Sonochemical reactors: important design and scale up considerations with a special emphasis on heterogeneous systems

The spectacular effects observed during acoustic cavitation phenomena have been successfully employed for a number of applications on laboratory scale of operation but a well defined design and scale up methodology is lacking. The present work aims at developing a unified approach for the selection of different operating and geometric parameters for large scale sonochemical reactors with a special emphasis on heterogeneous systems. In the case of heterogeneous systems, apart from optimum selection of operating and geometric parameters, it is also important to understand the mixing and hydrodynamic characteristics due to the presence of solid/gas phases in the liquid medium. Also the quantification of attenuation of the incident sound energy has been discussed, which can be important design consideration in heterogeneous systems. Recommendations have been made for optimum selection of frequency of irradiation and power dissipation rate/irradiation intensity as well as the liquid phase physicochemical properties for the given physicochemical transformation. The discussion also highlights' the recent advances in development of sonochemical reactors focusing on reactor geometry and location of transducers in batch and continuous scale of operation

Optimization of prismatic spouted bed apparatuses using novel experimental setup and discrete particle modelling

No abstract

Experimental and numerical investigations of a pseudo-2D spout fluidized bed with draft plates

\u3cp\u3eSpout fluidized beds are often utilized for gas-solid contacting operations involving physical and/or chemical transformations with simultaneous heat and mass transfer such as drying, coating, granulation, combustion, gasification etc. This is because these beds combine advantages of both spouted and fluidized beds. Since the development of the spout fluidized bed, several geometrical modifications have been proposed to optimize the bed performance. One of these modifications often applied in granulation and coating industries includes a draft tube insertion inside the bed, which results in improved performance by providing a restriction on lateral particle flow providing clear distinction for wet spout and dry annulus zones. Moreover, the insertion of the draft tube leads to a stable spouting at lower flow rates, due to the reduced bypassing of the inlet gas (from spout to annulus).In this work, the hydrodynamic characteristics of a spout fluidized bed with draft plates was studied to identify the flow characteristics by constructing a flow regime map by image analysis and a fast Fourier transform of the measured pressure signal. In addition, the captured images were used to determine the particle velocity via particle image velocimetry (PIV). Furthermore, simulations were carried using a discrete particle model with a sub grid scale turbulence model for two regimes, namely the spouting-with-aeration and fluidized bed-spouting-with-aeration (dispersed spout), which are of most interest from an industrial view point. The obtained results were compared with previously obtained experimental data i.e. PIV. This study highlights various flow pattern observed during operation of spout fluidized bed with a draft plate over a wider operating conditions, which is useful to select proper operating conditions; whereas the experimental data can be used for computational fluid dynamic (CFD) model validation, which serve as a building block for design and scale-up at higher operational scales. Besides this, the quantitative information such as particle velocity, residence time distribution, solid mixing and circulation can be obtained after suitable post processing hence useful in optimizing the bed performance.\u3c/p\u3

Spout fluidized bed : hydrodynamic studies with multiscale modelling approach

Nowadays spout fluidized bed reactors are gaining immense attention of scientific community, due to the unified characteristics both from the spouted and the fluidized bed reactors. In the present work, we study the hydrodynamic behaviour (flow regime map) of a spout fluidized bed reactor with draft plates. Furthermore, the effect of variation of the physical properties of the particles, entrainment height and the bed aspect ratio on the overall flow development has been investigated by experimental and numerical means. The experimental investigations were performed through particle image velocimetry and digital image analysis, and the obtained results were compared with a discrete particle model

Coefficient of restitution for particles impacting on wet surfaces: An improved experimental approach

The coefficient of restitution is widely used to characterize the energy dissipation rate in numerical simulations involving particle collisions. The challenge in measuring the coefficient of restitution is the strong scatter seen in experimental data that results from varying particle properties, i.e. shape and surface roughness, and from imperfections in the experimental technique. To minimize this scattering, a novel experimental setup was developed based on two synchronized high-speed cameras capturing the collision behaviour of a particle in three dimensions. To measure the wet restitution coefficient, which describes particle impact in the presence of a liquid layer in the contact region, additional accuracy can be achieved by measuring the liquid layer thickness by a high-precision optical confocal sensor. The coefficient of restitution was measured for glass particles with two different diameters, at different relative velocities and liquid layer thicknesses, with a focus on small collision velocities and thin liquid layers, using both the improved (three dimensional) and the conventional (two dimensional) approaches to quantify the improvement of the new method's accuracy

CFD-DEM model for coupled heat and mass transfer in a spout fluidized bed with liquid injection

In this paper, we present a novel CFD–DEM model for coupled heat and mass transfer in a spout fluidized bed with liquid injection. In our CFD–DEM approach both particles and droplets are treated as discrete elements. Before actual simulations were conducted, a number of tests were performed to determine the optimum particle collision time step by analysing the error in the prescribed restitution coefficient (difference between defined and applied values). Subsequently we test the model for a selected case as a proof-of-principle. In this test case, the effect of liquid injection on dynamics of a pseudo-2D spout fluidized bed with draft plates was demonstrated for the fluidized bed-spouting-with-aeration (dispersed spout) regime with injection of water droplets. The computational results were compared with experimental results that were obtained through a unique combination of particle image velocimetry (PIV) and infrared thermography (IRT)