Bubble column reactors fitted with tube bundles(BCR TB)belong to common heat transfer equipment in the field of chemical engineering,yet the complicated thermal-hydraulics performance of BCR TB has not been deeply rev...Bubble column reactors fitted with tube bundles(BCR TB)belong to common heat transfer equipment in the field of chemical engineering,yet the complicated thermal-hydraulics performance of BCR TB has not been deeply revealed.To fill this gap,the present study proposes a novel variable bubble size modeling approach based on the Euler-Euler two-fluid framework,which is coupled with the population balance model considering comprehensive interphase forces.On the basis of verifying numerical reliability using experimental data,the mechanism of bubble swarm flow around the tube bundle and the effects of gas sparger configurations on the thermal-hydraulics performance of BCR TB are investigated.Results indicate that the entire tube bundle can be divided into three distinct zones,namely the sparger effect zone,fully developed zone and interface effect zone in view of the local mixture-to-wall heat transfer coefficient.The maximum peak value of the mixture-to-wall heat transfer coefficient always appears at 210°of heat exchange tubes.When the orifice diameter is 4 mm,the axial gradient of gas holdup is relatively large due to more intense shearing and fragmentation effects.Interestingly,the fractions of medium-sized and large-sized bubbles are not sensitive to orifice angle.Both the mixture-to-wall heat transfer coefficient and the friction factor decrease initially and then increase when the installation height increases.Under the optimized gas sparger structure configuration,the mixture-to-wall heat transfer coefficient increases by 10.23%,accompanied by the reduction of pressure drop by 8.14%,ultimately attaining a system energy conversion efficiency of 97.88%and performance evaluation criterion of 1.087.Finally,a new dimensionless and semi-theoretical Nusselt correlation incorporating a structural correction factor with an average absolute deviation of 5.15%is developed.The findings can offer useful guidance for the optimal design of BCR TB.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supported by the project 2024J01421supported by Fujian Provincial Natural Science Foundation.
文摘Bubble column reactors fitted with tube bundles(BCR TB)belong to common heat transfer equipment in the field of chemical engineering,yet the complicated thermal-hydraulics performance of BCR TB has not been deeply revealed.To fill this gap,the present study proposes a novel variable bubble size modeling approach based on the Euler-Euler two-fluid framework,which is coupled with the population balance model considering comprehensive interphase forces.On the basis of verifying numerical reliability using experimental data,the mechanism of bubble swarm flow around the tube bundle and the effects of gas sparger configurations on the thermal-hydraulics performance of BCR TB are investigated.Results indicate that the entire tube bundle can be divided into three distinct zones,namely the sparger effect zone,fully developed zone and interface effect zone in view of the local mixture-to-wall heat transfer coefficient.The maximum peak value of the mixture-to-wall heat transfer coefficient always appears at 210°of heat exchange tubes.When the orifice diameter is 4 mm,the axial gradient of gas holdup is relatively large due to more intense shearing and fragmentation effects.Interestingly,the fractions of medium-sized and large-sized bubbles are not sensitive to orifice angle.Both the mixture-to-wall heat transfer coefficient and the friction factor decrease initially and then increase when the installation height increases.Under the optimized gas sparger structure configuration,the mixture-to-wall heat transfer coefficient increases by 10.23%,accompanied by the reduction of pressure drop by 8.14%,ultimately attaining a system energy conversion efficiency of 97.88%and performance evaluation criterion of 1.087.Finally,a new dimensionless and semi-theoretical Nusselt correlation incorporating a structural correction factor with an average absolute deviation of 5.15%is developed.The findings can offer useful guidance for the optimal design of BCR TB.
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.
