Temperature Dependent Heat Generation Research Articles

Temperature-dependent electrochemical heat generation in a commercial lithium-ion battery

Lithium-ion batteries suffer from inherent thermal limitations (i.e., capacity fade and thermal runaway); thus, it is critical to understand heat generation experienced in the batteries under normal operation. In the current study, reversible and irreversible electrochemical heat generation rates were measured experimentally on a small commercially available C/LiFePO4 lithium-ion battery designed for high-rate applications. The battery was tested over a wide range of temperatures (10–60 °C) and discharge and charge rates (∼C/4–5C) to elucidate their effects. Two samples were tested in a specially designed wind tunnel to maintain constant battery surface temperature within a maximum variation of ±0.88 °C. A data normalization technique was employed to account for the observed capacity fade, which was largest at the highest rates. The heat rate was shown to increase with both increasing rate and decreasing temperature, and the reversible heat rate was shown to be significant even at the highest rate and temperature (7.4% at 5C and 55 °C). Results from cycling the battery using a dynamic power profile also showed that constant-current data predict the dynamic performance data well. In addition, the reversible heat rate in the dynamic simulation was shown to be significant, especially for charge-depleting HEV applications.

Heat transfer study through porous fins (Si3N4 and AL) with temperature-dependent heat generation

In this study, three highly accurate and simple analytical methods, Differential Transformation Method (DTM), Collocation Method (CM) and Least Square Method (LS) are applied for predicting the temperature distribution in a porous fin with temperature dependent internal heat generation. The selected porous fin’s materials are Si3N4 and AL and generated heat varies linearly with temperature. The heat transfer through porous media is simulated using passage velocity from the Darcy’s model. Results reveal that DTM, CM and LS are very effective and accurate in comparison with the numerical results. Moreover the temperature distribution is depended to the Darcy and Rayleigh numbers. In addition the results show that using the AL as a porous fin’s substrate leads to higher value of temperature than Si3N4 element. A higher heat generation rate leads to higher fin temperatures since more amount of heat is dissipated to the surrounding.

Viscoelastic fluid flow over a moving vertical cone and flat plate with variable electric conductivity

A study has been carried out to analyze the effects of variable electric conductivity, non-uniform heat source/sink and higher order chemical reaction on unsteady, free convective viscoelastic (Walters liquid model-B) fluid flow over a moving vertical cone and a flat plate saturated with porous medium. The constitutive equations for the boundary layer regime are solved by an efficient finite difference scheme of the Crank-Nicolson type. The features of the fluid flow, heat and mass transfer characteristics are analyzed by plotting graphs and the physical aspects are discussed in detail to interpret the effect of various significant parameters of the problem. It is observed that the impact of variable electric conductivity with magnetic field has significant effect on the viscoelastic fluid flow through porous medium. The effect of temperature dependent heat generation is much stronger than the effect of surface dependent heat generation. The mass transfer of the reactive species strongly depends on the chemical reaction parameter as well as the order of chemical reaction. It is stronger for the first-order reaction than that for the higher order reaction.

Effects of variable electric conductivity and non-uniform heat source (or sink)on convective micropolar fluid flow along an inclined flat plate with surfaceheat flux

Numerical simulations have been carried out to investigate the effects of the fluid electric conductivity and non-uniform heat source (or sink) on two-dimensional steady hydromagnetic convective flow of a micropolar fluid (in comparison with the Newtonian fluid) flowing along an inclined flat plate with a uniform surface heat flux. The local similarity solutions are presented for the non-dimensional velocity distribution, microrotation, and temperature profiles in the boundary layer. The significance of the physical parameters on the flow field is discussed in detail. The results show that the values of the skin-friction coefficient and the Nusselt number are higher for the case of constant fluid electric conductivity compared with those for the variable fluid electric conductivity. The effect of temperature dependent heat generation is much stronger than the effect of surface dependent heat generation. The results also show that effects of the fluid electric conductivity and non-uniform heat generation in a micropolar fluid are less pronounced than that in a Newtonian fluid.

MHD Flow of a Micropolar Fluid past a Stretched Permeable Surface with Heat Generation or Absorption

This work considers steady, laminar, MHD flow of a micropolar fluid past a stretched semi-infinite, vertical and permeable surface in the presence of temperature dependent heat generation or absorption, magnetic field and thermal radiation effects. A set of similarity parameters is employed to convert the governing partial differential equations into ordinary differential equations. The obtained self-similar equations are solved numerically by an efficient implicit, iterative, finite-difference method. The obtained results are checked against previously published work for special cases of the problem in order to access the accuarcy of the numerical method and found to be in excellent agreement. A parametric study illustrating the influence of the various physical parameters on the skin friction coefficient, microrotaion coefficient or wall couple stress as well as the wall heat transfer coefficient or Nusselt number is conducted. The obtained results are presented graphically and in tabular form and the physical aspects of the problem are discussed.

Finite Element Modeling of Thermal Stability and Quench Propagation in a Pancake Coil of PbBi2223 Tapes

The initiation and propagation of quench events in a high temperature superconducting (HTS) pancake coil were modeled using finite element software package ANSYS. The nonlinear temperature dependent heat generation in HTS composite over a wide current sharing range is calculated based on power-law E-J characteristics with temperature dependence of the n-value and critical current density. Thermal properties of the HTS composite and coil sections were measured and compared with estimated values based on data for individual coil components and the fill factor of the coil construct. The effect of replacing the complex coil winding structure with an effective continuum was investigated by examining the normal zone temperature profiles and minimum quench energy (MQE). With reducing operating temperature from 77 K to 30 K, MQE reduces correspondingly from 30 J to 15 J. Simulation results are found in satisfactory agreement with experimental results from a test coil wound with PbBi2223 tape.

Étude des transferts de chaleur non linéaires dans les ailettes longitudinales

This work aims to quantify the effects of non-simplified situations on longitudinal fins efficiency. For this purpose a more realistic model, which has been developed here, is based on variable profile and temperature-dependent thermophysical properties in transient two-dimensional fin with internal non-uniform heat generation. An explicit exponential finite-difference method, conditionally stable, is extended in this study for the discretization of the governing equations. The numerical procedure consists in solving series of nodal temperature distribution according to the type of node, in order to reach the steady-state heat exchange. Then, the numerical simulation is used to present the sensitivity of some parameters on efficiency. Numerical results of interest are illustrated for a direct comparison with the traditional solutions. Extensive numerical experiments were conducted and showed that temperature-dependent heat transfer coefficient and generation lead to a significant reduction of fin-efficiency. The simultaneous effects of parameters for this non-linear problem are not negligible.

Transport to a Chemically Active Thin Liquid Film Over a Spinning Disk

An analytical solution for the process of mass transfer from a spinning disk to a chemically active thin liquid film flowing over the disk is presented. By analogy, the results are also applicable to heat transfer to the film with temperature-dependent heat generation. The process is modeled by establishing equations for the conservation of mass, momentum, and species concentration, and solving them analytically. The partial differential equation for species concentration is solved using the separation of variables technique along with the application of the Duhamel’s theorem. Tables for eigenvalues and eigenfunctions are presented for a number of reaction rate constants. A parametric study was performed using Reynolds number, Ekman number, and chemical reaction rate as parameters. It was found that Sherwood number increases with Reynolds number (flow rate) as well as inverse of Ekman number (rate of rotation). These fundamental results will be useful to design advanced energy transport processes for a low-gravity space environment.

FINITE ELEMENT PROCEDURE FOR HEAT CONDUCTION PROBLEMS WITH INTERNAL HEATING

Heat transfer problems involving temperature-dependent heat generation are formally equivalent to those involving variable specific heat such as occur in phase change situations. The use of distributed and lumped capacitance finite element methods for solving these problems is investigated. The technique is successfully applied to very severe internal heating problems such as the self-ignition of biological materials.

Thermal modeling of polymerizing polymethylmethacrylate, considering temperature-dependent heat generation.

A methodology for the modeling of unsteady heat conduction in polymethylmethacrylate (PMMA) during its exothermic polymerization is presented. The emphasis is on the formulation of a model for the volumetric rate of heat generation, including its temperature-dependent characteristics. Three parameters appear in the proposed model. The empirical determination of these parameters using Differential Scanning Calorimetry is demonstrated. The incorporation of the proposed model into finite volume methods is also demonstrated, in the context of unsteady, one-dimensional, radial heat conduction in cylindrical coordinates. In addition, the application of the proposed model to two test problems is presented and discussed. The results are encouraging, and the proposed methodology appears to be applicable to the thermal modeling of exothermic polymerization processes in general.

Thermal analysis of a substrate with power dissipation in the vias

As power dissipation at the chip level increases, current levels through power distribution wires increase correspondingly. This current flow results in Joule heating in the package, which must be included in any sizing of the package cooling requirements. An analysis of the temperature field resulting from the Joule heating in a metal wire surrounded by a nonheat generating (electrically insulating) material is presented. Exact analytical solutions are given for when the heat generation rate is constant (independent of temperature) and linearly dependent on the temperature. Asymptotic solutions are given for arbitrarily temperature-dependent heat generation, when the insulating material thermal conductivity is much less than the thermal conductivity of the wire. A numerical example of practical interest is then considered. It is shown that neglecting the Joule heating in the wires can result in significant under-prediction of the temperature. The effect of temperature on the electrical resistivity of the wire is shown to be negligible. The phenomenon of thermal runaway is also examined using stability theory and is shown to be unimportant in practical circumstances.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

ANALYSIS OF HEAT TRANSFER PROBLEMS WITH COMPUTER-EXTENDED PERTURBATION SERIES

The method of computer extension of perturbation series and its subsequent improvement are applied to four problems in nonlinear heat conduction. The nonlinearities involve temperature-dependent thermal properties, temperature-dependent heat generation, and simultaneous conduction-radiation interaction. The series are improved by techniques such as the extraction of singularity. Fade approximants, and Euler and Shanks transformations. The improvement achieved highlights the usefulness of the approach.

Analysis Of Heat Transfer Problems With Computer-Extended Perturbation Series

The method of computer extension of perturbation series and its subsequent improvement are applied to four problems in nonlinear heat conduction. The nonlinearities involve temperature-dependent thermal properties, temperature-dependent heat generation, and simultaneous conduction-radiation interaction. The series are improved by techniques such as the extraction of singularity. Fade approximants, and Euler and Shanks transformations. The improvement achieved highlights the usefulness of the approach.

Steady state heat transfer within porous medium with temperature dependent heat generation

A theoretical analysis of internally energised porous reactor is presented. Constant and temperature-dependent rate of heat generation are assumed. The fluid passed through the heated porous element medium changes phase from liquid to vapour and the vapour is further superheated. It is assumed that the regions of different phases are “separated” by two phase change “interfaces”, the first of which denotes the average distance where evaporation starts and the second denotes the average distance where complete evaporation is reached. The characteristics of the various parameters affecting the performance of a hollow cylindrical porous element are evaluated and presented for a representative range of the viscous flow regime where the inertia forces are neglected. The concept of generating temperature-dependent rate of heat within the porous element is aimed at gaining stability in operation and protecting the solid from burnout.