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Leverett function

Introduce as new basic variables the effective saturation and the pressure of the water phase by substitutingPg = Pw+ Pc se)- The functionpc se) often is called the Leverett function . The new system would read as ... [Pg.304]

Remarks. Close inspection of the nonequilibrium model outputs reveals that assumption of nonequilibrium capillary pressure in the studied range of experimental conditions was not necessary and static equilibrium described by PcxPg-Pe was sufficient to account for the interfacial forces [54], However, recourse to empirical capillary relationships, such as the Leverett /-function, is unnecessary as the nonequilibrium two-phase flow model enables access to capillary pressure via entropy-consistent constitutive expressions for the macroscopic Helmholtz free energies. Also, the role of mass exchange between bulk fluid phase holdups and gas-liquid interfacial area was shown to play a nonnegligible role in the dynamics of trickle-bed reactor [ 54]. By accounting for the production/destruction of interfacial area, they prompted much briefer response times for the system to attain steady state compared to the case without inclusion of these mass exchange rates. [Pg.104]

It is difficult to incorporate the LBM-based GDL model with other PEFC component models to predict full-cell performance. Macroscopic modeling is a more popular approach adopted when the entire fuel cell is the focus. A number of macroscopic models have been developed to capture the two-phase characteristics in GDLs [2-5]. They mostly treat the GDL as a uniform hydrophilic or hydrophobic medium. The gradient of capillary pressure is found to be the major driving force for liquid flow in GDLs. The capillary pressure can be expressed as a function of saturation via the Leverett function (see Figure 30.11) [3] ... [Pg.855]

It should be pointed out that the Leverett function was originally developed for liquid water transport in soils and, as such, it may not be directly applicable to liquid-water transport in the GDLs owing to their unique pore characteristics. To take this into account, Wang and Nguyen [41] proposed an empirical correlation based on experimental data (see Figure 30.12). [Pg.856]

Leverett Function The most important relationship that must be estabUshed for an accurate prediction of the liqnid-gas transport in the DM is the relationship between the capillary pressure and the liqnid saturation. Capillary pressure depends on a variety of parameters, inclnding temperature through surface tension and the morphology, tortuosity, and pore size of the material bnt most importantly liqnid saturation. [Pg.254]

Several empirical and semiempirical expressions are available which attempt to describe the behavior of capillary pressnre in terms of a porous media and fluid properties. A generic Leverett function from soil science has been commonly employed to describe the capillary transport behavior of the porons media in multiphase models. Since many porous media share similar characteristic behavior, for PEFC gas diffusion layer material, a Leverett-type function has been nsed to represent this behavior as a first step toward achieving an accurate two-phase transport model. Udell [45] used Leverett s approach [46] to develop a semiempirical relation correlating capillary pressure and saturation data for clean unconsolidated sands of various permeability and porosity by means of defining a capillary pressure function ... [Pg.254]

Modified Leverett Function Appropriate for Fuel Cell Media The standard Leverett function has been found to be appropriate for qualitative matching of the flow characteristics through the media however, actual measurements of PEFC diffusion media show different quantitative behavior. Kumbur et al. [47] presented a modified Leverett function appropriate for thin-film fuel cell DM to estimate the capillary pressure as a function of liquid saturation and hydrophobic additive content This empirical fit was derived from the direct measurement of capillary pressure-saturation for different types of DMs (cloth and paper) with PTFE content ranging from 0 to 20% of weight and a nnicrop-orous layer. Figure 5.35 depicts the measured capillary pressure (Pc) versus nonwetting liquid saturation for carbon paper DM tailored with 20% PTFE content. The nature of the capillary pressure-saturation curves exhibits a continuous S shape, rather than J shape, and yields four inflection points. For saturation leads under 0.5, the capillary pressure in the DM was fit to a modified Leverett function, appropriate for the hydrophobic pores ... [Pg.255]

Figure 5.35 Measured capillary pressure (Pc) and predicted Pc by Leverett function versus saturation for carbon paper DM tailored with 20% PTFE content [48]. Figure 5.35 Measured capillary pressure (Pc) and predicted Pc by Leverett function versus saturation for carbon paper DM tailored with 20% PTFE content [48].
This relationship shows the critical role that pore size and surface tension have in controlling the capillary flow through porous media. The smaller the pore size, the higher the capillary pressure. This fact is responsible for driving liquid from small-pore-size areas to areas with larger pore sizes. However, the capillary pressure is not solely a function of pore size. It is also a function of the level of saturation in the media. In order to link the saturation, capillary pressure, and liquid flow in porous media, a Leverett function has been written such that... [Pg.278]

If the Leverett function is known for each rock type of the profile, the saturation profile—referenced to free water level—can be calculated. In Fig. 2.42, a single /-function was applied to the whole reservoir. The additionally plotted red curve connects layers with similar reservoir properties of about 3600 md. [Pg.76]

FIGURE 2.42 Water saturation profile calculated from the Leverett function and porosity and permeability data.. The red curve connects layers with similar reservoir property (about 3600 md). Curve from Hirasaki (2000). [Pg.77]


See other pages where Leverett function is mentioned: [Pg.226]    [Pg.719]    [Pg.858]    [Pg.893]    [Pg.298]    [Pg.324]    [Pg.254]    [Pg.254]    [Pg.278]    [Pg.75]   
See also in sourсe #XX -- [ Pg.304 ]

See also in sourсe #XX -- [ Pg.855 ]

See also in sourсe #XX -- [ Pg.298 ]

See also in sourсe #XX -- [ Pg.254 , Pg.257 ]

See also in sourсe #XX -- [ Pg.75 ]




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