Effect of vapor dynamics on interfacial instabilities

Instabilities at fluid-fluid interfaces are of interest to researchers on account of their role in many industrial and natural processes. These instabilities are often accompanied by phase-change between liquids and their vapors, and in some instances are caused by it.;In this study, evaporative instabilities are analyzed theoretically and experimentally at the interface between a liquid and its vapor where both the liquid and the vapor are fluid dynamically active in order to investigate and understand the role of vapor dynamics on evaporative and interfacial instabilities. In the theoretical model, the Navier Stokes and energy equations in the liquid and vapor domains were using linear and nonlinear perturbation methods with the assumption that both fluids are incompressible using the Boussinesq approximation. The linear theory tells us the conditions at the onset of instability and the critical point at which the interface becomes unstable. The weak nonlinear method tells us the behavior of the system slightly beyond the onset of the instability. The linear and weak nonlinear theories are of importance for the experimental reasons as they provide us with the information on how and when the instability will occur.;In a separate study of non-evaporative systems, experiments were performed in a liquid-gas bilayer system in a circular container with the intention of studying instabilities in the absence of evaporation. The depth of the gas layer was changed to observe the effect of the fluid dynamics in the gas layer on the onset flow pattern and conditions. These experiments were then compared with a corresponding theoretical model and it was concluded that the gas dynamics played an ever-increasing role as the gas layer height was increased. Past workers had assumed the vapor to be a conductive, fluid dynamically passive medium. However, the experiments show us that deep enough vapor layers can cause the bilayer system to convect earlier than expected by thermally coupling with the liquid at the interface.;In summary, from theoretical studies it was found out that active vapor layers play an important role on the evaporative instabilities even in the absence of natural convection. Moreover, it is discovered that the fluid dynamically active vapor plays a very strong stabilizing role on the evaporation problem. In addition to that, from the experimental studies in the absence of phase-change it was revealed that the vapor layers can and do affect the onset flow pattern and conditions. Both theoretical and experimental studies also indicate that the commonly used infinitely deep vapor layer assumption is not always true and can lead to errors. (Abstract shortened by UMI.).