Effect Of Non-uniform Temperature Distribution Research Articles

(Digital Presentation) Effects of Non-Uniform Temperature Distribution on the Degradation of Liquid-Cooled Lithium-Ion Cells

Non-uniform temperature distribution develops inside lithium-ion (Li-ion) cells due to heat generation and low thermal conductivity in the thickness direction. Such non-uniform temperature distribution can cause non-uniform and accelerated degradation of Li-ion cells, as shown in our previous work on an air-cooled stack consisting of five Li-ion cells1, 2. Compared with air cooling, liquid cooling is more widely used for large-size Li-ion cells due to its stronger cooling capability. Liquid cooling would cause larger temperature gradient in Li-ion cells than air-cooling. It was therefore hypothesized that the degradation of liquid-cooled Li-ion cells will be more non-uniform than air-cooled cells. To test the hypothesis, a stack of water-cooled parallel-connected Li-ion cells, as schematically shown in Figure 1, were tested and compared with the air-cooled stack. Each cell has a nominal capacity of 3 Ah. As expected, the temperature distribution in the liquid-cooled stack was very non-uniform (Figure 2) and the cells degraded differently (Figure 3). Unexpected, however, the middle cell in the water-cooled stack degraded slower than the side cells, which is opposite to the trend of the air-cooled stack. Further investigation suggested that the opposite trend can be attributed to the combined effects of temperature rise and temperature gradient. Moreover, capacity drop and recovery was observed for the cells in the liquid-cooled stack after reference performance test, which could be attributed to the anode overhang effects3. References G. M. Cavalheiro, T. Iriyama, G. J. Nelson, S. Huang and G. Zhang, Journal of Electrochemical Energy Conversion and Storage, 17 (2020).H. J. Gonzalez Malabet, G. M. Cavalheiro, T. Iriyama, A. Gabhart, G. J. Nelson and G. Zhang, Journal of The Electrochemical Society, 168, 100507 (2021).B. Gyenes, D. A. Stevens, V. L. Chevrier and J. R. Dahn, Journal of The Electrochemical Society, 162, A278 (2014). Figure 1

LES study on the turbulent thermal stratification and thermo-mechanical fatigue analysis for NPP surge line

Thermal stratification caused the significant temperature differentials from top to bottom inside the pipe that imposed fluctuating high stresses on the wall of the pipe and eventually could lead to severe structural integrity concerns and degrade fatigue strength. This study aimed to evaluate the transient thermal distribution and fatigue damage caused by thermal stratification in the pressurizer surge line (SL) of Nuclear Power Plants (NPP). In this paper, the effects of nonuniform temperature distributions caused by thermal stratification were investigated by performing a detailed Computational Fluid Dynamic (CFD) study using the Large Eddy Simulation (LES) approach. The fluid flow was simulated using a full buoyancy model and conjugate heat transfer at the pipe inner wall and the fluid interface. Numerical results of the investigation in the SL pipe were validated with similar experimental setup data obtained from a prototype experimental facility of a pressurized water reactor. Fatigue damage due to induced thermal stresses in the SL model was investigated and fatigue hotspots were also identified. This work provides a comprehensive case study of thermal stratification for estimating pressurizer surge pipeline structural integrity.

Effects of Nonuniform Temperature Distribution on Degradation of Lithium-Ion Batteries

Abstract The effects of nonuniform temperature distribution on the degradation of lithium-ion (Li-ion) batteries are investigated in this study. A Li-ion battery stack consisting of five 3 Ah pouch cells connected in parallel was tested for 2215 cycles and compared with a single baseline cell. The behaviors of temperature distribution, degradation, and current distribution of the stack were characterized and discussed. Results supported the hypothesis that nonuniform temperature distribution causes nonuniform and accelerated degradation. All cells in the stack experienced higher temperature rise and degraded faster than the baseline cell. In particular, capacity retention of the middle cell in the stack decreased to 50.7% after 2215 cycles, while the baseline cell capacity retention was still 87.8%. The resistance of cells in the stack experienced nonuniform but similar pattern of variation with cycling. The resistances remained stable in early cycles, then experienced a rapid increase, and then became stable again. The middle cell resistance increased abruptly in the last 20 cycles before failure. Current distribution behaviors of the stack also changed significantly during cycling, which was consistent with cell resistance behaviors. The middle cell experienced much higher C rate than average, suggesting that its accelerated degradation can be attributed to the synergized effects of higher local temperature and higher local current.

Effect of non-uniform temperature distribution on entropy generation and enthalpy for the laminar developing pipe flow of a high Prandtl number fluid

In this article, Entropy generation and enthalpy are investigated on the pipe wall in developed laminar flow for 7 cases. Variation of entropy generation and enthalpy are shown along the radius. Entropy generation and enthalpy along the radius are obtained. Heat transfer is increased with the flow of fluid through the pipe, in inlet of pipe points to the output. The amount of entropy generation in the pipes of higher temperature is more than other points. Enthalpy is proportional to temperature in surface variation of 7 cases. In the points of higher temperature in elementary cases, the enthalpy value is increasing and it is increasing in other cases. Fluctuations of enthalpy and entropy generation are producted in interface points of pipe surfaces. The diagram data can be used to measure the minimum entropy generation in pipe heat transfer. Minimum entropy generation is in surface whit high temperature. The enthalpy in centerline is constant and inlet enthalpy of the tube is greater than other point with higher temperatures in radial flow. The lowest enthalpy is obtained in tubes with lowest initial temperature (case 7). Minimum entropy generation is presented in surface whit high temperature at the beginning (case 1-3) or high at the ending (case 5-7).

An Improved Thermal-Resistance-Capacitance Model for Vertical Single U-Tube Ground Heat Exchanger

Abstract Based on four-thermal-resistance-capacitance network within a borehole, an improved thermal-resistance-capacitance model (TRCM), which takes into account the effect of nonuniform temperature distribution along the borehole perimeter, is proposed for vertical single U-tube ground heat exchanger. For a given geometric and physical parameters of ground heat exchanger, the numerical simulations of the conventional TRCM based on three-thermal-resistance-capacitance network within borehole, the improved TRCM based on four-thermal-resistance-capacitance network within borehole and three-dimensional (3D) finite volume computational fluid dynamics (CFD) model by using fluent software were conducted, respectively. Through the comprehensive comparisons of simulation results between these above-mentioned three models for vertical single U-tube ground heat exchanger, it could be concluded that the proposed improved TRCM could not only provide relatively high accurate results, but also remarkably decrease the solving time as compared to the benchmark 3D finite volume CFD model. Since the proposed TRCM has better performance than the one based on three-thermal-resistance-capacitance network within borehole and 3D finite volume CFD model, a new reliable and feasible TRCM for vertical single U-tube ground heat exchanger could be available for the design and optimization of ground heat exchanger, the data interpretation of thermal response test (TRT) and other applications of ground heat exchanger in real industrial engineering.

Effects of Non-Uniform Temperature Distribution on Degradation of Lithium-Ion Cells

Lithium-ion cells degrade much faster at temperatures higher than 25 °C mainly due to accelerated solid-electrolyte interface (SEI) growth in anode and degeneration of cathode [1, 2]. It is also known that temperature distributions in lithium-ion cells are not uniform [3] due to very low thermal conductivity of battery materials. The non-uniform temperature distributions could cause non-uniform degradation, thus exacerbating the thermal degradation problem, especially for large-format lithium-ion cells during high power operation. The effects of non-uniform temperature distributions on degradation of lithium-ion cells will be investigated and progress will be presented.

Fatigue life evaluation and failure analysis of light beam direction adjusting mechanism of an automobile headlight exposed to random loading

Failure of the light beam direction adjusting mechanism (LDAM) of an automotive headlight might occur after hundreds of driving hours, though the strength of components conforms to the requirement specified in the random vibration bench test standard. In order to determine the causes of the failure, fatigue life prediction and failure analysis based on numerical method of the LDAM exposed to random loading both in bench test and field experiment were carried out. In the bench test analysis, the Dirlik method was utilized to calculate the lifetime by taking the power spectrum density in the frequency domain. In the fatigue analysis for the field experimental loading, to consider the effect of nonuniform temperature distribution, a numerical process in time domain is developed to calculate the lifetime of the LDAM subjected to the random vibration caused by road surface roughness. As a result, the predicted life and failure locations are in good agreement with real life and actual failure regions, respectively.

Effect of non-uniform temperature distribution on surface absorption receiver in parabolic dish solar concentrator

A flat surface absorption receiver was experimentally investigated with a parabolic dish solar concentrator in order to study the effect of receiver temperature distribution on heat gain and losses. The addition of specially designed metal fins in the inner surface of the receiver surface side the receiver transfers the incident heat flux to heat transfer fluid. The receiver surface temperature increased with increase in concentration ratio, intensity of beam radiation, and ambient temperature, but decrease with wind speed. The absorptivity of black coated mild steel of 0.85 and also the 0.15 emissivity of mild steel reduced the heat loss from the surface and improved heat gain to heat transfer fluid. The temperature gradient between the receiver periphery and centre is around 150?C. Fluid flow direction like straight and curved paths have been discussed for effective heat absorption and reduced operational duration. The thermal efficiency and operational duration were determined for a flow rate of 80 litres per hour through the receiver. Water flow though the curved path was observed with improved thermal efficiency of 3.8% and 20% reduction in operational duration when compared to the vertical flow through the receiver at same flow rate.

Temperature dependent subgroup formulation with number density adjustment for direct whole core power reactor calculation

The method and performance of the temperature dependent subgroup formulation based on the concept of number density adjustment are presented for the application to the direct whole core calculation of power reactors that involves substantial thermal feedback. The number density of each resonant nuclide is adjusted such that the resulting macroscopic cross section can carry proper temperature dependence even though the microscopic cross section is evaluated at the uniform average temperature. Specifically, the non-uniform temperature distribution is replaced by the corresponding temperature dependent number density distribution and by the uniform temperature for the microscopic cross section of the resonant nuclide. The number density adjustment is introduced not only in the subgroup fixed source problem, but also in the Bondarenko iteration to obtain the effective cross sections for the mixture. The subgroup level dependency of the number density adjustment factor is also introduced. In order to examine the effect of non-uniform temperature profiles on power reactor calculations, the OPR1000 fuel pin problems consisting of several cases having different power levels are constructed. The performance of the proposed method was verified by analyzing the OPR1000 fuel pin problems and by comparing with the corresponding Monte Carlo solutions in the aspect of group-wise cross sections as well as the reactivity. It is demonstrated that the proposed temperature dependent subgroup formulation can predict quite accurately the effects of non-uniform temperature distribution on the fuel temperature coefficients and the shielded cross sections.

Effects of non-uniform temperature distribution on critical member temperature of steel tubular truss

This paper examines the effects of thermal restraint, caused by non-uniform temperature distribution in different members, on the failure temperatures of critical members of steel tubular trusses. Non-uniform temperature distribution develops in trusses exposed to localised fire attack. The truss member nearest to the fire source experiences the highest temperature, with reduced temperatures in the nearby members. The number of the nearby truss members being heated and their temperatures will affect the failure temperature of the critical truss member which has the highest temperature. The aim of this paper is to develop a simplified method to account for the effects of different numbers of members being simultaneously heated to different temperatures on the development of compression force and failure temperature of the critical member.Finite Element (FE) simulations were carried out for Circular Hollow Section (CHS) trusses using the commercial Finite Element software ABAQUS v6.10-1 which has previously been validated by the authors. The simulation trusses were subjected to constant mechanical loads and then increasing temperatures until failure. The elevated temperature stress-strain curves were based on EN-1993-1-2 [1]. Initial geometrical imperfections were included, based on the lowest buckling mode from eigenvalue analysis.The numerical study examined the effects of truss type, critical member slenderness, applied load ratio and axial restraint stiffness ratio on the failure temperatures of the critical truss members. The numerical simulation results were used to check the accuracy of a proposed simplified calculation method, combining linear elastic static truss analysis at ambient temperature and analytical equations to calculated the failure temperatures of thermally restrained truss members based on the regression equations of Wang et al. [2]. The calculation method was shown to be sufficiently accurate for fire resistant design purpose.

Theoretical Analysis of the Influence of Longitudinal Stress Changes on Band Dimensions During Continuous Rolling Process

The paper presents the results of studies on the effect of nonuniform temperature distribution over the length of feedstock on the variation of longitudinal stresses in the rolling direction and band dimension change during the continuous rolling process. The studies were performed based on actual engineering data for a 160x160 mm square cross-section feedstock of steel S355J0. Numerical modelling of the rolling process was performed using Forge 2008®, a finite-element based computer program. Thermovision measurements and bars geometrical dimension changes were carried out in a domestic steelworks.

The Effects of Non-uniform Temperature Distribution on Neutral Plane Level in Non-adiabatic High-Rise Shafts During Fires

The location of neutral plane level (NPL) of a high-rise shaft is an important factor for the evaluation of risks of smoke spreads in high-rise buildings, where the shaft internal pressure is equal to that of the building floor at the same height. The current method to determine the location of NPL assumes uniform temperature distribution inside a shaft, which causes concerns over accuracy of the predicted NPL for high-rise shafts with non-uniformly distributed temperatures during fires. To address the effect of temperature distribution on NPL location, this paper introduces a method to calculate temperature distribution and its associated NPL location based on a coupled model of smoke temperature profile, flow rate and pressure distribution inside a shaft. The measured data from a 1/3 scale experiment is used to validate the method and used to develop two empirical equations for NPL locations in terms of dimensionless numbers: one empirical equation based on shaft top temperature and the second based on shaft bottom temperature. A sensitivity study of the empirical equations is then conducted to evaluate the applicability of the developed equations when compared to the existing NPL method. It was found that for the existing NPL equation based on uniform temperature assumption may under-/overestimate the NPL locations, and the NRMSE would be over 50%, while the NRMSE of the empirical equation is only around 6% based on the results of coupled equations. For non-adiabatic shafts, the effects of non-uniform temperature distribution on NPL should be considered and the suggested empirical equations can predict NPL locations with a reasonable accuracy.

Effect of Non-Uniform Temperature Distribution over the Cross-Section in Steel Frame Structure

The paper deals with the effect of non-uniform temperature over the cross-section in the steel frame structure under fire loading. The unequal temperature distribution causes additional bending moments in statically indeterminate structures. Numerical results of thermal and structural analysis from the commercial computer software ANSYS are compared with the experimental measurements on the steel frame exposed to high temperature.

Influence of Temperature Change on the Energy Parameters during Round Bars Rolling Process

The paper presents results of experimental studies on the effect of non-uniform temperature distribution over the metallic charge length on the energy parameters change during round bars rolling process. Experimental tests were conducted on the D370 Continuous Shape Mill in industrial works. From the tests carried out, it has been found that the main cause of occurrence of the non-uniform distribution of temperature over the charge length is the process of heating the metallic charge in the walking beam furnace. During rolling of bars from metallic charge with non-uniform temperature distribution over its length, changes in friction conditions in the zone of contact between the band and the rolls and in the plastic properties of steel being rolled occur. For decrease temperature during metallic charge rolling process about 100 °C (Fig. 2) in walking beam furnace, increase of rolling torque and total rolling power about 30% during rolling process metallic charge in first continuous shape mill stand was observed.

The effects of non-uniform temperature distribution and locally distributed anisotropic properties on thermal buckling of laminated panels

The present paper is concerned with the optimal design problem of thermal buckling for fiber reinforced laminated panels. The effects of non-uniform temperature fields and locally distributed anisotropic properties on the thermal buckling behavior are studied. In this analysis, based on the classical lamination theory in conjunction with the Hamilton’s principle, the critical thermal buckling temperature difference is deduced. The numerical results show that under the non-uniform thermal loads the isotropic panel performs as anisotropic structure and it also show that the center of panel is more sensitive to the thermal effects than the edges. The effects of thermal load on panels with different boundary conditions are also investigated and it is found that the panel edges with loose constraint are more sensitive to temperature effect than with strict constraint. In the optimal fiber design problem for thermal buckling, by comparing the critical thermal buckling temperature difference of nine types of panels with different fiber distribution, it is found that the short fiber distribution can largely improve the critical thermal buckling temperature difference of fiber reinforced laminated panels. Finally, using the genetic algorithm the optimal fiber distribution is obtained for an eight-layer symmetrical panel.

Development of semi-empirical model for tritium permeation under non-uniform temperature distribution at heat exchanger tube wall

Prediction and mitigation of tritium permeation is an important safety issue in high temperature gas-cooled reactors (HTGRs) especially for industrial applications such as hydrogen production and process heat. This study investigated the effect of non-uniform temperature distribution on the tritium permeation rate through the heat exchanger wall and improved the prediction capability of the existing models by reflecting it. To be more explicit, the effective diffusivity (Dm) and the effective temperature (Tm) was newly defined for the heat exchanger wall, and the effective weight (xeff) was derived from one-dimensional diffusion equation. Based on the data collected by numerical methods, an empirical correlation for xeff was developed by a linear regression method and it was validated by comparisons with randomly generated separate numerical solutions. As a result, the new permeation model based on the effective temperature (Teff) showed very good agreement with the numerical results within an error of 1.28% on average while the existing model based on the average wall temperature (Tm) showed large discrepancies exceeding 200% in the maximum error. This study concludes that the newly developed tritium permeation model significantly improves the prediction capability on the tritium permeation rate through the heat exchangers. Which is the main tritium transport path in the high temperature reactor and the integrated industrial process systems.

Review of current fire design rules for cold-formed steel wall systems

Light gauge steel frame wall systems are commonly used in industrial and commercial buildings, and there is a need for simple fire design rules to predict their load capacities and fire resistance ratings. During fire events, the light gauge steel frame wall studs are subjected to non-uniform temperature distributions that cause thermal bowing, neutral axis shift and magnification effects and thus resulting in a combined axial compression and bending action on the studs. In this research, a series of full-scale fire tests was conducted first to evaluate the performance of light gauge steel frame wall systems with eight different wall configurations under standard fire conditions. Finite element models of light gauge steel frame walls were then developed, analysed under transient and steady-state conditions and validated using full-scale fire tests. Using the results from fire tests and finite element analyses, a detailed investigation was undertaken into the prediction of axial compression strength and failure times of light gauge steel frame wall studs in standard fires using the available fire design rules based on Australian, American and European standards. The results from both fire tests and finite element analyses were used to investigate the ability of these fire design rules to include the complex effects of non-uniform temperature distributions and their accuracy in predicting the axial compression strength of wall studs and the failure times. Suitable modifications were then proposed to the fire design rules. This article presents the details of this investigation on the fire design rules of light gauge steel frame walls and the results.

A novel temperature-aware distributed interconnect power model

Base on the lumped resistance-capacitance （RC） tree power model，a novel distributed interconnect dynamic power analytical model was proposed，which considers the effect of non-uniform temperature distribution along the interconnect. The new model overtakes the defect that the lumped model cannot represent the effect of non-uniform temperature distribution on the resistance of interconnect，and estimates the total power consumption of RC tree under a non-ideal unit step input. The proposed model is used to calculate the total power consumption of interconnect under nanometer-scale complementary metal-oxide semiconductor （CMOS） typical process. The results show that the longer the interconnected line is，the greater the effect of non-uniform temperature distribution on the power consumption is，and the dynamic power per unit length keeps constant under different processes. The proposed model can accurately calculate the dynamic power of interconnects，thus can be used to optimize design of large scale interconnect router and clock network in network-on-chip structure.

Numerical investigations on springback characteristics of aluminum sheet metal alloys in warm forming conditions

In this study, we investigated the effect of temperature gradients on the final part quality (i.e., springback) in warm forming of lightweight materials. Thermo-mechanically coupled finite element analysis (FEA) models encompassing the heating of the sheet blank and tooling, forming, part ejection, and cooling were developed for simple channel drawing process. A comparison was made between the 2D rigid and 3D elastic tooling FEA models to evaluate the effect of non-uniform temperature distribution and tooling distortion on the forming performance and part quality. The accuracy and reliability of the rigid FEA model were successfully validated through the comparison with the experiments reported in the literature. By accurately measuring the springback amount in three distinct tooling regions (i.e., die corner, punch corner, and side wall), the effect of forming temperature distribution on the part quality were explained in detail under a wide range of operating conditions. In addition, the dependence of springback on blank holder force (BHF), friction condition, and forming rate was also analyzed. The detailed stress distribution of the blank elements was compared to gain a fundamental understanding of the springback mechanism in warm forming process.

The effects of non-uniform temperature distribution on the ignition of a lean homogeneous hydrogen–air mixture

To characterize the ignition process in homogeneous charge compression ignition engines, high fidelity simulations are performed to study the effects of different initial temperature distributions on the autoignition of a turbulent homogeneous mixture at high pressure. The effects of the initial temperature distribution on the ignition and subsequent heat release are studied by comparison of simulations with three initial random temperature fields having different skewness. It is found that the scalar mixing and turbulence have a significant influence on the initial location and further evolution of the ignition kernels. A comparison of the integrated heat release rates shows that the presence of a hot core leads to early ignition and increased duration of burning, while a cold core leads to a dormant end gas, which is consumed by slow combustion. The extent of flame fronts is quantified by a temperature gradient cut-off, revealing distinct behavior in the appearance of flame fronts for the three cases. Finally, two distinct ignition regimes, namely the spontaneous propagation and the deflagration regimes, are identified, and a predictive criterion is defined based on the spontaneous propagation speed and deflagration speed at the local mixture conditions. The predictions are found to be consistent with the observed results, suggesting a potential strategy in the modeling of HCCI combustion process.