Bed Of Solid Particles Research Articles

Processing of brass open-cell foam by silica-gel beads replication

Cellular metals can be produced by several routes, including molten metal infiltration of a leachable bed of solid particles, also known as space holder. The space holder is usually a mineral salt (i.e. NaCl) with relatively low melting point, but this is a limitation for processing high melting point metals and alloys. This work introduces the use of amorphous SiO 2 (silica-gel) particles as space holder and wet solutions of hydrofluoric acid (HF) as solvent for Cu-based open-cell foams production. Commercial grade CW614N brass (solidification interval: 880–895 °C) was successfully foamed through the proposed route, resulting in open-cell foams having relative density ≈0.30 and almost spherical cell morphology. Because of the high chemical stability of SiO 2 particles no interaction with the metallic system during liquid infiltration has been found. On the other hand, due to the corrosion resistance of that alloy to HF attack there has been no evidence of damage on the treated alloys.

Removal of Zn +2 and Ni +2 by adsorption in a fixed bed of wheat straw

Zn +2 and Ni +2 in a solution were removed by biosorption in a fixed bed of wheat straw Triticum aestivum. The removal rate and the mass transfer coefficient for Zn +2 and Ni +2 were found to be proportional to the liquid superficial velocity to the power of 0.31 for the range of the particle Reynolds number from 18 to 445 (equivalent liquid rates of 0.00070–0.0175 m 3 m −2 s −1). This agrees well with reported literature for mass transfer in a packed bed of solid particles under a laminar flow regime. Effect of the solution pH, temperature and the particle size (0.5, 1.0, 1.5 and 2.0 in.) on biosorption of Zn +2 and Ni +2 was also investigated. Biosorption of both Zn +2 and Ni +2 increased significantly with the solution pH from 4.0 to 7.0. On the other hand, Zn +2 and Ni +2 removal appeared to be insensitive to liquid temperature from 25 to 30 °C. Nevertheless, a 25% increase in the percentage removal of metal ions was observed with further increase of liquid temperature from 30 to 35 °C. However, the biosorbent particle size did not seem to have a systematic effect on the biosorption of Zn +2 and Ni +2. In addition, biosorption of Zn +2 was not affected considerably by co-adsorption of the bimetal solution while biosorption of Ni +2 decreased about 14%.

Hydraulic resistance of a granular bed in a rising liquid flow

Studies have been made on the hydrodynamics of the fluidized bed (FB) of solid particles in a rising liquid flow. The apparatus scheme is indicated. The hydraulic resistance in the region of an immobile layer is dependent on the initial height and increases in direct proportion to the velocity of the fluidizing medium. The experimental data agree satisfactorily with calculations from an equation that incorporates the effects of the ratio of the equipment diameter to the particle diameter for the bed of granular material on the hydraulic resistance.

Effect of injection-nozzle operating parameters on the interaction between a gas–liquid jet and a gas–solid fluidized bed

The objective of the present study was to provide insight into the effect of operating conditions on the performance of gas-assisted nozzles injecting liquid into gas–solid fluidized beds. Acquisition of such knowledge is relevant to many industrial applications where liquid injections into fluidized beds of solid particles are performed via spray nozzles. In the fluid coking process, for example, product yields and reactor operability strongly benefit from a rapid and uniform distribution of the liquid feed on fluidized solid particles, which, in turn, is greatly affected by the performance of the liquid-injection system used. A novel experimental technique was employed to investigate the effect of varying the air-to-liquid ratio (ALR), the liquid mass flow rate, and the nozzle size on the contact efficiency of injected liquid on fluidized bed particles. Increasing the ALR or the liquid flow rate increased the nozzle spraying efficiency. On the contrary, increasing the nozzle size while keeping the gas and the liquid flow rates constant, and hence decreasing the pressure at the nozzle tip, lowered the liquid–solid contact efficiency. The effect of increasing the ALR on the liquid–solid contact resulting from nozzle-injections into the fluid bed, was correlated to both the nozzle atomization performance, as determined by open-air tests using a laser-photocell equipment, and the solids entrainment into the gas–liquid jet, as predicted by a model.

Noninvasive Measurements of Gas Exchange in a Three-Dimensional Fluidized Bed by Hyperpolarized 129Xe NMR

We present a novel nuclear magnetic resonance (NMR) technique that provides a noninvasive, direct measurement of gas exchange in a three-dimensional gas-fluidized bed of solid particles. The NMR spectrum of hyperpolarized 129Xe gas in an Al2O3 particle bed displays three resolved peaks corresponding to xenon in bubbles, the interstitial spaces (emulsion), and adsorbed on particles. Modified NMR exchange and saturation recovery sequences, together with data analysis based on an exchange-coupled set of Bloch equations, yield gas exchange rate constants between the emulsion and adsorbed phases, and between the bubble and emulsion phases. The results are in approximate agreement with previously unverified predictions from well-known models of fluidized bed behavior. Incorporation of NMR imaging methodologies would straightforwardly allow similar measurements on a spatially resolved basis.

Novel triboelectric method for characterizing the performance of nozzles injecting gas-atomized liquid into a fluidized bed

Liquid injections into fluidized beds of solid particles are widely employed in many industrial applications, such as fluid coking, fluid catalytic cracking, and gas-phase polymerization, where rapid and uniform distribution of the liquid feed on fluidized solid particles is of crucial importance for minimizing the formation of undesired agglomerates, and maximizing product yields. Previous studies have shown that the quality of the interaction between liquid jets and a fluidized bed strongly depends upon the injection nozzle technology. To date, however, most of the experimental techniques available for assessing the efficiency of the injection of liquid sprays into a fluid bed are not suitable for scale up. The aim of this work was, thus, to develop at laboratory scale a novel experimental method, which could be easily implemented at larger scales. The signal generated by a triboelectric probe was used to define a performance index for nozzles injecting air-atomized water into a gas–solid fluidized bed. A second performance index was defined, which characterizes the quality of the liquid–solid mixing by means of bed temperature measurements. A linear relationship was found between the two nozzle performance indices.

Coupling between CFD and a bed model in a rotary kiln: application to the processing of aluminium waste

This paper deals with the coupling of Computational Fluid Dynamics (CFD) with 'home made' software for the prediction of pyrolysis within a rotary kiln. The 'home made' software describes the phenomena that occur within a bed of solid particles submitted to pyrolysis. It requires the net specific heat flux originating from the surroundings while it yields the specific mass flow of volatiles released from the bed. Used as a boundary profile condition into a CFD software, this specific mass flow rate of volatiles allows for prediction of oxidation phenomena in the gaseous phase.

Dynamic behavior of a solid particle bed in a liquid pool: SIMMER-III code verification

Dynamic behavior of solid particle beds in a liquid pool against pressure transients was investigated to model the mobility of core materials in a postulated disrupted core of a liquid metal fast reactor. A series of experiments was performed with a particle bed of different bed heights, comprising different monotype solid particles, where variable initial pressures of the originally pressurized nitrogen gas were adopted as the pressure sources. Computational simulations of the experiments were performed using SIMMER-III, a fast reactor safety analysis code. Comparisons between simulated and experimental results show that the physical model for multiphase flows used in the SIMMER-III code can reasonably represent the transient behaviors of pool multiphase flows with rich solid phases, as observed in the current experiments. This demonstrates the basic validity of the SIMMER-III code on simulating the dynamic behaviors induced by pressure transients in a low-energy disrupted core of a liquid metal fast reactor with rich solid phases.

Simulation of the Dynamic Behavior of the Solid Particle Bed in a Liquid Pool: Sensitivity of the Particle Jamming and Particle Viscosity Models

In order to model the mobility of the postulated disrupted core in a core disruptive accident of a liquid metal faster reactor and to provide data for the verification of a reactor safety analysis code (SIMMER-III) a series of experiments was performed to simulate the behavior of a solid particle bed in a liquid pool against pressure transients. Experimental analyses using the SIMMER-III code show that physical models and methods used in the code can reasonably represent the transient behaviors of pool multiphase flows with rich solid phases as observed in the experiments. The validation of several key models of SIMMER-III was also discussed for treating transient behaviors of the solid-particle phase in multiphase flows.

Simulation of the Dynamic Behavior of the Solid Particle Bed in a Liquid Pool: Sensitivity of the Particle Jamming and Particle Viscosity Models

In order to model the mobility of the postulated disrupted core in a core disruptive accident of a liquid metal faster reactor and to provide data for the verification of a reactor safety analysis code (SIMMER-III) a series of experiments was performed to simulate the behavior of a solid particle bed in a liquid pool against pressure transients. Experimental analyses using the SIMMER-III code show that physical models and methods used in the code can reasonably represent the transient behaviors of pool multiphase flows with rich solid phases as observed in the experiments. The validation of several key models of SIMMER-III was also discussed for treating transient behaviors of the solid-particle phase in multiphase flows.

Coffe drying on fluidised bed

All coffee is harvested as cherry grains which are then crushed and extracted traditionally or by applying the Becolsub method. Once the coffee parchment obtained has been washed, it is naturally or mechanically dried. Static dryers are the most used mechanical dryers, generally producing lack of uniformity in the grain's final humidity content which must range from 10% to 12% b.h. Drying by fluidization was used in the present research work; this turns a solid particle bed into a suspended and expanded mass, possessing many of the properties of a liquid. A 5,000 g capacity prototype was designed and constructed in which coffee was dried at three air drying temperatures: 42°C, 46°C and 49°C; drying time lasted 6 to 8 hours. Good uniformity in final grain humidity content was obtained, differences being less than 0.86%. As well as the grain test, a control cup test was used, finding that the product presented good organoleptic qualities.

Dynamic behavior of a solid particle bed in a water pool

In order to model the mobility of the postulated disrupted core in a core disruptive accident (CDA) of a liquid metal faster breeder reactor (LMFBR), a series of experiments was performed to simulate the behavior of a solid particle bed in a water pool against pressure transients. Numerical simulations with SIMMER-III code have been performed to verify the validity of SIMMER-III code and to check the influence of the particle jamming model and the particle viscosity model, which are adopted in the code. Comparisons between analytical results and experimental results show that SIMMER-III can well simulate the pressure transients and the particle bed axial height change in the first moment of the nitrogen gas expansion, while giving an earlier second pressure peak value than experiments. The simulation somewhat underestimates the gas volume change in the pressure vessel and the water pool. SIMMER-III results show that the particle jamming model and different assignments of velocity field have obvious influences on the particle volume fraction distribution inside the particle bed.

Measurement of Adhesive Forces during Coking of Athabasca Vacuum Residue

Processes for thermal conversion of vacuum residues in fluidized or moving beds of solid particles require excellent distribution of feed liquid onto the solid particles and free flow of the solids. Forces between the solid particles will be determined by the changing quantity and properties of the liquid material during reaction. This paper presents a unique apparatus for measuring pull-off forces between particles due to reacting liquid films. In the case of 25−30-μm-thick films of Athabasca vacuum residue at 503 °C, the maximum pull-off force occurred after ca. 12 s of reaction and then declined gradually until no force was detected after ca. 24 s of reaction. These data suggest that solid particles coated with vacuum residue would be adhesive for this period of time, while the film of feed material is still liquid and undergoing reaction.

A mechanistic model to determine the critical flow velocity required to initiate the movement of spherical bed particles in inclined channels

This study presents a mechanistic model that predicts the critical velocity, which is required to initiate the movement of solid bed particles. The model is developed by considering fluid flow over a stationary bed of solid particles of uniform thickness, which is resting on an inclined pipe wall. Sets of sand bed critical velocity tests were performed to verify the predictions of the model. An 80 mm flow loop with recirculation facilities was constructed to measure the critical velocities of the sand beds. The tests were carried out by observing the movement of the bed particles in a transparent pipe while regulating the flowrate of the fluid. Water and aqueous solutions of PolyAnoinic Cellulose were used as a test fluid. The critical velocities of four sand beds with different particle size ranges were measured. The model was used to predict the critical velocities of the beds. The model predictions and experimentally measured data show satisfactory agreement. The results also indicated that the critical velocity is influenced by the properties of the fluid, flow parameters, and particle size.

Simulation of Channel Growth in a Burning Bed of Solids

Packed beds of solid particles are widely used in solid fuel combustion, waste incineration, drying and filtration processes etc. where gases flow through the beds at a certain superficial velocity. Non-uniformity in the bed porosity causes uneven distribution of the gas flow rate across the bed, and in extreme cases free-flowing channels or passages can be formed in the beds, downgrading the performance of the bed processes. In this paper, experimental observations of channelling in the burning beds of municipal solid waste incinerators are described and detailed numerical simulation of the growth of an individual burning channel is carried out.

The Variable-Voidage Effect on Modeling the Minimum Liquid Fluidization Velocity of Gas-Liquid Fluidized Beds

By taking account of the experimentally determined variation of voidage with the gas velocity at minimum gas-liquid fluidization of a bed of solid particles, it is shown, using the same experimental database as in the earlier paper by Lee et al. (2001a), that the model which best predicts the minimum liquid fluidization velocity is a variant of the gas-perturbed liquid model of Zhang et al. (1995), but with the buoyancy term based on the gas-liquid mixture rather than the liquid alone. The best value of the constant in the viscous term of the Carman–Ergun drag equation involved is 165, intermediate between Carman’s 180 and Ergun’s 150.

FLUID BED ENCAPSULATION OF PARTICLES: PRINCIPLES AND PRACTICE

ABSTRACT The fluid bed encapsulation process consists of spraying a coating solution into a fluidized bed of solid particles. After several cycles of wetting–drying, a continuous film is formed. This paper provides an overview of the physical and transport phenomena involved in this process, especially in the so-called Wurster mode. Both qualitative and quantitative results are presented for several industrial applications. The main parameters affecting the process are flow-rate and pressure of the spraying liquid, composition and rheology of the coating solution, flow-rate and temperature of the fluidizing air. The particle size can range from 0.1 to several millimeters in equivalent diameter. The characteristics of the particle surface are important in determining adhesion of the liquid coating as well as its encapsulation properties.

Pressure Drop in Packed Shallow Beds of Cylindrical Cork Stoppers

The pressure drop through a packed bed of solid particles has been thoroughly studied and equations relating the pressure drop and the fiow rate of the fiuid were developed by many authors, mainly for relatively deep bed conditions. On the contrary, pressure drop evolution in shallow packed beds of cylindrical particles is still being studied, and standard equations for fixed beds are applicable to this situation only with gross limitations. The study and characterisation of air fiow through packed shallow beds of cork stoppers was carried out and consequently a simple analysis was developed and correlations obtained from experimental data.

Models for Minimum Liquid Fluidization Velocity of Gas-Liquid Fluidized Beds.

The gas-perturbed liquid model of Zhang et al. (1995) is modified in an effort to improve its prediction of the minimum liquid velocity of fluidization, Ulmf, of a bed of solid particles in the presence of a low or moderate cocurrent flow of gas. Variants of the model are considered where the buoyancy term is based on the gas-liquid mixture, instead of the liquid alone, and with the frictional pressure gradient given by several alternative equations to the Ergun equation employed in the original gas-perturbed liquid model. All versions of the model provide similar dependence on such factors as gas velocity, particle diameter, particle density and liquid viscosity as those seen experimentally. The mixture buoyed equation with the drag based on an equation suggested by Foscolo et al. (1983) gives improved predictions over the original Zhang et al. (1995) model, but the best overall agreement is with buoyancy based on the liquid alone and the first term in the drag equation with the Carman (1937) constant of 180 instead of Ergun's 150. The predictions are sensitive to the minimum fluidization voidage, which is measured, assumed, or estimated. Further work is required to investigate minimum liquid fluidization velocities experimentally for particles of density closer to that of the liquid, and for high-viscosity liquids.

Flow and Heat Transfer Within Segregated Beds of Solid Particles

Flow and Heat Transfer Within Segregated Beds of Solid Particles