Effect Of Cohesive Forces Research Articles

Gas-solid reaction induced particle collision and aggregation

Chemical reaction induced particle collision and aggregations in gas-solid phase reaction were presented in this work. The characteristics of particle collision and aggregations in non-catalytic gas-solid phase reaction- petcoke particles combustion process in air was experimentally analyzed. The reason for the formation of different aggregation structures is the reactant concentration distribution and particle position. Different spatial positions of solid particles caused the non-uniform concentration distribution of gaseous reactant and product around particle surface. The non-uniform distribution of gaseous reactant results in cohesive force, which lead to particle collision and aggregations. The aggregates of multi-particles tend to show “I” and “L” structure with the effect of cohesive force and drag force. Simulation work also were conducted to analyze the reactant and product concentrations, release velocity of product and bearing force of solid particles. The mechanisms of different particle aggregation patterns were demonstrated.

Geldart classification for wet particles

Cohesion may have a significant effect on particle fluidization. Strong cohesive forces may result in a non-fluidized bed of particles. The effect of cohesive forces mainly depends on the magnitude of the forces and the particle weight. Geldart's classification places materials into four groups based on particle diameter and density difference between the particles and the fluid. Each group has different fluidization characteristics caused by the cohesive forces; specifically, in Geldart's experiments, these were Van der Waals forces (VdWFs). This study presents an investigation of the cohesive forces in fluidized beds. Using Geldart's classification, it attempts to predict the classification of moist particulate materials, affected by the liquid bridge forces (LBFs) and fluidized in air. In order to do so, a model which calculates the LBFs was developed. The classification of the wet particles is predicted by calculating an equivalent diameter and using it in the Geldart chart.

Dynamic Effect of Soil-Tunnel Interface Under Dynamic Loading

The resilience of the Daikai subway station during the Kobe earthquake is taken as a case study of tunnel endurance at various points under different soil conditions. The Mohr-Coulomb material model is used. The effect of peak ground acceleration, overburden depth, and soil-tunnel interaction is analyzed. The effect of cohesive force on stresses for various soil tunnel interface conditions (full slip, partial slip, and no slip) is studied. The model is validated by comparing axial force and displacement, and its results are consistent with those presented in the literature.

Bubble Behaviors of Large Cohesive Particles in a 2D Fluidized Bed

Fluidization hydrodynamics is greatly influenced by interparticle cohesive forces. In this paper, we study the bubbling behaviors of cohesive Geldart B particles in a 2D fluidized bed, using the “polymer coating” approach to introduce cohesive force. The effect of cohesive force on bubbles can be differentiated into two regimes: (i) by increasing the cohesive force within a low level, the bubble number increases, while the bubble fraction and bubble diameter decrease; (ii) when the force is large enough to cause the particles to adhere to the side walls of the bed, the bubble numbers and the bed expansion sharply decrease. With the increasing cohesive force, the bubble shape changes from roughly circular shape, to oblong shape, leading to the “short pass” of fluidizing gas through the bed. Finally, we analyzed the switching frequency and standard deviation of local pixel values to characterize the bubble dynamics.

On the Effect of Cohesive Forces on Behavior of Thin-walled Elements in Overlapping Joints

Joints of longitudinal splicing of thin-walled purlins are as a rule a kind of overlapping bolted connections without preloading. The so connected elements are subject to mutual pressure while deforming under applied loads. The cohesive forces between the adjoining surfaces may be important. It can be forces of friction or cohesive forces in a glutinous layer between adjoining areas of profiles. In the joints of rallied runs fixed on girders, pasting can essentially prevent local buckling of flat parts of flanges and walls.Such three-layer structure can also help to avoid crushing and shrinkage of metal in the holes for bolts. Comparative results of numerical analysis for some joint variants with cohesion are considered.

Numerical simulation of particle settling and cohesion in liquid

In this study, the motions of particles and particle clusters in liquid were numerically simulated. The particles of two sizes (Dp=40μm and 20μm) settle while repeating cohesion and dispersion, and finally the sediment of particles are formed at the bottom of a hexahedron container which is filled up with pure water. The flow field was solved with the Navier-Stokes equations and the particle motions were solved with the Lagrangian-type motion equations, where the interaction between fluid and particles due to drag forces were taken into account. The collision among particles was calculated using Distinct Element Method (DEM), and the effects of cohesive forces by van der Waals force acting on particle contact points were taken into account. Numerical simulations were performed under conditions in still flow and in shear flow. It was found that the simulation results enable us to know the state of the particle settling and the particle condensation.

SIMULATION OF DRYING SUSPENSIONS IN SPOUT-FLUID BEDS OF INERT PARTICLES

In spouted and spout fluid bed dryers, the suspension is spread into the bed of inert particles, covering these particles with a thin layer. As the inert particles circulate, this suspension layer is dried and must become brittle enough to break off by the particle attrition. The powder produced is then carried out by air. Problems with the spout stability, particle agglomeration and powder deposits inside the column should be overcome by controlling the drying operation. The present work is aimed at modeling and simulating the drying of suspensions, such as organic and biological pastes, in conical spout-fluid beds of inert particles. A computer program has been developed combining the air flow and particle circulation models with the mass and energy balances and the drying kinetic equations in order to describe this drying process. The effect of cohesive forces is also incorporated to the fluid flow model. Simulation results are analyzed and compared with experimental data reported in the literature. Implication of these results in drying suspensions is also discussed.

Effect of cohesive forces on fluidized and spouted beds of wet particles

Fluid beds are now being used for processing pasty materials including production of fine powders through drying suspensions in beds of inert particles; coating of tablets or pellets; granulation, etc. In such processes, the fluid bed operation becomes more complex due to the development of cohesive forces resulting from liquid bridges between particles. Such forces can affect gas and solids flow leading to uncontrollable particle agglomeration and to poor gas–solid contact. This work is aimed at analyzing and quantifying the differences of flow behavior in fluidized and spouted beds of wet and dry particles. Experimentally, surface stickiness is induced by application of metered amounts of glycerol. Based on pressure drop vs. fluid flow rate curves, solids circulation rates and bed porosity variations, two types of particle–particle interaction forces are identified and their effect on air–solid flow is quantified as a function of glycerol concentration. Implications of these results in coating, granulation and drying of suspensions in these beds are also discussed.

The maximum acceleration of seismic ground motion

abstract A prediction of earthquake strong motion is attempted by studying the initial form of the seismic source-time function associated with a fracturing process described under idealized physical conditions. The effect of cohesive force on the source function is examined in detail, and the following relations are derived for the maximum particle velocity u⋅ M and the maximum acceleration u M u ˙ M ~ ( σ o / μ ) c , u ¨ M ~ ( σ o / μ ) 2 ( c 2 / D o ) where σ o is the strength of material, D o is the slip displacement required for the initial formation of crack surface, c is the rupture velocity, and μ is the rigidity. Using these relations, it is concluded that the earthquake source motion is not directly governed by the interatomic cohesion, but rather by the gross strength of rocks. In fact, if 1 kbar for σ o and 10 cm for D o are assumed, reasonable results, such as u⋅ M ∼ 1 m/sec and u M ∼ 1 g, are obtained, with the characteristic period and distance 0.1 sec and 100 meters, respectively. This result implies that the specific surface energy for the earthquake may be as large as 10 10 erg/cm 2 , which is much larger than the typical values (10 3 ) observed for rocks in the laboratory.