Interphase Mass Transfer Process Research Articles

The Phase Distribution Characteristics and Interphase Mass Transfer Behaviors of the CO2-Water/Saline System under Gathering and Transportation Conditions: Insights on Molecular Dynamics.

In order to investigate the interphase mass transfer and component distribution characteristics of the CO2-water system under micro-scale and nano-scale transport conditions, a micro-scale kinetic model representing interphase mass transfer in the CO2-water/saline system is developed in this paper. The molecular dynamics method is employed to delineate the diffusion and mass transfer processes of the system's components, revealing the extent of the effects of variations in temperature, pressure, and salt ion concentration on interphase mass transfer and component distribution characteristics. The interphase mass transfer process in the CO2-water system under transport conditions can be categorized into three stages: approach, adsorption, and entrance. As the system temperature rises and pressure decreases, the peak density of CO2 molecules at the gas-liquid interface markedly drops, with their aggregation reducing and their diffusion capability enhancing. The specific hydration structures between salt ions and water molecules hinder the entry of CO2 into the aqueous phase. Additionally, as the salt concentration in water increases, the density peak of CO2 molecules at the gas-liquid interface slightly increases, while the density value in the water phase region significantly decreases.

Heat and mass transfer performance analysis of a vertical tubular ammonia/water bubble absorber based on CFD modeling

Bubble absorbers are highly efficient in mass transfer processes, but their popularization is limited by the risks associated with too much ammonia charging. In order to reduce the ammonia charge, it is essential to optimize the heat and mass transfer performance in the absorber. Existing models provide in-depth analysis of bubble motion and morphology, but insufficient attention has been paid to the concentration distribution and interfacial heat and mass transfer resistance. In this study, a two-dimensional axisymmetric vertical tubular ammonia/water bubble absorber was modeled based on Fluent and phase equilibrium, absorption heat data based on Aspen was imported. The relative deviations were 9%, 0.45%, and 4.1% in terms of the completely absorbed height, the liquid phase ammonia mass fraction, and the outlet temperature, respectively. The results showed that the mass transfer deterioration point was at the gas column closure and the heat transfer deterioration point was at the gas column contraction. Variable parameter studies have shown that turbulence effects at the gas–liquid interface can lead to enhancement and deterioration of local heat and mass transfer, which in turn cause local oscillations in the concentration and temperature profiles. While increasing the interphase mass transfer driving force promotes the interphase mass transfer process, it hinders the diffusion mass transfer process within the liquid phase. This effect is particularly pronounced in the absence of intense cooling, leading to an increase in the complete absorbed height.

Simulation analysis of bubble coalescence behavior characteristics in non-Newtonian fluids based on the phase field method

Gas-liquid two-phase flow is widely used in various fields of chemical production because of its stability. The bubble coalescence behavior has a significant impact on the size, shape and movement of bubbles. These parameters are important parameters for affecting the interphase mass and heat transfer processes and equipment performance. This paper presents a simulation study of the bubble coalescence behavior of non-Newtonian fluids using the phase field method through simulation software. The relative location of bubbles were divided into three types: vertical, parallel and random; and also the distribution of bubbles can be divided into three cases: symmetric, left-skewed and right-skewed. This paper focuses on the influence of the arrangements of the bubbles on their coalescence behavior in non-Newtonian fluids. The results show that in non-Newtonian fluids, the relative distance of the bubbles and the flow characteristics of the fluid are both key factors in whether bubble coalescence can occur, and they exhibit different patterns of action when the bubbles are in different arrangements. Also bubbles show different patterns of motion in different distributions.

APPROACHES TO MODELING CONDITIONS OF THERMOACOUSTIC INSTABILITY IN NON-EQUILIBRIUM TWO-PHASE COOLANT OF NUCLEAR REACTORS

The consequences of thermoacoustic instability of the coolant in the active zone of nuclear reactors can be high-amplitude, high-frequency dynamic loads on the internal structures and a violation of the tightness of the TVEL shells. However, until now, there are no reactor control/diagnostic systems and operational instructions for managing accidents in conditions of thermoacoustic instability of the coolant in the reactor core. The main reason for this situation is the lack of substantiated methods for modeling the criteria and conditions for the occurrence of thermoacoustic instability in the active zone. The purpose of the work is the development of a criterion method for modeling the conditions of thermoacoustic instability of the coolant in the active zone of the reactor to substantiate the appropriate reactor control systems and symptom-oriented emergency instructions. An original method of determining the criteria and conditions of thermoacoustic instability of the coolant in the active zone depending on the determining parameters of the thermodynamic state of the reactor plant has been developed.. Based on the thermodynamic approach, which takes into account the level of completion of interphase heat and mass transfer processes in acoustic pressure waves, the criteria and area of thermoacoustic instability of the coolant in the reactor core are determined. The established area of thermoacoustic instability of the coolant in the reactor core was verified on the basis of known experimental data obtained at the experimental installation, which meets the criteria of thermodynamic similarity to the core of the VVER-1000 core. Based on the developed criterion method, the main provisions and requirements for the relevant reactor control/diagnostic systems and symptom-oriented instructions for managing accidents in conditions of thermoacoustic instability of the coolant in the active zone of the reactors are defined.

Modeling and simulation of gas vortex flow dynamics to understand the nature of mass transfer enhancement

Vortex flow has been demonstrated to be an effective way of process intensification for interphase mass transfer. However, the underlying principles of this phenomenon are not yet fully known. To understand the nature of gas vortex flow in improving process intensification from a fluid flow perspective, this work conducts an experimental investigation and numerical simulations to compare the differences in energy loss, static pressure, main velocity, and turbulent kinetic energy between the vortex and the axial gas flow inside a countercurrent contactor operated at a flow rate of 50–250 L/min. The results indicate that the energy loss increases with increasing gas flow rate, while the Euler number remains stable at 2.49 ± 0.17, which is 21.05% higher than the conventional axial flow. The vortex flow displays higher values and gradients in the distribution of static pressure, tangential, axial velocity, and turbulent kinetic energy, which is directly linked to the enhanced interphase contact, mixing, and mass transfer processes. Additionally, the tangential velocity of vortex flow exhibits a decaying behavior, but it also has an extra tangential dimension, which was a critical factor for process enhancement compared to conventional axial flow. Moreover, semi-empirical models are developed to characterize the parameters of the maximum tangential velocity and its radial position for the vortex flow with R2 = 0.892 and 0.919, respectively. The results may provide a positive reference for the design, optimization, and operation of countercurrent vortex contactors.

Mass transfer during surfactant-enhanced DNAPL remediation: Pore-scale experiments and new correlation

Surfactant-enhanced solubilization has been proven successful to remediate aquifers contaminated with non-aqueous phase liquids (DNAPLs). Understanding mass transfer from DNAPLs to the surfactant solution is highly important for improving remediation efficiency. However, the pore-scale mechanisms underlying the effect of surfactants on mass transfer behaviors have not been fully understood. Here we use microfluidic experiments to investigate the fundamental physical processes and quantify the impacts of surfactants on mass transfer rate at the pore scale. We find that surfactants can induce droplet breakup behaviors due to the interfacial disparity of mass transfer strength, resulting in the subsequent micro-movement of daughter blobs due to capillary force. Through image-based measurements, we find a significant inhibition of the mass transfer rates by surfactants at concentrations above the critical micelle concentration, and the inhibition becomes more pronounced as the concentration increases, which can be explained by an increase in stagnant film thickness. But the total mass transfer flux is improved because of the enhanced driving force caused by the surfactant-enhanced concentration gradient. In light of the observed physical processes and the behavior of mass transfer inhibition, we finally develop a new empirical model that explicitly considers the effects of surfactant concentration, DNAPL distribution, effective interface area, and flow rate to predict the mass transfer rate. This work provides pore-scale underpinnings of the mass transfer behaviors and a new mass transfer model considering the effect of surfactants, which improves the understanding of interphase mass transfer processes under the action of surfactants in subsurface hydrological and engineering systems.

Pore network and Darcy scale modelling of DNAPL remediation using ethanol flushing: Study of physical properties in DNAPL remediation

Co-solvent flushing into contaminated soils is one of the most effective techniques for Dense Non-Aqueous Phase Liquid (DNAPL) remediation. In addition to the increase of DNAPL solubility, co-solvents (e.g. ethanol) can alter the viscosity and density of aqueous phase and diffusion coefficient of solute. Any changes in these parameters can change the flow behaviour and alter the upscaled DNAPL mass transfer coefficient which is a key parameter controlling soil and groundwater remediation at Darcy-scale. While numerous studies have investigated DNAPL remediation using co-solvents at the Darcy scale, pore-scale modelling of co-solvent enhanced DNAPL remediation has not been well investigated. In this work, a three-dimensional pore-network model was developed to simulate the 1,2-dichlorobenzene (DCB) remediation experiments using ethanol-water flushing solution. The model simulates the effect of changes in solubility, viscosity, density, and diffusion coefficient during co-solvent flushing of the DNAPL. The results of pore network modelling for ethanol-water flushing for the DCB remediation were also validated using the experimental data. In addition to pore-scale modelling, a continuum scale modelling (Darcy-scale) was used for the DCB remediation using ethanol-water flushing. The results of both pore network and continuum scale modelling demonstrated that the ethanol content and flushing velocity influence the interphase mass transfer and DNAPL dissolution process. The results indicated while the mass transfer coefficient decreased in the presence of ethanol, the process of NAPL remediation was improved due to the substantial increase of solubility in the presence of co-solvent. The large scale modelling showed that NAPL bank can be formed in the front of ethanol-water mixture flushing.

Dimensional effects of inter-phase mass transfer on attenuation of structurally trapped gaseous carbon dioxide in shallow aquifers

Based on experimental evidence and using mathematical modeling, inter-phase mass transfer processes of CO2 exsolving from and dissolving into water in heterogeneous porous media are investigated under two fundamentally different flow conditions: in a quasi one dimensional vertical column and in a two-dimensional tank with a lateral background water flow, both at laboratory scale. In both cases, the CO2 dissolved in water under a given overpressure is injected for a certain period at the bottom of the tank, exsolves, and migrates upwards. A layer of fine sand is present in the tanks designed to mimic geological scenarios of accumulation and trapping of exsolved CO2 in shallow aquifers. Then, clean water is injected and the accumulated CO2 is dissolved back into the flowing water. The study aims to point out the differences in the mass transfer processes between the quasi-1D and 2D cases using a mathematical model of two-phase compositional flow in heterogeneous porous media calibrated to the experimental datasets, and expose strategies that should be explored in future research. Additionally, temperature variations observed during the 2D experiments allow for analysis of isothermal versus non-isothermal effects on the processes of multiphase CO2 evolution. The mathematical model is discretized and solved using the mixed hybrid finite element method in 2D that allows for the simulation of both advection- and diffusion-dominated processes accurately.

Influence of interphase mass transfer and diffusion processes on CO2-brine displacement in saline aquifers

The geological storage of CO2 in saline aquifers involves various geophysical and geochemical mechanisms, in which different mechanisms play different roles at different time scales and different stages as well. At the initial stage during CO2 continuously injected into saline aquifers, the non-equilibrium mass transfer process is one of the main factors affecting the interfacial evolution of two-phase flow. In this work, a model that couples the two-phase displacement process in saline aquifers with single-phase dissolution-diffusion is established for the initial stage of CO2 injection, which features that the non-equilibrium mass transfer method is used to describe the interfacial evolution during the two-phase flow. The model is numerically solved and verified. The influences of mass transfer and diffusion on the distributions of CO2 plume and CO2 concentration in the wetting phase are investigated. In the initial stage of CO2 injection, the Stanton number (St), representing the ratio between mass transfer process and convection process, significantly affects both the non-wetting phase at the leading edge and the CO2 concentration distribution in the wetting phase. The Peclet number (Pe), representing the ratio between convection process and diffusion process, is a secondary factor and has limited effects on the non-wetting phase saturation and wetting phase CO2 concentration distribution. At the initial stage, the dissolution of CO2 during injection into saline aquifers is dominated by a large St or small Pe. The proposed model provides a useful tool and insight in analyzing the interfacial evolutions of the CO2-brine displacement process when interfacial mass transfer is considered.

Numerical investigation on the interfacial characteristics of steam jet condensation in subcooled water flow in a restricted channel

As a kind of direct contact condensation, steam jet condensation in subcooled water flow is very common in various industrial applications. Particle model has been employed to investigate the interfacial characteristics of the steam jet condensation in subcooled water flow in a restricted channel, in which a thermal phase change model was inserted into ANSYS CFX as CFX Expression Language (CEL) to simulate the interphase heat and mass transfer process. To validate the model correctness, the steam plume and temperature profiles were compared with the experimental data. The interfacial characteristics including the variation of steam-water interface, local heat transfer coefficient and local condensation rate have been discussed under different operating conditions. Based on the dynamic equilibrium of steam supply and its condensation by the ambient water flow, the steam plume variation was analyzed. The axial profiles of thermodynamic parameters along the nozzle axis were studied with the theory of expansion and compression waves to reveal the formulation mechanism of ellipsoidal steam plume. Then the supersonic flow was observed at some distances from the straight nozzle exit in the numerical results as the related experimental results indicated. The numerical results show that steam plume expands with steam mass flux and water temperature increasing, while it contracts with the increase of water Reynolds number. With the increase of water inlet temperature, the local condensation rate decreases. As the Reynolds number of water flow increases, the local heat transfer coefficient increases and the local condensation rate increases as well.

Mass Transfer of CO2 in a Carbonated Water–Oil System at High Pressures

In this paper, CO2 diffusion coefficients in a carbonate water–oil system are determined by measuring the pressure buildup in the closed water–oil system experimentally and modeling the pressure change mathematically. The mathematical method of investigating one-dimensional, time-dependent heat conduction in a composite medium is adopted to solve the mass transfer problem between two liquid phases. The model is combined with well-designed trial-and-error method to determine diffusion coefficients of CO2 in both water and oil phases at the same time. The model considers a moving interface between carbonated water and oil as well as variations of interface concentrations of CO2 in these two phases, which more effectively conforms to reality. Results show that the pressure buildup during the diffusion process resulted from the increased density and swelling of the oil phase. The diffusion coefficient of CO2 in the water phase plays a major role in the interphase mass transfer process.

Study on the transient interfacial tension in a microfluidic droplet formation coupling interphase mass transfer process

In two‐phase dispersion coupling interphase mass transfer process, the variation of interfacial tension is an important factor affecting the dispersion. In this study, we described a microfluidic method for the determination of the transient interfacial tension (TIFT). The method has the advantage of determining TIFT during the whole droplet formation process, rather than only at the rupture moment as reported in previous studies. The TIFTs of several systems were determined. In certain systems, it has been found that the droplet size decreased with the increase of the dispersed phase flow rate, which is obviously different from the constant interfacial tension system. It has also been found that TIFT was mainly affected by two‐phase flow rates, solute type and concentration, and droplet size. A semiempirical equation was finally established to predict TIFT. It has the potential to be used in a variety of industrial equipment with dispersion–mass transfer coupling process. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2542–2549, 2016

The interphase mass transfer in liquid–liquid systems with Marangoni effect

In this paper, we review the related studies on the interphase mass transfer process accompanied with Marangoni effect in liquid-liquid systems. The Marangoni effect is triggered by the local variation of interfacial tension and influenced by many factors, such as the physicochemical properties of the system, the solute concentration and the bulk flow. The onset criterion of the Marangoni effect has been discussed extensively via theoretical analysis and experimental verification, but a unified and universal criterion was still not developed due to the complex system geometry and boundary conditions. When the Marangoni convection occurred, the bulk flow adjacent to the interface was spontaneously disturbed, normally leading to an enhanced mass transfer coefficient. Besides, the surface active agent has been found to affect the solute transport across the interface, by either promoting or inhibiting the Marangoni convection according to the nature of additives.

Numerical Simulation of the Solute‐Induced Marangoni Effect with the Semi‐Lagrangian Advection Scheme

AbstractThe level set method is combined with the concentration transformation method to solve the interphase mass transfer process. However, the artificial diffusion generated in the mass transfer convection term across the interface is inevitable, especially when large shape deformation is encountered at high Reynolds numbers. A semi‐Lagrangian advection scheme is introduced to overcome this disadvantage. The methyl isobutyl ketone (MIBK)‐acetic acid‐water system is adopted to study the unsteady mass transport process accompanied with the Marangoni effect of a single deformable drop ascending in the infinite continuous phase. The predicted overall mass transfer coefficients agree with experimental data very well. The configuration of Marangoni convection is revealed and its effect on the interphase mass transfer process is investigated.

Assessment of CO2 Injectivity and Storage Capacity in a Depleted Pinnacle Reef Oil Field in Northern Michigan

The Midwest Regional Carbon Sequestration Partnership is conducti ng a large-scale CO 2 injection test in a depleted Niagaran Pinnacle Reef in northern Michigan. The focus of the dynamic modeling tas k described in this paper is to evaluate the CO 2 injectivity and storage capacity of this closed carbonate reef structure. We discuss the history-matching process to characterize the closed reservoir model using primary and secondary recovery data and its validation with the field pressures in the current CO2 injection phase. Two alternative conceptual geologic models of the reef are constructed to evaluate the level of detail necessary to efficiently model dynamic reservoir behavior without compromising geologic accuracy. We find that our initial black oil formulation under-predicts reservoir pressure and hence over -predicts injectivity during the CO 2 injection phase. Transition to a compositional model is currently underway to better represent reservoir dynamics by effectively accounting for interphase and intercomponent mass transfer processes. Lessons learned from this exercise can be drawn upon for possible use in injectivity evaluation of other reefs in the region.

Biological reduction of chlorinated solvents: Batch-scale geochemical modeling

Simulation of biodegradation of chlorinated solvents in dense non-aqueous phase liquid (DNAPL) source zones requires a model that accounts for the complexity of processes involved and that is consistent with available laboratory studies. This paper describes such a comprehensive modeling framework that includes microbially mediated degradation processes, microbial population growth and decay, geochemical reactions, as well as interphase mass transfer processes such as DNAPL dissolution, gas formation and mineral precipitation/dissolution. All these processes can be in equilibrium or kinetically controlled. A batch modeling example was presented where the degradation of trichloroethene (TCE) and its byproducts and concomitant reactions (e.g., electron donor fermentation, sulfate reduction, pH buffering by calcite dissolution) were simulated. Local and global sensitivity analysis techniques were applied to delineate the dominant model parameters and processes. Sensitivity analysis indicated that accurate values for parameters related to dichloroethene (DCE) and vinyl chloride (VC) degradation (i.e., DCE and VC maximum utilization rates, yield due to DCE utilization, decay rate for DCE/VC dechlorinators) are important for prediction of the overall dechlorination time. These parameters influence the maximum growth rate of the DCE and VC dechlorinating microorganisms and, thus, the time required for a small initial population to reach a sufficient concentration to significantly affect the overall rate of dechlorination. Self-inhibition of chlorinated ethenes at high concentrations and natural buffering provided by the sediment were also shown to significantly influence the dechlorination time. Furthermore, the analysis indicated that the rates of the competing, nonchlorinated electron-accepting processes relative to the dechlorination kinetics also affect the overall dechlorination time. Results demonstrated that the model developed is a flexible research tool that is able to provide valuable insight into the fundamental processes and their complex interactions during bioremediation of chlorinated ethenes in DNAPL source zones.

Using PHREEQC for modelling and simulation of dynamic leaching tests and scenarios

This paper presents an extension of the application field of PHREEQC geochemical software for modelling the dynamic leaching tests (and scenarios) by taking into account the leachant compartment as complex reactive/transport system and the coupling of many reactive compartments linked by substance fluxes. This study focuses on the specific case of dynamic leaching of monolithic porous materials (particularly the case of continuous monolithic leaching test, CMLT) where reaction/diffusion occurs in the porous matrix and where the leachant is a complex reactor in which chemistry coupled with inter-phase mass transfer and convection processes take place. It is demonstrated here that the modelling of open reactors (convection) is possible with PHREEQC by using RATES and KINETICS keyword data blocks. The PHREEQC model was validated by results comparison with analytical solutions of the system equations. Coupling a diffusion compartment with an open reactor (complex boundary conditions for the diffusion equation) requires the introduction of a stagnant cell on the first grid cell of the diffusion compartment in TRANSPORT data block and the use of MIX function for model the monolith/leachant interface transfer. The proposed model was validated by comparison with numerical solutions obtained with MATLAB and by a numerical sensibility study. Finally, the model equations are given for a complex dynamic leaching process of a porous monolith involving beside reaction/diffusion in the monolith, reactions, interface mass transfers, gas absorption and convection in the leachant. Examples of PHREEQC modelling are presented: (1) the case of continuous leaching of a cement based material using carbonated water and (2) a field scale water storage pool constructed with a solidified/stabilised material. The comparison with the experimental leaching data shows the simulation results are very satisfying.

Numerical simulation of the Marangoni effect on mass transfer to single slowly moving drops in the liquid–liquid system

The Marangoni effect is a frequently observed phenomenon of enhancement of interphase mass transfer in liquid–liquid systems. Such an effect, originating from the hydrodynamic instability induced by surface tension sensitivity to surface concentration of transferred solute, is mathematically formulated and numerically simulated for slowly moving single spherical drops in an axisymmetric boundary-fitted coordinate system by solving coupled fluid flow and solute mass transfer equations. Numerical simulation demonstrates the occurrence of the Marangoni effect under typical conditions in liquid–liquid systems, and is in reasonable agreement with the classic theoretical analysis. Sufficient spatial and temporal resolution in simulation reveals the multi-scale interaction of the drop-scale Marangoni effect with the sub-drop-scale local interfacial convection. The effect of solute transfer direction, Peclet number, surface tension sensitivity to solute concentration, and level of random perturbation on surface concentration are investigated numerically. It is shown that the Marangoni effect occurs in the middle stage of a transient interphase mass transfer process, and the Marangoni convection at the interface does not necessarily results in the Marangoni effect of mass transfer enhancement. Besides, the Marangoni effect occurs only when the surface tension sensitivity to the solute concentration variation is above certain critical level. The present axisymmetric simulation of the Marangoni effect provides necessary basis for further work on three-dimensional numerical analysis.

Mass Transfer Correlation for Nonaqueous Phase Liquid Volatilization in Porous Media

To investigate the Nonaqueous Phase Liquid (NAPL)−vapor phase mass transfer, a series of NAPL volatilization experiments was carried out using toluene as the contaminant. Three sizes of glass beads and a medium silica sand were selected as the porous media. Experiments were performed for a NAPL saturation range of 13.8−71% and a pore gas velocity in the range of 0.1−2 cm/s. Previously, the interphase mass transfer process was characterized as a lumped parameter together with the interfacial area between the phases because of the complexity of the porous medium and the NAPL morphology. In this paper, actual vapor phase mass transfer was evaluated using the corresponding air−liquid interfacial area. The value of air−liquid interfacial area was calculated following the procedure presented in our previous studies. An empirical correlation for the actual NAPL−vapor phase mass transfer process was developed statistically for the variable zone of NAPL saturation, and the model showed that the interphase mass tra...

Modelling the fate of oxidisable organic contaminants in groundwater

Subsurface contamination by organic chemicals is a pervasive environmental problem, susceptible to remediation by natural or enhanced attenuation approaches or more highly engineered methods such as pump-and-treat, amongst others. Such remediation approaches, along with risk assessment or the pressing need to address complex scientific questions, have driven the development of integrated modelling tools that incorporate physical, biological and geochemical processes. We provide a comprehensive modelling framework, including geochemical reactions and interphase mass transfer processes such as sorption/desorption, non-aqueous phase liquid dissolution and mineral precipitatation/dissolution, all of which can be in equilibrium or kinetically controlled. This framework is used to simulate microbially mediated transformation/degradation processes and the attendant microbial population growth and decay. Solution algorithms, particularly the split-operator (SO) approach, are described, along with a brief résumé of numerical solution methods. Some of the available numerical models are described, mainly those constructed using available flow, transport and geochemical reaction packages. The general modelling framework is illustrated by pertinent examples, showing the degradation of dissolved organics by microbial activity limited by the availability of nutrients or electron acceptors (i.e., changing redox states), as well as concomitant secondary reactions. Two field-scale modelling examples are discussed, the Vejen landfill (Denmark) and an example where metal contamination is remediated by redox changes wrought by injection of a dissolved organic compound. A summary is provided of current and likely future challenges to modelling of oxidisable organics in the subsurface.