Deformation of water drop in oil under electric field.

Deformation of water drop in oil under electric field.

Model GeometryElectric Field (+ve)Electric Field (-ve)2D Axial Symmetry ElectrodeElectrodeInsulationInsulationContinuous phase Continuous phase DROPMulti-physics models Applied Electrostatics Navier-Stokes EquationWeak form

Electrostatics (es) ModeSub-domain settings

Electrostaics (es) ModeBoundary settings Axial symmetryElectric PotentialZero ChargeSurface charge

Weak formTo incorporate surface charge accumulation at the boundary interfaceIts an integral form equivalent to the original PDEIts derived by multiplying PDE with a test function and then integrating over the domain. In comsol the function can be performed using test operator in weak form mode.

Weak form (wb)Boundary settings

Navier Stokes mode (chns)Subdomain settings

Boundary Condition SymmetryWall/No slipContinuity

Task to perform From external force applied in NS equation displacement s is calculated.

Deformation is calculated through

Plot D vs t to get deformation pattern

Torza Analysis Topic: Electrohydrodynamic Deformation and burst of liquid drops.

Aim: Conducted experiments with liquid drops suspended in a second immiscible liquid which deforms into pro-late spheroids under 60 Hz electric fields oriented in its direction. He performed experiments for 22 drop/medium combinations.

Developed theory for predicting shapeTheory: - Oblate/Prolate depends upon dielectric constant and resistivity of the drop and medium.He introduced critical frequency concept where drop remained spherical at all field strengths.He also claimed that burst of liquids are of two different types electric and electrohydrodynamic burst by electric stresses alone and then by combination of electric and hydrodynamic stress.He developed theory which predicts: a) The formation of both oblate and prolate spheriods depends upon the ratios of dielectric constants, electric resistivity and viscosity of the two phases. b) Existence of critical values of the ratios at which the drop remains spherical.He claimed the existence of critical frequency where there is no deformation independent of electric field applied.In theory developed the drop is assumed to be nearly spherical.The velocity inside and outside drop is generated by electric stress.Different type of stress derived are:Electric stress at the drop surface:

such that the steady transverse stress at a given point on the drop surface changes sign at Rq = 1(It influences the direction of the electrically induced flow on both sides of the interface).Rq>1 : Flow is pole to equatorRq=1: No flow (This criteria is valid for )Rq