Simulation and experimental studies on fluidization properties in a pressurized jetting fluidized bed

In this study, the optimization of a gas–solid fluidized bed structure under oscillating conditions is carried out, and the traditional equal-diameter structure is improved to a variable-diameter structure. In this paper, a 300 mm diameter equal-diameter fluidized bed is taken as the benchmark model, and the research team uses numerical simulation to analyze the changing law of bubble size and the percentage of non-fluidized area. It is found that under the condition of the same gas volume, the “cone-contraction” fluidized bed with variable-diameter structure can reduce the bubble size by about 25% and the percentage of non-fluidized area by about 11%. The effects of the specific operating parameters are as follows: the operation of increasing the gas volume will lead to an increase in bubble size but will lead to a decrease in the percentage of non-fluidized area; the increase in the initial bed height will simultaneously increase the bubble size and the percentage of non-fluidized area; the increase in the amplitude of the oscillation will lead to an increase and then a decrease in the bubble size, and will lead to a continuous expansion of the percentage of non-fluidized area; and the change in the oscillation period will not have a significant effect on the two. A comparison of the experimental data shows that the overall performance of the variable-diameter fluidized bed is better than that of the equal-diameter fluidized bed, as shown in the following: the bubble size is reduced by 24~32%, and the percentage of non-fluidized area is reduced by 6~12%. This study provides an effective direction for the structural optimization of fluidized beds.

Simultaneous electrical capacitance tomography measurements for two planes were performed to obtain detailed information on bubble characteristics in a pressurized fluidized bed. Average permittivity values were used to get estimates of bubble sizes, while cross correlation was applied to the signals of both planes to obtain average bubble rise velocities. At low pressures, a wide variation in bubble size was observed. Large stable bubbles tend to affect fluidization smoothness significantly. At higher pressure, bubbles possessed a more uniform size and were in general smaller. Consequently fluidization behavior was observed to be smoother at higher pressures.

Investigation of wetting and drying process in a gas-solid fluidized bed by electrical capacitance tomography and pressure measurement

It is difficult to know the details of material distribution in a fluidised bed. Electrical capacitance tomography (ECT) technology has been developed for imaging industrial processes containing dielectric materials. This paper discusses the principles of ECT and presents the first experimental results of using ECT to measure gas/solids distribution in square circulating fluidised beds (CFB). A wide range of fluidisation conditions was tested, from bubbling to circulating fluidisation. It has been shown that over the range, ECT can provide solids concentration and voids distribution instantaneously. Different fluidisation regimes could also be identified from the reconstructed images.

While fluidized beds are commonly used in the pharmaceutical industry, the understanding of the fluidization processes is limited because no efficient tool is available for real-time online monitoring and measurement. In recent years, electrical capacitance tomography (ECT) has been used to investigate granulation, drying and coating processes in pharmaceutical fluidized beds. For measuring drying and granulation processes, a novel online calibration method was proposed and implemented to deal with continuous change in the moisture content of solids. Experiments were carried out using various fluidized beds of different scale, and good results were obtained. For monitoring the coating process in a Wurster fluidized bed, a unique ECT sensor is designed with three sets of electrodes. By this electrode combination, all regions of the Wurster fluidized bed can be monitored. Based on the work done so far, it is concluded that ECT is a very useful tool for monitoring and measurement of pharmaceutical fluidized beds.

Bubble velocity in fluidized beds: The effect of non-vertical bubble rise on its measurement using submersible probes and its relationship with bubble size

Influence of pressure and fluidization velocity on the hydrodynamics of a fluidized bed containing horizontal tubes

We have studied xenon and argon bubbles formed in the subsurface region of Al(111) by x-ray photoelectron spectroscopy. As a consequence of the nanometer size of the bubbles, the photohole formed by $\mathrm{Xe}\phantom{\rule{0.2em}{0ex}}3d$ or $\mathrm{Ar}\phantom{\rule{0.2em}{0ex}}2p$ photoemission is screened by the Al conduction electrons, which substantially lowers the binding energy (BE) as compared to the gas phase. As the bubble size increases, the Al conduction electron screening decreases and the BE increases. On the basis of density functional theory, we show that the change in the bubble pressure with size is not responsible for the BE shift of inner shell core levels, such as $\mathrm{Xe}\phantom{\rule{0.2em}{0ex}}3d$ or $\mathrm{Ar}\phantom{\rule{0.2em}{0ex}}2p$. On the other hand, an increase in BE with bubble size for outer shell core levels, such as $\mathrm{Ar}\phantom{\rule{0.2em}{0ex}}3p$, could be due to a decrease in both pressure and Al conduction electron screening. The core level line shape also changes with bubble size. For example, the spectra are broadened due to the distribution of the bubble radius around its mean value, and an asymmetry for small bubbles is observed that decreases for larger bubbles. An annealing of Xe and Ar bubbles after an implantation up to $640\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ shows that the BE increases with annealing temperature. Since it is well known that bubble size increases with annealing temperature, this further supports our contention of BE shift with bubble size. A defect induced partial disorder of the Al(111) surface by Xe and Ar bombardment is observed by low energy electron diffraction, but this does not affect the $\mathrm{Al}\phantom{\rule{0.2em}{0ex}}2p$ BE and line shape.

The flow behaviour of a lab-scale fluidised bed with a central jet has been simulated. The study has been performed with an in-house computational fluid dynamics (CFD) model named FLOTRACS-MP-3D. The CFD model is based ona multi-fluid Eulerian description of the phases, where the kinetic theory for granular flow forms the basis for turbulence modelling of the solid phases. A two-dimensional Cartesian co-ordinate system is used to describe the geometry. This paper discusses whether bubble formation and bed height are influenced by coefficient of restitution, drag model and number of solid phases. Measurements of the same fluidised bed with a digital video camera are performed. Computational results are compared with the experimental results, and the discrepancies are discussed.

Pipelines made of dielectric materials such as Polyethylene (PE) are becoming increasingly popular. With no suitable inspection technique for dielectric pipes, there is an urgent need to develop new technology for their inspection. This paper presents a novel pipe inspection technique using Electrical Capacitance Tomography (ECT) imaging. Traditionally ECT is used for industrial process tomography as a low resolution but fast tomographic imaging technique. Typically commercial ECT can provide a resolution of approximately 10 percent of the imaging region. In this paper a limited region tomography technique is developed take into account prior knowledge about the geometry of the pipe. This has signiflcantly enhanced the imaging resolution of the ECT system, making it a viable pipe inspection solution. The experimental results in this study demonstrate an interior wall loss area as small as 0.195 percent of the ECT cross sectional imaging region is repeatable and can be reliably detected. A narrowband pass fllter method (NPFM) is used as a means to limit the region for the ECT algorithm. This results in an unprecedented resolution, making ECT a viable non-destructive evaluation (NDE) technique for plastic pipes. The NDE application of the ECT for PE pipes is demonstrated in this paper with several experimental results. A wall loss of depth of 1.5mm could be detected for an ECT sensor array of 150mm in diameter, showing a high resolution and high deflnition ECT (HD-ECT) imaging that has not been reported before.

Measurement of the effects of physical and chemical variables on bubble size

Numerical investigation on coupled heat transfer of an immersed tube with sCO2 working fluid in a fluidized bed at high temperature and pressure

Experiments were performed at ambient temperature and pressure in a 127 mm inner diameter column with a 55% wt. aqueous glycerol solution, 6‐mm spherical borosilicate beads and four gases — helium, air, carbon dioxide and sulphur hexafluoride — giving a 35‐fold gas density range. The dispersed bubble flow regime was sustained to higher gas velocities and gas holdups for denser gases. This finding appears to be due to the reduction of the maximum stable bubble size (i.e. enhanced bubble break‐up), rather than to formation of smaller bubbles at the distributor with increasing gas density. The effect of gas density was significant both with and without the particles present, with gas holdup increasing, bed voidage increasing and liquid holdup decreasing with increasing gas density. The holdup correlations of Han et al. (1990) have been modified to incorporate the effect of gas density.

Fundamental particle fluidization behavior and handling of nano-particles in a rotating fluidized bed

Bubble size as a function of impeller speed in a self-aeration laboratory flotation cell