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Investigation On Gas-solid Two-phase Flow Characteristics Of Irregularly Shaped Particle In A Bubbling Fluidized Bed

Posted on:2015-02-10Degree:MasterType:Thesis
Country:ChinaCandidate:S N YanFull Text:PDF
GTID:2181330422490852Subject:Thermal Engineering
Abstract/Summary:PDF Full Text Request
Fluidized bed has a wide application in the field of petroleum, chemicalengineering, energy, environment protection, pharmacy, food processing and soon. No matter in the aspects of practical application or theoretical research,bubbling bed, which is the classical bed pattern of fluidized bed, has been a hottopic of relevant personnel. In the practical application, the particles in thebubbling fluidized bed usually are irregularly shaped. Compared with the regularshaped particles, the irregularly shaped particles can affect the gas-solid flowbehaviors of bubbling fluidized bed. The gas-solid flow behaviors of glass beadswith ellipsoidal shape, black millet with irregular spherical shape, yellow milletwith irregular spherical shape and sorghum rice with ellipsoidal shape wereinvestigated numerically and experimentally.In the numerical simulation, Euler-Euler two-fluid model is employed. Theconstitutive equation of solid-phase stress is closed on the basis of kinetic theoryof granular flow. Gidaspow drag model is adopted to investigate the exchange ofmomentum between gas and solid phase. The gas-solid flow behaviors of glassbeads and black millet, such as the distribution of voidage, concentration,velocity and granular temperature, are studied under the operating conditions ofdifferent inlet superficial gas velocities, different restitution coefficients anddifferent specularity coefficients. In the experiment, PIV (Particle ImageVelocimetry) is used to measure the velocity distribution of black millet, yellowmillet and sorghum rice in the bubbling fluidized bed.It is shown that, from the simulation results of gas-solid flow behaviors ofglass beads, the distribution of voidage, concentration, velocity and granulartemperature under different inlet superficial gas velocities are different. With theincrease of the superficial gas velocity, the movement of particles becomes moreviolent and the size of bubble becomes larger. Particles rise from the bottom ofthe bed and move downward at the top and side wall of the bed, which forms thecyclical movement of the particles in the bubbling bed. The granular temperatureat the top of the bed is larger than that at the bottom of the bed. The granulartemperature at the side wall of the bed is larger than that at the center and bottom of the bed. The concentration and axial velocity of the particles is higherwith higher restitution coefficient. The concentration of the particles increaseswith the increase of the specularity coefficient at the bottom and center of thebed, while it is just the opposite at the top of the bed. With the increase of thesuperficial gas velocity, the movement of black millet becomes more violent, andthe expansion of the bed becomes larger. The size of bubble becomes larger andnarrower. The granular temperature at the top of the bed is larger than that at thebottom of the bed. The granular temperature at the side wall of the bed is largerthan that at the center and bottom of the bed.Experimental investigation of black millet,yellow millet and sorghum riceshows that PIV can be applied to measure the velocity field of solid phase in thedense gas-solid two-phase flow. With the increase of the superficial gas velocity,the surface expansion of the black millet bubbling bed becomes larger. What’smore, the interaction of the gas and solid phase becomes stronger, and the shapeof the bubble becomes more irregular. The hydrodynamic characteristics of thebubbling bed is affected by the increase of the initial bed height. There arevisible differences among particles with different sizes. Black millet is theeasiest to be fluidized, while the sorghum is the hardest to be fluidized. Thefluidization of black millet presents the typical characteristics of bub blingfluidization. Desired results are obtained by comparing simulation withexperiment.
Keywords/Search Tags:bubbling fluidized bed, irregularly shaped particle, two-fluid model, PIV, velocity field
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