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781.
J. M. P. Q. Delgado 《Heat and Mass Transfer》2006,42(12):1119-1128
The present work describes the mass transfer process between a moving fluid and a slightly soluble cylinder, with the axis perpendicular to flow direction, buried in a packed bed of small inert particles, with uniform voidage. Fluid flow in the packed bed around the cylinder was assumed to follow Darcy’s law and, at each point, dispersion of solute was assumed to be determined by radial and axial dispersion coefficients, in the cross-stream and streamwise directions, respectively. Numerical solutions of the differential equation describing solute mass conservation were undertaken to obtain the concentration field near the soluble surface and the mass transfer flux was integrated to give the Sherwood number as a function of the relevant parameters. Mathematical expressions are proposed that describes accurately the dependence found numerically between the value of the Sherwood number and the values of Peclet number, Schmidt number and the ratio between the diameter of cylinder and the diameter of inerts. 相似文献
782.
A CORRELATION EQUATION FOR CALCULATING INCLINED JET PENETRATION LENGTH IN A GAS-SOLID FLUIDIZED BED 总被引:1,自引:0,他引:1
Ruoyu Hong Haibing Li Jianmin Ding Hongzhong Li 《中国颗粒学报》2005,3(5):279-285
Numerical simulation of gas-solid flow in a two-dimensional fluidized bed with an inclined jet was performed. The numerical model is based on the two-fluid model of gas and solids phase in which the solids constitutive equations are based on the kinetic theory of granular flow. The improved ICE algorithm, which can be used for both low and high-velocity fluid flow, were used to solve the model equations. The mechanism of jet formation was analyzed using both numerical simulations and experiments. The emergence and movement of gas bubbles were captured numerically and experimentally. The influences of jet velocity, nozzle diameter, nozzle inclination and jet position on jet penetration length were obtained. A semi-empirical expression was derived and the parameters were correlated from experimental data. The correlation equation, which can be easily used to obtain the inclined jet penetration length, was compared with our experimental data and published correlation equations. 相似文献
783.
Bing Du W. Warsito Liang-Shih Fan 《中国颗粒学报》2006,4(1):1-8
1. Introduction Injections of evaporative liquids into fluidized solid parti- cles are routinely practiced in industrial processes involv- ing gas-solid fluidization systems such as fluid catalytic cracking, polymerization, and plastic coating (Fan et al., 2001). In the FCC riser system, heavy oil is injected into the system to evaporate rapidly by contact with the hot catalyst particles. Simultaneously, thermal and catalytic cracking reactions take place. During a polymerization process, a … 相似文献
784.
The application of a volume average Navier-Stokes equation for the prediction of pressure drop in packed beds consisting of uniform spherical particles is presented. The development of the bed permeability from an assumed porous microstructure model is given. The final model is quasi-empirical in nature, and is able to correlate a wide variety of literature data over a large Reynolds number range. In beds with wall effects present the model correlates experimental data with an error of less than 10%. Numerical solutions of the volume averaged equation are obtained using a penalty finite element method.Nomenclatures
d
length of a representative unit cell
-
d
e
flow length in Representative Unit Cell
-
d
p
characteristic pore size
-
D
T
column diameter
-
D
P
equivalent particle diameter
-
e
v
energy loss coefficient for elbow
-
f
app
apparent friction factor
-
f
v
packed bed friction factor, defined by Equation (30)
-
F
term representing impermeability of the porous medium
-
I
integral defined by Equation (3)
-
L
length of packed column
-
N
Number of RUC in model microstructure
-
P
pressure
-
P
interstitial pressure
-
P
pressure deviation
- Rep
Reynolds number,v
p
d
p/
- Res
Reynolds number,v
s
d/gm
- Reb
Reynolds number,v
s
D
p/
-
S
fs
fluid solid contact area
-
T
tortuosity
-
v
fluid velocity
-
v
velocity deviation
-
v
p
velocity in a pore
-
v
s
superficial velocity in the medium
-
v
interstitial velocity
-
V
o
total volume of representative unit cell
-
V
pore volume of representative unit cell
-
change in indicated property
-
u
normal vector onS
fs
-
porosity
-
viscosity
-
density
-
coefficient in unconsolidated permeability model 相似文献
785.
786.
Hongzhong Li 《中国颗粒学报》2005,(2)
A theory of nonfluidized gas-solids flow, which combines the theory of multiphase flow with the mechanics of particulate media, was proposed on the basis of understanding that the particles contact each other, solids and gas are in movement, and the drag force on the particles caused by interstitial gas flow is similar to gravity force having the property of mass force. Then this theory was verified by experiments on vertical and inclined moving beds, and was applied to calculation and design of equipment and devices with moving beds, such as pneumatic moving bed transport,dipleg, V-value, L-valve, orifice flow, and arching prevention. It can be used to guide the design and operation of moving beds and fixed beds. 相似文献
787.
H. Zhang J.-X. Zhu 《中国颗粒学报》2006,4(3):167-177
In a 9.3 m high and 0.10 m i.d. gas-solids downflow fluidized bed (downer), the radial and axial distributions of the local solids holdups and particle velocities along the downer column were measured with the superficial gas velocity set to zero. A unique gas-solids flow structure was found in the downer system with zero gas velocity, which is completely different from that under conditions with higher gas velocities, in terms of its radial and axial flow structures as well as its micro flow structure. The gas-solids flow pattern under zero gas velocity conditions, together with that under low gas velocity conditions, can be considered as a special regime which differs from that under higher gas velocity conditions. According to the hydrodynamic properties of the two regimes, they can be named the "dense annulus" regime for the flow pattern under zero or low gas velocity conditions and the "dense core" regime for that under higher gas velocity conditions. 相似文献
788.
Shoichiro Fukusako Masahiko Yamada Hisashi Morizane Myoung-Hwan Kim 《Experimental Thermal and Fluid Science》1993,6(4):353-359
An experimental study was performed to determine the melting heat transfer characteristics along a horizontal heated circular tube immersed in a solid-air-liquid three-phase fluidized liquid ice bed. A mixture of fine ice particles and ethylene glycol acqueous solution was adopted as the liquid ice for the test. Measurements were carried out for a range of parameters such as airflow rate, heated tube diameter, and initial concentration of acqueous binary solution. It was found that the heat transfer coefficient for the fluidized liquid ice bed might be more than 20 times as large as that for the fixed liquid ice bed. 相似文献
789.
Because of their advantages of high efficiency and low cost, numerical research methods for large-scale circulating fluidized bed (CFB) apparatus are gaining ever more importance. This article presents a numer- ical study of gas-solid flow dynamics using the Eulerian granular multiphase model with a drag coefficient correction based on the energy-minimization multi-scale (EMMS) model. A three-dimensional, full-loop, time-dependent simulation of the hydrodynamics of a dense CFB apparatus is performed. The process parameters (e.g., operating and initial conditions) are provided in accordance with the real experiment to enhance the accuracy of the simulation. The axial profiles of the averaged solid volume fractions and the solids flux at the outlet of the cyclone are in reasonable agreement with experimental data, thereby verifying the applicability of the mathematical and physical models. As a result, the streamline in the riser and standpipe as well as the solids distribution contours at the cross sections is analyzed. Computational fluid dynamics (CFD) serves as a basis for CFB modeling to help resolve certain issues long in dispute but difficult to address experimentally. The results of this study provide the basis of a general approach to describing dynamic simulations of gas-solid flows. 相似文献
790.
《Particuology》2014
A computational fluid dynamics (CFD) modeling of the gas–solids two-phase flow in a circulating fluidized bed (CFB) riser is carried out. The Eularian–Eularian method with the kinetic theory of granular flow is used to solve the gas–solids two-phase flow in the CFB riser. The wall boundary condition of the riser is defined based on the Johnson and Jackson wall boundary theory (Johnson & Jackson, 1987) with specularity coefficient and particle–wall restitution coefficient. The numerical results show that these two coefficients in the wall boundary condition play a major role in the predicted solids lateral velocity, which affects the solid particle distribution in the CFB riser. And the effect of each of the two coefficients on the solids distribution also depends on the other one. The generality of the CFD model is further validated under different operating conditions of the CFB riser. 相似文献