Fig. 2.

Pressure created by variation of ζ-potential along the direction of the current flow. A field of 1000 V m⁻¹ was impressed across the vertical dimension. ζ-potential values are indicated in their respective domains. Porous properties are the same for all domains and are defined as follows: porosity (ε)=0.4; tortuosity (λ)=1.4; conductivity (σ)=1.43 S m⁻¹; density (ρ)=1×10³ kg m⁻³; permeability (κ, calculated using the Kozeny–Carman equation for a packed bed of 10 µm particles)=5×10⁻¹⁴ m²; dynamic viscosity (η)=8.9×10⁻⁴ Pa s. The pressure at the top and bottom boundaries is set to the arbitrary value of zero so that the net pressure drop applied across each 0.8 mm-thick object is zero. Calculations were performed with COMSOL Multiphysics v4.4