共查询到20条相似文献,搜索用时 593 毫秒
1.
Lazar Kovačević Pal Terek Aleksandar Miletić Damir Kakaš 《Heat and Mass Transfer》2014,50(8):1115-1124
Interfacial heat transfer coefficient at the metal–mold interface (IHTC) was estimated by an iterative algorithm based on the function specification method. An Al–9 wt% Si alloy plate casting was made in a sand mold prepared by CO2 process. Thermal history obtained from the experiment was used to solve an inverse heat conduction problem. Acquired transient IHTC values are then given in function of the casting surface temperature at the interface. By comparing the obtained results with previous findings, the influence of grain fineness number and consequently of mold roughness on maximum IHTC values is revealed. 相似文献
2.
Liqiang Zhang Carl Reilly Luoxing Li Steve Cockcroft Lu Yao 《Heat and Mass Transfer》2014,50(7):945-955
The interfacial heat transfer coefficient (IHTC) is required for the accurate simulation of heat transfer in castings especially for near net-shape processes. The large number of factors influencing heat transfer renders quantification by theoretical means a challenge. Likewise experimental methods applied directly to temperature data collected from castings are also a challenge to interpret because of the transient nature of many casting processes. Inverse methods offer a solution and have been applied successfully to predict the IHTC in many cases. However, most inverse approaches thus far focus on use of in-mold temperature data, which may be a challenge to obtain in cases where the molds are water-cooled. Methods based on temperature data from the casting have the potential to be used however; the latent heat released during the solidification of the molten metal complicates the associated IHTC calculations. Furthermore, there are limits on the maximum distance the thermocouples can be placed from the interface under analysis. An inverse conduction based method have been developed, verified and applied successfully to temperature data collected from within an aluminum casting in proximity to the mold. A modified specific heat method was used to account for latent heat evolution in which the rate of change of fraction solid with temperature was held constant. An analysis conducted with the inverse model suggests that the thermocouples must be placed no more than 2 mm from the interface. The IHTC values calculated for an aluminum alloy casting were shown to vary from 1,200 to 6,200 Wm?2 K?1. Additionally, the characteristics of the time-varying IHTC have also been discussed. 相似文献
3.
This paper is concerned with a method for solving inverse heat conduction problem. The method is based on the controlled random
search (CRS) technique in conjunction with modified Newton–Raphson method. The random search procedure does not need the computation
of derivative of the function to be evaluated. Therefore, it is independent of the calculation of the sensitivity coefficient
for nonlinear parameter estimation. The algorithm does not depend on the future-temperature information and can predict convective
heat transfer coefficient with random errors in the input temperature data. The technique is first validated against an analytical
solution of heat conduction equation for a typical rocket nozzle. Comparison with an earlier analysis of inverse heat conduction
problem of a similar experiment shows that the present method provides solutions, which are fully consistent with the earlier
results. Once validated, the technique is used to investigate another estimation of heat transfer coefficient for an experiment
of short duration, high heating rate, and employing indepth temperature measurement. The CRS procedure, in conjunction with
modified Newton–Raphson method, is quite useful in estimating the value of the convective heat-transfer coefficient from the
measured transient temperature data on the outer surface or imbedded thermocouple inside the rocket nozzle. Some practical
examples are illustrated, which demonstrate the stability and accuracy of the method to predict the surface heat flux. 相似文献
4.
Juan José del Coz Díaz Paulino José García Nieto Alfonso Lozano Martínez-Luengas María Placeres González Martínez 《Meccanica》2010,45(5):619-634
This work is to study the performance of an ecological ventilated self-weighted wood panel used on roofs in order to get a
high energy savings. With this aim, we have carried out a convective heat transfer analysis of the panel by the finite volume
method (FVM). Pure conduction is found in the wood panel through their thermal properties. Heat transfer by convection is
always accompanied by conduction, that is to say, among the external air and the upper internal surface of the panel, and
the internal air and the inner lower surface of the panel taking into account the heat conduction of the internal ribs. The
finite volume method (FVM) is a method for representing and evaluating partial differential equations as algebraic equations.
Similar to the finite difference method, values are calculated at discrete places on a meshed geometry. ‘Finite volume’ refers
to the small volume surrounding each node point on a mesh. In the finite volume method, volume integrals in a partial differential
equation that contain a divergence term are converted to surface integrals, using the divergence theorem. These terms are
then evaluated as fluxes at the surfaces of each finite volume. Because the flux entering a given volume is identical to that
leaving the adjacent volume, these methods are conservative. One advantage of the finite volume method over the finite difference
method is that it does not require a structured mesh, although a structured mesh can be used. The FVM can solve problems on
irregular geometries. Furthermore, one advantage of the finite volume method over the finite element method is that it can
conserve the variables on a coarse mesh easily. This is an important characteristic for fluid problems just as in this case.
Finally, conclusions of this study are exposed. 相似文献
5.
Prabal Talukdar F. V. Issendorff D. Trimis C. J. Simonson 《Heat and Mass Transfer》2008,44(6):695-704
Interaction of conduction and radiation in 3D enclosures is carried out with a gray participating media. Application of block
structured grid is shown with the finite volume method (FVM). Radiation modeling is performed with the FVM and is coupled
with an ‘in-house’ code to solve the set of transport equations. The detailed numerical results are presented for a cubical
and a cylindrical enclosure as these results are not available in the literature. The numerical simulation for the cylindrical
enclosure is performed using a block-structured ‘O’ grid. Two additional geometries are considered in order to show the applicability
of the present work. Results of temperature, radiative heat flux and total heat flux distributions are presented for different
optical thicknesses, scattering albedoes, emissivities and conduction–radiation parameters. The 3D results are validated with
the available 2D results or results with pure radiation problems as limiting cases. 相似文献
6.
7.
The two-dimensional quasi-steady conduction equation governing conduction controlled rewetting of an infinite tube, with
outer surface flooded and the inside surface subjected to a constant heat flux, has been solved by Wiener–Hopf technique.
The solution yields the quench front temperature as a function of various model parameters such as Peclet number, Biot number
and dimensionless heat flux. Also, the dryout heat flux is obtained by setting the Peclet number equal to zero, which gives
the maximum sustainable heat flux to prevent the dryout of the coolant.
Received on 6 September 2000 / Published online: 29 November 2001 相似文献
8.
A. Loghman A. Ghorbanpour Arani A. R. Shajari S. Amir 《Archive of Applied Mechanics (Ingenieur Archiv)》2011,81(12):1853-1864
Time-dependent creep stress redistribution analysis of rotating disk made of Al–SiC composite is investigated using Mendelson’s
method of successive elastic solution. All mechanical and thermal properties except Poisson’s ratio are radial dependent based
on volume fraction percent of SiC reinforcement. The material creep behavior is described by Sherby’s constitutive model using
Pandey’s experimental results on Al–SiC composite. Loading is an inertia body force due to rotation and a distributed temperature
field due to steady-state heat conduction from inner to outer surface of the disk. Using equations of equilibrium, stress
strain, and strain displacement, a differential equation, containing creep strains, for displacement is obtained. History
of stresses and deformations are calculated using method of successive elastic solution. It is concluded that the uniform
distribution of SiC reinforcement does not considerably influence on stresses. However, the minimum and most uniform distribution
of circumferential and effective thermoelastic stresses belongs to composite disk of aluminum with 0% SiC at inner surface
and 40% SiC at outer surface. It has also been found that the stresses, displacement, and creep strains are changing with
time at a decreasing rate so that after almost 50 years the solution approaches the steady-state condition. 相似文献
9.
The objective of this study relates to the numerical simulation of the free surface during the two-dimensional flow and solidification
of aluminum in the horizontal cylinder and mold cavity of the high pressure die casting HPDC machine with cold chamber. The
flow is governed by the Navier–Stokes equations (the mass and the momentum conservations) and solved in the two phase’s liquid
aluminum and air. The tracking of the free surface is ensured by the VOF method. The equivalent specific heat method is used
to solve the phase change heat transfer problem in the solidification process. Considering the displacement of the plunger,
the geometry of the problem is variable and the numerical resolution uses a dynamic grid. The study examines the influence
of the plunger speed on the evolution of the interface aluminum liquid–air profile, the mass of air imprisoned and the stream
function contours versus time. Filling of a mold is an essential part of HPDC process and affects significantly the heat transfer
and solidification of the melt. For this reason, accurate prediction of the temperature field in the system can be achieved
only by including simulation of filling in the analysis. 相似文献
10.
Two space marching methods for solving the one-dimensional nonlinear inverse heat conduction problems are presented. The
temperature-dependent thermal properties and the boundary condition on the accessible part of the boundary of the body are
known. Additional temperature measurements in time are taken with a sensor located in an arbitrary position within the solid,
and the objective is to determine the surface temperature and heat flux on the remaining part of the unspecified boundary.
The methods have the advantage that time derivatives are not replaced by finite differences and the good accuracy of the method
results from an appropriate approximation of the first time derivative using smoothing polynomials. The extension of the first
method presented in this study to higher dimensions inverse heat conduction problems is straightforward.
Received on 3 May 1999 相似文献
11.
Dynamic analysis of functionally graded plates using the hybrid Fourier-Laplace transform under thermomechanical loading 总被引:1,自引:0,他引:1
In this study, the analytical solution is presented for dynamic response of a simply supported functionally graded rectangular
plate subjected to a lateral thermomechanical loading. The first-order and third-order shear deformation theories and the
hybrid Fourier-Laplace transform method are used. The material properties of the plate, except Poisson’s ratio, are assumed
to be graded in the thickness direction according to a power-law distribution in terms of the volume fractions of the constituents.
The plate is subjected to a heat flux on the bottom surface and convection on the upper surface. A third-order polynomial
temperature profile is considered across the plate thickness with unknown constants. The constants are obtained by substituting
the profile into the energy equation and applying the Galerkin method. The obtained temperature profile is considered along
with the equations of motion. The governing partial differential equations are solved using the finite Fourier transformation
method. Using the Laplace transform, the unknown variables are obtained in the Laplace domain. Applying the analytical Laplace
inverse method, the solution in the time domain is derived. The computed results for static, free vibration, and dynamic problems
are presented for different power law indices for a plate with simply supported boundary conditions. The results are validated
with the known data reported in the literature. Furthermore, the results calculated by the analytical Laplace inversion method
are compared with those obtained by the numerical Newmark method. 相似文献
12.
The approximate solutions to the non-linear heat conduction problems in a semi-infinite medium are investigated. The entire temperature range is divided into a number of small sub-regions where the thermal properties can be approximated to be constant. The resulting problems can be considered as the Stefan’s problem of a multi-phase with no latent heat and the exact solutions called Neumann’s solution are available. In order to obtain the solutions, however, a set of highly non-linear equations in determining the phase boundaries should be solved simultaneously. This work presents a semi-analytic algorithm to determine the phase boundaries without solving the highly non-linear equations. Results show that the solutions for a set of highly non-linear equations depend strongly on the initial guess, bad initial guess leads to the wrong solutions. However, the present algorithm does not require the initial guess and always converges to the correct solutions. 相似文献
13.
Hyperbolic heat conduction in a plane slab, infinitely long solid cylinder and solid sphere with a time dependent boundary
heat flux is analytically studied. The solution is based on the separation of variables method and Duhamel’s principle. The
temperature distribution, the propagation and reflection of the temperature wave and the effect of geometry on the shape of
the wave front are studied for the case of a rectangular pulsed boundary heat flux. Comparisons with the solution obtained
for Fourier heat conduction are performed by considering the limit of a vanishing thermal relaxation time. 相似文献
14.
In this paper, we consider the efficient estimation of local boiling heat fluxes from transient temperature measurements in
the heater close to the heater surface. For accurate prediction, heat flux estimation is formulated as a transient three-dimensional
(3D) inverse heat conduction problem (IHCP). This inverse problem is ill-posed and cannot be treated straightforwardly by
established numerical methods. In order to obtain a regularized stable solution, a large-scale time-dependent PDE-constrained
optimization problem has to be solved and an appropriate stopping criterion for the termination of the iterative solution
process has to be chosen. Since the boiling heat flux is non-uniformly distributed on the heater surface due to the strong
local activity of the boiling process, the use of a fixed uniform spatial discretization is not efficient. Instead, an adaptive
mesh refinement strategy can be used to obtain an appropriate discretization which significantly reduces the total computational
effort. In this work, we present an automatic algorithm incorporating an adaptive mesh refinement via a heat flux-based a-posteriori
error estimation technique. The suggested algorithm can cope with both spatially point-wise or highly resolved temperature
observations efficiently. It is applied to real measurement data obtained from two different types of pool boiling experiments.
The numerical results show that the computational effort can be reduced significantly for given estimation quality. This adaptive
IHCP solution technique can be also viewed as an efficient soft sensor to deduce unmeasurable local boiling heat fluxes. 相似文献
15.
A technique for determining the heat transfer on the far surface of a wall based on measuring the heat flux and temperature on the near wall is presented. Although heat transfer measurements have previously been used to augment temperature measurements in inverse heat conduction methods, the sensors used alter the heat flow through the surface, disturbing the very quantity that is desired to be measured. The ideal sensor would not alter the boundary condition that would exist were the sensor not present. The innovation of this technique in that it has minimal impact on the wall boundary condition. Since the sensor is placed on the surface of the wall, no alteration of the wall is needed. The theoretical basis for the experimental technique as well as experimental results showing the heat flux sensor performance is presented. 相似文献
16.
采用近场动力学微分算子(Peridynamic Differential Operator, PDDO)理论建立正交各向异性板热传导的非局部模型。通过构造近场动力学函数,将边界条件和热传导方程由局部微分形式转化为非局部积分形式,引入Lagrange乘子,采用变分分析对含裂纹正交各向异性板温度及裂纹尖端的热通量分布进行求解。通过对比算例,验证了该模型具有较好的收敛性和有效性。分析了正交各向因子、材料铺设角、裂纹倾角及间距对裂纹尖端热通量的影响。结果表明,基于PDDO建立的含裂纹正交各向异性板热传导模型,考虑了热传导问题中的非局部性,能有效提高计算精度,预测含裂纹板中裂纹尖端出现的奇异性。 相似文献
17.
P. R. Hakenesch 《Experiments in fluids》1999,26(3):257-265
In order to overcome the shortcomings of conventional temperature instrumentation to compute heat transfer rates, a novel
technique for heat transfer measurement is presented. Stemming from infrared thermography, the potential for further development
of the ‘Thin Layer Thermography’ is demonstrated. This new measurement technique is based on the wavelength dependent transmissivity
of thin layers. It captures temperature distributions on the wall surface and simultaneously in a prescribed and well defined
depth of the wall of a given object of interest. This enables the calculation of a temperature gradient normal to the surface
and therefore the determination of the wall heat flux.
Received: 8 April 1998/Accepted: 12 August 1998 相似文献
18.
R. Kandasamy I. Muhaimin Hashim Bin Saim 《Journal of Applied Mechanics and Technical Physics》2010,51(6):887-897
A group analysis has been carried out to study heat and mass transfer characteristics of an incompressible Newtonian fluid
having a temperature-dependent viscosity over a vertical stretching surface in the presence of thermal radiation and a chemical
reaction. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The vertical surface
is assumed to be permeable so as to allow for possible wall suction or injection. The governing differential equations are
derived and transformed using the Lie group analysis. The transformed equations are solved numerically by applying the Runge—Kutta—Gill
scheme with the shooting technique. Favorable comparisons with previously published works on various special cases of the
problem are obtained 相似文献
19.
Benoit Stutz Monique Lallemand Fabien Raimbault Julio Passos 《Heat and Mass Transfer》2009,45(7):929-935
Nucleate and transition boiling are performed in a horizontal narrow space between a heated upward-facing copper disk and
an unheated surface for saturated n-pentane. The heat flux and the wall temperature are determined by mean of an inverse heat conduction method. The influence
of the confinement on the boiling curves and the flow patterns are analysed. Characteristic instabilities are observed at
low heat flux and during the transition regime. 相似文献
20.
In this paper, the authors introduce a robust numerical technique for radiation–conduction heat transfer in the high temperature
fields of gas turbine combustors. The conduction and radiation effects are analyzed by a differential and an integral equation,
respectively. Using discrete ordinates for the angular discretization of the integral equation for the radiation effects and
a Galerkin discretization for the heat equation, the authors propose a fast multilevel algorithm to solve the fully discretized
problem. The algorithm uses the same mesh hierarchy for both radiation and conduction effects, but with two different smoothing
operators. Numerical results are shown for test problems in three space dimensions, and comparisons to other methods are also
given. 相似文献