| The heat transfer and interfacial characteristics of a small constrained system under stress in the form of an evaporating extended meniscus, with an adsorbed thin film, at the exit of a circular slot feeder were studied. The stress level in the completely wetting liquid-solid system was increased by decreasing the overall size of the film and thereby increasing the relative importance of the interfacial phenomena.;The liquid film thickness profile, which characterized the pressure field, was accurately measured using ellipsometry and microcomputer enhanced interferometry. The accuracy and efficiency of the high resolution image processing techniques were successfully exploited to integrate these two measurements and to obtain an essentially continuous film profile.;A model for the transport processes in the contact line region, based on the augmented Young Laplace equation and kinetic theory, was developed. Numerical solutions of the model were used to evaluate the experimental data. A Taylor series expansion of the fourth order nonlinear transport model was used to obtain the extremely sensitive initial conditions at the interline. The numerical scheme was tested for its accuracy.;The present study demonstrated that the theory based on the concepts of disjoining pressure, curvature and kinetic theory can be successfully compared to the experimental results. The excellent match between the theory and the experiments was used to obtain consistent values of the solid-liquid-vapor Hamaker constants. The description of the pressure field illustrated the details of the coupling between the disjoining and capillary pressures. In the very thin film, disjoining pressure gradients control the fluid flow, whereas, capillary forces govern the flow in the thicker portion of the meniscus. The sensitivity of the meniscus profile to small changes was also demonstrated.;The results showed that to support higher rates of evaporation, the profile became steeper with a higher curvature and the adsorbed film thickness decreased as the heat input to the system is increased. The study also demonstrated that since there were significant resistances to heat transfer in the system due to interfacial forces, viscous stresses and thermal conduction, the "ideal constant heat flux" could not be obtained. |
