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761.
《Particuology》2014
In this work, a new drag model for TFM simulation in gas–solid bubbling fluidized beds was proposed, and a set of equations was derived to determine the meso-scale structural parameters to calculate the drag characteristics of Geldart-B particles under low gas velocities. In the new model, the meso-scale structure was characterized while accounting for the bubble and meso-scale structure effects on the drag coefficient. The Fluent software, incorporating the new drag model, was used to simulate the fluidization behavior. Experiments were performed in a Plexiglas cylindrical fluidized bed consisting of quartz sand as the solid phase and ambient air as the gas phase. Comparisons based on the solids hold-up inside the fluidized bed at different superficial gas velocities, were made between the 2D Cartesian simulations, and the experimental data, showing that the results of the new drag model reached much better agreement with experimental data than those of the Gidaspow drag model did. 相似文献
762.
污水污泥流化床气化焦油的化学组成分析 《燃料化学学报》2017,45(6):761-768
以空气为气化剂、并通过GC-MS分析,研究了污水污泥流化床气化时气化温度(650、750和850 ℃)和污泥性质对污泥气化焦油产率及其化学组成的影响。结果表明,污泥气化焦油产率随气化温度的升高而降低,且厌氧消化污泥气化焦油的产率比未消化污泥的低。污泥气化焦油中的化学组成可分为五类:脂肪族化合物、脂环化合物、芳香烃、芳香烃衍生物和杂环化合物。随气化温度的升高,A2/O工艺的未消化污泥气化生成的焦油中脂肪族化合物和脂环化合物的产率均明显降低,芳香烃衍生物的产率则有显著地提高,而芳香烃和杂环化合物的产率均先增加后减少。气化温度为650 ℃时,活性污泥法消化污泥气化焦油中五类有机物的产率均低于未消化污泥的,而A2/O工艺消化污泥气化焦油中芳香烃产率高于未消化污泥的,其他四种有机物的产率则均低于未消化污泥的。 相似文献
763.
A. A. Shapiro P. G. Bedrikovetsky A. Santos O. O. Medvedev 《Transport in Porous Media》2007,67(1):135-164
A population balance model for particulate suspension transport with capture of particles by porous medium accounting for
complete and incomplete plugging of pores by retained particles is derived. The model accounts for pore space accessibility,
due to restriction on finite size particle movement through the overall pore space, and for particle flux reduction, due to
transport of particles by the fraction of the overall flux. The novel feature of the model is the residual pore conductivity
after the particle retention in the pore and the possibility of one pore to capture several particles. A closed system of
governing stochastic equations determines the evolution of size distributions for suspended particles and pores. Its averaging
results in the closed system of hydrodynamic equations accounting for permeability and porosity reduction due to plugging.
The problem of deep bed filtration of a single particle size suspension through a single pore size medium where a pore can
be completely plugged by two particles allows for an exact analytical solution. The phenomenological deep bed filtration model
follows from the analytical solution. 相似文献
764.
The steady axisymmetric flow of an incompressible fluid into a vertical well hydrodynamically perfectly drilled into a stratified inhomogeneous half-space consisting of three layers with different permeabilities is considered. The boundaries of the layers are assumed to be horizontal planes and the roof of the upper layer is assumed to be impermeable. The flow obeys a linear Darcy’s law. The pressure distribution on the well is assumed to be given, which is the main obstacle to finding an exact solution of the problem. Beginning with the classical studies of Muskat and Charnyi [1, 2], approximate solutions of such problems have been constructed as a superposition of flows generated by point sources with given intensities, distributed along the well axis in accordance with a fairly simple law. In the present study, this approach is used to obtain an integral equation for the source density distribution, which is then solved numerically. Comparison with the known exact solution for a thin elongated ellipsoid (“needle”) shows that this approach makes it possible to ensure an accuracy which at any rate is sufficient for applications. 相似文献
765.
766.
A three-dimensional simulation study is performed for investigating the hydrodynamic behaviors of a cross-flow liquid nitrogen spray injected into an air-fluidized catalytic cracking (FCC) riser of rectangular cross-section. Rectangular nozzles with a fixed aspect ratio but different fan angles are used for the spray feeding. While our numerical simulation reveals a generic three-phase flow structure with strong three-phase interactions under rapid vaporization of sprays, this paper tends to focus on the study of the effect of nozzle fan angle on the spray coverage as well as vapor flux distribution by spray vaporization inside the riser flow. The gas-solid (air-FCC) flow is simulated using the multi-fluid method while the evaporating sprays (liquid nitrogen) are calculated using the Lagrangian trajectory method, with a strong two-way coupling between the Eulerian gas-solid flow and the Lagrangian trajectories of spray. Our simulation shows that the spray coverage is basically dominated by the spray fan angle. The spray fan angle has a very minor effect on spray penetration. The spray vaporization flux per unit area of spray coverage is highly non-linearly distributed along the spray penetration. The convection of gas-solid flow in a riser leads to a significant downward deviation of vapor generated by droplet vaporization, causing a strong recirculating wake region in the immediate downstream area of the spray. 相似文献
767.
P.R. Tortora S.L. Ceccio T.J. O’Hern S.M. Trujillo J.R. Torczynski 《International Journal of Multiphase Flow》2006
An electrical impedance tomography (EIT) system has been developed to non-invasively measure particle distributions in the riser of a pilot-scale circulating fluidized bed (CFB). Although EIT systems have often been applied to yield qualitative information about gas–solid flows, the present EIT system yields quantitative information that is validated by comparison to a gamma densitometry tomography (GDT) system. EIT and GDT were applied to the CFB riser (14-cm inner diameter, 5.77-m height) containing fluid catalytic cracking particles in air. The flows examined were annular with a dilute core and had average and near-wall solids volume fractions up to 0.25 and 0.66, respectively. For all cases, the average and near-wall solids volume fractions from EIT and GDT agreed to within 0.03 and 0.07, respectively. This good agreement suggests that, where feasible, EIT can be used in place of GDT, which is advantageous since EIT systems are often safer, less expensive, and faster than GDT systems. 相似文献
768.
769.
A population balance model for a particulate suspension transport with size exclusion capture of particles by porous rock
is derived. The model accounts for particle flux reduction and pore space accessibility due to restriction for large particles
to move through smaller pores – a particle is captured by a smaller pore and passes through a larger pore. Analytical solutions
are obtained for a uniform pore size medium, and also for a medium with small pore size variation. For both cases, the equations
for averaged concentrations significantly differ from the classical deep bed filtration model. 相似文献
770.
Amaury C. Alvarez Gustavo Hime Dan Marchesin Pavel G. Bedrikovetsky 《Transport in Porous Media》2007,70(1):43-62
Deep bed filtration of particle suspensions in porous media occurs during water injection into oil reservoirs, drilling fluid
invasion of reservoir production zones, fines migration in oil fields, industrial filtering, bacteria, viruses or contaminants
transport in groundwater etc. The basic features of the process are particle capture by the porous medium and consequent permeability
reduction. Models for deep bed filtration contain two quantities that represent rock and fluid properties: the filtration
function, which is the fraction of particles captured per unit particle path length, and formation damage function, which
is the ratio between reduced and initial permeabilities. These quantities cannot be measured directly in the laboratory or
in the field; therefore, they must be calculated indirectly by solving inverse problems. The practical petroleum and environmental
engineering purpose is to predict injectivity loss and particle penetration depth around wells. Reliable prediction requires
precise knowledge of these two coefficients. In this work we determine these quantities from pressure drop and effluent concentration
histories measured in one-dimensional laboratory experiments. The recovery method consists of optimizing deviation functionals
in appropriate subdomains; if necessary, a Tikhonov regularization term is added to the functional. The filtration function
is recovered by optimizing a non-linear functional with box constraints; this functional involves the effluent concentration
history. The permeability reduction is recovered likewise, taking into account the filtration function already found, and
the functional involves the pressure drop history. In both cases, the functionals are derived from least square formulations
of the deviation between experimental data and quantities predicted by the model. 相似文献