PhD Position: Advanced Characterization of Densified Cryogenic Hydrogen

Department Environmental and Applied Fluid Dynamics
Deadline Dec. 1, 2021

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“A scientist studies what is, whereas an engineer creates what never was“, Théodore von Kármán

Duration: 4 years

Deadline Submission: 1st December 2021

About the research topic

One of the main challenges of using gaseous or liquid hydrogen as energy carrier is related to its very low volumetric energy density. A promising solution to increase the energy storage capabilities of hydrogen is to densify it to its slush state: a multi-phase mixture of vapor, liquid and solid crystals near to the thermodynamic triple point temperature. Slush hydrogen features, indeed, 15% higher volumetric energy density and 18% lower enthalpy with respect to the single-phase liquid state, resulting in a better resistance against boil-offs and heat losses. These characteristics enable longer holding time and reduced insulation requirements in hydrogen energy storage and transportation. However, such benefits come with many scientific and technical challenges.

This research topic ambitiously aims to dive deeper in the advanced characterization of thermodynamic slush properties, such as the slush composition (crystals shape and size), the slush rheological features, and the aging dynamic (stratification and melting). The focus would be to better describe and model the slush during storage, both experimentally and numerically.

Figure 1 Left: CryMe cryostat, Right: Nitrogen slush

Experimentally, nitrogen slush (as shown in Figure 1 right) would be generated at the von Karman Institute using the CryMe (Cryogenic Microgravity Experiments) facility, shown in Figure 1 left, which is a fully customized cryostat, for the characterization of cryogenic sloshing, boiling and thermal stratification on earth and in microgravity conditions at temperature down to 70 K. Measurement techniques would be then adapted to experimentally characterize the particle size distribution and shape of the generated slush particles, as well as the evolution of these parameters with time (ageing).

In parallel, numerical simulations using the direct-forcing immersed boundary method for the simulation of the particles, would allow to determine the rheological properties of the mixture. The direct-forcing immersed boundary method belongs to the family of Fictitious Domain Methods where the flow equations can be solved on a fixed grid while the presence of the solid bodies immersed in the flow is imposed by means of adequately formulated source terms added to the Navier-Stokes equations. The idea is to determine a singular force distribution at Lagrangian positions, coinciding with the physical boundary of the rigid body immersed in the flow as shown in Figure 2, and to apply it to the flow equations in the fixed reference frame.

Such model has already been developed in 2D in the framework of understanding the interaction of molten fuel with liquid metal in case of leakage from the core, in the framework of the development for the generation 4 nuclear reactor Myrrha, as part of safety protocol to estimate the damages connected to the worst-case scenario of the core meltdown. The focus of this PhD would be to further develop it to 3D, further improve the modeling of arbitrary shaped particles using IBM, and then use the model in control volume to determine the rheological properties, and the ageing of the slush.

Figure 2 Left: schematic of immersed boundary method. Right: 2D evolution of radioactive, arbitrary shaped particles

About Be-Hyfe:

The von Karman Institute for Fluid Dynamics is proud to be part of the project Be-HyFE (Belgian university Hydrogen Fundamental Expertise), the Belgian base for hydrogen expertise. Ghent University, together with 13 partners, is building a PhD network for academic hydrogen expertise in which VKI is full partner and is hosting one of the PhDs.

With the PhD network, we will support the industry in their technical and societal challenges related to hydrogen R&D. 16 Early Stage Researchers (PhDs) will execute a PhD in selected hydrogen topics, covering the whole hydrogen value chain.
In addition to the research itself, emphasis will be placed on acquiring specialized skills through training and the exchange of knowledge within the academic-industrial network. The project will run for 4,5 years, is coordinated by Ghent University, and is financially supported by the Belgian federal Energy Transition Fund and the FPS Economy.


Good mathematical background and basic numerical algorithm is required. Good programming skills are required in at least one of the following languages: C, C++ as well Matlab or Python. Experience in numerical methods (preferably finite element method, finite volume method and pseudo-spectral methods) is a plus. Experience or development of simulation tools for fluid dynamics or other discipline is highly appreciated. In parallel, knowledge in image processing and elementary laboratory experience in measurement techniques for fluid dynamics is a strong plus.

The candidates are expected to:

- have a very good knowledge of English (spoken and written);

- be team players;

- be able to work independently, accurately and methodically;

- should be willing to present research findings at national and international conferences and publish in international journals.


Employed for 48 months by the von Karman Institute for Fluid Dynamics in one of the most attractive areas of central Europe in the neighborhood of Brussels.

Work at the internationally renowned von Karman Institute in a key role advancing technologies for future energy systems;

Work in close collaboration with Belgian universities as well as an industry network;

Become part of the VKI network with global access to industry experts and academics in the field of fluid dynamics, aerospace, propulsion, and energy conversion;

Experience the unique international workshop character of the VKI working environment.

Access to specialized seminars and lecture series and to world-unique facilities.


Candidates can be of any nationality.

Candidates must not have yet been awarded a doctoral degree.

VKI does strictly adhere to the ethical standards of the European Charter for Researchers and Code of Conduct for the Recruitment of Researchers ( . Female scientists are particularly encouraged to apply. A strict equal opportunity, gender-neutral and internationally comparable recruitment procedure is implemented.

Contact information

For further information, please contact Pr. Delphine Laboureur ( and by phone (+32 2 359 96 14).

How to apply

Applications must contain a CV, motivation letter, publication list, contact information of two referees, copy of the Degree and Master title. CV must clearly indicate the exact dates of (1) each position hold in the past, and (2) countries of residence in the last 5 years.

All the fields (including pdf files and references) should be filled in to allow you to confirm your application. Only full applications will be taken into account. Please do not use white spaces or special characters to name your files. If you have not received a confirmation email it means that you have not fulfilled all required fields.

Short-listed candidates are called for an interview with the search committee at the von Karman Institute. The selected candidate must comply with the internal procedures of the von Karman Institute before she or he can begin to work. The von Karman Institute reserves the right not to appoint a candidate if no suitable candidate is found.

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