Darcy permeability

Flow resistance descriptors of DPF walls, experimental protocols for their determination and useful correlations have been previously presented in Konstandopoulos (2003). At the filter wall scale flow resistance is determined by the Darcy permeability and the Forchheimer coefficient /i of the wall. 

The electrical conductivity of agarose gel increased with increasing water volume fraction, Figure 1. This is attributed primarily to the dependence of ion diffusivity on water volume fraction [14], An empirical model for relative ion diffusivity (D/Do) is proposed to be a function of the hydrodynamic radius ( rs) of solute and intrinsic Darcy permeability (k) of gel ... 

Therein, kg = bp/p, represents a specific friction parameter concerning the Darcy permeability kF and the effective shear viscosity p . Moreover, m denotes a van Genuchten parameter. 

Values for the Darcy permeability constant for the PCL scaffolds are given in Table 5. 

Sample Sample identity Theoretical porosity (%) Darcy permeability constant Minimum pore diameter (urn) Median pore diameter (urn) Largest pore diameter (urn) NaCl particle size range (pm)... 

The purpose of this study is to develop a simple model which retains some of the features of the above complex process to predict the lay-up thickness as a function of time during the squeeze-flow lamination of circular prepreg lay-ups. The prepreg of interest is of the type commonly adopted in the board manufacturing industry. It is composed of two outer resin layers and a fabric core constructed of interlaced yarns oriented in two directions perpendicular to each other (Figure 1). The fabric core is treated as a porous slab characterized by a constant Darcy permeability coefficient (see k in Darcy s law% i.e.. Equation 2 below) which can be estimated from fabric parameters such as the yarn diameter and the pitch distances. The lay-up thickness predictions provided by this model have been found to be in reasonable agreement with experiment for the lamination of up to five epo.xy prepreg layers. 

Figure 4. Pressure waveforms illustrating the length scale effect on fast and slow P-wave events. Waveforms correspond to vug sizes of I, 1.5, 2, and 3 cm, in a matrix of 3 Darcy permeability.

Here dw( ) is the macroscopic EOF velocity (Darcy velocity) field through the neutrally charged porous medium inside the microcapillary. < ) = < )(r) is the local porosity distribution of the porous medium, determined by Eq. 9. The Darcy permeability K is defined by the Carman-Kozeny equation [7], K = a — ( )), and the inertial coefficient F =, with a = 150 and b = 1.75... 

Remember, the Darcy permeability is proportional to r, where Tp is the pore radius, and therefore to dp, where dp is the packing diameter (since it is essentially proportional to the effective diameter of the interpacking opening). 

The information given in Table 2 shows that permeation with the acids leads to an approximate 5 to 12-fold increase in the fluid conductivity of the bentonite specimens as measured by the Darcy permeability coefficients in comparison to that determined using water as the permeant. It is interesting to note that a decrease in acid concentration has little effect on the ratio (A f = final k value to k value and ky, — k value when water is the permeant). The differences or modifications in soil permeability in relation to chemistry of the permeating fluid can be attributed to ... 

The pemeabihty of a porous medium, defined by Darcy s law, is called Darcy permeability which has dimensions NT L T. However, the permeability so defined depends both on the material and on the fluid. For permeation flows which are geometrically similar (in practice, Newtonian liquids in laminar flow in inert non-swelling media), the Darcy permeability varies inversely with the fluid viscosity r]. Therefore, an intrinsic permeabihty k can be defined, as shown in Eq. 3.24 ... 

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