Drop Mass Transfer Research Articles

Hierarchically Porous Structured Adsorbents with Ultrahigh Metal-Organic Framework Loading for CO2 Capture.

Metal-organic frameworks (MOFs) have emerged as promising candidates for CO2 adsorption due to their ultrahigh-specific surface area and highly tunable pore-surface properties. However, their large-scale application is hindered by processing issues associated with their microcrystalline powder nature, such as dustiness, pressure drop, and poor mass transfer within packed beds. To address these challenges, shaping/structuring micron-sized polycrystalline MOF powders into millimeter-sized structured forms while preserving porosity and functionality represents an effective yet challenging approach. In this study, a facile and versatile strategy was employed to integrate moisture-stable and scalable microcrystalline MOFs (UiO-66 and ZIF-8) into a poly(acrylonitrile) matrix to fabricate readily processable, millimeter-sized hierarchically porous structured adsorbents with ultrahigh MOF loadings (∼90 wt %) for direct industrial carbon capture applications. These structured composite beads retained the physicochemical properties and separation performance of the pristine MOF crystal particles. Structured UiO-66 and ZIF-8 exhibited high specific surface areas of 1130 m2 g-1 and 1431 m2 g-1, respectively. The structured UiO-66 achieved a CO2 adsorption capacity of 2.0 mmol g-1 at 1 bar and a dynamic CO2/N2 selectivity of 17 for a CO2/N2 gas mixture with a 15/85 volume ratio at 25 °C. Furthermore, the structured adsorbents exhibited excellent cyclability in static and dynamic CO2 adsorption studies, making them promising candidates for practical application.

Water-retaining slurry washcoat for high-loading and robust CuMnOx structured catalyst toward durable monoxide oxide purification from real flue gas

Structured catalysts play key roles in many industries with the advantages of low pressure drop and efficient mass transfer. The copper-manganese oxide (CuMnOx) as a cost-effective catalyst has been widely applied in gas purification, but still lack efficient structured catalyst due to the challenge in controlling its slurry and coating quality. In this work, this challenge was addressed by introducing the water-retaining agent (WRA) into slurry with sophisticatedly designed conditions. The effects of the type and dosage of WRA, pH value, and temperature on slurry properties including viscosity, stability, and water-retention were systematically studied, and the slurry property-coating quality relationship was correlated. The preferred slurry and coated layer could be segregated into sub-millimeter-sized water-retaining regions where catalyst and binder particles were well dispersed and connected. After slow release of water and organic during drying and calcination, the CuMnOx structured catalyst with uniform, defect-free and dense coating was obtained, showing high loading (>160 kg/m3), great mechanical strength (powder shedding rate < 1 wt%), and no blockage for practical use. The robustness of the structured catalysts was validated by a scale-up preparation of 2 m3 volume amount for CO purification from real ore-sintering flue gas in a steel plant, which achieved the CO catalytic efficiency maintaining over 90 % for more than 1440 h. This work showcases an efficient strategy for structured catalyst preparation and expands the gas purification application of the industrially-favored CuMnOx.

Prototyping of rotating packed bed structural internals

A rapid prototyping method was developed for quick and inexpensive design of various geometrical solutions for rotating packed bed internals. Sixteen geometries were designed with the use of 3D modeling software and subsequently 3D-printed, if possible. The printed packings were tested for dry pressure drop to reject the ones generating too high air flow resistance. Eventually, the packings were tested for wet pressure drop and effective mass transfer area generated in specified conditions. An evaluation method was designed to compare the results from the different packings and determine the geometry most suited for the absorption process.

Favorable trade-off between heat transfer and pressure drop in 3D printed baffled logpile catalyst structures

Additive manufacturing has the potential to unlock a large degree of geometric freedom in the shaping of catalytic material, thereby providing new possibilities to optimize catalyst holdup, pressure drop and heat and mass transfer characteristics. In this modelling study, baffled logpile structures are proposed as a promising candidate to exploit this potential, by shaping the catalytic material as a static mixer, generating cross-flow. An OpenFOAM Computational Fluid Dynamics study was performed on various 2D structure designs to map the trade-off between heat transfer, pressure drop and residence time distribution as a function of the design, length and gap spacing of the baffle. It is observed that structures with the longest baffles provide optimal heat transfer performance, and that the baffle gap spacing can be used to tailor the trade-off between heat transfer and pressure drop. In comparison to a packed bed filled with spherical particles, the novel structures offer a heat transfer rate four to six times as high at the same pressure drop. Whilst full 3D simulations, validated by experiments, remain to complete the analysis, the current work illustrates the potential of this novel class of structured catalyst materials for intensified chemical reactors.

Mass transfer and size control of partially miscible fluid drops in a flow focusing microfluidic device

We conducted laboratory experiments and numerical simulations to investigate the formation and evolution of drops formed by partially miscible two-phase fluid, n-butanol (the continuous phase) and water (the dispersed phase), in a flow focusing microfluidic system. We carefully calibrated the numerical model to obtain good agreement with experimental data in drop velocity and mass transfer, demonstrating the model's capability to capture realistic drop dynamics. Our detailed investigation of the numerical results allowed us to determine the mechanism of drop formation and obtain a relevant criterion in terms of the disperse-to-continuous flow ratio beyond which the tubing patterns would occur. Additionally, we found that the mass transfer between the two phases, specifically at the drop interface, strongly depends on the local distribution of dissolved concentration of the dispersed phase. To enhance mass transfer, we conducted numerical simulations on alternating curved channels, which allows for the lateral advection of the dispersed phase concentration in the continuous phase at the curved section. We found that this lateral movement enhances mass transfer at the drop interface. Through detailed investigation of numerical results, we addressed mechanisms of mass transfer enhancement in the curved channel. Overall, our findings provide insight into the mechanisms of drop formation and mass transfer in partially miscible two-phase fluids in microfluidic systems, which could be useful in designing and optimizing such systems for various applications.

Heat and mass transfer of drops of concentrated solutions during spray dehydration under conditions of convective-radiation energy supply

The results of modeling the dehydration of drops of a concentrated liquid, on the example of ceramics, with convective-radiation energy supply under conditions of direct-flow and counter-current phase motion, as well as pulsed counter-flows of gas, are presented. A model for the dehydration of a single drop is formulated based on the equations of heat conduction with a source term and diffusion of moisture, taking into account the change in its size due to evaporation. This takes into account the influence of the convective vapor flow from the evaporating droplet surface (Stefan flow), as well as the blowing of evaporating vapor into the hot gas flow on the heat transfer coefficient (Spalding correction). The impact of infrared radiation is described by the Bouguer equation. The equation of motion of a drop in a gas flow takes into account the forces due to gravity, the difference in velocities and phase densities. As a result of numerical simulation, it was found that with countercurrent phase movement, the intensity of dehydration is higher than with cocurrent flow. This is due to both an increase in the relative velocity of the phases and an increase in the residence time of the drop in the intense region of infrared radiation. It is shown that further intensification of evaporation is possible due to the creation of pulsed counter gas flows. The calculated results are compared with the experimental data, which confirms the adequacy of the model. The results of the study can be useful in the development of new heat technologies and devices for dehydration of concentrated solutions and suspensions.

Diffusion and reaction in foam-based catalysts: Identifying the shape factor

The application of foam based catalysts in heterogeneous catalysis is attracting researcher’s attention due to their favourable properties of lower pressure drop and better heat and mass transfer in packed bed reactors. Foam structure is, however, complicated and transport phenomena in foam is not yet well understood, thus, making design of foam based catalytic systems difficult. This article aims to provide a definition of the shape factor for foam catalysts using heterogeneous modelling of the unit cell based on finite element methods. The identification of shape factor or diffusion length helps in generalizing the effectiveness factorfor use in pseudo-homogeneous reactor models for any geometry of foam andkinetics of interest. Foam almost obeys the Aris’ correlation for effectiveness factor vs Thiele modulus with small deviationattributed to different diffusion lengths of the nodes and struts and use of mixed particle approach is observed to narrow the difference.

Thermal performance study of thermochemical reactor using net-packed method

Thermochemical energy storage (TCES) is proving to be a promising option for residential energy storage applications. Many studies have indicated that the pressure drop and heat and mass transfer efficiency of the reactor are two key determinants with TCES technologies. In this paper, net-packed method is used to carry out thermal performance enhancement study for a thermochemical reactor. Compared with and the without net packed methods, copper mesh shows better thermal performance. The copper mesh method of zeolite achieved maximum temperature rise of 38.6 °C, which is 4.4 °C and 2.3 °C higher than that of the non-packed and aluminum mesh, respectively. The pressure drop is reduced by 28.1% and higher water adsorption has been realized. In addition, the energy storage density of 784.4 kJ/kg and thermal efficiency of 38.2% are obtained with the copper mesh. These are 1.6 and 2.4 times the results of the non-packed tests respectively.

3D Printed PEI Containing Adsorbents Supported by Carbon Nanostructures for Post-combustion Carbon Capture From Biomass Fired Power Plants

Processes that utilize solid adsorbents to capture CO2 are promising alternatives to state-of-art Amine based technologies for capturing CO2 from large point sources. Although the energy needs of solid sorbent-based processes are low, the process footprint and consequently the capital cost connected to its implementation can be large due to the relatively long cycle times needed to get the required purity and recovery of the CO2 product. To overcome this challenge, processes having structured adsorbents like laminates, monoliths etc. are needed due to their low pressure drop and better mass transfer characteristics. The aim of this multiscale study is to evaluate the process-based performance of a 3D printed sorbent containing polyethyleneimine (PEI) and multiwalled carbon nanotubes (MWCNT) for capturing CO2 from a biomass fired power plant flue gas. A 6-step vacuum swing adsorption (VSA) cycle was simulated and optimized using equilibrium and kinetics data obtained from volumetry and breakthrough experiments. The optimization study showed that it was possible to achieve purity values &amp;gt;95% and recovery values &amp;gt;90% from dry CO2 feed streams containing 10 and 15% CO2 respectively. The minimum specific energy values were 0.94 and 0.6 MJ/kg and maximum productivity values were 0.8 and 2.2 mol/m3 ads s, respectively, for the two scenarios.

A Review of the Critical Aspects in the Multi-Scale Modelling of Structured Catalytic Reactors

Structured catalytic reactors are enjoying an increasingly important role in the reaction engineering world. At the same time, there are large and growing efforts to use advanced computational models to describe such reactors. The structured reactor represents a multi-scale problem that is typically modelled at the largest scale only, with sub-models being used to improve the model granularity. Rather than a literature review, this paper provides an overview of the key factors that must be considered when choosing these sub-models (or scale bridges). The example structured reactor selected for illustration purposes is the washcoated honeycomb monolith design. The sub-models reviewed include those for pressure drop, inter- and intra-phase mass and heat transfer, and effective thermal conductivity.

Thermohydrodynamic Processes in Spray Drying with Convective–Radiation Energy Supply

The results of numerical modeling of the heat and mass transfer of drops during drying of a liquid under the conditions of convective–radiation energy supply and counterflows of the heat-transfer fluid are presented. The effect of various parameters, in particular, density of the infrared flux, velocity of the counterflows of the heat-transfer fluid, and overheating temperature of the liquid before drying, on the kinetics of evaporation of the drops, is analyzed. The possibilities for the reduction of the duration of drying of the drops due to the radiation action are shown. The results of experimental studies of the effect of the infrared flux on the performance indicators of a spray drying unit are presented, which provide evidence of a decrease in the specific energy costs for moisture evaporation and an increase in the moisture tension, productivity, and efficiency coefficient of the unit.

Gas-Liquid Flow and Interphase Mass Transfer in LL Microreactors

This work investigates the impact of fluid (CO2(g), water) flow rates, channel geometry, and the presence of a surfactant (ethanol) on the resulting gas–liquid flow regime (bubble, slug, annular), pressure drop, and interphase mass transfer coefficient (kla) in the FlowPlateTM LL (liquid-liquid) microreactor, which was originally designed for immiscible liquid systems. The flow regime map generated by the complex mixer geometry is compared to that obtained in straight channels of a similar characteristic length, while the pressure drop is fitted to the separated flows model of Lockhart–Martinelli, and the kla in the bubble flow regime is fitted to a power dissipation model based on isotropic turbulent bubble breakup. The LL-Rhombus configuration yielded higher kla values for an equivalent pressure drop when compared to the LL-Triangle geometry. The Lockhart–Martinelli model provided good pressure drop predictions for the entire range of experimental data (AARE &lt; 8.1%), but the fitting parameters are dependent on the mixing unit geometry and fluid phase properties. The correlation of kla with the energy dissipation rate provided a good fit for the experimental data in the bubble flow regime (AARE &lt; 13.9%). The presented experimental data and correlations further characterize LL microreactors, which are part of a toolbox for fine chemical synthesis involving immiscible fluids for applications involving reactive gas–liquid flows.

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

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

Compartment‐model for the simulation of the separation performance of stirred liquid–liquid‐extraction columns

AbstractFor detailed simulation and evaluation of stirred extraction columns a CFD based compartment‐model was developed. Instead of simulating all effects in a computational expensive PBE‐CFD‐model, the velocity field calculation of the continuous phase is decoupled from the calculation of the dispersed phase (one‐way coupling). In CFD only the continuous phase is simulated and the resulting velocity profile is used in the compartment‐model to simulate the drop movement, coalescence, breakage and mass transfer for a representative number of drops (Monte‐Carlo Method). This decoupling has a major impact on the calculated fluid‐dynamics. Thus, the velocity profile of the CFD results is modified in the model to account for phase interaction. The compartment‐model is applied for the simulation of a Kühni extraction column with the system toluene/water/acetone. The simulation results, namely holdup, drop size and concentration profiles over the column height, are in good agreement with experiments for different loads and different stirrer speeds.

Hydrodynamic studies in sectionalised external loop air lift reactors

ABSTRACT 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.

Numerical simulation of hydrate particle size distribution and hydrate particle bedding in pipeline flowing systems

In offshore operations, hydrate hazards are now posing a great threat to deep water flow assurance. Pipeline hydrate particle size distribution is closely related to the viscosity of hydrate slurry, flow pressure drop and interface heat and mass transfer. Hydrate particle bedding could lead to pipeline hydrate plugging. Therefore, hydrate particle size distribution and hydrate particle bedding have a significant impact on pipeline hydrate flow assurance. In order to simulate hydrate particle size distribution and hydrate particle bedding in pipeline flowing systems, a new hydrate agglomeration model was used and then solved by the software FLUENT 14.5 together with some CFD models. In the simulations, the type and characteristics of hydrate particle size distribution and the characteristics of pipeline hydrate particle bedding were focused on. In addition, the influences of hydrate particle size initial distribution type, hydrate volume fraction, flow rate and initial hydrate particle diameter were investigated. The conclusions in this work can provide guidance for the development of deep water flow assurance.

A state-of-the-art review on single drop study in liquid–liquid extraction: Experiments and simulations

Abstract The experimental and numerical investigations of single drop in liquid/liquid extraction system have been reviewed with particular focus on experimental techniques and computational fluid dynamic simulation approaches. Comprehensive surveys of available experimental techniques and numerical approaches for single drop rising and falling were given. Subsequently, single drop mass transfer was also reviewed both experimentally and numerically. Additionally, single drop breakage and coalescence process and the influencing factors were summarized and compared, so as to establish sub-models for population balance model. Future directions on single drop mass transfer, drop breakage and coalescence were suggested. It is believed that the single drop is a powerful tool to assist extraction process design from lab-scale to pilot-scale.

Measurement of Gas-Phase Mass Transfer Coefficients in a Humidification Column through Random Packing

Packed columns are an important part of the broad selection of mass and heat transfer equipment. Nowadays, the use of packed columns is increasing, which is because of its lower pressure drop, higher capacity and higher mass transfer in comparison to tray columns. The experiential tests and the hypothetical analysis display that the chemical dehumidification of air by hygroscopic salt solutions confirms the stable reduction in humidity ratio, which is appropriate for uses to air conditioning or drying processes The mass transfer factors in the pulse were found to correspond nearly to the factors that would be achieved in the distributed bubble flow regime In the present study, parameters that affect column performance, such as, fluid retention and gas-phase mass transfer coefficient in a humidification column using random packing in towers with 0.1 m and 0.2 m diameters and 1m height, were measured Air velocity was 1.32 to 3.92 m3 per hour and liquid velocity was 10 to 70 m3 per hour. In this research, the Nakajima model was used to calculate the effective area. Thereafter, experimental values for gas-phase mass transfer coefficients were compared to Zech, Shi, Grouff, Shulman, Billet and Ondamodels The mean relative errors of these models with the present study’s experimental findings were 7%, 15%, 29%, 21%, 45% and 195%. Findings showed that by decreasing the column diameter, the gas-phase mass transfer coefficient (Kg.ae) also increases Further, the obtained retention values showed that retention in the column with a 0.1 m diameter was higher than the column with a 0.2 m column.

CFD based compartment-model for a multiphase loop-reactor

In multiphase devices, fluid dynamics have a high impact on concentration profiles and mass transfer between the phases and therefore influence efficiency. Standard models often assume ideally mixed conditions or plug flow. The application of such models for multiphase devices with complex flow patterns causes inaccuracies, if the flow deviates from ideally mixed or plug flow conditions. Therefore, for a precise model based design and operation parameter determination of devices with complex flow patterns, the local fluid dynamics should be considered. CFD simulations for multiphase systems including mass transfer, population balance equations for coalescence and breakage as well as reactions are still time consuming. Thus, we developed a compartment-model based on prior calculated CFD flow-data. In the CFD simulations, the time consuming population balance equations for coalescence and breakage, mass transfer and reactions are neglected. These phenomena are considered in the compartment-model. Thereby we reduce the overall computing time.This paper presents the CFD based compartment-model applied on a loop-reactor. First, a three-phase CFD model of the developed multiphase loop-reactor is introduced. Following, the paper presents the compartment-model and the application of a time-driven constant-number Monte-Carlo approach to solve population balances. Finally, the compartment-model is applied to the liquid-liquid extraction part of the loop-reactor calculating the drop size distribution and mass transfer based on previously calculated CFD data.

Численное исследование массопереноса в капельно-пленочных системах с использованием регуляризованной разностной схемы в испарительной литографии

Массоперенос в высыхающих каплях и пленках интересен с практической точки зрения, так как применяется в задачах испарительной литографии. При создании условий неравномерного испарения с поверхности жидкого слоя возникают компенсационные потоки, перемещающие коллоидные частицы в области интенсивного испарения. Это позволяет получать на твердой поверхности микро- и наноструктуры требуемой формы. В работе описана нестационарная модель массопереноса в капельно-пленочных системах. Особенность модели заключается в совместном учете вязких, гравитационных и капиллярных сил. Для решения неустойчивой дискретной задачи о высыхающей капле (пленке) предложена регуляризованная разностная схема, на базе которой разработан комплекс программ. По результатам проведенных вычислительных экспериментов предложен способ получения кольцевых структур из микро- и наночастиц методом испарительной литографии.