液滴撞击水平固体表面的可视化实验研究

对液滴撞击水平固体表面的现象及特性进行了可视化实验研究,并对影响液滴撞击的参数进行了研究.实验工质是蒸馏水.重点是定性和定量测定这些参数对液滴撞击后铺展过程的影响.实验结果表明:固体表面的润湿性和表面粗糙度对液滴铺展过程的后面阶段有很大的影响,液滴的大小的影响比较小.     

液滴在异形凹槽表面上运动特性的模拟

采用格子Boltzmann方法中的伪势模型对凹槽表面上液滴的运动情况进行了数值模拟。首先根据激光烧蚀金属表面后的痕迹提出了一种异形凹槽结构,建立了异形凹槽表面的二维模型;然后模拟了不同深度的异形凹槽表面上液滴的运动情况。模拟结果表明,异形凹槽深度越浅,液滴运动速度越快。最后在异形凹槽的基础上比较了前后沿不同结构对液滴运动特性的影响,发现将异形凹槽表面上凸起的前后沿改成直角结构会增大凹槽表面对液滴运动的阻力。     

液滴撞击不同固体表面的数值模拟研究

采用CLSVOF(coupled level set and volume of fluid)方法,对低We情况下液滴撞击不同固体表面的过程进行了数值模拟研究。分析了液滴撞击平板表面的动态过程,构建了液滴衰减振荡的数学模型,探究了不同的表面润湿性、撞击速度及表面微尺度结构对液滴动态特性的影响。结果表明:液滴撞击固体表面的过程包含铺展、回缩、振荡等多个现象,其最大铺展因子及振荡周期随着表面接触角的增大而减小,随着撞击速度的增大而增大;撞击表面的微尺度结构会对液滴的动态特性产生影响,微尺度结构会对液滴的铺展及回缩运动产生阻碍作用,导致液滴的振荡特性减弱;液滴在矩形沟槽表面达到最大铺展因子的用时最短,在三角形沟槽表面的最大铺展因子最小。     

液滴撞击低温超疏水表面运动状态的数值模拟研究

本文针对液滴撞击固体表面后出现的反弹和黏附两种运动状态,通过引入基于连续温度函数的能量方程,建立了用于计算液滴运动、传热和相变过程的数值模型,并与实验结果对比,验证了数值模型的准确性。进而模拟了具有不同韦伯数We和奥内佐格数Oh的液滴撞击低温超疏水表面的运动、传热和相变过程。结果表明：液滴撞击后的运动状态主要取决于奥内佐格数Oh,临界范围是0.022-0.026,而基本不受韦伯数We的影响。当液滴撞击后的运动状态为反弹时,韦伯数We越大的液滴,最大铺展直径越大。而当韦伯数相同时,随着奥内佐格数Oh的增大,液滴与表面的接触时间越大。     

加热板上液滴沸腾实验研究

采用高速摄像技术研究了不同加热表面上液滴蒸发和沸腾的相变特性和壁面温度变化特性,讨论了局部相变行为对壁面温度变化的影响.同时定量的研究了三种不同表面特性的加热板对沸腾和传热的影响,以及液滴初始体积对相变的影响.结果表明,表面特性和液滴尺寸对沸腾传热有较大影响.     

固体表面液滴在吹风作用下的振荡特性

利用可视化实验观察了水平表面液滴在吹风条件下的振荡现象。针对水液滴在不同型号砂纸打磨的铜表面进行实验,观察到液滴在吹风条件下发生上下和左右两种振荡模式,在一定的条件下两种模式可以相互转化。通过细致的观察分析,总结归纳了振荡及转化发生的规律。实验结果表明：液滴的振荡特性同表面租糙度、液滴尺寸、风速等有一定的关系。振荡周期随着液滴尺寸增大而增大,随着风速的增大阶跃式增大;随粗糙度增大,液滴振荡周期有先增大再减小的趋势。     

具有微结构超疏水润湿梯度表面液滴的蒸发行为研究

采用标准微电子机械系统(Micro-Electro-Mechanical System,MEMS)加工工艺,设计并加工了一种具有圆柱微结构的超疏水润湿梯度表面,搭建了研究液滴蒸发过程的可视化光学实验平台,同时从不同角度观察了液滴在具有圆柱状微结构超疏水润湿梯度表面的蒸发行为。通过实验研究发现:液滴在具有圆柱状微结构的超疏水润湿梯度表面的蒸发过程中,随着液滴的蒸发,液滴体积、液滴与表面的接触半径均不断减小,蒸发过程遵循混合蒸发模型;液滴边缘的三相线跳跃与移动均只发生在相对疏水的区域一侧;而在相对亲水的一侧,液滴边缘始终处于静止状态,直至液滴完全蒸发;在超疏水润湿梯度表面上的液滴蒸发过程中,液滴质心仅在具有润湿梯度的方向上移动,且液滴质心移动方向与润湿梯度方向相反(朝亲水侧移动)。最后基于液滴蒸发过程中的能量变化理论,解释了出现上述现象的原因。     

液滴在化学非均匀表面上铺展的格子Boltzmann方法模拟

采用格子Boltzmann方法模拟二维液滴在非均匀表面上的铺展。非均匀表面由两块面积相等但润湿性不同的均匀表面拼接而成,左半部分为亲水表面(θeq=35.00°),右半部分为疏水表面(θeq=115.00°)。液滴初始为圆形,位于亲疏水表面交界处。由于表面两侧平衡接触角θeq相差较大,铺展的Young驱动力FY=γlg(cosθeq-cosθD)有显著差异,因而液滴左右呈现出不同的铺展规律。模拟结果显示,铺展可分为三个阶段:第一阶段,液滴向两侧铺展直至疏水侧铺展速度为0,但亲水侧铺展速度始终快于疏水侧;第二阶段,整个液滴向亲水侧运动,直到液滴右侧到达亲疏水表面交界处;第三阶段,液滴在亲水表面铺展直至平衡。当液滴初始位于亲水侧或疏水侧,且其质心与亲疏水表面交界处的横向距离小于50lu时,液滴呈现出三种不同铺展形式,然而由于亲水侧更大的Young驱动力,最终的平衡液滴均位于亲水侧。     

单液滴在多孔介质内碰壁过程的数值模拟

应用数值模拟方法研究不同尺寸单一液滴碰撞常温多孔介质内壁面时的运动与变形行为.界面跟踪采用基于VOF的体跟踪模型,简化的多孔介质结构应用孔隙网络模型.主要考查了初始液滴碰撞动能、表面能及液滴与多孔介质内壁面相对尺寸大小对液滴碰壁现象的影响,分析了液滴在多孔内壁面上形成液膜、液膜延展碰撞喉道壁面及飞溅破碎等过程的动力学特...     

玻璃丝布表面处理炉的设计

介绍玻璃丝布表面预烘,固化炉炉型结构以及对卧式炉与立式炉两种炉型进行比较。     

On the sliding and profile of a liquid droplet on a rotating disk

This theoretical and experimental study was conducted to investigate the critical condition at which a liquid droplet starts to move on a rotating disk. The critical rotational speed ω was theoretically calculated based on the force balance between the surface tension and the centrifugal force, where ω was experimentally measured for each combination between three kinds of test plates and test liquids. The movements of droplets were judged from the careful observation of infinitesimal motion of the three‐phase contact line. The calculated rotational speeds agreed well with measured ones for arbitrary contact angle when the droplets were set on the plate. The three‐dimensional surface profiles of droplets were calculated from the approximate Laplace equation in which the contact line was assumed as the combination of two ellipses with different ratio of measure to minor axis. The measured profiles on the rotating disk were approximated well by the method proposed in this study. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20276     

A numerical study of air entrapment during the droplet impact on a solid substrate

A numerical investigation is conducted to study the air entrapment phenomenon when two different liquids such as water and diesel droplet are impacted on the solid surface. The beginning of the air entrapment process was observed during droplet impact on a solid substrate forming a dimple underneath the droplet. The air film thus trapped underneath the droplet started evolving into the air bubble. This journey of evolution mainly comprises phases like an inertial retraction of air film, contraction, and pinch-off of the secondary droplet inside the air bubble for a water droplet impact case. The volume of fluid approach has been utilized to track the progress of air film evolution. The influence of surface wettability has been observed on the evolution of air film into the air bubble by taking four different values of contact angle pertaining to the hydrophilic surface (θ = 10° and 35°) and hydrophobic surface (θ = 90° and θ = 120°). The air bubble was found to get detached from the substrate for the hydrophilic surface (θ = 35°) and observed to remain attached to the substrate for the hydrophobic surface. The variation of pressure underneath the droplet was also investigated as the droplet reaches the substrate. The effect of surface tension has been studied on the evolution of air film by impacting the diesel droplet on the same substrate keeping the same wettability condition (θ = 35°). The lower surface tension of the diesel droplet as compared to the water droplet delayed the process of air film evolution and consequently decreases the retraction speed of air film. Also, the air bubble remains attached to the surface. Furthermore, the air bubble detaches from the surface for an even higher wettability condition (θ = 10°). Thus surface wettability and surface tension become two important factors governing the development of entrapped air film and bubble elimination in many practical applications.     

太阳能辐射资料库的创建

介绍了所创建的我国太阳辐射资料库,其内容包括适合于太阳能利用的遍布全国的太阳能辐射资料、不同方位和倾角的表面上太阳辐照量的计算方法及相应的计算程序.这些将为系统的优化设计创造有利的条件,对于提高太阳能供热和光伏系统的可靠性和降低投资费用都具有重要的作用.     

在绝热流动情况下非球形水滴的运动特性

采用非球形颗粒的阻力系数关联式，建立了水滴在绝热逆流空气中的动力学方程，得出了水滴所受阻力及其最终沉降速度的计算方法。在此基础上，分析了水滴变形程度和内部流动对水滴运动特性的影响，结果表明水滴变形程度增加使得水滴受到的空气阻力增大，而最终沉降速度减小，水滴的内部流动导致其受到的空气阻力减小，计算条件下最大偏差可达15％。     

悬垂水滴与悬浮气泡表面气体水合物形成特性对比

基于悬垂水滴和悬浮气泡表面形成气体水合物的可视化耐高压实验装置,分析探讨了反应压力、温度、水质等因素对水滴和气泡表面气体水合物成核和生长规律的影响.对已有的关于研究单个静止悬垂水滴和悬浮气泡表面气体水合物生长特性的实验现象及结果进行了对比分析,得出结论:温度和压力是影响表面水合物结晶与生长的重要因素;温度的降低或压力的升高均使水合反应速度加快.研究为发展喷雾法和鼓泡法这两种强化制备水合物的方式提供了有效的实验支撑.     

Identifying rotation and oscillation in surface tension measurement using an oscillating droplet method

We proposed a new approach to identify the frequencies of droplet rotation and m=±2 oscillation that degrade the accuracy of surface tension measurement by an oscillating droplet method. Frequencies of droplet rotation and m=±2 oscillation can be identified by a phase unwrapping analysis of time dependence of the deflection angle for the maximum diameter of the droplet image observed from above. The present method was validated, using test data with given frequencies. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(7): 421–430, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20214     

Evaporation of an oil‐in‐water type emulsion droplet on a hot surface

Evaporation characteristics of an Oil‐in‐Water (O/W) emulsion droplet were examined experimentally. The evaporation time per unit of initial surface area of a droplet τ^* was used to estimate the evaporation characteristics of droplets with different diameters and to compare a water droplet and an emulsion droplet. Results show that τ^* of an O/W emulsion droplet is shorter than a water droplet in the Leidenfrost film boiling regime. The four evaporation modes of O/W type emulsion droplets were observed. These depended on the mixing ratio of water and oil, G_S, and hot surface temperature, T_W. Increasing G_S increases the emulsion droplet's Leidenfrost temperature when the droplet is used as a die‐cast releasing agent. Microexplosions were observed during Leidenfrost film boiling when T_W was greater than 250^°C. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(7): 527–537, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20081     

A note on diffuse solar radiation on a tilted surface

We are presenting a note on comparative study of diffuse component of solar radiation on tilted surface with different angle of inclination. The monthly mean daily diffuse radiation have been calculated on inclined surfaces from the data of horizontal surface using the Circumsolar and Isotropic model and the anisotropic model of Klucher and Hay at Lucknow (Latitude 26.75°, Longitude 80.85°), Uttar Pradesh, India. These calculated results are compared with our measured value. The comparison shows that Klucher model who considered the effect of cloudy sky conditions gives comparatively good estimations particularly at low inclination angles.