To power all the functions of future decarbonized aircraft, a much greater amount of electricity will be required than is currently available today, propulsive or otherwise. However, traditional heat exchangers are not efficient enough, too bulky and too heavy, and therefore not the answer when it comes to releasing the heat flows generated by this extra electricity.
This challenge gave rise to the ECCAD project (Compact Heat Exchanger for Decarbonized Aircraft), supported by France's Civil Aviation Authority (DGAC), France Relance, and the EU. Between 2021 and 2024, the project also brought together Sogeclair Aerospace (project manager and additive manufacturing heat exchanger expert), AddUp, ONERA (French National Office for Aerospace Studies and Research) and two CEA institutes: Liten and List.
From design to mockup testing: deploying an innovative, comprehensive chain
“We have been chosen specifically for our expertise in heat exchangers and equipment.
For three years we have been deploying an innovative, comprehensive chain: design, simulations, optimizing additive manufacturing, designing a test bench, mockup testing, etc.," explains Pierre Coste, Project Manager at Liten.
In search of a more compact solution, a prototype proposed by two ECCAD partners was immediately favored over the classic parallelepipedal exchanger. However, its convergent circular shape meant that additive manufacturing (AM) had to be used. The challenge lay in meeting the increasingly significant power and integration needs of the heat exchangers. “Our main aim was to optimize its design, to achieve far superior performance while also accounting for the constraints of AM."
Rough parts are an advantage, not a disadvantage
Researchers developed a comprehensive model exchanger, before using multiparameter optimization algorithms to determine the ideal shape for both the hot (water-glycol fluid) and cold (air) sides of the exchanger. With further optimization in mind, they also took into account the inherent roughness of aluminum alloy parts printed in 3D. According to Pierre Coste, “it isn't necessarily a disadvantage, and may even enhance the performance of the exchanger."
This work has facilitated a comparison between the performance of the three different fin shapes, more specifically those increasing the surface area of the walls between fluids. While the first two of these fins, OSF and Wavy, are already used in commercially available products, TPMS was brand-new. Although not included in the project's final solution, having been deemed insufficiently developed, this unprecedented part did pave the way for the filing of two patents.
Improving the shapes of exchangers for all kinds of applications
An existing test bench was adapted to validate the design on reduced-sized mockups (100 x 100 x 200 mm). This led to changes that included the addition of temperature, pressure and flow sensors; and of powerful compressors to reproduce the airflows of an airborne aircraft. “It was on this test bench that we determined that the OSF's shape was better suited than that of the others."
The OSF fins that were chosen are nevertheless innovative in terms of their pointed shape, tilt and ultra-thinness that push the limits of mechanical strength. A Liten team also focused on the 3D printing recipes and the post-treatment processes, carrying out more tests on samples. “ECCAD has enhanced our internal expertise in the design of innovative exchanger shapes.We can now use that in many other applications," says Pierre Coste.
Credit CEA