The current paper evaluates the thermal performance of immersion cooling for an Electric Vehicle (EV) battery module comprised of NCA-chemistry based cylindrical 21700 format Lithium-ion cells. Efficacy of immersion cooling in improving maximum cell temperature, cell’s temperature gradient, cell-to-cell temperature differential, and pressure drop in the module are investigated by direct comparison with a cold-plate-cooled battery module. Parametric analyses are performed at different module discharge C-rates and coolant flow rates to understand the sensitivity of each cooling strategy to important system performance parameters. The entire numerical analysis is performed using a validated 3D time-accurate Computational Fluid Dynamics (CFD) methodology in STAR-CCM+. Results demonstrate that immersion cooling due its higher thermal conductance leads to a lower maximum cell temperature and lower temperature gradients within the cells at high discharge rates. However, a higher rate of heat rejection and poor thermal properties of the dielectric liquid results in a much higher temperature non-uniformity across the module. At lower discharge rates, the two cooling methods show similar thermal performance. Additionally, owing to the lower viscosity and density of the considered dielectric liquid, an immersion-cooled battery module performs significantly better than the cold-plate-cooled module in terms of both coolant pressure drop.
Dustiness quantifies the propensity of a finely divided solid to be aerosolized by a prescribed mechanical stimulus. Dustiness is relevant wherever powders are mixed, transferred or handled, and is important in the control of hazardous exposures and the prevention of dust explosions and product loss. Limited quantities of active pharmaceutical powders available for testing led to the development (at University of North Carolina) of a Venturi-driven dustiness tester. The powder is turbulently injected at high speed (Re ~ 2 × 104) into a glass chamber; the aerosol is then gently sampled (Re ~ 2 × 103) through two filters located at the top of the chamber; the dustiness index is the ratio of sampled to injected mass of powder. Injection is activated by suction at an Extraction Port at the top of the chamber; loss of powder during injection compromises the sampled dustiness. The present work analyzes the flow inside the Venturi Dustiness Tester, using an Unsteady Reynolds-Averaged Navier-Stokes formulation with the k-ω Shear Stress Transport turbulence model. The simulation considers single-phase flow, valid for small particles (Stokes number Stk <1). Results show that ~ 24% of fluid-tracers escape the tester before the Sampling Phase begins. Dispersion of the powder during the Injection Phase results in a uniform aerosol inside the tester, even for inhomogeneous injections, satisfying a necessary condition for the accurate evaluation of dustiness. Simulations are also performed under the conditions of reduced Extraction-Port flow; results confirm the importance of high Extraction-Port flow rate (standard operation) for uniform distribution of fluid tracers. Simulations are also performed under the conditions of delayed powder injection; results show that a uniform aerosol is still achieved provided 0.5 s elapses between powder injection and sampling.
An effective cooling mechanism is the backbone of a good automotive battery thermal management system (BTMS). In addition to prevention of extreme events such as thermal runaway, an automotive BTMS must be able to efficiently tackle aggressive environmental temperatures, and/or discharge and charge conditions during electric vehicle operation. Moreover, electrical performance and cycle life of the battery modules and packs are closely tied to the battery temperatures and thermal gradients, which increase with increase in C-Rates. In order to keep the battery temperatures to be under the operational temperature limit, it is crucial that the selected cooling mechanism provides efficient transport of the heat generated by the battery modules and packs to the cooling media under all discharge and charge conditions. Owing to its efficient thermal performance, liquid cooling is preferred by most electric vehicle manufacturers for battery thermal management. This usually incorporates battery modules exchanging heat with a flowing coolant via cold plate or cooling channels during operation. The current work aims to investigate different liquid cooling configurations and compare their relative thermal performance during operation of a high energy density Pouch Cell. The four configurations selected for this comparison are (1) Face cooling, (2) Single-Sided cooling, (3) Double-Sided cooling, and (4) a Hybrid cooling configuration. Test setups comprising of a commercially available 9 A-h NMC Pouch cell, cold plates, pump, heat exchanger, refrigeration cooling unit, and thermal sensors are built for the above four cooling configurations. During the tests, the selected cell is discharged at different discharge rates (C-Rates), i.e., 3C, 4C, and 5C. The overall cell temperatures and thermal gradient across the cell are measured using T-type thermocouples for the four cooling configurations. In order to capture the thermal gradient across the Pouch cell accurately, several thermocouples on the face of the cell are installed using a thermal interface material. Results show the superiority of Face cooling configuration in terms of overall thermal performance under all considered test conditions. Lowest cell temperatures and thermal gradients across the cell are observed for the Face cooling configuration, while highest temperatures and thermal gradients are observed for the Single-Sided cooling configuration. Much improved thermal performance is also observed in the case of the Hybrid cooling configuration as compared to the Single and Double-Sided cooling configurations. As implementation of the Face cooling configuration at the battery pack level may result in higher weight and cost of the battery pack, owing to its good thermal performance and straightforward scaling to battery pack level, the proposed hybrid liquid cooling mechanism provides a viable alternative to Face cooling for battery thermal management.
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