Freely draining

The quantity of water that can be retrieved from a medium is related to size and shape of the connected pore spaces within that medium. The quantity of water that can be freely drained from a unit volume of porous medium is referred to as the specific yield. The volume of water retained in the medium by capillary and surface active forces is called the specific retention. The sum of specific retention and specific yield is equal to the effective porosity (see Table 3.4). Neither term has a time value attached. Drainage can occur over long periods (i.e., weeks or months). 

Note A freely draining macromolecule and a non-draining macromolecule are two extremes of the concept of a partially draining macromolecule. 

The Bueche model is based on random-flight statistics of freely draining polymer molecules. Accordingly, two possible relations exist between g and g". (1) For the Zimm-Kilb model, combining Equations 2, 3, 8, and 11 the relation obtained is given by ... 

The situation of a freely-draining macromolecule without excluded-volume effects and internal viscosity, when zv = 2, and the above eigenvalues reduce to (1.17), is especially simple. In this case, equation (2.29) describes Rouse modes, and it is convenient to use the largest orientation relaxation time... 

The value of the index in this formula changes from 1/2 to 1 for different situations. For example, (z — 2)v = 1 for a freely-draining macromolecule without volume effects (Rouse case). 

A generalisation of the theory for the case of arbitrary values of internal viscosity was done by Pokrovskii and Tonkikh (1988). We may note that the case when ( i=0 and zv = 2, corresponds to an ideally flexible freely-draining macromolecule, and reproduces the relations indicated by Rouse (1953). 

To freely drain any liquid, so that stagnant liquid pockets are minimized Stagnant liquid contributes little to mass transfer and wastes packing surface. 

Hence, r]eff =z0/y up to extremely high shear rates. For freely draining films the calculations indicate that r 0.026[Pg.585]

Theories of the frictional properties of polymer solutions, from which the relationship between viscosity and molecular weight must ultimately be derived, can proceed in various ways, but we will mention just two models. In the first, it is assumed that the velocity of the solvent is barely affected by the presence of the polymer, so that it streams or freely drains through the coil in a largely unperturbed fashion (Figure 12-31). 

Freely Draining Gaussian Chain (Rouse Theory) Dominant HI Theta Solvent (Zimm Theory) Dominant HI Good Solvent... 

The first successful molecular model of polymer dynamics was developed by Rouse. The chain in the Rouse model is represented as N beads connected by springs of root-mean-square size b, as shown in Fig. 8.2. The beads in the Rouse model only interact with each other through the connecting springs. Each bead is characterized by its own independent friction with friction coefficient (. Solvent is assumed to be freely draining through the chain as it moves. 

This table is part of Fig. 7-4. It shows the major proton donors and the major weathering reactions occurring in the different compartments (horizons) of a soil profile. It is assumed that the parent material consists of unconsolidated granite, materials are freely drained, and pedogenic impeding layers are absent. Also, no perched or fluctuating water is present. 

Figure 3.2. Schematic of the STR PEM fuel cell. The exposed electrode area is 1 cm on each side, with gas volumes above the anode and cathode of 0.2 cm. The MEA employed ETEK electrodes and a Nafion 115 membrane. The original versions of the fuel cell did not permit liquid water to freely drain they could only be operated with water activity less than one (no liquid water). Newer versions have the cell rotated by 90° and the effluents designed to permit liquid water to drain without accumulating in the gas plenums.

Now consider the case of flexible polyelectrolytes such as DNA. There are two dominant hydrodynamic models for polymer motion, the Rouse model and the Zimm model [4]. In the Rouse model, the different parts of the chain are assumed to be hydrodynamically independent, so that the total friction of the chain is simply the sum of the friction of each segment The Rouse model is also referred to as freely draining, since the polymer chain appears to be hoUow to the fluid. The Zimm model includes both the Rouse friction of the individual segments with the fluid and the hydrodynamic interactions between different segments. The Zimm model is not freely draining the polymer appears as a solid object to the surrounding fluid. 

The control strategy, presented in Fig. 11.35, provides smooth transfer with precise control. It must allow controlled venting as well as controlled transfer to compression, and so it requires two control valves and split-range control. The cell room header pressure is measured by a d/p cell with a Monel diaphragm. If desired, a flush-type cell can be used. It is located on top of the header as it leaves the cell room. It is important that connections to the d/p cell be freely draining. 

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