CFD simulation of gas–liquid flow in a hig(4)

distribution

axial velocity

Fig.7 shows the effect of operating pressures on radial distribution of gas rising results at four gas velocities show a gradual decrease from the center to the column wall,and the gas velocity increases with the increase in the operating pressure and apparent gas variation trend was consistent with the experiment reported by Wilkson et al.[34]

holdup on radial distribution(uG=0.160,0.215,0.253,0.317 m·s?1).

axial velocity

Fig.8 shows the effect of pressure on the radial profiles of water axial can be seen from Fig.8 that the axial liquid velocity gradually decreases from the center to the wall of the liquid velocity is positive in the center of the column and negative near the side wall of the indicates that the liquid phase appears to circulate in the liquid circulation is in favor of gas–liquid fully difference in axial velocity is not significant at different operating pressures,indicating that the liquid velocity is not greatly affected by the simulated results affected by pressure at other apparent gas velocities(0.215,0.253,0.317 m·s?1)are similar to result of 0.160 m·s?1.

diameter in the radial direction(uG=0.160,0.215,0.253,0.317 m·s?1).

of the Modified CFD-PBM Coupled Model

The experiment of Wilkson and Dierendonck[34]mainly examined the influence of pressure on gas hold-up and bubble size in bubble column had a diameter of 0.16 m,the height of column was 2.0 m.The liquid was deionized water(20°C),and gas was the research of Reilly et al.[35]it is known that the influence of column diameter on gas-holdup can be we choose the experimental data of gas-holdup versus superficial gas velocity for the water/nitrogen system[34]to validate the modified CFD-PBM coupled model.

Fig.9 shows the comparison between simulation results by the modified CFD-PBM coupled model and Wilkson's experimental data[34]under each pressure(0.5,1.0,1.5 MPa)at different apparent gas can be seen,the simulation results of gasholdup are basically in agreement with the experimental data.So it shows that the modified CFD-PBM coupled model according to the experimental data of Qin[14]can be applied to the simulation under other experimental conditions.

of operating pressure on bubble size distribution at 0.160 m·s?1.

The work focused on simulating the effects of operating pressure on hydrodynamic CFD-PBM coupled model was employed to investigate the gas–liquid flow in a high-pressure bubble the work,the following conclusions can be draw n:

water velocity at different pressure simulated with Ce(uG=0.160 m·s?1).

(1)From the comparison between experimental data and simulation results by two models(the CFD-PBM coupled model and the modified CFD-PBM coupled model),it can be seen that the latter model offers good agreement with experimental data.So the effects of operating pressure on the hydrodynamic parameters can be well predicted by the modified CFD-PBM coupled model.

(2)The effects of operating pressure on the bubble size distribution were predicted by the modified CFD-PBM coupled model in gas–liquid flow.The bubble size became smaller and more uniform at elevated pressure.

(3)Through the validation of the modified CFD-PBM coupled model with the water-nitrogen system of Wilkson and Dierendonck[34],it can be seen that the simulation results are in good agreement with the experimental the modified model may be applied to other experimental systems.

axial velocity at different gas velocities and pressures.

holdup under different apparent gas velocities.

Nomenclature

CDdrag coefficient

CD,∞ideal state drag coefficient

CLtransverse lift coefficient

CTDturbulent dispersion coefficient

CWLwall lubrication coefficient

dBdiameter of bubble,m

E0parameter E0

Fexinterphase forces

FDdrag force,N·m?3

FLtransverse lift,N

FTD,LFTD,Gturbulent dispersion force,N

fTD,limitingturbulent diffusion force model limiting function

FWLwall lubrication force,N

Gkturbulence energy generation

Gbk term of turbulent kinetic energy

g gravity acceleration,m·s?2

k,kLturbulent kinetic energy,m2·s?2

P operating pressure,Pa

Poatmospheric pressure under standard conditions,Pa

P(ViVj) bubble coalescence efficiency

Uivelocity,m·s?1,i=1:gas phase,i=2:liquid phase

uGgas velocity,m·s?1

uLliquid velocity,m·s?1

uijcharacteristic velocity of bubble collision\

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