Mass Transfer Intensification Research Articles

Experimental study of food grain drying in a gas–solid vortex reactor

In the present research, a parametric study of a pilot-scale gas–solid vortex reactor (GSVR) with static geometry dryer has been carried out. It is an intense and clean energy technology of the granular material drying, which is highly applicable in various industrial operations, namely particulate coating, granular drying, mixing, agglomeration, separation, milling, combustion, etc. The foremost feature of this reactor is its compact size through which higher heat and mass transfer take place. Observing intense heat and mass transfer characteristics of the GSVR reactor, a pilot-scale GSVR dryer has been developed that dry the granular material rapidly. The goal of the present study is to examine the performance of the developed reactor, by means of experimental investigations, considering various operating parameters such as air pressure, temperature, suspension density, drying air temperature, airflow rate, and inventory of paddy. The results obtained from the experimental study revealed that the maximum and minimum time of drying is found to be 40 and 20 min for the maximum and minimum loading capacity of 1000 and 400 g, respectively. Hence, overall drying efficiency is improved by increasing the inventory of paddy (800–1000 g).

Mass transfer intensification of CO2 absorption in monoethanolamine using high frequency ultrasonic technology in continuous system

Intensification technology for absorption process is of interest for the separation of CO2 from natural gas in the offshore. High frequency ultrasonic absorption technology in batch system has shown remarkable potential for offshore application due to high operating flexibility and mass transfer performance. Therefore, in this work, a high frequency ultrasonic absorption (HiFUA) of CO2 from natural gas using monoethanolamine is proposed for continuous system to suit the industrial mode of operation. The effect of the operating parameters on the overall mass transfer coefficient was investigated, thus the optimum condition was identified using central composite design coupled with response surface methodology. Based on the results, the optimum condition was found at the gas flow rate of 30 SLPM, liquid flow rate of 0.15 SLPM, pressure of 10 bar and ultrasonic voltage of 30 V, which resulted to maximum mass transfer coefficient of 268.9 mol/kPa.m3.hr. The presence of high frequency ultrasonic irradiation has enhanced the absorption process 7 times higher as compared to the case of without ultrasonic irradiation due to its physical effects which are the acoustic streaming, fountain and atomization. The enhancement in continuous system is lower than the batch system reported in the literature due to the difference in the reactor configuration. Nevertheless, HiFUA has intensified the mass transfer performance 12 times higher as compared to conventional packed bed column for CO2-MEA system. This work has shown great potential of high frequency ultrasonic irradiation as an intensification technology for CO2 absorption process.

High-gravity-assisted engineering of Ni2P/g-C3N4 nanocomposites with enhanced photocatalytic performance

Graphitic carbon nitride (g-C3N4) with transition metal phosphides has been studied extensively as potential photocatalysts for hydrogen evolution. However, in-situ approaches to realize intimate interfacial contacts have rarely been reported. In this study, Ni2P nanoparticles-decorated g-C3N4 photocatalysts were prepared via liquid exfoliation of g-C3N4 followed by in-situ loading of Ni2P nanoparticles in a rotating packed bed (RPB) reactor. The optimized Ni2P/g-C3N4 exhibits high performance in visible-light-driven (λ > 420 nm) hydrogen evolution (∼561 μmol g−1 h−1), which is 103 times higher than that of pristine g-C3N4. The superior photocatalytic performance and durability originate from the robust interfacial structure. Therefore, a Z-scheme route with enhanced transfer of photoinduced electron was proposed, and Ni2P/g-C3N4 composites with smaller bandgaps than those of g-C3N4 were realized. Due to the intensified mass transfer and mixing of RPB reactor, the adsorption and nucleation processes of Ni2P on g-C3N4 were enhanced, enabling scalable solar light-driven H2 production.

Process intensification through staggered herringbone micro-channels: Mass transfer enhancement to a reactive wall

In the present study, the flow behaviour through different micro-herringbone channels configurations (1-peak, 2-peak, 1–2 alternated peak herringbone channel and a flow inversion geometry) have been numerically analysed as a mean of intensifying mass transfer to a reactive boundary. Results showed that the mass transfer coefficients were higher for the 1–2 alternated herringbone structure than those with, either, 1-peak or 2-peak structures. Moreover, the flow inversion structure mass transfer coefficients were double those obtained for the staggered herringbone channel. The alternated herringbone channel combines a different set of herringbone structures that are efficient at removing the boundary layer at different parts of the channel. The combination of these structures provide an enhanced mass transfer performance as compared to a standard herringbone channel. The obtained results showed that a 2D simplified model which uses hydrodynamic data from CFD simulations is a reasonable substitute for full 3D particle tracking simulations in terms of the mass transfer behavior of the 1PSHC with a 97.5 % of accuracy related to the asymptotic Sherwood number. The mixing capacity of the herringbones was accounted for by an apparent effective diffusion coefficient. The agreement between the 3D and 2D simulation was reasonable.

Intensification of Mass Transfer in the Extraction Process with a Nanofluid Prepared in a Natural Deep Eutectic Solvent

AbstractThe phytotoxic residues after olive oil production and residue leaves after pruning contain valuable bioactive compounds. A natural deep eutectic solvent (NADES) and an ethanol‐water mixture were used for polyphenol extraction from olive pomace and leaves. Type of solvent, extraction temperature, and particle size of the leaves were optimized. NADES demonstrated better efficiency in the extraction process than conventional solvents; with higher temperature and smaller fraction of olive leaves, a higher yield of polyphenols was obtained from leaves. Extraction with a nanofluid as solvent was carried out. A stable nanofluid was prepared from NADES by adding Al2O3 nanoparticles. A higher yield was obtained with nanofluid from leaves, while an improvement of polyphenol extraction was achieved after the removal of oil from olive pomace.

Experimental Evidence of Enhanced Adsorption Dynamics at Liquid-Liquid Interfaces under an Electric Field.

In this work, we investigate the adsorption of surface-active compounds at the water-oil interface subjected to an electric field. A fluid system comprising a pendent water drop surrounded by an asphaltene-rich organic phase is exposed to a DC uniform electric field. Two subfractions of asphaltenes having contrasting affinities to the water-oil interface are used as surface-active compounds. The microscopic changes in the drop shape, as a result of asphaltene adsorption, are captured and the drop profiles are analyzed using our in-house code for axisymmetric drop shape analysis (ADSA) under an electric field. The estimates of dynamic interfacial tension under different strengths of the field (E0) and concentrations of the asphaltene subfractions (C) are used to calculate adsorption dynamics and surface excess. The experimental observations and careful analyses of the data suggest that the externally applied electric field significantly stimulates the mass-transfer rate at the liquid-liquid interface. The enhancement in mass transport at the water-oil interface can be attributed to the axisymmetric electrohydrodynamic fluid flows generated on either side of the interface. The boost in mass transport is evident from the growing decay in equilibrium interfacial tension (γeq) and increased surface excess (Γeq) upon increasing strength of the applied electric field. The mass-transfer intensification does not increase monotonously with the electric field strength above an optimum E0, which is in agreement with the previous theoretical studies in the literature. However, these first explicit experimental measurements of adsorption at an interface under an electric field suggest that the optimum E0 is determined by characteristics of the surface-active molecules.

Assessment of mass transfer intensification potential for a CO2 capture process using three-phase fluidized bed

In order to assess the post-combustion CO2 capture intensification potential, a detailed mathematical model was developed for a three-phase fluidized bed. As solvents, various aqueous solutions were used e.g. NaOH and MEA with and without glycerol addition. An innovative mass transfer equipment is presented, a three-phase gas-solid-liquid fluidized bed absorber, in which the bed of low-density inert solid particles is fluidized by the counter current flow of gas as a continuous phase and liquid as a dispersed phase. Experimental data from a pilot plant was used to validate the developed model. The hydrodynamic parameters determined were the followings: fluidized bed expansion ratio, liquid holdup and bed pressure. The most important efficiency parameter, the effective mass transfer area, was assessed. The results show that by using a three-phase fluidization column, the mass transfer parameters exhibit significant increases (8–10 times) in comparison to conventional packed beds. In addition, introducing glycerol to NaOH and MEA solutions was investigated as a potential method to further improve the overall CO2 absorption performance. As the results show, the glycerol addition intensifies the CO2 absorption process by about 10 %.

Numerical study of thermal wall protection from a hot air by the evaporation of a binary liquid film

In this paper, a numerical study is performed to investigate the influence of adding glycol or alcohol to water on the thermal protection of a channel wall from hot air by evaporating this binary liquid film. The coupled governing equations in both phases with the boundary and interfacial conditions are solved using a finite difference numerical scheme. The effectiveness of adding a fraction of glycol or ethanol to water for the thermal wall protection is analysed. The influence of the film composition, the liquid mass flow, the velocity and the gas flow temperature at the inlet, on the intensity of heat and mass transfer is discussed. The results indicate that with a lower inlet liquid flow, the mixture ethanol-water presents the best solution for the thermal wall protection compared to ethylene glycol-water mixture. However, for higher inlet liquid flow rate, the two mixtures have the same trends for a water amount higher than 60%. The presence of ethylene glycol in the mixture reduces the heat transfer by latent mode. Consequently, the decrease of the wall temperature is mainly due to the sensible heat flux. The ethylene glycol-water mixture offers the best wall protection from the hot air stream. Accordingly, the most important factor for the wall protection is the thickness of the film that acts as an insulator. The pure water presents a better thermal protection but a very bad conservation of the liquid film. Furthermore, the heat transfer by sensible heat exchange contributes efficiently in wall protection than heat transfer by latent mode.

TiO2 nanofluid for oxygen mass transfer intensification in pulsed plate column

Oxygen mass transfer coefficient (kLa) is a key parameter in biochemical, photochemical, or other reactors. Pulsed plate column (PPC) has a potential application as a gas-liquid contactor. In the present work, TiO2 nanofluid mediated oxygen mass transfer intensification in PPC is studied. The pulsing velocity (A × f) and nanoparticle loading in volume percent (Φ) have an interacting effect on kLa. The effect of Φ on kLa, showed a dual regime of an increase in kLa with an increase in Φ up to a critical loading (Φ CL ) and decrease in kLa on further increase in Φ. The effect of (A × f) on kLa showed three regimes. Φ CL & kLa were found to decrease as the nanoparticle's size increased. Dimensionless correlations based on multiple regression analysis and ANN models were developed to predict the kLa values in PPC with TiO2 nanofluids.

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.

Intensification of mass transfer in the pulsed bubble column—Comparison of the efficiency of static and pulsed aerator

Introduction of pulsations to the classical bubble columns makes it possible to reduce the size and velocity of flowing gas bubbles and to obtain nearly spherical shape. As a result, gas hold-up and interfacial area are increased which obviously has an effect on the intensification of mass transfer.In the work the values of gas hold-up and volumetric mass transfer coefficient obtained in the pulsed bubble columns with static and pulsed aerator were compared. In the tests two types of aerators were used: the first one was static, while the other one was a pulsed aerator fixed rigidly on the surface of the exciter disk. In both cases pulsations with the resonant frequencies up to 70 Hz and amplitude of 0.25–2 mm were introduced into the system, and the apparent gas velocity was set within 3.1–9.3 mm/s.Equations were proposed to calculate gas hold-up and volumetric mass transfer coefficient with accuracy of ±25% and ±30% for the aerator pulsating at resonance frequencies.Using a pulsed aerator in most cases lower gas hold-up was obtained than in the case of a static aerator. The volumetric mass transfer coefficient was higher when the static aerator was used.

Kinetics of Extraction of Dioscine from Vegetable Raw Materials in Vibrocavitation Homogenizer

Introduction. In recent years, substances extracted from plant materials have been widely used in the pharmaceutical, cosmetic and food industries. Such substances are used as solutions, dry extracts for the manufacture of medicines, dietary supplements, cosmetic creams, food additives in various forms – tablets, capsules, solutions, granular powders. The extraction of valuable substances from plant materials is carried out using the extraction process, which is carried out by various methods and in apparatuses of various designs. Earlier, a comparative study of the extraction of dioscin from fenugreek by various methods was carried out: in devices with a stirrer, in an ultrasonic field, supercritical, fluid CO2 extraction, and in a vibro-cavitation homogenizer. It is shown that the most effective method is the extraction carried out in a vibrocavitation homogenizer.Aim.To analyze the kinetics of the extraction of dioscin from fenugreek seeds, to determine the optimal values of the required degree of grinding of the raw materials, working temperature, the concentration of ethyl alcohol in the solution and the rotational speed of the rotor of the vibrocavitation homogenizer. Determine the effective mass transfer coefficient responsible for the intensity of mass transfer inside the particles.Materials and methods. An experimental study of the extraction of valuable components from plant materials was carried out in a laboratory unit with a vibrocavitation homogenizer of periodic action. As raw materials were used seeds of hay fenugreek, ecotype of Morocco, acquired in the company Fitokasa, Casablanca (Morocco), which we used for research. Commodity analysis showed that raw materials comply with the requirements of the State Pharmacopoeia XIVth edition. As extractants, aqueous solutions of ethanol with an alcohol concentration of 40, 50, 60, 70, 80, and 90 %. The analysis of the kinetics of the process was based on the following ideas. Extraction begins with the surface of the particles of plant material. As the extracted component moves into the volume of the solution, the extractant penetrates into the internal pores of the particles, and the surface on which the extractant and the extracted component interact is gradually shifted into the individual particles. In this case, the resistance to mass transfer in the region between the specified surface and the outer surface of the particle increases over time.Results and discussion. An analysis of the results shows that the rotor speed significantly intensifies the process. In addition, the influence of the rotor speed is most pronounced at the initial stage of the process, when the surface layers of particles of plant material are extracted. It was also found that the resistance to mass transfer inside particles increases significantly as it approaches the final stage of the process, and with an increase in the rotor speed, it increases, especially at the initial stage of the process, which is associated with the intensity of cavitation and the weakening of its effect as the process deepens inward particles.Conclusions. The obtained dependences are necessary to determine the duration of the extraction process in a batch mode, or the average residence time of seeds in the working volume when organizing the process in a continuous mode.

Direct conversion of terminal alkenes to aldehydes via ozonolysis reaction in rotating zigzag bed

In this study, continuous ozonolysis of terminal alkenes in a rotating zigzag bed was developed. Rotating zigzag bed is a new type high gravity unit relative to the previous rotating packed bed and can intensify mass transfer remarkably. The rotating zigzag bed takes advantage of centrifugal force to mix liquid and gas phase effectively. The H2O in acetone acts as an in situ reducing agent for the carbonyl oxide intermediate, providing aldehydes directly from the reaction mixture. Critical factors were investigated and achieved optimum reaction conditions. Under these conditions, the yields of series aldehydes ranged from 72.3 to 95.8%. The discrepancy in product yields among different olefin substrates likely originates from the electronic stability of the carbonyl oxide intermediate, which is longer lived for aryl olefines with electron donor group and longer carbon chain alkene (CnH2n, n ≥ 10).

Wave-absorbing material aided microwave freeze-drying of vitamin C solution frozen with preformed pores

To explore the effect of wave-absorbing material aided microwave heating on freeze-drying of initially porous frozen material, a lab-scale microwave freeze-dryer was designed with solid-state source selected as the microwave source instead of the traditionally used magnetron. Vitamin C was employed as the solute in aqueous solution. “Soft-ice” freezing technique was adopted to prepare solid and porous frozen materials. Experimental results showed that the solid sample by soft-ice freezing can successfully avoid structural collapse during freeze-drying, and the porous frozen material can significantly intensify mass transfer of the freeze-drying process. Under the operating conditions of 35 °C and 20 Pa, the drying time of the porous sample with the initial saturation of 0.25 decreased by 30.4% compared with the solid one, and the residual moisture content of dried product decreased with the initial saturation reducing. SEM images of the dried products revealed that the porous material had a loose pore structure and a tenuous solid skeleton, which is favorable to the migration of sublimated/desorbed vapor and the desorption of bound moisture. Evidences also showed that appropriately increasing radiation temperature led to reducing the drying time, while changing chamber pressure had an insignificant effect on freeze-drying. With sintered silicon carbide (SiC), which is a kind of wave-absorbing material, as the supporting pad of sample, microwave heating can greatly improve heat transfer of the freeze-drying process. Under the same operating conditions, the drying time of the porous sample with the microwave input power of 5 W was 28.1% shorter than that of the same sample without microwave heating, and 50.0% shorter than that of the solid sample for conventional freeze-drying. Wave-absorbing material aided microwave freeze-drying of the porous material frozen with preformed pores is a feasible and effective way to achieve the simultaneous intensification of heat and mass transfer in freeze-drying.

A 3D Radiation Hydrodynamic AGB Binary Model

Abstract The origin of chemically peculiar stars and nonzero eccentricity in evolved close binaries have been long-standing problems in binary stellar evolution. Answers to these questions may trace back to an intense mass transfer during the asymptotic-giant-branch (AGB) binary phase. In this work, we use AstroBEAR to solve the 3D radiation hydrodynamic equations and calculate the mass transfer rate in AGB binaries that undergo the wind-Roche-lobe overflow or Bondi–Hoyle–Lyttleton (BHL) accretion. MESA produces the density and temperature of the boundary condition of the AGB star. To improve the resolution of the dynamics of a circumbinary disk, we implement an azimuthal angle dependent 3D radiation transfer. We consider optically thin cooling and obtain the number density of the coolants by solving Saha equations. One of the goals of this work is to illustrate the transition from the wind-Roche-lobe overflow to BHL accretion. Both circumbinary disks and spiral structure outflows can appear in the simulations. Circumbinary disks may form when the optical thickness in the equatorial region increases. The increase of the optical thickness is due to the deflected wind. The resulting mass transfer efficiency in our models is up to a factor of 8 times higher than what the standard BHL accretion scenario predicts, and the outflow gains up to 91% of its initial angular momentum when it reaches 1.3 binary separations. Consequently, some AGB binaries may undergo orbit shrinkage, and some will expand. The high mass transfer efficiency is closely related to the presence of the circumbinary disks.

Evaporative cooling of the liquid film in slot channels with capillary-porous walls under natural convection

Implementation of resource-saving technologies can be based on improving the qualitative characteristics of heat and mass transfer equipment, which is widely used in power engineering, chemical, petrochemical, gas and food industries.One of the most effective ways of interaction between the coolant and the working medium is the direct contact of a gravitationally flowing liquid film and a gas. A promising method for passive intensification of heat and mass transfer between the liquid film and gas is the use of contact surfaces with regular roughness, with capillary-porous or mesh coating of channel walls.The launch and emergency stop of the heat and mass transfer device may generate a transition in the cooling mode of liquid from forced to natural convection. This leads to a change in the conditions of heat and mass transfer, and, consequently, to a change in the parameters of the coolant at the output of the device. In this case, using the dependences obtained for forced convection in the channel leads to a significant error in determining the parameters of the heat carrier. Therefore, in order to design and manufacture heat-mass-transfer units of contact type, one would need the information on the patterns of heat and mass transfer under different operating conditions.An important condition for ensuring the efficiency of contact-type devices is to know the features of the interaction between the liquid and gas mediums. The development of boundary layers in the film and gas leads to the need to allocate the initial thermal region and the stabilized heat and mass transfer region. These factors are not taken into account in the engineering calculation methods that exist today.

High-gravity-assisted green synthesis of rare-earth doped calcium molybdate colloidal nanophosphors

Abstract In this work, we report an innovative route for the synthesis of rare-earth doped calcium molybdate (CaMoO4) nanophosphors by using high gravity rotating packed bed (RPB) technology and paraffin liquid as the solvent. The significant intensified mass transfer and micromixing of reactants in the RPB reactor are benefiting for homogeneous doping of rare-earth ions in the host materials, leading to nanophosphors with high quantum efficiency. The use of liquid paraffin as the solvent eliminates the safety risks associated with volatile organic compounds, increasing the potential for clean production of nanophosphors. Under excitation of deep ultraviolet (DUV) light, the CaMoO4:Na+, Eu3+ nanophosphors exhibit red emission at peak wavelength of 615 nm and quantum yield of up to 35.01%. The CaMoO4:Na+,Tb3+ nanophosphors exhibit green emission at peak wavelength of 543 nm with quantum yield of up to 30.66%. The morphologies of the nanophosphors are tunable from nanofibers through nanorods to nanodots and the possible mechanism of controlling the formation of different nanostructures is proposed on the basis of experimental results and theoretical analysis of mesoscience. These nanophosphors are highly dispersible in organic solvents and utilized for fabricating fabrication of flexible, freestanding luminescent films based on silicone resin. We also demonstrate the red LEDs consisting of the hybrid films of CaMoO4:Na+,Eu3+ nanoparticles as color-converting phosphors and DUV LEDs as illuminators, offering strong potential for future nanophosphors-basedsolid-state lighting systems.

Optimal design of helical heat/mass exchangers under laminar flow: CFD investigation and correlations for maximal transfer efficiency and process intensification performances

Highly curved helical pipes (HCHPs) offer tremendous potentialities for intensified heat/mass transfer performances as they generate intense Dean-type vortices. However, these designs have not been explored so far in the literature, probably because they are difficult to build using traditional manufacturing techniques. Nowadays, thanks to a witnessed progress in 3D-printing, the fabrication of HCHPs has become achievable. Therefore, investigating their performance in terms of heat and mass transfer intensification presents significant interest from both academic and industrial points of view.In this paper, CFD simulations are carried out to determine the heat/mass transfer efficiency in helical pipes (particularly highly curved ones) under laminar flow conditions. The packing density (i.e. interfacial area) of these geometries is evaluated using a CAD software. The results reveal that HCHPs not only allow achieving much higher transfer rates than straight and classical helical pipes, but they can also be densely packed. Therefore, when appropriate designs are selected, impressive process intensification factors are achievable, with up to 8-fold volume reductions.Finally, correlations are developed for evaluating the interfacial area and the heat/mass transfer efficiency in classical and highly curved helical pipes. In future works, these correlations will be used in model-based optimization for determining the optimal designs of helically coiled heat/mass exchangers.

Classification, Function, and Construction of Modern Static Mixers

Well-known data concerning the classification, function, and structural features along with operating mechanisms used in modern industry to produce homogeneous mixtures and emulsions, to generate dispersion, and to intensify mass transfer and accelerate chemical reactions are generalized.

Aromas flow: eco-friendly, continuous, and scalable preparation of flavour esters

Flow-based biocatalysis offers advantages to perform multiphase reactions, including liquid–liquid reactions, due to intensified mass transfer, compartmentalization and high local concentration of the catalyst. Enzymatic immobilization leads to stable biocatalysts, with the possibility to incorporate them in continuous reactors. The combination between the two technologies allows for intensified process with high substrate concentration and high product recovery. The present paper is an excellent example of automated continuous biocatalytic process where a transferase from Mycobacterium smegmatis (MsAcT) was immobilized onto agarose beads and exploited for the preparation of a variety of flavour-esters, utilizing exclusively natural substrates, with excellent yields in 5-min reaction times. The corresponding products can be labelled and commercialized as natural too, thus increasing their market value.