Development of modeling and simulation of bubble‐liquid hydrodynamics in bubble column

Abstract

In the present work, the investigation on strategies to alleviate the cell death in terms of bubble‐liquid two‐phase hydrodynamics in bubble column was performed using the modeling and numerical simulation approaches. A multifluid bubble‐liquid turbulent model based on the second‐order moment algorithm was developed to predict turbulent hydrodynamics. In this model, the anisotropic characteristics of Reynolds stresses and the interactions between bubble and liquid phases are considered by means of the defined bubble‐liquid two‐phase fluctuation velocities correlation. Hydrodynamic parameters such as turbulent energy dissipation rate, the turbulent kinetic energy, the distributions of bubble normal and shear stresses, and the operation conditions of gas entrance velocity and height to diameter of column are accurately simulated. A proposed correlation named turbulent energy production rate is revealed successfully the higher cell death rate at the gas inlet regions that cannot be verified by the rest of the two‐phase hydrodynamics. Superficial gas velocity is the predominant influence on this value distribution as smaller the ratio of height to diameter of bubble column, which reduced by two order of magnitude under decreased by one level of gas velocity. Near inlet region with large height‐to‐diameter ratio, this value is always larger than those of small one.

A novel design on smooth rotor profile with meshing clearance for screw vacuum pump

“…The semi-implicit pressure linked equations-corrected (SIMPLEC) algorithm to correct p-v correlation with tri-diagonal marching algorithm (TDMA) line-by-line iteration, underrelaxation quadratic upstream interpolation, convective kinematics (QUICK) procedure and the central difference scheme (CDS) for the diffusion terms are made for the solution of the finite differential equations and this algorithm will be improved in the future based on our previous works. [26][27][28] The pressure boundary condition is set to the inlet and outlet, and the velocity boundary condition is set to the outer surface of the rotors. The boundary conditions are listed as follows: the inlet pressure is 861 Pa, outlet pressure is about 101,325 Pa, the female rotor speed is approximately 2900 r/min, the male rotor speed is 2900 r/min, respectively.…”

Hydrodynamic Modeling of Turbulence Modulation by Particles in a Swirling Gas–Particle Two-Phase Flow

“… 41 The threshold of particle volume fraction (α) to characterize effects of particle on gas turbulence was firstly proposed, that is the one-way coupling (α < 10 –6 ), the two-way coupling (10 –6 < α < 10 –3 ), and the four-way coupling (α > 10 –3 ). 42 By using the DNS algorithm, gas turbulence was attenuated by fine particles in developing the boundary layer and fully developed channel flows when mass loading ratios are greater than 10%. 18 Turbulence modulation is more highly sensitive to the effect of mass loading rather than the particle response.…”

“…Turbulence modification was characterized into augmentation and attenuation categories using a developed intuitive parameter, which is the ratio of the particle diameter to a characteristic size of large eddies . The threshold of particle volume fraction (α) to characterize effects of particle on gas turbulence was firstly proposed, that is the one-way coupling (α < 10 –6 ), the two-way coupling (10 –6 < α < 10 –3 ), and the four-way coupling (α > 10 –3 ) . By using the DNS algorithm, gas turbulence was attenuated by fine particles in developing the boundary layer and fully developed channel flows when mass loading ratios are greater than 10% .…”

“…A two-phase turbulent Reynolds stress model to predict the swirling particle dispersions in behind a sudden tube expansion was improved for simulation; results show that the fine particle attenuates the gas turbulence of up 25% . A series of the second-order moment gas–particle and gas–liquid turbulent models to simulate the anisotropic dispersions of particle and bubble, and hydrodynamics of gas–particle, and bubble-particle two-phase flows were developed to successfully reveal the anisotropic characteristics, the redistributions of Reynolds stresses of two phases, and the mixing and separation behaviors. − …”

Hydrodynamics of Irregular-Shaped Graphite Particles in Coaxial Two-Phase Jet Flow

“…The aim of the present study is to explore the effects of irregular shape on the hydrodynamics of ultralight expanded graphite turbulent flows. The first proposed second-order moment model have successfully simulated the anisotropic dispersions of the particle and bubble and the hydrodynamics of gas–particle and bubble–particle two-phase flows. − ,− In this work, a frictional kinetic stress coupling second-order moment model was improved to simulate the swirling nonspherical particle flow in a coaxial chamber. Momentum interactions between nonspherical particles and gas are described by Yan’s model .…”