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We have found that periodic flow inversions of free-flowing materials may be used to effectively eliminate both size and density segregation in free-surface flows. In a rotating cylinder, these inversions may be induced by placement of an axially located baffle within the flow. In this work, we report on an experimental study of radial mixing and segregation for binary mixtures of granular materials in a rotating cylinder both with and without an axially-located baffle. Qualitative and quantitative measures of the segregation/mixing are shown via digitized images and the intensity of segregation, respectively. We define a mixing improvement factor (ψ) to quantify the relative impact of the axial baffle for a variety of baffle placements and geometries. We find that the maximum extent of mixing is achieved when the baffle size is equal to the radius of the cylinder and fixed either at the free surface or within the shear layer. In contrast, we show that segmenting the baffle, baffle placement outside the shear layer (in fixed bed), or placement at the periphery of the cylinder resulted in an insignificant increase in mixing. Mixing was found to be independent of the shape of a baffle.

The dynamics involved in powder mixing remains a topic of interest for many researchers; however the theory still remains underdeveloped. Most of the mixers are still designed and scaled up on empirical basis. In many industries, including pharmaceutical, the majority of blending is performed using “tumbling mixers”. Tumbling mixers are hollow containers which are partially loaded with materials and rotated for some number of revolutions. Some common examples include horizontal drum mixers, v-blenders, double cone blenders and bin blenders. In all these mixers while homogenization in the direction of rotation is fast, mediated by a convective mixing process, mixing in the horizontal (axial) direction, driven by a dispersive process, is often much slower. In this paper, we experimentally investigate a new tumbling mixer that rotates with respect to two axes: a horizontal axis (tumbling motion), and a central symmetry axis (spinning motion). A detailed study is conducted on mixing performance of powders and the effect of critical fundamental parameters including blender geometry, speed, fill level, presence of baffles, loading pattern, and axis of rotation. In this work Acetaminophen is used as the active pharmaceutical ingredient and the formulation contains commonly used excipients such as Avicel and Lactose. The mixing efficiency is characterized by extracting samples after pre-determined number of revolutions, and analyzing them using Near Infrared Spectroscopy to determine compositional distribution. Results show the importance of process variables including the axis of rotation on homogeneity of powder blends.

This study embodies experimental characterization of emitted particulate and filtration performance under varied situation in a pulse-jet cleaning process. Tests were conducted under simulated condition in a filtration apparatus consisting four bags. The effect of four different factors such as fabric punch density, baffle plate height, air to cloth ratio and cycle time have been investigated on the key parameters; emission, pressure drop along with PM2.5 and average particle diameter of emitted particulate matter in a pulse-jet filtration process. Experimental investigation based on L9-orthogonal design shows that emission is reduced with the increases in punch density and pulse cycle time; but it increases up to a certain extent with the increase in air to cloth ratio. However baffle plate height has no effect on the emission. On the other hand pressure drop across the tube sheet increases with the material consolidation, air to cloth ratio and pulse cycle time; but the above parameter first decrease with the increase in baffle plate height. PM2.5 (based on the number distribution) is found to be mainly affected by the baffle plate height and cycle time; as it first increases and then decrease with the increase in baffle plate height but it shows reverse trend with the increase in cycle time. Average particle diameter based on number volume is found to be mainly affected by the baffle plate height and cycle time. With the increase in time of filtration, both emission and pressure drop tend to increase without affecting PM2.5 and average particle diameter based on number volume.

Granular materials are utilized in a wide variety of industrial applications. The complex hydrodynamics of granular flow is still not fully understood. The flow characteristics of solid particles in a two-dimensional moving bed were studied experimentally and theoretically. The effects of mass velocity, properties of particles and the shape of moving bed on flow pattern were examined. The experiments show that the mass velocity of solid particles and the placement of baffles in stagnant zones have no effect on flow pattern. The shape, size and repose angle of particles affect the flow pattern greatly. The particles have more liquidity and the mixture between particles is easier with the increasing of sphericity degree of particles and the decreasing of particle size. The shape of flowing zone becomes more sharp-angled with the increasing of the repose angle, and the stagnant zone becomes larger. The kinematic model was used to simulate the particle flow. For center discharge the simulation results are in agreement with experiment data very well, while for eccentric discharge the simulation couldn't show the effects of side walls on particle flow. An analytic solution of kinematic model was obtained by Lie transformation group. It shows that the velocity of particle flow is the maximum when x equals 0. The method of translational coordinate was used to modify the traditional kinematic model in order to make sure the x value of each point on the maximum particles velocity distribution lines is zero. The modified kinematic model could simulate the eccentric discharge well, and the field of kinematic model applications was expanded.

Experiments were conducted in the geometrically- and dynamically-scaled UBC half-column to test different configurations that might significantly reduce stripper shed fouling and increase run length, while providing little or no decrease in stripping efficiency in two commercial fluid cokers. The results showed that a series of horizontal gas jets, without baffles, constrained to use no more steam than in the existing commercial operations, were unable to fully match the stripping efficiency of the strippers with shed internals. Wall baffles were also of little assistance. However, relatively large crossed-sheds, called “mega-sheds,” combined with a limited number of staggered gas jets, provide a promising geometry, with more tolerance to fouling and stripping efficiency equivalent to that of the existing commercial units.

The segregation of binary particle mixtures was investigated in a horizontal screen baffle packed fluidized bed, which was operated continuously. In this study, the effects of the gas velocity, baffle spacing, screen size, feeding location, feeding rate, and bed height on particle segregation were examined. The results showed that the efficiency of particle segregation increases as the gas velocity, baffle spacing, and screen hole diameter decrease.

Bed expansion data were obtained for unbaffled and two different types of baffled (coaxial rod and coaxial blade) gas–solid fluidized beds for varying operating parameters: fluid mass velocity, particle size, density and initial static bed heights. Correlations have been developed for the prediction of bed expansion. For this, the values of minimum fluidization mass velocity (Gmf) and settling mass velocity (GS, considered as hindered settling) have been calculated with the help of available equations. The correlations developed are modified versions of those of Beranek and Sokol, where mass velocity ratio (GR) has been used in place of velocity (U)

The influence of horizontally placed internals on the physical behaviour of a dense fluidized bed has been observed using an X-ray technique. The internals were sieve-like baffles with an aperture size two orders of magnitude larger than the diameter of the bed particles. Both a freely bubbling bed and single injected bubbles were observed. For the latter, the bubbles were made to emerge from a layer more opaque to X-rays into one more transparent. In this way, the flow pattern around the bubble and the wake could be observed. The results show that the baffles do not influence the mean bubble size or velocity significantly, confirming earlier indirect observations. It is also shown that the wake material is removed from the fluidization bubbles by the baffles. Results are given as statistics for bubble size and rise velocity as a function of the fluidization velocity with and without baffles present, and sequences of X-ray images showing the effect of the baffles.

This paper presents a method of influencing the axial mixing of particles and promoting segregation in fluidized beds without otherwise changing the character of the bed substantially (at least at low to moderate gas velocities). The method is based on the introduction in the bed of horizontal screen-like baffles with a relatively large free area. It will be shown that such baffles promote the particle segregation significantly, producing a layer of almost pure heavy/large particles in a binary mixture which would be well mixed when fluidized in a conventional bed at the same velocity. The effect of three different types of baffles, of the number of baffles and of the fluidization velocity on the quality of separation is examined. A physical reason for the demixing effect is suggested.

A novel and easily controlled technique, which uses jet pumps for circulating solids between parallel fluidized beds, has been successfully developed. A preliminary study in two-dimensional fluidized beds with small-diameter jet pumps for observing flow behaviour and characteristics justified extending the investigation by using two parallel, rectangular, stainless steel fluidized beds with larger-diameter jet pumps. Sand (262 and 366 μm mean diameter) was fluidized (2 < N < 5) at atmospheric pressure and solid circulation rates were measured using an analytical model based on heat balance equations, at jet pump flow rates between 100 and 900 cm3/s. The results showed that circulation fluxes greater than 20 gm/(cm2s) and transfer ratios in excess of 30 could be obtained. These values were dependent on fluidizing velocity, air flow rate to the jet pump, jet pump position relative to the distributor and the use of vertical baffles.