电子器件制造过程中的一种均匀化加热法的数值研究

本文提出了喷嘴沿被加热物体宽度方向往复移动式射流冲击加热方法,该加热方法可提高被加热物体的等温性。通过进行数值模拟,得到了在任意时刻,被加热物体的温度分布及全体计算时间内被加热物体表面平均温度分布,进而得到了喷嘴移动周期与被加热物体的等温性的关系。     

半透明介质表面红外测温的辐射传输模拟

考虑不透明漫射基底的反射/发射和半透明介质层的吸收/发射,建立半透明介质层表面红外测温过程的辐射传输模型,采用反向蒙特卡罗法进行模拟,获得探测表面在热像仪的指示辐射温度。与不透明表面红外测温进行比较,分析表面形状、基底发射率ε_s及介质层光学厚度τ的影响。结果表明,半透明介质层表面的指示辐射温度在ε_s1.0时,随τ的增大而增大,τ≥2时数值趋于ε_s=1.0时的结果,与不透明表面存在较大差异;针对复杂形状或内凹曲面红外测温,不透明表面和半透明介质层表面均受到反射其他部位辐射现象的影响。     

强化辐射换热涂层的性能研究

本文以实验研究与数值模拟相结合的方式,对喷涂了不同厚度的两种不同涂料的一系列CPU散热片进行了自然对流条件下的辐射强化换热研究,以测试这两种涂料的辐射强化换热性能,并找出其强化辐射换热的相关规律.实验与数值模拟的结果表明,这两种涂料的确能够强化辐射换热;散热片散热热阻在有适当厚度涂层时比无涂层时减少了10%左右;在相同热载荷及边界温度条件下,散热片温度在有涂层时比无涂层时降低多达4℃;对于同种涂料,涂层厚度越薄强化散热能力越强;对于相同厚度的涂层,涂料导热率越大其辐射散热能力越强.     

湍流射流火焰热辐射影响的数值研究

以美国Sandia实验室火焰D为研究对象,在采用κ-ε湍流模型、概率密度函数(PDF)法及详细化学反应机理模拟湍流燃烧的基础上,研究了辐射换热对湍流射流燃烧过程的影响。模拟中采用离散坐标法(DOM)求解辐射传递方程,并分别采用普朗克平均吸收系数和箱带模型计算燃烧气体的辐射特性参数。结果表明,考虑辐射换热的影响时,火焰温度及组分浓度分布计算值与实验值吻合更好,且采用考虑气体光谱辐射效应的箱带模型比仅随温度变化的普朗克平均吸收系数的计算值更接近实验值。因此,研究燃烧气体的辐射换热问题具有重要意义,同时需要考虑其光谱辐射效应。     

气动加热下高温陶瓷材料内的瞬态耦合换热

采用控制容积法结合蒙特卡罗法与谱带模型,数值模拟了气动加热下高温陶瓷内的辐射与导热瞬态耦合换热.分析了冷却边界条件、各向同性散射和表面特性对高温陶瓷内瞬态温度分布的影响.结果表明,高温下陶瓷内的辐射换热作用十分明显,陶瓷材料的表面特性对瞬态温度分布影响很大,各向同性散射也有明显影响.     

薄膜和半无限大介质间的近场辐射换热研究

研究了硼掺杂硅(记为Si-19)薄膜和半无限大物体(Si-19和SiC)在100 nm真空间距下的近场辐射换热随薄膜厚度的变化。研究结果表明,当半无限大物体和薄膜为相同的Si-19材料时,由于表面波激发并相互耦合,使得近场辐射换热随薄膜的厚度变化比较复杂。当半无限大物体为SiC材料时,由于表面波的耦合遭到破坏以及辐射体的高发射率频率区和吸收体的高吸收率频率区不匹配,导致表面波的激发对不同材料间的近场辐射换热的增强程度降低,因此在相同计算区域内热流密度随厚度的增加单调增加,没有出现极值点。     

载人航天器舱壁温度动态分析

本文分析了采用三层结构舱壁的载人航天器在轨飞行时由于热辐射环境的变化引起的舱壁温度波动及温度分布,数值计算结果表明内防护层的温度分布比较均匀,受外部辐射变化影响很小,而对内部空气温度的波动响应比较大。并根据此结果提出了地面模拟的简化模型,分析了模型时间常数的影响因素,用数值计算验证了缩小实验周期的可能。     

T型微通道气液两相流流动与传热的数值研究

为进行微通道气液两相流动及传热研究,建立了T型微通道模型,利用VOF方法进行数值模拟,对弹状流流型进行了数值分析,考察了弹状流的形成过程、速度、表面张力和粘度对弹状流流型的影响,计算了气泡速度和液膜厚度,并与经验关联式进行比较。结果表明:液体粘度对弹状流的影响较大;而表面张力对弹状流几乎没有影响,当气速一定时,液速越大,气泡的长度越小而液柱的长度越大。气泡速度和液膜厚度与经验关联式的计算结果误差分别为2.57%和4.87%。     

两侧有固体层负载时板中Lamb波的传播

本文研究了薄板二面有固体导负载时板中Ｌａｍｂ波的传播，从弹性波理论出发并结合应的边界条件，导出板中Ｌａｍｂ波的色散方程，数值计算表示，不管作为自由状态时板中Ｌａｍｂ波相速（板厚取定时）是大于或小于外层固体的声表面波波速，板中对称及反对称模式的Ｌａｍｂ波相速都随着外层固体层厚度增加而变化并且渐近于外层固体的声表面波波速，数值计算又表明，对很薄的板，板中对称及反对称模式的相速均随负载板的厚度呈线性变化     

一种辐射声场近似计算方法——单元辐射叠加法

提出一种基于表面振速预报辐射声场的近似方法--单元辐射叠加法.研究表明,声传递向量中的每项元素等于对应单元以单位速度振动、其它单元振速都为零时的辐射声压,即刚性障板上活塞面以单位速度振动时的辐射声压.在此基础上,利用刚性障板上单位速度振动活塞面的辐射声压直接建立表面振速与辐射声压之间的传递关系,根据这个传递关系对表面振速进行加权、求和便得到总的辐射声压.计算时采用规则形状障板面去拟合实际障板面,以规则形状障板上振动活塞面的辐射声压去近似实际障板上振动活塞面的辐射声压.相对于边界元方法,该方法在计算速度与存储空间上具有很大的优势.计算表明该近似方法是合理的、可行的.     

基于(火积)理论的“+”形高导热构形通道实验研究

基于构形理论和■理论,对"+"形高导热通道的方形构造体开展导热实验研究,并对不同优化目标和不同高导热通道布置形式下的构造体导热性能进行比较.结果表明:对于"+"形高导热通道的方形构造体,实验和数值计算所得到的构造体最高温度点均位于"+"形高导热通道两分支之间,实验和数值计算所得到的构造体平均温差和■耗散率的误差均在可接受范围内,这从定性和定量的角度证明了导热构形优化结果的正确性.与"H"形高导热通道的方形构造体相比,构造体内高导热通道采用一级"+"形布置使得其导热■耗散率得到降低.■耗散率最小的一级"+"形高导热通道构造体最优构形与最大温差最小的构造体最优构形相比,前者的导热■耗散率降低了5.98%,但最大温差提高了3.57%.最大温差最小目标有助于提高构造体的热安全性,■耗散率最小目标有助于提高构造体的整体导热性能.在保证热安全性能的前提下,实际微电子器件设计中可采用■耗散率最小的构造体最优构形以提高其整体导热性能.     

Dual solutions in boundary layer flow of a moving fluid over a moving permeable surface in presence of prescribed surface temperature and thermal radiation

An analysis of the heat transfer for a boundary layer forced convective flow past a moving permeable flat surface parallel to a moving fluid is presented. Prescribed surface temperature at the boundary is considered. A thermal radiation term in the energy equation is considered. The similarity solutions for the problem are obtained and the reduced ordinary differential equations are solved numerically. To support the validity of the numerical results, a comparison is made with the available results for some particular cases of this study. Dual solutions exist when the surface and the fluid move in the opposite directions.     

Metal surface temperature induced by moving laser beams

Whenever a metal is irradiated with a laser beam, electromagnetic energy is transformed into heat in a thin surface layer. The maximum surface temperature is the most important quantity which determines the processing result. Expressions for this maximum temperature are provided by the literature for stationary cases. In practice, however, moving beams are of more importance.Based on a fast numerical algorithm which allows calculation of the induced temperature profile, the maximum surface temperature for stationary and moving laser beams is calculated. Next, two types of approximating functions are presented relating the scanning speed to the maximum surface temperature. Using dimensionless numbers, the results can be applied to different materials.     

Unsteady radiative nanofluid flow near a vertical heated wavy surface with temperature-dependent viscosity

In the present contribution, a numerical treatment is provided to describe unsteady nanofluid flow near a vertical heated wavy surface. A memorable feature of the present work is the investigation of nanofluid flow associated with thermal radiation that acts as a catalyst for heat transfer rates. Likewise, the effectiveness of variable viscosity is examined as it controls fluid flow as well as heat transfer. It is necessary to study heat and mass transfer for complex geometries because predicting heat and mass transfer for irregular surfaces is a topic of fundamental importance, and irregular surfaces frequently appear in many applications, such as flat-plate solar collectors and flat-plate condensers in refrigerators. A simple coordinate transformation from the wavy surface into a flat one is employed. The non-dimensional boundary layer equations that governing both heat transfer and nanofluid flow phenomena along the wavy surface are solved via a powerful numerical approach called the implicit Chebyshev pseudospectral (ICPS) method with Mathematica code. A comparison graph of the current numerical computation and the published data shows a perfect match. Figures depict the effect of various physical parameters on nanofluid velocities, temperature, salt concentration, nanoparticle concentration, skin friction, Sherwood, nanoparticle Sherwood, and Nusselt numbers. According to the numerical results, increasing the variable viscosity parameter value causes a drop in the local skin friction coefficient value and an increase in the steady-state axial nanofluid velocity profile near the wavy surface. Furthermore, as heat radiation is increased, the local Nusselt number decreases but the nanoparticle Sherwood number increases.     

Radiative Effects on Mixed Convection in a Uniformly Heated Vertical Convergent Channel with an Unheated Moving Plate

Fluids engineering is extremely important in a wide variety of materials processing systems, such as soldering, welding, extrusion of plastics and other polymeric materials, Chemical Vapor Deposition (CVD), composite materials manufacturing. In particular, mixed convection due to moving surfaces is very important in these applications. Mixed convection in a channel, as a result of buoyancy and motion of one of its walls has received little research attention and few guidelines are available for choosing the best performing channel configuration, particularly when radiative effects are significant. In this study a numerical investigation of the effect of radiation on mixed convection in air due to the interaction between a buoyancy flow and an unheated moving plate induced flow in a uniformly heated convergent vertical channel is carried out. The moving plate has a constant velocity and moves in the buoyancy force direction. The principal walls of the channel are heated at uniform heat flux. The numerical analysis is accomplished by means of the commercial code Fluent. The effects of the wall emissivity, the minimum channel spacing, the converging angle and the moving plate velocity are investigated and results in terms of air velocity and temperature fields inside the channel and wall temperature profiles, both of the moving and the heated plates, are given. Nusselt numbers, both accounting and not for the radiative contribution to heat removal, are also presented.     

气流床气化炉壁面熔渣行为模拟

本文对气流床煤气化炉内高温合成气和壁面渣层的流动与传热传质过程进行了分析,建立了渣层流动、传热传质和相变数理模型,采用VOF方法对渣层和气体之间自由界面进行追踪,采用射线追踪方法(DTRM)计算辐射换热,采用焓法计算渣层相变,熔融态渣滴在渣层表面的沉积通过源项引入.应用所建立的数学模型对实验室规模的Texaco煤气化炉进行了模拟.结果表明:气化炉壁面换热系数从上到下先增加再减少最后再增加;炉膛温度升高,固态渣层厚度减少;壁面温度升高,固态渣层厚度减少.     

LAMOST围挡通道的壁面传热影响分析

运用热分析软件Icepak对望远镜LAMOST的圆顶围挡通道进行了热计算与分析，重点分析了围挡壁面的热辐射和热传导对整个温度场的影响。在通风管道冷却方案的基础上，分别建立了壁面辐射和传导的热模型，描述了壁面的传热结构。仿真计算了增加壁面热辐射和热传导时主光学组件——焦面的温度场分布，并对此作了对比分析。数值计算与仿真结果表明：壁面传热对其内部温度场的影响不大;利用通风管道的冷却措施可将焦面的最大温度梯度控制在0.4℃／m；围挡的特性结构对传热有效。     

仿生射流孔形状减阻性能数值模拟及实验研究

针对横流中的侧向射流能够减小仿生射流表面摩擦阻力问题, 建立仿生射流表面模型, 利用SST k-ω湍模型对不同射流孔形状的仿生射流表面模型进行数值模拟, 并对数值模拟结果进行了实验验证. 结果表明: 当射流孔的流向长度和展向长度不变时, 3号模型的折线形射流孔减阻效果最好; 将折线形射流孔简化为圆弧形, 当r=3–5 mm时, 减阻率随着射流速度的增大而增大, 当r=4 mm时减阻效果最好, 最大减阻率为9.51%. 减阻原因: 通过射流孔向横向主流场中注入射流流体, 改变了射流表面附近边界层的流场结构, 使得边界层黏性底层厚度增加, 垂直于射流表面的法向速度梯度减小, 从而减小了壁面剪应力; 低速的射流流体被封锁在边界层内, 降低了高速流体对壁面的扫掠, 达到了减阻目的.     

CaS电子结构和热力学性质的第一性原理计算

根据密度泛函理论,采用平面波赝势和广义梯度方法,计算了Ca S的晶体结构和电子结构.通过准谐徳拜模型预测了硫化钙的体积变化率、体弹模量、热膨胀系数分别与温度和压强的变化关系,以及热容和温度的变化关系.     

Effect of melting heat transfer and thermal radiation on Casson fluid flow in porous medium over moving surface with magnetohydrodynamics

In this study, the effects of variable fluid properties on heat transfer in MHD Casson fluid melts over a moving surface in a porous medium in the presence of the radiation are examined. The relevant similarity transformations are used to reduce the governing equations into a system of highly nonlinear ordinary differential equations and those are then solved numerically using the Runge–Kutta–Fehlbergmethod. The effects of different controlling parameters, namely, the Casson parameter,melting and radiation parameters, Prandtl number,magnetic field, porosity, viscosity and the thermal conductivity parameters on flow and heat transfer are investigated. The numerical results for the dimensionless velocity and temperature as well as friction factor and reducedNusselt number are presented graphically and discussed. It is found that the rate of heat transfer increases as the Casson parameter increases.