Air-bubble generator is the key part of the self-inspiration type swirl flotation machines,whose flow field structure has a great effect on flotation.The multiphase volume of fluid(VOF),standard k-ε turbulent model a...Air-bubble generator is the key part of the self-inspiration type swirl flotation machines,whose flow field structure has a great effect on flotation.The multiphase volume of fluid(VOF),standard k-ε turbulent model and the SIMPLE method were chosen to simulate the present model;the first order upwind difference scheme was utilized to perform a discrete solution for momentum equation.The distributing law of the velocity,pressure,turbulent kinetic energy of every section along the flow direction of air-bubble generator was analyzed.The results indicate that the bubbles are heavily broken up in the middle cross section of throat sect and the entrance of diffuser sect along the flow direction,and the turbulent kinetic energy of diffuser sect is larger than the entrance of throat sect and mixing chamber.展开更多
Bubble dispersion greatly relies on spargers. Single or ifice and porous spargers were tested inside a bubble column under a low gas thr oughput to study their influences on gas dispersion and gas-liquid interface ar ...Bubble dispersion greatly relies on spargers. Single or ifice and porous spargers were tested inside a bubble column under a low gas thr oughput to study their influences on gas dispersion and gas-liquid interface ar ea. A PBE model without considering the effect of bubble coalescence was develo ped to describe axial bubble distribution. Both simulation and experimental res ults showed that bubbles broke up much faster than coalesced under low gas veloc ity. For a single orifice sparger, breakage was a dominant feature for bubbles after they left the orifice. Initial bubbles formed over the orifice were mostl y larger than the largest stable bubble. They broke up quickly and their sizes were reduced below the maximum diameter d_s of stable bubbles. In contrast , a porous sparger produced a large amount of initial bubbles smaller than the l argest stable bubble. The bubbles possessed smaller size and narrower distribut ion compared with the bubbles obtained by single orifice spargers. With the por ous sparger, gas-liquid surface area was increased by 5—6 times even though th e gas holdup changed insignificantly. High mass transfer area could be obtained by injecting more small initial bubbles with diameters under d_s.展开更多
A transient two-phase and three-dimensional computational fluid dynamics(CFD)simulation within the Eulerian framework has been carried out to investigate the influence of drag models on the radial gas hold-up profile ...A transient two-phase and three-dimensional computational fluid dynamics(CFD)simulation within the Eulerian framework has been carried out to investigate the influence of drag models on the radial gas hold-up profile of a bubble column.The effect of the sparger modeling is investigated as well.It can be concluded that:(1)the approximate modeling method for the sparger in this work is capable of reasonably predicting the radial gas holdup profile;(2)the CFD simulation with the Tomiyama’s drag model differs little from the Ishii-Zuber drag model at the low superficial velocity,while at the high gas velocity,the former leads to an over-prediction of the gas hold-up profile;(3)the correction factor of drag coefficient has a larger influence on the radial gas holdup profiles for high superficial gas velocity than low velocity.展开更多
基金Project supported by the Scientific Research Foundation of Hebei University of Technology of China
文摘Air-bubble generator is the key part of the self-inspiration type swirl flotation machines,whose flow field structure has a great effect on flotation.The multiphase volume of fluid(VOF),standard k-ε turbulent model and the SIMPLE method were chosen to simulate the present model;the first order upwind difference scheme was utilized to perform a discrete solution for momentum equation.The distributing law of the velocity,pressure,turbulent kinetic energy of every section along the flow direction of air-bubble generator was analyzed.The results indicate that the bubbles are heavily broken up in the middle cross section of throat sect and the entrance of diffuser sect along the flow direction,and the turbulent kinetic energy of diffuser sect is larger than the entrance of throat sect and mixing chamber.
文摘Bubble dispersion greatly relies on spargers. Single or ifice and porous spargers were tested inside a bubble column under a low gas thr oughput to study their influences on gas dispersion and gas-liquid interface ar ea. A PBE model without considering the effect of bubble coalescence was develo ped to describe axial bubble distribution. Both simulation and experimental res ults showed that bubbles broke up much faster than coalesced under low gas veloc ity. For a single orifice sparger, breakage was a dominant feature for bubbles after they left the orifice. Initial bubbles formed over the orifice were mostl y larger than the largest stable bubble. They broke up quickly and their sizes were reduced below the maximum diameter d_s of stable bubbles. In contrast , a porous sparger produced a large amount of initial bubbles smaller than the l argest stable bubble. The bubbles possessed smaller size and narrower distribut ion compared with the bubbles obtained by single orifice spargers. With the por ous sparger, gas-liquid surface area was increased by 5—6 times even though th e gas holdup changed insignificantly. High mass transfer area could be obtained by injecting more small initial bubbles with diameters under d_s.
文摘A transient two-phase and three-dimensional computational fluid dynamics(CFD)simulation within the Eulerian framework has been carried out to investigate the influence of drag models on the radial gas hold-up profile of a bubble column.The effect of the sparger modeling is investigated as well.It can be concluded that:(1)the approximate modeling method for the sparger in this work is capable of reasonably predicting the radial gas holdup profile;(2)the CFD simulation with the Tomiyama’s drag model differs little from the Ishii-Zuber drag model at the low superficial velocity,while at the high gas velocity,the former leads to an over-prediction of the gas hold-up profile;(3)the correction factor of drag coefficient has a larger influence on the radial gas holdup profiles for high superficial gas velocity than low velocity.
