不同直径液滴撞击亲水壁面动态特性实验研究

本文通过可视化实验研究了不同直径液滴撞击亲水壁面的动态特性.实验利用光学原理同时记录了液滴撞击壁面过程的正面及底面图像。实验结果表明:液滴最大铺展因数随液滴初始直径近似呈线性增长关系;随液滴直径增大,液滴铺展至最大时需要的绝对时间、滞留时间、回缩时间均增长,稳定时的液固接触面积变大;液滴铺展至最大铺展因数所需要的无量纲时间约为1.68;液滴直径越小,则撞击后液膜回缩更为迅速.     

双液滴撞击平面液膜的流动与传热特性

采用耦合的水平集-体积分数法(CLSVOF)对双液滴连续撞击恒定壁温壁面上的热液膜的流动和换热特性进行了数值模拟及分析,得到了双液滴撞击热液膜后形态演变的过程.分析了液滴垂直间距、撞击速度、液膜厚度以及液滴直径对双液滴撞击液膜后的流动与传热特性的影响,结果显示,壁面平均热流密度随液滴撞击速度的增大而增大,液滴垂直间距、液膜厚度和液滴直径对平均热流密度的影响较小,但会对热流密度在撞击区域和交界区的分布产生重要影响.     

高炉渣熔融液滴撞击壁面行为特性实验研究

针对高温熔渣粒化技术的开发,本文通过可视化实验研究了高炉渣熔融液滴撞击不锈钢壁面的动态行为特性。结果表明:随液滴雷诺数增大,撞击过程液滴形态演变模式依次由铺展-回缩转变为铺展-回缩破碎和铺展-破碎-凝固;增大壁面粗糙度可减弱与壁面换热,抑制液滴铺展;减小壁面粗糙度促进液滴发生破碎;液膜回缩过程普遍出现回卷现象,壁面倾角越大,液膜回卷和液滴滚动现象越显著,且液滴铺展面积越大,在壁面停留时间越长;减小液滴雷诺数、减小壁面粗糙度并采用垂直粒化仓壁面有利于壁面防黏结。     

单液滴正碰球面动态行为特性实验研究

在考虑空气阻力影响,确定液滴撞击球面速度的基础上,对较高韦伯数液滴撞击干燥球面动态行为过程进行了实验研究,分析了球面曲率与韦伯数对液滴撞击行为和铺展因子的影响,并与前人撞击平面结果进行了对比.实验表明,靠近撞击球面时,液滴降落速度出现明显波动;球面曲率对液滴撞击后行为影响明显,曲率较大时,液滴撞击后铺展液膜会超出球面直径并滑落,曲率较小时,液滴撞击后在球面上呈现明显的铺展、回缩、震荡、着附动态变化行为,此时最大铺展因子受曲率影响小,随曲率减小,逐渐趋向于撞击平面时的最大铺展因子;韦伯数对液膜铺展速率影响较小,但对液膜回缩时间影响明显,最大铺展因子随韦伯数增加逐渐增大,获得的关联式呈指数变化.     

液滴撞击热壁面的相变行为研究

本文基于格子Boltzmann方法建立了液滴撞击热壁面的数学模型,研究了撞击过程液滴相变传热机制,重点分析了壁面温度与We数的影响规律.结果表明,随着壁面温度升高,液滴撞击壁面出现接触沸腾、膜态沸腾相变模式.接触沸腾过程中液滴内部与壁面接触的三相线附近出现最大局部热流.当壁面温度超过Leidenfrost点后,撞击液滴因界面蒸发产生的气膜托举作用而与壁面无接触地铺展、回缩直至完全反弹形成膜态沸腾,这一阶段液滴所能达到的最大铺展因子与液滴We数呈幂次关系(指数为0.313).     

喷雾冷却中微液滴碰撞薄液膜的流动与换热

在喷雾冷却过程中,液滴撞击对壁面薄液膜的流动与换热特性有重要影响。本文采用Volume-of-Fluid(VOF)方法,对单液滴与双液滴撞击恒温壁面上薄液膜的换热特性进行了数值模拟分析。结果表明,液滴冲撞作用会使壁面产生很大热流,液滴初始直径越大、速度越快,换热系数越大。对于多液滴,撞击产生的扰动可以彼此迭加,从而进一步增强换热。     

液滴撞击超亲水表面冷液膜的研究

液滴撞击过程因具有较强的传热传质性能被广泛应用于工业领域中。本文利用高速摄影机和红外热像仪,研究了液滴撞击超亲水表面冷液膜的水力学特性和温度分布,探讨了撞击We数和液膜温度对撞击过程中水力学特性以及液膜温度分布的影响.总结了液滴在超亲水表面的液膜上的水力学特征的变化规律。实验结果表明,液滴铺展速度和最大铺展直径随撞击We数的增大而增大。同时,液膜温度会影响液滴撞击薄液膜后的水力学特性.在低We数下液滴撞击低温薄液膜后液膜的温度呈高低相间的环状分布,随着撞击We的增大,该环状温度分布消失。这对要求精确喷雾控温的工业过程起到了十分重要的意义.     

液滴碰撞液膜润湿壁面空气夹带数值分析

采用复合水平集-流体体积法并综合考虑传热及接触热阻的作用, 对液滴碰撞液膜润湿壁面空气夹带现象进行了数值分析. 揭示了夹带空气形成机理, 探索了夹带空气特性参数随碰撞速度和液膜厚度的变化规律, 获得了夹带空气作用下液滴碰撞润湿壁面的传热机理. 研究结果表明: 撞壁前气液两相压力差是引起气液相界面拓扑结构变化以及夹带空气形成的主要原因; 液滴碰撞速度与压缩空气层内压力以及相界面形变高度密切相关; 液滴接触液膜时, 碰撞轴上液滴底部和液膜表面速度相等, 大约是碰撞速度的1/2; 碰撞速度对夹带空气层底部到破碎点的无量纲弧长和最大无量纲夹带空气直径均存在较大的影响; 液滴和液膜的无量纲形变高度与斯托克斯数密切相关; 液膜初始厚度对液滴和液膜的无量纲形变高度和最大无量纲夹带空气直径影响较大; 撞壁初始阶段, 碰撞中心区域夹带空气对壁面热流密度分布存在较大的影响.     

液滴撞击加热壁面雾化弹起模式及驻留时间

液滴撞击壁面是一种常见的现象,减少撞击过程中液滴在壁面的驻留时间在很多应用中非常重要.本文在对液滴撞击加热壁面的动力学过程的研究中,发现了一种能够大幅减少液滴驻留时间的弹起模式,即雾化弹起模式.与液滴撞击壁面过程中的回缩弹起模式相比,雾化弹起模式的液滴驻留时间能减少约40%.与其他试图减少液滴驻留时间的手段相比,本文中驻留时间的减少仅需加热壁面,因此该方法容易实施而且非常可靠.最后,本文对雾化弹起模式下液滴驻留时间减少的机理进行了讨论,提出了一个针对膜态沸腾区域雾化弹起模式发生条件的简化理论模型,并得出了膜态沸腾区域液滴从雾化弹起模式到回缩弹起模式过渡边界的幂次关系,该幂次关系与实验数据吻合良好.此外,该理论模型也能解释过渡沸腾区域两种弹起模式的过渡边界的变化规律.     

剪切变稀液滴撞击不同浸润性壁面的数值模拟研究

基于有限元法,采用水平集方法捕捉相界面的移动,构建了液滴撞击固体壁面的数值模型.通过修正的幂律模型描述流体的非牛顿剪切变稀特性,探讨了剪切变稀特性对液滴撞击固体壁面后铺展行为的影响,分析了撞击不同浸润性壁面时剪切变稀特性对液滴撞击壁面行为的影响差异.研究结果表明:随着幂律指数m的减小,液滴撞击过程中的黏性耗散减小,液滴的形貌变化及无量纲参数变化更为显著.接触角为55°的情况下:当m降低至0.85时,液滴铺展过程中开始出现显著区别于牛顿流体液滴的振荡现象;当m降低至0.80时,液滴在回缩过程中会出现中心液膜断裂的情况.接触角为100°时,剪切变稀液滴均会出现振荡行为,振荡幅度随着m的减小而增大.接触角为160°时,牛顿流体液滴与剪切变稀液滴均会在回缩过程中弹起,但剪切变稀液滴的弹起速度更快.此外,基于数值计算结果,本文提出了接触角为55°情况下剪切变稀液滴撞击壁面后的最大无量纲铺展直径预测模型.     

关于"太阳在银河系中所受引力与到银心距离r的关系"的讨论

讨论了银道面内的引力场强分布和太阳在银河系中所受引力与到银心距离r的关系，指出引力场强g并不是与r的平方成反比，这是由于银河系的大小和形状不能忽略造成的．强调了万有引力定律的适用条件．     

On the predictability of the positions of the convergence zones in the ocean

The disagreement between the experimental and calculated positions of the first convergence zone are known from many publications. The most probable cause for such a disagreement, namely, the incorrect specification of the input data for the calculations, is considered. The lack of simultaneity between the hydrological surveys of the region and the acoustic experiments is emphasized. The experimental data obtained by the author in five ocean regions are presented. These data characterize the diurnal variability of the distance from the source to the nearest boundary of the convergence zone. The relations proposed by different researchers for calculating the sound speed from the temperature, salinity, and hydrostatic pressure are analyzed. It is shown that these relations lead to a substantial difference in the estimated depth dependence of the hydrostatic gradient of the sound speed. The position of the first convergence zone is calculated for the propagation conditions determined by vertical temperature and salinity profiles with the subsequent recalculation of these profiles into sound speed profiles by using eight different formulas known from the literature. It is shown that different formulas lead to different values of the distance to the first zone; this difference is substantially greater than that between the calculations and experiment. The necessity of improving the recalculation relations in view of the experimental data on sound propagation in natural oceanic waveguides, including the data on the actual positions of the convergence zones, is emphasized.     

On the calculation of the bremsstrahlung in the region of the plasma frequency

On the basis of the classical theory of radiation produced in incomplete Coulomb interaction, a formula is derived for the coefficient of the bremsstrahlung of fully ionized plasma. In the region of rectilinear approximation a comparison is made with the results of the quantum formula derived from the Born approximation. Furthermore, the influence of dispersion upon the emission coefficient is taken into account; some relations for the region of dispersion are given.     

Dependence of the Intensity of the Spectral Lines and the Composition of the Sample and the Plasma Parameters of the Unipolar Arc

The investigation was made of the dependence of the intensity of Tl, Ga, Mo, Mg, Mn, Sn, Bi, Ni, Zn, Pt and Au spectral lines and the plasma parameters (temperature T, electron concentration n_e, degree of 6 ionnization α) from concentration of lithium additive.     

Set the controls for the heart of the Sun

In this paper we describe experiments conducted with high-power lasers that are attempting to replicate, for a very short time and in miniature, conditions found in the Sun. Experiments to date have reached conditions in the outer part of the Sun. To reach the Sun's centre requires compression of material to very much greater than solid density and heating to over ten million degrees. To achieve this, a new class of experiments and a new generation of high-power lasers are required.     

On the Question of the Source of the Apokamp

Technical Physics - The object of this work is the apokamp—a new type of plasma jet, which is formed from a bright offshoot emerging at the bending point of a channel of a high-voltage...     

Extracting the wavefunction of the LSP at the LHC

We consider associated production of squarks and gluinos with the lightest supersymmetric particle (LSP), or states nearly degenerate in mass with it. Though sub-dominant to pair production of color SU(3)-charged superpartners, these processes are directly sensitive to the wavefunction composition of the lightest neutralinos. Exploiting event-shape variables - including some introduced here for the first time - we are able to identify the composition of the LSP by selecting events involving a single high-pT jet recoiling against missing transverse energy. We illustrate the proposed technique on a set of benchmark cases and propose methods for applying these results in more realistic experimental environments.