High-Temperature Heat Flux Sensor Based on Tungsten–Rhenium Thin-Film Thermocouple

Heat flux sensors (HFSs) are extensively used in combustion-related applications to collect important engineering data. However, most non-water cooling HFSs lack the durability to survive in the harsh, high-temperature environments where they are employed. A new type of thin-film HFS based on a W-5Re/W-26Re thermocouple has been developed for high-temperature heat flux measurement. The sensor consists of 136 pairs of micron-sized W-5Re/W-26Re thin-film thermocouples, an SiO2 thermal-resistance layer, and an AlN substrate. The SiO2 layer is sandwiched between the substrate and thermocouples, and allows the measurement of temperature differences arising from the difference in thermal conductivity between the substrate and the SiO2 layer. A protective layer with a sandwich structure prevents the tungsten-rhenium thin film from oxidizing at high temperatures in air. This small HFS with a protective layer can survive for 1 h in 1000°C air. Calibration data show that the HFS exhibits repeatable and fast thermal responses when a pulsed heat flux of 1000 kW/ $\text{m}^{2}$ is applied, and its sensitivity is 3.8* $10^{-6}$ V/(kW/ $\text{m}^{2}$ ). The experimental data agree with the simulated results. It can be concluded from the experimental results that the tungsten-rhenium thin film has a good thermoelectric response to high temperatures after the size is reduced to a micron. Thus the developed HFS can be a suitable alternative for applications in thermal systems, such as engines, turbines, and rockets.