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

Abstract

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 SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thermal-resistance layer, and an AlN substrate. The SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is applied, and its sensitivity is 3.8*10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> V/(kW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). 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.