薄膜流研究进展

薄膜流研究进展班级：机械工程专硕1班学号：6160805020姓名：程帅摘要：液体在重力作用下以薄层形式沿壁面向下流动，称为液体薄膜流。

它具有小流量、小温差、高传热传质系数、高热流密度、结构简单、动力消耗小等独特优点，己作为一项高效传热传质技术在化工、能源、航天、石油、制冷、电子等许多工业领域得到了广泛应用。

本文介绍了非牛顿流体层流降膜流、新型薄膜覆盖材料、薄膜流涎机。

正是由于实际应用的重要性和迫切性，在液体薄膜流的水动力过程和传热传质特性力一面，近几十年来开展了大量的深入研究。

本文通过全面阐述液体薄膜流动和传热特性的研究现状，分析目前研究中存在的问题与不足，为未来研究提供借鉴。

关键词：液体薄膜流、非牛顿流薄膜流、新型薄膜覆盖材料、薄膜流涎机1.液体薄膜流表面特征对于液膜沿倾斜壁或垂直管壁向下流动的情形，从实验上观察到三种不同的流动状态:当Re=4T/v<20~30 (T为单位湿周的体积流率，v为流体的运动粘度)，流动为层流，膜表面呈平滑状态且膜厚为常数;当200<Re<1000~2000，流动呈波动的层流，其中表面波叠加在向前运动的液膜表面；当Re>1000~2000，流动呈波动性剧烈的紊流。

在工业应用的雷诺数范围内，降膜呈现出非常不规则的波动表面。

对于波峰高度是底层厚度两倍以上，且其周围存在至少一个波长长度的平坦部分的波，称之为孤立波，如图1所示。

它起始于粘性底层，具有陡峭的波前和相对平缓的波后，在波后逐渐没入粘性底层。

对于波幅是其底层厚度2}5倍的大波，其携带着大部分流动质量，对波内、波与壁面、波与外界的传热传质速率，起着明显的控制作用。

一般说来，界面处的波动会在膜内、特别是在接近界面处将产生良好的混合。

实验测量表明，紊流对动量传递的影响与波动的影响相比要小一些。

(a)波峰高度/底层厚度=2.8 (b)波峰高度/底层厚度=3.68图1不同波峰高度/底层厚度比下的流动特性，R=600大多数模拟结果显示:在孤立波内存在与主流方向相反的回流区，而在其周围的微波内不存在回流区(图1)。

回流区的存在，加快了界面处和膜内冷热流体的混合，在一定程度上加强了传热效果，而且，液体表面波的存在，尤其是大孤立波，可有效地喇氏平均液膜厚度，.这些特征可以从理论上解释在波动膜状态下具有强传热传质速率的机理。

2、非牛顿流薄膜流2.1非牛顿流体层流降膜流非牛顿流体层流降膜流中质量传递过程.实验系采用温壁塔测定二氧化碳在高分子水溶液中吸收速率。

这些溶液符合幂律模型.实验证明非牛顿幂律流体降膜流中考虑速度分布的微分方程精确解是正确的;对拟塑性流体,用无因次长度Z<0.1作为渗透论适用范围的判据是合适的，而精确解则不受此范围的限制。

首先，理论研究方面，液膜表面波动具有三维特征，在传热特性的理论研究中，通常假设液膜为二维流动，且表面无波动和界面切应力保持不变，这与实际的三维波动液膜表面和沿流动方向不断减小的切应力存在一定的差距;而且，影响传热特性的因素种类繁多，如何从理论上进一步完善物理模型有待探讨。

其次，实验研究方面，目前所得液膜厚度和传热特性实验关联式间相差较大，实验数据相对缺乏，建立合理的简化的物理模型或寻求适合工程应用的实验关联式，这也值得进一步深入研究。

2.2流延带的材料最早用以制造流延带的材料是纯铜。

纯铜有良好的延展性，有利于加工成无端带;铜带在使用过程中的变形可用辊压法展平。

因纯铜对一般成膜溶液不具有良好的化学稳定性，同时铜带表面的光洁度和平面度不够高，不适于直接在其表面上流延薄膜，而需先在其表面上流延一定厚度的镜面层，在此镜面层上再流延薄膜。

镜面层只能使用一定的期限，这样就增加了生产过程的复杂性，又降低了设备的生产能力。

虽然如此，由于镜面层的质量改进和用期的延长，仍可见到使用铜带的报道。

目前广泛使用的流延带是不锈钢无端带。

薄膜和塑料工业的发展要求提高流延带的物理和化学性能。

用以制造流延带的不锈钢材应有高的机械强度和硬度(抗拉强度9 (Y一100kg/mm2，表面硬度Hd300^-320)，以保证在正常操作张力下不产生变形并且有高的抗擦伤能力;应能易于加工，使之达到镜面光洁度;同时对于成膜溶液应有高度的稳定性。

18/8型不锈钢的某些品种(例如AISI304冷轧带材)可以满足这些要求。

经过特殊机械加工制成的不锈钢流延带，可达到高度的厚度均一性和获得峰到谷的平均高度值小于0.1微米的镜面。

因此，可以直接在这样的带的表面上流延薄膜。

国外还制造纯镍带。

镍具有高的腐蚀抵抗力，亦不需要中间层，物料可直接在其表面上流延。

牛顿型流体薄膜流中的物质传递与热传递在吸收器、蒸馏塔、薄膜反应器、蒸发器以及吸收式致冷机中的广泛应用，已为人们所熟知。

近年来发现，非牛顿流体薄膜流中的传质和反应对于高分子加工、发酵液、生物制药等领域，其潜在的应用也十分广泛。

特别是扩散系数的测定，由于非牛顿流体只有在其流动受剪的情况下才显示其特性，所以，一般的非流动情况下扩散系数的测定技术似乎难以利用。

因此，对非牛顿薄膜流中的传质和传热加以研究就显得十分必要。

3.薄膜流的应用新型薄膜覆盖材料的研究和开发是我国设施农业的重要研究方向。

根据我国的国情,为满足市场需求,本文在国内首次提出采用日产的明净华涂层薄膜作为我国设施农业的保温覆盖材料。

基于材料本身多方面优异性能,研究其在国内设施农业方面的应用前景。

通过对新型薄膜覆盖材料的性能分析及其应用效果的研究，在理论和实践两方面加以验证。

理论上推论出其具有良好的保温效果,并在后面的应用效果中得到证实。

在应用效果上,只对棚内种植番茄的叶数、株高、茎粗、产量、果实等进行了测试和比较分析,作物生长受到光照、温度、水分、肥料、空气等影响。

实验在尽量保持温、光、水、肥等基本一致的条件下对作物生长进行对比,在作物的生长阶段里可以较明显的看出日产的明净华涂层膜下的作物长势好、产量高、品质好等华盾棚膜次之。

总之，日产的明净华涂层膜在环境特性、光学特性及应用效果等各方面都具有较好的性能,基本上满足市场的需求，为解决目前我国设施农业存在的问题提出一种新的解决方法。

薄膜流涎机是生产包装薄膜的主要生产设备。

随着国民经济的高速发展，人们对包装薄膜的需求越来越旺盛,要求也越来越高，这就促使薄膜流涎机生产企业必须高效、高质量地开发、生产符合客户要求的薄膜流涎机。

薄膜流涎机模块化参数化设计技术研究,就是利用当前最先进的模块化设计技术并结合参数化CAD设计技术解决薄膜流涎机快速开发设计的问题,提高企业竞争力。

现如今的设计，首先对薄膜流涎机模块化参数化设计进行了需求分析,在此基础上,制定了适合薄膜流涎机模块化参数化设计系统的总体方案,并搭建了薄膜流涎机模块化参数化设计系统的框架；然后根据模块化设计的基本原则和方法,并结合薄膜流涎机的功能以及自身结构特点,建立了以固定模块、通用模块和一般模块为基本单元模块,以功能模块为高级单元模块的层次分明的模块结构体系,建立了基本的三维模块库；根据薄膜流涎机自身零部件设计的要求和特点,提出了适合其零部件的参数化设计方法,并以薄膜流涎机收卷机为例,详细介绍了收卷机中各个零部件的参数化设计计算流程,完成了收卷机的参数化设计计算；最后以Visual Basic为二次开发工具,利用SolidWorks的二次开发技术并结合Access数据库,开发出了薄膜流涎机收卷机参数化设计系统。

经实例运行可知,此系统可以快速实现收卷机的三维建模,提高设计效率,有较强的实际应用价值。

4.薄膜流国外研究现状A new approximate analytical technique to address for non-linear problems, namely Optimal Homotopy Asymptotic Method (OHAM) is proposed and has been applied to thin film flow of a fourth grade fluid down a vertical cylinder. This approach however, does not depend upon any small/large parameters in comparison to other perturbation method. This method provides a convenient way to control the convergence of approximation series and allows adjustment of convergence regions where necessary. The series solution has been developed and the recurrence relations are given explicitly. The results reveal that the proposed method is very accurate, effective and easy to use. the unsteady thin film flow of a fourth grade fluid over a moving and oscillating vertical belt. The problem is modeled in terms of non-nonlinear partial differential equations with some physical conditions. Both problems of lift and drainage are studied. Two different techniques namely the adomian decomposition method (ADM) and the optimal homotopy asymptotic method (OHAM) are used for finding the analytical solutions. These solutions are compared and found in excellent agreement. For the physical analysis of the problem, graphical results are provided and discussed for various embedded flow parameters.The thermally activated flux flow effect has been studied in epitaxial FeSe 0.6 Te 0.4 thin film grown by a PLD method through the electrical resistivity measurement under various magnetic fields for B //c and B //ab. The results showed that the thermally activated flux flow effect is well described by the nonlinear temperature-dependent activation energy. The evaluated apparent activation energy U 0 ( B ) is one order larger than the reported results and showed the double-linearity in both magnetic field directions. Furthermore, the FeSe 0.6 Te 0.4 thin film shows the anisotropy of 5.6 near T c and 2D-like superconducting behavior in thermally activatedflux flow region. In addition, the vortex glass transition and the temperature dependence of the high critical fields were determined.We report the design methodology of thin film capacitor (TFC) device using thermal evaporation technique for quality study or material differentiation application by testing with liquid (different concentration) and solid. A simple and special modification was incorporated in thermal evaporation setup for depositing semi cylindrical capacitor design on a capillary tube (CT). In order to avoid the disturbance due to electrostatic noise disturbance, TFC was covered with another glass tube, aluminum (Al) metal foil (as shield) and finally by plastic tube cover. Electrodes were taken from the film using silvers paste and connected as input to the LCR-Z meter. The capacitance value of the thin film was varied up to 15-16 pF from the initial value (Al: 129 pF, Cu: 130 pF) when subjected to the static flow. A low cost embedded micro controller module with Liquid Crystal Display (LCD) was developed for the real time testing of TFC.We present results of a numerical study of turbulent droplet-laden channel flow with phase transition. Previous studies of the same system did not take into account the presence of gravity. Here, we do so introducing a thin film of water at the bottom wall and permitting droplets to fall into and merge with it. We treat the carrier phase with the Eulerian approach. Each droplet is considered separately in the Lagrangian formulation, adopting the point-particle approximation. We maintain the film thickness constant by draining water from the bottom wall to compensate for (a) the droplets that fall onto the film and (b) evaporation/condensation. We also maintain on average the total mass of water in the channel by inserting new droplets at the top wall to compensate for the water that has been drained from the bottom wall. We analyze the behavior of the statistically averaged gas and droplet quantities focusing on the heat exchange between the two phases. We increase (a) the initial droplet diameter keeping the same initial droplet volume fraction and (b) the initial number of droplets in the channel keeping their diameter the same. In both parameter studies we find that droplets grow less than in the reference case. In case (a) this is explained by the larger velocity with which they travel to the bottom wall and in case (b) by the lower rate of condensation of vapor due to the presence of neighboring droplets.And we presents an investigation for unsteady MHD flow and radiation heat transfer of a nanofluid in a finite thin film over stretching surface in which the effects of heat generation, thermophoresis and Brownian motion are taken into account. Boundary layer governing differential equations are formulated and reduced into a set of ordinary differential equations by suitable similarity transformations. Solutions are obtained numerically and some interesting results are found. Results show that the film thickness decreases monotonically with unsteady parameter and the magnetic parameter increase but increases with the power law index number m . The temperature profile decreases while the nanoparticle volume fraction increases as the thermophoresis parameter increases. More effects of involved parameters on velocity, temperature and concentration fields are graphically presented and analyzed in detail.Electrophoretic deposition (EPD) of colloidal nanocrystals (NCs) under flow is explored as a general method for the fabrication of semiconducting thin films. For photovoltaic applications, a low process voltage is highly desirable to avoid damaging the accreting semiconductor. Here we report a continuous flow reactor design that can operate at reduced voltage compared to a traditional batch reactor while preserving the electrophoretic velocity of the NCs by utilizingnarrow electrode spacing. In a batch reactor, the low ratio of reactor volume to electrode surface area dictated by such a narrow spacing of the electrodes would impose a limit on the mass of nanocrystals that are resident in the reactor and therefore the thickness of the films that can be deposited. By continuously flowing the colloidal dispersion of NCs this limitation is obviated and thick films can be deposited. Through modeling and experiment we demonstrate the process parameters necessary to completely utilize the NCs in the feed solution, thereby achieving nearly 100% atom economy in the deposition process. The reactor design is compatible with large area substrates and is specifically designed to enable continuous, high-rate fabrication of the active layer of photovoltaic cells.The approach to calculating a new form of the exact analytic solution of thin film fluid flows rests upon a sequence of transformations including the modification of the classic technique due to Scipione del Ferro and Niccolò Fontana Tartaglia. Next the authors establish a lemma that justifies the new expression of the exact analytic solution for thin film fluid flows of fourth-grade fluids. Second, the authors apply a modification of the systematic ADM to quickly and easily calculate the sequence of analytic approximate solutions for this strongly nonlinear model of thin film flow of fourth-grade fluids. The ADM has been previously demonstrated to be eminently practical with widespread applicability to frontier problems arising in scientific and engineering applications. Herein, the authors seek to establish the relative merits of the ADM in the context of the thin film flows of fourth-grade fluids.;The ADM is shown to closely agree with the new expression of the exact analytic solution. The authors have calculated the error remainder functions and the maximal error remainder parameters in the error analysis to corroborate the solutions. The error analysis demonstrates the rapid rate of convergence and that we can approximate the exact solution as closely as we please; furthermore the rate of convergence is shown to be approximately exponential, and thus only a low-stage approximation will be adequate for engineering simulations as previously documented in the literature.;This paper presents an accurate work for solving thin film flows of fourth-grade fluids. The authors have compared the approximate analytic solutions by the ADM with the new expression of the exact analytic solution for this strongly nonlinear model. The authors commend this technique for more complex thin film fluid flow models.Evaporation in a thin film induces pronounced temperature gradient and surface tension gradient along the liquid-vapor interface and in turn engenders thermocapillary flow. This study aims to investigate the fluid flow characteristics attributed to the thermocapillarity in an evaporating thin liquid film of polar and nonpolar liquids. A numerical steady-flow model is derived based on the fundamental principles of fluid flow and heat transfer by applying the long-wave evolution technique. To scrutinize the underlying physical transport phenomena associated with the significance of thermocapillary effect in an evaporating thin liquid film, we investigate the hydrodynamic characteristics of thermocapillary convection which is typically characterized by the recirculation flow patterns. The two-dimensional recirculation flow patterns in different excess-temperature regimes are analyzed and a critical turning point at where the flow is reversed due to the thermocapillary action can be identified. Compared to other working fluids, water depicts a unique thermocapillary flow characteristic where its flow lines manifests in the form of swirls along the liquid-vapor interface. The normal and the shear stress distributions further provide a clearer picture on the strength of thermocapillarity to identify the manifestation of thermocapillary flow. The analysis of flow patterns and hydrodynamic behaviors of evaporatingthin liquid films provide essential insights in discerning the occurrence of thermocapillary flow as well as the significance of thermocapillarity in polar and nonpolar liquids.The purpose of this paper is to study the thin film flow of a fourth grade fluid subject to slip conditions in order to understand its velocity profile. Design/methodology/approach。