平行流蒸发器耦合传热的数值模拟

为了验证模型的正确性,针对一种平行流蒸发器,建立了3D和2D计算模型。并采用fluent软件和3D耦合传热计算模型,分析了迎面风速变化时空气侧的主要结构参数(翅片间距、翅片厚度、百叶窗间距和百叶窗角度)对空气侧传热系数和压降的影响规律。     

混合物冲击温度的数值模拟

 介绍温度的数值模拟方法，采用三维动力学有限元程序模拟冲击压缩状态，分析了数值模拟的准确性。模拟了铜和铝两种金属单质组成混合物的冲击压缩性能，在分析了热传导影响后，计算了混合物的冲击温度和冲击绝热线。     

板式蒸发式冷凝器气-液两相流流动的数值模拟

基于VOF算法,建立了波纹板蒸发式冷凝器的计算模型,考察了气相、板面结构和喷淋水量对液膜流动的影响.结果表明:当空气与水逆流时,会引起雾沫挟带,水膜厚度增加;当空气与水顺流时,水膜厚度会被空气削薄;波纹板结构对液膜的流动形式有重要影响,尺寸较大、凹槽较浅的波纹板有利于水膜的均匀分布;液膜的厚度随着喷淋水量的增大而增加,同时液膜内部振荡加剧,但不影响其流动结构.     

双组元姿控发动机反流特性的DSMC模拟

为准确获得双组元姿控发动机的羽流及其反流特性,采用直接模拟蒙特卡罗(DSMC)方法结合可变软球(VSS)模型数值模拟以N2O4/MMH为推进剂的真空羽流。喷口参数由喷管流动的DSMC法计算得到。与文献比较表明本文计算程序可信。模拟结果表明,分子质量越小的气体越容易进入反流区;本文的计算条件下,在偏离X轴正向116°~140°范围内,组分数密度和质量流率以及温度均出现了最大值。     

气液爆轰波及冲击波传播的数值研究

采用高分辨率ＴＶＤ格式、ＭａｃＣｏｒｍａｃｋ格式和二维轴对称气液两相方程组数值模拟了气液爆轰的发展过程及冲击波误减规律,计算结果与国内外研究结果符合良好。     

微观偏析对凝固传热传质数值模拟的影响

总结比较了多种微观偏析模型,并针对反向凝固工艺实验研究的传热传质现象进行了数值模拟。讨论分析了溶 质的重新分布对宏观凝固传输过程数值模拟的影响,并与实验数据进行了比较,认为微尺度固液相界面上的溶质再分配对 新生相生长的影响不可忽略。     

HCCI工况下氨氢混合物燃烧的直接数值模拟

本文利用直接数值模拟方法对均质压燃(HCCI, Homogeneous Charge Compression Ignition)工况下氨氢混合物的着火和燃烧特性进行了研究。结果表明,着火首先从局部孤立区域处发生,随后发展到整个计算区域;最高燃烧温度和热释率随着掺氢比的增加而增加;通过与零维计算结果对比,发现湍流和热分层使得氨氢混合物着火提前。利用直接数值模拟数据计算了反应锋面的位移速度,并据此分析了自着火和火焰传播这两种燃烧模式。发现在低掺氢比的情况下,燃烧模式以自着火为主;而在高掺氢比的情况下,燃烧模式以火焰传播为主。     

Level Set方法及其在两相流数值模拟研究中的应用

本文介绍了一种崭新的捕捉两相流相界面的 Ｌｅｖｅｌ Ｓｅｔ方法,并应用该方法对两种互不相容流体间的平面界面波动现象进行了数值模拟,捕捉到了两相流界面波动过程中的一些复杂现象。计算结果与实验观测现象符合良好,表明这种方法是一种很有前途的两相流数值模拟方法,很值得进一步研究和推广。     

On the Statistical Mechanics and Surface Tensions of Binary Mixtures

Within a lattice model describing a binary mixture with fixed concentrations of the species we discuss the relationship between the surface tension of the mixture and the concentrations.     

Nonradiative Relaxation of Thiacarbocyanine Dyes in Binary Mixtures

It was found that preferential solvation of cyanine dyes in binary mixtures can strongly affect both their isomerization and aggregation; the comparison of absorption and fluorescence excitation spectra might be a useful tool for studying these nonradiative processes.     

高斯噪声诱导二元混合物/粒子系统有序结构的形成

采用蒙特卡罗方法研究高斯噪声场对添加硬球粒子的二元混合物系统自组装的驱动作用.发现硬球粒子与组分之间的相互作用决定硬球粒子在畴中存在的区域.当硬球粒子与组分之间的相互作用较大,硬球粒子浓度n≤0.05时,对于足够强的高斯噪声场,存在一个最佳噪声作用概率区域(p=0.005~0.02),其间高斯噪声已完全消除硬球粒子的钉扎效应,使体系快速生长并形成取向性很好的条状畴结构.     

煤炭超临界水流化床制氢反应器内颗粒流动及传热特性的数值分析

煤炭超临界水气化是极具发展前景的高效洁净煤转化利用技术,深入研究反应器内流动和传热过程对反应器的设计及优化具有重要意义.本文基于欧拉-拉格朗日方法,耦合化学反应动力学模型,建立了煤炭超临界水流化床制氢反应器的三维瞬态CFD模型,研究了反应器内流动和传热特性、颗粒及产物组分的分布转化规律,得到了煤炭颗粒表面的对流和辐射换热系数,并从传热学的角度,揭示了颗粒粒径对煤炭转化速率的影响机理。     

Numerical Simulation Study on Flow Laws and Heat Transfer of Gas Hydrate in the Spiral Flow Pipeline with Long Twisted Band

The natural gas hydrate plugging problems in the mixed pipeline are becoming more and more serious. The hydrate plugging has gradually become an important problem to ensure the safety of pipeline operation. The deposition and heat transfer characteristics of natural gas hydrate particles in the spiral flow pipeline have been studied. The DPM model (discrete phase model) was used to simulate the motion of solid particles, which was used to simulate the complex spiral flow characteristics of hydrate in the pipeline with a long twisted band. The deposition and heat transfer characteristics of gas hydrate particles in the spiral flow pipeline were studied. The velocity distribution, pressure drop distribution, heat transfer characteristics, and particle settling characteristics in the pipeline were investigated. The numerical results showed that compared with the straight flow without a long twisted band, two obvious eddies are formed in the flow field with a long twisted band, and the velocities are maximum at the center of the vortices. Along the direction of the pipeline, the two vortices move toward the pipe wall from near the twisted band, which can effectively carry the hydrate particles deposited on the wall. With the same Reynolds number, the twisted rate was greater, the spiral strength was weaker, the tangential velocity was smaller, and the pressure drop was smaller. Therefore, the pressure loss can be reduced as much as possible with effect of the spiral flow. In a straight light flow, the Nusselt number is in a parabolic shape with the opening downwards. At the center of the pipe, the Nusselt number gradually decreased toward the pipe wall at the maximum, and at the near wall, the attenuation gradient of the Nu number was large. For spiral flow, the curve presented by the Nusselt number was a trough at the center of the pipe and a peak at 1/2 of the pipe diameter. With the reduction of twist rate, the Nusselt number becomes larger. Therefore, the spiral flow can make the temperature distribution more even and prevent the large temperature difference, resulting in the mass formation of hydrate particles in the pipeline wall. Spiral flow has a good carrying effect. Under the same condition, the spiral flow carried hydrate particles at a distance about 3–4 times farther than that of the straight flow.     

Demixing in Isotropic Binary Mixtures of Rodlike Macromolecules

A binary mixture of long rigid rods of diameters D _i and lengths L _i (i=1, 2) may demix into two isotropic phases, and we give necessary conditions on the molecular size parameters for this transition to exist. These conditions imply that the two diameters must be sufficiently unequal, D ₂/D ₁>( + )², or D ₂/D ₁<( + )², while the length ratio is limited to an interval f _–(D ₂/D ₁)<L ₂/L ₁<f ₊(D ₂/D ₁). The functions f _± are given explicitly.     

等离子枪体中冷却水流动与换热的数值模拟

基于计算流体力学和传热学,建立等离子喷涂枪喷嘴冷却水流动和换热分析模型,以SIMPLE方法对其进行了耦合计算.结果表明,喷嘴冷却存在薄弱部位,即热源附近的喷嘴壁面和喷嘴后端的密封垫圈.在此基础之上,对不同冷却水流速和流向进行了对比分析,得出较为理想的冷却水流速,合理的进水方式.     

Ground-State Properties and Phase Separation of Binary Mixtures in Mesoscopic Ring Lattices

We investigated the spatial phase separation of the two components forming a bosonic mixture distributed in a four-well lattice with a ring geometry. We studied the ground state of this system, described by means of a binary Bose–Hubbard Hamiltonian, by implementing a well-known coherent-state picture which allowed us to find the semi-classical equations determining the distribution of boson components in the ring lattice. Their fully analytic solutions, in the limit of large boson numbers, provide the boson populations at each well as a function of the interspecies interaction and of other significant model parameters, while allowing to reconstruct the non-trivial architecture of the ground-state four-well phase diagram. The comparison with the L-well (L=2,3) phase diagrams highlights how increasing the number of wells considerably modifies the phase diagram structure and the transition mechanism from the full-mixing to the full-demixing phase controlled by the interspecies interaction. Despite the fact that the phase diagrams for L=2,3,4 share various general properties, we show that, unlike attractive binary mixtures, repulsive mixtures do not feature a transition mechanism which can be extended to an arbitrary lattice of size L.     

平板电解槽内电解质湍流运动和传质的直接数值模拟

应用流体动力学、传质学和电化学理论,建立三维电解槽二元电解质溶液湍流运动的物理和数学模型,针对Butler-Volmer定律下极限电流和恒电流两种情况,通过直接数值模拟研究电解质溶液传质和运动特性,分析不同Schmidt数对电解质溶液平均浓度和脉动浓度的影响,考察湍流的脉动量控制电沉积的过程规律.对瞬时脉动浓度云图的分析可知,在高Schmidt数下脉动浓度拟序结构间距密集,且集中在壁面附近,表明高Schmidt数下传质过程主要由近电极处薄层内的流动行为所主导.     

四缸柴油机冷却水套流动与传热仿真研究

冷却液的流动与传热性能对发动机工作产生重要影响.本研究以四缸柴油机冷却水套为研究对象,建立了简化几何模型.在对物理模型、边界条件分析的基础上,利用商用软件FLUENT进行流动与传热数值仿真研究,得到冷却水套传热特性参数和流场分布,并据此提出了针对此型发动机冷却水套结构设计的改进建议.