scholarly journals Inhomogeneous Temperature Distribution Affecting the Cyclic Aging of Li-Ion Cells. Part II: Analysis and Correlation

Batteries ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 12 ◽  
Author(s):  
Daniel Werner ◽  
Sabine Paarmann ◽  
Achim Wiebelt ◽  
Thomas Wetzel
Keyword(s):  
Boundary Conditions ◽  
Lithium Ion ◽  
Temperature Gradients ◽  
Transient Temperature ◽  
Aging Behavior ◽  
Thermal Boundary Conditions ◽  
Temperature Boundary ◽  
Inhomogeneous Temperature ◽  
Temperature Levels ◽  
Definition Of

Temperature has a significant influence on the behavior of batteries and their lifetime. There are several studies in literature that investigate the aging behavior under electrical load, but are limited to homogeneous, constant temperatures. This article presents an approach to quantifying cyclic aging of lithium-ion cells that takes into account complex thermal boundary conditions. It not only considers different temperature levels but also spatial and transient temperature gradients that can occur despite-or even due to-the use of thermal management systems. Capacity fade and impedance rise are used as measured quantities for degradation and correlated with the temperature boundary conditions during the aging process. The concept and definition of an equivalent aging temperature (EAT) is introduced to relate the degradation caused by spatial and temporal temperature inhomogeneities to similar degradation caused by a homogeneous steady temperature during electrical cycling. The results show an increased degradation at both lower and higher temperatures, which can be very well described by two superimposed exponential functions. These correlations also apply to cells that are cycled under the influence of spatial temperature gradients, both steady and transient. Only cells that are exposed to transient, but spatially homogeneous temperature conditions show a significantly different aging behavior. The concluding result is a correlation between temperature and aging rate, which is expressed as degradation per equivalent full cycle (EFC). This enables both temperature-dependent modeling of the aging behavior and its prediction.

scholarly journals Inhomogeneous Temperature Distribution Affecting the Cyclic Aging of Li-Ion Cells. Part I: Experimental Investigation

Batteries ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 13 ◽  
Author(s):  
Daniel Werner ◽  
Sabine Paarmann ◽  
Achim Wiebelt ◽  
Thomas Wetzel
Keyword(s):  
Boundary Conditions ◽  
Heat Dissipation ◽  
Single Cells ◽  
Internal Heat ◽  
Lithium Ion ◽  
Ambient Air ◽  
Substantial Impact ◽  
Temperature Changes ◽  
Thermal Boundary Conditions ◽  
Cyclic Degradation

Alongside electrical loads, it is known that temperature has a strong influence on battery behavior and lifetime. Investigations have mainly been performed at homogeneous temperatures and non-homogeneous conditions in single cells have at best been simulated. This publication presents the development of a methodology and experimental setup to investigate the influence of thermal boundary conditions during the operation of lithium-ion cells. In particular, spatially inhomogeneous and transient thermal boundary conditions and periodical electrical cycles were superimposed in different combinations. This required a thorough design of the thermal boundary conditions applied to the cells. Unlike in other contributions that rely on placing cells in a climatic chamber to control ambient air temperature, here the cell surfaces and tabs were directly connected to individual cooling and heating plates. This improves the control of the cells’ internal temperature, even with high currents accompanied by strong internal heat dissipation. The aging process over a large number of electrical cycles is presented by means of discharge capacity and impedance spectra determined in repeated intermediate characterizations. The influence of spatial temperature gradients and temporal temperature changes on the cyclic degradation is revealed. It appears that the overall temperature level is indeed a decisive parameter for capacity fade during cyclic aging, while the intensity of a temperature gradient is not as essential. Furthermore, temperature changes can have a substantial impact and potentially lead to stronger degradation than spatial inhomogeneities.

scholarly journals Research on the Internal Thermal Boundary Conditions of Concrete Closed Girder Cross-Sections under Historically Extreme Temperature Conditions

2020 ◽  
Vol 10 (4) ◽  
pp. 1274
Author(s):  
Jianhui Lin ◽  
Junqing Xue ◽  
Fuyun Huang ◽  
Baochun Chen
Keyword(s):  
Boundary Conditions ◽  
Cross Sections ◽  
Extreme Temperature ◽  
Temperature Gradients ◽  
Simulation Methods ◽  
Vertical Temperature ◽  
Box Girders ◽  
Thermal Boundary Conditions ◽  
Temperature Distributions ◽  
Hourly Temperature

The accuracy of the finite element model (FEM) for concrete closed girder cross-sections is significantly influenced by thermal boundary conditions. The internal thermal boundary conditions can be simulated by inputting the convection heat transfer coefficient and the temperatures inside the cavities or by establishing air elements in the FEM. In order to analyze the influence of different simulation methods for the internal thermal boundary conditions on temperature distributions for concrete closed girder cross-sections, the temperature distributions on the cross-sections of a box girder, small box girders, and adjacent box girders were monitored, and the corresponding FEMs were implemented. By comparing the temperature data obtained from the field test and FEMs, the numerical hourly temperature curves calculated by using the measured temperatures inside the cavities provide the closest agreement with the measured results; however, the measurements of the temperatures on site are cost- and time-prohibitive. When there is a lack of measured temperatures inside the cavities, the numerical hourly temperature curves calculated by establishing air elements in the FEM provide the closest agreement. The influences of different simulation methods for the internal thermal boundary conditions on the highest hourly average effective temperatures and the trends of the vertical temperature gradients for concrete closed girder cross-sections were small. The FEM with air elements can be adopted to analyze the temperature distributions on concrete closed girder cross-sections under historically extreme temperature conditions. It can be predicted that the longitudinal thermal movement of concrete closed girders would be underestimated by considering variations in the one-year measured average effective temperature of the cross-sections or the Chinese-code-specified design effective temperature for the highway bridge structures, which are thus unconservative for engineering applications. The Chinese-code-specified design vertical temperature gradients are conservative for the bridge deck surface and unconservative for the bottom flange.

scholarly journals Effects of temperature and temperature gradient on concrete performance at elevated temperatures

2017 ◽  
Vol 21 (8) ◽  
pp. 1223-1233 ◽  
Author(s):  
Quang X Le ◽  
Vinh TN Dao ◽  
Jose L Torero ◽  
Cristian Maluk ◽  
Luke Bisby
Keyword(s):  
Temperature Gradient ◽  
Boundary Conditions ◽  
Elevated Temperatures ◽  
Concrete Structures ◽  
Constitutive Models ◽  
Concrete Surface ◽  
Temperature Gradients ◽  
Image Correlation ◽  
Test Setup ◽  
Thermal Boundary Conditions

To assure adequate fire performance of concrete structures, appropriate knowledge of and models for performance of concrete at elevated temperatures are crucial yet currently lacking, prompting further research. This article first highlights the limitations of inconsistent thermal boundary conditions in conventional fire testing and of using constitutive models developed based on empirical data obtained through testing concrete under minimised temperature gradients in modelling of concrete structures with significant temperature gradients. On that basis, this article outlines key features of a new test setup using radiant panels to ensure well-defined and reproducible thermal and mechanical loadings on concrete specimens. The good repeatability, consistency and uniformity of the thermal boundary conditions are demonstrated using measurements of heat flux and in-depth temperature of test specimens. The initial collected data appear to indicate that the compressive strength and failure mode of test specimens are influenced by both temperature and temperature gradient. More research is thus required to further quantify such effect and also to effectively account for it in rational performance-based fire design and analysis of concrete structures. The new test setup reported in this article, which enables reliable thermal/mechanical loadings and deformation capturing of concrete surface at elevated temperatures using digital image correlation, would be highly beneficial for such further research.

Mass Nature of Heat and Its Applications V: Entransy, Entransy Dissipation and Heat Transfer Irreversibility

2010 ◽  
Author(s):  
Xin-Gang Liang ◽  
Qun Chen
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Thermal Resistance ◽  
Energy Equation ◽  
Energy Utilization ◽  
Entransy Dissipation ◽  
Temperature Boundary ◽  
Flux Boundary Conditions ◽  
Heat Transfer Optimization ◽  
Definition Of

Heat transfer optimization is ubiquitous because improving heat transfer performance could increase the energy utilization or reduce the weight or size of heat transfer equipments. This article discusses the optimization in heat transfer using the new physical quantity, entransy, in recent years. Entransy describes the heat transfer ability. When heat is transferred from a high temperature to a low temperature and entransy dissipation is produced. Heat transfer is irreversible from the viewpoint of entransy. The entransy transfer efficiency can be defined using the concept of entransy. Definition of entransy, entransy flux, and entransy dissipation are given and the entransy balance equations are derived for conduction, convection and thermal radiation based on the energy equation. The minimum entransy dissipation principle for prescribed heat flux boundary conditions and a maximum entransy dissipation principle for prescribed temperature boundary conditions are investigated. These two principles are called entransy dissipation extreme (EDE) principle. An equivalent or average thermal resistance of a system can be defined based on the entransy dissipation and the EDE principle becomes the minimum thermal resistance principle. These principles can be used to optimize heat transport with constraints and some examples are presented. The relation of entransy with thermomass is discussed and comparison between EDE and entropy generation optimization is made. The essence of the entansy is the energy of thermomass.

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