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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - ICOPE (Innovative COoling system for embedded Power Electronics)

Teaser

Summary

The main issue being addressed in ICOPE project is the design of innovative and efficient air cooled heat sinks to cool the power electronics modules that are a key component of the more electrical aircraft power management centre design.
This topic is of importance for the society because the improvement of air-cooled solutions in front of liquid cooled or twophase cooled units, implies the reduction of weight in the electric components of any application, together with a simplification of the system that at the end increase its reliability.
If one considers the huge penetration of electric solutions in the field of transport (electric cars, trains and high speed trains, more electrical aircraft,..) and in the renewable energy field (wind energy and solar energy conversion systems), it remains even more clear that any improvement in the performance/weight/reliability of the corresponding cooling solutions is a key factor for further developments.
Then, the overall objective of the project is the development of innovative air-cooled heat sinks, by the integration and combination of two new advanced thermal materials: Annealed Pyrolitic Graphite (APG) and Metal Matrix Composites (MMC). APG is a graphite based heat spreader, intended to reduce the temperature gradients in the base plate of the heat sink, and thus allowing to reduce poor thermal performance areas. On the other hand, MMC is a composition of aluminium and graphite, which improves the aluminium features in terms of thermal conductivity, thermal diffusivity, and thermal expansion coefficient. It is intended to replace the aluminium as APG encapsulant.
On the other hand, the integration of the heat sinks into a power management bay is also an important objective, as the success of the new heat sinks also relies on a good platform to be integrated in the aircraft. The management of the airflows and pressure drops is oriented to assure sufficient and well-distributed airflow at the heat sinks inlet.

Work performed

During the P1 project period, the work has been focused on the predesign and design phases of both the heat sink with APG and of the power management bay.
The predesign study, also supported by an interesting and detailed analysis of the state-of-the-art, has provided heat sink and bay designs that fulfil the project requirements. A combination of optimization techniques and detailed numerical studies has supported this process.
The subsequent design phase has been tackled in the P2 period, thus refining the predesign, assuring the optimum implementation of APG and MMCs into the heat sink, considering the manufacturing limits, refining some of the restrictions to obtain improved performances, etc.
Regarding Stage A, the Project has almost finished the activities, with the design, manufacturing and testing of the corresponding heat sinks. Some additional refinement/complement of the tests is still under progress. The results are fully satisfactory, accomplishing the limitations in terms of temperature level, pressure drop and weight.
Regarding the integration of APG and MMC (Stage B), some coupon samples have been investigated, analysing not only their coupling and bonding, but also trying to find the best possible MMC material for the current application. The corresponding experimental results indicate a promising bonding between both technologies. An additional numerical set-up is providing even further analysis to this particular experiment. In parallel to the coupon sample analysis, the Stage B design has also progressed, with three options in parallel to be manufactured and tested. The heat sinks are now in the manufacturing process, to be finished by the end of the year.
In relation with the bay, the design is closed for the whole structure, while still refining with the Topic Manager some details of the internal PEM (box enclosing the heat sinks).

Final results

We can summarize the progress beyond the state of the art in three fundamental points:
1-A heat sink integrating APG material has been manufactured and tested, showing results accomplishing the project requirements. This is a new application of APG, typically implemented as heat spreaders between solid surfaces.
2-The APG sheets have been successfully encapsulated by MMC instead of aluminium. This combination is a strong innovation compared to the state of the art. Further testing is required to consolidate the initial results.
3-The feasibility of the implementation of the new heat sinks has been assured by the successful design of a power management bay that minimizes the space needed while providing a good flow distribution for the different heat sinks. This needs to be confirmed by the corresponding experiments.