Pore size hydraulic

Nonwoven filter media are mostly used for filter medium filtration with pore clogging. Because of the relatively low cost of this medium, it is often replaced after pore clogging. In some cases, nonwoven media are used for cake filtration. In this case, cake removal is so difficult that it must be removed altogether from the filter medium. Nonwoven filter media can be prepared so that pore sizes decrease in the direction from the surface of the filter media contacting suspension to the surface contacting the supporting device. This decreases the hydraulic resistance of... 

Hydraulic conductivity is one of the characteristic properties of a soil relating to water flow. The movement of water in soil depends on the soil structure, in particular its porosity and pore size distribution. A soil containing more void space usually has a higher permeability. Most consolidated bedrocks are low in permeability. However, rock fractures could create a path for water movement. 

Saturation (v) is the volume fraction of the total void volume occupied by a specific fluid at a point. Saturation values can vary from zero to 1 with the saturation of all fluids equal to 1. Residual saturation (Sr) is the saturation at which the NAPL becomes discontinuous and immobile due to capillary forces. Residual saturation is dependent upon many factors, including pore size distribution, wettability, fluid viscosity and density ratios, interfacial surface tension, gravity and buoyancy forces, and hydraulic gradients. 

The hydraulic permeation model in Eikerling ef al. helped rationalize main dependence of fhe critical currenf densify on membrane parameters. A sharply peaked 5-function-like pore size disfribufion. 

The gel usually has a much lower hydraulic permeability and smaller apparent pore size than the underlying membrane. (The gel layer and the concentradon gradient between the gel layer and die bulk concentration are called the gel-polarization layer.)... 

To characterize the size of pores, the hydraulic radius ah was introduced. The hydraulic radius is the ratio of void volume and void area. For a long cylindrical pore of length l and radius r (r -C /) the hydraulic radius is for instance... 

The flux solvent evolution of pure water with the transmembrane pressure across NF/LPRO membranes are reported in Fig. 6. The linear dependence of fluxes with the transmembrane pressure shows that Darcy s law is verified. As expected, the hydraulic permeabilities determined from the slopes (Table 3) show higher values for NF than LPRO membranes, due to their larger pore size. The NF90 membrane shows the higher hydraulic permeability with Z p = 14.8 Lh 1 m 2bar 1. 

This deposit is composed of suspended particles similar to conventional filter cakes, and more importantly, a slime that forms as retained solutes exceed their solubility. The gel concentration C is a function of the feed composition and the membrane-pore size. The gel usually has a much lower hydraulic permeability and smaller apparent pore size than the undedying membrane (27). The gel layer and the concentration gradient between the gel layer and the bulk concentration are called the gel-polarization layer. 

Because pore sizes in the cake and filter plate are small and the liquid velocity through the pores is low, the flow of filtrate may be considered laminar and Poiseuille s law is applicable. Filtration rate is directly proportional to the difference in pressure and inversely proportional to the fluid viscosity, as well as to the hydraulic resistance of the cake and filter plate. Because the pressure and hydraulic resistances of the cake and filter plate change with time, the variable rate of filtration may be expressed as ... 

For soil systems contaminated with Na+, kinematic viscosity is not significantly affected, thus the components controlling water flow velocity are the hydraulic gradient (A< >/AX) and soil permeability (k). The latter component (k) is influenced by clay dispersion, migration, and clay swelling. These processes may cause considerable alteration to such soil matrix characteristics as porosity, pore-size distribution, tortuosity, and void shape. 

The ratio of specific pore volume to specific surface area, vja, has been used for many years as a simple means of characterizing the pore size. This volume-to-surface ratio, when applied to a group of pores, is known as the hydraulic radius, rh, and has an unambiguous physical significance provided that the pore geometry can be specified by a single parameter (Everett 1958). 

Figure 8.19 shows the flux-time profiles obtained in filtration of 5% yeast cell suspension using a mbular membrane of 6 mm i.d. (inside diameter) and 0.14 pm pore size with a helical baffle (HB), a rod baffle (RB), and the mbular membrane without baffle (NB) [35]. The comparison has been made at the same hydraulic-dissipated power, which is defined as the product of the flow rate and the pressure drop along the mbular membrane, or the energy consumed to generate the crossflow through the mbular membrane. Using the hydraulic-dissipated power rather than the crossflow rate as a control parameter for the comparison of the mbular membrane with and without inserts eliminates the effect of the reduced crossflow section by... 

Generally, high selectivity is related to membrane properties, such as small pores and high hydraulic resistance or low permeability. It can be compromised by a broad pore size distribution. The permeability increases with increasing density of pores, and the overall membrane resistance is directly proportional to its thickness. Therefore, a good membrane must have a narrow range of pore sizes, a high porosity, and a thin layer of material. 

In order to estimate the pore size distributions in microporous materials several methods have been developed, which are all controversial. Brunauer has developed the MP method [52] using the de Boer t-curve. This pore shape modelless method gives a pore hydraulic radius r, which represents the ratio porous volume/surface (it should be realised that the BET specific surface area used in this method has no meaning for the case of micropores ). Other methods like the Dubinin-Radushkevich or Dubinin-Astakov equations (involving slitshaped pores) continue to attract extensive attention and discussion concerning their validity. This method is essentially empirical in nature and supposes a Gaussian pore size distribution. 

Brunauer, Mikhail and Bodor (13) developed a method of pore structure analysis which employs a hydraulic radius, rj, as a measure of pore size. This radius is defined as r[ = V/S where V is the volume of a group of pore "cores" with the wall surface area S. The "core" refers to the empty... 

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