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Heat transfer in ordered porous media with application to batteries
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0001-9779-7447
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In recent decades, promising technological advancements in clean energy production and green transportation, driven by the depletion of oil resources, energy security issues, environmental challenges, and associated health concerns, have moved the world closer to a sustainable energy outlook. However, this approach has led to a high reliance on electricity and the need for optimized electricity storage systems. Among different options, lithium battery systems have gained considerable attention, particularly for electric vehicles, owing to their superior properties, such as high energy density, fast charging capacity, and long lifespan, making them compatible with both stationary and mobile applications. Nevertheless, the safe and long-term operation of lithium battery systems depends on their working temperature, as the aging process of batteries accelerates with the temperature rise, and at critical temperatures, the exothermic reactions within battery cells might lead to thermal runaway and explosion. This necessitates employing a suitable strategy to regulate the temperature within lithium batteries, which could be quite challenging due to design restrictions related to geometry, coolant selection, cost, weight, and battery system size, especially at fast charging/discharging rates. Hence, it is essential to initially have a thorough understanding of how the system operates under different working conditions and then employ an effective strategy to improve its performance. 

In this framework, the present thesis first investigates the thermal behavior of a single cylindrical battery cell with varying geometrical parameters for the jelly roll. The study is based on a mathematical model predicting the temperature field within the cell to identify design considerations at the cell level to minimize thermal issues for the battery thermal management system. The best balance between thermal concerns and capacity was found for 21700 cylindrical cells, wherein the optimum thicknesses for the positive active material, the negative active material, the positive current collector, and the negative current collector were 180, 34, 21, and 20 μm, respectively. The thesis then shifts focus to the module-level study, evaluating the performance of air-based battery thermal management systems that meet many design criteria for battery applications but present challenges due to the low thermal conductivity of air as a coolant medium. The thermofluid characteristics of the air-based cooling system under discussion were investigated using computational fluid dynamics (CFD) simulations and compared to free cross-flow heat exchangers. The study suggests the  k-kl-ω transition model as a computationally efficient and fairly accurate turbulence model for such heat exchangers. Moreover, it was determined that under certain conditions, two-dimensional models of free cross-flow heat exchangers could replace computationally demanding three-dimensional models for wall-bounded cross-flow heat exchangers intended for battery cooling. These findings serve as a basis for developing a novel approach for modeling the performance of large air-cooled battery systems, termed the simplified modeling approach.

The simplified modeling approach consists of three sub-models, including a CFD model to simulate heat and flow characteristics around a cell in a periodic flow region, a set of approximate equations to determine the heat transfer rate for each row along the battery module, and an analytical model to predict the temperature field within individual cells. The employment of these sub-models, along with their independent functioning, significantly reduces computing costs. This model was employed to investigate cell spacing within an air-cooled battery module. At a constant mass flow rate to the system, the study suggests that maintaining transverse and longitudinal center-to-center distances of 1.7D and 0.9D between the cells, respectively, results in a fair balance between the maximum temperature rise and temperature gradient within the module. Following this, the model was combined with an empirical capacity degradation model to study how cell spacing and cooling conditions affect the number of cycles a battery module can operate. According to the study, proper cell spacing may extend the lifetime of the battery module by up to 55%. However, this life cycle extension comes at the cost of greater power consumption, which significantly raises cyclical costs, especially in densely packed battery modules. To address this issue, splitter plates were integrated into the design of densely packed battery modules. It was observed that splitter plates with lengths comparable to wake size could mitigate the maximum temperature rise and capacity degradation process within the batteries without causing extra cyclical costs. 

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2024.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords [en]
battery thermal management system, cylindrical battery, heat transfer, simplified modeling approach, CFD, analytical model, jelly roll, cell spacing, splitter plate, lifespan
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-107346ISBN: 978-91-8048-602-6 (print)ISBN: 978-91-8048-603-3 (electronic)OAI: oai:DiVA.org:ltu-107346DiVA, id: diva2:1869540
Public defence
2024-09-27, A109, Luleå University of Technology, Luleå, 13:00 (English)
Opponent
Supervisors
Available from: 2024-06-13 Created: 2024-06-13 Last updated: 2024-06-13Bibliographically approved
List of papers
1. Design considerations to prevent thermal hazards in cylindrical lithium-ion batteries: An analytical study
Open this publication in new window or tab >>Design considerations to prevent thermal hazards in cylindrical lithium-ion batteries: An analytical study
2021 (English)In: Journal of Energy Storage, ISSN 2352-152X, E-ISSN 2352-1538, Vol. 38, article id 102525Article in journal (Refereed) Published
Abstract [en]

Lithium-ion batteries have a high energy content, which makes them a great option for mobile storage applications. However, there are some serious concerns regarding their performance in terms of uncontrolled overheating. In this study, an analytical thermal model is developed based on the integral transform technique to predict the temperature field in a cylindrical lithium-ion cell. The temperature rise and the thermal gradient, as the significant parameters for the safety and performance assessment of lithium-ion batteries, are investigated for the lithium-ion cell. Moreover, the thermal behavior of the lithium-ion cell is comprehensively studied for different thicknesses of the component layers. It is found that the optimum thickness of the positive active material, the negative active material, the positive current collector, and the negative current collector for the efficient thermal operation of the lithium-ion cell is 180, 34, 21, and 20 μm, respectively. Furthermore, the performance of the optimized jelly-roll is assessed for the different types of cylindrical lithium-ion cells. The results indicate that the 21700 cell has the best thermal performance for use in high charge/discharge applications.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Lithium ion battery, Thermal evaluation, Temperature distribution, Heat conduction, Analytical model
National Category
Energy Engineering
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-83679 (URN)10.1016/j.est.2021.102525 (DOI)000670222300006 ()2-s2.0-85104054964 (Scopus ID)
Note

Validerad;2021;Nivå 2;2021-04-15 (alebob);

Finansiär: STandUp for Energy

Available from: 2021-04-15 Created: 2021-04-15 Last updated: 2024-06-13Bibliographically approved
2. A comparative study on thermo-fluid characteristics of free and wall-bounded cross-flow heat exchangers
Open this publication in new window or tab >>A comparative study on thermo-fluid characteristics of free and wall-bounded cross-flow heat exchangers
2023 (English)In: Thermal Science and Engineering Progress, ISSN 2451-9057, Vol. 40, article id 101746Article in journal (Refereed) Published
Abstract [en]

In recent years, wall-bounded cross-flow heat exchangers have gained significant attention for battery cooling applications. Due to similarities in geometry, these systems are often evaluated based on the heat and flow knowledge of free cross-flow heat exchangers. To determine the reliability of this assumption, this study performs a numerical comparison of the thermo-fluid behavior of wall-bounded and free cross-flow heat exchangers. Both heat exchangers have similar dimensions, with transverse and longitudinal pitch ratios of 2.074 and 1.037, respectively, and are investigated at a Reynolds number of 40000 using the Unsteady Reynolds-Averaged Navier–Stokes (URANS) method. It is observed that the  transition model provides the most accurate predictions of the flow field when compared to available experimental data. The results suggest that for wall-bounded heat exchangers with an aspect ratio of 2 or larger, the flow behavior in the central flow region resembles that of a free heat exchanger, but with varying magnitudes due to the increase in velocity in the core region to counterbalance the reduction near the walls. The area-averaged mean Nusselt number from 2D and 3D models for free heat exchangers shows no significant difference compared to wall-bounded heat exchangers. However, there are considerable differences in the local Nusselt number distributions in the angular and spanwise directions. Overall, it is determined that certain conditions must be satisfied to ensure that applying the thermo-fluid characteristics of a free cross-flow heat exchanger to wall-bounded cross-flow heat exchangers in battery thermal management systems is accurate.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Heat exchanger, Cross-flow, URANS model, Wall effect, Battery thermal management system
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-95442 (URN)10.1016/j.tsep.2023.101746 (DOI)000955267900001 ()2-s2.0-85149617478 (Scopus ID)
Funder
StandUp, 197140
Note

Validerad;2023;Nivå 2;2023-03-20 (joosat);

Licens fulltext: CC BY License

This article has previously appeared as a manuscript in a thesis.

Available from: 2023-02-01 Created: 2023-02-01 Last updated: 2024-06-13Bibliographically approved
3. A study on the effect of cell spacing in large-scale air-cooled battery thermal management systems using a novel modeling approach
Open this publication in new window or tab >>A study on the effect of cell spacing in large-scale air-cooled battery thermal management systems using a novel modeling approach
2023 (English)In: Journal of Energy Storage, ISSN 2352-152X, E-ISSN 2352-1538, Vol. 72, article id 108418Article in journal (Refereed) Published
Abstract [en]

Recent studies have revealed that effective thermal management systems are necessary to maintain the performance, lifespan, and safety of lithium battery systems. A unique and novel modeling approach is presented in this work with the aim of estimating the thermal performance of air-based cooling systems for large-scale lithium battery packages. The overall model consists of sub-models, including an analytical model for battery cells and a numerical heat and flow model for the battery module, which are validated against experimental data and empirical correlations, respectively. The chosen approach implies that the sub-models can operate independently, allowing accurate transient simulations with reduced processing time. The model is employed to evaluate the effect of cell spacing on the thermal performance of an air-cooled battery system designed for a hybrid electric vehicle. The results demonstrate that the maximum temperature within the cells positively correlates with transverse and longitudinal pitch ratios; however, the maximum temperature difference in the module has a negative correlation with these pitch ratios. In contrast, temperature uniformity shows non-monotonic behavior, making it an applicable criterion to balance between temperature rise and thermal gradients. Moreover, considerable temperature non-uniformity is noted in the early rows, which becomes less significant as pitch ratios decrease.

Place, publisher, year, edition, pages
Elsevier Ltd, 2023
Keywords
Analytical model, Battery thermal management system, Cylindrical lithium battery, Spacing effect, URANS model
National Category
Energy Engineering
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-99551 (URN)10.1016/j.est.2023.108418 (DOI)001054869800001 ()2-s2.0-85166477264 (Scopus ID)
Note

Validerad;2023;Nivå 2;2023-08-14 (joosat);

Funder: StandUp for Energy

Licens fulltext: CC BY License

Available from: 2023-08-14 Created: 2023-08-14 Last updated: 2024-06-13Bibliographically approved
4. Investigating the Potential and Limitations of Cell Spacing Adjustment for Optimized Air-Based Battery Thermal Management Systems
Open this publication in new window or tab >>Investigating the Potential and Limitations of Cell Spacing Adjustment for Optimized Air-Based Battery Thermal Management Systems
2024 (English)In: Energy Transitions toward Carbon Neutrality: Part VI, Scanditale , 2024Conference paper, Published paper (Refereed)
Abstract [en]

A reliable battery thermal management system plays a crucial role in the safe, efficient, and long-term operation of a high-performance lithium battery system. This study evaluates the temperature rise, pressure drop, capacity loss, and cyclical cost of an air-cooled battery system consisting of 90 cylindrical battery cells placed ina staggered arrangement in the module. The effect of spacing between the adjacent cells and inflow velocity is investigated for the battery system operating at high charge/discharge rates of 3C and 5C. The results demonstrate that the hybrid model, which consists of the battery life model integrated with the simplified modeling approach for the thermal evaluation of battery packs, provides a cost-effective tool for multi-objective analysis and optimization of air-cooled battery packages.The results reveal that the air-based cooling system has the potential to fulfill the safety standards in all studied cases, and employing battery modules with larger cell spacing at a constant inflow velocity may reduce the maximum temperature, pressure drop, and cyclical cost by up to 2.14%, 93.36%, and 35.69%, respectively, while extending the lifespan of the battery system by up to 55.45%. However, it is found that the air-based cooling system approaches its limit of thermal performance at high inflow velocities. A novel index (MCR index) is proposed in this paper to characterize the limitationsassociated with adjusting cell spacing for air-based battery cooling systems. It is observed that for systems with an MCR index beyond 600, the effect of cell spacingon thermal performance becomes negligible. This can be used as a useful guideline for optimizing air-based battery thermal management systems or integratingthem with other cooling methods.

Place, publisher, year, edition, pages
Scanditale, 2024
Series
Energy Proceedings, ISSN 2004-2965 ; 43
Keywords
battery thermal management system, cylindrical lithium battery, air-cooled system, spacing effect, simplified modeling approach, cyclical cost
National Category
Energy Engineering
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-105141 (URN)10.46855/energy-proceedings-11036 (DOI)2-s2.0-85190869646 (Scopus ID)
Conference
15th International Conference on Applied Energy (ICAE 2023), Doha, Qatar, December 3-7, 2023
Note

Funder: StandUp for Energy; Green Transition North;

Full text license: CC BY 4.0;

Available from: 2024-04-17 Created: 2024-04-17 Last updated: 2024-06-25Bibliographically approved
5. Effect of splitter plates and flow rate on the performance of air-based battery thermal management systems
Open this publication in new window or tab >>Effect of splitter plates and flow rate on the performance of air-based battery thermal management systems
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Considering the widespread incorporation of lithium batteries for different applications and the concerns regarding their safety and lifespan, the importance of developing efficient battery thermal management systems increases. In this work, splitter plates (SP), as a passive enhancement method, are attached to an air-cooled battery module consisting of 87 cylindrical 26650 LFP cells in a staggered arrangement to study their effect on the performance of the module at a 5 C charge/discharge rate. A hybrid modeling approach is employed to enable a multi-objective assessment of the system with minimal computational costs. The model includes a CFD model, evaluating the effect of SP on the thermo-hydraulic performance of compact systems as a present battery cooling system. In addition, an analytical thermal model and an empirical life model are linked to the CFD model to investigate the operation of the module, including maximum temperature, capacity fading, and cyclical costs. The Reynolds number is allowed to vary from 7600 to 28000, and the study is performed for SP with lengths ranging between 0.25-0.5625 of a cell's diameter. The results indicate that attachment and lengthening of SP enhance thermo-hydraulic performance, reduce maximum temperature rise, and extend the cycle life of the battery module. However, unlike the widely-spaced tube banks, using SP in the current case does not necessarily reduce the friction factor. Moreover, despite large values for the performance evaluation criterion (>3.4), the applied cyclical cost index demonstrates that modules with long SP are inefficient, where extended lifespans and lower working temperatures do not justify increased costs associated with airflow circulation. 

Keywords
battery thermal management system, cylindrical lithium battery, hybrid modeling approach, CFD model, splitter plate, lifespan
National Category
Fluid Mechanics and Acoustics Energy Engineering
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-107279 (URN)
Available from: 2024-06-12 Created: 2024-06-12 Last updated: 2024-06-13

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