Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Pressure-driven

Measurements of pressure driven fluxes may also be performed on mixtures, and here care must be exercised in interpretation, since the fluxes of the two substances are not in proportion to their mole fractions in the mixture. Consequently the fluxes and must, in principle, be measured... [Pg.90]

For most hydrardic pressure-driven processes (eg, reverse osmosis), dense membranes in hoUow-fiber configuration can be employed only if the internal diameters of the fibers are kept within the order of magnitude of the fiber-wall thickness. The asymmetric hoUow fiber has to have a high elastic modulus to prevent catastrophic coUapse of the filament. The yield-stress CJy of the fiber material, operating under hydrardic pressure, can be related to the fiber coUapse pressure to yield a more reaUstic estimate of plastic coUapse ... [Pg.147]

The pressure difference between the high and low pressure sides of the membrane is denoted as AP the osmotic pressure difference across the membrane is defined as Att the net driving force for water transport across the membrane is AP — (tAtt, where O is the Staverman reflection coefficient and a = 1 means 100% solute rejection. The standardized terminology recommended for use to describe pressure-driven membrane processes, including that for reverse osmosis, has been reviewed (24). [Pg.146]

Piston Cylinder (Extrusion). Pressure-driven piston cylinder capillary viscometers, ie, extmsion rheometers (Fig. 25), are used primarily to measure the melt viscosity of polymers and other viscous materials (21,47,49,50). A reservoir is connected to a capillary tube, and molten polymer or another material is extmded through the capillary by means of a piston to which a constant force is appHed. Viscosity can be determined from the volumetric flow rate and the pressure drop along the capillary. The basic method and test conditions for a number of thermoplastics are described in ASTM D1238. Melt viscoelasticity can influence the results (160). [Pg.182]

Ultrafiltration is a pressure-driven filtration separation occurring on a molecular scale (see Dialysis Filtration Hollow-fibermembranes Membrane TECHNOLOGY REVERSE osMOSis). Typically, a liquid including small dissolved molecules is forced through a porous membrane. Large dissolved molecules, coUoids, and suspended soHds that caimot pass through the pores are retained. [Pg.293]

Reverse Osmosis and Ultrafiltration. Reverse osmosis (qv) (or hyperfiltration) and ultrafilttation (qv) ate pressure driven membrane processes that have become well estabUshed ia pollution control (89—94). There is no sharp distinction between the two both processes remove solutes from solution. Whereas ultrafiltration usually implies the separation of macromolecules from relatively low molecular-weight solvent, reverse osmosis normally refers to the separation of the solute and solvent molecules within the same order of magnitude in molecular weight (95) (see also Membrane technology). [Pg.382]

Cavitation and Flashing From the discussion on pressure recoveiy it was seen that the pressure at the vena contracta can be much lower than the downstream pressure. If the pressure on a hquid falls below its vapor pressure (p,J, the liquid will vaporize. Due to the effect of surface tension, this vapor phase will first appear as bubbles. These bubbles are carried downstream with the flow, where they collapse if the pressure recovers to a value above p,. This pressure-driven process of vapor-bubble formation and collapse is known as cavitation. [Pg.789]

Advantages to Membrane Separation This subsertion covers the commercially important membrane applications. AU except electrodialysis are pressure driven. All except pervaporation involve no phase change. All tend to be inherently low-energy consumers in the-oiy if not in practice. They operate by a different mechanism than do other separation methods, so they have a unique profile of strengths and weaknesses. In some cases they provide unusual sharpness of separation, but in most cases they perform a separation at lower cost, provide more valuable products, and do so with fewer undesirable side effects than older separations methods. The membrane interposes a new phase between feed and product. It controls the transfer of mass between feed and product. It is a kinetic, not an equihbrium process. In a separation, a membrane will be selective because it passes some components much more rapidly than others. Many membranes are veiy selective. Membrane separations are often simpler than the alternatives. [Pg.2024]

FIG. 22-47 Schematic of pressure-driven processes showing nomenclature. [Pg.2024]

Plate-and-Frame (Conceptually the simplest, it is veiv much like a filter press. Once found in RO, UF, and IVIF, it is still the only module commonly used in electrodialysis (ED). A fevy applications in pressure-driven membrane separation remain (see Sec. 18 for a description of a plate-and-frarne filter press). [Pg.2027]

Basic Principles of Operation RO and NF are pressure-driven processes where the solvent is forced through the membrane by pressure, and the undesired coproducts frequently pass through the membrane by diffusion. The major processes are rate processes, and the relative rates of solvent and sohite passage determine the quality of the product. The general consensus is that the solution-diffusion mechanism describes the fundamental mechanism of RO membranes, but a minority disagrees. Fortunately, the equations presented below describe the obseiwed phenomena and predict experimental outcomes regardless of mechanism. [Pg.2034]

The most common membrane systems are driven by pressure. The essence of a pressure-driven membrane process is to selectively permeate one or more species through the membrane. The stream retained at the high pressure side is called the retentate while that transported to the low pressure side is denoted by the permeate (Fig. 11.1). Pressure-driven membrane systems include microfiltration, ultrafiltration, reverse osmosis, pervaporation and gas/vapor permeation. Table ll.l summarizes the main features and applications of these systems. [Pg.262]

The non-intrusive manipulation of carrier gas effluent between two columns clearly has significant advantages in two-dimensional GC. In addition, a pressure-driven switch between the columns introduces no extra band broadening to an eluting peak. [Pg.52]

The flow profiles of electrodriven and pressure driven separations are illustrated in Figure 9.2. Electroosmotic flow, since it originates near the capillary walls, is characterized by a flat flow profile. A laminar profile is observed in pressure-driven systems. In pressure-driven flow systems, the highest velocities are reached in the center of the flow channels, while the lowest velocities are attained near the column walls. Since a zone of analyte-distributing events across the flow conduit has different velocities across a laminar profile, band broadening results as the analyte zone is transferred through the conduit. The flat electroosmotic flow profile created in electrodriven separations is a principal advantage of capillary electrophoretic techniques and results in extremely efficient separations. [Pg.199]

Figure 9.2 Pressure-driven (a) and electrodriven (b) flow profiles. Laminar flow in pressure-driven systems results in a bullet-shaped profile, wliile the profile of electroosmotic flow is plug-shaped, wliich reduces band broadening. Figure 9.2 Pressure-driven (a) and electrodriven (b) flow profiles. Laminar flow in pressure-driven systems results in a bullet-shaped profile, wliile the profile of electroosmotic flow is plug-shaped, wliich reduces band broadening.
Membranes used for the pressure driven separation processes, microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO), as well as those used for dialysis, are most commonly made of polymeric materials. Initially most such membranes were cellulosic in nature. These ate now being replaced by polyamide, polysulphone, polycarbonate and several other advanced polymers. These synthetic polymers have improved chemical stability and better resistance to microbial degradation. Membranes have most commonly been produced by a form of phase inversion known as immersion precipitation.11 This process has four main steps ... [Pg.357]

Ideally, cross-flow microfiltration would be the pressure-driven removal of the process liquid through a porous medium without the deposition of particulate material. The flux decrease occurring during cross-flow microfiltration shows that this is not the case. If the... [Pg.363]

Ultrafiltration is one of the most widely used of the pressure-driven membrane separation processes. The solute retained or rejected by ultrafiltration membranes are those with... [Pg.365]

Qu W, Mala GM, Li D (2000) Pressure driven water flows in trapezoidal silicon micro-channels. Int J Heat Mass Transfer 43 353-364... [Pg.142]

Figure 8.4 illustrates pressure-driven flow between flat plates. The downstream direction is The cross-flow direction is y, with y = 0 at the centerline and y = Y at the walls so that the channel height is 2Y. Suppose the slit width (x-direction) is very large so that sidewall effects are negligible. The velocity profile for a laminar, Newtonian fluid of constant viscosity is... [Pg.285]

FIGURE 8.4 Pressure driven flow between parallel plates with both plates stationary. [Pg.285]

This velocity profile is commonly called drag flow. It is used to model the flow of lubricant between sliding metal surfaces or the flow of polymer in extruders. A pressure-driven flow—typically in the opposite direction—is sometimes superimposed on the drag flow, but we will avoid this complication. Equation (8.51) also represents a limiting case of Couette flow (which is flow between coaxial cylinders, one of which is rotating) when the gap width is small. Equation (8.38) continues to govern convective diffusion in the flat-plate geometry, but the boundary conditions are different. The zero-flux condition applies at both walls, but there is no line of symmetry. Calculations must be made over the entire channel width and not just the half-width. [Pg.290]

Repeat Example 8.1 and obtain an analytical solution for the case of first-order reaction and pressure-driven flow between flat plates. Feel free to use software for the S5anbolic manipulations, but do substantiate your results. [Pg.306]

Which is better for isothermal chemical reactions, pressure driven flow or drag flow between flat plates Assume laminar flow with first-order chemical reaction and compare systems with the same values for the slit width (2Y=H), length, mean velocity, and reaction rate constant. [Pg.307]

Derive the equations necessary to calculate Vz y) given iJi y) for pressure-driven flow between flat plates. [Pg.308]

The last category is the pressure-driven gas flows, which are typical in micro gas fluidic and micro heat transfer systems. Because the channel diameter or width in micro gas fluidic systems is in the scale of sub-micrometer or less, ultra-thin gas lubrication theory plays an important role in... [Pg.114]

Styring, P., Kumada-Coiriu reactions in a pressure-driven microfiow reactor. [Pg.114]

Fernandez-Suarez, M., Wong, S. Y. F., Warrington, B. H., Synthesis of a three-member array of cycloadducts in a glass microchip under pressure driven flow. [Pg.121]

In chemical micro process technology there is a clear dominance of pressure-driven flows over alternative mechanisms for fluid transport However, any kind of supplementary mechanism allowing promotion of mixing is a useful addition to the toolbox of chemical engineering. Also in conventional process technology, actuation of the fluids by external sources has proven successful for process intensification. An example is mass transfer enhancement by ultrasonic fields which is utilized in sonochemical reactors [143], There exist a number of microfluidic principles to promote mixing which rely on input of various forms of energy into the fluid. [Pg.209]


See other pages where Pressure-driven is mentioned: [Pg.11]    [Pg.55]    [Pg.68]    [Pg.165]    [Pg.182]    [Pg.171]    [Pg.144]    [Pg.2008]    [Pg.2037]    [Pg.356]    [Pg.12]    [Pg.262]    [Pg.266]    [Pg.49]    [Pg.354]    [Pg.361]    [Pg.367]    [Pg.470]    [Pg.168]    [Pg.183]    [Pg.527]   


SEARCH



Characteristic flux behaviour in pressure driven membrane operations

Combined Pressure-Driven Flow and

Combined Pressure-Driven Flow and Electroosmotic

Current pressure-driven

Flow, fluid pressure-driven

Microchannels transport pressure-driven flows

Microvalves pressure-driven

Mixing pressure-driven

Motor-driven compressor, pressure

Motor-driven compressor, pressure increase)

Nanofiltration membranes pressure-driven membrane

Partial pressure driven processes

Plug pressure-driven

Pressure driven devices

Pressure driven flows rheometers

Pressure driven processes

Pressure driven species transport

Pressure-Driven Flow Viscometers

Pressure-Driven Rheometers

Pressure-Driven Single-Phase Gas Flows

Pressure-Driven Single-Phase Liquid Flows

Pressure-Driven Two-Phase Flows

Pressure-driven convection

Pressure-driven debris expulsion

Pressure-driven dynamic simulation

Pressure-driven flow

Pressure-driven foam generation

Pressure-driven gas flow

Pressure-driven hydrogen separation

Pressure-driven hydrogen separation membranes

Pressure-driven leaks

Pressure-driven membrane

Pressure-driven membrane filtration processes

Pressure-driven membrane process

Pressure-driven microreactor

Pressure-driven nanofiltration membranes

Pressure-driven piston cylinder capillary

Pressure-driven plug flow

Pressure-driven simulation

Pressure-driven systems

Pressure-driven vapor generators

Seal leaks pressure-driven

Viscoelastic pressure-driven

© 2024 chempedia.info