Asymmetric feeding

Similarly the solids feed system is generally asymmetric, feeding solids to one side of the reactor, or, for large units, to a limited number of discrete feed positions on the periphery of the reactor. 

Let us consider first the situation where the values of the two concentration variables of our reaction-diffusion model, u and v, are kept fixed at the two boundaries a = 0 (reduced upper-branch state) and x = 1 (oxidized lower-branch state) according to Equation (4). As long as the fronts are located far enough from the two CSTRs at both ends of the Couette reactor, this seems to be a rather good approximation of the experimental situation with asymmetric feeding [31-33] (Figure 2). Let us suppose that e is kept fixed to a (small) positive value. 

PROS REJECT jcls Section 3.6, Fig. 1.29 In a production environment there are often several superimposed processes that yield measurement series like that depicted in the lower panel there is drift that unexpectedly changes slope, there is bias and measurement noise, and there are operators who take corrective action. The model includes the probability of drift occurring and a feed-back loop that permits both positive and negative coefficients. The operators can be ordered to react if a single value exceeds a set limit, or only if 2, 3, or more successive values do so. The program calculates the two-sided (asymmetric) total probability of a value being OOS and depicts this in the upper panel on a log(p) scale. The red horizontal is the upper limit on the total risk as set in cell B20. 

Asymmetric membranes have a tight, low-permeability, retentive zone that performs the desired separation and a more open, high-permeability zone that provides mechanical strength to the overall membrane. This structure is particularly critical to the economic viability of reverse-osmosis membranes. Asymmetric membranes operated in TFF mode must have the tight side facing the feed channel so that particles are retained on its surface and can be acted upon by the tangential flow. Asymmetric membranes operated in NFF mode can... 

A second choice to be made relates to the size of the flow domain. It may be worthwhile to limit the calculational job by reducing the size of the flow domain, e.g., by identifying an axis or plane of symmetry, or, in a cylindrical vessel with baffles mounted on the wall, due to periodicity in the azimuthal direction. Commercial software accomplishes these choices by means of symmetry cells and cyclic cells, respectively although such choices reduce the size of the simulation, they may eliminate the possibility of finding the real (asymmetric, unstable, or transient) 3-D flow field. The presence of feed pipes or drain or withdrawal pipes may also make the use of symmetry or cyclic cells impossible. Again, this issue only plays a role in RANS-type simulations. 

As with the modified S S membrane, the L-S membrane was found to be asymmetric. The side of the membrane away from the casting surface had to be in contact with the feed brine during se rvi ce,... 

Figure 10. Salt rejection of heat-treated asymmetric and homogeneous PVA membranes as a function of feed concentration at aP = 1000 psi and t = 30°C ( <>) ASS ( J AS23 (O) AS4 (9) AS3. The solid lines represent the data obtained for the heat-treated homogeneous PVA membranes.

Fig. 1. Water flux and NaCl rejection of several membrane types (10), where (D) represents seawater membranes, which operate at 5.5 MPa and 25°C ( ), brackish water membranes, which operate at 1500 mg/L NaCl feed, 1.5 MPa, and 25°C and (SSI) nanofiltration membranes, which operate at 500 mg/L NaCl feed, 0.74 MPa, and 25°C. A represents cellulose acetate—cellulose triacetate B, linear aromatic polyamide C, cross-linked polyether D, cross-linked fully aromatic polyamide E, other thin-film composite membranes F, asymmetric membranes G, BW-30 (FilmTec) H, SU-700 (Toray) I, A-15 (Du Pont) J, NTR-739HF (Nitto-Denko) K, NTR-729HF (Nitto-Denko) L, NTR-7250 (Nitto-Denko) M, NF40 (FilmTec) N, NF40HF (FilmTec) O, UTC-40HF (Toray) P, NF70 (FilmTec) Q, UTC-60 (Toray) R, UTC-20HF (Toray) and S, NF50 (FilmTec). To convert MPa to psi,...

Fig. 23.4 Organophilic pervaporation (PV) for in situ recovery of volatile flavour compounds from bioreactors. The principle of PV can be viewed as a vacuum distillation across a polymeric barrier (membrane) dividing the liquid feed phase from the gaseous permeate phase. A highly aroma enriched permeate is recovered by freezing the target compounds out of the gas stream. As a typical silicone membrane, an asymmetric poly(octylsiloxane) (POMS) membrane is exemplarily depicted. Here, the selective barrier is a thin POMS layer on a polypropylene (PP)/poly(ether imide) (PEI) support material. Several investigations of PV for the recovery of different microbially produced flavours, e.g. 2-phenylethanol [119], benzaldehyde [264], 6-pentyl-a-pyrone [239], acetone/buta-nol/ethanol [265] and citronellol/geraniol/short-chain esters [266], have been published...

Two Asymmetric Membrane Sheets, Sandwiching A Porous "Spacer", Are Adhesively Bonded At Edges And Spirally Wrapped About Permeate "Core", To Which "Spacer" Empties Through Penetrations. These Spiral Wraps Are Separated From One Another By An Open-Lattice Feed-Channelling Material, Concurrently Wrapped With The Membrane "Sandwich". The Resultant Permeator Element Is Then Over-Wrapped With Fiberglass Lay-Up, And Provided Necessary Seals And Fittings. 

The configurations of the asymmetric centers of tiliacorine and tiliacorinine were shown by separately feeding only one labeled enantiomer of Al-meth-ylcoclaurine. (S)- and (/ )-iV-methylcoclaurine were incorporated equally into tiliacorine, but the labeled (5) form (22 ) was converted 70 times more readily than the other enantiomer into tiliacorinine. Alkaline permanganate oxidation of the dimethiodides of tiliacorine derived separately from labeled antipodes de-... 

The thiomethyl- and mcthoxy-v-triazines, as well as the asymmetrical triazine metribuzin, were not carcinogenic -some even in the SD rat - and at feeding levels exceeding the MTD the exception was terbutryn, where an increased incidence of mammary, thyroid, and liver tumors were observed in female SD rats at feeding levels that exceeded the MTD. 

Figure 1.92 Regular arrangement of liquid lamellae in the focusing chamber of the SuperFocus micro mixer (steel version large arc of interdigital feeds). For better flow visualization, an asymmetric flow ratio (5 1) was chosen, setting the dyed water solution at a lower flow rate [39].

Salts rejected by the membrane stay in the concentrating stream but are continuously disposed from the membrane module by fresh feed to maintain the separation. Continuous removal of the permeate product enables the production of freshwater. RO membrane-building materials are usually polymers, such as cellulose acetates, polyamides or polyimides. The membranes are semipermeable, made of thin 30-200 nanometer thick layers adhering to a thicker porous support layer. Several types exist, such as symmetric, asymmetric, and thin-film composite membranes, depending on the membrane structure. They are usually built as envelopes made of pairs of long sheets separated by spacers, and are spirally wound around the product tube. In some cases, tubular, capillary, and even hollow-fiber membranes are used. 

Good quality RO membranes can reject >95-99% of the NaCl from aqueous feed streams (Baker, Cussler, Eykamp et al., 1991 Scott, 1981). The morphologies of these membranes are typically asymmetric with a thin highly selective polymer layer on top of an open support structure. Two rather different approaches have been used to describe the transport processes in such membranes the solution-diffusion (Merten, 1966) and surface force capillary flow model (Matsuura and Sourirajan, 1981). In the solution-diffusion model, the solute moves within the essentially homogeneously solvent swollen polymer matrix. The solute has a mobility that is dependent upon the free volume of the solvent, solute, and polymer. In the capillary pore diffusion model, it is assumed that separation occurs due to surface and fluid transport phenomena within an actual nanopore. The pore surface is seen as promoting preferential sorption of the solvent and repulsion of the solutes. The model envisions a more or less pure solvent layer on the pore walls that is forced through the membrane capillary pores under pressure. 

FIGURE 4 Flux in GFD (gal/ft2/day) and rejection of NaCI at 25°C for atmospheric pressure permeate with increasing applied feed pressure with a 5000 mg/L salt feed. The membrane is an asymmetric polyamide. 

Fig. 1.14. Experimental proof-of-concept of asymmetric operation with distributed air feed [26]. Left Schematic set-up of the bench-scale reformer. Right Periodic steady-state temperature profiles at the beginning of successive cycles.

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