Volumetric Liquid-phase Mass Transfer Coefficient Research Articles

Mathematical Modelling and CFD Simulation for Oxygen Removal in a Multi-Function Gas-Liquid Contactor

This paper presents and compares the mathematical models and computational fluid dynamics (CFD) models for degassing of oxygen from water in a laboratory-scale multi-function gas-liquid contactor under various operating conditions. The optimum correlations of the overall volumetric liquid-phase mass transfer coefficient (kLa) are determined by the mathematical models of specific contactors. Both the continuous-reactor model and semi-batch model can evaluate the degassing efficiency with relative errors within ±13%. Similarly, CFD models agree with experimental data with relative errors of ±10% or less. Overall, the mathematical models are deemed easy to use in engineering practice to assist the selection of efficient contactors and determine their optimum operation parameters. The CFD models have a wider applicability, and directly provide the local mass transfer details, making it appropriate for harsh industrial scenarios where empirical correlations for important quantities are unavailable. Combining these two types of models can effectively guide the design, optimization, and operation of the high-throughput degassing system.

Unified Approach for Prediction of the Volumetric Mass Transfer Coefficients in a Homogeneous and Heterogeneous Bubble Column Based on the Non-Corrected Penetration Theory: Case Studies

A critical review on the improvement of penetration theory is presented in this work. The volumetric liquid-phase mass transfer coefficients kLa in seven different liquids (1-butanol, 2-propanol, anilin, decalin, nitrobenzene, tetralin, and ethylene glycol) aerated with air in a small bubble column (BC) (inner diameter: 0.095 m) were measured at ambient conditions and further analyzed. It was found that the kLa values can be predicted satisfactorily on the basis of the classical Higbie’s penetration model. The gas–liquid contact time was defined as the ratio of the Sauter-mean bubble diameter to bubble rise velocity. Moreover, the experimental kLa values were well predicted, not only in the homogeneous regime, but also in the transition and heterogeneous regimes. This is a new finding, since to date, it was considered that the penetration theory needs a correction factor for a successful application to any liquid, even in the homogeneous regime. The predictions of the mass transfer coefficients kLa in the above-mentioned seven liquids imply that the mean bubble diameters are always ellipsoidal or spherical, which is the key condition for the applicability (without a correction) of penetration theory. In the presented (in this work) model-based kLa predictions, the Sauter-mean bubble diameters were estimated by means of the reliable correlation of Wilkinson et al., which always predicts a gradually decreasing bubble size at higher gas velocities.

Hydrodynamics and Mass Transfer in a Concentric Internal Jet-Loop Airlift Bioreactor Equipped with a Deflector

The gas–liquid hydrodynamics and mass transfer were studied in a concentric tube internal jet-loop airlift reactor with a conical bottom. Comparing with a standard design, the gas separator was equipped with an adjustable deflector placed above the riser. The effect of riser superficial gas velocity uSGR on the total gas holdup εGT, homogenization time tH, and overall volumetric liquid-phase mass transfer coefficient kLa was investigated in a laboratory bioreactor, of 300 mm in inner diameter, in a two-phase air–water system and three-phase air–water–PVC–particle system with the volumetric solid fraction of 1% for various deflector clearances. The airlift was operated in the range of riser superficial gas velocity from 0.011 to 0.045 m/s. For the gas–liquid system, when reducing the deflector clearance, the total gas holdup decreased, the homogenization time increased twice compared to the highest deflector clearance tested, and the overall volumetric mass transfer coefficient slightly increased by 10–17%. The presence of a solid phase shortened the homogenization time, especially for lower uSGR and deflector clearance, and reduced the mass transfer coefficient by 15–35%. Compared to the gas–liquid system, the noticeable effect of deflector clearance was found for the kLa coefficient, which was found approx. 20–29% higher for the lowest tested deflector clearance.

Gas–liquid mass transfer using advanced optical probe in a mimicked FT slurry bubble column

Abstract Gas-liquid volumetric liquid-phase mass transfer coefficient (k L a) was studied in a slurry bubble column at the conditions mimicking Fischer–Tropsch synthesis. To avoid the hydrodynamic disturbances due to the gas switching, oxygen enriched air dynamic absorption method was used. Influence of reactor models (CSTR, ADM and RCFD) on the volumetric mass transfer coefficient was investigated. Effect of operating pressure, superficial gas velocity and solids loading were investigated. From the reactor models investigated, it is recommended to use ADM model for k L a study. If the CSTR model is used, applicability of the model should be checked. With increase in the superficial gas velocity and operating pressure, volumetric liquid-phase mass transfer coefficient increases, while it decreases with the solids loading corroborating with the literature.

Defining mass transfer in a capillary wave micro-bioreactor for dose-response and other cell-based assays

For high-throughput cell culture and associated analytics, droplet-based cultivation systems open up the opportunities for parallelization and rapid data generation. In contrast to microfluidics with continuous flow, sessile droplet approaches enhance the flexibility for fluid manipulation with less operational effort. Generating biologically favorable conditions and promoting cell growth in a droplet, however, is particularly challenging due to mass transfer limitations, which has to be solved by implementing an effective mixing technique.Here, capillary waves induced by vertical oscillation are used to mix inside a sessile droplet micro-bioreactor (MBR) avoiding additional moving parts inside the fluid. Depending on the excitation frequency, different patterns are formed on the oscillating liquid surface, which are described by a model of a vibrated sessile droplet. Analyzing mixing times and oxygen transport into the liquid, a strong dependency of mass transfer on the oscillation parameters, especially the excitation frequency, is demonstrated. Oscillations at distinct capillary wave resonant frequencies lead to rapid homogenization with mixing times of 2 s and volumetric liquid-phase mass transfer coefficients of more than 340 h−1. This shows that the mass transfer in a droplet MBR can be specifically controlled via capillary waves, what is subsequently demonstrated for cultivations of Escherichia coli BL21 cells. Therefore, the presented MBR with vertical oscillation mixing is a promising analytical tool to perform cellular assays and experiments in parallel with intensified and tailored mass transfer.

Dynamics and mass transfer characteristics of CO2 absorption into MEA/[Bmim][BF4] aqueous solutions in a microchannel

Abstract The evolution of the size and velocity of CO2 bubble absorbed into MEA/[Bmim][BF4] aqueous solutions was in-line investigated by a high-speed camera. The coupling effect between the variation of volume and the velocity of bubbles was highlighted. According to the evolution of average mass transfer coefficient, the mass transfer performance in the whole flow process was studied. The results indicated that both the length and velocity of bubble decreased gradually in the flow process due to mass transfer. A linear correlation between the relative velocity (the ratio of average bubble velocity to two-phase superficial velocity) and the relative lost length (the ratio of the lost length to the initial length) was proposed. The increase in overall liquid-phase volumetric mass transfer coefficient (kLa) at higher gas flow rate could be ascribed to the shorter residence time and larger specific surface area. While the increase of kLa at higher liquid flow rate and MEA or [Bmim][BF4] concentration was resulted from intensified mass transfer. An empirical correlation of overall liquid-phase volumetric mass transfer coefficient was proposed taking the gas-phase Reynolds number, liquid-phase Reynolds number and Damkohler number into account.

Multiphase microreactors with intensification of oxygen mass transfer rate and mixing performance for bioprocess development

This research is focused on the development of a borosilicate glass-based microbioreactor (MBR) to address two of the challenges that MBRs may be confronted with: poor mixing and mass transfer limitations. To overcome these challenges, a microbubble column-bioreactor (μBC) for biotechnological research was developed and characterized. Pressurized air was supplied through a nozzle (hydraulic diameter 26 μm) at the bottom of the μBC (reactor volume 60 μL). The airflow was accelerated, generating a continuous stream of microbubbles that rose through the μBC. This investigation describes the hydrodynamic and mass transfer characterization of the μBC. The aim of the study was to prove that the pneumatic aeration through a micro nozzle provided sufficient aeration to satisfy the high demand of oxygen of aerobic bioprocesses, and at the same time, it enabled the homogenization of the cultivation broth and avoided the cell sedimentation. For this, the influence of the superficial gas velocity on the volumetric liquid-phase mass transfer coefficient is shown as well as the influence on other mass transport-related parameters, e.g. gas hold-up, Sauter mean bubble diameter, bubble rise velocity, superficial liquid velocity, volumetric power input, and mixing time. Additionally, a simplified computational fluid dynamic model was developed as a complement to this experimental research. The model serves as a supporting numerical tool to estimate the fluid dynamics inside the μBC.

Adsorption Characteristics of Activated Carbon for the Reclamation of Colored Effluents Containing Orange G and New Solid–Liquid Phase Equilibrium Model

Adsorption characteristics of activated carbon for the removal of orange G, an acid dye from aqueous solutions, have been investigated. The effect of initial dye concentration, temperature, and pH on the removal of orange G was investigated. The removal of orange G decreased from 95% to 82%, when the pH was increased from 2 to 12. The study of the effect of temperature and associated thermodynamic properties revealed the process of removal of dye is exothermic and spontaneous. Kinetic and mass transfer studies of the process were also carried out. The experimental data were used to develop a new solid–liquid phase equilibrium isotherm model. The average absolute relative deviation of the experimental data from the proposed model equation was 5.68%. In order to scale up the batch process for the removal of orange G, the concentration versus time data were analyzed to obtain mass transfer coefficient. The liquid-phase volumetric mass transfer coefficient (kLapL) was found to decrease from 0.008057 to 0.0028...

Theoretical prediction of mass transfer coefficients in both gas–liquid and slurry bubble columns

The gas–liquid contact time has been defined in a new way (bubble surface-to-rate of surface formation) and the range of applicability of the penetration theory in both gas–liquid and slurry bubble columns has been examined. In both reactors, the mass transfer coefficients were predicted successfully not only in the homogeneous regime but also in the heterogeneous regime (superficial gas velocities up to 0.08ms−1).The results in the article demonstrate the importance of the geometrical characteristics (length and height) of the oblate ellipsoidal bubbles for the accurate calculation of the contact time and thus the volumetric liquid-phase mass transfer coefficient kLa. The gas–liquid interfacial area has been calculated in both reactors in the classical way, i.e. as a function of the gas holdup and inversely proportional to the Sauter-mean bubble diameter. It was found that in the gas–liquid bubble column (0.095m in ID) the modified penetration theory was applicable to tap water, 9 organic liquids (decalin, nitrobenzene, 2-propanol, 1,4-dioxane, ethanol (99%), tetralin, xylene, 1,2-dichloroethane, ethylene glycol) and two liquid mixtures (water-glycol and tetralin-ethanol). Tetralin was aerated with both nitrogen and helium, whereas xylene was aerated with hydrogen and helium. The correction factor introduced by Calderbank (1967) was found useful for improving the kLa predictions in 1,2-dichloroethane, ethanol (99%), xylene(-hydrogen) and toluene–ethanol 97.2%. In the case of a slurry bubble column, the new approach was found applicable (at low solids concentrations) to four different gas–liquid–solid systems: air–tetralin–Al2O3, air–water–Al2O3, air–water-activated carbon and air–Na2SO4–kieselguhr. It is noteworthy that in some cases (air–water-Al2O3) the new definition of the contact time was found applicable up to solids concentrations of 6.29%. In the case of a slurry bubble column, it was found that when the theoretical kLa value is multiplied by the inverse value of the correction factor the predictions improve with about 5%.Finally, in the slurry bubble column the contact time was defined on the basis of the length of the micro-eddies and the kLa values in both air–water-alumina and air–water-activated carbon systems were successfully predicted. This is also a potentially good approach.

Prediction of mass transfer coefficients in a slurry bubble column based on the geometrical characteristics of bubbles

The experimental volumetric liquid-phase mass transfer coefficients kLa measured in a slurry bubble column (0.095m in ID) operated with several three-phase systems (air–ligroin–polyvinylchloride (PVC), air–ligroin–polyethylene (PE) and air–water–activated carbon) were predicted successfully based on a correction of Higbie's (1935) penetration theory. A correction factor (which is a single function of the Eötvös number) developed earlier (Nedeltchev et al., 2007) in gas–liquid bubble columns was found applicable to slurry bubble columns. It varied from 0.22 to 1.91 in the above-mentioned three-phase systems. As the bubble size becomes bigger, the correction factor increases and vice versa.The two major changes in the algorithm (applied to slurry bubble columns) are associated with the calculation of the Sauter-mean bubble diameter (Lemoine et al., 2008) and the gas–liquid interfacial area. In the case of a slurry bubble column, both the slurry density and effective viscosity were used in the model correlations. It was found that the model yielded good results not only in the homogeneous regime but also in the heterogeneous regime (up to gas velocities of 0.08m/s). It worked also well at relatively high solids concentrations (up to 15%). When the bubble Reynolds number is higher than 700 and when the superficial gas velocity is beyond 0.04m/s, then the penetration theory based on the new definition of the contact time can be applied straightforwardly (without any correction factor). The developed model is applicable to ellipsoidal bubbles and it demonstrates the important effect of the geometrical characteristics (length and height) of these bubbles on the mass transfer coefficients.

New Correlations of Volumetric Liquid-Phase Mass Transfer Coefficients in Gas-Inducing Agitated Tank Reactors

Abstract Volumetric liquid-phase mass transfer coefficient (kLa) is one of the most important parameters for the evaluation of the performance of a gas-inducing agitated tank (GIAT). In this paper, two equations in terms of power input per unit liquid volume (P/VL) and relative gas dispersion parameter (NI/Ncd), respectively, are developed according to data in literature. They can correlate existing kLa values within ±20% of measured ones for bladed impellers with different impeller submergence to tank diameter ratios in the range of 0.5 -1.23. In order to validate these equations, the liquid phase mass transfer coefficients in a continuous GIAT equipped with a 4-blade straight impeller were measured by removal of oxygen from water. It was found that the equation in P/VL criterion could correlate kLa values within ±12% of the experimental data, and the equation in NI/Ncd criterion could correlate kLa values within ±15.6% with an exception of 26.8% for NI = 16.7 Hz.

Study on the mass transfer of bubble swarms in three different rheological fluids

The mass transfer of the absorption of carbon dioxide bubble swarms into three different rheological fluids (Newtonian fluids, shear thinning fluids and viscoelastic fluids) were investigated experimentally. The volumetric liquid-phase mass transfer coefficients under different operating conditions were determined by using a carbon dioxide probe. The influences of gas flow rate and liquid properties on volumetric liquid-phase mass transfer coefficient were studied. Results indicated that the volumetric liquid-phase mass transfer coefficient increased with gas flow rate but decreased with increasing liquid apparent viscosity. Moreover, the viscoelasticity of liquid resulted in a decrease of mass transfer rate. A semi-empirical model was developed, the prediction by this model showed a satisfactory agreement with the experimental data in all three types of liquids studied.

Liquid-Phase Volumetric Mass Transfer Coefficient for Dilute Alcohol Solution in an External-Loop Airlift Reactor with a Porous Plate (Effect of Pore Size of Porous Plate)

The aim of this work is to investigate the influence of the addition of alcohol on the behavior of an external-loop airlift reactor with a porous plate. The mass transfer parameter in dilute aqueous solutions of three aliphatic alcohols (methanol, ethanol and n-propanol) was examined using five kinds of porous plates. The results showed that dilute alcohol addition enhanced dramatically liquid-phase volumetric mass transfer coefficient, kLaR, in the riser, especially led to the remarkable enhancement of that for the porous plate having small pore diameter due to smaller bubble diameter than with water system. This behavior is enhanced by alcohols with long carbon chain lengths probably due to the inhibition of bubble-bubble coalescence at the porous plate and in the liquid. This surprising result might be explained by a strong increase in kL values in liquid-phase volumetric mass transfer coefficient due to the increasing amount of small bubbles leading to large partial pressure of transfer component within bubbles based on capillary pressure as explained previously [1]. Also, the results showed that the liquid-phase volumetric mass transfer coefficient increased with the concentration of alcohol, but led to reduction of the volumetric mass transfer coefficient over any critical concentration for each porous plate. Moreover, empirical equation for liquid-phase volumetric mass transfer coefficient is obtained.

Gas−Liquid Mass Transfer in Taylor Flow through Circular Capillaries

Based on computational fluid dynamics (CFD), gas−liquid mass transfer in upward Taylor flow through vertical circular capillaries was studied. To save computational resources and time, the numerical simulations were carried out in a moving frame of reference attached to Taylor bubbles. Three consecutive Taylor bubbles were used to mimic the behavior of Taylor flow in an infinitely long capillary. Steady-state solutions of concentration fields were obtained to describe gas transfer from Taylor bubbles to the liquid phase. The liquid-phase volumetric mass-transfer coefficient, KLa, was investigated as a function of various parameters, including the liquid-film length, liquid-slug length, liquid-film thickness, bubble rise velocity, liquid-phase diffusivity, capillary diameter, and gravity. One fitted equation, expressed with three dimensionless numbers, was developed to quantify the relationship between KLa and the above parameters. The examples show that the equation could predict KLa well. The contributions of the cylindrical bodies and hemispherical caps of Taylor bubbles on the overall mass transfer were studied separately.

D-arabitol production from lactose by Kluyveromyces lactis at different aerobic conditions

BACKGROUND: The pentitol D-arabitol has been produced from D-glucose utilizing osmophilic yeast strains, however, there are remarkably few reports available on the production of D-arabitol from lactose. Previous studies in the laboratory have shown that the osmophilic yeast Kluyveromyces lactis NBRC 1903 can convert lactose to extracellular D-arabitol without extracellular accumulation of D-glucose or D-galactose. The present study was undertaken to determine the participation of aeration on the D-arabitol synthesis in K. lactis NBRC 1903. RESULTS: The highest D-arabitol concentration of 91.7 mmol L−1 was achieved after 120 h cultivation in medium containing 555 mmol L−1 of lactose with initial volumetric liquid-phase mass transfer coefficient of oxygen (kLa)0 of 85.5 h−1. The fractional yield of D-arabitol was affected by not only aeration but also growth phase. The highest fractional yield of D-arabitol in terms of lactose consumption was 0.255 that was obtained at stationary phase with (kLa)0 of 85.5 h−1. CONCLUSION: It was found that oxygen supply is a key factor in the production of D-arabitol. Patterns of metabolism were classified according to the level of oxygen supply and the growth phase. Copyright © 2010 Society of Chemical Industry

Influence of Alcohol Addition on Liquid-Phase Volumetric Mass Transfer Coefficient in an External-Loop Airlift Reactor with a Porous Plate

In this work, the effect of alcohol addition on the liquid-phase volumetric mass transfer coefficient, kLaR, is studied in an external-loop airlift reactor with a porous plate using an air–water system to which methanol, ethanol or propanol was added in concentrations ranging from 0.002 to 1 wt%. The experimental results show that the addition of small amounts of alcohol increases dramatically the liquid-phase volumetric mass transfer coefficient in the riser, due to smaller bubble diameter than with the water system. This behavior is enhanced by alcohols with long carbon chain lengths, which may be probably explained on the basis of the inhibition of bubble-bubble coalescence at the gas sparger plate and in the liquid. This surprising result can be explained by a strong increase in kL values in liquid-phase volumetric mass transfer coefficients due to the increasing amount of small bubbles leading to larger partial pressure of transfer component within bubbles based on capillary pressure. A remarkable effect of alcohol addition on liquid-phase volumetric mass transfer coefficient was not observed above the critical concentration of each alcohol.

Gas-liquid Mass Transfer in Three-phase Inverse Turbulent Bed Reactor

The characteristics of gas-liquid mass transfer of three-phase system comprising air, tap water/wastewater and hollow glass beads were studied in a laboratory-scale inverse turbulent bed reactor. The influence of operational factors and liquid property on volumetric liquid-phase mass transfer coefficient k La was investigated under the conditions of superficial gas velocity (0.53-10 mm·s −1), solid hold-up (0-0.3), and superficial liquid velocity (0-0·2 mm·s −1). The results showed that the coefficient value was 0.0456-1.414 min −1, which increased with superficial gas velocity and liquid velocity. The coefficient attained the maximum value at solid hold-up of 0.05-0.08. Compared with the coefficient value in tap water, the one in synthetic wastewater and industrial wastewater is decreased by 39.0 % and 50.9 %, respectively. These data have provided a basis for the process analysis and mathematical simulation of the inverse turbulent bed reactor.

Hydrodynamics, Mass Transfer and Gas Scrubbing in a Co-current Droplet Column Operating at High Gas Velocities

The main objective of this work was to propose a new process for household fume incineration treatment: the droplet column. A feature of this upward gas-liquid reactor which makes it original, is to use high superficial gas velocities (13 m s–1) which allow acid gas scrubbing at low energy costs. Tests were conducted to characterize the hydrodynamics, mass transfer performances, and acid gas scrubbing under various conditions of superficial gas velocity (from 10.0 to 12.0 m s–1) and superficial liquid velocity (from 9.4·10–3 to 18.9·10–3 m s–1). The following parameters characterized the hydrodynamics: pressure drops, liquid hold-ups, and liquid residence time distribution were identified and investigated with respect to flow conditions. To characterize mass transfer in the droplet column, three parameters were determined: the gas-liquid interfacial area (a), the liquid-phase volumetric mass transfer coefficient (kLa) and the gas-phase volumetric mass transfer coefficient (kGa). Gas absorption with chemical reaction methods were applied to evaluate a and kGa, while a physical absorption method was used to estimate kLa. The influence of the gas and liquid velocities on a, kLa, and kGa were investigated. Furthermore, tests were conducted to examine the utility of the droplet column for the acid gas scrubbing, of gases like hydrogen chloride (HCl) and sulfur dioxide (SO2). This is a process of high efficiency and the amount of pollutants in the cleaned air is always much lower than the regulatory European standards imposed on household waste incinerators.

Mass transfer from Taylor bubbles rising in single capillaries

Gas–liquid mass transfer from Taylor bubbles rising in 1, 2 and 3 mm diameter capillaries of circular and square cross-sections was investigated for air–water system. The liquid-phase volumetric mass transfer coefficient k L a was obtained from experimental oxygen absorption dynamics. The experimental k L a values are in good agreement with the model developed by van Baten and Krishna (2004. Chemical Engineering Science 59, 2535–2545), with the additional assumption that the dominant mass transfer contribution is to the film surrounding the bubble.

Non-Newtonian Fluids in Spout-Fluid Beds: Mass Transfer Coefficient at Low Reynolds Numbers

Following on from the work of Anabtawi et al. (2003), this study examined how the volumetric liquid-phase mass transfer coefficient, k L a, of oxygen in air in three-phase spout-fluid beds was affected by varying the system parameters of bed height, bed diameter, gas velocity, and liquid velocity. The liquid used was 0.1% CMC solution, displaying a pseudo-plastic rheology, with 1.75 mm glass spheres as packing. The values of the Sherwood number were lower than in previous studies (Anabtawi et al., 2003), in the range 9,000–186,000. Gas velocity had a similar effect on k L a as in a bubble column, with results also giving good agreement with previous work on two-phase and three-phase spouted bed systems. The correlation obtained for the effect of liquid velocity on k L a compared well with that of Schumpe et al. (1989). An increase in the height of packing increased k L a to the power of 0.319, with an increase in column diameter also causing an increase in k L a, which is in agreement with the results of Akita and Yoshida (1973).