This paper describes a series of experiments tracing a single radioactive particle in a fluidized bed in an ECAT EXACT HR+ PET camera in order to obtain 3-D paths for an actual bed particle – i.e. a particle typical for the bed material – with a high spatial and temporal resolution. The paper describes how "lines of response" (LORs) were calculated from the binary list-mode files from the camera, and how particle positions (1 per ms) were computed from the LORs. It also gives a condensed account of how the data were analyzed further. The particle movement in the bed is shown graphically, and the findings interpreted in light of the theories o­n mechanisms behind particle movement in fluidized beds. Among other things the issue of fast, short-range movement of particles in fluidized beds is discussed. The findings are consistent with the notion of upward particle motion in the wakes of fluidization bubbles, and downward motion in the bulk.

Spray-drying is known to produce predominantly amorphous material because of rapid solidification.1 The detection and control of the amorphous portion of powdered material is of utmost importance, as different physical forms of materials have different physicochemical properties that give rise to significant differences in functionality when used in dosage forms. The influence of spray-drier feed concentration o­n the degree of crystallinity and the crystal form of lactose (β-lactose, anhydrous α-lactose, α-lactose monohydrate) has been described previously.2It is known2 that the spray-drying process can be made to produce completely amorphous lactose particles. Furthermore, it is clear that the amorphous form is unstable and that it will revert to the crystalline form.

The fluidized bed is a process, which is difficult to manipulate: it either works or it doesn't. How it works has been the subject of much research, o­nly a few studies have considered how the operation of a fluidized process may be influenced. This article describes how fluidized beds can be manipulated to some extent by using internals: the natural tendency for particle segregation in the bed can be enhanced (e.g. for particle classification), and the application range of fluidization can be extended to finer or more sticky powders.


For full article Click Here

A stochastic model describing the axial particle transport and the particle residence time distribution (RTD) in continuous fluidized beds is presented. This model has the advantage of clarity and intuitive appeal. Moreover, the method of solution of the model is far simpler and more powerful than for the traditional modelling approach based o­n conservation equations. After presentation of the model and the method of solution, predictions for the transient axial distribution of tracer particles in a fluidized bed are shown graphically. Predicted RTD curves are also shown graphically and compared with experimental data from the literature. Agreement is good, although some discrepancy between prediction and experiment remains. A discussion is provided.


For full article Click Here

With a view to investigating the potential of a four-compartment interconnected fluidized bed for the combustion of biomass, the motion of relatively large pellets in the bed has been examined. Different experimental techniques were used to look into the following aspects: the pellet distribution between the beds, the pellet circulation rate and the pattern of movement of individual pellets in the compartments. The results from the different types of experiments are shown and related to each other. Emphasis is laid o­n the quality and rate of pellet circulation and the dynamics and mode of transport of the individual pellets in the compartments. Pellet circulation was found to be unsatisfactory when the slow compartments were aerated at or above the rate required to fluidize the material. The pattern of axial movement is shown to be consistent with upwards motion mainly in the wakes of fluidization bubbles, and downwards motion in the bulk.

The movement of particles in fluidization processes in a model test reactor has been studied using an imaging technique from medical healthcare: Positron Emission Tomography (PET). With this noninvasive technique, tracer particles were followed o­n their way through the fluidized bed. Experiments were performed with pulses of tracer particles in different alignments. The results give a good impression of both axial and radial distribution of particles in fluidized bed. In this paper, the experimental results confirm the basic assumptions of the model. Our stochastic model captures the dynamic movement of particles qualitatively, but indications are that the system exhibits ‘gulfstreaming’, a feature which is not accounted for in the model, but is common in fluidized beds in practice.




For full article Click Here

One of the ingredients in Granular Dynamics (or DEM) is a description of interparticleforces. In this paper the effect of surface roughness o­n Hamaker and liquid bridgeinteractions is investigated. Three different models are used (excluded volume, stochasticroughness and explicit asperities). In general, the latter two give similar results. Roughnessdecreases interactions up to several orders of magnitude for rigid surfaces. To validate theanalytical results o­n liquid bridge interactions at low humidity, molecular dynamicssimulations were also performed o­n model systems.



For Full Article Click Here

HERCULES : Pharmaceutical Technology Report

by CJTech.co.Ltd

The granulation of powder to produce pharmaceutical solid dosage is an essential dosage form unit and the use of Fluid bed Technology provides a rapid and cost -effective means of drying the granules



For full article Click Here

A system for fluidized bed granulator automation with in-line multichannel near infrared (NIR) moisture measurement and a unique air flow rate measurement design was assembled, and the information gained was investigated. The multivariate process data collected was analyzed using principal component analysis (PCA). The test materials (theophylline and microcrystalline cellulose) were granulated and the calibration behavior of the multichannel NIR set-up was evaluated against full Fourier Transform (FT) NIR spectra. Accurate and reliable process air flow rate measurement proved critical in controlling the granulation process. The process data describing the state of the process was projected in two dimensions, and the information from various trend charts was outlined simultaneously. The absorbence of test material at correction wavelengths (NIR region) and the nature of material-water interactions affected the detected in-line NIR water signal.