Suspensions gas-solid

Reference [55] provides additional details beyond the bag filter applications, and Reference [60] provides a technical and analytical review of flowing gas-solids suspensions. 

Boothroyd, R. G., Flouring Gas-Solids Suspension, Ghapman and Hall, 1971,... 

The prime difficulty of modeling two-phase gas-solid flow is the interphase coupling, which deals with the effects of gas flow on the motion of solids and vice versa. Elgobashi (1991) proposed a classification for gas-solid suspensions based on the solid volume fraction es, which is shown in Fig. 2. When the solid volume fraction is very low, say es< 10-6, the presence of particles has a negligible effect on the gas flow, but their motion is influenced by the gas flow for sufficiently small inertia. This is called one-way coupling. In this case, the gas flow is treated as a pure fluid and the motion of particle phase is mainly controlled by the hydrodynamical forces (e.g., drag force, buoyancy force, and so... 

Szekely and Carr 58 have studied the heat transfer between the walls of a cyclone and a gas-solid suspension, and have shown that the mechanism of heat transfer is quite different from that occurring in a fluidised bed. There is a high rate of heat transfer directly from the wall to the particles, but the transfer direct to the gas is actually reduced. Overall, the heat transfer rate at the walls is slightly greater than that obtained in the absence of the particles. 

Rossetti SJ, Pfeffer R (1972) Drag reduction in dilute flowing gas-solid suspensions AIChE J18 31... 

Elperin et al. [3, 36] investigated experimentally the hydrodynamics of co-axial gas-solid suspension impinging streams. The dimensions of the device they used are ... 

Kitron, A., Elperin, T. and Tamir, A. (1990). Montte-Carlo simulation of gas-solid suspension flows in impinging streams. Inter. J. Multiphase Flow, 16 1-17. 

The Basset force may be negligible when the fluid-particle density ratio is small, e.g., in most gas-solid suspensions, and the time change is much longer than the Stokes relaxation time or the acceleration rate is low. 

The minus sign indicates that the force is in the opposite direction of the pressure gradient [Tchen, 1947]. The significance of this force is evident, for example, when a shock wave propagates through a gas-solid suspension. 

In a gas-solid suspension system, let nq be the charge density and V be the effective domain. The electrostatic force of a particle carrying a charge q in the direction of n can be expressed by... 

Charge transfer occurs when particles collide with each other or with a solid wall. For monodispersed dilute suspensions of gas-solid flows, Cheng and Soo (1970) presented a simple model for the charge transfer in a single scattering collision between two elastic particles. They developed an electrostatic theory based on this mechanism, to illustrate the interrelationship between the charging current on a ball probe and the particle mass flux in a dilute gas-solid suspension. This electrostatic ball probe theory was modified to account for the multiple scattering effect in a dense particle suspension [Zhu and Soo, 1992]. 

Zhu, C. and Soo, S. L. (1992). A Modified Theory for Electrostatic Probe Measurements of Particle Mass Flows in Dense Gas-Solid Suspensions. J. Appl. Phys., 72, 2060. 

An account of the behavior of acoustic wave propagation in a gas-solid suspension or particle movement in a turbulent eddy requires comprehensive knowledge of the dynamics of particle motion in an oscillating flow field. This oscillating flow can be analyzed in terms of one-dimensional simple harmonic oscillation represented by... 

For the ball-probe measurement of charge current in a dilute gas-solid suspension, prove that, for a given type of particle and a given mass flow ratio, the current measured is independent ofthe particle size for db 3> dp. It is assumed that the charge transfer coefficient is constant. 

Thus, from Eqs. (4.16) and (4.17), Nup 10, indicating that the Nup of a single particle due to thermal conduction in a gas-solid suspension roughly varies from 2 to 10. A more detailed discussion on the variation of Nup with S/dp is given by Zabrodsky (1966). 

In gas-solid suspensions and fluidized beds, the heat transfer between particles and the wall surface or between a particle at one temperature and a group of other particles at another temperature is largely due to particle impacts. Thus, the average rate of heat transfer may be expressed in terms of a collisional heat transfer coefficient hc, which is defined by... 

Scaling for a dilute gas-solid suspension may represent a simple case of using the nondimensionalization method. The following example is a simplified version of the work of Chao (1982). 

The propagation of pressure waves such as acoustic wave, shock wave, and Prandtl-Meyer expansion through a gas-solid suspension is a phenomenon associated primarily with the transfer of momentum although certain processes of energy transfer such as kinetic energy dissipation and heat transfer between gas and solids almost always occur. Typical applications of the pressure wave propagation include the measurements of the solids concentration and flow rate by use of acoustic devices as well as detonation combustion such as in a rocket propellant combustor or in the barrel of a gun. 

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