On the Validity of the “Thin” and “Thick” Double-Layer Assumptions When Calculating Streaming Currents in Porous Media

Table 1

Nomenclature.

Symbol	Description	Units
𝐶𝑓	Fluid concentration	M
e	Charge on an electron	C
ε	Fluid permittivity	Fm^−1
I	Electrical (streaming) current	A
𝐼𝑑	Dimensionless streaming current	—
k	Boltzmann’s constant	m^2kgs^−2K^−1
κ	Permeability	m^2
L	Capillary length	m
λ	Debye length	m
μ	Fluid viscosity	Pa s
𝑁A	Avogradro’s number	Mol^−1
P	Fluid pressure	Pa
q	Volumetric flow rate	m^3s^−1
Q	Excess charge density	Cm^−3
𝑄𝑠	Surface charge density	Cm^−2
𝑄𝑑	Dimensionless surface charge density	—
r	Capillary radius	m
𝑟𝑑	Dimensionless capillary radius	—
R	Dimensionless radial position	—
𝜎𝑓	Fluid conductivity	Sm^−1
T	Temperature	K
V	Electrical potential	V
𝜓	Dimensionless electrical potential	—
y	Radial position	m
ζ	Zeta potential	V