Modelling the coupled transfer of mass and thermal energy in the vapour–liquid region of a nitrogen–oxygen mixture

Current non-equilibrium distillation models do not explicitly include the coupling between thermal and mass fluxes. We present a calculation model for the coupled transfer of mass and thermal energy in the vapour–liquid region of a binary mixture. The region is modelled as a vapour–liquid interface in between two homogeneous films. The entropy production in the vapour–liquid region can be calculated using both irreversible thermodynamics and the entropy balance. The film thickness ratio is found by requiring the entropy production calculated with the two methods to be equal, while keeping the vapour film thickness fixed. Using a nitrogen–oxygen mixture as example, we show that neglecting the coupling between thermal and mass fluxes can have a large impact on the magnitude and direction of the theoretical (net) fluxes. The size of the impact depends on the vapour film thickness, but it is significant for all thicknesses. By increasing the number of control volumes that is used to represent the liquid and vapour films, we also show that the fluxes depend highly on the resistivity profiles in the films. They depend slightly on the interface resistance. A sensitivity analysis of the transport properties shows that accurate values of the Maxwell–Stefan diffusion coefficients in both homogeneous phases and of the liquid phase heat of transfer are most important. Especially the measurable heat flux at the liquid boundary of the system is sensitive to neglect of coupling, to neglect of the interface resistance and to uncertainties in the transfer properties.     

Micro-computed tomography for the investigation of stationary liquid–liquid and liquid–gas interfaces in capillaries

For better understanding and optimization of multiphase flow in miniaturized devices, micro-computed tomography (μCT) is a promising visualization tool, as it is nondestructive, three-dimensional, and offers a high spatial resolution. Today, computed tomography (CT) is a standard imaging technique. However, using CT in microfluidics is still challenging, since X-ray related artifacts, low phase contrast, and limited spatial resolution complicate the exact localization of interfaces. We apply μCT for the characterization of stationary interfaces in thin capillaries. The entire workflow for imaging stationary interfaces in capillaries, from image acquisition to the analysis of interfaces, is presented. Special emphasis is given to an in-house developed segmentation routine. For demonstration purposes, contact angles of water, liquid polydimethylsiloxane, and air in FEP, glass, and PMMA are determined and the influence of gravity on interface formation is discussed. This work comprises the first steps for a systematic 3D investigation of multiphase flows in capillaries using μCT.     

Experimental investigation of liquid–liquid flow in an inclined pipe using dimensionless numbers

Two-phase flow is a common phenomenon in the energy industry, where flow patterns significantly affect heat transfer and pressure drop in different systems. However, there is no unique or comparable flow map because of its dependency on dimensional parameters. Therefore, an analysis using dimensionless numbers makes the results comprehensive. To do so, a series of liquid–liquid flow experiments (1296 experiments) were conducted in a transparent pipe at the different velocities of the phases. The flow patterns were captured using a high-speed camera. The experiments were performed at eight different inclinations within the range of −20 to +20 degrees. Six flow patterns are observed at different inclinations; stratified flow with mixing at the interface (STMI), dispersion of water in oil (Dw/o), dispersion of oil in water (Do/w), dual continuous (DC), slug, and wavy stratified (WST), where the first five flow patterns are presented in the upward flow and the two last flow patterns disappear in some of the downward flow. The pattern of boundaries for each flow pattern in the upward flow shows dependency on inclination, while in the downward flow condition, a rather general format can be applied to most of the patterns. The analysis illustrates that gravity and buoyancy forces are the dominating forces in the system compared to other forces, such as viscous, inertia, and interfacial tension, which are due to the inclination of the pipe.     

Simultaneous liquid–liquid and vapour–liquid equilibria predictions of selected oxygenated aromatic molecules in mixtures with alkanes,alcohols, water,using the polar GC-PC-SAFT

Phase equilibria of oxygen-bearing aromatic compounds, hydrocarbons and water mixtures are of essential interest in many processes using feeds originating from biomass. The strong non-ideal thermodynamic behavior of these systems sometimes results in immiscibility with both water and alkanes.To address this problem, the GC-PPC-SAFT equation of state [Tamouza et al., 2004; Nguyen-Huynh et al., 2008a] is extended to some selected components: phenol, alkyl-phenols, alkyl-benzoates, benzaldehyde and anisole. However, as in these multifunctional compounds, the proximity of polar functional groups may result in a lack of transferability of the parameters from the monofunctional homologous species, some parameters have been adapted in view of physical arguments. Next, liquid–vapour and liquid–liquid equilibria of mixtures with n-alkanes were evaluated, using a predictive method for the binary interaction parameters (k_ij) [Nguyen-Huynh et al., 2008b]. Finally, mixtures with other associating compounds, as alcohols and water have also been considered.In all cases, both correlations and predictions are qualitatively and quantitatively satisfactory. The relative deviations obtained on bubble pressure of vapor–liquid equilibria are 4–8%, that is comparable to those obtained on previously investigated systems.     

Salting-out-assisted liquid–liquid extraction and reverse-phase high-performance liquid chromatographic monitoring of thiacloprid in fruits and vegetables

Salting-out-assisted liquid–liquid extraction (SALLE) was developed to extract thiacloprid (THI) from fruits and vegetables. SALLE conditions (NaCl/Na₂SO₄, pH, and solvent polarity) were investigated at various levels for the optimal recovery of THI. Meanwhile, reverse-phase high-performance liquid chromatographic (RP-HPLC) conditions were balanced over 1–100 µg/mL of THI. The optimized SALLE-RP-HPLC method offered 78.33–92.00% recovery of standard THI at an acceptable repeatability 1.81–4.30% and reproducibility 1.08–4.74%. The detection and quantification limits were found to be 0.03 and 0.05 µg/mL, respectively. The real-time analysis verifies its suitability and ease of use for the determination of THI in agricultural commodities.     

Synthesis and liquid crystalline behavior of phosphorus-containing aliphatic–aromatic copoly(ester-imide)s

A series of phosphorus-containing copoly(ester-imide)s was prepared by polycondensation reaction of 2-(6-oxido-6H-dibenz<c,e><1,2>oxaphosphorin-6-yl)-1,4-naphthalene diol, 1, or of various mixtures of 1 and 1,12-dodecanediol, 3, with an aromatic diacid chloride containing preformed imide rings, 2, namely 4-chloroformyl-N-(p-chloroformylphenyl)-phthalimide. The polymers exhibited thermotropic liquid crystalline behavior, as was observed by means of polarized light microscopy, differential scanning calorimetry, and X-ray investigations. The copoly(ester-imide)s showed good thermal stability having the temperature of 5% weight loss above 365–408 °C and char yield at 700 °C in the range 8.8–48%.     

Modelling and numerical simulation of liquid–solid circulating fluidized bed system for protein purification

A novel liquid–solid circulating fluidized bed (LSCFB) was modelled for protein recovery from the feed broth. A typical LSCFB system consists of downer and riser, integrating two different operations simultaneously. A general purpose, extensible, and dynamic model was written based on the tanks-in-series framework. The model allowed adjusting the degree of backmixing in each phase for both columns. The model was validated with previously published data on extraction of bovine serum albumin (BSA) as model protein. Detailed dynamic analysis was performed on the protein recovery operation. The interaction between the riser and downer were captured. Parametric studies on protein recovery in LSCFB system were carried out using the validated model to better understand the system behaviour. Simulation results have shown that both production rate and overall recovery increased with solids circulation rate, superficial liquid velocity in the downer and riser, and feed solution concentration. The model was flexible and could use various forms of ion exchange kinetics and could simulate different hydrodynamic behaviours. It was useful to gain insight into protein recovery processes. The general nature of the model made it useful to study other protein recovery operations for plant and animal proteins. It could also be useful for further multi-objective optimization studies to optimize the LSCFB system.     

Development of a model for thin-film stability and spreading in solid–liquid–liquid systems

The presence of thin aqueous films and their stability has a profound effect on reservoir rock–fluids interactions involved in spreading and adhesion. The stability of thin wetting aqueous films on rock surfaces is governed by several variables including pH, brine and crude oil compositions, and capillary pressure. These variables govern the wetting states in the solid–liquid–liquid systems. The wetting states influence the residual oil saturation and the oil-water relative permeabilities and, consequently, the oil recovery. The objective of this study was to deduce a functional dependence of thin-film stability on the above parameters by considering intermolecular and surface interactions in rock–crude oil–brine systems. The surface forces are manifested as disjoining pressure in thin films. The disjoining pressure isotherms for the selected solid–liquid–liquid systems have been computed in terms of the bulk properties of the media. The equilibrium contact angles have also been computed from the integration of the Young–Laplace equation, which relates contact angle to the capillary pressure and disjoining pressure isotherm of the system. The contact-angle data obtained from sessile-drop experiments have been compared with the calculated results, as well as with other published results. Adhesion maps, which relate the film stability to brine pH and molarity, have been developed. The rock–fluids systems considered for this study consisted of smooth glass, quartz and Yates reservoir fluids. The DLVO theory has been used to model the intermolecular forces. The structural forces are incorporated to overcome the limitations of the DLVO theory. A charge regulation model has been used to analyze the crude oil–brine and glass–brine interfaces. The effects of multivalent ions have been incorporated using an equivalent molarity concept. The overall computational model developed in this study is aimed at providing a priori prediction capability of rock-fluids interactions in petroleum reservoirs for inclusion in reservoir simulators.     

Process intensification and waste minimization in liquid–liquid–liquid phase transfer catalyzed selective synthesis of mandelic acid

Conversion of biphasic reactions into triphasic reactions can lead to process intensification, waste minimization and selectivity enhancement. Unlike liquid–liquid (L–L) PTC, the Liquid–Liquid–Liquid phase transfer catalysis (L–L–L PTC) offers high order of intensification of rates of reaction and catalyst reuse. The rate of reaction is remarkably enhanced by the catalyst-rich middle phase, which is the main reaction phase. Separation of catalyst can be done easily and the separated catalyst can be reused several times by using L–L–L PTC. This leads to waste minimization and other benefits of Green Chemistry. Mandelic acid and its derivatives are used for their dual activities as antibacterial and anti-aging agents. In this work, mandelic acid was produced by L–L–L PTC reaction of dichlorocarbene with benzaldehyde. Dichlorocarbene was generated in situ by the reaction of chloroform and sodium hydroxide in the presence of poly ethylene glycol (PEG) 4000 as the catalyst. The selectivity to mandelic acid was 98%. The reaction mechanism and kinetics model were established to validate the experimental data.     

Analysis of the flow pattern and periodicity of gas–liquid–liquid three-phase flow in a countercurrent mixer-settler

In contrast to the concurrent mixer-settler, the interaction between the mixing and settling chambers have to be taken into account in the simulation of the countercurrent mixer-settler, and no work has been reported for this equipment. In this work, a three-phase flow model based on the Eulerian multiphase model, coupled with a sliding mesh model is proposed for a countercurrent mixer-settler. Based on this, the dispersed phase distribution, flow pattern, and pressure distribution are investigated, which can help to fill the gap in the operation mechanism. In addition, the velocity vector distribution at the phase port shows an intriguing phenomenon that two types of vectors with opposite directions are distributed on the left and right sides of the same plane, which indicates that the material exchange in the mixing and settling chambers is simultaneous. Analysis of this variation at this location by a fast Fourier transform (FFT) method reveals that it is mainly influenced by the mixing chamber and is consistent with the main period of the outlet flow fluctuations. Therefore, by monitoring the fluctuation of the outlet flow and then analyzing it by the FFT method, the state of the whole tank can be determined, which makes it promising for the design of control systems for countercurrent mixer-settlers.     

Cathodic reduction of α-bromopropiophenone in an aprotic medium

The cathodic reduction in an aprotic medium of α-bromopropiophenone produces 1,4-diphenyl-2,3,-dimethyl-1,4-butanedione. This product is transformed by dehydration in 2,5-diphenyl-3,4-dimethylfuran. The reduction process is rationalized via anionic intermediates.     

Characteristics of liquid slugs in gas–liquid Taylor flow in microchannels

The hydrodynamics of liquid slugs in gas–liquid Taylor flow in straight and meandering microchannels have been studied using micro Particle Image Velocimetry. The results confirm a recirculation motion in the liquid slug, which is symmetrical about the center line of the channel for the straight geometry and more complex and three-dimensional in the meandering channel. An attempt has also been made to quantify and characterize this recirculation motion in these short liquid slugs (L_s/w<1.5) by evaluating the recirculation rate, velocity and time. The recirculation velocity was found to increase linearly with the two-phase superficial velocity U_TP. The product of the liquid slug residence time and the recirculation rate is independent of U_TP under the studied flow conditions. These results suggest that the amount of heat or mass transferred between a given liquid slug and its surroundings is independent of the total flow rate and determined principally by the characteristics of the liquid slug.     

Analysis of concentration polydispersity in mixed liquid–liquid systems

Inter-phase mass transfer for each chemical component is typically modelled with one material balance for the continuous and one for the dispersed phase. This approach contains inherently an assumption that the phases are well mixed at least locally. For the dispersed phase, this assumption requires that breakage and coalescence are significantly faster compared to the mass transfer, which is not necessarily true. It is important to carry out preliminary assessment whether the dispersed phase segregation is important and should be considered in subsequent modelling efforts, before embarking heavy multidimensional simulations where all possible dispersed phase variations are considered. In this work, relevant time scales are first defined and used for analyzing dispersed phase mixedness in liquid–liquid systems with mass transfer between the phases. Then appropriate dispersed phase modelling tools for the purpose are evaluated. Simple droplet number density based analysis is shown to estimate mixedness reasonably well. Furthermore, the drop number density approach is also shown to predict the average drop sizes with almost comparable accuracy than the full population balances.     

Spray and mixing characteristics of liquid jet in a tubular gas–liquid atomization mixer

For the design and optimization of a tubular gas–liquid atomization mixer,the atomization and mixing characteristics of liquid jet breakup in the limited tube space is a key problem.In this study,the primary breakup process of liquid jet column was analyzed by high-speed camera,then the droplet size and velocity distribution of atomized droplets were measured by Phase-Doppler anemometry (PDA).The hydrodynamic characteristics of gas flow in tubular gas–liquid atomization mixer were analyzed by computational fluid dynamics (CFD) numerical simulation.The results indicate that the liquid flow rate has little effect on the atomization droplet size and atomization pressure drop,and the gas flow rate is the main influence parameter.Under all experimental gas flow conditions,the liquid jet column undergoes a primary breakup process,forming larger liquid blocks and droplets.When the gas flow rate (Q_g) is less than 127 m~3·h~(-1),the secondary breakup of large liquid blocks and droplets does not occur in venturi throat region.The Sauter mean diameter (SMD) of droplets measured at the outlet is more than 140μm,and the distribution is uneven.When Q_g127 m~3·h~(-1),the large liquid blocks and droplets have secondary breakup process at the throat region.The SMD of droplets measured at the outlet is less than 140μm,and the distribution is uniform.When 127Q_g162 m~3·h~(-1),the secondary breakup mode of droplets is bag breakup or pouch breakup.When 181Q_g216 m~3·h~(-1),the secondary breakup mode of droplets is shear breakup or catastrophic breakup.In order to ensure efficient atomization and mixing,the throat gas velocity of the tubular atomization mixer should be designed to be about 51 m·s~(-1)under the lowest operating flow rate.The pressure drop of the tubular atomization mixer increases linearly with the square of gas velocity,and the resistance coefficient is about 2.55 in single-phase flow condition and 2.73 in gas–liquid atomization condition.     

Numerical simulation of micro-mixing in gas–liquid and solid–liquid stirred tanks with the coupled CFD-E-model

The coupled CFD-E-model for multiphase micro-mixing was developed, and used to predict the micro-mixing effects on the parallel competing chemical reactions in semi-batch gas–liquid and solid–liquid stirred tanks. Based on the multiphase macro-flow field, the key parameters of the micro-mixing E-model were obtained with solving the Reynolds-averaged transport equations of mixture fraction and its variance at low computational costs. Compared with experimental data, the multiphase numerical method shows the satisfactory predicting ability. For the gas–liquid system, the segregated reaction zone is mainly near the feed point, and shrinks to the exit of feed-pipe when the feed position is closer to the impeller. Besides, surface feed requires more time to completely exhaust the added H⁺ solution than that of impeller region feed at the same operating condition. For the solid–liquid system, when the solid suspension cloud is formed at high solid holdups, the flow velocity in the clear liquid layer above the cloud is notably reduced and the reactions proceed slowly in this almost stagnant zone. Therefore, the segregation index in this case is larger than that in the dilute solid–liquid system.     

Modelling and grinding characteristics of unidirectional C–SiCs

At present, many scholars are experimentally investigating the grinding performance of ceramic matrix composites (C–SiCs). However, accurately reflecting the microscopic mechanisms of crack initiation and extension and the material removal mechanism (MRM) is difficult. To research the micro-MRM of C–SiCs, a theoretical model (TTM) and a numerical simulation model (NSM) were established in this study and were proven to be reliable by experiments. The TTM was established according to the kinematics and dynamics of a single abrasive particle. In the procedure of establishing the NSM, the SiC matrix (SiCM) and carbon fibre reinforcement (CFRT) were each modelled based on the internal structure characteristics of C–SiCs and then combined by an interface layer. The TTM, NSM and verification experiments all showed that fibre pull-out, fibre outcrop, matrix cracking and interfacial debonding were the basic defects in the C–SiCs. As the grinding depth (a_p) increased, the grinding performance of the C–SiCs gradually deteriorated. The material removal characteristics of C–SiCs can be directly modelled at the microlevel by the NSM. The NSM showed that the grinding force fluctuated periodically because the CFRT and SiCM have different properties. High stresses occurred mainly in the SiCM. This research can supply a scientific basis for understanding the micro-MRM of C–SiCs and provide important guidance for the high-quality grinding of C–SiCs.     

Effect of operating factors on liquid–liquid mass transfer and dispersion pattern of sedimentary liquid in a mechanically stirred vessel

Liquid–liquid dispersion and mass transfer were investigated in mechanically stirred vessels without baffles by changing operation factors such as an impeller rotation speed, off-bottom clearance, volumetric liquid ratio, etc. The dispersion regime was categorized into five groups: the sedimentary liquid was kept at the vessel bottom (I), partially elevated without any collision (II), partially dispersed by colliding with the impeller bottom (III), both liquids were partially dispersed by collisions with impeller blades (III’), and the sedimentary liquid was completely dispersed (IV). The dispersion switched to I → II → III → IV with the increasing rotation speed and decreasing off-bottom clearance. The liquid–liquid mass transfer rate was significantly enhanced with the collision of the sedimentary liquid with the impeller bottom, and subsequently increased with the increasing rotation speed, volumetric liquid ratio, and vessel diameter and with the decreasing off-bottom clearance. A multiple regression analysis method was applied to determine the mass transfer rates of III and III’.     

Mixing and recirculation characteristics of gas–liquid Taylor flow in microreactors

The effects of operating parameters (capillary and Reynolds numbers) and microchannel aspect ratio (α=w/h=[1;2.5;4]$\alpha =w/h=[1;2.5;4]$) on the recirculation characteristics of the liquid slug in gas–liquid Taylor flow in microchannels have been investigated using 3-dimensional VOF simulations. The results show a decrease in the recirculation volume in the slug and an increase in recirculation time with increasing capillary number, which is in good agreement with previous results obtained in circular and square geometries (Thulasidas et al., 1997). In addition, increasing the aspect ratio of the channel leads to a slight decrease in recirculating volumes but also a significant increase in recirculation times.     

Effective and simple recovery of 1,3-propanediol from a fermented medium by liquid–liquid extraction system with ethanol and K_3PO_4

1,3-Propanediol,traditionally obtained from fossils,has numerous industrial applications,including use in the production of high performance polymers.The microbial production of 1,3-propanediol presents several opportunities,and the final purity grade determines its price and commercial viability.The development of novel separation technology could improve the economic viability of the bioproduction of 1,3-propanediol.Thus,we investigated salting-out extraction as a novel process for 1,3-propanediol recovery from fermentation broth.Initially,a screening for the best salt/solvent combination was conducted and then optimized using the response surface methodology.The solvents studied were methanol,ethanol,isopropanol and acetone,and the salts examined were K_2HPO_4,Na_2CO_3,K_2CO_3,(NH_4)_2SO_4,NaHPO_4,K_3PO_4 and C_6H_5NaO_7.The optimal extraction system consisted of 34 wt%K_3PO_4,28 wt% ethanol,and 38 wt% fermentation broth containing 23.0 g·L~(-1)1,3-propanediol,which gave the highest partition coefficient of 33 and recovery yield of 97%.The results demonstrated that salting-out extraction was a promising method for 1,3-propanediol recovery from fermentation broth.