By electrical resistance tomography (ERT) the cross sectional profiles of gas hold-up in a φ56mm bubble column are obtained with four designs of gas sparger. The effect of sparger geometry on the bubble distribution ...By electrical resistance tomography (ERT) the cross sectional profiles of gas hold-up in a φ56mm bubble column are obtained with four designs of gas sparger. The effect of sparger geometry on the bubble distribution is re-vealed by applying a sensitivity conjugated gradients reconstruction method (SCG). Experimental results show that over-all hold-up obtained by ERT is generally in good agreement with those measured with the pressure transducer and the ERT system produces informative evidence that the radial profiles of hold-up is very similar to the sparger design in the lower section of bubble column. Meanwhile, the rise velocity of bubble swarm and the Sauter mean bubble size are evaluated using ERT based on dynamic gas disengagement theory. The experimental results are in good agreement with correlations and conventional estimation obtained using pressure transmitter methods.展开更多
In many gasliquid processes, the initial bubble size is determined by a series of operation parameters along with the sparger design and gasliquid flow pattern. Bubble formation models for variant gasliquid flow pat t...In many gasliquid processes, the initial bubble size is determined by a series of operation parameters along with the sparger design and gasliquid flow pattern. Bubble formation models for variant gasliquid flow pat terns have been developed based on force balance. The effects of the orientation of gasliquid flow, gas velocity, liquid velocity and orifice diameter on the initial bubble size have been clarified. In ambient airwater system, thesultable gasllquid flow pattern is important to obtain smaller bubbles under the low velocity liquid crossflow con ditions with stainless steel spargers. Among the four types of gasliquid flow patterns discussed, the horizontal orifice in a vertically upward liquid flow produces the smallest initial bubbles. However the orientation effects of gas and liquid flow are found tobe insgnifican whenliq.uid velocity is.higher than. 3.2 m;sa or theorifice diameter is small enough.展开更多
An apparatus, designed to simulate bubbling of sieve tray operatedin froth regime, was employed. Bubble contact angles in and above theincipient weeping regime for an air-water-plexiglas system wereinvestigated. The i...An apparatus, designed to simulate bubbling of sieve tray operatedin froth regime, was employed. Bubble contact angles in and above theincipient weeping regime for an air-water-plexiglas system wereinvestigated. The influence of both liquid cross-flow and gas up-flowupon bubble contact angles was examined. A model consider- Ing theinfluence of liquid cross-flow was developed to predict bubble sizefrom a sieve hole in froth operation regime. The comparison showsthat the bubble sizes predicted by the present model are consistentwith our experimental Values and the available published experimentaldata.展开更多
The flow fields surrounding two parallel moving bubbles rising from two identical orifices submerged in non-Newtonian fluid of carboxymethylcellulose （CMC） solution of three different mass concentration were measure...The flow fields surrounding two parallel moving bubbles rising from two identical orifices submerged in non-Newtonian fluid of carboxymethylcellulose （CMC） solution of three different mass concentration were measured experimentally by the use of particle image velocimetry （PIV）. The influences of gas flowrate, solution mass concentration, orifice interval and the angle between two bubble centers line and vertical direction on the flow field surrounding bubbles were discussed respectively by analyzing the velocity vector, velocity contours as well as individual velocity components. The results show that the liquid velocity both in front of two bubbles and behind increases with gas flowrate duo to shear-thinning effect of previous bubbles, whereas decreases with the increase of CMC concentration due to the increase of drag force acting on bubbles. The effect of the orifice interval on the flow field around two moving bubbles becomes gradually obvious as the interval becomes closer. Moreover, two adjacent side-by-side bubbles repulse each other during rising, leading to the practical interval between them increased somewhat above the orifice interval. When the distance between bubbles is less than the orifice interval 10 mm, the interaction between two neighboring bubbles changed from mutual repellence to attraction with the decrease of the angle of the line of linking two bubble centers to the vertical direction.展开更多
Dispersed multiphase flows,including gas-particle(gas-solid),gas-spray,liquid-particle(liquid-solid) ,liquid-bubble,and bubble-liquid-particle flows,are widely encountered in power,chemical and metallurgical,aeronauti...Dispersed multiphase flows,including gas-particle(gas-solid),gas-spray,liquid-particle(liquid-solid) ,liquid-bubble,and bubble-liquid-particle flows,are widely encountered in power,chemical and metallurgical,aeronautical and astronautical,transportation,hydraulic and nuclear engineering. In this paper,advances and re-search needs in fundamental studies of dispersed multiphase flows,including the particle/droplet/bubble dynamics,particle-particle,droplet-droplet and bubble-bubble interactions,gas-particle and bubble-liquid turbulence interac-tions,particle-wall interaction,numerical simulation of dispersed multiphase flows,including Reynolds-averaged modeling(RANS modeling),large-eddy simulation(LES) and direct numerical simulation(DNS) are reviewed. The research results obtained by the present author are also included in this review.展开更多
Bubbly gas-liquid Taylor-Couette vortex flow has been the subject of several recent investigations both because of interest in bubble-induced drag reduction and because such devices have potential applications to a va...Bubbly gas-liquid Taylor-Couette vortex flow has been the subject of several recent investigations both because of interest in bubble-induced drag reduction and because such devices have potential applications to a variety of chemical and biochemical processing problems. In order to quantitatively describe the hydrodynamics of highly turbulent two phase Taylor-Couette flow, a rigorous two-fluid computational fluid dynamics （CFD） model was developed and compared with previously published experimental data. This model includes a comprehensive description of the constitutive closure for inter-phase forces and turbulence was simulated using both the k- and k-to models. In addition, the mechanism by which the dispersed fluid attains a non-uniform radial and axial distribution is analyzed and the relative importance of various interphase forces is discussed. Lastly the model was validated by comparison of simulation predictions with experimental data, and it is shown that the CFD model correctly predicts phase velocity, velocity fluctuation, and gas distribution, and may provide guidance for reactor design and scale-up.展开更多
The chaotic characteristics of bubbles rising with accompanying coalescences in pseudoplastic aqueous carboxymethylcellulose sodium(CMC)solution were studied by means of smoothed pseudo Wigner-Ville distribution and W...The chaotic characteristics of bubbles rising with accompanying coalescences in pseudoplastic aqueous carboxymethylcellulose sodium(CMC)solution were studied by means of smoothed pseudo Wigner-Ville distribution and Wigner-Hough distribution.The temporal signal of bubble passage was measured utilizing a photoconductive data acquisition system.As bubble coalescence occurred,the smoothed pseudo Wigner-Ville distribution of the signal revealed that the signal could be divided into low-frequency and high-frequency ranges and the transition range according to the distribution feature of frequency domain,which reflected eddy motion of fluid,high frequency fluctuations of fluid velocity and other random components measured in the signal,and bubbles rising accompanied with coalescences,respectively.However,bubble coalescence occurred in the lower position and the frequency range of bubbles motion became wide under higher gas flowrate,while the frequency range of bubbles motion became narrow when the CMC concentration increased.The typical dynamics of bubbles motion,such as periodicity,bifurcation and chaos,could be easily found in terms of the Wigner-Hough distribution.展开更多
In this work, a numerical study for designing a new kind of MHD （Magneto-Hydrn-Dynamic） pumps is presented. This technique makes a compromise between electrolysis prevention and high flow rate performance. This tech...In this work, a numerical study for designing a new kind of MHD （Magneto-Hydrn-Dynamic） pumps is presented. This technique makes a compromise between electrolysis prevention and high flow rate performance. This technique should eliminate electrolytic bubble generation, electrodes wear and fluid propriety modification. All these side phenomena are prevented by considering isolated electrodes. The numerical presented results in this paper demonstrate that continuous MHD pumping is possible with isolated electrodes. The MHD excitation combines a high frequency altering current with a low frequency altering magnetic field. In order to validate our results, two independent theoretical methods for computing flow rate are followed. The two presented independent approaches show that high flow rate is possible even with isolated electrodes. To overcome the problem of dimensioning this kind of pumps, a generic numerical analysis is proposed. Hence, the pump performances as functions of the external parameter are studied and tools to calculate for a given fluid and the optimal high frequency regime are provided.展开更多
文摘By electrical resistance tomography (ERT) the cross sectional profiles of gas hold-up in a φ56mm bubble column are obtained with four designs of gas sparger. The effect of sparger geometry on the bubble distribution is re-vealed by applying a sensitivity conjugated gradients reconstruction method (SCG). Experimental results show that over-all hold-up obtained by ERT is generally in good agreement with those measured with the pressure transducer and the ERT system produces informative evidence that the radial profiles of hold-up is very similar to the sparger design in the lower section of bubble column. Meanwhile, the rise velocity of bubble swarm and the Sauter mean bubble size are evaluated using ERT based on dynamic gas disengagement theory. The experimental results are in good agreement with correlations and conventional estimation obtained using pressure transmitter methods.
基金Supported by the National Natural Science Foundation of China （20736009）.
文摘In many gasliquid processes, the initial bubble size is determined by a series of operation parameters along with the sparger design and gasliquid flow pattern. Bubble formation models for variant gasliquid flow pat terns have been developed based on force balance. The effects of the orientation of gasliquid flow, gas velocity, liquid velocity and orifice diameter on the initial bubble size have been clarified. In ambient airwater system, thesultable gasllquid flow pattern is important to obtain smaller bubbles under the low velocity liquid crossflow con ditions with stainless steel spargers. Among the four types of gasliquid flow patterns discussed, the horizontal orifice in a vertically upward liquid flow produces the smallest initial bubbles. However the orientation effects of gas and liquid flow are found tobe insgnifican whenliq.uid velocity is.higher than. 3.2 m;sa or theorifice diameter is small enough.
文摘An apparatus, designed to simulate bubbling of sieve tray operatedin froth regime, was employed. Bubble contact angles in and above theincipient weeping regime for an air-water-plexiglas system wereinvestigated. The influence of both liquid cross-flow and gas up-flowupon bubble contact angles was examined. A model consider- Ing theinfluence of liquid cross-flow was developed to predict bubble sizefrom a sieve hole in froth operation regime. The comparison showsthat the bubble sizes predicted by the present model are consistentwith our experimental Values and the available published experimentaldata.
基金Supported by the National Natural Science Foundation of China （20476073）, the State Key Laboratory of Chemical Engineering （SKL-ChE-08B03） and the Programs of Introducing Talents of Discipline to Universities 0306006）.
文摘The flow fields surrounding two parallel moving bubbles rising from two identical orifices submerged in non-Newtonian fluid of carboxymethylcellulose （CMC） solution of three different mass concentration were measured experimentally by the use of particle image velocimetry （PIV）. The influences of gas flowrate, solution mass concentration, orifice interval and the angle between two bubble centers line and vertical direction on the flow field surrounding bubbles were discussed respectively by analyzing the velocity vector, velocity contours as well as individual velocity components. The results show that the liquid velocity both in front of two bubbles and behind increases with gas flowrate duo to shear-thinning effect of previous bubbles, whereas decreases with the increase of CMC concentration due to the increase of drag force acting on bubbles. The effect of the orifice interval on the flow field around two moving bubbles becomes gradually obvious as the interval becomes closer. Moreover, two adjacent side-by-side bubbles repulse each other during rising, leading to the practical interval between them increased somewhat above the orifice interval. When the distance between bubbles is less than the orifice interval 10 mm, the interaction between two neighboring bubbles changed from mutual repellence to attraction with the decrease of the angle of the line of linking two bubble centers to the vertical direction.
基金Supported by the Key Projects of National Natural Science Foundation of China （50736006 9587003-13） the State Key Development Program for Basic Research of China （G1999-0222-08） the National Pandeng Project of China （85-06-1-2）
文摘Dispersed multiphase flows,including gas-particle(gas-solid),gas-spray,liquid-particle(liquid-solid) ,liquid-bubble,and bubble-liquid-particle flows,are widely encountered in power,chemical and metallurgical,aeronautical and astronautical,transportation,hydraulic and nuclear engineering. In this paper,advances and re-search needs in fundamental studies of dispersed multiphase flows,including the particle/droplet/bubble dynamics,particle-particle,droplet-droplet and bubble-bubble interactions,gas-particle and bubble-liquid turbulence interac-tions,particle-wall interaction,numerical simulation of dispersed multiphase flows,including Reynolds-averaged modeling(RANS modeling),large-eddy simulation(LES) and direct numerical simulation(DNS) are reviewed. The research results obtained by the present author are also included in this review.
基金Supported by the National Science Foundation(CBET-1236676)
文摘Bubbly gas-liquid Taylor-Couette vortex flow has been the subject of several recent investigations both because of interest in bubble-induced drag reduction and because such devices have potential applications to a variety of chemical and biochemical processing problems. In order to quantitatively describe the hydrodynamics of highly turbulent two phase Taylor-Couette flow, a rigorous two-fluid computational fluid dynamics （CFD） model was developed and compared with previously published experimental data. This model includes a comprehensive description of the constitutive closure for inter-phase forces and turbulence was simulated using both the k- and k-to models. In addition, the mechanism by which the dispersed fluid attains a non-uniform radial and axial distribution is analyzed and the relative importance of various interphase forces is discussed. Lastly the model was validated by comparison of simulation predictions with experimental data, and it is shown that the CFD model correctly predicts phase velocity, velocity fluctuation, and gas distribution, and may provide guidance for reactor design and scale-up.
基金Supported by the National Natural Science Foundation of China （20476073）, the Opening Project of State Key Laboratory of Chemical Engineering （SKL-ChE-08B03） and the Program of Introducing Talents of Discipline to Universities （B06006）.
文摘The chaotic characteristics of bubbles rising with accompanying coalescences in pseudoplastic aqueous carboxymethylcellulose sodium(CMC)solution were studied by means of smoothed pseudo Wigner-Ville distribution and Wigner-Hough distribution.The temporal signal of bubble passage was measured utilizing a photoconductive data acquisition system.As bubble coalescence occurred,the smoothed pseudo Wigner-Ville distribution of the signal revealed that the signal could be divided into low-frequency and high-frequency ranges and the transition range according to the distribution feature of frequency domain,which reflected eddy motion of fluid,high frequency fluctuations of fluid velocity and other random components measured in the signal,and bubbles rising accompanied with coalescences,respectively.However,bubble coalescence occurred in the lower position and the frequency range of bubbles motion became wide under higher gas flowrate,while the frequency range of bubbles motion became narrow when the CMC concentration increased.The typical dynamics of bubbles motion,such as periodicity,bifurcation and chaos,could be easily found in terms of the Wigner-Hough distribution.
文摘In this work, a numerical study for designing a new kind of MHD （Magneto-Hydrn-Dynamic） pumps is presented. This technique makes a compromise between electrolysis prevention and high flow rate performance. This technique should eliminate electrolytic bubble generation, electrodes wear and fluid propriety modification. All these side phenomena are prevented by considering isolated electrodes. The numerical presented results in this paper demonstrate that continuous MHD pumping is possible with isolated electrodes. The MHD excitation combines a high frequency altering current with a low frequency altering magnetic field. In order to validate our results, two independent theoretical methods for computing flow rate are followed. The two presented independent approaches show that high flow rate is possible even with isolated electrodes. To overcome the problem of dimensioning this kind of pumps, a generic numerical analysis is proposed. Hence, the pump performances as functions of the external parameter are studied and tools to calculate for a given fluid and the optimal high frequency regime are provided.
