Filtration mechanism

To compare the different mechanisms of filtration, the governing equation of filtration must be rearranged. The starting expression is  

Replacing V by q, and denoting the actual filtration rate (dq/dx) as W, the governing filtration equation may be rewritten for a unit area of filtration as follows  

The numerator of Equation 79 characterizes the cake resistance. The denominator contains information on the driving force of the operation. Constant K (sec/m ) characterizes tile intensity at which the filtration rate decreases as a function of increasing filtrate volume. 

Substituting 1/R for W in Equation 78 and taking the derivative with respect to q, we obtain  

The expression states that the intensity of increase in total resistance for cake filtration is constant with increasing filtrate volume. Replacing W by dq/dx in Equation 78 and integrating over the limits of 0 to q between 0 and x we obtain  

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Fig. 2. Schematic diagram of a surface filter, ie, the cake filtration mechanism.

By filtration mechanism. Although the mechanism for separation and accumulation of solids is not clearly understood, hvo models are generally considered and are the basis for the apphcation of theoiy to the filh ation process. When solids are stopped at the surface of a filter medium and pile upon one another to form a cake of increasing thickness, the separation is called cake filtration. When solids are trapped within tne pores or body of the medium, it is termed depth, filter-medium, or clarifying filtration. 

The governing equations (Equations 42, 67, 74 and 81) describing the filtration mechanisms are expressed as linear relationships with parameters conveniently grouped into constants that are functions of the specific operating conditions. The exact form of the linear functional relationships depends on the filtration mechanism. Table 1 lists the coordinate systems that will provide linear plots of filtration data depending on the controlling mechanism. 

A type of high-temperature operation, ion-exchange plant. It can remove contaminants from condensate by both exchange and filtration mechanisms. 

Figure 15.2(a). The membrane impedes further penetration of even smaller particles through the porous filter media. In many filtration applications, this filtration mechanism is valid for an axial velocity greater than about 4 to 6 m/s. 

Figure 2.31 Separation of particulates can take place at the membrane surface according to a screen filtration mechanism (a) or in the interior of the membrane by a capture mechanism as in depth filtration (b)...

Ultrafiltration and microfiltration membranes produce high porosities and pore sizes in the range of 30-100 nanometers (UF) and higher (MF), which enable the passage of larger dissolved particles and even some suspended particles. The separation-filtration mechanism is based on molecule/particle sizes. The nanofiltration membrane lies between the UF and RO membranes, combining the properties of both so that the two mechanisms coexist. In addition, the NF membrane may be... 

The three principal filtration mechanisms (Fig. 4) by which aerosols are collected on the HEPA filtration medium are ... 

Other filtration mechanisms, such as sedimentation and electrostatic attraction, provide some degree of aerosol collection, however most particulates are removed from the airstream by the above methods. 

Figure 1. Diagram of filtration mechanisms for A) flat-membrane filters and B) hollow-fiber filters, showing the concentration polarization on the flat filters.

The main objective in the mechanical method of water cleaning is to remove insoluble or solid contaminants from waste water by settling and filtration. Mechanical solid contaminants are separated by grids or fine filters depending on the size of the contaminant particles. Liquid contamination from crude oil or its prod-... 

The glomeruli provide an elTicienl filtration mechanism for ridding the body of waste products and toxic substances. To ensure that important constituents such as water, sodium, gluco.se and amino acids are not lost from the body, tubular reabsorption must be equally efficient. For example. 1 HO litres of lluid pass into the glomerular filtrate each day. and more than 99% of this is recovered. Compared with the GFR as an assessment of glomenjlar function, there arc no easily performed tests which mca.surc tubular function in a quantitative manner. 

The basic equation leads to four filtration models have been derived by Hermia (1982). By plotting t/V and Exp(t) over filtration time t and volume V, it is possible to determine which filtration mechanism is... 

A number of experiments were selected for the analysis. Plotting t/V and Exp(t) over filtration time and volume allows the determination of which filtration mechanism is valid. This analysis was applied here to verify the observations of rejection and flux decline as a function of primary particle size. 

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