Drop formation in Newtonian and non -Newtonian liquid jets.

摘要

The major objective of this thesis is to develop accurate computational models to predict evolution of two types of liquid jets. A secondary objective is formation of satellite drops, and a study of the conditions under which their diameter can be controlled. The two jets examined here are a purely viscous non-Newtonian jet, and a Newtonian jet covered with an insoluble surfactant.;The theoretical approach of Galerkin-finite element analysis is used solve the complete two-dimensional set of axisymmetric governing equations and the kinematic and dynamics boundary conditions at the free surface. The effect of shear thinning behavior on break-up is studied in detail, in the case of an infinitely long non-Newtonian jet. It is found that the shear thinning behavior may be useful in controlling satellite drop sizes. It is seen that an increase in the shear thinning behavior leads to drop elongation at low Reynolds numbers (Re = 1). It is also seen that increasing the shear thinning behavior at moderate Reynolds number (Re = 5) leads to an initial increase in the satellite drop size, followed by a subsequent decrease.;The effect of surfactant perturbation on drop breakup in Newtonian jets is then examined. It is seen that at low Reynolds numbers (Re = 0.01), and for a surfactant with low diffusivity, an increase in the surfactant strength leads to satellite drop formation. It is also seen that an increase in the diffusivity eliminates the satellite drop at high surfactant strengths. At high Reynolds numbers (Re = 100), it is seen that an increase in the surfactant strength leads to an initial decrease in the satellite drop size, followed by subsequent increases.;Experimental validation for the theory developed is then performed in the case of a shear thinning non-Newtonian jet. The experimental fluid is pumped through a capillary and drop shapes are obtained using a high speed camera. These experimentally obtained shapes are compared to those obtained using the theory and results are found to be in good agreement.