Search

This paper explores the dynamic control of thermally coupled ternary extractive distillation process containing two extractive columns with recycle splitting of mixed separating agent by taking the separation of tetrahydrofuran/ethanol/water as a demonstrating example. A series of control structures are devised and assessed by the large (20%) perturbations of throughput and feed composition, and the robust regulatory control is achieved since the purities of all three products are closely going back to their initial steady-state design specifications when facing the large (20%) feed flowrate and composition disturbances. Besides, the dynamic response performance for control strategy with product ethanol purity controlled by manipulating the reflux ratio is superior to that with manipulating solvent flowrate in terms of peak dynamic transients, settling time and steady-state offsets when facing the large (20%) throughput and feed composition disturbances for extractive rectifier column C2. The direct dynamic response performance comparisons for conventional and thermally coupled processes with mixed entrainer are also investigated and showed that there is no conflict (tradeoff) between the steady-state economics and dynamic controllability for this system.

The numbering-up of microchannel could cause negative effects on the hydrodynamics and mass transfer of gas-liquid two-phase flow under inappropriate operating conditions. In this study, the hydrodynamics and mass transfer of gas-liquid two-phase flow in a tree-shaped parallel microchannel constructed by T-type bifurcations are investigated. Four flow regimes are obtained: bubbly flow, slug-foam flow, slug flow and compact slug flow. The results show that, there exists a critical ratio of gas flow rate to liquid flow rate to attain ideal flow distribution and optimal mass transfer performance. Beyond the critical point, the flow regime would become much different with before, the change of hydrodynamics could cause the remarkable deteriorations in flow distribution and mass transfer efficiency. The influencing mechanism of the operating conditions on hydrodynamics and mass transfer performance are analyzed. Furthermore, the correlations for predicting the volumetric mass transfer coefficient are proposed.

Dynamics of elastic droplet breakup and stretching of polymeric filaments in a microfluidic T-junction are investigated experimentally. Through comparisons between cases of Newtonian droplet and a series of viscoelastic droplets with similar shear viscosity, the effect of elasticity on breakup dynamic of droplet is especially focused. Four sequential stages of droplet breakup in a microfluidic T-junction are observed: (I) squeezing, (II) transition, (III) pinch-off and (IV) filament rupture stages. For former three stages (I–III), dynamic behaviors of viscoelastic droplets with lower molecular weight (Mw = 1 × 105 g/mol and 3 × 105 g/mol) and Newtonian droplet are similar, while for viscoelastic droplet with higher molecular weight (Mw = 1 × 106 g/mol), the spatial obstruction of previous filaments accelerates the shrinkage of droplet neck. Additionally, the transformation of dominant force from inertial to capillary force leads to the variation of scaling laws describing the neck evolution. For filament rupture stages (IV), with extension of polymer molecules chain, the elastocapillary balance contributes to the exponential thinning of the polymeric filament, while the width of thread neck decreases linearly with the time for Newtonian droplet. Furthermore, more effort has been devoted to investigate the stretching dynamic of filament. The stretching rate of filament is independent of elasticity, but proportional to two-phase flow rates.

The formation process of ferrofluid droplets in the Y-shaped flow-focusing microchannels with a cross section of 400 μm × 400 μm and different angles was investigated experimentally by a high-speed...

The self-sustained coalescence-breakup cycles of ferrodrops were investigated for the first time by a high-speed camera under various magnetic fields. Under an axial magnetic field, the upper ferrodrop would deform into a conic shape before coalescing with the bottom ferropeak. Within 0.2 ms after coalescence, the minimum width of the expanding neck obeys a power-law relationship with time, while the exponents increase with the magnetic field and deviate with a decreasing trend in the later coalescence. The cone angle of the upper ferrodrop before coalescence gradually decreases while it increases before breakup with the magnetic field. A critical magnetic field around 35 mT was reported, above which the ferrofluid column undergoes the periodic phenomenon of coalescence and breakup. The frequency for the whole coalescence-breakup cycle increases exponentially with the applied magnetic field. A simplified force balance allows capturing the periodic mechanism involved in this driven harmonic oscillator.

The bubble formation in highly viscous liquids in a microfluidic flow-focusing device is highlighted. The influences of viscosity and flow rate of liquid phase on the bubble formation are studied. The glycerol-water solution (94–1000 mPa s) is used as the liquid phase, and nitrogen as the gas phase. Two different stages are observed in the gaseous breakup during bubble formation: at first, the relation between the neck radius of the gaseous thread and the remaining time can be expressed as a power law; while in the final stage, the gaseous thread thins linearly with time. Under constant gas flow rate, the exponent in the power law stage is influenced by the liquid viscosity, and the thinning rate of the linear pinch-off stage decreases with the increase of the liquid viscosity. The liquid flow rate has no obvious effect on the variation of the neck radius of the gaseous thread with time in both stages. The results show that the increase in liquid viscosity enhances the confinement effect on gas-liquid interface during bubble formation.

The gas–liquid two-phase flow and mass transfer performance of CO2 absorption into 2-amino-2-methyl-1-propanol (AMP) with ethylene glycol (EG) non-aqueous solution in a microchannel were investigated under different gas–liquid two-phase flow rates and AMP concentrations. A new correlation was proposed for accurately predicting the liquid side volumetric mass transfer coefficient by considering the enhancement factor. It was verified that the volumetric mass transfer coefficient of CO2 absorption in the microchannel is obviously higher than that in the traditional macroscopic column. Therefore, with the usage of microchannel for AMP-EG non-aqueous solution, both low energy consumption and high efficient absorption could be reached.

The densities and viscosities of binary solutions of (N-methyldiethanolamine + ethanol), (monoethanolamine + ethanol) and (N-methyldiethanolamine + monoethanolamine) as well as ternary solution of (N-methyldiethanolamine + monoethanolamine + ethanol) were measured at T = 293.15 K, 303.15 K, 313.15 K, 323.15 K. The volumetric and viscometric properties, such as the excess molar volume VE, the partial molar volume V ¯ , the partial molar volume at infinite dilution V ¯ ∞ and the viscosity deviation Δη, were calculated from the experimental densities and viscosities. The excess molar volumes and viscosity deviations of binary and ternary solutions were correlated by the Redlich-Kister equation and the Cibulka’s equation, respectively. The intermolecular interactions in binary and ternary solutions were analysed.

The enhancement of gas-liquid mass transfer by baffles embedded in a microchannel was investigated experimentally for CO2 absorption into monoethanolamine/1-butyl-3-methylimidazolium tetrafluoroborate (MEA/[Bmim][BF4]) aqueous solutions. The influences of baffle size on mass transfer rate and pressure drop were studied through varying the MEA/[Bmim][BF4] concentration ratio, gas-liquid flow rate and blockage ratio. Experimental results showed that the proper baffle configuration could improve effectively gas-liquid mass transfer performance. Although the pressure drop of the baffled microchannel has slight increase (the maximum growth 0.3 kPa, or 20% in relative term) in comparison with the unobstructed microchannel, it is acceptable for industrial application. Under lower MEA/[Bmim][BF4] concentration ratios, higher two-phase flow rates and blockage ratios, the mass transfer enhancement is more pronounced and the enhancement factor could reach to 1.5. A new empirical correlation of enhancement factor is proposed with good predictive performance.

The formation process of alternating droplets at the T-junction with a cross-sectional area of 400 μm × 400 μm was investigated using a high-speed camera. The alternating droplets were consisted of glycerol aqueous solution and ferrofluid droplets. Two formation types of alternating droplets were observed: normal formation and the upstream droplet squeezing formation. The existence of the magnetic field delayed the transition from the normal farmation to the upstream droplet squeezing formation. The effects of two-phase flow rate and magnetic flux density on the dynamics of the tip and the neck of the ferrofluid and the formation period were studied. The results show that the neck evolution of ferrofluid could be divided into the expansion stage and pinch-off stage. The expansion stage was dominated by the flow of ferrofluid, and the pinch-off stage was insensitive to fluid flow and was a self-similar process. The length of the tip of ferrofluid increases almost linearly with time during the pinch-off stage, and the increasing rate rose with the flow rates. The formation period of the droplets reduces as the fluid flow rate increases. When the formation type is normal formation, the existence of the magnetic field shortens the formation period. When the formation type is the upstream droplet squeezing regime, the existence of the magnetic field prolongs the formation period. This paper provides a new method for the generation of alternating droplets.

Gas injection plays an important role in bubble formation in microfluidics. The effects of the gas feed on the formation of N2 bubbles in a microfluidic T-junction is highlighted under constant-pre...

The gas-liquid two-phase flow distribution and mass transfer performance of CO2 absorption into 2-amino-2-methyl-1-propanol (AMP) with ethylene glycol (EG) in two parallelized microchannels in a microfluidic loop were investigated. Four flow patterns were observed: filtering flow, repartition flow, breakup flow and irregular flow. The results showed that the uniformity of flow distribution is jointly affected by bubble length at T-junction and the hydrodynamic feedback of the downstream channels. Meanwhile, the uniform flow distribution facilitates the mass transfer performance. Furthermore, a prediction model of liquid side volumetric mass transfer coefficient under breakup flow in parallel microchannels was established by considering the relative error Er characterizing the flow maldistribution.

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.

The mass-transfer process of CO2 absorption into aqueous solution of N-methyldiethanolamine (MDEA) + diethanolamine (DEA) in a T-shaped microchannel was studied using a high-speed camera. The effec...

The mass transfer characteristics of CO2 absorption into aqueous solution of ionic liquid in microchannel was investigated experimentally by a high speed camera. The influences of the ratio of gas and liquid flow rates (QG/QL) and the concentration of ionic liquid on the liquid side volumetric mass transfer coefficient (kLa), liquid side mass transfer coefficient (kL) and length of mass transfer zone (LM) were studied systematically. The results show that both kLa and kL increase but LM decreases with the increasing QG/QL and the concentration of ionic liquid. Taking the enhancement of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) on the mass transfer into account, a dimensionless correlation for predicting kLa was proposed. This work is conducive to the design, optimization and the application of the microchannel reactor for CO2 capture and removal.

The dynamics of the gas-liquid two-phase flow are of great significance for the heat and mass transfer performance in a microreactor. In this paper, the flow pattern, void fraction and frictional pressure drop of gas-liquid two-phase flow of CO2 and MEA/[Bmim][BF4] aqueous solution accompanied by the chemical reaction in a 400 μm square microchannel were investigated experimentally by a high-speed camera and pressure sensor. Three kinds of flow regimes were observed: slug-bubbly flow, slug flow and slug-annular flow. The void fraction and frictional pressure drop in the slug flow regime were mainly investigated, and the applicability of models without consideration of the mass transfer proposed in the literature was assessed. Considering the effect of chemical absorption, two correlations were proposed with the Hatta number for predicting the two-phase void fraction and Chisholm parameter C, which showed good prediction performance.

Background Droplet coalescence in rectangular microchannel is universally applied in microchemical process, however, the effect of aspect ratio on interfacial evolution and dynamics of coalesced droplets has not yet been elucidated. Methods Process of coalescence in microchannels with different aspect ratios was recorded by visualization technology, and the interfacial evolution of liquid bridge was investigated experimentally. Findings The evolution of neck width could be divided into two stages: dispersed phase controlling stage and continuous phase controlling stage, and the neck evolution conforms to power law in the both two stages. However, the exponents in the two stages are different under various flow rate ratios of two phases and aspect ratios of rectangular microchannels. There exists a turning point between the two stages. The neck width at turning point increases linearly with the two-phase flow rate ratio, and the arrival time of turning point decreases exponentially with the increase of flow rate ratio.

International audience; The breakup process of viscous droplets in Y-shaped microchannel was visually investigated. The dynamics of droplet breakup with partial obstruction was primarily studied due to its wide operating range and applicability. The rupture process of droplet could be divided into squeezing, transition and rapid pinch-off stages. In the squeezing stage, the minimum neck width displays a power-law relation with time, and the power-law index α decreases with increasing two-phase viscosity ratio λ. The effect of the capillary number of continuous phase Cac and the length of the mother droplet l0 on α is nearly negligible. In the transition stage, the minimum neck width varies linearly with time, and the slope increases with decreasing λ, increasing Cac and l0. In the rapid pinch-off stage, the minimum neck width declines exponentially with time, and the power-law index β decreases with increasing λ and decreasing l0, however, it is almost independent of Cac

The dynamics of droplet formation in T-junction microchannel was visually investigated. Three different droplet formation flow patterns were observed: single satellite droplet, no satellite droplet, multiple satellite droplets. The formation process of droplets could be divided into four sequential stages: squeezing stage, transition stage, pinch-off stage, and filament thinning stage. In the squeezing stage and pinch-off stage, the minimum neck width of the droplet varies linearly with time, and the neck thinning rate is independent of continuous phase capillary number. In the transition stage, the minimum neck width of the droplet follows power-law relation with time, and the thinning rate of the droplet neck increases with continuous phase capillary number. In the filament rupture stage, the rupture mode of the filament varies with the increase of continuous phase flow rate. The different satellite droplet formation flow patterns and mechanisms were studied and elucidated.

The local deformation and the head-on coalescence dynamics of droplets in a cross-focused microchannel are experimentally investigated. The dynamic process of droplets after collision is divided into squeezing stage and decompressing stage, and the flow patterns are divided into squeezing coalescence, decompressing coalescence and non-coalescence based on the moment when the liquid film ruptures. The local nipples caused by the lubrication force in the thin film arise in the decompressing stage and facilitate coalescence. The effects of the dispersed to continuous-phase viscosity ratio and the concentration of surfactant to the dynamic process, operating range of each flow pattern, and the extent of local deformation are investigated, and the predictive equation of the nipple angle is proposed. This research combines the local deformation with coalescence and provides a reference for further understanding the mechanism of droplet coalescence.

The key step in micro-chemical technology from basic research to industrial applications is the scaling-up of micro-chemical processes. In order to realize the high-throughput, easy-to-control and uniform production of the products in the industrialized operation, the “numbering-up” of the micro-chemical process is mainly achieved from two directions: fluid distribution among the multi-channels and splitting of products step-by-step. Based on the two major directions, in the present review, the key scientific issue of “uniformity of distribution of multiphase flow in parallel microchannels” is focused, the progress of the numbering-up of micro-chemical process is described, and the directions for the research in the future are prospected.

Dynamics for droplet breakup with tunnels and formation of satellite droplets in a symmetric microfluidic T-junction are investigated using a high-speed digital camera. The breakup process of droplet could be divided into four sequential stages: squeezing, transition, pinch-off, and thread rupture stages. Effects of the viscosity ratio of both phases λ , the capillary number of the continuous phase Ca c , and the dimensionless droplet length l 0 / w c on the breakup process of droplet are analyzed. In the squeezing stage controlled by squeezing pressure, the variation of the minimum width of the droplet neck with time could be scaled as a power-law relationship with exponent related to λ and l 0 / w c . The transition stage is dominated by the velocity of the fluid, and the pinch-off stage is mainly driven by the capillary force. For these two stages, the evolution of the minimum width of the droplet neck with the remaining time could be described as other power-law relationship with exponent related to λ . In the thread rupture stage controlled by viscous stresses of both phases and the surface tension, the minimum width of droplet neck decreases linearly with time, and the coefficient of the linear function depends on λ . Additionally, for the formation of satellite droplets, the size of satellite droplet increases with the increase of superficial velocity of the fluid and droplet viscosity. Furthermore, a critical capillary number 0.03 is observed in low viscosity of the droplet, which divides the variation of the size of the main satellite droplet with the capillary number into constant area and growth zone.

The manipulation of a droplet at a microfluidic T-junction is achieved via adding reagents into the droplet with the same solution. Three types for droplet coalescence at the T-junction were observed: tail coalescence, slipping coalescence and unsteady coalescence behaviors with a new droplet formation. The final droplet size decreased (increased) with increasing the capillary number when the flow rate of the dispersed (continuous) phase was fixed. The final droplet size increased with increasing the capillary number of the added phase. The correlations for predicting the coalesced droplet size for tail and slipping coalescence were proposed.

This study experimentally investigates velocity evolution for the coalescence of two in-line bubbles rising in non-Newtonian fluids by using a high speed camera. Due to the wake of the leading bubble and the shear-thinning effect of non-Newtonian fluids, the following bubble is accelerated to approach the leading bubble, leading to the coalescence of the two bubbles. Based on the Newton’s second law and Schlichting’s wake theory, a theoretical model was developed to estimate the instantaneous rising velocity of the following bubble in the coalescence process of the two bubbles. The predicted values by the present model showed a good agreement with the experimental data.

The densities and viscosities of aqueous solutions of sodium glycinate, sodium l -alaninate, sodium l -valinate, sodium l -threoninate and sodium l -argininate were measured at T = (293.15 to 333.15) K under the atmospheric pressure. The effects of temperature and concentration on the densities and viscosities of binary solutions were investigated. The volumetric and viscometric properties such as the apparent molar volume (Vφ), the limiting partial molar volume (Vφ0), the viscosity B-coefficient (B) and the activation energy for viscous flow (Ea) were calculated by the experimental density and viscosity data and analyzed based on the molecular structure and intermolecular interaction. Moreover, the group contribution method was utilized to study the limiting partial molar volume (Vφ0), and the contributions of the end group (-NH2,-COONa), CH- group, CH2- group, CH3- group, OH- group and CNHNHNH2- group to the limiting partial molar volume (Vφ0) were obtained. The results show that all these groups have positive contributions to the limiting partial molar volume (Vφ0).

The breakup dynamics of the dispersed thread for droplet formation in shear-thinning fluids in a flow-focusing device was highlighted. The breakup process of the shear-thinning dispersed thread could be divided into four stages: the droplet growth stage and the squeezing stage, both of them are dominated by the squeezing pressure, the stretching stage controlled by the viscous stresses of dispersed phase and the surface tension, and the pinch-off stage controlled by the viscous stresses of both phases and the surface tension. The breakup dynamics of the dispersed thread for the shear-thinning fluids in each stage is very similar to that of the constant viscosity Newtonian liquids, signifying that the breakup is almost unaffected by the shear-thinning rheological properties.

The effects of viscoelasticity on formation process, size and generation frequency of bubbles in T-junctions within symmetrical parallelized microchannels are investigated by a high-speed camera system. Air and polyethylene oxide (PEO)-glycerol solutions with 0.3% SDS are used as the dispersed and continuous phases, respectively. Three flow patterns are observed including slug, bubbly and beads-on-string flows. The evolution of the gaseous neck during bubble formation under various flow patterns, flow rate ratios of liquid and gas, and molecular weights of PEO is studied based on the distribution of elastic stress in the microchannel. The results reveal that the increase of the Weissenberg number is beneficial to the bubble breakup, and the uniformity of bubble size in the parallelized microchannels is better with higher flow rate ratios of liquid and gas. Finally, the semi-empirical formulas for the size and generation frequency of bubbles in the parallelized microchannels are established.

Step emulsification technology is an important breakthrough for the industrial application of microfluidic devices. In this paper, the influences of microdevice structures and physical properties of fluids on the droplet (around 1 mm in size) generation in a step emulsificator with a single microchannel are studied. Through the analysis of the interface evolution process during droplet generation, we found that increasing the width of the terrace (0.4–1.0 mm) and the size of the collection cavity, decreasing the viscosity of the dispersed phase (0.89–54.61 mPa·s) result in the increase in the range of the dripping flow regime, obtaining a larger emulsion flux of the microdevice. The prediction equation for the droplet size is proposed by considering the inertial and viscous forces of the dispersed phase: D h = 1.63 O h 0.17 W e 0.14 + D 0 h - 0.47 O h 0.24 . Finally, the relationship between the satellite droplet size formed by the neck rupture and the manipulation variables is presented.

The breakup flow patterns, the neck dynamics and the tip dynamics of bubbles stabilized by adsorptive nanoparticles in microfluidic Y-junction were investigated. Three flow patterns were observed in the Y-junction: non-breakup, breakup with partial obstruction, and breakup with permanent obstruction. Compared with bubbles stabilized only by surfactants (conventional bubbles), bubbles stabilized by nanoparticles (hardening bubbles) are more difficult to breakup. The breakup process with partial obstruction could be divided into three stages: squeezing, transition and pinch-off. Nanoparticles have little effect on the squeezing stage, but could greatly prolong the transition stage while accelerate the pinch-off stage. The difference between hardening and conventional bubbles is weakened, even disappears as the dispersion flow rate increases. Besides, the “rigid” surface of hardening bubbles could cause the decrease of the curvature of daughter bubble tips and the tunnels between the daughter bubbles and the channel wall in comparison with conventional bubbles.

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.

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.

In this study, the densities and viscosities of the binary solutions 1-dimethylamino-2-propanol (1DMA2P) + H2O, benzylamine (BZA) + H2O, 1DMA2P + BZA and ternary solution 1DMA2P + BZA + H2O were measured at T = (298.15−333.15) K. Furthermore, the volumetric and the viscometric properties including the excess molar volume, partial molar volume, apparent molar volume, limiting apparent molar volume, viscosity deviation, excess Gibbs energy of activation for viscous fluid and Grunberg-Nissan interaction parameters were obtained in terms of experimental data, respectively. The excess molar volumes of binary and ternary solutions were fitted by the Redlich-Kister equation and Cibulka equation, besides, the viscosity and viscosity deviation of binary solution were correlated by using the Grunberg-Nissan equation and Redlich-Kister equation. Moreover, the intermolecular interactions were analyzed based on the volumetric and viscometric properties of solutions.

Dynamics of non-Newtonian droplet (CMC aqueous solution) breakup with partial obstruction in microfluidic Y-junction was visually investigated. Three breakup stages were found: squeezing, transition and pinch-off. The effects of the concentration c of CMC, continuous capillary number Cac and dispersed phase local capillary number Cad on droplet breakup were studied. In squeezing stage and transition stage, the breakup process could be promoted by increasing Cad or decreasing c. The pinch-off stage relied primarily on the surface tension and was almost independent of inertial force and viscous force. For the shear thinning non-Newtonian droplet, the length of the daughter droplet was always linearly stretched with time until breakup and the maximum gap width increased with Cac, but decreased with the increases of c and Cad.

In many applications of microdroplets, the high monodispersity of the product is usually an essential requirement, the appearance of undesired satellite droplets needs to be avoided. In this study, the deformation of droplets and the formation of tail satellite droplets in microchannel were investigated experimentally, and the process mechanism was also explored. Three flow regimes of moving droplets were observed: (1) droplet with convex cap; (2) droplet with tip; (3) droplet with satellite. It was found that the rear cap of the droplet was more prone to deformation. The shearing force on the droplet becomes strengthened with the increase of the superficial velocity of the droplet, the flow rate ratio of two phases or the viscosity of the continuous phase, which facilitates the formation of tail satellite droplets. The critical criterion for formation of tail satellite droplets was proposed, which is at good agreement with the experiment result.

Based on the online method, the absorption kinetics and mass transfer of CO2 in potassium carbonate solution in a serpentine minichannel are studied. Three flow patterns are observed: slug-bubbly flow, slug flow, and slug flow with precipitation of SiO2. It is observed that the length of bubble decreases linearly with the increase of the travelling distance of bubble x in slug flow, based on which the volumetric mass transfer coefficient (kLa) is calculated. The results show that the average bubble velocity vb is only a function of the gas and liquid flow rates, and it remains unchanged in the whole flow process. Based on the online method, the instantaneous mass transfer coefficient, and instantaneous pH are studied. It’s found that the instantaneous mass transfer coefficients kLa and kL increase with the mass transfer of bubbles along the flow direction in the slug flow. It is concluded that the convection in the liquid slug plays a major role in controlling the mass transfer of fast chemical absorption in a serpentine minichannel.

Densities and viscosities of binary mixtures {[Bmim][BF4] + MDEA}, {MDEA + H2O} and ternary mixture {[Bmim][BF4] + MDEA + H2O} were measured at T = (293.15–333.15) K. The volumetric and viscometric properties of binary and ternary mixtures, such as excess molar volume (VE), viscosity deviation (Δη), excess Gibbs energy of activation of viscous flow (ΔG⁎E), and Grunberg-Nissan interaction parameter (G12), were deduced from experimental data. The excess molar volumes and viscosities data were used to calculate the Redlich-Kister and Jouyban-Acree equations coefficients for binary mixtures, and Singh et al. and Jouyban-Acree extended equations coefficients for ternary mixtures. The intermolecular interactions in binary and ternary mixtures were discussed through volumetric and viscometric properties and FT-IR spectroscopic analysis.

Densities and viscosities of glycine, L-alanine, L-valine, L-threonine and L-arginine in aqueous (0.1–0.5) mol·kg− 1 myo-inositol solutions were measured at T = (293.15, 303.15, 313.15 and 323.15) K and p = 0.101 MPa. The volumetric properties such as the apparent molar volume (Vφ), the limiting partial molar volume (Vφ0), the limiting partial molar volumes of transfer (ΔtrVφ0), the limiting apparent molar expansibility (E20), Hepler's constant and the isobaric thermal expansion coefficient (α2) were calculated through density. The viscometric properties such as the B-coefficient, the free energies of activation per mole of solvent (Δμ10 ≠) and solute (Δμ20 ≠) were obtained from the experimental viscosity data. The derived parameters hydration number and solvation number were also calculated through apparent molar volume and B-coefficient. From the volumetric and viscometric properties, the solute-solute and solute-solvent interactions in the studied systems were analyzed on the basis of co-sphere overlap model and transition state theory. Finally, the group contribution method was applied to calculate the contribution of (NH3+, COO−), CH2, OH and CNHNHNH2 of amino acids to Vφ0, B-coefficient and Δμ20 ≠.