THERMOPHORESIS OF PARTICLES IN GAS-PARTICLE TWO-PHASE FLOW WITH RADIATION EFFECT

The radiation effect on the thermophoresis of particles is analyzed for a gas-particle twophase laminar flow. Two-phase radiation by both gas and particles is considered; in addition, the thermal nonequilibrium between gas and particle is taken into account. It is concluded that the particle diffusion velocity as well as particle concentration depends strongly on the optical radius of gas or particle. In general, the radiation was found to decrease the particle diffusion. In case that gas as well as particle radiation exists, the deposition of particle is mainly influenced by the gas. The effects of parameters such as the optical radius, conduction to radiation parameter, thermal loading ratio, and wall emissivity on the cumulative collection efficiency E ( x ) are also considered. As the optical radius and tube wall emissivity increase, E ( x ) decreases. The increase in conduction to radiation parameter N and thermal loading ratio CL leads to an increase in E ( x ).     

WAVE PROPAGATION IN TWO-PHASE FLOW BASED ON A NEW HYPERBOLIC TWO-FLUID MODEL

A high-resolution up wind scheme based on the flux vector splitting method is developed for the two-fluid six-equation model to solve the wave propagation problems of two-phase flow. The interfacial pressure jump terms make the governing equations hyperbolic without any conventional source terms in the momentum equations. Real eigenvalues are obtained for all the bubbly, slug, and annular flow regimes. Calculated speeds of sound have shown excellent agreement with the existing experimental data. Solutions to wave propagation problems withinitial pressure and void distribution are presented. The Edwards pipe problem accompanied by sudden depressurization and flashing also is solved as a benchmark test.     

ON THE PROPAGATION OF THE THERMAL WAVES IN MATERIALS WITH MEMORY

The propagation of one-dimensional acceleration waves in linear thermoelastic materials with thermal memory is analyzed. It is shown that two types of waves may exist, and the properties of velocities and attenuation of these waves are examined. The obtained results are compared with the data of the previous works     

THE EFFECTS OF RADIATION ON NATURAL CONVECTION IN A RECTANGULAR ENCLOSURE DIVIDED BY TWO PARTITIONS

The phenomena of radiation-affected steady-laminar natural convection in a rectangular enclosure with two incomplete partitions are numerically examined under a large temperature difference. Pure convection, convection with surface radiation, and convection with surface gas radiation are considered and compared. To examine the effects of two incomplete partitions on thermofluid dynamics behavior, they are assumed to be very thin and adiabatic. The finite-volume method (FVM) is used for solving the radiative transport equation, assuming that partitions are radiatively opaque. After validating the numerical procedures, the detailed radiation effects were sought. Based on the results of this study, it was found that the radiation played a significant role in developing the fluid dynamic and thermal distributions compared with cases without radiation. Once radiation was involved, the surface radiation was dominant over the gas radiation. The baffle configuration was also found to affect the results of radiation.     

ANALYSIS OF TWO-PHASE RADIATION IN THERMALLY DEVELOPING POISEUILLE FLOW

Combined conductive and radiative heat transfer in a thermally developing two-phase Poiseuille flow in a cylindrical duct is studied here. A two-phase radiative transfer equation (RTE) considering radiation by both gas and particles is taken into account. A complexform of nonlinear integrodifferential RTE is solved by the discrete ordinates method (DOM, or so called SN method) in axisymmetric geometry. After such validation, namely, the solution in a two-dimensional channel flow between two flat plates is compared with that solved by the zone method, the program is then applied to fully developed gas-particle two-phase flow in a cylindrical duct. A parametric study is performed for gas and particle absorption coefficients, particle number density, particle emissivity, and wall emissivity. The results show a significant effect of two-phase radiation on the thermal characteristics. However, in all cases, it was found that conduction is predominant near the wall.     

ROLE OF ABSORPTION COEFFICIENT IN THE FREQUENCY DEPENDENCE OF THE THERMAL STRESSES IN A PARTIALLY ABSORBING PLATE SUBJECTED TO CYCLIC THERMAL RADIATION: A BRIEF NOTE

The frequency dependence of the thermal stresses in a partially absorbing plate subjected to cyclic thermal radiation is shown to be a function of optical thick ness.     

STUDY OF THERMOELASTIC WAVE PROPAGATION IN A HALF-SPACE USING GN THEORY

Thermoelastic interactions in an isotropic homogeneous elastic half-space are studied using mathematical methods under the purview of the GN model of linear theory of generalized thermoelasticity. Of specific concern here is the propagation of waves owing to ramp-type heating of the bounding surface, which is either (i) traction-free or (ii) held rigidly fixed whereby the displacement is constrained. Using the integral transform approach, approximate solutions valid in the small time range are obtained for the situation when Fourier conductivity is dominant. Also exact solutions for temperature, displacement, and stress fields are obtained for the same problem for cases where conductivity is ignorable. Numerical estimates are also obtained for a particular example.     

EFFECTS OF COATING LAYER WITH PIGMENT ON THE REFLECTANCE OF EXTERNAL RADIATION

A coating layer with pigment is known to reflect radiation. This knowledge can be used to reduce the hazard of combustible materials exposed to fire. In order to obtain high reflectivities in the infrared range ( 0.4-10 μm), several dielectric pigments, such as titanium dioxide, iron oxide, and silicon, can be synthesized to polymer coatings. In this numerical analysis of radiation, the effects of the dependent scattering, the absorption in a polymeric binder, and the internal interface reflection on the reflectance are elucidated. The finite volume method is used to solve the nongray radiative transfer equation for the absorbing, emitting, and highly anisotropic scattering medium. The results show that a coating layer with pigment size in the range 1.5-2.5 μm and volume fraction in the range 0.1— 0.2 is found to be very effective in retarding the surface temperature increase of the substrate. A detailed temperature variation in the semitransparent coating layer and an opaque substrate ( polymethyl metaerylate, or PMMA) is also obtained to examine the thermal effects of the coating with a view toward fire safety.     

溃坝洪水波在天然梯级水库中的传播

将双曲型方程的ＴＶＤ和ＥＮＯ格式推广于一维浅水方程组，构造了一种守恒算法，将其用于天然河溃坝波传播计算，算得结果和解析解符合好，分辨率高，实际天然梯级水库溃坝洪水波传播的数值模拟表明该格式稳定，适应性强。     

建筑室内人体太阳辐射得热特性及数值模拟

太阳辐射对建筑室内人体热舒适和建筑能耗有着显著影响.通过实测验证了daylight coefficient(DC)算法模拟太阳辐射强度的准确性.随后基于假人仿真模型采用DC算法计算室内人体平均辐射温度增量(ΔMRT),与SolarCal(SC)算法结果作对比,并对SC算法进行改进.相比原SC算法,改进SC算法与DC算法...     

太阳辐射下不同地表覆盖物的热反应及对城市热环境的影响

该文利用红外热像仪等设备研究了建筑物表面、绿地、柏油路面、水泥砖地面等城市地表覆盖物对太阳辐射的热反应，指出在同一天中，柏油路面温度最高，水泥砖和建筑物表面次之，绿地温度最低。通过分析各种覆盖物在城市中所占比例，得出建筑物对城市热环境影响较大的结论，并提出了改善城市热环境的几种方法。     

THE DISCRETE MAXIMUM PRINCIPLE IN FINITE-ELEMENT THERMAL RADIATION ANALYSIS

Under certain conditions, usually intense surface heat transfer associated with radiation, finite-element solutions display anomalous behaviors. These behaviors have been traced to the violation of a discrete maximum principle. Here, necessary and sufficient conditions for satisfaction of the discrete maximum principle are discussed. Special elements that satisfy a discrete maximum principle for a wider range of parameters, thereby improving the accuracy of the solution, are introduced into standard finite-element formulations for the heat conduction equation. The improved performance of these elements is then demonstrated by means of a few examples.     

MODELING OF THERMAL CRACKING IN ELASTIC AND ELASTOPLASTIC TWO-PHASE SOLIDS

A review is given about fracture mechanical investigations concerning the thermal crack initiation and propagation in one of the segments or in the material interface of two-arid three-dimensional self-stressed two-phase compounds. The resulting boundary value problems of the stationary thermoelasticity and thermoplasticity for the cracked two- and three-dimensional bimaterial structures considered are solved using the finite element method. Furthermore, by applying an appropriate crack growth criterion based on the numerical calculation of the total energy release rate G of a quasistatic mixed-mode crack extension the further development of thermal crack paths starting at the intersection line of the material interface with the external stressfree surface of the two- and three-dimensional elastic bimaterials could be predicted. In the case of the disklike two-phase compounds, the theoretically predicted crack paths show a very good agreement with results gained by associated cooling experiments. Several specimen geometries consisting of different material combinations and subjected to uniform and nonuniform temperature distributions have been studied using the relevant methods of fracture mechanics. Thereby thermal cracks propagating in one segment of an elastic bimaterial only obey the condition G_II = 0, whereas for interface cracks a mixed-mode propagation is always existent where the G_II values play an important role. Moreover, by applying the proposed crack growth criterion the possible crack kinking direction ? of an interface crack tip out of the interface could be predicted by taking into consideration the finite thickness of an interlayer (interphase). In addition, an analysis of the stress and strain fields in the vicinity of thermal interface cracks in the discontinuity area of two- and three-dimensional elastoplastic two-phase compounds has been performed by using the FE-method. Thereby a heat source Q was assumed in one of the two materials in the neighborhood of an interface crack tip. The corresponding stress states in the bimaterial structuresand especiallyin the vicinity of the interface crack tip have been calculated by applying the incremental I₂-plasticity and using a bilinear hardening material law and based on a sequentially coupled solution of the heat transfer and the thermal stress boundary value problems. Finally, the failure assessment has been performed on the basis of the local J-integral which, for three-dimensional interface cracks, was recently generalized by two of the authors.     

近地倾斜轨道航天器在轨热辐射分析

根据航天器轨道动力学和热辐射理论，建立了运行于近地倾斜轨道的圆柱形航天器外热流数学模型；用数值方法对外热流和等效热沉温度进行求解，计算出瞬态工况及周期平均工况下的航天器表面辐射热流及辐射散热器和防辐射涂层表面等效热沉温度的波动。结果表明，航天器受到的辐射热流除了随航天器绕地球公转变化外，还随其轨道面的旋转在更长的周期上产生更大的变化；对柱面上的不同位置受到的辐射作了比较，发现辐射散热器布置在顶部时其等效热沉温度最低。     

ELECTROMAGNETO-THERMOELASTIC PLANE WAVES WITH THERMAL RELAXATION IN A MEDIUM OF PERFECT CONDUCTIVITY

The model of the two-dimensional equations of generalized magneto-thermoelasticity with one relaxation time in a perfectly conducting medium is established. The normal mode analysis is used to obtain the exact expressions for the temperature distribution, thermal stresses, and the displacement components. The resulting formulation is applied to three different concrete problems. The first deals with a thick plate of perfect conductivity subjected to a time-dependent heat source on each face; the second concerns the case of a heated punch moving across the surface of a semi-infinite thermoelastic half-space of perfect conductivity subject to appropriate boundary conditions; and the third problem deals with a plate with thermo-isolated surfaces subjected to time-dependent compression. Numerical results are given and illustrated graphically for each problem. Comparisons are made with the results predicted by the coupled theory and with the theory of generalized thermoelasticity with one relaxation time.     

EFFECT OF INTERFACE REFLECTIONS AND ANGLE OF INCIDENCE OF RADIATION ON THERMAL STRESSES IN SEMI-TRANSPARENT MATERIALS

The objectives are to determine the effects of internal reflections on the thermal stresses generated by radiation absorption in a semi-transparent flat plate, and to study the effect of varying the angle of incidence. Both suddenly applied and suddenly removed radiation from an established steady-state condition are considered.     

PROPAGATION OF A PLANE WAVE IN A THERMOELASTIC HALF-SPACE UNDER SMOOTH HEATING OF ITS BOUNDARY

In this paper a closed-form solution to a plane wave propagation problem for a half-space subject to a uniform time-dependent healing of its boundary in the framework of dynamic theory of thermal stresses is presented. The solution is given for two variants of smooth boundary heating. The numerical results are shown in the form of graphs of stress and temperature versus the distance from the loaded boundary.     

EFFECTS OF THERMAL RELAXATIONS ON THERMOVISCOELASTIC INTERACTIONS IN AN UNBOUNDED BODY WITH A SPHERICAL CAVITY SUBJECTED TO A PERIODIC LOADING ON THE BOUNDARY

Thermoviscoelastic interactions in an infinite homogeneous viscoelastic medium with a spherical cavity are studied. The cavity surface is subjected to a periodic loading and zero temperature change. The classical dynamical theory of thermoelasticity as well as the generalized theories of thermoelasticity are applied to consider the thermoelastic coupling. The analytical expressions for the closed-form solutions of displacement, temperature, and stresses are obtained; and the thermal relaxation effects on the interactions are studied to compare the three theories. The numerical values of the physical quantities are computed for a suitable material. The results are presented graphically to illustrate the problem.     

太阳辐射影响下的城市户外热环境评价指标

根据室内热舒适指标PMV，建立了评价城市户外热环境的舒适性指标，该指标在室内能与PMv很好的吻合，在户外能反映太阳辐射的影响，可与热应力指标wBGT一起作户外全范围的热环境质量评价，对城市环境的规划与设计有重要的指导意义。