Immobile, porous media

The volume-averaging technique has been developed by Whitaker (7), Slattery (8), Bear (33), and Lundgren (9). Assuming that the solid matrix of the porous medium is incompressible, immobile, and not supported by the fluid, equations 17 and 18 can be subjected to a volumeaveraging procedure in an REV and reduce to the following equations (32) ... 

Macroscopic droplets of oil (the less wetting phase) are contained within one or more interconnected pore bodies that are formed by solid phases of the porous medium. These immobilized portions of the oil phase, which can be referred to as ganglia or blobs, are surrounded with continuously connected reservoir brine (the more wetting phase). At the three-phase contact lines which are formed on the solid surfaces where the two immiscible liquids meet, the apparent contact angles reflect the relative affinities of the three phases for each other, surface textures, surface compositions, and solid surface saturation histories. 

Barros, R.J., Wehtje, E., Garcia, F.A.P. and Adlercreutz, P (1998) Physical characterization of porous materials and correlation with the activity of immobilized enzyme in organic medium. Biocatalysis and Biotransformation, 16, 67-85. 

Facilitated transport has been briefly described in Chapter 1. In facilitated transport, the selective transport medium is a liquid or molten salt contained or immobilized in a porous support. The liquid membrane is held tightly in the support pores by capillary forces. The liquid or molten salt selectively reacts with a gas or vapor species and the reacting species diffuses across the liquid or salt and desorbed on the other side of the facilitated transport membrane. The major advantage of the facilitated transpoa is that diffusion is generally several orders of magnitude faster than diffusion through solid membranes. The support is, therefore, not a membrane by definition. Comprehensive... 

Perfusion systems have also been used for successful scale-up of MoAb production. During the culture period, cell growth occurs exponentially until the cell density reaches a maximum. At that point, the medium needs a continuous supplementation of fresh nutrients and elimination of waste. In perfusion systems, fresh nutrients are supplied and wastes are removed continuously so that the medium meets the physiological needs of the cells. At steady state, the cell concentration is determined by space and other limitations. High cell densities have been achieved by immobilizing the cells in porous ceramic matrices or hollow fiber devices. Intermediate cell densities have been achieved by perfusion reactors with a spin filter, or in a fluidized bed reactor in which the cells are embedded in sponge-like... 

Beshay et al. reported conditions for the short-term continuous cultivation of D. discoideum cells on porous supports (SIRAN beads) in HL-5C medium ]108]. D. discoideum cells actively colonized the porous carrier (Fig. 5.5), after which the colonized beads can be freely suspended in medium. Gell densities of free amoebae remained at about 10 per mL for most of the cultivation time, whereas the cell density on the SIRAN beads reached up to 10 per mL and remained constant for at least 16 days of fermentation [108, 109]. By using broken pumice or CeramTec (a ceramic catalyst support), the immobilized cells reach... 

As an alternative to the use of a porous disk as a rigid supporting medium, it is possible to immobilize liquid exchangers in tough I VC membranes. In this type of electrode, the liquid ion exchanger and PVC are dissolved in a solvent such as tetrahydrofuran. The soivcnl is evaporated to leave behind a flexible membrane lhal can be cut. shaped, and bonded to the end of a glass or plastic tube. Membranes formed in this way behave in much the same way is those in which the ion exchanger is encased as a ljt uid in the pores of a disk. Most liquid-membrane electrodes arc of this newer type. 

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