Safouene Ouenzerfi's defense (mechanical engineering department)

Battery thermal management systems are essential for high-performance electric vehicles, where the ability to remove heat and homogenize temperatures in individual cells and packs are key considerations. There are currently a number of BTMS (Battery Thermal Management Systems) available, ranging from active air cooling to indirect methods based on external liquid circulation. Liquid-based systems are generally capable of removing greater quantities of heat than air-cooled systems, due to their high convective transfer coefficient and specific heat capacity.

However, this extra performance often comes at the expense of system complexity and weight. An emerging alternative to these BTMS is the use of immersion cooling, where the cells are directly in contact with an electrically insulating working fluid. The advantage of this approach is that high rates of heat transfer can be achieved through direct contact of the cells with the immersion fluid. The other advantage is that this fluid can also act as a flame propagation retardant if its flash point is high enough.

Fluid properties (including viscosity, thermal conductivity, density, heat capacity, flammability and material compatibility) are crucial in evaluating the immersion solution. Similarly, fluid circulation, flow rate and flow regime are key parameters for optimizing cooling. That's why MOTUL, which specializes in the design, development and distribution of engine lubricants, is teaming up with the LAMIH laboratory to study and optimize immersion cooling solutions for battery modules.

The main objective of this thesis is to design and implement an experimental test bench dedicated to the study of immersion cooling for battery modules. This work aims to develop new innovative cooling fluids, optimized for this specific application, by considering many influential parameters.

To this end, an exhaustive literature review was carried out to identify the various cooling techniques suitable for batteries and to characterize the fluids used in immersion systems. Experimental and numerical simulation methodologies were developed to evaluate the overall heat transfer coefficient, a key parameter for measuring system efficiency.

Experimental results revealed the influence of several important parameters, such as fluid flow rate, power dissipated by the battery, fluid type and system geometric configuration. In particular, the addition of triangular baffles was studied to understand how they can intensify heat transfer and improve cooling efficiency.

Empirical correlations were also developed to predict the heat transfer coefficient as a function of Prandtl and Reynolds numbers, providing tools for the design and optimization of immersion cooling systems.

• Matthieu Fénot, Professor at ISAE-ENSMA, Poitiers (Rapporteur)
• Mohammed LACHI, Professor at the University of Reims Champagne Ardenne (Rapporteur)
• Valérie SARTRE, Professor at INSA Lyon (Examiner)
• Souad Harmand, Professor at UPHF-INSA Hauts de France, LAMIH (Thesis supervisor)
• Rodrigo Amorim Dias, R&D engineer in thermal management at MOTUL (Company Supervisor)
• Julien Plet, R & D Department Manager at Motul (Company Supervisor)

Immersion, Dielectric fluid, Thermal management
.