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Pulsating Heat Pipes for Hybrid Propulsion systems

Periodic Reporting for period 2 - PHP2 (Pulsating Heat Pipes for Hybrid Propulsion systems)

Reporting period: 2020-05-01 to 2021-10-31

The project has 3 main objectives:
- Build a test bench and manufacture Pulsating Heat Pipes (PHP)
- Create a results database from a set of experimental campaigns and numerical simulation
- Develop and validate a physical as well as a mathematical numerical models
Technical challenges are numerous due to an incomplete understanding of PHP operation in the scientific literature, e.g. the lack of good design theories and of viable, comprehensive simulation tools to describe the thermal/hydraulic performance of a PHP. Furthermore, PHP are a new disruptive cooling technology that need to gain their acceptance into engineering practice.
The present project offers cooperation between JJ Cooling Innovation and Provides, leaders in the modelling, design and fabrication of high-performance micro-two-phase cooling systems using state-of-the-art components and heat exchangers, and Altran, world-leader in Engineering Solutions and outsourced R&D, through their Expertise Centres “Fluids and Thermal Engineering” and “Scientific Computing Methods and Tools”.
Eventually, the outcome model delivery will allow the Topic Leader to propose a new generation of PHP’s to better serve the cooling needs for hybrid propulsion systems. Finally, EU industrials, scientific community and environment shall greatly benefit from this study, thanks to the dissemination of this work.
Achieving high fidelity information and methods developed for the design and characterization of PHP cooling elements will help in:
- minimizing the number/size/weight/fluid charge of these cooling elements to cool power electronics
- optimizing the heat exchange performances
- reducing the maintenance costs in mechanical parts (as pumps and fans will be eliminated) as well as reducing the volume/mass of the cooling systems

By using more accurate methods and models, industrials will develop more efficient systems with less conservative approaches for cooling systems and thermal protection. All these improvements will result in lower engine weight and space optimization, therefore less fuel consumption and pollution. This will directly benefit to the whole European Union population through cleaner air and cheaper travel.
WP1 consists of Project Management and Dissemination throughout the project life. The work carried corresponds to what was expected at the beginning.
Signature of the agreements are quite on time (signature and upload delay). Dissemination and Exploitation plans have been delivered on time.
The PHP2 website has been created on time and it is currently available:
In October 2021, all partners attended a Workshop in Toulouse (hosted by Altran and LTS). Altran, JJ Cooling Innovation and Provides have been collaborating to disseminate information on the project and results by different means:
• Altran, JJ Cooling Innovation and Provides internal dissemination processes (internal reviews, conferences and press)
• Public conferences
• Scientific publications and seminars

WP2 aims to develop a PHP modelling tool.
A detailed bibliography dedicated to the state of the art on PHP modelling methods and recent achievements has been delivered (D2.1).
The principal task of this WP is however to develop an advanced 1D numerical tool capable of describing the behaviour and performances of a PHP. The consortium has designed consistent PHP demonstrators (tubular PHPs) for the validation, improvement and further development of the 1D numerical tool for PHP modelling. Such an engineering tool is expected to improve the efficiency/speed of the development of future PHP designs and multiply their application domains. During the second period of the project two main topics were addressed: the implementation of several improvements to the numerical code and the validation of the code using the experiments as reference. With these improvements, the accuracy and stability of the code have been increased and the simulation time has been reduced.
Since the beginning of the project, more than 3600 simulations were run with the PHP2 experimental data to test and validate the several updates made on the model.

WP3 includes The Design of Experiments (DoE), the experimental campaign and the construction of a macro-mathematical model capable of predicting the performances of a “random” tubular PHP design.
The consortium is in charge of the design of the PHP demonstrators used for the experimental tasks of this WP. The number of experiments has been fixed in this WP and agreed by all the partners. The consortium has chosen to manufacture the first prototype to validate the 1D model developed by JJ Cooling Innovation from WP2 and Altran has developed the DoE based on geometrical and experimental specifications defined jointly. The Design of Experiment report (D3.1) has also been delivered on time. Provides is leading the experimental campaign using the test bench and the design of experiment designed during the first period. Up to the end of period 2, 7 prototypes have been tested. For each geometry, several operating conditions are tested (i.e. fluid, filling ratio and angles).
Using the database gathered with this experimental campaign, Altran trained and validated several mathematical macro-models. An optimization loop has been developed with an FMU/FMI compliant interface in order to use the trained model for pre-design purposes: given, for example, a set of operating conditions, the optimizer will find the geometry that minimize the thermal resistance.
According to these conclusions, the next geometry to test is constantly re-evaluated by the consortium to optimize both the knowledge gained with the tests and the performance of the macro-model.
Pulsating heat pipes are a promising disruptive passive heat transfer technology ready to emerge, but have been hindered in industrial applications by the lack of a suitable thermal-fluidic design method. The current method proposed for that task within this project implements a mechanistic numerical 1D model of PHP operation, which tracks, via a transient 1-D model, the motion and heat transfer to/from vapour bubbles, liquid slugs and liquid films as distinct phases.
The 1D detailed model used in PHP2 project adapts a state-of-the-art, well-validated prediction method for microchannel evaporation to PHPs, specifically, one which offers a physical basis where and when phase change occurs relative to slug passage and a model to predict the initial liquid film thickness. This will unlock the possibility to find the best trade-offs between thermal performance, micro-fabrication capabilities and its tooling for the microchannels of the PHP.

The project has chosen to develop a new pre-design tool using several macro-mathematical methods based on the wide experimental and numerical database. The construction of those reduced models based on accurate numerical or experimental results allows reducing considerably the restitution time of results. Therefore, time and money are saved while keeping a correct accuracy. The use of surrogate models is part of new studies and many industrials will improve their pre-design phase by using similar methodologies for reduced models.