Search

In this study, the authors carried out a multiparametric assessment of the influence of swirl patterns during aerosol flow on the shape of the interfacial area that forms the cone based on data obtained from experimental measurements using the PIV and LLS methods. The results were correlated with the disinfection process occurring in the near and far fields of the aerosol (direct surface disinfection and volume fogging). In this study, parameters such as turbulent kinetic energy (TKE), swirl strength (SS), pressure fields, and Sauter mean diameter (d32) are used to investigate the relationship between aerosol spray morphology and flow dynamics under different operating conditions. Three different geometrical settings of the aerosol-generating system and two different pressures corresponding to the air supply to the spray nozzle have been adopted. By evaluating the results obtained, the influence of each parameter on the formation of the aerosol displacement trajectory, the stabilization of the spray cone, and its degradation was identified. The shape of the boundary between the dynamically moving aerosol and the surrounding air was also evaluated. The conditions for swirling and straight-line flows within the aerosol cone, and, thus, the conditions for the volumetric development of swirling phenomena, were further clarified. [ABSTRACT FROM AUTHOR]

The specific interface area transport equation is derived from first principles, and a closure model for turbulent flow is proposed. The flow is modelled by a two-phase method providing velocities of both phases at the bubbly, spray and the intermediate large scale interface (LSI) regimes. The interface area is transported by the interface velocity – a linear combination of corresponding phase velocities and a turbulent drift velocity. The resulting equation includes the source terms due to the bubble (droplet) breakup and coalescence, and turbulent splashes at the interface. A model is proposed for the source term in the LSI regime. The model is implemented in the developer's version of the Simcenter STAR-CCM+ $ \circledR $ ® CFD code. The new model is applied to self-aerating water flows down stepped chutes; the results are in reasonable agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Abstract This study investigates an oil/water two-phase system to assess the potential efficacy of a novel passive mixer in enhancing the liquid-liquid interfacial area within a micro-channel contactor. In this system, two fluids are introduced into a microchannel with a diameter of 800 μm and a length of 20 cm, which is equipped with a stainless-steel helical wire measuring 250 μm in diameter. Throughout the experiments, both fluids are supplied at equal flow rates, and the dominant forces, including attachment and detachment forces, are examined. The results reveal a critical Weber number of 3.8 × 10−³, at which the first detachment occurs. A comparison between microchannels with and without the passive micromixer demonstrates that greater slug breakup occurs in the system incorporating the helical wire micromixer. This innovative configuration results in a significant reduction in slug/droplet size compared to a microchannel without a barrier, decreasing from approximately 600 μm to 390 μm at a flow rate of 0.8 mL/min. Additionally, a flow map is presented, illustrating three distinct flow regimes: flow contains long slug, Slug-droplet flow, and droplet flow regimes, with the droplet flow regime covering the largest area. The findings indicate that the implementation of this innovative passive mixer substantially increases the interfacial area, providing significant advantages for mass transfer applications.

This study investigates an oil/water two-phase system to assess the potential efficacy of a novel passive mixer in enhancing the liquid-liquid interfacial area within a micro-channel contactor. In this system, two fluids are introduced into a microchannel with a diameter of 800 μm and a length of 20 cm, which is equipped with a stainless-steel helical wire measuring 250 μm in diameter. Throughout the experiments, both fluids are supplied at equal flow rates, and the dominant forces, including attachment and detachment forces, are examined. The results reveal a critical Weber number of 3.8 × 10−³, at which the first detachment occurs. A comparison between microchannels with and without the passive micromixer demonstrates that greater slug breakup occurs in the system incorporating the helical wire micromixer. This innovative configuration results in a significant reduction in slug/droplet size compared to a microchannel without a barrier, decreasing from approximately 600 μm to 390 μm at a flow rate of 0.8 mL/min. Additionally, a flow map is presented, illustrating three distinct flow regimes: flow contains long slug, Slug-droplet flow, and droplet flow regimes, with the droplet flow regime covering the largest area. The findings indicate that the implementation of this innovative passive mixer substantially increases the interfacial area, providing significant advantages for mass transfer applications. [ABSTRACT FROM AUTHOR]

Surface modification of a crystalline filler is a powerful method for increasing the thermal conductivity (κ) of filler-impregnated composites. Herein, boron nitride (BN) filler was functionalized with cationic molecules of different sizes to directly recognize the effect of an amorphous area on the filler-polymer matrix interface. Measured thermal conductivity and temperature rise for a polymer composite was up to 67.1 % and 15.3 % greater, respectively, in the sample to which the smallest molecule-modified BN was added, compared to the comparable sample with free BN. The smaller the size of the modifier molecule, the better it bonds with the resin and the smaller the non-crystalline area. Such changes improve the heat transfer at the interface by reducing interfacial thermal resistance. These findings can serve as a reference to develop alternative and effective strategies for filler modification, an alternative approach instead of focusing on functional groups and modifiers. [Display omitted] [ABSTRACT FROM AUTHOR]

The bubble size, gas holdup, and interfacial area in a swirling contactor were investigated through experiments and simulations. The interfacial area was obtained for liquids and gases with Reynolds numbers Rel and Reg, respectively. The contactor was divided into twelve subregions. Rel was negatively related to bubble size, gas holdup, and interfacial area, whereas Reg was positively associated. The maximum bubble interfacial area for the entire swirling contactor was 196.3 m−1 with a gas‐liquid ratio of 0.022. There is a trade‐off between centrifugal acceleration and bubble size for interfacial area. [ABSTRACT FROM AUTHOR]

Structured packing is an important equipment and has wide applications in chemical separation process. In this study, the complex hydrodynamics characteristics of structured sinusoidal corrugated sheets packings were investigated by 2D liquid film model and 3D Representative Element Unit model. Volume of Fluid method was employed to investigate the effect of eleven different structures of sinusoidal corrugated sheets packings (i.e. wavelength, amplitude, and corrugated angle) on liquid holdup, wet pressure drop, and interfacial area. In addition, a shape factor was proposed to characterize the effect of flow regime on packing hydrodynamics characteristics and wetting performance. The packing shape factor analysis method proposed in this study could provide a reference for the structural optimization and evaluation of structured packing in the future. • Multi-scale CFD simulation of multiphase flow in sinusoidal corrugated sheets packings with VOF method. • Effect of geometry structure on hydrodynamics characteristics. • A shape factor analysis method that reveals the relationship between packing shape and flow regime. • Effect of flow regime on hydrodynamics characteristics. [ABSTRACT FROM AUTHOR]

The challenging task in our ecosystem is to reduce acidic gas emissions to some extent. Many gases are emitted from the industries like H2S, CO, CO2, SO2, NO, and NO2 as exhaust gases. Among these gases, CO2, NO2, and SO2 are acidic, which results in adverse effects on humans, animals, and plants. The increase in the emission of CO2 gases from both anthropogenic and industrial sources resulted in CO2 mitigation studies. CO2 absorption studies were carried out using iron oxide nanofluid with the novel structured packed absorption column. Iron oxide nanoparticles were synthesized and characterized using XRD, SEM, and TEM analysis. Ammonia is used as an absorbent along with iron oxide nanofluid of three different concentrations (0.0001 w/v%, 0.001 w/v%, and 0.0015 w/v%). It was found that the iron oxide nanofluid of 0.0015 w/v% showed an improved % CO2 removal efficiency. This enhanced % CO2 removal efficiency was due to the increased interfacial area of the ameliorated contact between the liquid and gas phases. In addition, the magnetic field was introduced along with the packed column, which increased CO2 removal efficiency by 1.5%.

Small-size CaCu3Ti3.95Zr0.05O12 enhanced dielectric constant of LDPE by 88.5% due to enhancing interfacial polarization included by ultrahigh interfacial area (∼3.0 × 105 m2) and played a prominent role in homogenize electric field distribution in LDPE composite.

While experimental designs developed in recent decades have contributed to research on dynamic nonequilibrium effects in transient two-phase flow in porous media, this problem has been seldom investigated using direct numerical simulation (DNS). Only a few studies have sought to numerically solve Navier–Stokes equations with level-set (LS) or volume-of-fluid (VoF) methods, each of which has constraints in terms of meniscus dynamics for various flow velocities in the control volume (CV) domain. The Shan–Chen multiphase multicomponent lattice Boltzmann method (SC-LBM) has a fundamental mechanism to separate immiscible fluid phases in the density domain without these limitations. Therefore, this study applied it to explore two-phase displacement in a single representative elementary volume (REV) of two-dimensional (2D) porous media. As a continuation of a previous investigation into one-step inflow/outflow in 2D porous media, this work seeks to identify dynamic nonequilibrium effects on capillary pressure–saturation relationship (Pc–S) for quasi-steady-state flow and multistep inflow/outflow under various pressure boundary conditions. The simulation outcomes show that Pc, S and specific interfacial area (anw) had multistep-wise dynamic effects corresponding to the multistep-wise pressure boundary conditions. With finer adjustments to the increase in pressure over more steps, dynamic nonequilibrium effects were significantly alleviated and even finally disappeared to achieve quasi-steady-state inflow/outflow conditions. Furthermore, triangular wave-formed pressure boundary conditions were applied in different periods to investigate dynamic nonequilibrium effects for hysteretical Pc–S. The results showed overshoot and undershoot of Pc to S in loops of the nonequilibrium hysteresis. In addition, the flow regimes of multistep-wise dynamic effects were analyzed in terms of Reynolds and capillary numbers (Re and Ca). The analysis of REV-scale flow regimes showed higher Re (1 < Re < 10) for more significant dynamic nonequilibrium effects. This indicates that inertia is critical for transient two-phase flow in porous media under dynamic nonequilibrium conditions.

In the literature, different calculation relationships are often presented to describe the same process taking place in the given equipment. This article presents the different forms of the correction factor (Ackermann correction factor) used in describing the processes in which heat and mass transfer occur simultaneously. The form of the equations determining the value of the Ackermann correction factor basically depends on the choice of the orientation of the coordinate system. The article presents the derivation of two forms of equations, on the basis of which the value of this factor is usually determined. Finally, the article also contains the equations that describe the simultaneous transfer of heat and mass. These are used in the design of various types of equipment that are part of the various industrial technologies (e.g., in agricultural, chemical, and food industries). From the point of view of these equations, the article mainly emphasizes that, if it is necessary to work with several equations describing the same process, care should be taken to ensure that these equations are compatible with each other. In this case, compatibility means that there is no need to use a sign correction when substituting the result from one equation into another.

The distillation of three binary test systems differing in the surface tension gradient along the column, namely: cyclohexane/n-heptane (negative), cyclohexane/toluene (neutral), n-hexane/cyclohexane (positive), has been performed under total reflux in the i.d. 0.3 m distillation column packed with MellapakPlus 452. Y structured packing. Although all constituents are C 6 – C 7 hydrocarbons with close physical properties in the gas phase, the resulting HETP differ by up to 20 %. Further analysis suggests that system negativity causes the approx. 30 % decrease of the effective interfacial area with respect to positive and neutral systems, which behave comparably. Indeed, observation of the distillation on the inclined plate in the IR spectra shows breakage of the negative system liquid films into rivulets, supporting the result. [Display omitted] • HETP, kGa of MellapakPlus 452. Y measured in 0.3 m distillation column. • Significant difference between HETP of negative and neutral/positive systems. • Distillation effective interfacial area evaluated using kG chemisorption correlation. • Liquid film of the negative system breaks into rivulets as conveniently observed in IR spectra. [ABSTRACT FROM AUTHOR]

Multiphase fermentations are still poorly understood since much of the available information focused on global rather than local data and the most used parameter to control the dispersion of gas in the stirred tank is the agitation rate. However, the energy dissipated in the stirred tank is influenced by the properties of the broths, such as viscosity. Therefore, the objective of this work was to use a retrofitted power input strategy in order to maintain constant the total power input per unit volume (P g /V), studying the local gas hold-up (φ) and interfacial area (a) values in three regions in a pilot-scale stirred tank at different values of Trichoderma harzianum mycelial biomass concentration, airflow rate and constant P g /V. We found that the constant P g /V regime was an effective strategy that allows to discern the effects of different parameters in the local values of gas hold-up and interfacial area. Under constant retrofitted total gassed power input, the biomass concentration showed no influence on the local values of interfacial area and gas hold-up. Depending on the position of the probe, φ and a varied up to 60.6% and 63.8%, respectively. The highest P g /V and airflow rate conditions determined the highest values in φ and a , but not in the same proportion in the three zones tested. [Display omitted] • Local φ and a were analyzed under a constant P g /V regime with a mycelial broth model. • If P g /V is kept constant, biomass concentration had no effect on gas hold-up (φ). • Depending on the port analyzed, mass transfer area (a) varied up to 63.8%. [ABSTRACT FROM AUTHOR]

The experimental distillation apparatus presented here serves to simulate the hydrodynamic and mass transfer conditions in a distillation column packed with the structured packing. It produces a film of the boiling liquid mixture flowing down the inclined plate with counter-currently flowing vapour of that mixture under total reflux with the mass transfer proceeding between the phases. The inclined plate instead of the sheet of structured packing is used for its simplicity as the first approximation in this work. The apparatus enables observation of the liquid film by means of a thermal imaging camera through a heated KBr window. Thermograms of films of IR-translucent mixtures (such as the cyclohexane/n-heptane mixture) provide information on the spatial distribution of the film thickness, while those of films of IR-opaque mixtures (such as methanol/propanol mixture) should reveal the spatial distribution of the mass transfer intensity across the interface. So far the results remain qualitative. Monitoring of the IR-opaque liquid surface is complicated by the relatively well-visible vapour phase in the IR spectrum, which unpredictably and irregularly hinders the view. • Observation of the distillation process in the IR. • Qualitatively different information from termograms of the IR-translucent and IR-opaque liquid films. • Measurement of the IR absorption coefficients of the distillation mixtures constituents in the liquid and vapour phases. [ABSTRACT FROM AUTHOR]

The scale transition from discrete pore network model (PNM) simulations to one-equation continuum model (CM) of drying has been investigated in previous studies for uniformly structured porous media. This investigation is extended in the present work to porous media with widely different pore size distributions, as well as to those with spatially correlated networks of small and large pores. The key questions examined here are how and to what extent pore-structural features can be reflected in the local macroscopic parameters of the one-equation CM derived by traditional homogenization. For this purpose, three-dimensional model capillary structures with monomodal and bimodal pore size distributions are generated and drying simulations are conducted at the limit of viscous-capillary dominated regime. By leveraging volume-averaged data obtained from PNM simulations the one-equation CM is parameterized and thus its local parameters are expressed in dependence on the pore structure. The simulation results show that for the monomodal and bimodal pore structures the profiles of the moisture transport coefficients are complex and non-unique over the entire drying process. Moreover, the deviation of the water vapor partial pressure from the saturation vapor pressure in the presence of liquid water – which is referred to as non-local equilibrium effect – is less pronounced for the bimodal pore structure compared to the monomodal pore structures. Finally, comparisons are performed between the volume-averaged data obtained at different stages of drying by the discrete simulations with monomodal and bimodal pore structures and results of the continuum model of drying. [ABSTRACT FROM AUTHOR]

• New two-group interfacial area concentration (IAC) model was developed. • Two-group drift-flux model (DFM) was used to obtain void fractions of each group. • Two-group IAC and predictions showed good agreement with experimental data. • Developed IAC model was applicable to dispersed flows in large-diameter pipes. • Developed two-group IAC and DFM can be implemented in 1D analysis codes. Interfacial area concentration (IAC) plays a critical role in heat and mass transfers between gas and liquid phases through the interfaces. As interfacial area increases, mass and heat transfers between phases increase. Hence, a reliable IAC estimation is important for two-phase flow numerical simulations to conduct engineering designs and safety analyses. Gas bubbles show different behavior according to their shapes and sizes. Based on the size, gas bubbles can be classified into two groups that show different characteristics, such as IAC. Hence, two-group modeling helps to achieve a general approach for estimating the IAC in bubbly to beyond-bubbly flow regimes. Available models in the literature use empirical correlations to obtain group one and group two void fractions. These empirical approaches are not reliable for different flow conditions. In addition, these models are usually complex with several empirical constants. This study aims to develop a two-group area-averaged IAC model for upward vertical dispersed flows through large-diameter pipes. In addition, this study proposes using a general approach based on the two-group drift-flux model to calculate two-group void fractions rather than applying empirical correlations. The models are evaluated using 156 two-group measured data points in dispersed flow conditions through large-diameter pipes. The resulting prediction errors for group one and group two IAC models are 24.1 % and 34.2 %, and the errors for group one and group two void fraction predictions are 22.8 % and 25.6 %, respectively. [ABSTRACT FROM AUTHOR]

Various factors affect the processes that take place in the devices. Knowledge of these factors is important, especially for technical practice. If these were omitted in the design of the device, the expected changes in the properties of the substances would probably not occur in the device. Different processes occur in the devices, often involving simultaneous heat and mass transfer through the interfacial area. In this case, it is true that the description of the heat transfer cannot be based on ordinary laws. It is necessary to proceed from their corrected forms because, generally, the mass transfer influences the heat transfer. This impact can be taken into account using the correction factor adjusting the commonly reported relationships, as mentioned in this article.

The aim of the present work is to account for polydisperse effects in a two-phase flow with a simple and fast method. Polydisperse two-phase flows arise in numerous applications. Fire sprinkler systems are relevant examples as they release clouds of polydisperse droplets. Another relevant example is the polydisperse two-phase flow created by the detonation of an explosive charge surrounded by a liquid layer. In such a situation, material interfaces are initially present and the created two-phase flow consists of a carrier gas phase and a liquid phase involving many droplets of various sizes. Spherical particles or droplets are usually assumed in two-phase flow computations. When dealing with explosion situations involving both dense and dilute flow regimes, multiple particle diameters can be addressed but at the price of introducing as many additional equations that describe mass, momentum and energy balance of the various particle classes. Consequently, the computation time needed to address numerical resolution increases tremendously. Under explosion situations involving many particle diameters, the method becomes intractable and is usually reduced to a single diameter, which is often insufficient. A simplified approach is developed in the present work to account for a substantial number of particles of different sizes with few extra computational cost. The approach is said to be simplified as a single velocity and a single temperature are considered for all the spherical particles, regardless of their diameters. This type of modeling seems apt for the target explosion situations. The focus is placed on the interfacial area, which is the main parameter involved in the coupling of the two phases. In the present work, Gamma-like continuous probability distributions are considered to address the various sizes of particles. The effects of the size distribution are only summarized in the specific interfacial area, yielding consequently few code modifications while taking into account the polydisperse aspect of the two-phase flow. [ABSTRACT FROM AUTHOR]

In this article, CaCu3Ti4O12 (CCTO) and Zr-doped CaCu3Ti3.95Zr0.05O12 (CCTZO) particles were fabricated by the sol–gel combustion method, and then, CCTO/LDPE and CCTZO/LDPE composite films were prepared by the melt-blending and hot briquetting. The microstructures and dielectric properties of fillers and LDPE composites were investigated in detail. Results showed the lattice expansion of CCTZO caused by Zr doping reduced grain size, increased size uniformity, and remarkably reduced dielectric loss and conductivity. Compared with CCTO, small-size CCTZO enhanced dielectric constant of LDPE by 88.5% (∼3.45) due to enhanced interfacial polarization included by ultrahigh interfacial area (∼3.0 × 105 m2), remaining a lower loss tangent (0.013) and conductivity (2.42 × 10−13 S·cm−1) for the 10 vol% CCTZO/LDPE composite. Furthermore, finite element simulation proofed small-size and uniform CCTZO particles played a prominent role in homogenize electric field distribution in LDPE composite, which was beneficial for the use of these composites in the high voltage power cable field. Small-size CaCu3Ti3.95Zr0.05O12 enhanced dielectric constant of LDPE by 88.5% due to enhancing interfacial polarization included by ultrahigh interfacial area (∼3.0 × 105 m2) and played a prominent role in homogenize electric field distribution in LDPE composite. [ABSTRACT FROM AUTHOR]

• Analysis is performed on interfacial area transport in bubbly flows at varying orientations. • Decreasing angle causes drop in average interfacial area concentration. • Modeling interfacial area transport possible with existing closure models. • Closure models require treatment of covariances to account for distribution effects. • Interfacial area concentration is predicted within 9% for all bubbly flow cases. The present work develops closure models for the interfacial area transport equation for inclined-upward bubbly two-phase flows. This includes frictional pressure drop through a Lockhart-Martinelli method; void fraction and void-weighted gas velocity through a drift-flux analysis; and covariance of bubble interaction mechanisms through a novel void-fraction distribution reconstruction method. Bubbly flow data collected in a 25.4 mm air–water test facility for five angles (0°, 30°, 60°, 80°, and 90°) is used for the development and evaluation of the models. The novel void reconstruction models are able to predict the covariance of bubble interaction terms within ± 30 % , and the transport of interfacial area can be predicted within 9 %. [ABSTRACT FROM AUTHOR]

Carbon dioxide capture via solvent absorption in packed columns has emerged as a potential technology to mitigate coal‐fired power plant CO2 emissions. Parameters, including packing types, solvent properties, and operating conditions, could potentially affect the packed column CO2 capture efficiency. To understand the importance of those parameters and help packed column optimization, a design of experiments (DoEs) method was proposed to generate input parameter matrix. Combined with multiphase computational fluid dynamics (CFD), the random packed column parameter influence on the liquid holdup and interfacial area can be efficiently investigated. Surrogate‐based sensitivity analysis shows that the solvent flow rate and contact angle are key factors dictating liquid holdup and interfacial area. On the other hand, solvent viscosity has a marginal impact on the interfacial area. The sensitivity scores were calculated for each input parameter to guide the selection of dimensionless numbers for the liquid holdup and interfacial area correlation development. [ABSTRACT FROM AUTHOR]

Interfacial area is an important factor during two-phase flow in porous media because mass-transfer mechanisms take place at the interfaces of immiscible phases. The objective of this work is to quantify how grain-size distribution affects the temporal development of interfacial area during two-phase flow through porous media. A two-phase lattice Boltzmann model (color gradient method) was used to simulate drainage (displacement of a wetting fluid by a non-wetting fluid) and imbibition (displacement of the non-wetting fluid by the wetting fluid) in an ensemble of two-dimensional porous media samples. Five groups of porous media, each comprising 20 realizations, were characterized by their median grain size (d50) and coefficient of uniformity (Cu). For all 100 realizations, simulations of drainage and imbibition were conducted until steady-state saturation was achieved, and interfacial area was monitored throughout the simulations. During both drainage and imbibition, the interfacial area initially increases with time until reaching a peak area, then decreases, and then plateaus at a steady-state value. Interfacial area is higher during imbibition than during drainage. The temporal evolution of interfacial area, as quantified by peak area and time to reach peak area, was similar in the three groups characterized by small grain size (d50 ≈ 7.7 lattice units) and relatively uniform grain-size distribution (Cu ≈ 1.21, 1.49, 1.85), for both drainage and imbibition. This suggests that, for the fluid conditions considered here, nonuniformity of grain size is not important below a certain threshold value of Cu. However, two groups with larger grain size (d50 ≈ 8.9 lattice units) and relatively nonuniform grain-size distribution (Cu ≈ 1.85, 2.29) exhibited differences from each other, suggesting that nonuniformity of grain size affects interfacial area when Cu is above a certain value. Furthermore, median grain size was observed to have important effects on temporal evolution of interfacial area. [ABSTRACT FROM AUTHOR]

In the literature, different calculation relationships are often presented to describe the same process taking place in the given equipment. This article presents the different forms of the correction factor (Ackermann correction factor) used in describing the processes in which heat and mass transfer occur simultaneously. The form of the equations determining the value of the Ackermann correction factor basically depends on the choice of the orientation of the coordinate system. The article presents the derivation of two forms of equations, on the basis of which the value of this factor is usually determined. Finally, the article also contains the equations that describe the simultaneous transfer of heat and mass. These are used in the design of various types of equipment that are part of the various industrial technologies (e.g., in agricultural, chemical, and food industries). From the point of view of these equations, the article mainly emphasizes that, if it is necessary to work with several equations describing the same process, care should be taken to ensure that these equations are compatible with each other. In this case, compatibility means that there is no need to use a sign correction when substituting the result from one equation into another. [ABSTRACT FROM AUTHOR]

The dispersed phase holdup and drop size in solvent extraction columns vary along the column height and this affects the mass transfer coefficient and interfacial area. In this article, mass transfer study was performed experimentally using a 25 mm diameter agitated pulsed column. The axial distribution of mass transfer coefficient was determined by coupling population balance equation and axial dispersion model by taking the longitudinal variation in hydrodynamic performance into consideration. Feasibility of different mass transfer models in predicting concentration profiles was evaluated and a novel correlation based on effective diffusivity was developed. The results showed that both overall and volumetric mass transfer coefficients have significant change along the column height and greatly depends on the agitation speed and pulsation intensity. Increasing dispersed phase velocity also augments the overall mass transfer coefficient. The maximum number of transfer unit was measured to be 10 m−1 at agitation speed of 1000 rpm. [ABSTRACT FROM AUTHOR]

With enormous interfacial area for particle collection, microbubbles exhibit great application prospect in the mineral flotation. Under certain ionic strength, microbubbles can be produced continuously in the microbubble column without extra reagent addition. In this work, multiphase flow characteristics (Sauter mean diameter, bubble size distribution, gas holdup & interfacial area) were studied systematically with variables including the salt type, salt concentration, and operating conditions. Based on mathematical model, critical coalescence concentration was determined for each investigated salt. According to experimental results, a mathematical correlation was established between the Sauter mean diameter and ionic strength. For the formation of microbubble system, the lowest ionic strength was approximately 0.5 mol/L. Multiphase flow characteristics in the microbubble column depended highly on the ionic strength. The interfacial area and gas holdup increased by 38 times and more than 3 times respectively, with the ionic strength of Al2(SO4)3 rising from 0 to 1.5 mol/L. The critical coalescence concentration ranged from 0.037 mol/L (Al2(SO4)3) to 0.517 mol/L (NaCl), which correlated with the ionic strength of each salt. [ABSTRACT FROM AUTHOR]

An accurate description of the relative permeability–saturation function is crucial for reliable predictions of multi‐phase flow behavior in subsurface applications. Although extensive efforts have been put forth to investigate the relative permeability behavior in different types of porous media, only few studies have focused on rough‐walled fractures. In this work, we present an entirely new, cost‐effective, heavily‐parallelized, dynamic pore‐network modeling framework that is employed to conduct a systematic study of relative permeability curves under two‐phase flow conditions in rough‐walled fractures. We first build a two‐dimensional (101.42 × 24.86 mm2) equivalent pore network of a Berea sandstone fracture from its x‐ray images. Subsequently, dynamic primary drainage and imbibition simulations are conducted in the fracture. We show that the two‐phase fluid occupancy maps predicted from the simulations agree well with the fracture fluid configurations obtained via X‐ray computed tomography. Afterward, the validated model is used to probe two‐phase flow properties in a series of synthetic aperture fields generated with a broad range of geometric characteristics including aperture spatial correlation length (normalized correlation length varying from 0.05 to 0.95), anisotropy factor (0.25–4), surface roughness (normalized fracture roughness varying from 0.05 to 0.4), and mean aperture size (50–800 μm). The generated results provide novel insights into the effects of these features on two‐phase flow properties such as fluid–fluid interfacial area, phase interference, and relative permeability. Moreover, based on the simulation results we propose two new correlations to describe the relative permeability curves for primary drainage and imbibition processes in rough‐walled fractures. Plain Language Summary: Modeling two‐phase flow in rock fractures still remains a challenge because of the highly irregular geometries of the rough‐walled fractures. For example, there is still no consensus regarding how two‐phase flow properties behave in a single fracture. To address this problem, we developed a new dynamic pore‐scale modeling platform. It rigorously solves for the forces associated with two‐phase displacements in fracture spaces and has an advantage of being computationally efficient. As a result, we are able to conduct a comprehensive and systematic study of two‐phase flow properties in a large number of synthetic fractures designed with varying geometric features. The generated results not only significantly improve the understanding of the effects of the aperture geometries on the two‐phase flow properties but also allow us to propose new correlation equations describing fluid flow properties of rough‐walled fractures that can be directly adopted for use in predicting flow behaviors in fractured media at the large scale (meters to kilometers). Key Points: A new, computationally efficient, dynamic pore‐network model for two‐phase flow in rough‐walled fractures is developed and validatedImpacts of correlation length, aperture anisotropy, fracture roughness, and aperture size on fracture relative permeability are studiedNew relative permeability models are proposed for drainage and imbibition processes in rough‐walled fractures [ABSTRACT FROM AUTHOR]

Micropacked bed reactors (μPBRs) shows excellent mass transfer characteristics, but related mass transfer experimental and models are inadequate for CO 2 absorption. Herein, a gas-side overall volumetric mass transfer coefficient (K G a) model of μPBRs was developed based on the two-film theory. Effects of bed inner diameter and water contact angle (CA) of particle on effective interfacial area (a) were discussed. Then, the mass transfer model was validated by MEA-CO 2 absorption efficiency (η) with AARD of 7.72%. The K G a of μPBRs (2.16–13.16 kmol/(m3·h·kPa)) is much larger than that of the traditional multiphase reactors. The ceramic beads with big water CA for d c / d p more than 10 and glass beads with small water CA for d c / d p less than 10 can enhance CO 2 absorption efficiency in μPBRs. Additionally, the empirical correlation of a and K G a were proposed. [ABSTRACT FROM AUTHOR]

A new method is developed to approximate a first-order Hamilton–Jacobi equation. The constant motion of an interface in the normal direction is of interest. The interface is captured with the help of a “Level-Set” function approximated through a finite-volume Godunov-type scheme. Contrarily to most computational approaches that consider smooth Level-Set functions, the present one considers sharp “Level-Set”, the numerical diffusion being controlled with the help of the Overbee limiter (Chiapolino et al. in J Comput Phys 340:389–417, 2017). The method requires gradient computation that is addressed through the least squares approximation. Multidimensional results on fixed unstructured meshes are provided and checked against analytical solutions. Geometrical properties such as interfacial area and volume computation are addressed as well. Results show excellent agreement with the exact solutions. [ABSTRACT FROM AUTHOR]

Silica as a stable and biocompatible material has attracted a great deal of interest, particularly concerning the synthesis of porous silica. Hierarchical Porous Silica (HPS) can be synthesized through nanoemulsion templating and sol–gel. The oil droplets of NE acted as a pore-forming agent and the sol-gel built the matrix around the oil droplets. The O/W-NE was prepared by the phase inversion composition (PIC) method. The effect of nanoemulsion volume (2.5, 25, and 50) and the effect of oil droplet diameter (65, 105, 150, 200, and 400 nm) on the HPS was studied. Samples were characterized by many characterization techniques. The microstructure of the samples is versatile with macropores distributed homogenously through the mesoporous silica matrix or hollow macroporous spheres. Both volume and hydrodynamic diameter of the nanoemulsions influence the microstructure through the oil/water interfacial area. The surface area ranges between 158 and 281 m2/g and the pore volume is between 0.63 and 6.59 cc/g. Highlights: Role of sodium silicate concentration/interfacial area is crucial. Hierarchical porous silica with a macroporous matrix or hollow spheres. Surface area ranges from 158 to 281 m2/g. The pore volume ranges between 0.63 and 6.59 cc/g. Surface roughness for pure silica is 2.48 and increases to 2.95 by nanoemulsion templating. [ABSTRACT FROM AUTHOR]

The manner in which added non‐catalytic proteins during enzymatic hydrolysis of lignocellulosic substrates enhances hydrolysis mechanisms is not completely understood. Prior research has indicated that a reduction in the non‐specific adsorption of enzymes on lignin, and deactivation of enzymes exposed to air–liquid interface provide rationale. This work investigated root causes including effects of the air–liquid interface on non‐catalytic proteins, and effects of lignin on endoglucanase. Three different experimental designs and three variables (air–liquid interfacial area, the types of lignin (acid or enzymatic lignin), and the presence of non‐enzymatic protein (bovine serum albumin [BSA] or soy proteins) were used. The results showed that acid isolated lignin adsorbed almost all endoglucanase activity initially present in supernatant, independent of air interface conditions (25 or 250 ml flasks) with the presence of BSA preventing this effect. Endoglucanase lost 30%–50% of its activity due to an air–liquid interface in the presence of lignin while addition of non‐enzymatic protein helped to preserve this enzyme's activity. Langmuir and Freundlich models applied to experimental data indicated that the adsorption increases with increasing temperature for both endoglucanase and BSA. Adsorption of the enzyme and protein were endothermic with an increase in entropy. These results, combined, show that hydrophobicity plays a strong role in the adsorption of both endoglucanase and BSA on lignin. [ABSTRACT FROM AUTHOR]

In this research, an ultrasound assisted CO 2 absorption system using different absorbents has been investigated. Ultrasonic atomization technology is one of the efficient methods to increase gas-liquid interfacial area, thereby absorption rate. First of all, the significance of each operational parameter on the absorption rate was investigated by applying the experimental design methodology. The response surface methodology (RSM) and Box-Behnken design were employed to determine the experimental design. The analysis of variance revealed the adequacy and accuracy of the proposed models. The results indicated that among the investigated variables, the input power played more important role in the absorption rate. In addition, the absorption rate was not sensitive to the temperature. Moreover, a comparative study using water absorbent indicated that applying ultrasonic atomization led to five times faster CO 2 absorption rate compared to the conventional stirring method and 20 times faster rate compared to the silent condition (no ultrasonic and no stirring). [ABSTRACT FROM AUTHOR]

External loop air lift reactor (EL-ALR) is widely used for multiphase reactions. They offer lower pressure drop and good heat and mass transfer rates compared to conventional bubble column reactors. In the case of fermentation applications where a medium is highly viscous and coalescing in nature, sectionalisation of riser helps in the improvement of the interfacial area as well as the reduction in liquid-phase backmixing. The present work deals with the measurement of the gas hold-up, mixing time, liquid dispersion, Sauter mean bubble diameter over a broad range of superficial gas velocities in sectionalised EL-ALR. Effects of electrolytes and surfactants have also been studied. Different plate designs have been studied for the sectionalisation. The correlations have been proposed for the gas hold-up, liquid circulation velocity, Sauter mean bubble diameter for superficial gas velocities. Abbreviations: EL-ALR: external loop air lift reactor; IL-ALR: internal loop air lift reactor; ADC: analog to digital converter; DAC: digital to analog converter. [ABSTRACT FROM AUTHOR]

A variety of two‐phase flow experiments, currently available in the literature, are compared to study the effect of fluid relaxation on interfacial area generation. Interfacial area is an important parameter that controls mass transfer in many engineered multiphase systems, so it is important to develop accurate predictive tools describing multiphase flow to engineer efficient processes. An empirical predictive relationship was developed describing a specific interfacial area‐wetting saturation relationship that depends on the number of quasi‐equilibrium relaxation points obtained during a drainage or imbibition experiment. The empirical expression was tested and verified using a number of existing datasets. We found that different relationships were needed depending on the fluid properties as well as the porous medium. However, clear trends were observed that can, once a predictive relationship is established for the system, allow us to design multiphase flow systems to produce a desired amount of interfacial area tailored to a particular application. Key Points: Empirical expressions, which will depend on the number of relaxation points, can predict interfacial area‐saturation relationships for a porous mediumDuring a flow event, overall interfacial area generation decreases with an increased number of relaxation points, independent of fluid pairInterfacial relaxation generally has a greater effect on interfacial generation at lower wetting saturations than at high saturations [ABSTRACT FROM AUTHOR]

This work presents high surface area sp2 carbon allotropes as important tools to design and prepare lightweight materials. Composites were prepared based on either carbon black (CB) or carbon nanotubes (CNT) or hybrid CB/CNT filler systems, with either poly(1,4-cis-isoprene) or poly(styrene-co-butadiene) as the polymer matrix. A correlation was established between the specific interfacial area (i.a.), i.e. the surface made available by the filler per unit volume of composite, and the initial modulus of the composite (G′γmin), determined through dynamic mechanical shear tests. Experimental points could be fitted with a common line, a sort of master curve, up to about 30.2 and 9.8 mass% as CB and CNT content, respectively. The equation of such master curve allowed to correlate modulus and density of the composite. Thanks to the master curve, composites with the same modulus and lower density could be designed by substituting part of CB with lower amount of the carbon allotrope with larger surface area, CNT. This work establishes a quantitative correlation as a tool to design lightweight materials and paves the way for large scale application in polymer matrices of innovative sp2 carbon allotropes.

A high foam stability (FS) is important for manufacturers and is mainly achieved through high protein concentrations. Consequently, the increase of FS at lower protein concentrations is desirable from an economic point of view, especially for proteins that show a lower foamability and FS, such as pea protein isolate (PPI). The hypothesis of this study was that if the viscosity of a PPI dispersion is adjusted to a higher protein concentration (i.e. 5 wt% PPI adjusted to the viscosity of 7.5 wt% PPI), a similar FS can be obtained, while reducing the needed protein concentration. Therefore, the influence of energy density (Evol) and viscosity on FS was examined. For this, foams were prepared (Evol = 3.6 × 108 J m−3 to 14.4 × 108 J m−3) with PPI (c = 5, 7.5, 10 wt%), as well as with mixtures of PPI and non-surface-active maltodextrin (MD) to modulate the viscosity of the continuous phase. Overall, it was shown that MD was able to considerably improve FS of PPI. Mixtures of PPI and MD with the same viscosity as the pure PPI dispersions exhibited a similar FS. For example, the addition of MD to 5 wt% PPI for adjustment of the viscosity to that of the pure 7.5 wt% PPI facilitated a FS of 1664 s ± 2 s compared to 1354 s ± 122 s. Generally, the addition of MD led to a higher viscosity of the continuous phase and an increase in protein surface load, which both attributed positively to FS. [ABSTRACT FROM AUTHOR]

The development of high-resolution in situ imaging has allowed contact angles to be measured directly inside porous materials. We evaluate the use of concepts in integral geometry to determine contact angle. Specifically, we test the hypothesis that it is possible to determine an average contact angle from measurements of the Gaussian curvature of the fluid/fluid meniscus using the Gauss-Bonnet theorem. We show that it is not possible to unambiguously determine an average contact angle from the Gauss-Bonnet theorem. We instead present an approximate relationship: 2 π n (1 - cos θ) = 4 π - ∫ κ G 12 dS 12 , where n is the number of closed loops of the three-phase contact line where phases 1 and 2 contact the surface, θ is the average contact angle, while κ G 12 is the Gaussian curvature of the fluid meniscus which is integrated over its surface S 12 . We then use the results of pore-scale lattice Boltzmann simulations to assess the accuracy of this approach to determine a representative contact angle for two-phase flow in porous media. We show that in simple cases with a flat solid surface, the approximate expression works well. When applied to simulations on pore space images, the equation provides a robust estimate of contact angle, accurate to within 3 ° , when averaged over many fluid clusters, although individual values can have significant errors because of the approximations used in the calculation. [ABSTRACT FROM AUTHOR]

The dynamic two-phase flow in porous media was theoretically developed based on mass, momentum conservation, and fundamental constitutive relationships for simulating immiscible fluid-fluid retention behavior and seepage in the natural geomaterial. The simulation of transient two-phase flow seepage is, therefore, dependent on both the hydraulic boundaries applied and the immiscible fluid-fluid retention behavior experimentally measured. Many previous studies manifested the velocity-dependent capillary pressure–saturation relationship (Pc-S) and relative permeability (Kr-S). However, those works were experimentally conducted on a continuum scale. To discover the dynamic effects from the microscale, the Computational Fluid Dynamic (CFD) is usually adopted as a novel method. Compared to the conventional CFD methods solving Naiver–Stokes (NS) equations incorporated with the fluid phase separation schemes, the two-phase Lattice Boltzmann Method (LBM) can generate the immiscible fluid-fluid interface using the fluid-fluid/solid interactions at a microscale. Therefore, the Shan–Chen multiphase multicomponent LBM was conducted in this study to simulate the transient two-phase flow in porous media. The simulation outputs demonstrate a preferential flow path in porous media after the non-wetting phase fluid is injected until, finally, the void space is fully occupied by the non-wetting phase fluid. In addition, the inter-relationships for each pair of continuum state variables for a Representative Elementary Volume (REV) of porous media were analyzed for further exploring the dynamic nonequilibrium effects. On one hand, the simulating outcomes reconfirmed previous findings that the dynamic effects are dependent on both the transient seepage velocity and interfacial area dynamics. Nevertheless, in comparison to many previous experimental studies showing the various distances between the parallelly dynamic and static Pc-S relationships by applying various constant flux boundary conditions, this study is the first contribution showing the Pc-S striking into the nonequilibrium condition to yield dynamic nonequilibrium effects and finally returning to the equilibrium static Pc-S by applying various pressure boundary conditions. On the other hand, the flow regimes and relative permeability were discussed with this simulating results in regards to the appropriateness of neglecting inertial effects (both accelerating and convective) in multiphase hydrodynamics for a highly pervious porous media. Based on those research findings, the two-phase LBM can be demonstrated to be a powerful tool for investigating dynamic nonequilibrium effects for transient multiphase flow in porous media from the microscale to the REV scale. Finally, future investigations were proposed with discussions on the limitations of this numerical modeling method.

The effects of cellulose, surfactants, and their combination on the hydrodynamic behavior and the liquid‐side mass transfer coefficient of a bubble column were evaluated. For that purpose, different aqueous solutions containing surfactants (sodium dodecyl sulfate) and cellulose (microcrystalline cellulose, MCC) were investigated. The interfacial areas were calculated from the bubble diameters, the bubble frequencies, and the terminal bubble rising velocities. The liquid‐side mass transfer coefficients were determined from the volumetric mass transfer coefficients measured by the dynamic method. In the concentration range under test, the experimental results proved that the addition of MCC to the studied liquid phases did not affect the mass transfer coefficient. [ABSTRACT FROM AUTHOR]

Conservation of energy is used to derive a thermodynamically-consistent contact angle, θ t , when fluid phase 1 displaces phase 2 in a porous medium. Assuming no change in Helmholtz free energy between two local equilibrium states we find that Δ a 1 s cos θ t = κ ϕ Δ S 1 + Δ a 12 , where a is the interfacial area per unit volume, ϕ is the porosity, S is the saturation and κ the curvature of the fluid-fluid interface. The subscript s denotes the solid, and we consider changes, Δ , in saturation and area. With the advent of high-resolution time-resolved three-dimensional X-ray imaging, all the terms in this expression can be measured directly. We analyse imaging datasets for displacement of oil by water in a water-wet and a mixed-wet sandstone. For the water-wet sample, the curvature is positive and oil bulges into the brine with almost spherical interfaces. In the mixed-wet case, larger interfacial areas are found, as the oil resides in layers. The mean curvature is close to zero, but the interface tends to bulge into brine in one direction, while brine bulges into oil in the other. We compare θ t with the values measured geometrically in situ on the pore-scale images, θ g . The thermodynamic angle θ t provides a robust and consistent characterization of wettability. For the water-wet case the calculated value of θ t gives an accurate prediction of multiphase flow properties using pore-scale modelling. [ABSTRACT FROM AUTHOR]