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The purpose of this paper is to review the state of our knowledge of the effects of operating pressure on the hydrodynamic behavior of fluidized beds. With the development of coal combustion and gasification fluidized bed processes in the early 1970s, many academic and industrial researchers have studied the effect of pressure on fluidized bed behaviour. This review covers experimental and theoretical studies of effects of elevated operating pressure on fluidization, published in the literature before August, 2002.The review begins with the discussion of the effect of pressurized conditions on non-bubbling fluidization and several methods for better prediction of minimum fluidization velocity at elevated pressure are presented. The effects of pressure on non-bubbling bed expansion in the region between minimum fluidization and minimum bubbling velocities are considered and areas of uncertainty or disagreement are highlighted. The influence of pressure on the dynamics of gas bubbles and bubbling bed expansion is described next. In addition to fundamental hydrodynamics of fluidization, bed-to-surface heat transfer, jet penetration, solids mixing and particle entrainment are mentioned.

The influence of operating pressure on the motion of particles near the fluidized-bed wall surface was studied for Geldart group A and B particles using luminescent pigment as bed solids in a vessel of diameter 146 mm. A pulse of bright light transmitted from outside the pressure vessel via fiber optics was used to illuminate a 7-mm-diameter region of the bed particles adjacent to a transparent vessel wall. Digital image analysis of the motion of the illuminated region of bed particles and its decay in luminosity permitted the determination of the influence of pressure on a particle exchange frequency in the direction perpendicular to the wall surface, the mean particle residence time at the wall, and the velocity of bed solids adjacent to the wall. These findings are related to the observations of the effect of pressure on bed-to-surface heat transfer in fluidized beds reported by other workers.

ВступProblem statement. Increasing the range and kinetic energy of a submerged fluid jet is a topical problem in fluid jet technologies, in particular, power waterjet guns. The main deterrent to its solving is the unavoidable jet breakup process. There is no common approach to control this phenomenon. Hence, for each process, a technique is chosen to enable using the jet before it breaks up. An effective technique is fluid discharge in an elastic or plastic container. However, each discharge preparation procedure restricts using the technique. Recently, unique fountains have appeared with a solid translucent jet several meters long. Visually, these jets are considered laminar ones; however, as will be shown below, such a view is erroneous. At the same time, the flow in these fountains has interesting features that deserve closer attention.Jet breakup is caused by interaction of external and internal destructive factors. Fluid turbulence originates as early as in the channel. In the jet, it develops into strong turbulence and creates conditions for jet dispersion and aeration under the effect of the force of gravity and air resistance.It is impossible to avoid turbulence in a highvelocity flow. However, existing conceptions and prospects enable passing artificially to turbulent flow, which has passed the active phase and does not create large turbulent eddies. Such properties belong to small-scale turbulence (SST) formed within the decaying turbulence. It must be propelled to a jet to delay its destruction.Analysis of the latest researchers and publications. The basis for choosing SST as a means against eddy formation stems from the energy spectrum of fully developed turbulence at high Reynolds numbers. It was represented by Kolmogorov's phenomenological theory [1], whose statements are a basis for studying all turbulent flows [2][3]. According to them, the kinetic energy of turbulence is cascaded without loss from large to small scales according to the Richardson-Kolmogorov cascade. Energy dissipation occurs at the end of the sequence under the effect of viscosity, with virtually all SST properties being determined by the dissipation rate [4]. According to Kolmogorov [1], SST wave numbers belong to the inertial energy interval, which has no dissipation and local interaction. Such turbulence depends weakly on the mean flow velocity. Hence, a conditional flow with SST will be resistant to influences to a certain degree.The actual composition and local characteristics of developed turbulence [4] differ from the simplified model presented. In particular, there exists a nonequilibrium turbulence with an appropriate law of nonequilibrium dissipation [5], which co-exists with the common law of equilibrium dissipation in different areas of the same flow. Hence, the complexity of developed turbulence only drives more the need for an experimental search of conditions that produce an intensive SST and its localisation in a flow at high Reynolds numbers.Purpose of the article. The main purpose of the article is to demonstra...

Since bubbling fluidized-bed scaling laws were first developed, there has been some debate about their correct application and the relative importance of the various scaling parameters, in particular, the solid-to-gas density ratio. In this paper, we highlight the differences in the existing literature and present the results from experimental fluidized-bed systems where the solid-to-gas density ratio has been changed by varying degrees. From our results, we conclude that there is some flexibility for altering the solid-to-gas density ratio when scaling bubbling beds of Geldart group B materials up to particle Reynolds numbers of at least 12, but further work is needed to clarify the range of particle Reynolds numbers over which the density ratio requirement can be relaxed. In contrast, when scaling group A materials, we find that the density ratio is an important parameter even if the particle Reynolds number is small.