Beyond the limits of cooling systems
The miniature sensor was designed within the EU-funded project CORA (Sensor for convective and radiative heat loss) to detect heat transfer due to convection and radiation separately. This is of particular interest in the tough avionics environment where electronic and mechanical equipment needs to be cooled. In particular, electronic components depend on the passage of electric current to perform their duties and become sites for excessive heating because current flow through a resistance is accompanied by heat generation. The miniaturisation of these systems has resulted in a dramatic increase of heat generated per unit volume. The main feature of the new sensor to be installed on the surface of such components is its extremely small dimensions. Flexibility in its geometric construction also ensures that for the same air flow conditions, a twist of the sensor would not have a noteworthy effect on the measurement result. With the CORA sensor, heat transfer is determined by commercial thermoelectric cooler modules, also known as Peltier modules. The temperature of the surface is determined with an integrated thermocouple. Two heat flux sensors serve as sensing elements. To achieve the measurement precision needed under extreme conditions, a dedicated calibration procedure was developed. A suitable test set-up was constructed to ascertain thermal and electrical properties of the sensor components experimentally. Besides the sensor elements, the evaluation encompassed the electronics, the electrical connection to the data logging system, and the graphical user interface for measurement and configuration. The tests confirmed a current resolution of about 2 W/m2 that can be further improved by filtering. By arranging several sensors in an array, hotspots can be identified and, if necessary, eliminated by making structural modifications. This way, it is possible to utilise larger areas for the cooling of aircraft components and passively dissipate the excessive heat. The sensor device developed within the CORA project is especially attractive for future more-electric aircraft architectures that will pose new challenges for the management of electric power.
Keywords
Heat transfer, sensor, electronic equipment, aircraft, CORA, heat loss