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Development, construction, integration, and progress toward to two-phase device monitoring and qualification on aircrafts

Final Report Summary - AEROL-HP (Development, construction, integration, and progress toward to two-phase device monitoring and qualification on aircrafts)

Executive Summary:
The developed technology in the Aero-L HP program corresponds to a thermal system for aeronautical applications (business jets) based on two-phase heat transfer phenomenon; it means that the heat is evacuated thanks to vaporization and condensation of a fluid contained in the thermal device.
This device is passive so that no electrical input is necessary to make it function, its activation is only due to the heat dissipation. This device allows carrying heat from equipment’s located in the inner aircraft side (cabin calculators and wing actuators equipment’s) to the aircraft structure (cold source) thanks to its flexibility (piping). Indeed, the thermal device is composed of 5 mini-loop heat pipes (mini-LHP) filled with acetone that are distributed on the face of the equipment to be cooled (on their evaporators) and share the total heat to dissipate. The condenser lines of the mini-loop heat pipes are assembled on saddles which are connected to the plane structure.
Such a solution has been selected for the cooling as the best compromise between thermal, hydraulic, mechanical performances, mass, flexibility, cost and modularity criteria’s.
The integration of such a two-phase thermal device in an aircraft allows significantly reducing the maximal temperature at equipment using a light and passive thermal device. This leads to an increase of equipment’s reliability combined with a fuel consumption reduction.
In addition, a monitoring solution has been proposed to allow managing the AeroL-HP cooling device implemented in an aircraft. The monitoring study has demonstrated the detection of all degraded or failure modes of the LHP’s identified in the risk analysis.

This project has been performed in collaboration with Dassault Aviation (DAv) as topic manager, Fraunhöfer Institute for thermal tests in representative environment of aircraft and Epsilon as partner for the development of the thermal mathematical model (1D modelica model).

After tests in calorimeter (test set-up representing an aircraft fuselage) at Fraunhöfer Institute, EHP thermal device could reach TRL4 (Technology Readiness Level 4) following DAv evaluation; that is to say successful testing in a representative ground test facility.
The potential applications identified by Dassault for such thermal device are the cooling of battery control units, electrical ice protection units, electrical power distribution units, in-flight entertainment systems,...as well as Electromechanical actuators for horizontal tail plane trim and future actuators for flight control surfaces. All these equipment’s correspond to future high level business jets.

Project Context and Objectives:
The general objective of AeroL-HP is to strengthen the competitiveness of the European industry by introducing heat management systems, which will allow aircraft companies to:
1) make lighter and more efficient systems, leading to considerable savings in consumption of fuel,
2) reduce the environmental impacts with passive and maintenance free cooling devices,
3) increase the reliability of the controlled power equipment’s leading to extended life cycle.
All these elements will contribute to a global reduction of CO2 emission and will contribute to the success of the “all-electric” aircrafts.
The developed thermal device will offer remote accommodation of highly reliable power Electronics. This technology is based on the use of a flexible thermal device composed of 5 mini-loop heat pipes and will carry heat from equipment’s located in the inner aircraft side (cabin calculators and wing actuators equipment’s) to the aircraft structure (cold source).
The thermal dissipated power objective of 250W could be reached for the specified range temperatures between -55°C and +70°C. For the low temperatures range between -55°C and -10°C, a thermal power up to 450W could be reached. This performance is obtained for a thermal device mass of 1Kg.

Project Results:
A detailed aeronautical specification has been defined by Dassault Aviation in terms of power, temperatures and environment.
Based on this specification, a thermal device could be designed.
The selected thermal device design was the result of a trade-off between several potential thermal solutions and corresponds to the best compromise between thermal, hydraulic, mechanical performances, mass, cost, heritage and modularity criteria’s.
A breadboard (BB) has been manufactured and tested to mitigate the technological and design risks. This BB corresponds to one mini-LHP filled with acetone. The BB tests showed good performances in terms of heat transfer capacity, start-up capabilities and robustness to geometrical orientation.
The monitoring procedure of the thermal device has been defined. It allows detecting all degraded or failure modes of the LHP’s identified in the risk analysis.

This BB allowed defining with precision the qualification model (QM) design which corresponds to a set of 5 mini-LHP’s filled with acetone able to dissipate a power of 250W between -55°C and +70°C.
A thermal model (Modelica type) has been issued by Epsilon; design partner in the project.
For Dassault, this Modelica 1D model of the loop heat pipe developed in the frame of the AeroLHP project is very useful to perform high level architecture trade-offs. Indeed, it allows for assessing the thermal efficiency of a loop heat pipe integrated inside a complete aircraft thermal model, compared to other devices. This allows determining the intrinsic interest for such innovative technologies, and eventually make technology choices.
Dassault is very keen on knowing the state of the art as regards to thermal management of future Platforms.
After detailed design phase, the QM thermal device has been manufactured and successfully submitted to thermal acceptance tests at EHP and to thermal tests in representative environmental conditions at Fraunhöfer (tests of the thermal device mounted in the calorimeter).
No particular change in thermal behavior was noticed between EHP and Fraunhöfer tests.

The thermal dissipated power objective of 250W could be reached for the specified range temperatures between -55°C and +70°C. For the low temperatures range between -55°C and -10°C, a thermal power up to 450W could be reached. This performance is obtained for a thermal device mass of 1Kg.

The next step shall be an increasing of the TRL up to a qualification model level. This means the following qualifications:
* Aeronautical mechanical qualification (vibrations, shocks)
* DO160 environmental validations (fungus, fire,...)
In addition, an optimization of the mini-LHP design shall be performed in order to cope in a better way to aeronautical fluid constraints (acetone is used). Such an optimization will allow increasing the maximal power to be transferred per mini-LHP and so reducing the global mass of the thermal device.

Potential Impact:
After tests in calorimeter, EHP thermal device could reach TRL4 (following DAv evaluation); that is to say successful testing in a representative ground test facility with a fully functional (although still under development) design.
Following DAv, this configuration is suitable for aircrafts application with power loads <250W.
The potential applications identified by Dassault for such thermal device are the cooling of battery control units, electrical ice protection units, electrical power distribution units, in-flight entertainment systems,...as well as Electromechanical actuators for horizontal tail plane trim and future actuators for flight control surfaces. All these equipment’s correspond to future high level business jets.

Several dissemination activities have been done during the project. These correspond to international dissemination through presentation of EHP developments and products for aircraft applications out of Europe and through attendance to relevant European meeting/conferences.
After Aero_L project closure, dissemination of results will be proceeded each time a relevant conference will be identified and by presentations of final results and performances to customers.
The potential impact of integrating such a two-phase thermal device for electronic dissipating equipment is the increase of equipment reliability by a significant reduction of maximal temperature and by the use of a passive thermal device.
Such a thermal device can be integrated and used in aircraft dissipating equipment's but can also be extended to a wider field of applications for heat loads of 250W and environment temperature varying from -55°C to +70°C. The maximal heat load to be transferred can be increased by increasing the number of loop heat pipes integrated in the two-phase thermal device.

The next step shall be an increasing of the TRL up to a qualification model level. This means the following qualifications:
* Aeronautical mechanical qualification (vibrations, shocks)
* DO160 environmental validations (fungus, fire,...)
In addition, an optimization of the mini-LHP design shall be performed in order to cope in a better way to aeronautical fluid constraints (acetone is used). Such an optimization will allow increasing the maximal power to be transferred per mini-LHP and so reducing the global mass of the thermal device.