Rectangular Bed Research Articles

Granular temperature in a liquid fluidized bed as revealed by diffusing wave spectroscopy

We report granular temperature and solid fraction fields for a thin rectangular bed (20×200 mm cross-section and 500 mm high) of glass particles (mean diameter of 165 μm and density of 2500 kg/m 3) fluidized by water for superficial velocities ranging from 0.05 U t , which is approximately double the minimum fluidization velocity, to 0.49 U t , where U t is the particle terminal velocity estimated by fitting the Richardson–Zaki correlation to the bed expansion data. At superficial velocities below 0.336 U t , the solid fraction and granular temperature are uniform throughout the bed. At higher superficial velocities, the solid fraction tends to decrease with height above the distributor, whilst the granular temperature first increases to a maximum before decaying towards the top of the bed. Correlation of the mean granular temperature with the mean solid fraction and the local granular temperature with the local solid fraction both suggest that the granular temperature in the liquid fluidized bed can be described solely in terms of the solid fraction. The granular temperature increases monotonically with solid fraction to a maximum at φ≈0.18 where it then decreases monotonically as φ approaches the close-packed limit.

Contact time of an incident particle hitting a 2D bed of particles

Removal of particles from fouling layers due to an incident particle impact is affected by the fluid fluctuations in industrial applications if the contact time is larger than the fluctuations time scales. The contact time is an important parameter when analysing the influence of the fluid structure interaction on a fouling process. The contact time for a particle hitting a bed of particles is defined as the time it takes for the incident particle to bounce off the bed. The contact time for a particle hitting a bed of particles arranged in a rectangular and a hexagonal array is measured experimentally and calculated numerically based on the discrete element method. The incident particle and the bed particles are of the same size and material. It is found that the contact time is proportional to the number of bed layers in case of a rectangular bed array and independent of the number of bed layers in case of a hexagonal bed of particles. The contact time is inversely proportional to the impact speed. The rebound speed of the incident particle is independent of the number of bed layers in case of a hexagonal arrangement of particles and is exponentially dependent on the number of bed layers in case of a rectangular arrangement. A hexagonal bed of particles acts as a massive particle due to its large co-ordination number compared to a rectangular bed of particles. The force propagation speed in granular matter could be calculated by plotting the path of the force as a function of the contact time and finding the gradient of this graph.

Domestic wastewater treatment with a vertical completely drained pilot scale constructed wetland planted with Corchorus oliterius

�A pilot scale constructed wetland planted with Corchorus oliterius was developed for domestic wastewater treatment. The reactor system was composed of rectangular beds realized in cement. Each bed was filled from the bottom to the top with 0.1 m of gravel (15/25 mm) and 0.30 m of a uniformly distributed medium grain (mean sand diameter = 426,66; uniformity coefficient = 0,37) white sand from the Ebrie lagoon. Two beds planted with yang C. oliterius plants (high density: 40 plants/m≤; low density: 10 plants/m≤) and one control (unplanted bed) were used to perform the experiment. The beds filtrates pH was neutralized to 7. The planted beds removed the COD (low density = 61%, high density = 65%) more than the control (54%). Nutrients were also best removed in the planted beds (NH4 + : 67%, PO4 3: 52%) than in the control (NH4 + : 11%; PO4 3: 56%). The increase of the plant density did not influence significantly (p < 0.05) pollutants removal. However, this augmentation increased the bed performance. The plants leaves were less contaminated at 0.9 m above the bed surface, suggesting this height for their harvesting for sale.

Domestic wastewater treatment with a vertical completely drained pilot scale constructed wetland planted with Amaranthus hybridus

A pilot scale constructed wetland planted with Amaranthus hybridus was developed for domestic wastewater treatment. The reactor system was composed of rectangular beds realized in cement. Each bed was filled from the bottom to the top with 0.1 m of gravel (15/25 mm) and 0.30 m of a white sand originating from the Ebrie lagoon. Two beds planted with yang A. hybridus plants (high density: 40 plants/m≤; low density: 10 plants/m≤) and one control (unplanted bed) were used to perform the experiment. The pH of the overall filtrates decreased from 7 to around 8. Planted beds gave best COD removal (high density = 70%, low density = 66%) than the control (60%). Globally nutrients were best removed in the planted beds (NH4 + : 69%, PO4 3: 67%) than in the control (NH4

Nitrogen and phosphorus standing stock in Phalaris arundinacea and Phragmites australis in a constructed treatment wetland: 3-year study

Constructed wetland with sub-surface horizontal flow at Břehov near České Budějovice, Czech Republic is designed to treat sewage from 100 population equivalent. The system was put into operation in late 2003 and it consists of two rectangular beds (28 (L) × 9 (W) m each) planted with Reed canarygrass (Phalaris arundinacea) and Common reed (Phragmites australis) in bands parallel to the flow. Aboveground biomass of Phalaris and Phragmites was harvested in 2004, 2005 and 2006 during the peak standing crop of both species, i.e. in July for Phalaris and the early September for Phragmites. In 2004 and 2005, also belowground biomass was harvested. The major objective of the study was to evaluate the amount of nutrients sequestered in plant biomass and compare it with inflow loading. The analysis of the biomass indicated that the concentrations of nitrogen and phosphorus in various parts of both species were comparable in all three years. However, due to the higher biomass in 2005 and 2006 the nutrient standing stocks increased between 2004 and 2006 indicating that the most important factor for standing stock is the plant biomass. The results revealed that the amount of nutrients sequestered in the aboveground biomass and hence available for harvesting was low as compared to inflow load.

Effect of electric field on the hydrodynamics of fluidized nanoparticles

The effect of electric field on the hydrodynamics of nanoparticles was studied in a fluidized rectangular bed, with electrodes attached to two parallel walls. It was shown that the electric field of the order of 3 times the gravity markedly decreased the bed expansion and increased the solids volume fraction of nanoparticles fluidized by air. In these experiments, a light diode assembly was utilized to infer the local solids volume fractions within a rectangular bed of 10 nm silica particles. These experimental measurements yielded a two dimensional solids volume fraction distribution within the rectangular bed. The experimental results provided some new insights into the distribution of solids within the bed. The agglomerate diameters were computed using a momentum balance with the drag given by the Ergun equation and the empirical Richardson–Zaki method. Both methods yielded agglomerate diameters of the order of 100 μm and showed dependence on the strength of the electric field. The electric field decreased the granular temperature of the nanoparticles.

Spatially resolved measurement of anisotropic granular temperature in gas-fluidized beds

This paper reports the measurement of granular temperature in gas-fluidized beds using magnetic resonance. Experiments were performed using 0.5 and 1.2 mm diameter particles (Geldarts group B and D) in both a 3-dimensional cylindrical bed and a 2-dimensional rectangular bed. Measurements were performed over a range of motion encoding times to confirm that the experiments were in the ballistic regime. The results confirm that the granular temperature arises from shear induced by the bubble motion. It was found that the hydrodynamics in the 2D and 3D geometries were significantly different with lower bubble velocities but a higher bubble temperature in the 2D bed than in the 3D bed. The granular temperature was also found to be highly anisotropic, with T z up to 10 times greater than T x or T y .

Microdynamic modelling and analysis of the mixing and segregation of binary mixtures of particles in gas fluidization

This paper presents a study of the mixing and segregation of particle mixtures in a gas-fluidized bed by means of a discrete particle simulation. Particle mixtures are composed of spherical particles with diameter 2 mm for jetsam and 1 mm for flotsam. The particles are initially packed randomly in a rectangular bed and then fluidized by gas uniformly injected at the bottom of the bed. The gas injection velocity varies to cover fixed, partially and fully fluidized bed conditions, in order to establish a full picture about the effect of gas velocity. Segregation/mixing behaviour is analysed in terms of flow patterns, solid concentration profile and mixing kinetics. It is shown that segregation, as a transient process, is strongly affected by gas velocity. There is a gas velocity producing the maximum segregation for a given mixture. Below this velocity, segregation increases and above this velocity, segregation decreases with the increase of gas velocity. The time to reach a macroscopically stable state can be up to tens of seconds, decreasing with the increase of gas velocity. The mechanisms governing the segregation and mixing of particles are elucidated in terms of the interaction forces between particles and between particles and fluid. Particle–fluid interaction initiates fluidization and segregation. Particle–particle interaction, however, also plays an important role in governing the segregation of particles. The degree of segregation results from the complex dynamic balance of the two interactions either locally or globally.

Discrete particle simulation of size segregation of particle mixtures in a gas fluidized bed

This paper presents a study of the mixing/segregation behaviour of particle mixtures in a gas fluidized bed by use of the discrete particle simulation. Spherical particles with diameters 2 mm (jetsam) and 1 mm (flotsam) and density 2 500 kg·m −3 are used as solid mixtures with different volume fractions. The particles are initially packed uniformly in a rectangular bed and then fluidized by gas uniformly injected at the bottom of the bed. The gas injection velocities vary to cover fixed, partially and fully fluidized bed conditions. Segregation/mixing behaviour is discussed in terms of flow patterns, solid concentration profile and mixing kinetics. The results show that segregation, as a transient fluidization process, is strongly affected by gas injection velocities for a given particle mixture. With the increase of the volume fraction of flotsam, size segregation appears at lower velocities.

Computational fluid dynamics for dense gas-solid fluidized beds

Abstract Many computational fluid dynamics (CFD) models for describing the hydrodynamics of dense gas-solid flows in fluidized beds have been put forward in the past few decades. These models treat the solid phase as continuum or discrete particles, which leads to Eulerian-Eulerian or Eulerian-Lagrangian formulations, respectively. Different governing equations and closure relations essentially result from an insufficient understanding of the complex gas-particle and particle-particle interactions for gas-solid flows. The current status of these models is discussed briefly in this paper. All the approaches in the literature modify only the solid phase momentum balance equcation introducing various forms of the solid phase stress tensor and the solid phase pressure drop in the Eulerian-Eulerian models. Taking them into consideration, a new model for predicting the fluid behavior of dense gas-solid flows in fluidized beds has been developed, which contains new terms in both the particle and gas phase momentum balance equations and requires only the use of an experimental drag force correlation. Several results are shown to verify the model's reliability, which include the homogeneous fluidization of Geldart type A particles, the bubbling and jetting fluidization of Geldart type B particles in rectangular beds, and fluid dynamics in a complicated geometry for a bubbling-bed of a fast internally circulating fluidized-bed biomass gasifier.

Numerical study on adsorption enhancement of rectangular adsorption bed

The present paper has dealt with the one-sidewall cooling effect of spherical adsorbent particles packed in a rectangular bed on water vapor adsorption characteristics by a 2-dimensional numerical analysis. The analysis model was considered that one-sidewall of a rectangular packed bed with homogeneous spherical silica gel particles was cooled and another walls were adiabatic. The moist air flowed into the rectangular adsorption bed packed with spherical adsorbent particles. Fuji Sylsia silica gel B was selected as a suitable adsorbent with high adsorption ability over high relative humidity. Numerical results revealed the effects of moist air inlet humidity, airflow velocity, size of spherical silica gel particles, width of the rectangular packed bed, and the side-wall cooling temperature on the amount of water vapor adsorption.

Adorption Enhancement of Rectangular Packed Bed with Spherical Adonrbent by Side Wall Cooling in a Forced Convection Flow

The present paper has dealt with the one-sidewall cooling effect of spherical adsorbent paticles packed in a rectangular bed on water vapor adsorption characteristics by a 2-dimensional numerical analysis. The analysis model was considered that one-sidewall of a rectangular packed bed with the homogeneous spherical silica-gel particles was cooled and another walls were adiabatic. The moist air flowed into the rectangular packed bed with spherical adsorbent particles. The silica-gel B with high adsorption ability over high relative humidity was selected as a suitable adsorbent. Numerical results revealed the effects of moist air inlet humidity and airflow velocity, size of spherical silica-gel particles and width of the rectangular packed bed and the sidewall cooling terperature on the amount of water vapor adsorption.

Lattice Boltzmann simulation of capillary infiltration in agglomerates and beds of fine particles

Abstract Lattice Boltzmann methods (LBM) for one- and two-phase flows are used to model the capillary pressure-driven infiltration of fluids into porous spheres and rectangular beds. This simulates the soaking of fine particle agglomerates and powder compacts, respectively. The sensitivity of the infiltration behavior to physical parameters (such as porosity, permeability, degree of saturation and dimensions of the porous solid, as well as the dynamic viscosity and surface tension of the fluid) was investigated. Results of the LBM approach show good consistency with those from continuum models describing infiltration behavior. Additionally, the one-phase LBM was applied to investigate the influence of pore network structure on the infiltration behavior.

Analysis of liquid distribution in non-uniformly packed trickle bed with single phase flow

The distribution of liquid flow rate is measured in a rectangular bed non-uniformly packed with different particles. The effects of particle properties (size and wettability), liquid properties (viscosity and surface tension) and packed structure on the liquid flow rate distribution are examined. The liquid trickle flow is strongly affected by the capillary force. An experimental equation expressing the liquid flow distribution at the interface between different particles is derived by means of the capillary number. A percolation model combined with the above experimental equation is developed to simulate the liquid flow distribution in the trickle bed. For the trickle flow of liquid droplet, the gravitational and capillary forces are considered to work on the liquid droplet, and the driving force for stochastic liquid flow is assumed to be the potential of the local liquid holdup. Besides a dropping flow in the vertical direction, a permeation flow in the horizontal direction is supposed. The results calculated by the percolation model are in good agreement with the experimental data for various packed systems.

Liquid Flow Rate Distribution in Trickle Bed with Non-Uniformly Packed Structure.

Liquid flow rate distribution in a rectangular trickle bed with non-uniformly packed structure was experimentally studied. Two kinds of particles with different diameters were packed in each side of the packed bed at a certain angle. Glass beads were used for the hydrophilic particles, and glass beads coated with PTFE for the hydrophobic ones. Two-dimensional distribution of liquid flow rate was measured. Also a point-source tracer experiment was performed to observe the local liquid flow.Much of the liquid flows into the small particle side for the hydrophilic bed. The result is vice versa for the hydrophobic bed. These tendencies become more remarkable as the packed angle increases. An experimental equation on liquid distribution in the trickle bed with non-uniformly packed structure is proposed as a function of Capillary numbers of both particles and the packed angle.

On the effect of various momentum transfer coefficient models on bubble dynamics in a rectangular gas fluidized bed

In this paper a computational study of the effect of various gas—solid momentum transfer coefficient models on the bubble formation in a gas fluidized bed is presented. The numerical scheme developed is implicit in the gas—solid momentum transfer terms. The bed is modeled to be composed of gas and particulate phases. Beyond the minimum fluidization conditions the excess gas passes through the bed as bubbles. In addition to the gravitational effects on the solid particles, the overall behavior is characterized by the interphase momentum transfer and the pressure and viscosity of the solid phase. The momentum transfer coefficient is modeled for the flow around spherical particles and the solids pressure is modeled based on kinetic theory. The solid-phase viscosity is considered to be constant and a value of 1 Pa s is used as reported in the literature. The computations are performed for a two-dimensional rectangular bed of particles 500 μm in diameter. The bed has a single air jet in the middle at the bottom while the secondary air at minimum fluidization velocity comes in uniformly through the rest of the distributor. A jet velocity to distributed velocity ratio of 40:1 is used in the computations. The computations are started from minimum fluidization conditions and show the formation, growth, detachment, rise and subsequent bursting of the first bubble in the freeboard region. The results are presented in terms of void fraction contours. The computations are carried out for longer real times and the subsequent bubble dynamics is discussed. For different momentum transfer coefficients the bed was observed to demonstrate quite different behaviors after the collapse of the first bubble. For the prescribed flow rate only the first bubble was seen to be well defined and the gas tended to channel through a slender jet thereafter. A lower jet velocity case as well as uniformly fluidized case are also discussed for comparison purposes.

Anterior cervical vertebrectomy and interbody fusion

This report discusses the authors' technique in performing anterior cervical vertebrectomy and interbody fusion for multilevel cervical disease. The technique is performed with a high-speed drill and bone-bank fibular strut graft. After decompression of the cervical canal, ledges are made in the intact vertebral bodies to create a rectangular bed for safe seating of the bone graft. The bone-bank fibular strut graft is a feasible alternative to autograft. The simplified and safe nature of this procedure reduces postoperative morbidity as well as the length of hospital stay.

Villa Borghese: il giardino e Ie architetture

This volume studies the territory of the Villa Borghese, just outside the Porta Pinciana in Rome, from the seventeenth century to the present day. For those who only know the Borghesc's somewhat barren attempt at a giardino inglese during the more arid moments of a Roman summer (which was my first impression years ago), its history will come as a refreshing surprise. Beata Di Gaddo, an urban historian, presents in great detail - the illustrations are especially rich and useful - how the gardens were laid out after 1610 in a grid of restrained rectangular beds wholly unlike the contemporary baroque designs at Frascati to the south-cast. As well as examining the various buildings, fountains and statues which have variously decorated its spaces, she examines the interaction between garden, park (including a zoo) and the neighbouring city over four centuries. The author's final ambition, well articulated, is to highlight problems of conservation of such precious examples of Italian patrimony in the context of their extensive public use.