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Drop generation from jet breakup and drop-impact on thin films are two key processes in many spray, coating and deposition applications which are experimentally and computationally investigated in this dissertation. A high-speed camera is used to capture the drop formation and its impingement on thin films and a modified volume of fluid (VOF) method is used to accurately simulate jet/film breakup. It is shown that the proposed modifications in interfacial property evaluations for VOF method provide accurate predictions of moving interface for highly viscous liquids. To understand the parameters governing uniform drop generation, a numerical study of the jet disintegration process, supplemented by experimental observations, is conducted. The simulations show that while an increase in viscous force offers greater resistance to propagation of the surface undulations thus resulting in stretching of the liquid jet, surface tension determines the radius of curvature of the pinch-off location. The interplay of these two forces leads to deviations from uniform drop generation and two different modes of liquid jet pinch-off that lead to satellite drop creation are observed. It is shown that the occurrence of these modes is governed by the liquid Morton number. A semi-empirical relation is proposed to predict the onset of the two modes.In most spray applications, the drops formed from a jet are incident on a target surface usually with a thin layer of liquid film. While viscous resistance to impact of the drop is offered by the film thus controlling drop spreading and crown formation, surface tension is noted to primarily govern the growth and eventual break-up of the ejected crown. An empirical relation for the onset of splash is obtained from high-speed image analyses of the drop-film interactions. Numerical simulation of the process indicates that the contribution of the target film and impacting drop in the creation of ejected crown depends on the film thickness. At low liquid film thickness, the liquid from the impacting drop primarily forms a jet that is ejected post-impact. For thicker films, the liquid layer absorbs a part of the energy from the impacting drop and thus the ejected jet is formed from both the impacting drop as well as the liquid layer. The temporal dynamics of deposition of Newtonian drops on thin films indicates that while surface tension and inertial forces govern resultant crown height, their contribution on crown diameter is not as significant. Viscosity is noted as the key factor that governs the crown diameter. In addition, experimental investigation of drop impact dynamics of shear thinning polymeric solution is carried out to understand the effects of solution rheology on the temporal dynamics. For aqueous solution of HEC 250 HHR, the apparent viscosity is low during initial impact (high shear rate) and this increases the likelihood of splashing compared to a Newtonian liquid with the same zero shear viscosity. High-speed images of drop impact on thin film of aqueous solution of PEO WSR 303 indicate that extensional viscosity also plays an important role in governing the post-impact behavior.

An experimental investigation on the disintegration of circular liquid jets, ejected into a stagnant ambient atmosphere at low Weber number, is presented in this thesis. The process of breakup of the liquid jet was captured using a real-time image processing high-speed digital camera system. In order to understand the influence of inertial, surface tension, and viscous forces on the process of breakup, a range of Weber numbers from 5 to 110 was experimentally tested. A syringe pump was used to provide a constant flow rate and produce a jet at a given Weber number. The effects of surface tension and viscosity were investigated by using two viscous liquids (ethylene glycol and propylene glycol) apart from water. Nozzle diameters from 0.279 mm to 1.753 mm were used to study its influence on the liquid jet breakup. Results show that the jet breakup patterns for water at lower Weber numbers follow a different behavior than that for higher Weber numbers. In the former case, the breakup length depends not only on Weber number, but also quite significantly, on nozzle exit diameter. Moreover the functional dependence of jet breakup length in this range (We < 100), besides inertia and surface tension, is also governed by viscous and gravitational forces. The influence of liquid properties and nozzle diameter on jet breakup is discussed along with a parametric scaling of the different forces. A universal correlation to depict the breakup in any Newtonian liquid is established. The influence of elongational viscosity on the breakup of low Weber number large diameter jets is discussed along with the experimental findings.