Liquid Volumetric Mass Transfer Coefficient Research Articles

Mass transfer enhancement and hydrodynamic performance with wire mesh coupling solid particles in bubble column reactor

It is of vital significance to investigate mass transfer enhancements for chemical engineering processes. This work focuses on investigating the coupling influence of embedding wire mesh and adding solid particles on bubble motion and gas–liquid mass transfer process in a bubble column. Particle image velocimetry (PIV) technology was employed to analyze the flow field and bubble motion behavior, and dynamic oxygen absorption technology was used to measure the gas–liquid volumetric mass transfer coefficient kLa. The effect of embedding wire mesh, adding solid particles, and wire mesh coupling solid particles on the flow characteristic and kLa were analyzed and compared. The results show that the gas–liquid interface area increases by 33% to 72% when using the wire mesh coupling solid particles strategy compared to the gas–liquid two-phase flow, which is superior to the other two strengthening methods. Compared with the system without reinforcement, kLa in the bubble column increased by 0.5–1.8 times with wire mesh coupling solid particles method, which is higher than the sum of kLa increases with inserting wire mesh and adding particles, and the coupling reinforcement mechanism for affecting gas–liquid mass transfer process was discussed to provide a new idea for enhancing gas–liquid mass transfer.

Intensified ammonia stripping from landfill leachate using a high-performance rotating reactor

Rotating bed devices have proven their rapid and intensified mass transfer compared to conventional packed columns in separation processes, especially ammonia stripping. However, the prospect of implementing rotating bed devices for this purpose is still unclear since the previous data was only obtained from experiments with synthetic ammonia wastewater. Practical wastewater, such as landfill leachate, possesses various complex characteristics that have been reported to inhibit ammonia stripping efficiency. Therefore, this study was conducted to clarify the possibility of using the rotating bed device by investigating the stripping of ammonia from landfill leachate using the High-Performance Rotating Reactor (HP2R). The effect of parameters such as initial pH (pHi), rotational speed (ω), the gas-to-liquid flow rate ratio (QG/QL), and the liquid flow rate (QL) on the stripping efficiency (η) and volumetric liquid mass-transfer coefficient (KLa) was evaluated. The results of η and KLa varied from 17.1% to 71.8% and 0.0005 s−1 to 0.0039 s−1 at a controlled laboratory temperature of 30 °C under a variety of operational parameters. The ammonia stripping efficiency from leachate was slightly lower compared to the data of the synthetic wastewater experiment due to the solid particle formation from pre-alkalinization and precipitation of carbonate salts during the stripping process. The benefit of using HP2R over the conventional packed column in ammonia stripping was the improvement of η at lower pHi of 9.5 by optimizing the ω and QG/QL. Additional stripping cycles resulted in a higher ammonia stripping efficiency from leachate up to 94.6%.

Machine-learning-aided application of high-gravity technology to enhance ammonia recovery of fresh waste leachate

Stripping is widely applied for the removal of ammonia from fresh waste leachate. However, the development of air stripping technology is restricted by the requirements for large-scale equipment and long operation periods. This paper describes a high-gravity technology that improves ammonia stripping from actual fresh waste leachate and a machine learning approach that predicts the stripping performance under different operational parameters. The high-gravity field is implemented in a co-current-flow rotating packed bed in multi-stage cycle series mode. The eXtreme Gradient Boosting algorithm is applied to the experimental data to predict the liquid volumetric mass transfer coefficient (KLa) and removal efficiency (η) for various rotation speeds, numbers of stripping stages, gas flow rates, and liquid flow rates. Ammonia stripping under a high-gravity field achieves η = 82.73% and KLa = 5.551 × 10−4 s−1 at a pH value of 10 and ambient temperature. The results suggest that the eXtreme Gradient Boosting model provides good accuracy and predictive performance, with R2 values of 0.9923 and 0.9783 for KLa and η, respectively. The machine learning models developed in this study are combined with experimental results to provide more comprehensive information on rotating packed bed operations and more accurate predictions of KLa and η. The information mining behind the model is an important reference for the rational design of high-gravity-field-coupled ammonia stripping projects.

CO2 chemical absorption into AMP aqueous solution and mass transfer intensification in cascade sudden expansion microchannels

Carbon dioxide chemical absorption into 2-amino-2-methyl-1-propanol (AMP) aqueous solution and mass transfer enhancement in cascade sudden expansion microchannels were investigated by a high-speed digital camera. The influences of the flow rates of gas and liquid phases, the sudden expansion units and the concentration of AMP on the gas-liquid two-phase flow and mass transfer performance are studied systematically. Results showed that the increase of sudden expansion unit is conductive to increase liquid side volumetric mass transfer coefficient and enhancement factor. The maximal enhancement factor could reach to 1.33, and the maximally effective mass transfer efficiency could reach 1.6 under taking the energy consumption into account. The gas phase flow rate has slight effect on mass transfer enhancement factor E, while E decreases with increasing liquid phase flow rate. With the increase of AMP concentration, the volumetric mass transfer coefficient increases, but the enhancement factor decreases. A new correlation with good prediction performance was proposed for the volumetric mass transfer coefficient. Furthermore, the energy consumption and effective mass transfer efficiency were assessed.

Effect of particles on hydrodynamics and mass transfer in a slurry bubble column: Correlation of experimental data

AbstractThe effects of particle concentration and size on hydrodynamics and mass transport in an air–water slurry bubble column were experimentally studied. When the particle concentration αs increased from 0% to 20%, the averaged gas holdup decreased by ~30%, gas holdup of small bubbles and gas–liquid volumetric mass transfer coefficient decreased by up to 50%, while the gas holdup of large bubbles increased slightly. The overall effect of particle size was insignificant. A liquid turbulence attenuation model which could quantitatively describe the effects of particle concentration and size was first proposed. Semi‐empirical correlations were obtained based on extensive experimental data in a wide range of operating conditions and corrected liquid properties. The gas holdup and mass transfer coefficient calculated by the correlations agreed with the experimental data from both two‐phase and three‐phase bubble columns, with a maximum error <25%.

Experimental Investigation of Mass Transfer Intensification for CO2 Capture by Environment-Friendly Water Based Nanofluid Solvents in a Rotating Packed Bed

In this research, two intensification approaches for CO2 capture via a rotating packed bed (RPB) and nanofluids were examined simultaneously to maximize the experimental mass transfer coefficient. The two intensification approaches were done by using water as a green, environmentally friendly absorption solvent and as the base fluid for preparing nanofluids and also by using centrifugal acceleration in an RPB. Physicosorption of CO2 in an RPB was carried out by applying Al2O3, TiO2, and SiO2 nanofluids to intensify the mass transfer in water, and the operation parameters such as the angular speed of the rotor, concentration and type of nanoparticles, gas and liquid flow rates, and CO2 concentration in mass transfer intensification were evaluated and several nanofluids were selected to survey investigate how they affect the mass transfer at low pressure. The results show that the Al2O3 nanofluid was more effective than other nanofluids and that the 40 nm nanofluid of this type was more efficient than the 20 nm size. Therefore, a correlation is proposed in this paper for liquid volumetric mass transfer coefficient prediction that includes the microconvection of nanoparticles and surface tension.

Effects of internal structures on mass transfer performance of jet bubbling reactor

In the cold-mold device of jet bubbling reactor, the effects of the liquid nozzle outlet diameter (dj), the diameter of annular gas distributor with a baffle (dg), and the distance between the liquid nozzle outlet and gas distributor (L) on the liquid volumetric mass transfer coefficient (kLa) are investigated through the dynamic dissolved oxygen method. The liquid jet flow field measured through the PIV shows that the radial jet is formed after the jet impacts the gas distributor, which prolongs the bubble residence time in the reactor. When the energy input to the reactor is constant, with the dj increasing, the L shortening, or the dg decreasing, the radial jet velocity and shear stress at gas outlet increases, causing the overall gas holdup increases and the bubble size decreases, so the kLa increases. An empirical correlation of the kLa is established. The relative error between the predicted values through the model and the experimental data is less than 20%. The research results can provide theoretical guidance for the optimization of the internals and scale-up of the jet bubbling reactor.

High-gravity deoxygenation of jet fuels using rotating packed bed

It has been proven that dissolved oxygen has fatal effect on thermal oxidation stability of jet fuels, although it is present in extremely low levels (70 ppm). In this paper, high-gravity deoxygenation method of jet fuels via rotating packed bed (RPB) was proposed to intensify gas–liquid mass transfer process. The deoxygenation efficiency of jet fuels was up to 99% (less than 1 ppm), and the liquid volumetric mass transfer coefficient (kLae) is 0.01 ∼ 0.06 s−1. The effects of operation parameters on deoxygenation efficiency and liquid volumetric mass transfer coefficient (kLae) were studied systematically, including gas–liquid ratio, rotating speed, liquid flow rate and packing structure. This method showed remarkable advantages in many aspects, such as superior mass transfer performance, extremely high deoxygenation efficiency, small device volume, very high process speed, low gas consumption and high operation stability. In addition, the mass-transfer model of high-gravity deoxygenation of jet fuel was established basing on the surface renewal theory, which considered the influences of gas flow and other operation parameters. The model is in good agreement with the experimental results, and the deviation is within ± 15%. This research is of great significance for the development of innovative deoxygenation technology of jet fuels.

Gas–liquid mass transfer in the gas–liquid–solid mini fluidized beds

The gas–liquid–solid mini fluidized bed (GLSMFB) combines the advantages of fluidized bed and micro-reactor, and meets the requirements for safety and efficiency of green development of process industry. However, there are few studies on its flow performance and no studies on its mass and heat transfer performance. In this paper, the characteristics of gas–liquid mass transfer in a GLSMFB were studied in order to provide basic guidance for the study of GLSMFB reaction performance and application. Using CO2 absorption by NaOH as the model process, the gas–liquid mass transfer performance of GLSMFB was investigated. The results show that the liquid volumetric mass transfer coefficient and the gas–liquid interfacial area both increase with the increase of the superficial gas velocity within the experimental parameter range under the same given superficial liquid velocity. At the same ratio of superficial gas to liquid velocity, the liquid volumetric mass transfer coefficient increases with the increase of the superficial liquid velocity. Fluidized solid particles strengthen the liquid mass transfer process, and the liquid volumetric mass transfer coefficient is about 13% higher than that of gas–liquid mini bubble column.

Chlorine dioxide gas generation using rotating packed bed for air disinfection in a hospital

Chlorine dioxide (ClO2) has proven its efficiency as a fumigant toward bacteria and viruses. However, it still has challenges on its portability and simplicity of ClO2 generation to meet the demand for disinfection in public and medical sectors. In this study, ClO2 stripping process via a rotating packed bed (RPB) from the commercial ClO2 solution was developed to a non-chemical-reaction ClO2 generation for air sterilization in a hospital. The ClO2 stripping efficiency (η) and the volumetric liquid mass-transfer coefficient (KLa) were examined under various operating variables, such as initial liquid concentration (CLi), rotational speed (ω), gas-to-liquid flow rate ratio (QG/QL), and liquid flow rate (QL). The results indicated that the gaseous ClO2 can be rapidly and continuously generated via stripping using RPB with η varied above 97% in the certain range of CLi (100–2000 mg/L) and QL (0.04–0.250 L/min). The overall KLa depends on the change of QL and ω, varied from 0.009 s−1 to 0.027 s−1. The output concentration of gaseous ClO2 (CG) can be adjusted from around 10 ppm to over 1000 ppm based on the established prediction model and controlling CLi, QL, QG, and ω. The results of the on-site disinfection test in the Mycobacterium Tuberculosis Laboratory in a hospital have shown effective elimination of all sites of E. coli and 2 of 5 sites of G. stearothermophilus with a CT value at the gas monitoring point of 642 ppm-h and humidity of 81%.

Circulating jet for enhancing the mass transfer in a gas–liquid stirred tank reactor

AbstractThere are some problems in gas–liquid stirred tank reactor (STR), such as low mass transfer efficiency, high exhaust gas oxygen concentration, and low product conversion rate, due to limitations of stirring speed and input power. This article summarizes the effect of adding circulating jet internals on bubble size distribution, overall gas holdup, gas–liquid volumetric mass transfer coefficient, and power per unit volume of the STR. When circulating jet is added, the average bubble Sauter mean diameter in the STR is reduced to 1.26 mm, and the overall gas holdup is increased to 8.23%, which is an increase of 3.62 times of the original STR. The gas–liquid volumetric mass transfer coefficient is increased to 0.05556 s−1, which is 4.84 times of the original STR. The power per unit volume is increased by only 1.4 times. These data provide references for the design and scale‐up of new jet STRs.

Mass transfer enhancement of CO2 absorption into [Bmim][BF4] aqueous solution in microchannels by heart-shaped grooves

CO2 absorption into [Bmim][BF4] aqueous solution was investigated experimentally. To enhance gas-liquid mass transfer, the heart-shaped grooves were engraved in the microchannel. It was found that the grooves could cause eddy flow of liquid phase and accordingly promote turbulent and convective mass transfer. Liquid side volumetric mass transfer coefficient and mass transfer enhancement factor could be remarkably increased, and the enhancement factor could reach up to 2.2. Moreover, the effective mass transfer enhancement efficiency was analyzed considering the energy consumption, and its value could reach 2.1. A correlation was proposed to predict the liquid side volumetric mass transfer coefficient for the grooved microchannel.

Enhancement of gas-liquid mass transfer by nanofluids in a microchannel under Taylor flow regime

The gas-liquid two-phase flow and the enhancement of mass transfer by nanoparticles for the process of CO2 absorbed by SiO2 nanofluids were investigated in a microchannel under Taylor flow regime. The influences of the dispersed and continuous phase flow rates and particle concentration in slurry on liquid side volumetric mass transfer coefficient (KLa), mass transfer enhancement factor (E), CO2 absorption efficiency, and pressure drop were studied systematically. The results show that the presence of nanoparticles can effectively enhance the gas-liquid mass transfer. Both KLa and pressure drop increase, while the CO2 absorption efficiency decreases with increasing the gas-liquid flow rate ratio. Differently, KLa, CO2 absorption efficiency and pressure drop increase with the increase of particle concentration in slurry. Considering the energy consumption and mass transfer enhancement effect, the effective mass transfer enhancement efficiency is in the range of 1.2 ~ 2.4, which shows the excellent enhancement performance of nanoparticles on gas-liquid mass transfer.

Experiments and CFD simulation of mass transfer and hydrodynamics in a cylindrical bubble column

Flow visualization, Particle Image Velocimetry (PIV) and dissolved oxygen charging experiments are carried out in a small-scale cylindrical air-water bubble column at different superficial gas velocities. Void fraction profile, total gas holdup, liquid phase velocity field and volumetric mass transfer coefficient are obtained. Details of each experiment are given, with a new procedure for obtaining a 2D void fraction profile from flow visualization by image processing and time averaging which could provide useful information for CFD model validation. The experimental results are analyzed and compared with simulations where good agreement is found for both local and global flow patterns. The averaged governing equations and constitutive relations used in the simulation are discussed briefly, with emphasis on the proper comparison between simulations and experiments based on the derivation of the two-fluid model. By conducting three sets of experiments related to phase distribution, velocity field and mass transfer in the same apparatus, a validated CFD model for multiphase mass transfer is established and can be used in the future design of a multi-phase reactor.

Intensification of gas-liquid two-phase flow and mass transfer in microchannels by sudden expansions

The intensification of mass transfer of CO2 absorption into [Bmim][BF4] aqueous solution by continuous sudden expansion units was investigated experimentally in microchannels. The influences of two-phase flow rates and the number of sudden expansion units on pressure drop and volumetric mass transfer coefficient were studied systematically. The results indicate that the sudden expansion structure could remarkably enhance gas-liquid mass transfer. The enhancement factor of mass transfer increases with increasing the number of sudden expansion units and gas-liquid flow rate ratio, while the pressure drop has only slight elevation. The effective mass transfer enhancement efficiency was assessed according to the energy consumption and enhancement factor, which could achieve from 1.2 to 2.4, showing excellent mass transfer intensification effect of the sudden expansion structure. Moreover, a new correlation was proposed for predicting liquid side volumetric mass transfer coefficient.

Determination of mass transfer coefficients in high-pressure two-phase flows in capillaries using Raman spectroscopy

This study presents a method for the experimental determination of local volumetric mass transfer coefficients kLaL in a high-pressure two-phase flow of water (H2O) and carbon dioxide (CO2) in a micro-capillary using Raman spectroscopy. H2O and CO2 are continuously and co-currently fed at high pressure (8, 9 and 10 MPa) and moderate temperature (303 K) into a fused silica micro-capillary. A segmented two-phase flow is obtained therein and the fraction of CO2 in the water-rich phase is measured in-situ at different points along the capillary using Raman spectroscopy. A modified Henry’s law is used to compute the equilibrium compositions of the water-rich phase at the desired pressure and temperature. A mixture density model is used to convert the fraction of CO2 in the water-rich phase into a CO2 concentration. The volumetric liquid mass transfer coefficient is computed at various axial locations along the capillary, from the contacting zone to the end of the capillary. Experimentally derived kLaL values range between 2.10−3 and 5.10−3 s−1.

Performance comparison of swirl-venturi bubble generator and conventional venturi bubble generator

The bubble generation performance and liquid volumetric mass transfer coefficient kLa of the venturi microbubble generator and the swirl-venturi microbubble generator were evaluated through the high-speed photography and measurement of dissolved oxygen concentration. The results show that the swirl-venturi microbubble generator generates more bubbles with smaller Sauter mean diameter than the venturi microbubble generator. And the maximum stable bubble size of the swirl-venturi microbubble generator is also smaller than that of the venturi microbubble generator. Moreover, the maximum stable bubble size of the swirl-venturi microbubble generator is not sensitive to the increase of superficial gas velocity, which indicates that the swirl-venturi microbubble generator has a higher probability of breaking bubbles. Eventually, the liquid volumetric mass transfer coefficient kLa of swirl-venturi microbubble generator is measured and higher than that of the venturi microbubble generator at high superficial gas velocity. Based on all above, it can be concluded that the swirl-venturi microbubble generator is a more effective way to generate microbubbles.

Gas-liquid distribution and mass transfer of CO2 absorption into sodium glycinate aqueous solution in parallel multi-channel microreactor

The flow, gas-liquid distribution and mass transfer of CO2 absorption into sodium glycinate aqueous solution in microreactor with parallel multi-channel were investigated by using high-speed camera. The effects of the gas and liquid flow rates and the sodium glycinate concentration on gas-liquid distribution, CO2 absorption efficiency and volumetric mass transfer coefficient were studied. The increase of gas flow rate could aggravate the non-uniformity of gas-liquid distribution in the channels, while the increase of liquid flow rate or sodium glycinate concentration could weaken the non-uniformity of gas-liquid distribution in the channels. The absorption efficiency of CO2 increases firstly and then decreases with the increase of gas flow rate, and increases with the increase of liquid flow rate or the sodium glycinate concentration. The volumetric mass transfer coefficient of liquid side increases with increasing gas flow rate, liquid flow rate or liquid concentration. Within the experimental range, the average standard deviation of gas-liquid distribution in each channel is 5.6%, and the average liquid side volumetric mass transfer coefficient in parallel multi-channel microreactor is slightly lower than that in a single microchannel under the same conditions, indicating that the multi-channel microreactor used in this work has good distribution and mass transfer performance.

Evaluation of the gas absorption performance of a flow-type hydrate-based gas uptake system

As a means of assessing the viability of hydrate-based gas separation, this study examined the gas absorption performance of a flow-type gas–liquid contact device with static mixing. Assuming for the sake of simplification that the hydrate-based gas uptake occurred as a result of pseudo gas–liquid contact in a bubble-hydrate slurry solution, overall liquid side volumetric mass transfer coefficients were determined. An R134a–N2 mixture was used as a model gas because the corresponding hydrate readily forms under low pressure/high temperature conditions. At 0.325 MPa and 278 K, the average coefficients were determined to be in the range of 0.088–0.142 s−1. These values were more than ten times greater than those obtained from simple gas dissolution. The results of this work suggest that hydrate-based systems are preferable for the purpose of gas absorption and separation.

An Analysis Study of the impact of the main operating parameters on the ozone mass transfer rate in a Kenics Static Mixer Using the Steady State Back Flow Cell Model (BFCM)

The kenics static mixer (KMS) has been profoundly used in water and wastewater treatment processes, essentially in water ozonation for oxidation and disinfection purposes. since higher concentration of ozone is required, new contactors which operate efficiently at low gas/liquid ratio has been developed. The Kenics static mixer can fulfil these demands which lead to increase in the ozone mass transfer rate [1]. The main purpose of this paper is to use the steady state back flow cell model (BFCM) developed by Tizaoui and Zhang [1] so as to estimate the concentration profile of ozone in the liquid and the gas phases along the KMS. The study also aim to develop a Matlab code for the BFCM of the static mixer. Moreover, this research studied the effect of the main operating parameters: volumetric liquid mass transfer coefficient ,the length of the Kenics static mixer, flow rate of water , and gas flow rate , back flow ratio and the temperature on ozone concentration profile in the gas and liquid phases and respectively along the height of the Kenics static mixer.