Paper Number
NF32 

Session
Non-Newtonian Fluid Mechanics

Title
The role of surface charge convection in the electrohydrodynamics and breakup of prolate drops

Presentation Date and Time
October 11, 2017 (Wednesday) 4:10

Track / Room
Track 5 / Crestone B

Authors (Click on name to view author profile)

1. Sengupta, Rajarshi (Carnegie Mellon University, Chemical Engineering)
2. Walker, Lynn M. (Carnegie Mellon University, Chemical Engineering)
3. Khair, Aditya S. (Carnegie Mellon University, Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Rajarshi Sengupta, Lynn M. Walker, and Aditya S. Khair
Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA

Speaker / Presenter 
Sengupta, Rajarshi

Text of Abstract
The deformation of a weakly conducting, 'leaky dielectric,' drop in a density matched, immiscible, weakly conducting medium under a uniform DC electric field is quantified computationally. We exclusively consider prolate drops, for which the drop elongates in the direction of the applied field. Furthermore, we assume the drop and medium to have equal viscosities. Using axisymmetric boundary integral computations, we delineate drop deformation and breakup regimes in the Ca_E - Re_E parameter space, where Ca_E is the electric Capillary number (ratio of the electric to capillary stresses); and Re_E is the electric Reynolds number (ratio of charge relaxation to flow time scales), which characterizes the strength of surface charge convection along the interface. For so-called ‘prolate A' drops, where the surface charge is convected towards the ‘poles' of the drop, we demonstrate that increasing Re_E reduces the critical capillary number for breakup. Moreover, surface charge convection is the cause of an abrupt transition in the breakup mode of a drop from end-pinching, where the drop elongates and develops bulbs at its ends that eventually detach, to a breakup mode characterized by the formation of conical ends. On the contrary, the deformation of ‘prolate B' drops, where the surface charge is convected away from the poles, is essentially unaffected by the magnitude of Re_E.