Optimization of a Graphite Tube Blackbody Heater for a Thermogage Furnace

Design modifications are presented for a 289-mm long, 25.4-mm inner diameter blackbody heater element of a 48 kW Thermogage blackbody furnace, based on (i) cutting a small “heater zone” into the ends of the tube and (ii) using a mixture of He and Ar or N₂ to “tune” the heat losses and, hence, gradients in the furnace. A simple numerical model for the heater tube is used to model and optimize these design changes, and experimental measurements of the modified temperature profile are presented. The convenience of the Thermogage graphite-tube furnace, commonly used in many NMIs as a blackbody source for radiation–thermometer calibration and as a spectral irradiance standard, is limited by its effective emissivity, typically between 99.5% and 99.9%. The design simplicity of the furnace is that the blackbody cavity, heater, and electrical and mechanical connections are achieved through a single piece of machined graphite. As the heater also performs a mechanical function, the required material thickness leads to significant axial heat flux and resulting temperature gradients. For operation at a single temperature, changes to the tube profile could be used to optimize the gradient. However, it is desired to use the furnace over a wide temperature range (1,000–2,900°C), and the temperature-dependence of the electrical conductivity and thermal conductivity, and that of the insulation, makes this approach much more complex; for example, insulation losses are proportional to T ⁴, whereas conduction losses are proportional to T. In the results presented here, a slightly thinner graphite region near each end of the tube was used to “inject heat” to compensate for the axial conduction losses, and the depth, width, and position of this region was adjusted to achieve a compromise in performance over a wide temperature range. To assist with this optimization, the insulation purging gas was changed from N₂ to He at the lower temperatures to change the thermal conductivity of the felt insulation, and the effectiveness of this approach has been experimentally confirmed.     

翅片式蒸发器换热性能的数学模型

本文采用分布参数法对翅片式蒸发器建立了数学模型，通过计算局部换热系数和摩擦压降来简化翅片式蒸发器内复杂的三维流动关系，总结了文献已有的换热系数和摩擦压降的关联式，并添加到模型控制方程中，基于此模型，可对制冷剂在翅片式蒸发器中应用的换热性能进行模拟研究。     

全氧燃烧玻璃熔窑燃料消耗量理论计算的集总参数模型

在动态分析燃料输入量变化对窖炉燃烧空间传热影响的基础上,根据玻璃熔制的基本热要求,采用集总参数分析法,建立了全氧燃烧玻璃熔窑燃料消耗量理论计算的一种简化模型,并在计算机上进行了教值求解.随窑墙热阻增大,窑墙外表面温度和通过窑墙的散热损失明显降低,而窑墙内表面温度升高,火焰与窑墙传给玻璃料液面的热量显著增大.在保证玻璃熔制基本热要求的前提下,火焰温度可适当降低,因而燃料消耗量减小.胸墙越高,通过窑墙的散热损失越大,火焰与窑墙传给玻璃料液面的热量也相应增大,综合结果是燃料消耗量略微增大.     

制冷系统中蒸发器模型的建立和数值分析

本文对制冷剂在蒸发器中的流动进行了分析计算，在考虑了两相流动的基础上分别建立了能量、质量方程和动量计算公式，针对工质为R22的制冷系统编制的计算程序，该计算模型将对空调系统的优化     

电化学氧化改性石墨毡电极对VO2+/VO+2电对的催化活性

采用循环伏安和恒流充放电试验研究了电化学氧化改性石墨毡对VO2 /VO 2电对的催化活性,并利用XPS、FT-IR、SEM、BET对改性前后石墨毡碳纤维表面O/C、官能团变化、形貌和比表面积进行比较.结果表明,电化学处理后,石墨毡表面的O/C比例由0.085增加至0.15,增加的主要是COOH官能团.石墨毡碳纤维表面被刻蚀,比表面积有所增大.采用改性的石墨毡作为电极组装的全钒液流电池在50mA/cm2电流密度下,电压效率达75.99%,电流效率达96.79%,经多次循环性能稳定.电极活性的提高归因于碳纤维表面COOH官能团数目的增加和比表面积的增大.     

Cooperative Time-Reversal Symmetry Breaking Induced by a Magnetic Field in a Quasi-2D d-Wave Superconductor

A model of quasi-two-dimensional d-wave superconductor, with strong nesting properties of the Fermi surface is considered. The orbital effect of a moderate magnetic field applied perpendicularly to the conducting planes is studied in the mean field approximation. It is shown that the field can induce a time-reversal symmetry-breaking spin density wave order coexisting with the superconducting order and can open a gap over the whole Fermi surface. The anomalies recently observed in the heat conductivity, penetration depth, and zero-bias conduction in cuprates might be ascribed to this effect.     

Numerical 2D models of consolidation of dense flocculated suspensions

A mathematical 2D model for a consolidation process of a highly concentrated, flocculated suspension is developed. The suspension is treated as a mixture of a fluid and solid particles by an Eulerian two-phase fluid model. The suspension is characterized by constitutive relations correlating the stresses, interaction forces, and inter-particle forces to concentration and velocity gradients. This results in three empirical material functions: a permeability, a non-Newtonian viscosity and a non-reversible particle interaction pressure. Parameters in the models are fitted to experimental data. A simulation program using finite difference methods both in time and space is applied to one and two dimensional test cases. The effect of different viscosity models as well as the effect of shear on consolidation rate is studied. The results show that a shear thinning viscosity model yields a higher consolidation rate compared to a model that only depends on the volume fraction. It is also concluded that the size of the viscosity influences the time scale of the process and that the expected effect of shear on the process is not weil reproduced with any of the models.     

用数值模型研究RTM工艺树脂流动规律

RIM成型过程中,树脂对纤维增强体的充分浸润是非常重要的一环。本文对树脂流动过程的特点进行了研究,建立了树脂流动控制方程。采用贴体坐标/有限差分法模拟了不同时刻树脂流动前沿曲线,计算结果与其他研究成果吻合良好。     

Numerical simulation of flow behavior of particles in a liquid-solid stirred vessel with baffles

Flow behavior of particles is simulated by means of two-fluid model combining with kinetic theory of granular flow in a liquid-solid stirred vessel with baffles. The Huilin-Gidaspow drag model is used to obtain interphase interaction of liquid and solids phases. The virtual mass force is considered in simulations. The moving reference frame is applied to the rotation of numerical domain. Predictions are compared with experimental data measured by Pianko-Oprych et al. (2009) in a liquid-solid stirred vessel. This comparison shows that the present model can capture the liquid-solid flow in a liquid-solid stirred vessel. The distributions of velocity and solids volume fraction are predicted at the different heights. The effects of particle density on flow behavior of particles are generally scarce using CFD. Simulations indicate the stirred vessel consists of three regions based on distributions of velocity and turbulent kinetic energy, they are blade circulation region, conical induced region and near-wall region. As an increasing of the impeller speed, the turbulence kinetic and solids phase velocity rise, and the particles fluctuation is intensified.     

Numerical simulation of strength test on graphite moderator bricks using a continuum damage mechanics model

Experimental tests on graphite moderator bricks with keyways have been simulated using a failure model recently developed by the authors based on continuum damage mechanics. Failure of the specimens, induced by the application of pure bending moment, is characterised by unstable crack propagation, with very small cracks and damage zones formed at the keyway corners immediately before final rupture. Sensitivity of the predictions to the keyway corner radius, variations in material properties and the presence of methane holes have also been investigated. Good agreement has been achieved between the predicted failure strengths and the available experimental data.     

工质为R134a绝热型毛细管数值模拟

根据均相流等多项假设,运用两相流动基本方程建立了绝热毛细管分布参数的稳态数学模型。模型中分别利用了常用的2种计算沿程摩阻系数方法（Churchill关联式、Jung等人推荐工质为R22的摩阻系数关联式）,模拟结果表明用这2种方法来模拟均能获得较高精度,但工质为R134a时优先考虑前者,因此在模拟毛细管时不同工质有不同的最佳摩阻系数关联式。     

SiC_w/ZrO_2(6mol%Y_2O_3)陶瓷中晶须增韧的数值模型

SiCw／ZrO2（6mol％Y2O3）陶瓷的实验研究表明，晶须桥联和裂纹偏转是其主要增韧机制在两种机制协同增韧的基础上，建立了晶须增韧的数值模型，对材料的三点弯曲断裂过程的计算结果表明：载荷／位移曲线呈锯齿状，是由于晶须桥联作用使得裂纹扩展与停止这一过程反复出现而引起的；随晶须含量增加，复合材料韧性提高，晶须桥联和裂纹偏转两种增韧贡献都增加，但是占主导地位的增韧机制由裂纹偏转机制逐步过渡到裂纹桥联机制．计算结果与材料的测试结果很吻合．     

爆破数学模型浅析

本文系统地论述了爆破块度分布模型,爆破参数优化的经济数学模型和计算机模拟爆破的综合数学模型,分析了评价也各种模型在实际应用中存在的问题,并讨论了发展爆破数学模型的途径。     

Model for calculating the refractive index of a III–V semiconductor

An empirical relationship modeled by a theoretical numerical model has been presented for estimating the refractive indices of semiconductors, especially the III–V semiconductors, relative to their energy gaps.

This model is based on the fact that there is a strong correlation between the energy gap and the refractive index of a given material. This physical relationship remains strictly intrinsic and specific to the material considered.

The performance of this model is compared with that of some other numerical models established by other authors. An analysis based on calculations of the errors between this model and the experimental data has also been carried out.

For the first time, the present model is applicable to the whole range of energy gaps, taking into account the fact that the refractive index for an infinite energy gap is equal to one.

Good agreement is observed between the computed values and the refractive indices reported in the literature for well-known semiconductors.     

射频等离子系统中微弧放电的解析模型

最近我们在实验中发现：射频等离子体系统中的高电位可以引发微弧放电，这种微弧放电现象不是发生在射频系统的输入极上而是发生在接地极上。这种相对于电极呈非对称分布的微弧放电现象不是我们期待的结果，也不能用现有的理论来解释它。本文在Child-Langmuir鞘层模型理论和电流连续性理论的基础上，推导建立了一个用于表述射频等离子体系统中的这种非对称型微弧放电现象的解析模型。从我们的推导过程可以发现鞘层内外的电位差取决于接地极鞘层面积与输入极鞘层面积之比。当接地极的鞘层面积大于输入极鞘层面积时，接地极鞘层电位差的最小值成为高电位，从而引发电弧放电。而输入极鞘层电位差的最小值不发生变化。这个模型和推导结果与实验现象和PIC仿真数据有较好的一致性。     

Numerical analysis of unsteady behavior of cloud cavitation around a NACA0015 foil

Three-dimensional unsteady cavitating flow around a NACA0015 hydrofoil fixed between the sidewalls was simulated and the mechanism of U-shaped cloud cavity formation was clarified. A local homogeneous model was used for the modeling of the vapor–liquid two-phase medium. The compressible two-phase Navier–Stokes equations as the governing equations were solved. To describe the phase change between water and vapor, the mass transfer model based on the theory of evaporation/condensation on a plane interface was introduced. The cell-centered finite volume method was employed to discretize the governing equations. Assuming turbulent flow, the turbulent eddy viscosity coefficient was computed by using the Baldwin–Lomax model with the Degani–Schiff modification. As a result, even in the case of cavitating flow without sidewalls, the shed cloud cavities has slightly 3D structure, which was not so much large as extending across the whole spanwise direction. On the other hand, in the case of cavitating flow with sidewalls, the end of sheet cavities bows in the spanwise direction because of the development of boundary layer near both sidewalls. After that, due to the occurring of the reentrant jet towards the mid-span region, the sheet cavities breaks off from mid-span region near the leading edge of the hydrofoil, and became the vortical cloud cavities, which have the large-scale U-shaped structure.     

热固性树脂基复合材料构件固化变形数值模型

针对树脂基复合材料构件固化过程中的固化翘曲变形这一关键技术问题,通过引入剪切系数的方法来代替固化过程中模具与复合材料之间的相互作用,建立了预报树脂基复合材料构件固化变形的数值计算模型。通过少量实验数据来确定模具与复合材料之间的剪切系数,进而预测复合材料构件的固化变形。通过与文献中实验结果的比较证明了所建立的模型具有较高的可靠性。实验与计算结果表明,该模型能够在不考虑复杂的材料参数变化的情况下对不同结构尺寸及不同工艺参数下的复合材料构件的固化变形进行较为准确地预测。     

空调设计用简易气象模型相关参数的确定

本文在一简化气象模型的基础上,综合考虑了纬度、水陆分布、地形以及城乡差异等多种因素的影响,并对参数加以确定.在普遍意义上,其具有一定的准确性,为空调设计研究提供了参考依据.     

Numerical simulation of a novel blast wave mitigation device

This paper proposes a novel blast wave mitigation device, consisting of a piston–cylinder assembly. A shock wave is induced inside the device when it is subject to a blast wave. The shock wave propagates inside the device and is reflected repeatedly. The physical processes within the blast wave mitigation device are simulated numerically. Numerical predictions are in excellent agreement with analytical solutions for special cases of the investigated problem that are available in the literature. The peak pressure on the base of the device caused by the blast wave is studied using a number of design parameters. The numerical simulation shows that, although the transmitted impulse remains practically unchanged, the peak pressure of the blast wave can be reduced by as much as 98%, or even higher, depending on the design parameters chosen.     

两种CPU散热器换热特性的数值研究

对整体平直翅片与分段开缝平直翅片两种不同结构的CPU散热器，在不同加热功率和不同风速下的散热特性进行了数值模拟。采用商业软件FLUENT6．0进行计算，结果显示：对流换热表面传热系数和热阻主要与风速有关，与加热功率关系不大，对流换热表面传热系数的计算结果和实验数据趋势一致。在低风速下，加热功率对这两种散热器压降的影响也不大。采取数值模拟的方法对CPU散热器进行研究是实验方法的可靠补充，计算所得的结果有助于分析CPU散热器的换热过程，并可为电子设备的设计和改进提供参考。