Deformation and breakup of liquid drops and threads in extensional flow field



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The deformation and breakup of liquid drops as well as the instability of liquid threads are the fundamental mechanisms involved in the problems of liquid dispersion. In the present work, the nature of these phenomena in extensional flow fields is theoretically and experimentally investigated for both Newtonian and non-Newtonian (viscoelastic) systems. Deformation results for both Newtonian and non-Newtonian drops closely approximate the first-order theory of Taylor over a larger deformation range than expected. A criterion for the breakup of Newtonian drops in extensional flow fields has been ncCd developed in terms of a critical deformation parameter E[subscript c] = [eta subscript c]Cd/[sigma] and the viscosity ratio [eta subscript D]/[eta subscript c] (where [eta subscript D],[eta subscript c] are the dispersed phase and the continuous phase viscosities, C is the extensional rate, d is the drop diameter and [sigma] is the interfacial tension). Just as in the case of breakup in simple shear fields, a minimum value of E[subscript c] is found in the viscosity ratio range 0.1 [less than or equal to] ([eta subscript D]/[eta subscript c]) [less than or equal to] 1.0, and there appear to be upper and lower bounds on ([eta subscript D]/[eta subscript c]) , between which breakup is possible, and these bounds for extensional flow fields cover a much broader range than those in the simple shear cases. As for the breakup of viscoelastic drops, elastic effects give higher values of E[subscript c] than those in the coreesponding Newtonian cases. [...]