H. Littman

Measurements of spout voidage distributions, particle velocities and particle circulation rates in spouted beds of coarse particles—II. Experimental verification

Experimental data are presented using 2.7 mm and 4.9 mm spherical glass particles spouted with air to verify the particle circulation theory presented in Morgan et al. (Chem. Engng Sci.40, 1367–1377 (1985)) The particle mass flowrate, particle circulation rate and spout voidage profiles are in excellent agreement with the theory. To fit the particle velocity profile, the spout must contract slightly near the inlet to the bed and then expand to the average spout diameter.

Spout voidage distribution, stability and particle circulation rates in spouted beds of coarse particles. I: Theory

Abstract Mass and momentum balance equations are used with a derived expression for the interaction force between the fluid and particle phases to calculate the axial spout voidage distribution and particle circulation rate in a spouted bed of coarse particles. The voidage profiles above minimum spouting are found to follow a similarity relationship and an explicit equation for the circulation rate is developed using that relationship and the calculated voidage at the top of the spout. Criteria for stability and spouting regime identification are discussed.

Variational model for prediction of the fluid-particle interphase drag coefficient and particulate expansion of fluidized and sedimenting beds

Abstract An equation for prediction of the fluid-particle interphase drag coefficient in particulately fluidized and sedimenting beds is derived and experimentally verified. This equation is obtained by modeling the dimensionless drag coefficient-voidage relationship in a bed in which the superficial fluid velocity varies from minimum fluidization to terminal as a single constraint isoperimetric problem of the calculus of variations. The solution contains a single dimensionless parameter, U mF 2 / U 2 t ϵ mF 3 , and no adjustable constants. An equation for the superficial velocity-voidage relationship in the bed is also derived and experimentally verified. Fluidization and sedimentation experiments were conducted using water and spherical glass particles 1.20, 1.94 and 2.98 mm in diameter in columns 36, 40 and 50 mm in diameter to verify the model. Both the drag coefficient and velocity for voidages varying from minimum fluidization to 0.96 are predicted extremely well. Several empirical equations are shown to give limited descriptions of the data when considered over the whole range of voidages from minimum fluidization to terminal.

Modeling and measurement of the effective drag coefficient in decelerating and non-accelerating turbulent gas—solids dilute phase flow of large parti

Abstract The one-dimensional modeling of decelerating and non-accelerating turbulent dilute phase flow has been studied by transporting 1 mm glass spheres with

The pressure field around a two-dimensional gas bubble in a fluidized bed

Abstract Measurements of the entire pressure field around a two-dimensional bubble rising in an incipiently fluidized bed are reported. Above the center of pressure line, the field is Laplacian and reasonably well described by Davidsons theory. The pressure wake is closed. It extends for 12 bubble radii below the stagnation point and four radii on either side of the vertical axis of symmetry.

Studies on modeling and control of spouted bed reactors—I: Reactor modeling

Abstract This paper presents for the first time a theoretical nonisothermal dynamic model for spouted bed catalytic reactors. A pseudo-homogeneous on-dimensional model is developed for an adiabatic spouted-bed with a first order reaction. The effects of various design parameters on the steady-state reactor performance are established.

A new choking velocity correlation for vertical pneumatic conveying

A new choking correlation is presented here, based on the assumption that choking occurs at the inlet to the transport line when a parameter γ(e)=0. The voidage at the inlet required to calculate γ(e) is obtained using a correlation for the slip velocity. This new correlation is shown to give better predictions than Yangs (1983) correlation for monodisperse particles. A significant improvement in the prediction of the choking velocity of polydisperse particle, compared with the Briens and Bergougnou (1986) model, is also illustrated

The effective buoyancy and drag on spheres in a water-fluidized bed

We are concerned with measurements of the effective buoyancy and fluid-dynamic drag on large particles of varying density settling or rising in a water-fluidized bed of monodisperse spheres of smaller size

Effect of particle diameter, particle density and loading ratio on the effective drag coefficient in steady turbulent gas-solids transport

Abstract Extending earlier work [1], effective drag coefficients for particles in steady turbulent gas-solids transport in a 28.45 mm vertical transport pipe 5.49 m long have been determined for 1 and 2 mm glass spheres and 1.99 mm rapeseed. The data are well represented by the equation C dn = 4 3 ∈Ar Re p 2 so that in the range studied, Cdn increases proportionally with dp and (ϱ p −ϱ f ) ϱ f and is essentially independent of loading ratio. Slip Reynolds numbers ranged from 469 to 1847 and pipe Reynolds numbers from 21400 to 33600. Loading ratios were varied from 7.03 to 45.4. The data reported here for Cdn fall below the standard drag curve as the slip velocity is increased due to the effects of freestream turbulence. The effect of neglecting particle-wall friction in our two-fluid model on the calculation of the solids fraction, slip velocity and drag coefficient is discussed.

Exploring the effect of dry premixing of sand and cement on the mechanical properties of mortar

A spout-fluid bed device was developed for dry premixing sand and cement to produce mortar. The goal of the work was to explore the efficacy of a new method for dispersing cement in sand to produce a mortar with better mechanical and physical properties. This strategy was found to work best at high sand/cement ratios, indicating that the dry premixing is more effective as the cement content is reduced and that it may be possible to produce commercially acceptable mortars with a lower cement content. Other properties of the mortar are also positively affected, including a decrease in the shrinkage and an increase in the workability.