Gas suspensions

Dispersion Characteristics The chief characteristics of gas-in-liquid dispersions, like those of hquid-in-gas suspensions, are heterogeneity and instabihty. The composition and structure of an unstable dispersion must be obsei ved in the dynamic situation by looking at the mixture, with or without the aid of optical devices, or by photographing it, preferably in nominal steady state photographs usually are required for quantitative treatment. Stable foams may be examined after the fact of their creation if they are sufficiently robust or if an immobilizing technique such as freezing is employed [Chang et al., Ind. Eng Chem., 48, 2035 (1956)]. 

U.S. Department of Energy, Clean Coal Technology Topical Reports. (1995). SOn Removal Using Gas Suspension Absorption Technology. Report No. 4 (April). Washington, DC U.S. Government Printing Office. 

The more common approach is to treat the particle-gas suspension as an equivalent gray surface parallel to the heat transfer surface. Equation (11) would than be used with Ftaken as unity. Grace (1986) suggests that the emissivity of the particle-gas suspension can be approximated as,... 

Gas Suspension Fluidized Bed Aeromatic-Fielder (GEA Niro) BWI Huttlin (Thomas Engineering) Fluid Air Glatt Vector... 

Gas suspension subclasses primarily are distinguished by the method by which the coating is applied to the substrate. 

Turning to the detonation of condensed EM we note that in this case the study of the equation of state of a dense gas in which repulsion of molecules is more important than their thermal motion turned out to be non-trivial (see the fundamental work by L. D. Landau and K. P. Stanyukovich).29 Water-filled EM were studied by Yu. B. Khariton.30 At present A. N. Dremin is developing ideas on the specific influence of a shock wave on the kinetics of reaction in an EM.31 For gas-dispersion systems the structure of detonation waves has become the subject of numerous studies related to explosions of coal dust husks in grain elevators, gas suspensions of dust in wood processing, etc.32,33 34 5 Works on gas suspensions have also been published abroad.36,37 In gas suspensions we may expect that the reaction rate is determined by diffusion and depends weakly on the temperature. 

Consider the impingement between two opposed particles-gas suspension streams from accelerating tubes of the same diameter. The assumptions made in the establishment of the model are (1) The streams are symmetrical with respect to both the jet axis and the impingement plane (2) The gas flow velocity and all the physical properties of gas and solid are kept constant and (3) The particles beyond collision penetrate into the opposing stream up to. rlllas, while any particle will be drawn out of the system immediately once it collides with another particle. 

Inside the accelerating tube the particles are accelerated by the air flow from zero to a certain velocity, usually 60-70% of the gas flow velocity. During acceleration, the relative velocity between the particles and the gas flow is very high. On the other hand, the concentration of particles in the solid-gas suspension to be processed with impinging streams is generally very small, as mentioned above, so that the interaction between particles can be neglected. Therefore the movement of particles can be described approximately with Newton s motion equations for a single particle, as follows ... 

In a gas-continuous impinging stream device with liquid as the dispersed phase, the liquid is usually atomized into fine droplets with nozzles of an appropriate type, and ejected into gas flows to form droplets-in-gas suspensions before impingement. This can be called the Primary Atomization, and it defines the primary dispersity of liquids. The mechanism of primary atomization and the methods for predicting size distribution (SD) and mean diameter (MD) of the sprayed droplets have been widely reported and some sources of references may be found, e.g., in Ref. [69]. 

In order to obtain experimental evidence for understanding the influence of the impingement between the opposing droplets-in-gas suspension streams on the dispersity of liquid, and also to get some practically applicable information for designing and operating impinging stream devices, the experimental investigation described below was carried out. 

The larger the value for cr, the greater the scattering of the size distribution, and, correspondingly, the poorer the uniformity of the droplet sizes. Part of the data measured at various air-to-liquid mass flow ratio, m.JmL, are shown in Table 5.1. It can be seen that, normally, the impingement between opposing droplets-in-gas suspension streams makes cr smaller. Only those obtained at in the third column of the... 

Essentially, the impingement between the two opposing droplets-in-gas suspension streams does not change the mean diameter of the droplets. 

It should be noted that the impingement or impacting of a solid-gas suspension stream on a solid surface can also result in the effect of grinding and milling. However, as mentioned in Section 8.1, flow configuration is beyond the scope of this book. 

Elperin, I. T. (1972). Transport Processes in Opposing Jets (Gas Suspension). Science and Tech. Press, Minsk, (pp. 213) (in Russ). 

Enyakin, Yu. P. (1984). Depth of penetration of solid or liquid phase particles in opposing gas-suspension jets. J. Eng. Physics of Fluids, 14 512-514. 

In gas suspensions, where very fine particles have to be removed, US action involves agglomeration of particles in order to increase their size and, consequently, to improve the collection efficiency of conventional filters (e.g. electrostatic precipitators, cyclone separators). These filters, while effective for large particle separation, are inefficient for retaining particles smaller than 2.5 pm. Therefore, acoustic agglomeration provides a means for separating fine particles released from industrial, domestic or vehicle sources, which, analytically, constitutes an excellent method for sampling in environmental analysis. 

Ciesla F. J. and Hood L. L. (2002) The nebular shock wave model for chondrule formation shock processing in a particle-gas suspension. Icarus 158, 281-293. 

Flash dryers are the simplest gas suspension pneumatic dryers and require the least amount of space. The basic components of a flash dryer are an air heater with a gas duct, a vertical drying column (flash tube) with an expansion joint, a feed conveyor, a venturi feed section, a cyclone collector with a discharge valve, and a system fan (Papagiannes, 1992). A fan pushes air through a heater and into the bottom of the flash tube. The wet feed enters the tube... 

Flash dryers have several advantages over more complex gas-suspension dryers such as fluid-bed or rotary dryers. They are relatively simple and take up less space, as noted earlier, hence, they require a lower capital investment. 

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