【作者】 叶学民；

【导师】 阎维平；

【作者基本信息】 华北电力大学（河北） ， 热能工程， 2003， 博士

【摘要】 液体薄膜流以其高传热传质系数、结构简单且动力消耗小等独特优点，已作为一项高效传热传质技术在传统工业和高新技术领域中得到了广泛的应用。现已成为国际传热传质科学与工程界的一个十分活跃的研究领域，其潜在的技术应用领域将非常广泛。正是由于实际应用的重要性，深入了解液体薄膜的水动力特性和传热传质规律，研究其破断过程、机理和控制条件，已成为近年来富有挑战性的研究课题。 本文针对在蒸发和冷凝条件下薄液膜流动的稳定性、在气液界面切应力协同下层流饱和蒸发降膜的传热特性和过冷液膜的永久破断特性进行了较为系统的理论研究、对过冷液膜的传热和破断特性进行了实验研究。主要包括以下内容：1. 在蒸发和冷凝条件下薄液膜流动稳定性的理论研究。从理论上推导沿倾斜壁面下降的，在蒸发、等温和冷凝状态下普遍适用的二维降落液膜表面波时域和空间演化方程。获取表征液膜稳定特征的中性稳定性曲线、扰动的时间和空间增长率、临界波数、最大波数、波速的变化趋势；分析雷诺数、倾角、热毛细力、表面张力、流体物性以及蒸发、等温或冷凝状态对液膜时域和空间稳定性的影响。对驻波的有关特性，如稳定性和波速进行讨论，并分析上述诸多因素的影响。2. 在气液界面切应力协同下的层流饱和蒸发降膜传热特性的理论研究。从理论上建立在同向或反向切应力作用下层流饱和蒸发液膜流动和传热特性的物理模型，推导其液膜厚度和传热系数的表达式，分析液膜厚度和传热系数沿流动方向上的变化趋势，深入探讨界面切应力、界面对流换热强度和雷诺数等因素的影响，揭示层流饱和蒸发液膜的传热机理。3. 在气液界面切应力协同下的受热过冷液膜永久破断特性的理论研究。从理论上建立对有界面切应力作用下受热液膜的永久破断力平衡模型，分别在重力驱动、重力和切应力驱动、切应力驱动下推导临界破断液膜厚度与最小润湿量和接触角、流体温度、气液界面切应力、壁面热流密度间的理论关系式，分析其变化趋势和各种因素的影响，探讨液膜发生永久破断现象的机理，并对力平衡模型中各个力的相对大小进行讨论。自行设计和建立实验台，通过采集实验件管壁温度、出入口水温和气体流速等数据，深入研究垂直降落过冷液膜在有、无同向或反向切应力协同下的传热特性和永久破断特性，提出新的关于传热特性和破断特性的实验<WP=4>4. 关联式，并与文献进行比较；在切应力协同下，分析不同方向和不同切应力大小对液膜传热和破断特性的影响规律及程度，并与常规换热和破断情形及理论计算结果进行分析和比较。更多还原

【Abstract】 The concept of a thin liquid film draining down an inclined wall has been widely used in traditional industries and hi-tech fields because it can enhance heat and mass transfer rates without incurring a lot of flow resistance and power consumption. The researches on liquid films are very stirring in international heat and mass transfer and engineering fields. Due to the importance and universality of application, it is extremely necessary to investigate the properties and mechanisms of the hydrodynamics, flow stability, heat and mass transfer and breakdown.The flow stability of the evaporating and condensing film and the heat transfer and breakdown with the interfacial shear stress are carried out in theory, and the characteristics of the heat transfer and breakdown are also conducted in experiment. The main contents of the present paper include:1. The theoretical investigation of the flow stability of the evaporating and condensing film. The universal linear temporal and spatial evolution formulations expressed in the film thickness are established with the collocation method for the evaporating or condensing and isothermal liquid films draining down an inclined wall. The neutral stability curves and the character parameters are given, including the temporal and spatial growth rate, the critical wave number, the maximum wave number and the wave celerity. And the effects on stability of the Reynolds number, the inclination angle, the thermocapillarity, the surface tension, the liquid property and the evaporation or condensation conditions are discussed in detail. The characteristics of the stationary wave are presented in this paper, including its stability and wave celerity.2. The theoretical investigation of the heat transfer character of the laminar saturated falling film under with interfacial shear stress. The physical models of the hydrodynamics and heat transfer are set up for the laminar saturated falling film under countercurrent and cocurrent interfacial shear stress, and the theoretical correlations of the film thickness and heat transfer coefficient are derived. The local film thickness and heat transfer coefficient on streamwise are showed, and the effects on hydrodynamics and heat transfer of the interfacial shear stress, the intensity of interfacial convection heat transfer and the Reynolds number are explained.3. The theoretical investigation of the permanent breakdown of the subcooling<WP=6>films with interfacial shear stress. The force balance model is founded for the permanent breakdown of the subcooling films with interfacial shear stress under the sensible heating condition. The relations of the critical film thickness and minimum wetting rate with the contact angle, the film temperature, the interfacial shear and heat flux are illustrated under driving by the gravity, the gravity and the interfacial shear, and the interfacial shear, respectively. The effects of the above factors on permanent breakdown are explained, and the mechanism of the breakdown is discussed. 4. The experimental investigation of the heat transfer and breakdown of the subcooling film with or without interfacial shear stress. By designing and founding the experimental apparatus and collecting the data of the tube temperatures, the inlet and outlet water temperatures and the air velocity, the properties of the heat transfer and breakdown with or without countercurrent or cocurrent interfacial shear stress are studied under the sensible heating condition, and the correlations of the heat transfer and critical heat flux are established and compared with the previous references. The effects of the Reynolds number, the Prantl number and the interfacial shear stress are discussed and compared with the conventional heat transfer and breakdown and theoretical results.更多还原