Flow Regimes in Bubble Columns with and without Internals: A Review

Hydrodynamics characterization in terms offlow regime behavior is a crucial task to enhance the design of bubble column reactors and scaling up related methodologies.This review presents recent studies on the typicalflow regimes established in bubble columns.Some effort is also provided to introduce relevant definitions pertaining to thisfield,namely,that of“void fraction”and related(local,chordal,cross-sectional and volumetric)variants.Experimental studies involving different parameters that affect design and operating conditions are also discussed in detail.In the second part of the review,the attention is shifted to cases with internals of various types(perfo-rated plates,baffles,vibrating helical springs,mixers,and heat exchanger tubes)immersed in the bubble columns.It is shown that the presence of these elements has a limited influence on the global column hydrodynamics.However,they can make the homogeneousflow regime more stable in terms of transition gas velocity and transi-tion holdup value.The last section is used to highlight gaps which have not beenfilled yet and future directions of investigation.

A Comprehensive Review of the Influence of Heat Exchange Tubes on Hydrodynamic,Heat,and Mass Transfer in Bubble and Slurry Bubble

Bubble and slurry bubble column reactors(BCRs/SBCRs)are used for various chemical,biochemical,and petro-chemical applications.They have several operational and maintenance advantages,including excellent heat and mass transfer rates,simplicity,and low operating and maintenance cost.Typically,a catalyst is present in addition to biochemical processes where microorganisms are used to produce industrially valuable bio-products.Since most applications involve complicated gas-liquid,gas-liquid-solid,and exothermic processes,the BCR/SBCR must be equipped with heat-exchanging tubes to dissipate heat and control the reactor’s overall performance.In this review,past and very recent experimental and numerical investigations on such systems are critically dis-cussed.Furthermore,gaps to befilled and critical aspects still requiring investigation are identified.

Experimental and Numerical Analysis of Oil-Water Flow with Drag Reducing Polymers in Horizontal Pipes

The well-known frictional effect related to liquid-liquid two-phaseflow in pipelines can be reduced using drag-reducing additives.In this study,such an effect has been investigated experimentally using a mixture of oil and water.Moreover,numerical simulations have been carried out using the COMSOL simulation software.The mea-surements were taken in a horizontal pipe with the length and diameter equal to 3 and 0.125 m,respectively.Moreover,Polyethylene oxide with 150 ppm was exploited to reduce the drag effect while considering different water-to-oil fractions(0.3,0.4,0.5,and 0.7)and a constant totalflow velocity of 2.3 m/s.As made evident by the results,a significant reduction can be obtained in terms of pressure drop,which becomes even more significant as the water to oil fraction is increased.The maximum achieved drag reduction is 70%with a water fraction of 0.7.The results also show that the addition of polymer additives can also have an impact on theflow pattern.Com-parison of experimental and numerically determined pressure drop indicates that the error is smaller than 7%.