. c : capillary pressure (Pa)
σ: interfacial tension (mN m
À1 )
θ: pore contact angle (
)
.: radius of the capillary tube (m)
From Eqs. (2.5) and (2.6), it is clear that the capillary pressure decreases as the
interfacial tension decreases, and as the contact angle increases. For a non-wetting
fluid (such as the DNAPLs) to penetrate into a water-saturated zone, a minimum
pressure is required to overcome capillary pressure resistance (i.e., entry pressure)
(Schwille 1988).
Relative Permeability
When several fluids are present in a porous medium, they compete to fill the pore
space. Because of this competition, the mobility of all fluids in the system will be
reduced. The concept of relative permeability describes this reduced mobility. It is
the ratio of the effective permeability of a phase to the intrinsic permeability
(permeability in a single-phase flow system). The relative permeability varies from
0 to 1 (Cohen and Mercer 1993). Several studies showed that the relative permeability of a fluid can be defined as a function of its saturation in the porous medium
(Luckner et al. 1989; Mualem 1976). Schwille (1988) proposed the relative permeability curve shown in Fig. 2.8 for a DNAPL–water system (Schwille 1988).
From the relative permeability curve, we see that the relative permeability of
DNAPL is normally greater than that of water at the same saturation, and that when it
decreases, the relative permeability of water increases.
Residual Saturation and Drainage Imbibition
The residual saturation is the volume of liquid that cannot be recovered from a
porous medium by applying a pressure gradient. Decreasing residual saturation is
one of the most important challenges in soil remediation engineering. The residual
saturation of non-wetting fluids can be measured in the laboratory by drainage–
imbibition experiments, detailed in Sect. 2.3.1. Various researchers have defined
Fig. 2.8 Relative
permeability curve for a
DNAPL–water system
(Schwille 1988)
2 Free Product Recovery of Non-aqueous Phase Liquids in Contaminated Sites:. . .
71
σ: interfacial tension (mN m
À1 )
θ: pore contact angle (
)
.: radius of the capillary tube (m)
From Eqs. (2.5) and (2.6), it is clear that the capillary pressure decreases as the
interfacial tension decreases, and as the contact angle increases. For a non-wetting
fluid (such as the DNAPLs) to penetrate into a water-saturated zone, a minimum
pressure is required to overcome capillary pressure resistance (i.e., entry pressure)
(Schwille 1988).
Relative Permeability
When several fluids are present in a porous medium, they compete to fill the pore
space. Because of this competition, the mobility of all fluids in the system will be
reduced. The concept of relative permeability describes this reduced mobility. It is
the ratio of the effective permeability of a phase to the intrinsic permeability
(permeability in a single-phase flow system). The relative permeability varies from
0 to 1 (Cohen and Mercer 1993). Several studies showed that the relative permeability of a fluid can be defined as a function of its saturation in the porous medium
(Luckner et al. 1989; Mualem 1976). Schwille (1988) proposed the relative permeability curve shown in Fig. 2.8 for a DNAPL–water system (Schwille 1988).
From the relative permeability curve, we see that the relative permeability of
DNAPL is normally greater than that of water at the same saturation, and that when it
decreases, the relative permeability of water increases.
Residual Saturation and Drainage Imbibition
The residual saturation is the volume of liquid that cannot be recovered from a
porous medium by applying a pressure gradient. Decreasing residual saturation is
one of the most important challenges in soil remediation engineering. The residual
saturation of non-wetting fluids can be measured in the laboratory by drainage–
imbibition experiments, detailed in Sect. 2.3.1. Various researchers have defined
Fig. 2.8 Relative
permeability curve for a
DNAPL–water system
(Schwille 1988)
2 Free Product Recovery of Non-aqueous Phase Liquids in Contaminated Sites:. . .
71