Investigation On Heat And Mass Transfer And Flow Stability Of A Thin Liquid Film Draining Down A Wall

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 subcoolingfilms 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.