Tortuousity

Barrier Phenomenon. In red cell filtration, the blood first comes into contact with a screen filter. This screen filter, generally a 7—10-) m filter, does not allow micro aggregate debris through. As the blood product passes through the deeper layer of the filter, the barrier phenomenon continues as the fiber density increases. As the path becomes more and more tortuous the cells are more likely to be trapped in the filter. 

The drainage theory breaks down for columns with tortuous cross section, large slugs of gas, or heavy coalescence in the rising foam. 

Two basic flow schemes are used tortuous path flow and sheet flow (Fig. 22-59). Tortuous path spacers are cut to provide a long path between inlet and outlet, providing a relatively long residence bme and high velocity past the membrane. The flow channel is open. Sheet flow units have a net spacer separating the membranes. Mass transfer is enhanced either by the spacer or by higher velocity. 

FIG. 22-59 Schematic of two ways to pass solution across an ED membrane. Tortuous flow (left) uses a special spacer to force the solution through a narrow, winding path, raising its velocity, mass transfer, and pressure drop. Sheet feed (right) passes the solution across the plate uniformly, with lower pressure drop and mass transfer. Coutiesy Elsevier.)... 

Fouling Fouling affec ts MF as it affects all membrane processes. One difference is that the fouling effect caused by deposition of a foulant in the pores or on the surface of the membrane can be confounded by a rearrangement or compression of the sohds cake which may form on the membrane surface. Also, the high, open space found in tortuous-pore membranes makes them slower to foiil and harder to clean. 

Irregular grooving can occur, especially on copper alloys after acid cleaning. Tubes can be only partially filled with cleaning solution. Condensation and running of the fluid down the tube interior cuts tortuous channels (Fig. 7.9). 

In a packed column the individual solute molecules will describe a tortuous path through the interstices between the particles and some will randomly travel shorter routes than the average and some longer. The multi-path effect is diagramatically depicted in Figure 5. 

Now, consider a packed GC column due to the turbulence resulting from the rapid changes in direction of the gas velocity as it winds its tortuous path between the... 

We may begin by describing any porous medium as a solid matter containing many holes or pores, which collectively constitute an array of tortuous passages. Refer to Figure 1 for an example. The number of holes or pores is sufficiently great that a volume average is needed to estimate pertinent properties. Pores that occupy a definite fraction of the bulk volume constitute a complex network of voids. The maimer in which holes or pores are embedded, the extent of their interconnection, and their location, size and shape characterize the porous medium. 

Depth filter A filter medium consisting of randomly distributed particles or fibers resulting in openings with a non-uniform and tortuous path. 

Depth filters on the other hand are composed of layers of fabric or fibers, which provide many tortuous paths for the fluid to flow through. The pores or passages must be larger than the rated size of the filter if particles are to be retained in the depth of the media rather than on the surface. 

Sprayed coatings have structures in which fine pores thread tortuous paths through the deposit, and it is necessary to apply a coating thickness of about 350 ftm if all these paths are to be closed. Scratch-brushing of the deposit, however, makes it possible to consolidate the surface and to achieve adequate continuity in thinner deposits, e.g. 200 m. 

Tye [38] explained that separator tortuosity is a key property determining the transient response of a separator (and batteries are used in a non steady-state mode) steady-state electrical measurements do not reflect the influence of tortuosity. He recommended that the distribution of tortuosity in separators be considered some pores may have less tortuous paths than others. He showed mathematically that separators with identical average tortuosities and porosities can be distinguished by their unsteady-state behavior if they have different distributions of tortuosity. 

Within these tortuous systems there exists considerable opportunity for process contamination, corrosion, and equipment malfunction to occur, with cause-and-effect problems creating further impact downstream and placing additional demands on monitoring and control efforts. 

In addition to the careful selection of structural metals, the cathodic protection of water-wetted parts may also be specified. For most boiler plant systems, however, because of the tortuous and extended waterside surfaces involved, the use of cathodic protection is only a partial solution to controlling corrosion and should never be the sole secondary protocol. Rather, cathodic protection functions well when employed as part of a more comprehensive program that includes appropriate internal chemical treatments. 

Because of the duty requirements of these systems, pipework layouts are often tortuous and may contain stagnant areas where localized corrosion may develop or sludge may accumulate. The breakdown of glycols may also contribute to the development of foulants and corrosion debris. It is therefore good practice to incorporate both general dispersants (say, a 4,000-5,000 MW polyacrylate) and iron dispersants (say, a terpolymer) in the inhibitor formulations. 

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