共查询到20条相似文献,搜索用时 0 毫秒
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N. Fox 《Applied Scientific Research》1964,13(1):144-148
Summary A derivation is given of the thermal stress system associated with a source of heat moving with uniform velocity through an infinite medium. 相似文献
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Mehdi Bidabadi Saeedreza Zadsirjan Seyed Alireza Mostafavi 《Heat and Mass Transfer》2014,50(6):759-767
In the present paper, combustion of dust clouds from the discrete point heat source method has been addressed. Time-place temperature profile generated by single particle burning has been obtained to study the dust combustion. The summation of the temperature profiles of burned and burning particles predict the temperature in the preheating zone so that the ignition time of layer in flame front can be determined. Consequently the flame propagating speed was obtained based on the dust concentration corresponding to particles spacing and particle diameter. This method has been validated with aluminum dust cloud combustion. Decrease in the dust concentration leads to the lean limit of dust combustion. Increase in particles diameter or reduction in the dust concentration causes higher lean limit and also reduction in the flame propagating speed. Adding the ignition energy as igniter to this system, provides the path to study the effects of ignition energy in the dust combustion. 相似文献
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This paper presents alternative approach in heat transfer analysis of plate heat exchangers. In order to obtain heat transfer
rate and effectiveness values of plate heat exchanger, neural network (NN) approach was used. Experimentally, system used
in plate heat exchanger for heating and cooling applications was designed and constructed. Experimental data were used for
training and testing network. The training and validation were performed with good accuracy. The correlation coefficient obtained
when unknown data were applied to the networks was 0.9994 for heat transfer rate and 0.9976 for effectiveness, which is very
satisfactory. Using the weights obtained from the trained network, a new formulation is presented for determination of heat
transfer rate and effectiveness. This formulation can provide simplicity in thermal analysis of plate heat exchanger. The
presented procedure can also help to heat exchanger designer and manufacturer. 相似文献
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Jung-Chang Wang 《Heat and Mass Transfer》2014,50(11):1487-1498
This study utilizes a versatile superposition method with thermal resistance network analysis to design and experiment on a thermal module with embedded six L-shaped or two U-shaped heat pipes and plate fins under different fan speeds and heat source areas. This type of heat pipes-heat sink module successively transfer heat capacity from a heat source to the heat pipes, the heat sink and their surroundings, and are suitable for cooling electronic systems via forced convection mechanism. The thermal resistances contain all major components from the thermal interface through the heat pipes and fins. Thermal performance testing shows that the lowest thermal resistances of the representative L- and U-shaped heat pipes-heat sink thermal modules are respectively 0.25 and 0.17 °C/W under twin fans of 3,000 RPM and 30 × 30 mm2 heat sources. The result of this work is a useful thermal management method to facilitate rapid analysis. 相似文献
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A generalized thermal boundary condition is derived for the hyperbolic heat conduction equation to include all thermal effects
of a thin layer, whether solid-skin or fluid film, moving or stationary, in perfect or imperfect thermal contact with an adjacent
domain. The thin layer thermal effects include, among others, thermal capacity of the layer, thermal diffusion, enthalpy flow,
viscous dissipation within the layer and convective losses from the layer. Six different kinds of thermal boundary conditions
can be obtained as special cases of the generalized boundary condition. The importance of the generalized boundary condition
is demonstrated comprehensively in an example. The effects of different geometrical and thermophysical properties on the validity
of the generalized thermal boundary condition are investigated.
Received on 23 May 2001 / Published online: 29 November 2001 相似文献
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Ján Beňačka 《Heat and Mass Transfer》2008,44(7):873-887
The paper gives the analytical solution to the one dimensional hyperbolic heat conduction equation in an insulated slab-shaped
sample that is heated uniformly on the front face with δ or laser impulse. The solution results in a formula that enables
to estimate the minimum mean free path of energy carriers in the sample to detect the second sound (i.e. the thermal wave)
at the sample rear face. A method of experimental data evaluation at the second sound effect is proposed, which gives the
thermal diffusivity of the sample and the parameters of heat propagation. 相似文献
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在急剧温度变化等强间断温度冲击作用下的生物层合组织非傅里叶热传导分析中,经典时域连续有限元方法(如Newmark等方法)会在波阵面以后的和层合组织界面附近的区域表现出强烈的数值振荡。这类数值振荡会影响问题求解精度,并带来较大不确定性。针对这类现象,本文发展了改进时域间断Galerkin有限元方法,进一步开展了相关问题的数值模拟。其控制方程的基本未知数(温度)及其时间导数在指定时间间隔内假设存在间断且独立插值。在有限元离散列式中引入比例刚度阵人工阻尼,以成功消除波前位置的虚假数值振荡行为。通过算例对比分析,相比Newmark方法和传统间断Galerkin方法,所提出的改进时域间断Galerkin有限元方法较好消除了波前、波后以及组织界面处的数值振荡,有效捕捉了波阵面的间断行为,提高了计算的精度。 相似文献
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The classical Green’s functions used in the literature for a heat source in a homogeneous elastic medium cannot lead to finite remote thermal stresses in the medium, so that they may not work well in practical thermal stress analyses. In this paper, we develop a practical Green’s function for a heat source disposed eccentrically into an elastic disk/cylinder subject to plane deformation. The edge of the disk/cylinder is assumed to be thermally permeable and traction-free. The full thermal stress field induced by the heat source in the disk/cylinder is determined exactly and explicitly via the Cauchy integral techniques. In particular, a very simple formula is obtained to describe the hoop thermal stress on the edge of the disk/cylinder, which may be conveniently useful for analyzing the thermal stresses in microelectronic components. 相似文献
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Phonon cross-plane transport across silicon and diamond thin films pair is considered, and thermal boundary resistance across the films pair interface is examined incorporating the cut-off mismatch and diffusive mismatch models. In the cut-off mismatch model, phonon frequency mismatch for each acoustic branch is incorporated across the interface of the silicon and diamond films pair in line with the dispersion relations of both films. The frequency-dependent and transient solution of the Boltzmann transport equation is presented, and the equilibrium phonon intensity ratios at the silicon and diamond film edges are predicted across the interface for each phonon acoustic branch. Temperature disturbance across the edges of the films pair is incorporated to assess the phonon transport characteristics due to cut-off and diffusive mismatch models across the interface. The effect of heat source size, which is allocated at high-temperature (301 K) edge of the silicon film, on the phonon transport characteristics at the films pair interface is also investigated. It is found that cut-off mismatch model predicts higher values of the thermal boundary resistance across the films pair interface as compared to that of the diffusive mismatch model. The ratio of equilibrium phonon intensity due to the cut-off mismatch over the diffusive mismatch models remains >1 at the silicon edge, while it becomes <1 at the diamond edge for all acoustic branches. 相似文献
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The theory of temperature variation at any point in an infinitely extending medium containing an infinitely long thin conducting wire, heated periodically, is applied to a probe having finite dimensions and thermal properties. The conditions for a minimal effect due to finite dimension of the medium and contact resistance between the probe and medium are discussed. The results of thermal conductivity and diffusivity, thus obtained, are reported. The thermal probe method under periodic conditions gives satisfactory results. 相似文献
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C.Wafo Soh 《International Journal of Non》2003,38(7):991-997
We prove that the incompressible 2D steady thermal boundary layer equations with temperature-dependent kinematic viscosity ν and thermal diffusivity α is maximally symmetric provided the Prantl number Pr=ν/α is constant and or ν=K2(AT+B)K1 if we neglect energy dissipation and if we take into account dissipation. This result corroborates assumptions often made in applications. When we disregard dissipation, the symmetry Lie algebra assumes the forms Lr⊕L∞, where L∞ is an infinite-dimensional Lie algebra and Lr is an r-dimensional Lie algebra with r∈{3,4,5,6}. If we include dissipation, r∈{2,3}. We notice that dissipation has a symmetry breaking effect.We also show how the symmetries can be employed for the calculation of invariant solutions. 相似文献
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With a previously developed numerical model, we perform a detailed study of the heat extraction process in enhanced or engineered geothermal system (EGS). This model takes the EGS subsurface heat reservoir as an equivalent porous medium while it considers local thermal non-equilibrium between the rock matrix and the fluid flowing in the fractured rock mass. The application of local thermal non-equilibrium model highlights the temperature-difference heat exchange process occurring in EGS reservoirs, enabling a better understanding of the involved heat extraction process. The simulation results unravel the mechanism of preferential flow or short-circuit flow forming in homogeneously fractured reservoirs of different permeability values. EGS performance, e.g. production temperature and lifetime, is found to be tightly related to the flow pattern in the reservoir. Thermal compensation from rocks surrounding the reservoir contributes little heat to the heat transmission fluid if the operation time of an EGS is shorter than 15 years. We find as well the local thermal equilibrium model generally overestimates EGS performance and for an EGS with better heat exchange conditions in the heat reservoir, the heat extraction process acts more like the local thermal equilibrium process. 相似文献
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The choices of the parameterizations for each component in a microwave emission model have significant effects on the quality of brightness temperature (T b) simulation. How to reduce the uncertainty in the T b simulation is investigated by adopting a statistical post-processing procedure with the Bayesian model averaging (BMA) ensemble approach. The simulations by the community microwave emission model (CMEM) coupled with the community land model version 4.5 (CLM4.5) over mainland China are conducted by the 24 configurations from four vegetation opacity parameterizations (VOPs), three soil dielectric constant parameterizations (SDCPs), and two soil roughness parameterizations (SRPs). Compared with the simple arithmetical averaging (SAA) method, the BMA reconstructions have a higher spatial correlation coefficient (larger than 0.99) than the C-band satellite observations of the advanced microwave scanning radiometer on the Earth observing system (AMSR-E) at the vertical polarization. Moreover, the BMA product performs the best among the ensemble members for all vegetation classes, with a mean root-mean-square difference (RMSD) of 4K and a temporal correlation coefficient of 0.64. 相似文献
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The effects of radiative losses on the thermal behavior of thin metal films, as described by the microscopic two-step hyperbolic heat conduction model, are investigated. Different criteria, which determine the ranges within which thermal radiative losses are significant, are derived. It is found that radiative losses from the electron gas are significant in thin films having [(CR ee4/3 T¥ 4 )/(ke1/3 L2/3 G)] 3 4.6 ×107{{C_R \epsilon _e^{{4 \over 3}} T_\infty ^4 } \over {k_e^{{1 \over 3}} L^{{2 \over 3}} G}}\geq 4.6 \times 10^7 for /o > 4 and FF < 1 and [(CR ee3/2 T¥ 9/2)/(ke1/2 L1/2 G)] 3 7.4 ×1010{{C_R \epsilon _e^{{3 \over 2}} T_\infty ^{{9 \over 2}}} \over {k_e^{{1 \over 2}} L^{{1 \over 2}} G}}\geq 7.4 \times 10^{10} for /o < 4 and FF > 1. 相似文献
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Intrinsic thermal stability denotes a situation where a superconductor can carry the operating current without Joule heating at all times after the occurrence of a localized release of thermal disturbance. The present work deals with the intrinsic thermal stability of an anisotropic thin-film superconductor under a localized release of thermal energy. A three-dimensional analysis is introduced to consider an instantaneous release of energy in the form of a point source at different locations. Through the transformation of coordinate, an exact solution is obtained by the method of separation of variables. Results from this study indicate that the thermal stability parameter of highly oriented films of superconductors is strongly under the influence of anisotropy. The stability parameter also depends on the location of point source, the amount of disturbance energy, the Biot number, and the aspect ratio in the plane of thin film and normal to it.Inhärente thermische Stabilität bezeichnet einen Zustand, in dem ein Supraleiter den Betriebsstrom zu allen, einer örtlich begrenzten thermischen Störung folgenden Zeiten ohne Joulesche Erwärmung transportieren kann. Die vorliegende Arbeit befaßt sich mit der inhärenten Stabilität eines anisotropen Dünnfilm-Supraleiters bei örtlich begrenzter Freisetzung thermischer Energie. Um die plötzliche Energiefreisetzung in Form einer Punktquelle an verschiedenen Stellen aufprägen zu können, wird die Untersuchung dreidimensional durchgeführt. Nach einer Koordinaten-transformation erhält man die exakte Lösung mittels der Methode der Variablentrennung. Die Ergebnisse dieser Studie zeigen, daß der thermische Stabilitätsparameter hochorientierter Supraleitfilme stark von Anisotropieeinflüssen abhängt, ferner von der Lokalisation der Punktquelle, dem Betrag der Störenergie, der Biot-Zahl sowie dem Seitenverhältnis in der Dünnfilm-Ebene und normal dazu. 相似文献
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《中国惯性技术学报》2015,(4)
自由转子陀螺是一种二自由度机电陀螺,其漂移特性可应用二次型漂移误差模型描述。从二次型漂移误差模型出发,推导了壳体翻滚条件下的调制平均漂移误差模型,并推广到空间稳定平台上工作的极轴陀螺和赤道陀螺;列写了二次型陀螺漂移误差模型驱动下的空间稳定平台标称运动方程;经过扰动线性化,求解出平台标称运动轨迹增量坐标的解析表达式;基于扰动线性化模型并考虑到加速度计测量误差,证明了观测变量为纬度误差、经度误差及冗余轴转角误差时,空间稳定平台运动方程的17项误差系数都是可辨识的;分析了该17项误差系数的估计精度与加速度计组合件测量误差的关系。仿真和实验结果表明本文提出的通用误差模型是有效的。 相似文献
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In this work, we analyse the influence of the sample shape on the experimental determination of the thermal diffusivity of
materials used in several engineering fields. By means of a simple method we obtain good estimations of the overall thermal
diffusivity for homogeneous or inhomogeneous materials. The method is based on the combination of simple temperature measurements
with the analytical solution of the 3D differential Fourier’s equation applied to cartesian geometry. The classical transient
analytical solution based on the separation of space and time variables is adapted to particular thermal boundary conditions.
By associating these solutions with the measurements obtained on a simple experimental bench, the thermal characterization
of materials can be achieved with a satisfactory precision. The present 3D study attempts to complete previous works dealing
with cartesian and cylindrical 1D and 2D models. Based on the same procedure, it sheds further light on the fast multidimensional
surface phenomena of heat exchange. Although we conclude that the 3D model does not provide the directional values typical
of anisotropic materials, our results revealed that thermal diffusivity can be useful in other respects, being advantageous
in the overall thermal characterization needed for sizing certain systems. 相似文献