Double-flow principle

Demonstration of the blood supply to the liver through the portal vein according to the double-flow principle by F. Glenard. 

With a double-column, the vapour and liquid flows within the individual column sections are not freely adjustable, unless additional enhancement recycles are applied. This is a speciflc characteristic of the double-column principle. As a consequence, the product yields are also more or less fixed. In particular, it is not possible to withdraw all the gas ascending to the top of the low-pressure column as pure nitrogen. However, a fraction of up to 50% of the processed air can be obtained as pure nitrogen (d) with an 02-content of 1 ppm, if residual gas with an 02-concentration ranging between 0.1-3% is withdrawn some trays below the top. Thereby the liquid/vapour-ratio in the top section, the so called nitrogen section , increases such, that the oxygen can be rectified downwards in this section. 

The promise of monolith is the achievement of a higher performance at a lower backpressure than a packed bed. While this is true in principle, current implementations are limited by the fact that the external wall to the structure is made from PEEK. At the time of this writing, the commercially available monoliths can only be used up to a pressure of 20MPa (200 atm, 3000 psi), while packed bed steel columns can be used up to double this pressure and higher. Also, the preparation of the monolith appears to be cumbersome. At the current time, the silica-based monoliths are available only with an internal diameter of 4.6mm. The speed is thus also limited by the flow rate achievable by the HPLC instrument. At the same time, the detector of choice today is the mass spectrometer, which can tolerate only much... 

It is based on a countercurrent-flow ion-migration through a series of membranes. A new electrolytic separation technique, based on the ion-exdusion principle is described by E. Glueckauf and G. P. Kitt. They used an add-base double membrane to separate uni-, di- and trivalent ions. This double membrane is so placed that the anion exchange side faces the anode and the cation exchange side faces the cathode. The salt ions can now only pass through the double membrane, if they first move part of the way as co-ions. 

Two UV detectors are also available from Laboratory Data Control, the UV Monitor and the Duo Monitor. The UV Monitor (Fig.3.45) consists of an optical unit anda control unit. The optical unit contains the UV source (low-pressure mercury lamp), sample, reference cells and photodetector. The control unit is connected by cable to the optical unit and may be located at a distance of up to 25 ft. The dual quartz flow cells (path-length, 10 mm diameter, 1 mm) each have a capacity of 8 (i 1. Double-beam linear-absorbance measurements may be made at either 254 nm or 280 nm. The absorbance ranges vary from 0.01 to 0.64 optical density units full scale (ODFS). The minimum detectable absorbance (equivalent to the noise) is 0.001 optical density units (OD). The drift of the photometer is usually less than 0.002 OD/h. With this system, it is possible to monitor continuously and quantitatively the absorbance at 254 or 280 nm of one liquid stream or the differential absorbance between two streams. The absorbance readout is linear and is directly related to the concentration in accordance with Beer s law. In the 280 nm mode, the 254-nm light is converted by a phosphor into a band with a maximum at 280 nm. This light is then passed to a photodetector which is sensitized for a response at 280 nm. The Duo Monitor (Fig.3.46) is a dual-wavelength continuous-flow detector with which effluents can be monitored simultaneously at 254 nm and 280 nm. The system consists of two modules, and the principle of operation is based on a modification of the 280-nm conversion kit for the UV Monitor. Light of 254-nm wavelength from a low-pressure mercury lamp is partially converted by the phosphor into a band at 280 nm. 

The double-pipe mixer was designed and so far only used for contacting and reacting immiscible fluids [134], The respective flow-pattern maps were derived and annular and slug flows as well as complete spread of the inner-tube fluid were identified as distinct regimes. Since in this chapter only miscible liquids are concerned, no protocol and no results are given for the mixer below. H owever, the device is mentioned, since it could in principle be used also for mixing miscible fluids. 

Another Mobius-type mixer is described in [142], Again, a two-fold 90° rotation is said to be the basic principle, doubling the number of layers for laminar flow. After the first rotation, the laminated fluids are split and thereafter recombined, restoring the original geometry. 

The processes used in industrial air-separation plants have changed very little in basic principle during the past 25 years. After cooling the compressed air to its dew point in a main heat exchanger by flowing counter current to the products of separation, the air feed, at an absolute pressure of about 6 MPa, is separated in a double distillation column. This unit is kept cold by refrigeration developed in a turbine, which expands a flow equivalent to between 8 and 15% of the air-feed stream down to approximately atmospheric pressure. 

Figure 5.7 shows a double-pass RO system. The design principles for the second pass are generally the same as for the first pass. However, because of the low concentration of dissolved and suspended solids in the influent to the second pass, the influent and concentrate flows can by higher and lower, respectively, than for the first-pass RO system (see Chapters 9.4 and 9.5, and Tables 9.2 and 9.3). Because the reject from the second pass is relatively clean (better quality than the influent to the first pass), it is virtually always recycled to the front of the first pass. This minimizes the waste from the system and also improves feed water quality, as the influent to the first pass is "diluted" with the relatively high-quality second-pass reject. 

In principle, parallel connection doubles the effective oxygen ion transfer surface area when compared with series connection, since the entire geometric electrolyte surface is utilized for oxygen ion transfer. This is a consequence of the geometry of the cross-flow monolith configuration. 

The selection of the electrolyte material is dependent on the electrode type. In principle, any ionic conductors can be used as the electrolyte material of a double-layer capacitor as long as the current due to the electrochemical reactions (Faradaic current) does not flow in the desired potential region. The electrolyte merely works as an ion source to form a double-layer. 

It has been experimentally demonstrated that the principles of temperature and concentration superposition of flow curves are applicable to melted keroplasts. In other words, in the fixed matrix FC compositions with different filler content, tp and T measured at different temperatures, can be interpolated through a flat and parallel displacement along the coordinate axes (in double logarithmic coordinates). 

In principle, like all electrochemical reactions initiated by the transfer of an electron across an electrode-electrolyte interface, photoelectrochemical transformations offer the possibility of more precise control than can be attained with reactions that take place in homogeneous solution [62, 63]. This better selectivity derives from three features associated with reactions that take place on surfaces, and hence with the photoelectrochemical event the applied potential (allowing for specific activation of a functional group whose oxidation potential is higher, even in a multifunctional molecule) the chemical nature of the electrode surface (and hence of the adsorption equilibrium constant of a specific molecule present in the double layer) and, finally, control of current flow (and hence a constraint on the number of electrons passed to an adsorbed reactant). 

The fused-silica surface also provides another mechanism, electro-osmosis, which drives solutes through the tube under the influence of an electric field. The principle of electro-osmotic flow (EOF) is illustrated in Fig. 1. The inner wall of the capillary contains silanol groups on the surface that become ionized as the pH is raised above about 3.0. This creates an electrical double layer in the presence of an applied electric field so that the positively charged species of the buffer which are surrounded by a hydrated layer carry solvent toward the cathode (negatively charged electrode). This results in a net movement of solvent toward the cathode that will carry solutes in the same direction as if the solvent were pumped through the capillary. This electrically driven solvent pumping mechanism results in a flat flow profile in contrast to... 

More recent viscoelastic 2C acrylate adhesives often adhere to low-energy surfaces as well, making them suitable for adhesion to polyolefins without pretreatment (3 M Scotch-Weld DP 8005). The 2C acrylate adhesives are often supplied in double cartridges (side-by-side cartridges), whereby the flow-mix principle is used. Users process the adhesive like a 1C system. These acrylate adhesives are transparent and UV-stable, making them suitable for braiding glass. They can also be painted over. 

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