Cool your jets: ICOPE tackles new challenges in thermal management
The trend in aviation towards electrification presents new challenges, one of which is managing the unwanted by-product of electrical systems: heat. An ineffective dissipation of heat could lead to a drop in the efficiency of specific airborne systems. Clean Sky’s ICOPE (Innovative COoling system for embedded Power Electronics) project explores new approaches to onboard thermal management using novel air cooled heat sinks and advanced materials.
With hydraulics and pneumatics becoming progressively superseded by electrical systems as aviation evolves into a more ecological future, Clean Sky has been focusing on effective and sustainable solutions oriented around thermal management. This not only improves the science of onboard cooling for aircraft systems, but also paves the way for boosting the European aviation industry’s knowledge and expertise in anticipation of the next generation of aircraft, when electricity will be used not just for the aircraft’s systems but also for propulsive power. Moreover, Clean Sky, backed by the European Commission, is creating the prerequisite techno-bricks that will enable hybrid-electric (and eventually fully electric) aircraft to cope with the heat management challenges associated with onboard high voltage electricity generation, storage and safe relaying to electric fans that will ultimately replace today’s turbine, turbofan and turboprop engines.
In recent years, the trending technologies used for cooling power electronics and other semiconductor devices have moved from air cooled solutions to liquid cooled (or twophase flow solutions, using evaporation), as these are more effective in managing higher levels of heat transfer density, enabling electronic equipment to function within suitable operating temperatures.
But with new types of power semiconductors becoming more commonplace in aircraft, which are made from heat-efficient materials, it now makes sense to re-evaluate the use of air cooled systems, as these weigh less and are generally more reliable and require less maintenance.
’Silicon carbide (SiC) and gallium nitride (GAN) can withstand much higher temperatures than usual materials, and also reduce the losses to evacuate,’ says Marc Pontrucher, research and technology development manager at Thales, referring to these new power semiconductors. ’These open a window to revisit the option of air cooling, which has many advantages in terms of equipment simplicity, reliability, environmental impact and cost.’
Mathieu Bouton, hardware specialities thermal and mechanical engineer at Thales, adds that ’there is a real advantage of using air cooling Power management bay cooling air duct assembly concept model because the overall mass of heatsink and cooling system will decrease, it’s an easier solution to be integrated into our products, and it’s a more reliable option. Regarding the air cooling, the only point to increase efficiency is to use innovative materials for the heatsink in order to obtain the maximum area of exchange and the minimum thermal resistance.’
Hence, Clean Sky’s ICOPE project, which started in May 2017 and is near completion, focuses on developing new concepts for air cooled heat sinks using advanced thermal management materials including annealed pyrolytic graphite (APG) and metal matrix composites (MMC) such as aluminium graphite, which have been identified as potentially suitable candidate materials. The project also looks at integrating some newly developed heat sinks into a thermal management bay.
The ICOPE Consortium draws on the expertise of heat sink and APG design specialists Aavid- Thermal Division of Boyd Corporation; as well as the knowhow of Schunk Carbon Technology, experts in the field of MMC. This team is complemented by the analytical skills of the Heat and Mass Transfer Technological Center (CTTC) of Universitat Politècnica de Catalunya (UPC) who have specific competences in analysing air cooled heat exchangers and air flow in enclosures.
The project involves the development of two new types of heat sink: (A) which uses annealed pyrolytic graphite (APG) and has folded fins, while the second type (B) combines metal matrix composites (MMC) with APG. A final task focuses on the design, manufacture and testing of a power management system bay which incorporates four heat sinks to provide even and efficient air distribution with an adequate flow and velocity distribution.
’ICOPE is investigating the development of novel air cooled heat sinks to go beyond the limit in terms of electronics air cooling,’ explains Dr. Joaquim Rigola, who is a professor at UPC and coordinator of the ICOPE project.
’The main innovat ive aspect is the implementation of advanced materials with outstanding thermal conductivities, which activate a higher primary surface of the heat sink, further beyond the surface of the heat sources (Stage A of the project prototypes). The project is also incorporating other materials that introduce an additional benefit in terms of expansion and contraction characteristics (Stage B of the project prototypes), aligning better with the behaviour of the semiconductors, then minimising the thermal stresses between them and increasing the reliability and safety of the units,’ indicates Dr. Carles Oliet, adjunct professor and researcher at UPC.
’The current status of the project is very advanced for Stage A prototypes,’ says Dr. Rigola. ’They have been already manufactured and successfully tested, covering the requirements set by the topic manager in terms of maximum base temperature, maximum pressure drop and maximum weight. Regarding Stage B prototypes, they have already been designed, suggesting three different combinations of materials. These alternatives are in different stages of development, one ready to be tested and the other two undergoing manufacture. Regarding the bay, the design is also closed and the manufacturing under progress. In summary, the project is evolving adequately with very interesting results and prototypes that cover the initial expectations.’
’The implementation of air cooling for the electronics is a simpler and more reliable option, that could avoid the use of additional circuits and components related to the liquid or two-phase cooling,’ says Dr. Oliet. ’The potential reduction in overall cooling system weight also implies a very interesting output to increase the competitiveness of the industry.’
Looking at the broader societal gains for Europe, Dr. Rigola says that the ICOPE project has benefits that are applicable in other sectors beyond aviation:
’Some outcomes of the new designs can also impact other energy generation and conversion industries, as the cooling of power electronics is in increasing demand in those sectors. For example, within the energy conversion in a wind turbine nacelle there are similar power management bays with several power conversion modules. Also within any variable-speed controlled motor in the cooling/refrigeration and heat pump industries, there is a need to cool down the associated power electronics.’