Radial pressure differences and their fluctuations in dense fluidized beds

90 ANNUAL LITERATURE SURVEY 1996 nation is given for the difference between the dispersed fluidization and the circulating fludization. (from Authors) Radial pressure differences and their fluctuations in dense fluidized beds Bi H.T. & Grace J.R., Chemical Engineering Science, 1996, 51/4 (663-665). In English. Pressure fluctuations have been widely used in the diagnosis of the flow behaviour of gas-solids fluidized beds. In this work, the local instantaneous pressures in both the wall and the core regions have been measured using pressure transducers in a fluidized bed operated in the bubbling and turbulent fluidization regimes. The local time-mean pressures and the standard deviations of pressure fluctuations were then calculated and used to evaluate the radial variation oflocal pressures. (from Authors) Gas-solid fluidization: a typical dissipative structure Jinghai Li, Guihua Qian & Lixiong Wen, Chemical Engineering Science, 1996, 51/4 (667-669). In English. In accordance with the controlling role of the particles and/or the fluid, Li et al. (1992) characterized the three major regimes in particle-fluid two-phase flow as: particle dominating (PD) for the fixed bed, particle-fluid compromising (PFC) for fluidization and fluid dominating (FD) for dilute transport. According to the theorem o fminimum entropy production (Prigogine, 1967), steady states of linear nonequilibrium systems prevail only when the entropy production rate is minimized. There is however no single and general variation theorem for nonlinear steady-state dissipative systems (Gage et al., 1966; Nicolis, 1994). This paper purports to examine the extremum behavior of fluidized systems in the light of nonequilibrium thermodynamics in order to explore valid approaches to elucidate the bifurcation phenomenon and dissipative structure for such complicated systems. (from Authors) Modeling of dilute sulfur dioxide absorption into calcium sulfite slurries Gerard P., Segantini G. & Vanderschuren J., Chemical Engineering Science, 1996, 51/12 (3349-3358). In English. The absorption rate of SO2 into calcium sulfite slurries is predicted by means of a model, based on the film theory, which considers absorption in a liquid film located at the gas-liquid interface and simultaneous dissolution of calcium sulfite in a liquid film surrounding the particles. The involved reactions are supposed to be reversible and instantaneous. Diffusive transport of ionic and molecular species in both films accounts for the effect of equilibrium and, due to unequal diffusivities of ions, for the effect of the electric potential gradient. (from Authors) Inviseid, slender, annular and liquid jets Ramos J.I., Chemical Engineering Science, 1996, 51/6 (981-994). In English. Regular pertubation expansions are used to analyse unsteady, inviscid, slender, incompressible (constant density), axisymmetric, annular liquid jets when the gases enclosed by and surrounding the jet are dynamically passive. Both inertia-and capillary-dominated annular jets are considered. It is shown that, for inertia-dominated jets, closure of the leading order equations is achieved at second order in the perturbation parameter which is the slenderness ratio, whereas closure is achieved at first order for capillary-dominated jets. The leading order equations are used to determine the fluid dynamics of steady annular jets. (Author) Fluidization of potato starch in a stirred vibrating fluidized bed Kuipers N.J.M., Stamhuis E.J. & Beenackers A.A.C.M., Chemical Engineering Science, 1996, 51/11 (27272732). In English. A novel gas-solid reactor for cohesive C-powders such as potato starch is introduced, designed and characterized, the so-called stirred vibrating fluidized bed. The effects ofa sinusoidal vibration of the gas distributor and/ or stirring of the bed are investigated. The fluidization index, bed expansion, torque and visual behaviour of the bed are determined as a function of air velocity, bed height and moisture content of the starch, stirred type and speed and vibration frequency and amplitude. By simultaneously applying both vibration and stirring of the aerated bed, it is possible to eliminate both channelling and starch agglomeration. Even homogeneous fluidization is possible. Optimal combinations of stirring and vibration parameters are reported for various bed heights and moisture contents. (from Authors) LDA measurements and CFD modelling of gas-liquid flow in a stirred vessel Morud K.E. & Hjertager B.H., Chemical Engineering Science, 1996, 51/2 (233-249). In English. Turbulent two-phase flow in a stirred vessel has been investigated experimentally and numerically. Mean and turbulent gas velocities are measured using a laser/phase Doppler anemometer (LDA/PDA). The effects of varying gas flow rates and impeller rotational speeds on axial, radial and tangential mean and turbulent velocities at three levels of the vessel are investigated. Furthermore, total gas fractions are measured by observing the level of the liquid surface. A two-dimensional computational fluid dynamics (CFD) two-fluid model, with a standard k-epsilon turbulent model, is used to predict the gas-liquid flow. (from Authors) Local solids concentration measurement in a slurry mixing tank Nasr-El-Din H.A., MacTaggart R.S. & Masliyah J.H., Chemic,TlEngineering Science, 1996, 51/8 (1209-1220). In English. The local solids concentration in a mixing tank was measured using both sample withdrawal and a new conductivity probe. The conductivity probe was used to assess the errors associated with various sample withdrawal techniques and to measure solids concentration profiles in the mixing tank. The effects of sampling tube design (tip shape, face angle and inside diameter), sampling position, bulk solids concentration and particle size on the sampling errors were examined in detail. Solids concentration profiles were also measured as a function of particle size, bulk solids concentration and mixer rotational speed. A strong variation in solids concentration