability, and flexibility in applications that could be achieved with an automated process. Additionally, the current design limits the maximum usable temperature to 500 °F. Further complicating the process, a sensor installed in a test article cannot typically be removed without destruction. Advanced ceramics manufacturing technology allows microelectronics features to be mass-produced at a micron scale. We propose a path to additive manufacturing of SB heat flux sensors that are compatible with operation at 1000 °C in air or oxidizing environments.  We propose to use ink and paste materials of type-K (chromel and alumel) thermocouple materials to print thermopiles on laser-machined alumina ceramics. Thermocouples fabricated  with these ink dispersions have already been tested to 300 °C and shown to response almost identically to wire-based type-K thermocouples.  We propose to use pins brazed into some of the vias to act as mechanical contacts for lead extensions from the heat flux sensor.  We propose to demonstrate operation to 815 °C with a stretch goal of 1000 °C.  We propose to use borosilicate glass frit to help match thermal coefficients of expansion (CTE)  and to promote adhesion of the type-K printed thermocouple materials.