超临界二氧化碳(S-CO2)气体箔片止推轴承动力特性研究

本文针对超临界二氧化碳(S-CO₂)气体箔片止推轴承的动态特性开展了数值研究。基于有限元分析软件ANSYS和计算流体动力学软件CFX,建立了气体箔片止推轴承动力特性的全三维非定常双向流固耦合数值预测方法,并采用不同气膜厚度下的轴承静态载荷和扭矩的实验数据验证了数值方法的有效性。计算分析了轴承受到轴向周期性扰动时,6种工质温度、5种工质压力、7种气膜厚度和6种扰动频率下的动态刚度和阻尼系数,获得了运行参数对S-CO₂气体箔片止推轴承动态性能的影响规律。     

复合润滑气体止推轴承静态特性数值模拟分析

平面螺旋槽气体止推轴承由于加工困难限制了其推广使用,袋式止推轴承具有与螺旋槽气体止推轴承接近的较高承载能力,加工简单,受到很大的重视。建立了一种袋式止推轴承的数值模拟模型,利用流体力学模拟软件FLUENT对气膜压力场的分布进行了数值模拟研究,分析了该结构参数对轴承静态性能的影响规律。     

透平膨胀机静压径向气体轴承优化设计

对静压径向气体轴承的承载性能进行了数值计算,分别研究了供气压力、偏心率、供气孔直径、数量、轴承间隙对轴承承载特性的影响。研究发现,在给定条件下,增加孔数,减小孔径并减小轴承间隙时,轴承具有最优承载特性。     

基于AVR的静压气体轴承性能检测装置控制系统设计

为了实现对静压气体轴承气膜厚度,压力分布和承载能力的自动检测,设计了一种基于单片机的检测装置和控制系统。该系统采用ATmega16L单片机作为平台运动控制和数据处理的核心,结合软件控制步进电机的转向和转速,实现了极坐标定位,并采集承载力,气膜压力和气膜厚度等数据,通过LCD显示和键盘输入,较好地实现了人机交互;同时,装置可以通过RS232与上位机通讯,实现上位机的直接控制。     

可倾瓦径向气体轴承支点分析

为了确定可倾瓦整体弹性支点的尺寸对轴承运转的影响,对可倾瓦径向动压气体轴承的支点进行模拟计算。通过求解气体润滑方程得到气膜压力分布,模拟四组不同支点尺寸的瓦块受力情况,分析瓦块支点处的受力和受力前后支点的变形情况,得出不同支点宽度所对应的最大位移量。对模拟结果进行实验,结合模拟结果和实验结果,说明瓦块支点宽度的大小对轴承稳定运转的影响,发现存在最佳宽度0.4mm,使瓦块支点在此宽度下具有一定的弹性形变,同时扭转刚度也能满足瓦块偏转的需求,使轴承能够稳定运转。     

变截面主流加速对超音速气膜冷却的影响

本文对扩张通道和直通道中的超音速气膜冷却进行了数值模拟,分析了主流加速和不加速两种情况下超音速气膜冷却的差异.计算结果表明,在主流加速的情况下,超音速气膜冷却的效果要好于相同进口条件下主流不加速的情况,并且这种差异越到下游越明显.同时,在本文计算的工况范围中,无论主流加速还是不加速,增大主流进口马赫数或者减少冷却流进口马赫数都使气膜冷却效率下降,而壁面静压则由主流气体决定.     

制冷剂润滑的径向波箔气体轴承承载特性分析

制冷离心压缩机采用制冷剂作为润滑介质,不仅能保证整个制冷系统无油,而且可以显著提高制冷能效。以离心压缩机中分别采用R410A和R407C润滑的径向波箔动压气体轴承为研究对象,基于有限差分法对定常雷诺方程和气膜厚度方程进行耦合迭代求解,通过数值计算得到了承载力和摩擦力矩随转速、偏心率和名义半径间隙的变化规律。结果表明：工质为R410A和R407C时,承载力和摩擦力矩均随转速和偏心率的增大而增大,随名义半径间隙的增大而减小。偏心率越大,承载力增大的梯度越大。在相同的蒸发温度条件下,工质为R410A时的承载力更大。名义半径间隙较小时,两种工质的承载力相差较大,但随着名义半径间隙的增大,承载力之间的差值逐渐减小。摩擦力矩是压力流和剪切流的共同作用,工质的动力粘度对摩擦力矩有着直接的影响,动力粘度越大,摩擦力矩也越大。     

竖直管道内湍流混合对流换热研究

本文对空气在竖直圆管中的湍流混合对流换热进行了实验研究和数值模拟,并对异种气体(氦气)对混合对流换热的影响进行了初步的实验研究。研究发现,空气在竖直圆管中向上流动时,随着热流密度的不断增大,出现换热恶化现象。如果浮升力足够大,则换热效果在降到最低点后又好转。在实验过程中,由于实验条件所限没有发现异种气体对混合对流换热有显著的影响。     

悬摆法测量气体推进剂激光推进冲量耦合系数

 给出了悬摆法测量激光推进冲量耦合系数的原理,分别以空气、氩气、氮气和氦气为推进剂,用悬摆法测量了抛物形推力器在能量不同的单脉冲TEA CO₂激光辐照下的冲量耦合系数。实验结果表明：氩气的冲量耦合系数最高,氦气的冲量耦合系数最低;在实验测试的激光能量范围内,4种推进剂气体的激光推进冲量耦合系数基本上都随着激光能量的增加而线性增大,冲量耦合系数的相对误差为5.4%~6.4%。实验结果与国外相关实验结论一致。     

辅助放电针对气体间隙直流自击穿特性的影响

为降低气体放电间隙直流条件下自击穿电压分散性,尽可能不影响其自击穿电压,基于环形电极放电间隙,设计了一种在阴极中心植入辅助放电针的辅助放电电极结构。通过电场仿真,研究了辅助放电针直径、长度和顶部倒角对放电间隙场畸变的影响。实验研究了放电间隙无辅助放电针和植入辅助放电针后,其在干燥空气和SF₆气体中的直流自击穿特性。结果表明：辅助放电针直径越小、长度越长,电极环对其电场屏蔽作用越弱,放电间隙场畸变强度越大;辅助放电针对SF₆气体放电间隙直流自击穿电压影响较小,随着场畸变系数的增大,同一气压下干燥空气自击穿电压下降百分数为SF₆气体自击穿电压下降百分数的2～3倍;辅助放电针对直流条件下干燥空气和SF₆气体放电间隙自击穿电压稳定性具有有益作用,分散性减小百分数较无辅助放电针结构均提高约25%。     

亚纳秒气体开关中气体击穿的数值计算

 对亚纳秒气体开关的放电过程，提出了气体击穿阶段的物理与数学模型以及数值计算方法，并对氢气和氮气的这一击穿过程进行了数值仿真。对于1mm氮气间隙，计算了充电电压波形为纳秒级上升的斜角平顶波时，开关放电时延以及击穿电压随气压和充电电压上升时间的变化。对于氢气，利用美国Sandia实验室的一个实验结果对数值仿真方法进行了验证，所得到的计算结果与实验结果很好地吻合，初步表明所建立的物理模型与计算方法的正确性。     

Effect of gas pressure on ionization of ambient gas

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In-water gas combustion in linear and annular gas bubbles

A new pulsed-cyclic method of in-water gas combustion was developed with separate feed of fuel gas and oxygen with the focus on development of new technologies for heat generators and submerged propellers. The results of calorimetric and hydrodynamic measurements are presented. In-water combustion of acetylene, hydrogen, and propane was tested with the operation frequency of 2–2.5 Hz and with a linear injector. The combustion dynamics of combustion of stoichiometric mixture with propane (C₃H₈+5O₂) was studied for a bubble near a solid wall; the produced gas bubble continues expansion and oscillations (for the case of linear and annular bubbles). It was demonstrated that gas combustion in annular bubbles produces two same-magnitude pulses of force acting on the wall. The first pulse is produced due to expansion of combustion products, and the second pulse is produced due to axial cumulative processes after bubble collapse. This process shapes an annular vortex which facilitates high-speed convective processes between combustion products and liquid; and this convection produces small-size bubbles.     

Ordering of gas bubbles during light ion gas implantation

There have been interesting observations about ordering of microstructures during irradiation. The formation of void lattices is amongst the better known examples. Ordering has also been observed in small gas filled bubbles formed during low energy light ion implantation in the energy range 30–100 keV. The basic underlying mechanism for ordering of gas bubbles has not been clearly understood so far. We identify in this paper a basic instability in the growth kinetics of such bubbles which can develop during irradiation. This instability is shown to be associated with the interstitial production due to the high pressure inside these bubbles and their differential bias due to the strain field interactions with vacancies and interstitials. It is shown that such an instability leads to a selection of a wavelength scale which agrees with the observed lattice parameter.     

微型填充式气相色谱柱的制备（英文）北大核心CSCD

为了分离永久性气体及低碳轻化合物,基于MEMS技术,研究制备了一种微型填充式的气相色谱柱。为了增加色谱柱的长度以及深宽比,色谱柱的沟道制备采用了激光刻蚀技术,这种技术可以方便的在玻璃基底上刻蚀出深沟道,这是其他化学腐蚀技术无法比拟的。研制的色谱柱其沟道横截面为1.2mm(深度)×0.6mm(宽度),深宽比为2∶1。实验结果表明,这种微型填充柱,具有较大的样品容量,能很好的实现CO和SO_2的分离。     

Interactions of rare gas cations with lighter rare gas atoms

High-level ab initio calculations are employed to generate potential energy curves for rare gas cations, RG⁺, interacting with neutral atoms of other rare gases, RG′, that are lighter (RG′ = Ne–Rn). The calculations employ the RCCSD(T) method, with doubly-augmented basis sets of quintuple-ζ quality. The interaction potential curves, with the full counterpoise correction applied, are calculated point-by-point. Spin-orbit coupling is applied analytically in an atom-based model. The potentials are used to calculate spectroscopic parameters, which are then compared to recent experimental work, and the very limited previous theoretical work. In addition, the potentials are used to calculate ion transport properties and the ion mobilities are compared to the few experimental data available.     

Hard-square lattice gas

We have studied the hard-square lattice gas, using corner transfer matrices. In particular, we have obtained the first 24 terms of the high-density series for the order parameter ₂– ₁. From these we estimate the critical activity to be 3.7962±0.0001. This is in excellent agreement with the earlier work of Gaunt and Fisher. It conflicts with the value 4.0 given by Müller-Hartmann and Zittartz's formula for the critical point of the antiferromagnetic Ising model in a field, so we conclude that this formula, while a good approximation, is not exact.     

Pulsed gas lenses

The concept of a pulsed gas lens is proposed. Potential applications are envisaged and preliminary experiments with pulsed ray refraction are reported.