Density-based kinetics for mesoscale simulations of detonation initiation in energetic materials

In this work we present one- and two-dimensional mesoscale simulations of detonation initiation in energetic materials. We solve the reactive Euler equations, with the energy equation augmented by a power deposition term. The reaction rate at the mesoscale is modelled using a density-based kinetics scheme, adapted from standard ‘Ignition and Growth’ models. The deposition term is based on previous results of simulations of void collapse at the microscale, modelled at the mesoscale as hot spots. For an isolated hot spot in a homogeneous medium, it is found that a critical size of the hot spots exists. If the hot spots exceed the critical size, initiation of detonation can be achieved. For sub-critical hot-spot sizes, we show that it takes a collection of hot spots to achieve detonation. We also carry out two-dimensional mesoscale simulations of random packs of HMX crystals in a binder, and show that the transition between no detonation and detonation depends on the number density of the hot spots, the initial radius of the hot spot, the post-shock pressure of an imposed shock, and the amplitude of the power deposition term.     

垂直圆管内向上稀疏层流泡状流相分布的实验研究

采用三维照相法对垂直圆管内稀疏层流泡状流充分发展段的相分布进行了实验研究。得到了８个流动工况下均匀尺寸气泡形成的泡状流的空泡率分布以及６个流动工况下非均匀尺寸气泡形成的泡状流的总体和大、小气泡组各自的空泡率分布．实验结果表明当气泡组的平均直径小于约３．５ｍｍ时,其空泡率分布在管壁附近出现尖峰;当气泡组的平均直径大于约 ３．５ ｍｍ时,其空泡率分布的尖峰移向管中心;气泡尺寸对泡状流的相分布有重要影响．     

多孔钼烧结体的静压p-V特性研究

 利用中等密度的多孔钼烧结体进行了中、低静压全程加载-卸载实验。研究了在不同直径（特别是较大尺寸）和不同初始密度时该材料的静压p-V特性曲线。实验发现，样品初始密度不同应变也不同；卸载曲线几乎不受样品初始密度、直径的影响。计算表明，泡沫钼在静压下具有较高的吸能性，吸能效率较高，但预压后的泡沫钼吸能性和吸能效率均有所下降。     

Experimental study on parameters of dust plasma in SiH4/C2H4/Ar discharges

Measurements of dust plasma parameters were carried out in the discharges of （SiH4/C2H4/Ar） mixtures. Dust particles were formed in the capacitively coupled radio-frequency discharge of these reactive mixtures in a cylindrical chamber. Langmuir probe was employed for diagnosing and measuring the important plasma parameters such as electron density and electron temperature. The results showed that the electron density dropped, and in contrast the electron temperature rose when the dust particles formed. The curves of the electron density and temperature versus the RF power and pressure were presented and analysed. Further, it was found that the wriations of electron temperature and the size of dust void with the RF power followed the similar trends. These trends might be useful for understanding more about the characteristics of dusty voids.     

冲击加载下孔洞诱导相变形核分析

用分子动力学方法模拟了冲击加载(沿［001］向)下单晶Fe中孔洞诱导相变形核及生长过程，并分析了初始温度对这一生长过程的影响.数值模拟显示：1) 相变形核首先出现在孔洞周围的(110)和(110)面上,并分别沿［110］，［110］向和［110］，［110］向生长成片状，之后核的生长方向则变为沿〈111〉向，形成“V”形板条状新相颗粒；2) 在相同冲击压力下，初始温度为300 K时在新相晶核边缘出现许多核胚，生成的新相颗粒比60 K时明显减小.这些现象表明，孔洞诱导相变形核及生长过程沿着特定晶向进行，而初     

泡状流局部界面浓度实验与理论研究

应用高速数字摄像系统,首先对双头电导探针测量泡状流局部界面浓度的几种模型进行了标定和评价。使用标定好的双头电导探针技术,对垂直上升管内气液两相泡状流局部界面浓度和含气率分布特性进行了深入的实验研究。试验段为内径40 mm的透明有机玻璃管。根据试验数据的分析结果,发展了一种垂直上升管内气液两相泡状流局部界面浓度预测模型。在本文实验条件下,该局部界面浓度模型预测结果能够与实验数据很好地符合。     

扁平管管内负压冷凝流动阻力特性研究

本文采用试验的方法对扁平管内的负压蒸汽冷凝过程进行了研究。研究结果表明,这类扁管的特殊结构使得管内的蒸汽充满度高,冷凝液占据整个流动截面的份额小,流动顺利,阻力小,是很好的有利于冷凝液流动的管型。研究结果给出了这类扁平管的管内冷凝流动摩擦阻力的计算方法,为这类管型在空冷凝汽器的应用提供了设计依据。     

Al‐density variation as one driving force for void formation in PERC solar cells

The reduction of void formation in local Al contact structures is of high interest in studies dealing with passivated emitter and rear contact (PERC) solar cells. So far, several processing parameters and their impact on local contact formation were investigated in detail. However, up to now density variation of Al in dependence on temperature and Si content in the melt were not taken into account as a principal reason for void formation. In this context the current assumption of a constant volume of the Al paste particles is discussed in more detail. Based on the results of energy dispersive X‐ray spectroscopy, void formation implies either an expansion of paste particles or their burst during contact formation.

     

多孔圆肋传热传质分析

多孔肋片传热传质过程在自然界中广泛存在,本文对水在多孔圆肋中流动产生的传热传质现象进行了研究,建立了相应的物理数学模型,通过数值计算获得肋片内水的温度和流量分布,以及水沿肋长方向蒸发率的变化。讨论了外界空气温度对多孔肋片中水的流量和蒸发率的影响,并对孔隙率、长径比等因素对肋片传热传质效率的作用进行了分析．     

Self-organized voids revisited:Experimental verification of the formation mechanism

We conduct several experiments to further clarify the formation mechanism of a self-organized void array induced by a single laser beam, including energy-related experiments, refractive-index-contrast-related experiments, depth-related ex- periments, and effective-numerical-aperture experiment. These experiments indicate that the interface spherical aberration is indeed responsible for the formation of void arrays.