Maximum Transient Temperature Research Articles

Dynamic internal resistance modeling and thermal characteristics of lithium-ion batteries for electric vehicles by considering state of health

Attempting to solve the problem of inconsistent dynamic thermal characteristics caused by transient changes in internal resistance of lithium-ion batteries (LIBs) for electric vehicles (EVs) under service conditions, taking a 9.4Ah prismatic LIB as the study object, the internal resistance data under different state of health (SOH), state of charge (SOC), temperature (T), charge/discharge rates of LIB are obtained through the mixed-rate hybrid pulse power characterization (MR-HPPC) test. Based on this, a dynamic internal resistance model (DIRM) considering the SOH is proposed by the prediction of the least squares support vector machines (LS-SVM) model. In this study, a thermoelectric coupling model and a resistance-thermal co-simulation of the LIB are established based on DIRM, and the temperature rise characteristics under constant rates and dynamic operating conditions are investigated at different SOH states. The maximum DIRM error (DIRME) between DIRM-based simulated maximum transient temperature (Tmax-tra) and test Tmax-tra is 0.88 °C at constant charge/discharge rate operating conditions, while the maximum DIRME between DIRM-based simulated Tmax-tra and test Tmax-tra is 0.21 °C under dynamic operating conditions. The results can provide a theoretical support for improving the modeling precision of the heat generation of LIBs with different aging levels for accurate thermal management design.

The Prediction of Frictional Temperature Increases in Dry, Sliding Contacts Between Different Materials

The work done in overcoming frictional resistance between sliding surfaces is transformed into heat at the separate, very small, and very highly loaded asperity contacts that make up the real area of contact. The temperature increases at these initial asperity contacts (the “flash temperatures”) are superimposed on the bulk temperature and give maximum temperatures at the asperity contacts which, although of very short duration, can cause important local changes at and near the surfaces. In an earlier paper (Smith and Arnell in Tribol Lett 53(3):407–414, 2013), the authors presented a new approach to calculating these maximum temperatures that relies on the solution, by finite-element analysis, of the three-dimensional equation for transient heat flow in a hemispherical asperity. Also, a design of experiments exercise produced predictions for the temperature that agreed extremely well with the FE calculations, and response surfaces were presented that facilitated the determination of maximum temperatures without resorting to FE analysis. The preliminary analysis described in Smith and Arnell (Tribol Lett 53(3):407–414, 2013) treated the simplest case of the interaction between two identical asperities of the same material. In this paper, the analysis is extended to the interaction of asperities of different materials with widely different thermal and mechanical properties, and it is shown that it can be applied successfully to such situations. Many earlier models of frictional heating have been designed to calculate the flash temperature rises, under the assumption that the total maximum temperature rise could then be predicted by adding the bulk temperature to the flash temperature rise. However, there is a generic problem with this approach as the bulk temperature varies rapidly immediately below the contacting asperities and monotonically to the heat sinks, so it is not clear what temperature should be chosen for the bulk temperature to add to the flash temperature. This is a significant problem as it is the maximum temperature that governs the rates of any thermally activated changes in the sliding materials. In contrast, the FE model used here predicts the maximum transient temperature for each asperity interaction directly and has the potential to model the cumulative rises in maximum temperature as successive interactions occur until a steady state is reached. Therefore, the need to specify the bulk temperature does not arise. In addition, it is shown that the same FE analysis can be extended to calculate the partition between the two materials of the heat generated at the sliding surface and this, with their known physical properties, can be used to predict their bulk temperature profiles. The results can act as a benchmark against which other theoretical approaches can be measured. The authors believe they have developed a method for predicting maximum contact temperatures between rubbing asperities of different materials which is a significant improvement on existing techniques.

Numerical Simulation of Spot Welding Galvanized Sheet with Insert Material

In this paper, with the ANSYS, a 2D axisymmetric coupled thermo-electro-mechanical model was developed to analyze the spot welding process（RSW） of zinc coated steels with copper strips as an insert material between electrode and workpiece. A transient temperature field obtained from a prior performed thermal–electrical simulation of RSW process is applied as nodal load on the model to simulate the stress distribution. The temperature and stress distributions in such a welding process were obtained and compared with a conventional resistance spot welding process. The results show that using the same welding process parameters, the maximum transient temperature at the electrode surface is lower than the conventional RSW process due to the use of copper strips, which helps to extend electrode lifetime. In addition, the presence of inserted copper strip increased the resistance of welding system, thus generated much more heat to form larger nugget.

Analysis of the Transient Single-Phase Thermal Performance of Micro-Channel Heat Sinks

The objective of this study is to examine the transient single-phase thermal behavior of micro-channel heat sinks during startup and over a short-duration power surge, and to investigate the effects of property and geometry parameters on this behavior. The transient analysis required the solution of three-dimensional conjugate heat transfer in the heat sink. These solutions were obtained numerically using the finite control-volume method and the numerical accuracy of the results was carefully assessed. Accuracy of the numerical model was validated by comparisons with available experimental data. The behavior of heat sinks with different values for the fin width, channel width, material thickness between the top of the channels and top of the heat sink, and different sink materials was examined during startup from a uniform initial temperature with a uniform input heat flux, followed by a short-duration power surge from the steady-state condition. It is concluded that increasing the fin width or channel width increases the steady-state and maximum transient temperatures in the solid, and that increasing the material thickness between the heat-sink channels and the chip or using a material with larger density and specific heat increases the transient period and lowers the maximum transient temperature in the solid during the power surge.

Optical and infrared study of individual reacting metallocene catalyst particles

AbstractPolymer particle agglomeration and melting causing sheet formation in fluidized bed reactors have been reported to occur during olefin polymerization. The cause of this deleterious sheet formation has not yet been established. Infrared and optical imaging were used to study the temporal temperature and size during polymerization of individual commercially active catalyst particles supported on a nylon mesh. Experiments conducted at 2100 kPa confirmed theoretical predictions that the temporal temperature rapidly attains a maximum after the start of the reaction. The magnitude of the temperature rise increases upon an increase of either reactor temperature, initial catalyst particle diameter, catalyst loading, or addition of hydrogen to the feed. The maximum transient temperature rise of single commercial catalyst particle during ethylene polymerization (7.5°C) is lower than that which can lead to local melting and polymer sheet formation. The temperature rise of particle clusters is much higher than that of individual particles, as the cluster acts as a particle with an effective diameter much larger than that of an individual particle. Thus, to circumvent polymer melting it is essential to avoid catalyst particles clustering, which may be caused by electrostatic attraction. The addition of hydrogen to the feed, often used to control polymer properties, significantly increased the initial particle temperature rise (almost double in some cases). © 2008 American Institute of Chemical Engineers AIChE J, 2008

Dual‐site supported metallocene catalyst design for bimodal polyolefin synthesis

AbstractThe processability of various polyolefins may be enhanced by producing one having a bimodal molecular weight distribution. Such polymers can be produced by loading the reactor with a catalyst on which two different catalytic sites are impregnated. The catalysts must be loaded with a proper ratio between the two catalytic sites to produce the desired polymer. The total loading should enable a maximum polymer production in the specified residence time while keeping the maximum transient temperature below a specified maximum, in order to avoid local melting and sheet formation. A model is presented that enables this catalyst design based on kinetic information about the initiation, propagation, and deactivation reaction rates of the two individual catalytic sites. The model simulations provide insight about the factors affecting the maximum safe loading of the two catalytic sites. We show here how to utilize kinetic information about each of the two catalytic sites to predict the optimum loading of dual‐site metallocene catalysts. As the maximum temporal temperature occurs during the initial stages of the reaction, the site that leads to a faster generation of a temperature peak, exerts a stronger bound on the total polymer production than the second site. The larger the propagation and/or the initiation rate constants or their activation energies are, the lower should be the catalyst loading. The deactivation rate constants affect both the relative site loading of the two sites as well as the total production. The total polymer production can be increased by decreasing the deactivation rate of the more active site. © 2007 American Institute of Chemical Engineers AIChE J, 2007

An analytic derivation for the transient temperature rise during an ultrasound pulse focused on bone

An analytic derivation is given for the maximum transient temperature rise due to millisecond ultrasound (US) pulses focused on bone. The temperature rise is found to have, within a small correction factor, a square-root dependence on the pulse duration and is independent of the focal diameter. The equation developed is essentially the same as that found in a previous paper (Herman and Harris 2002) that obtained the formula by numerical methods and subsequent curve fitting. (E-mail: bah@cdrh.fda.gov)

Transient Behavior of Low Enriched Uranium Silicide Plate-Type Fuel for Research Reactors during Reactivity Initiated Accident Conditions

Abstract This paper describes the results of transient experiments using a low enriched uranium silicide miniplate fuel for research reactor. The pulse irradiation was performed in the Nuclear Safety Research Reactor (NSRR) at the Japan Atomic Energy Research Institute (JAERI). The results obtained in this study are summarized as follows : (1) The tested fuel plates were damaged with energy depositions above 94 cal/g·fuel, but remained intact below 82cal/g·fuel. A failure threshold should therefore exist between these two values. (2) Four of the fuel plates that showed peak cladding surface temperatures <330°C were damaged by the thermal stress during quenching. These damaged fuel plates revealed small intergranular cracks that propagated perpendicularly to the axial direction of the plate, from the Al cladding surface to the fuel core, without significant dimensional changes. On the other hand, when peak cladding surface temperatures were >400°C, the test fuel plates were damaged mainly by melting of the Al cladding, accompanying significant dimensional changes. (3) The thermal stress of the damaged fuel plates calculated on the basis of the maximum transient temperature drop during quenching was greater than the tensile stress that occurred during fabrication.

Magnetic Head-Media Interface Temperatures—Part 3: Application to Rigid Disks

A thermal analysis has been used to predict transient temperature rises at a typical head-particulate-disk interface and a head-thin-film-disk interface. Thermal properties of the various thin-films used in the construction of magnetic rigid disks are measured. Average and maximum transient temperature rises for the assumed head-particulate-disk interface over the contact area are 34 and 44°C, respectively for an Al2O3-TiC slider. If the exposed magnetic particles or alumina particles contact the slider surface, the transient temperature rise could be more than 1000°C. Average and maximum transient temperature rises for the assumed head-thin-film-disk interface over the contact area are 56 and 81°C, respectively for an Al2O3-TiC slider and 77 and 110°C, respectively for an Mn-Zn ferrite slider. The durations of asperity contact generally are less than 100 ns. The thermal gradients perpendicular to the sliding surfaces are very large (a temperature drop of 90 percent in a depth of typically less than a contact diameter or less than a micron).

Transient effects in natural convection cooling of vertical parallel plates

This work presents results from a numerical study of transient natural convection between vertical parallel plates. Two boundary conditions – uniform wall temperature and uniform heat flux – are considered. Results presented include the rate of heat transfer for uniform wall temperature and the maximum wall temperature for uniform heat flux. Also presented are simple correlations to calculate the minimum heat transfer and the maximum wall temperature during the transient period. It is found that for uniform wall temperature the ratio of the minimum heat transfer to the steady state heat transfer decreases with length of the channel, and for uniform heat flux the maximum transient temperature has a maximum of about 9% over the steady state temperature.

Wrong‐way behavior of packed‐bed reactors: 1. The pseudo‐homogeneous model

AbstractA sudden reduction in the feed temperature to a packed‐bed reactor leads to a transient temperature rise, which is referred to as the wrong‐way behavior. A pseudo‐homogeneous plug‐flow model is used to analyze the structure of this transient behavior. The key parameters which determine the magnitude of this response are the dimensionless adiabatic temperature rise, activation energy, heat transfer capacity, coolant temperature, magnitude of temperature drop and length of the reactor. A simple expression is derived for predicing the maximum transient temperature rise.

Direct infrared measurements of filament transient temperature during switching in vanadium oxide film devices

Static and dynamic filament temperature profiles are shown in VO 2 film devices. The thermal switching is the consequence of the semiconductor to metal transition at 68°C arising from the fact that a conductive filament develops across the VO 2 device after switching. By use of an ir microscope, we have experimentally demonstrated large temperature spikes (some hundred degrees C) at the onset of switching in the growing filament. This maximum transient temperature (which may be destructive) is reached a few tens of microseconds after the generation of the filament. The external circuit parameters have a strong influence on this behavior. We have related this maximum filament temperature to the magnitude of the voltage drop during breakdown.