 Thus it is governed by the continuity equation

and momentum

where is the velocity vector, is the density of the fluid, formula_3 is the material derivative, is the viscosity of the fluid, is the electric charge density, is the applied electric field, is the electric field due to the zeta potential at the walls and is the fluid pressure.Laplace’s equation can describe the external electric field

while the potential within the electric double layer is governed by

where is the dielectric constant of the electrolyte solution and is the vacuum permittivity.This equation can be further simplified using the Debye-Hückel approximation

where is the Debye Length, used to describe the characteristic thickness of the electric double layer.