Liquid/particle system

The inter-particle force F can be computed as / = A]idol l2Hl), where Ah is the Hamaker parameter for the liquid-particle system and is the distance between two primary particles. The coordination number is based on experimental observation and can be calculated as kc 150p, where 0p is the volume fraction of solid within the aggregates. In the case of compact (or solid) particles 0p is close to unity, whereas in the case of fractal aggregates 0p can be determined once the fractal dimension T)f of the aggregates is known 0p = (0.414T)f - 0.21 l)(r/p/(io) , where dp is the size of the particle and do is the size of the primary particle (Vanni, 2000b). 

Liquid/particle system in the paste with capillaries not flooded by the liquid [27]. 

Impingement demister systems are designed to intercept liquid particles before the gas outlet. They are usually constructed from wire mesh or metal plates and liquid droplets impinge on the internal surfaces of the mist mats or plate labyrinth as the gas weaves through the system. The intercepted droplets coalesce and move downward under gravity into the liquid phase. The plate type devices or vane packs are used where the inlet stream is dirty as they are much less vulnerable to clogging than the mist mat. 

With the objective determination of the visibilitity of magnetic particle indications quantitative researches on the influence of the inspection parameters will be possible. The first part deals with the type testing of detection media which is as well on the course of adoption for type testing of liquid penetrant systems (prEN 751-2). 

Albertsson (Paiiition of Cell Paiiicle.s and Macromolecules, 3d ed., Wiley, New York, 1986) has extensively used particle distribution to fractionate mixtures of biological products. In order to demonstrate the versatility of particle distribution, he has cited the example shown in Table 22-14. The feed mixture consisted of polystyrene particles, red blood cells, starch, and cellulose. Liquid-liquid particle distribution has also been studied by using mineral-matter particles (average diameter = 5.5 Im) extracted from a coal liquid as the solid in a xylene-water system [Prudich and Heniy, Am. Inst. Chem. Eng. J., 24(5), 788 (1978)]. By using surface-active agents in order to enhance the water wettability of the solid particles, recoveries of better than 95 percent of the particles to the water phase were obsei ved. All particles remained in the xylene when no surfactant was added. 

Electrostatic precipitation is one of the fundamental means of separating solid or liquid particles from gas streams. This technique has been utilized in numerous applications, including industrial gas-cleaning systems, air cleaning in general ventilation systems, and household room air cleaners. 

A very important parr of the gas-deatimg process is the removal of the collected particles from the cleaning system. This should be as controlled as possible in order to avoid particle reenrrainmenr to the gas flow. This can be accomplished in the case of liquid particles such as acid fume or tar or oil smoke. olid particles are normally removed by periodic rapping of discharge and collection electrodes. Solid particles can also be removed with the aid of water, as is done in wet electrostatic precipitators. 

Each stage of particle formation is controlled variously by the type of reactor, i.e. gas-liquid contacting apparatus. Gas-liquid mass transfer phenomena determine the level of solute supersaturation and its spatial distribution in the liquid phase the counterpart role in liquid-liquid reaction systems may be played by micromixing phenomena. The agglomeration and subsequent ageing processes are likely to be affected by the flow dynamics such as motion of the suspension of solids and the fluid shear stress distribution. Thus, the choice of reactor is of substantial importance for the tailoring of product quality as well as for production efficiency. 

Wachi, S. and Jones, A.G., 1995. Aspects of gas-liquid precipitation systems for precipitate particle formation. Reviews in Chemical Engineering, 11, 1-51. 

Gas-liquid-particle operations are of a comparatively complicated physical nature Three phases are present, the flow patterns are extremely complex, and the number of elementary process steps may be quite large. Exact mathematical models of the fluid flow and the mass and heat transport in these operations probably cannot be developed at the present time. Descriptions of these systems will be based upon simplified concepts. 

It seems probable that a fruitful approach to a simplified, general description of gas-liquid-particle operation can be based upon the film (or boundary-resistance) theory of transport processes in combination with theories of backmixing or axial diffusion. Most previously described models of gas-liquid-particle operation are of this type, and practically all experimental data reported in the literature are correlated in terms of such conventional chemical engineering concepts. In view of the so far rather limited success of more advanced concepts (such as those based on turbulence theory) for even the description of single-phase and two-phase chemical engineering systems, it appears unlikely that they should, in the near future, become of great practical importance in the description of the considerably more complex three-phase systems that are the subject of the present review. 

The two models commonly used for the analysis of processes in which axial mixing is of importance are (1) the series of perfectly mixed stages and (2) the axial-dispersion model. The latter, which will be used in the following, is based on the assumption that a diffusion process in the flow direction is superimposed upon the net flow. This model has been widely used for the analysis of single-phase flow systems, and its use for a continuous phase in a two-phase system appears justified. For a dispersed phase (for example, a bubble phase) in a two-phase system, as discussed by Miyauchi and Vermeulen, the model is applicable if all of the dispersed phase at a given level in a column is at the same concentration. Such will be the case if the bubbles coalesce and break up rapidly. However, the model is probably a useful approximation even if this condition is not fulfilled. It is assumed in the following that the model is applicable for a continuous as well as for a dispersed phase in gas-liquid-particle operations. 

The absorption of reactants (or desorption of products) in trickle-bed operation is a process step identical to that occurring in a packed-bed absorption process unaccompanied by chemical reaction in the liquid phase. The information on mass-transfer rates in such systems that is available in standard texts (N2, S6) is applicable to calculations regarding trickle beds. This information will not be reviewed in this paper, but it should be noted that it has been obtained almost exclusively for the more efficient types of packing material usually employed in absorption columns, such as rings, saddles, and spirals, and that there is an apparent lack of similar information for the particles of the shapes normally used in gas-liquid-particle operations, such as spheres and cylinders. 

Optical systems can be used in multiphase flows at a very low volume fraction of the dispersed phase. Through a refractory index matching of hquid-liquid or liquid-solid systems, it is also possible to measure at high void fractions. However, it is not possible to obtain complete refractory index matching since the molecules at the phase boundary have different optical properties than the molecules in the bulk. Consequently, it is possible to measure at a higher fraction of the dispersed phase with larger drops and particles because of the lower surface area per volume fluid. 

In view of the importance of the particle/bubble contact, it may be assumed that the stress acting on the particles during gas sparging is determined by electrostatic interactions as well as by hydrophobic and hydrophilic interactions, which are determined by the nature of the liquid/solid system. The use of Pluronic as additive leads to the reduction of destruction process [44,47] possibly due to less bubble/floc contact which is also described by Meier et. al. [67]. 

Much higher shear forces than in stirred vessels can arise if the particles move into the gas-liquid boundary layer. For the roughly estimation of stress in bubble columns the Eq. (29) with the compression power, Eq. (10), can be used. The constant G is dependent on the particle system. The comparison of results of bubble columns with those from stirred vessel leads to G = > 1.35 for the floccular particle systems (see Sect. 6.3.6, Fig. 17) and for a water/kerosene emulsion (see Yoshida and Yamada [73]) to G =2.3. The value for the floe system was found mainly for hole gas distributors with hole diameters of dL = 0.2-2 mm, opening area AJA = dJ DY = (0.9... 80) 10 and filled heights of H = 0.4-2.1 m (see Fig. 15). 

In catalytic gas-liquid-solid systems mass transfer is more complex. The catalyst particles are present in the liquid phase. The expression for the rate of mass transfer from the gas to the liquid is identical to that for systems without a solid catalyst (Eqn. 5.4-67). However, now also mass transfer from the liquid to the solid surface (external mass transfer) and inside the particle (internal mass transfer) have to be considered. 

Particle collection at a liquid-liquid interface is a particularly favorable separation process when applied to fine-particle systems. Advantages of this type of processing include ... 

The behavior of a multi-particle system with a symmetric wave function differs markedly from the behavior of a system with an antisymmetric wave function. Particles with integral spin and therefore symmetric wave functions satisfy Bose-Einstein statistics and are called bosons, while particles with antisymmetric wave functions satisfy Fermi-Dirac statistics and are called fermions. Systems of " He atoms (helium-4) and of He atoms (helium-3) provide an excellent illustration. The " He atom is a boson with spin 0 because the spins of the two protons and the two neutrons in the nucleus and of the two electrons are paired. The He atom is a fermion with spin because the single neutron in the nucleus is unpaired. Because these two atoms obey different statistics, the thermodynamic and other macroscopic properties of liquid helium-4 and liquid helium-3 are dramatically different. 

In ICP-AES and ICP-MS, sample mineralisation is the Achilles heel. Sample introduction systems for ICP-AES are numerous gas-phase introduction, pneumatic nebulisation (PN), direct-injection nebulisation (DIN), thermal spray, ultrasonic nebulisation (USN), electrothermal vaporisation (ETV) (furnace, cup, filament), hydride generation, electroerosion, laser ablation and direct sample insertion. Atomisation is an essential process in many fields where a dispersion of liquid particles in a gas is required. Pneumatic nebulisation is most commonly used in conjunction with a spray chamber that serves as a droplet separator, allowing droplets with average diameters of typically <10 xm to pass and enter the ICP. Spray chambers, which reduce solvent load and deal with coarse aerosols, should be as small as possible (micro-nebulisation [177]). Direct injection in the plasma torch is feasible [178]. Ultrasonic atomisers are designed to specifically operate from a vibrational energy source [179]. 

An established school preparation of 2-propanone (acetone) involves the small-scale (and rather exothermic) oxidation of the alcohol with dichromate(VI). It was observed in several laboratories that when the acidified dichromate solution was added to the alcohol in small portions (1-2 cc) rather than dropwise as specified, small sparks or incandescent particles were produced which sometimes survived long enough to escape from the neck of the flask. This also happened if the alcohol and/or the oxidant solution were diluted with extra water, with old or new samples of alcohol, and if air were displaced from the flask by carbon dioxide. It is therefore important not to exceed the specified dropwise rate of addition of oxidant solution. It is very unusual for glowing particles to be produced from a homogeneous liquid reaction system. 

One approach that allows increased chromatographic flow rates without loss of resolution entails the use of microparticulate stationary-phase media of very narrow diameter. This effectively reduces the time required for molecules to diffuse in and out of the porous particles. Any reduction in particle diameter dramatically increases the pressure required to maintain a given flow rate. Such high flow rates may be achieved by utilizing high-pressure liquid chromatographic systems. By employing such methods, sample fractionation times may be reduced from hours to minutes. 

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