Lithium ion batteries for electric vehicles must operate within a certain range of temperatures to maintain their life and performance characteristics. Different conditions in the environment or power cycles applied generate heat in different levels across time and temperature domains. Hence battery thermal management becomes a critical factor for any high-performance battery system. Battery thermal simulation is done using computational fluid to design the cooling system.
Bold Engineering Services
Bold Valuable Technology offers design and manufacturing services to motorsport, aerospace and industry. We specialise in battery pack integration and structural composite & mechanical components. We provide added value from the design stage and take care of manufacturing to supply finished products to our customers. We leverage our experience in motorsport to deliver fast solutions at reasonable cost, from prototypes to large series production.
The design work is carried out in Girona, Spain. For manufacturing and testing, Bold uses a network of superb suppliers for raw materials, machining, composite part producers and testing, mainly from the UK.
We have experience working with large and small clients and can supply anywhere in the world. We are happy to adapt ourselves to our customer’s quality system requirements.
Battery thermal simulation for motorsport
In this project, Bold developed a battery concept for a high-end motorsport electric series. The scope of work comprised the development of a battery, based on a pre-selected cell, to perform mechanical packaging and cooling system design. Specifically, the cooling system is where the thermal simulations were required. The difficulties in accurately predicting the thermal behaviour and pumping losses in the cooling system were only possible to tackle using CFD tools. The main advantage we find in simulation is the speed at which we can try different ideas and design parameters. On top of that, the post processing tools allow us to understand the behaviour of the system so our engineers can come up with improvements or discover issues before building prototypes.
Without these tools, our approach in the past was to use analytical calculations which require a high degree of simplification, and physical testing. However, the latter is most times a nightmare when dealing with several suppliers located all over the world.
Battery thermal simulation approach for batteries
After comparing different CFD software, Simscale provided us with an easy-to-learn interface to set up the model in a simple way, with a cloud-based system environment. This makes things cheaper in terms of computing power, especially when we have consultants that work remotely. Furthermore, Simscale has an experienced support staff that explained how to use several tools and helped us with troubleshooting when we had issues. Furthermore, the SimScale option came with core hours included which saves us from having to worry about liaising with a third party for that.
For the cooling system design it was required to perform a conjugate heat transfer simulation. Before that, a solid heat transfer and an incompressible fluid analysis were performed as a starting point. First of all, Bold made a comparison amongst a dozen different cooling concepts through solid heat transfer analysis. This was a good method to make the first selection. Also, an incompressible fluid analysis was performed amongst the last three candidate concepts to estimate the pressure drop for each one. Finally, our team set up different models with a conjugate heat transfer simulation, including different boundary conditions like heat generation in the cells or air convection heat flux in the cells and the cooler. Different flow rates were simulated too, thermal gradients in the fluid and cells and pressure drop between coolers were compared.
One of the biggest challenges in the process was to create a mesh for our models, a vital step in all CFD simulations and crucial for obtaining valid results. The size of some solid components was only 0,3 mm thick and there were a number of thin fluid channels. With the help of SimScale's technical support we were able to solve these problems.
Analysis of results for battery thermal simulation
When doing the simulations, we found some issues before achieving convergence. But, after some research and the help of the support team, we fixed these problems and started comparing results amongst different designs.
For the whole project, Bold ran more than 100 simulations, with an average runtime of 30 core hours. Simscale was left to choose the number of cores used with its Automatic feature.
From these simulations, Bold obtained a large range of results, used as parameters to evaluate each cooling system. Some of these results were: max and min cell temperatures, internal cell gradients using cutting planes, coolant flow streamlines, pressure drop between inlet and outlet and coolant temperature gradient between inlet and outlet. The outlet fluid temperature was used as a monitor for evaluating the simulation’s convergence.
Working with Simscale has been such a great experience, despite some little problems that were solved with the help of the support team. Simscale has an intuitive interface, it makes setting up the model easier than other CFD softwares. The possibility of choosing the number of cores for each simulation and working in the cloud, gave us a lot of flexibility. Finally, Bold was able to use the plots directly from Simscale for reporting. We also exported the output file to analyse it in a third-party software to calculate a few parameters that were not obtainable with the Simscale platform.
Bold keeps pushing for better simulation results
Simscale has brought us a cost-effective solution saving money by reducing the number of experimental tests needed for the project. Furthermore, it has removed limitations like the number of cores available in our computers and has enabled the possibility of having different users working remotely at any moment.
Bold plans to expand on the use of simulation with more detailed models to better predict the thermal behaviour of our cooling systems. At the same time, we must keep the flexibility in our way of working and Simscale fits both requirements.
Battery module test rig development
Currently Bold is developing a test rig to perform thermal cycling on battery modules. This will be used in conjunction with the simulation capabilities to validate results and improve correlation between analytical solutions and real world tests.
The test rig is expected to be operational by the end of June 2020 and will be available to all our customers. The test rig will be able to operate with the common battery cooler fluids (glycol/water mixture, mineral oil, and engineered cooling fluids). Furthermore, Bold will be able to apply power cycles onto the cells with our programmable DC load tester at the same time cooling is applied.
Bold has been able to provide valuable solutions to our high-end motorsport customer using conjugate heat transfer simulations, that would have not been possible with other software due to cost and computational resources required. The SimScale team has been very helpful in every step of the way