Sweep fractions

Wang et al. [4,5] demonstrate that for a countercurrent hoUow fibre module the membrane resistance to water transport is negligible - the overall mass transfer coefficient is controlled by lumen and shell-side concentration boundary layers. Returning part of the retentate product as a permeate sweep increases the rate of water removal. The required membrane area decreases dramatically as the fraction of the retentate used as sweep is increased (sweep fraction). However, for sweep fractions greater than 0.1, the increase in productivity is offset by an increase in consumption of product gas as sweep. 

Figures 16.3 and 16.4 illustrate the effect of sweep fraction (i.e. fraction of the dry product returned as sweep to the shell) on module performance assuming uniform, ideal sweep distribution. For all sweep fractions, the product gas flow rate and recovery decrease as the dew point decreases since increased water removal is accompanied by increased loss of oxygen and nitrogen.

Increasing the sweep fraction dramatically increases the product gas flow rate. For example, Figure 16.3 indicates the dry gas flow rate increases by a factor of nearly 20 at a dew point of 0°F if the sweep fraction is increased to 0.2. This inaease in flow rate comes at the cost of reduced recovery. For high selectivities, recovery is reduced by an amount approximately equal to the sweep fraction. Figure 16.4 indicates recovery deceases from 0.88 to 0.79 at a dew point of O F as the sweep fraction is increased to 0.2. 

Figure 16.3 Dry gas flow rate as a function of dew point for various sweep fractions solid - 0 short dash -0.1 long dash -0.2...

The changes in performance for a lower water/nitrogen selectivity of 100 are illustrated in Figures 16.5 and 16.6. Relative to a selectivity of 1000, dry gas recovery decreases slightly but dry gas flow rates are significttntly lower. A dectease in recovery is expected with a decrease in selectivity since more dry air will permeate along with the water. For a dew point of 0°F and sweep fraction of 0.2, the recovery decreases from 0.79 to 0.75. 

Figures 16.7 and 16.8 illustrate the effect of sweep variation on module performance. An average sweep fraction of 0.1 was used for the calculations.

In all cases, for a given product dew point, the dry gas flow rate increases as the fraction of the product used as permeate sweep increases. However, the dry gas recovery (the fraction of the wet feed recovered as product) simultaneously decreases. The optimal sweep fraction will depend on the trade-off between increased productivity and fractional loss of the dry, high pressure product. 

The macroscopic sweep efficiency s the fraction of the total reservoir which is swept by water (or by gas in the case of gas cap drive). This will depend upon the reservoir quality and continuity, and the rate at which the displacement takes place. At higher rates, displacement will take place even more preferentially in the high permeability layers, and the macroscopic displacement efficiency will be reduced. 

Gas chromatographic analysis at 79° using a flame detector in conjunction with a 183 x 0.32 cm. stainless-steel column containing Dow-Corning 550 fluid on silanized support gave peaks for l-bromo-3-chloropropane (6.5 minutes) and 6-chloro-2-hexyne (9.3 minutes) whose areas were shown to be proportional to the mole fractions. The latter were determined by integration of the expanded (50 Hz sweep width)... 

In the case of phenylchlorosilanes some modifications are made to the process. Chlorobenzene is passed through the reaction tube, which contains a mixture of powdered silicon and silver (10% Ag), the latter as catalyst. Reaction temperatures of 375-425°C are significantly higher than for the chloro-methylsilanes. An excess of chlorobenzene is used which sweeps out the high boiling chlorophenysilanes, of which the dichlorosilanes are predominant. The unused chlorobenzene is fractionated and recycled. 

Changing the wettability of reservoir rock surfaces from oil-wet to water-wet, increases the permeability of the formation to oil, decreases the permeability to water, decreases mobility ratio, increases sweep efficiency, increases the flowing fraction of oil at every saturation, and increases oil recovery at the economic limit of the waterflood. 

Proton nmr spectra of fractions A, B and C and all bottoms products were recorded on a Varian HA lOOnmr spectrometer using a solution of the sample dissolved in pyridine-d5. Spectra were run at room temperature with tetra methyl silane (TMS) as an internal standard, with a sweep width of 0 to 1000 cps from TMS. Fraction D and the whole coal were only partly soluble in pyridine and it was therefore not possible to get representative spectra from them. 

With the equations entered as listed above, press F5 or solve/sweep under the solutions menu to solve the equations. The software indicates that x = 0.333. From this, the following mole fractions and partial pressures are obtained ... 

Kirkbride (1987) described the estimation of diazinon in human omental tissue (fatty tissue) after a fatal poisoning. In this method, the tissue was pulverized and extracted with acetone. After extract concentration and purification by sweep co-distillation and Florisil fractionation, diazinon was measured by gas chromatography (GC) with nitrogen-phosphorus detection (NPD). After another fatal diazinon poisoning, diazinon was quantified by GC/electron capture detection (ECD) and GC/flame ionization detection (FID) by Poklis et al. (1980). The diazinon in human adipose, bile, blood, brain, stomach contents, kidney, and liver was recovered by macerating the sample with acetonitrile followed by the addition of aqueous sodium sulfate and extraction into hexane. Following an adsorption chromatography clean-up, the sample was analyzed. 

As mustbc the case, the maximum and minimum sweeprates (2—20 mV s ) depend on assumptions (e.g., the minimum current density to be measured or the fraction of the time during a sweep in which the limiting current is reached). Depending on these variables, then, one can only conclude that the rate may vary according to the reaction characteristics and for likely current densities between about 1 and lOOmV s-1. 

Protons, which are nearly 2000 times more massive than electrons, contribute much more to the mass of an atom. Protons, however, are held within the atomic nucleus, which is only a tiny, tiny fraction of the volume of the atom. The size of the atom is spelled out by the electrons, which sweep through a relatively large volume of space surrounding the nucleus. 

The volume given by Eq. 9-33 is about 1.4 x 10-11 cm3, which could be represented approximately by a cube 2.4 pm on a side. If we compare this volume with that of a cell (Table 1-2) or of an organelle, we see that in one second an enzyme molecule will sweep out a large fraction of the volume of a small cell, mitochondrion, chloroplast, etc. 

B. The sweep is interrupted and the potential held for approximately 30 s at the cathodic switching limit. A small fraction of the short-lived p-cyanophenyl radical intermediate is captured by cyanide ion, the trapping agent, to give. . . ... 

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