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A method is proposed for determining the coefficient of ozone mass transfer between the gas phase and an aqueous solution of HCl + NaCl. The method is based on minimizing the functional of discrepancy between the dependences of the specific reaction rate of O3 with Cl–(aq) on the concentration of hydrogen ions determined from experiment and obtained from reference data. The method also allows estimation of the true Henry constant in acidic solutions of chlorides. [ABSTRACT FROM AUTHOR]

Selenium (Se) is an important nutritional element which exists at very low concentrations, easily accumulates via the food chain and creates adverse effects such as a deprived reproduction rate and diminutive growth in human and aquatic organisms. So, it has become a severe concern around the world. We explore electrocoagulation using Al and Fe electrodes and activated sludge process (ASP) in batch process and also in an integrated process to remove Se. The optimized parameters of the current density in the batch process were: 6.7 and 5.7 mA/cm2 for Al and Fe, respectively. The mass transfer coefficient has been estimated through numerical modelling for batch and integrated processes using the equations K = and K = ; the energy consumption and metal dissolution were 138240 and 384 MWh/m3, 60 and 3.58 g, respectively. The response surface methodology (RSM) was implemented in Box−Benken design to assess the parametric optimization, and the validation of experimental data was done using ANOVA and regression analysis. The obtained p-values and model F-values were 0.000 and 63.09 for Al and 0.000 and 79.98 for Fe, which indicated the significance of the model. The chemical oxygen demand (COD) reduction values estimated along with Se reduction in real effluent treatment were above 90 and 60% in electrolytic and 80% in an integrated ASP with very high-cost efficiency. The results assure that this proposed hybrid work will provide a higher reduction, improved energy and cost efficiency for the effluent with indeterminate influent Se and COD concentration. The proposed model also helps to make predictions of removal efficiency without requiring an extensive time and cost burden. [ABSTRACT FROM AUTHOR]

The boundary conditions for describing the mass transfer of carbon from oxygen-free low-pressure atmospheres into steel during vacuum carburizing are analyzed. The effect of the content of carbide-forming alloying elements on the values of the carbon potential of low-pressure acetylene atmospheres is determined depending on the temperature of the process of vacuum carburizing. Temperature dependences of the carbon mass transfer coefficient are derived. [ABSTRACT FROM AUTHOR]

The adsorptive removal of methylene blue (MB) from its aqueous solution using citric acid-modified arjun bark powder as an adsorbent was studied. Initially, the adsorbent was characterized by various analytical techniques (SEM, BET, FTIR, and pHpzc). After characterizing the adsorbent, it was used for carrying out batch study on the biosorption of MB. The batch experiments revealed a very high percentage removal of MB of about 100%. The batch experiment results followed Temkin isotherm. The maximum monolayer adsorption capacity observed was 512.82 mg/g at natural pH of 7.5. The Freundlich isotherm constant was found to be 300.15 l/g. The Temkin isotherm constant was found to be 21.32 l/mg. The sorption energy was calculated from the Dubinin–Radushkevich isotherm model, and it was found to be 10 kJ /mol. On the other hand, results followed the pseudo-second-order kinetic model. The energy of activation in the present study was estimated to be 10 kJ/mol. The adsorptive mass transfer coefficient was calculated to be 1.65 × 10–7 m/s, and the value of diffusivity was found to be 2.27 × 10–11. [ABSTRACT FROM AUTHOR]

Numerical and experimental studies were carried out for the analysis of hydrodynamics and volumetric mass transfer coefficient (kLa) in a cross-T junction microchannel for gas–liquid, two phase flow system. Initially, CO2–water hydrodynamics simulation was performed using ANSYS-FLUENT 2021 R2 and volume of fluid technique. Through the numerical simulation, fluctuation in pressure drop with variation in volume fraction was calculated for the slug flow in a 1 mm hydraulic diameter microchannel. After that mass transfer equations were coupled with the flow equations for CO2–ethyl glycol, CO2–water, and CO2–ethyl alcohol systems to understand the mass transfer mechanism using two film theory concepts. Computational fluid dynamics model was validated by comparing results with the experimental data. An empirical co-relation was also developed to measure the bubble length with its position in the direction of fluid flow. CO2 and solvents velocities were 0.21–0.424 m/s for both the phase. Effect of solvents and film thickness (0.01–0.05 mm) on volumetric mas transfer coefficient were investigated at different temperatures range i.e., T = 298.15 K and 303.15 K (experimental approach) and 298.15–318.15 K (numerical approach). The results obtained in numerical simulation and experimental work show that the total volumetric mass transfer coefficient (range 0.1–0.8 1/s) increases with the gas velocity however, it decreases with increasing film thickness (0.01–0.05 mm) and temperature (T = 298.15 K and 303.15 K). The present work gives an advantage over the conventional channel (e.g., packed bed column) and the other type of T-junction microchannel (e.g., symmetric T-junction) by providing a high mixing rate, interfacial area, and high mass transfer rate. [ABSTRACT FROM AUTHOR]

The experimental procedure is developed and tested on a laboratory scale and using layered samples of manmade geomaterials. Within the dual-permeability model, the procedure enables determining parameters that govern fluid flow and poroelastic deformation in fractured porous rock masses, namely, fracture permeability and mass transfer coefficient , as well as their dependence on stresses . The testing procedure is proposed and implemented. In the procedure, under the stepwise increasing normal stress , the stationary flow rates and are measured in a quasiregular fractured porous sample at the preset pressure difference: using a standard setup () and in closed end-face fractures (). The mathematical model of the experiment is constructed, and the analytical solution of the problem on stationary flow is obtained: pressure patterns in fractures, and stress-dependence of flow rates. The experimental data interpretation algorithm enables calculating and by the recorded flow rates and . It is shown that the permeability is proportional to , and remains almost unchanged. [ABSTRACT FROM AUTHOR]

The study of impurity removal kinetics in the refining and purification of industrial silicon is essential to refine the purification process and improve impurity removal efficiency. In this paper, influencing rules of slag system compositions, a mass ratio of slag to silicon (slag/silicon), and refining time with impurity aluminum content in industrial silicon were investigated by slagging refining experiments. The values of apparent rate constant (kAl) and mass transfer coefficient (βAl) of aluminum acquired from refining time and its corresponding impurity content were 1.42 × 10–4 s−1 and 7.90 × 10–7 m·s−1, respectively. Experimental results showed that the rate of silicon loss increases slightly with the increase of refining time during slagging refining compared to gas blowing refining. The influence of refining time on silicon loss during slagging refining is much less than that of gas blowing refining, which was more suitable for the refining operation of industrial silicon. [ABSTRACT FROM AUTHOR]

An ultrasound-negative pressure cavitation fractional precipitation method was developed to efficiently purify (+)-dihydromyricetin. The precipitation efficiency of the developed method was significantly higher than that of the ultrasound- and negative pressure-fractional precipitation methods. In particular, under an ultrasonic power of 180 to 250 W and a negative pressure intensity of −200 mmHg, highly pure (+)-dihydromyricetin could be obtained with a high yield of up to 97.56% in only one minute of precipitation. Kinetic analysis results showed that when both ultrasound and negative pressure were introduced during fractional precipitation, the rate constant increased by 1.4 to 7.1 times compared to the conventional fractional precipitation, and the activation energy decreased by −1,299 to −4,550 J/mol. In addition, the particle size of the precipitate was reduced by 1.9 to 4.0 times, and the diffusion coefficient increased by 2.3 to 5.0 times. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a microextraction approach for the extraction and separation of Mn(II) and Co(II) from sulfate solution simulating leachate of spent lithium-ion battery cathode materials using saponified di-(2-ethylhexyl)phosphoric acid system. The effects of the following operational variables were investigated: equilibrium pH, tri-n-butyl phosphate concentration, saponification rate, two-phase ratio and residence time. The results showcased that the microextractor can reach the extraction equilibrium within 20 s, thereby greatly reducing necessary extraction time comparing to that of conventional processes. The volumetric mass transfer coefficient showed 8–21 times larger than that of batch device. With the help of microextractor, 95% of Mn(II) was extracted with a single theoretical stage at a chosen two-phase ratio of 3:1, and the separation factor βMn/Co was as large as 65.5. In the subsequent stripping step, more than 99% of manganese from loaded phase was easily stripped under optimal conditions. The microextraction approach greatly enhances the mass transfer while enabling a continuous and controllable extraction process within a simple structure design. When extracting spent electrode material with microextractors, the comprehensive recovery of mangenese can reach 96%. The microextraction approach has a good applicability in the spent lithium-ion battery cathode materials recycling at both bench and industrial scales. [ABSTRACT FROM AUTHOR]

The mass transfer coefficient and the extraction degree of uranium was investigated from a leach liquor by Alamine 336 in a single drop column. The effect of operating and structural parameters were separately studied. The results showed that the increasing the extractant concentration has a direct impact on the mass transfer coefficient of drops. Also, the change of sulfate concentration to 0.2 causes an increase in the mass transfer coefficient, but with a further increasing in sulfate content, a decreasing trend is observed. The results obtained can be used for the design of the extraction column. [ABSTRACT FROM AUTHOR]

We designed and modelled a fluidized bed dryer. Based on the literature, modelling of a bed dryer is carried out for two situations: for spherical and non-spherical particles. Two case studies were taken from the literature for modelling the fluidized bed dryer for naphthalene balls and mushroom slices. Fluidized bed dryer design was carried out with respect to diffusivity of the bed materials. Drying characteristics in terms of effective diffusivity were studied for naphthalene balls and mushroom slices using a tapered fluidized bed dryer. The variation of effective diffusivity was obtained with change in inlet air temperature, velocity, thickness of slab and drying time. Experimental effective diffusivity as obtained from literature was compared with model predicted values, provided lower deviations with RMSE of less than 8.28% for spherical naphthalene balls and 0.936% for the mushroom slices. Mass transfer coefficient obtained for naphthalene balls was in the range of 2.1×10−4 to 4.857×10−3m sec−1. The diffusivity constant was evaluated using Fick's diffusion equation assuming surface moisture in equilibrium with the surrounding atmosphere. The value of diffusivity constant (D0) obtained is 1.828×10−9 m2sec−1 and the value of activation energy (Ea) obtained is 4.523 kJ mol−1. [ABSTRACT FROM AUTHOR]

An ultrasound-negative pressure cavitation extraction method was developed to remarkably improve the recovery efficiency of paclitaxel from Taxus chinensis. The paclitaxel yield was 94–100% through ultrasound-negative pressure cavitation extraction with an extraction time of 3 to 8 min. In particular, most paclitaxel could be recovered within 3 min of extraction at ultrasonic power of 380 W/negative pressure of −260 mmHg. Observation of the biomass surface with SEM before and after extraction showed that as the ultrasonic power and negative pressure increased, the surface was more disrupted. In addition, a pseudo-second order model was suitable for the kinetic analysis, and intraparticle diffusion played a dominant role in the overall extraction rate according to the intraparticle diffusion model. As the ultrasonic power and negative pressure increased, the extraction rate constant (6.8816–11.6105 mL/mg·min), the effective diffusion coefficient (1.550×10−12–11.528×10−12 m2/s), and the mass transfer coefficient (2.222×10−7–5.149×10−7 m/s) increased. [ABSTRACT FROM AUTHOR]

In this study, a drying process with ethanol pretreatment was developed for effective removal of residual moisture from the plant cell Taxus chinensis. Drying efficiency was improved remarkably by a simple rotary evaporation with ethanol pretreatment. At the optimal amount of ethanol for pretreatment (biomass/ethanol = 3:1, w/v), the drying time was shortened by 1.9 times (40°C), 1.5 times (50°C), and 1.3 times (60°C), respectively, compared to drying without ethanol pretreatment. The experimental data was applied to the representative kinetic drying models, and the modified Page model was shown to be the most suitable. Thermodynamic parameters represented the spontaneous and endothermic characteristics of the drying process by the ethanol pretreatment, and randomness during the drying process was also increased. The highest effective diffusion coefficient (6.216 × 10−14–7.940 × 10−14 m2/s at 40–60°C), Biot number (4.40 × 10−2–6.60 × 10−2 at 40–60°C), and mass transfer coefficient (64.34 × 10−12–123.39 × 10−12 m/s at 40–60°C) were observed when the biomass was pre-treated with an optimal amount of ethanol. In addition, as the drying temperature was increased with the same ethanol amount, these values were also increased. [ABSTRACT FROM AUTHOR]

The mechanism of a heterogeneous reaction that occurs during the bubbling of gas bubbles released during the reaction has been investigated. Theoretical provisions on the formation of gas bubbles in a heterogeneous solid–liquid–gas reaction based on the formation of a moving microlayer of a liquid reagent under a gas bubble are considered. Analogously with boiling, a hydrodynamic model of the formation of a microlayer and its reaction upon contact with a solid reducing agent is proposed. The model of "chemical boiling" gives qualitatively correct regularities of the reaction. The structure of the dependence of the bubble radius practically coincides with the previously considered models, which correlate quite satisfactorily with the experiment. Consideration of the hydrodynamics of bubbling gas bubbles by analytical and numerical methods makes it possible to get an idea of the shape of the flows of the liquid phase. The presence of hydrodynamic structures responsible for the ordered motion of the liquid for various methods of supplying the gas phase is characteristic. Relationships are obtained for the critical conditions of mass transfer. Unlike boiling in a heterogeneous reaction, the existence of a crisis regime is impossible due to the screening of the reaction surface. This regime is only extreme. We have previously shown that the degree of screening of the reaction surface by bubbles is insignificant. When boiling, this value is within 13%. [ABSTRACT FROM AUTHOR]

The present work aims to develop a 3-dimensional finite element (FE) model to analyze moisture migration during drying of pineapple ring considering moisture dependent diffusion coefficient (D) and mass transfer coefficient (hm) along with radial and longitudinal shrinkage. Pineapple rings were dried at 70 °C temperature and 0.6 m/s air velocity to study the moisture loss and shrinkage kinetics during drying. Thickness, outer radius and inner radius of hollow cylindrical pineapple slices were reduced by 79.3%, 32.2%, and 51.2%, respectively due to the occurrence of shrinkage during drying. Non-linear regression analysis showed the quadratic model to best fitted to the experimental moisture ratio data for explaining the shrinkage phenomenon in pineapple slice during drying. Shrinkage was accommodated into FE modelling using the arbitrary lagrange-eulerian method. Consideration of variable D showed better agreement with the experimental data than consideration of constant D, however constant and variable hm predicted similar results. Incorporation of shrinkage phenomena during modelling led to prediction of more accurate result showing 0.06% deviation from experimental curve, but neglecting the shrinkage resulted in a 17% deviation. Hence, model developed with consideration of shrinkage along with variable D and hm presented best fit with experimental drying curve. Developed model allowed the visualization of spatial moisture profile within the sample during drying, which would be useful for estimating the correct drying time, optimizing and designing of drying process. [ABSTRACT FROM AUTHOR]

With the rapid growth of pharmaceutical and biotechnology industry, stirred tank bioreactors have received much attention due to simple design, easy control of operating conditions, and low operating cost. In the development of commercial processes, however, a transition from laboratory to industrial scale faces great challenges because many properties related to size change nonlinearly as a system increases. In this context, along with an understanding of fluid dynamics, application of an efficient method for scale-up is critical for designing successful industrial process. Particularly in cell cultivation processes, it is important to evaluate the oxygen transfer and viscous properties of liquid medium. In the present study, the effect of various key operating variables such as agitation rate and aeration rate, impeller diameter, and bioreactor working volume for different impellers on the volumetric mass transfer coefficient (kLa) have been investigated in a stirred tank bioreactor for cultivating Escherichia coli BL21. It was found that the kLa tends to increase with the operating variables except the bioreactor working volume. Among the tested impellers, the pitched blade was observed to be most promising because of relatively higher kLa but less shear force owing to its low power number. It was also found that the liquid medium with E. coli behaves as a Newtonian liquid. Compared to conventional designs of Rushton turbines, dislocated Rushton turbine was found to deliver higher kLa. Finally, using dimensional analysis, the kLa for different impeller configurations was correlated in the form of dimensionless groups, suggesting that this approach can be used for predicting kLa in different scales of stirred tank bioreactors. [ABSTRACT FROM AUTHOR]

The results obtained from a drying experiment using infrared heating are compared to those obtained from an analytical model based on correlations for the mass transfer coefficients, which are commonly used to obtain evaporation rates for drying applications. It was shown that the mass transfer coefficients calculated by natural convection correlations are approximately ten times lower than those measured under infrared (IR) exposure. In an attempt to explain this discrepancy, which has been also observed in other studies and explained on the basis of thermal radiation effects, optical properties of the solvent are presented and the implications of the IR and near infrared (NIR) spectrum on the thermal radiation effects and ensuing evaporation rates are discussed. The results show that the correlation for mass transfer coefficient has to take into account the IR radiation temperature and the surface emissivity. This study provides important evaporation data on mass flux and mass transfer coefficients, which cannot be predicted using traditional correlations, for the design of IR assisted drying systems. [ABSTRACT FROM AUTHOR]

In this study, we investigated the kinetics, mechanism, and thermodynamics of vacuum drying and dehydration of plant cells of Taxus chinensis. The efficiency of vacuum drying increased with increases in the drying temperature (45–60°C). When the experimental data were fitted to typical kinetic models for drying, the Modified Page were the most appropriate. Thermodynamic parameters revealed the endothermic, irreversible, and spontaneous nature of the drying. The effective diffusion coefficient (3.6602 × 10−14−10.9810 × 10−14 m2/s) and mass transfer coefficient (2.2536 × 10−11−10.8110 × 10−11 m/s) increased with increasing drying temperature. The small Biot number (2.6167 × 10−2−4.1841 × 10−2) indicated that the process of mass transfer was externally controlled. [ABSTRACT FROM AUTHOR]

The studies were performed with 100 mg/L of Reactive Black 5 dye (RB5) in batch reactors on Ti/PtOx–RuO2–SnO2–Sb2O5 electrodes prepared indigenously. The electrodes were fabricated using titanium substrate (plate) and coated with mixed metals of a fixed composition by standard thermal decomposition (STD) and polymeric precursor thermal decomposition (PPTD) methods. The electrolysis up to 1 h was accomplished at a constant current density of 50 mA/cm2. For the process, an initial pH of 2 was maintained with the dosage of 4 g/L NaCl as supporting electrolyte. The effects of electrodes on colour, chemical oxygen demand, and total organic carbon removal were investigated for destruction of RB5. In this comparative study, while complete decolourizations of water containing RB5 were achieved on the electrodes prepared by STD and PPTD methods, but COD and TOC removal was found to be different for different electrodes at operating conditions. The 87% COD and 83% TOC removals were achieved on Ti/PtOx–RuO2–SnO2–Sb2O5 electrode prepared by PPTD method, in comparison to 83% COD and 80% TOC removals on the electrode prepared by STD method. The two types of electrodes were compared based on removal rate constant, mass transfer coefficient, instantaneous current efficiency, energy consumption, and accelerated life test. The energy demand for RB5 removal in this study was less than 250 kWh/kg COD, which is much lower than the reported values in similar studies. Further, the performance of electrodes was compared employing scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis for coating deposited on Ti substrate, and also by cyclic voltammetry. [ABSTRACT FROM AUTHOR]

In this study, the effects of medium carbon chain alcohol (1-heptanol)-enhanced air sparging (AS) on the remediation of benzene-contaminated aquifers in different media (medium sand, channelized flow; gravel, bubbly flow) were investigated by comparison with a commonly used surfactant (sodium dodecylbenzene sulfonate (SDBS)). The results showed that the addition of 1-heptanol and SDBS significantly increased the air saturation in AS process under different airflow modes. Combined with water retention curves, 1-heptanol had the same effect on reducing the surface tension of groundwater and stabilizing bubbles as SDBS. In the study of benzene pollution removal, when the removal efficiency of the benzene pollutant exceeded 95%, the time required for surfactant-enhanced AS (SEAS) and alcohol-enhanced AS (AEAS) in medium sand was shortened by 28.6% and 52.4%, respectively, and the time required for SEAS and AEAS in gravel media was shortened by 16.7% and 58.3%, respectively, compared with the time required for AS. This finding indicated that the addition of SDBS or 1-heptanol could significantly increase the removal rate of benzene pollutants. Under the same surface tension conditions, the removal effect of 1-heptanol on the benzene pollutant was better than that of SDBS. This difference was due to the disturbance of the flow field during AEAS process causing the 1-heptanol on the gas-liquid interface to volatilize in the carrying gas, thereby inducing Marangoni convection on the interface, enhancing the gas-liquid mass transfer rate, and increasing the removal rate of benzene on the interface. Therefore, 1-heptanol is promising as a new reagent to enhance AS to remediate groundwater pollution. [ABSTRACT FROM AUTHOR]

Vortex contact devices for gas introduction have been developed and studied. The devices make it possible to increase the gas and liquid loading on stages compared with valve and cap devices, to reduce the fluctuations of the gas–liquid medium on the liquid surface, and to increase the separation efficiency. Based on the experimental studies and numerical modeling, a scheme of liquid and gas motion at the stage was developed, and the velocity profiles during bubbling were calculated. The stage parameters were determined: hydraulic resistance, gas content, average surface diameter of bubbles, interphase surface area, efficiency, and mass transfer coefficients. The dependences for their calculation were presented. A vortex stage for the exhausting distillation column was designed, which provides a 1.5-fold reduction of metal consumption and increased efficiency at a velocity factor of up to 3 Pa0.5 and spray rate of 78 m3/(h m2) compared with the standard cap plate. [ABSTRACT FROM AUTHOR]

Modified atmosphere packaging (MAP) is applied to extend the shelf life of fresh and minimally processed produce. Commonly used films, such as oriented polypropylene (OPP), are too impermeable to gases for successful MAP for products with moderate to high respiration rates, which has led to perforated systems. In order to design the perforation profile to ensure MAP targets for extended shelf life, it is necessary to evaluate which parameters affect the mass transfer through the perforations significantly. Perforations (270 μm, 450 μm and 750 μm diameter) were made in an OPP film under different temperatures and circulating air velocities, considering also different locations for the perforations. The results obtained showed that the perforation diameter is the most important parameter and can even be more significant than the total area of perforation (and therefore the number of perforations). Air velocity around the package and storage temperature were also relevant. Stacking during storage risks blocking perforations and therefore it is recommended to pierce trays on the sides in order to ensure better robustness. The package gas composition itself also affected mass transfer due to the interplay of oxygen flux with other gas fluxes, with particular relevance to the case of water vapour. [ABSTRACT FROM AUTHOR]

Solid-liquid extraction of paclitaxel from the biomass of Taxus chinensis was investigated in order to understand the effect of temperature, solvent concentration and stirring speed on the mechanism and kinetics of extraction. Paclitaxel concentration-time data were analyzed using a second-order kinetic model to determine the kinetic parameters. A diffusion model was utilized to determine diffusivity and mass transfer coefficient taking into account both washing and diffusion phases together. The effective diffusion coefficient (1.2814 × 10−13-5.9765 × 10−13 m2/s), mass transfer coefficient (1.0020 × 10−7-1.2598 × 10−7 m/s), and Biot number (3.927–8.959) increased with increasing temperature (298–318 K), methanol concentration (75–100%) and stirring speed (170–570 rpm), which indicated that the external resistance to mass transfer is negligible due to efficient mixing of solute and solvent. [ABSTRACT FROM AUTHOR]

An experimental investigation on liquid-wall mass transfer at the internal wall of a coiled flow inverter is carried out. Computation of the mass transfer coefficient is made from measured limiting currents at point electrodes fixed flush with the inner surface of the coiled flow inverter. Variation of mass transfer coefficient with respect to liquid velocity is studied. The coiled flow inverter yielded an enhancement of 125% in mass transfer coefficient against the reported enhancement of 35% in heat transfer. The data were correlated using the least squares regression method and a correlation equation is obtained. [ABSTRACT FROM AUTHOR]

We investigated the characteristics and mechanism of microwave-assisted drying of amorphous paclitaxel for the removal of residual solvent, acetonitrile. The removal efficiency of residual acetonitrile increased with increasing drying temperature from 35 to 55°C. When the experimental data were applied to typical kinetic models, the Page model was determined to be the most suitable. Thermodynamic parameters revealed the spontaneous and endothermic nature of microwave-assisted drying. The effective diffusion coefficient of acetonitrile (0.865 × 10−8∼ 1.553 × 10−8 m2/s) and the convective mass transfer coefficient (2.138 × 10−7∼7.656 × 10−7 m/s) increased with increasing drying temperature. The small Biot number (0.001975∼ 0.003939) indicated that the process of mass transfer was externally controlled. [ABSTRACT FROM AUTHOR]

Dense non-aqueous phase liquids (DNAPLs) can easily penetrate into karst aquifers, may accumulate in the sediment-filled depressions of conduits, and constitute a long-term source of groundwater contamination. In contrast to porous media, DNAPL dissolution in karst settings has not received much attention. This study investigated the dissolution of sediment-entrapped DNAPLs using a laboratory analogue model corresponding to a syphon structure partly filled by sediments and using numerical simulations. The mass transfer rate increased with an increasing conduit Reynolds number (Re) and increasing conduit angle, as both of these factors led to a more intense hyporheic flow in the sediments. In addition, the mass transfer rate increased linearly with the average flow velocity in the sediment and was higher than expected for an infinite porous medium considered as a reference case. The enhanced mass transfer rate can be explained by the curved streamlines associated with hyporheic flow, which transport solutes away from the DNAPL interface. This study demonstrates that hyporheic flow through karst sediment is a possible mechanism for the mobilization of DNAPL components and might explain the persistent occurrence of such contaminants in karst springs. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical oxidation of synthetic textile effluent containing Azo-dye Acid Violet 7 (200 mg L−1) was investigated using planar disk electrodes placed in a one inlet-outlet (I-O) cylindrical reaction chamber. Two different I-O configurations were studied, one parallel and the other perpendicular to the electrodes. Both reactors were equipped with boron-doped diamond (BDD) anodes and titanium cathodes. The effect of cell design on the hydrodynamic characteristics and efficiency of the reactors in terms of colour and chemical oxygen demand (COD) removal was studied. Mass transfer coefficient (Km) values of 1.86 × 10−5 m s−1 and 2.56 × 10−5 m s−1 were obtained for the parallel and perpendicular I-O flow reactors, respectively, using the limiting current technique. The degradation results indicated that the colour elimination was quite efficient regardless of the type of reactor used and that complete colour removal could be reached in less than 80 min at applied current density of 30 mA cm−2 and above. However, higher COD removal efficiency was always achieved in the parallel I-O flow cell compared to perpendicular I-O flow reactor at all of the current densities studied, which can be attributed to the possibility of some stagnation in the lateral regions of the electrodes. These favour a longer contact time between the pollutants and the anode, also favouring its removal. Besides, similar electric energy consumption per g COD removal was observed during the treatment with either reactors; thus demonstrating the suitability of the parallel I-O flow cell for the efficient and economic treatment of textile effluent.Graphical abstract: [ABSTRACT FROM AUTHOR]

This study proposed an asymptotic relation to estimate the first-order mass transfer in multiprocess non-equilibrium model (MPNE) for solute transport through stratified porous media. The applicability of the proposed relation was tested with concentration data of reactive and non-reactive solutes through stratified porous media under the different hydraulic gradients. Semi-analytical solution of MPNE transport equation incorporating scale-dependent dispersivity was employed for simulating experimental breakthrough curves. MPNE transport model with scale-dependent dispersivity and constant mass transfer coefficient underestimated the solute mass at observation points. MPNE with constant and asymptotic mass transfer coefficient was then compared, and it was found that experimental breakthrough curves with the proposed relation were better simulated. The study concluded that averaging the mass transfer coefficient over higher scale and applied to a lower scale of observation, or vice-versa, will attribute to the scale dependent behavior. The skewed shape of breakthrough curve was also discussed in details, and it was found that immobile liquid phase was contributing to the prolonged tail concentration. This study further enhances the simulation and prediction capabilities of MPNE for large stratified aquifers. [ABSTRACT FROM AUTHOR]

Batch experimental studies were carried out for the ultrasound-assisted extraction of paclitaxel from Taxus chinensis while varying parameters such as ultrasound power, extraction temperature and contact time. The extraction of the majority of the paclitaxel (~99%) was achieved from the biomass by a single extraction at 380W of ultrasound power for a period of 10 min. The kinetics data obtained for the paclitaxel extractions, and the dominant role played by intraparticle diffusion, were found to be in concordance with the pseudo-second-order model, and the intraparticle diffusion model respectively. The effective diffusion coefficient of paclitaxel (4.1882 × 10-13 ~ 5.7093 × 10-13 m2/s) and the mass transfer coefficient (4.705 × 10-8 ~ 14.1160 × 10-8 m/s) increased when the extraction temperature and ultrasound power were raised. [ABSTRACT FROM AUTHOR]

Among the different methods of H2S removal, the wet desulfurization is widely used because of its unique advantages. Wet desulfurization usually employs alkaline Na2CO3-NaHCO3 buffer solution as desulfurization agent, which can react with H2S in absorber tower to produce HS−. Then, HS− is oxidized into sulfur in the presence of a catalyst such as phthalocyanine dicaryon sulfonates or other desulfurization catalysts. But unfortunately, Na2S2O3, Na2SO3, NaSCN and other by-product salts are inevitably generated in the oxidation process. However, the desulfurization pH and the physical properties of the solution such as surface tension, density and viscosity are notably affected by the content in Na2CO3 and by-product salts. Therefore, it is necessary to investigate the influence of by-product salts and Na2CO3 on desulfurization efficiency. In this work, the effect of different by-product salts and Na2CO3 content on the total volumetric mass transfer coefficient KGa of H2S absorption process is experimentally explored. The results revealed that the increase in the by-product salts content results in a decrease in KGa and pH values. On the contrary, with the increase in Na2CO3 content, KGa and pH values increased. A mathematical model of the absorption process is proposed and analyzed; the mass transfer coefficient in gas phase kG and in liquid phase kL as well as secondary reaction constant k2 is calculated. The results showed that KGa was changed mainly by k2 which reflects the effect of pH. The surface tension, density and viscosity had relatively small effect on KGa. The present results provide the required theoretical guidance for practical industrial applications. [ABSTRACT FROM AUTHOR]

This study deals determination of mass transfer coefficients on the obtaining of caffeine from tea stalk wastes by supercritical carbon dioxide extraction. Tea stalk wastes of Turkish tea plants that have no economical value were employed as raw material throughout determination of mass transfer experiments. Mass transfer coefficients were calculated at the caffeine extraction experiments with and without cosolvent. For this purpose, ethanol was pumped to the supercritical carbon dioxide extraction system as a cosolvent. In these experimental studies, extraction procedures were repeated at different temperature by keeping optimum conditions at specified the previous study. Optimized parameters in the caffeine leaching from tea stalks were fixed throughout the study such as pressure of 250 bar, the average particle size of 0.202 mm, CO2 flow rate of 10 g/min (5.23 g ethanol/100 g CO2). Correlation was obtained from retention time in order to calculate mass transfer coefficient. Using the correlation, coefficients were calculated in supercritical CO2 extraction with and without ethanol at 333 K temperature, kL=3.782×10-8m/min, kL=1.591×10-8m/min, respectively. Consequently, it has been observed that mass transfer coefficient is increased approximately 2.4 times when ethanol is utilized the amount of 5% besides of 95% CO2. On the other hand, more caffeine can be extracted in a shorter period by means of ethanol pumping as cosolvent. [ABSTRACT FROM AUTHOR]

The demanganization reaction kinetics of carbon-saturated liquid iron with an eight-component slag consisting of CaO-SiO2-MgO-FeO-MnO-Al2O3-TiO2-CaF2 was investigated at 1553, 1623, and 1673 K in this study. The rate-controlling step (RCS) for the demanganization reaction with regard to the hot metal pretreatment conditions was studied via kinetics analysis based on the fundamental equation of heterogeneous reaction kinetics. From the temperature dependence of the mass transfer coefficient of a transition-metal oxide (MnO), the apparent activation energy of the demanganization reaction was estimated to be 189.46 kJ·mol-1 in the current study, which indicated that the mass transfer of MnO in the molten slag controlled the overall rate of the demanganization reaction. The calculated apparent activation energy was slightly lower than the values reported in the literature for mass transfer in a slag phase. This difference was attributed to an increase in the “specific reaction interface” (SRI) value, either as a result of turbulence at the reaction interface or a decrease of the absolute amount of slag phase during sampling, and to the addition of calcium fluoride to the slag. [ABSTRACT FROM AUTHOR]

CO miscible injection method combined with surfactants and silica nanoparticles was studied to investigate the effect of these additives on CO mass transfer parameters to the light oil, including diffusion coefficient, mass transfer coefficient and solubility. Silica nanoparticles with controlled size distribution were synthesized in isooctane/1-hexanol/CTAB/ammonium hydroxide, a highly-stable reverse micellar system with w=5. The presence of Si-O-Si and Si-O-H bonds in FTIR spectra of the system revealed that silica nanoparticles are formed by partial hydrolysis of TEOS. Results of DLS indicated that the average size and size distribution of the synthesized nanoparticles were 27.6 nm and 13-76 nm, respectively. Diffusion tests were carried out using CO gas and three liquid systems: isooctane/1-hexanol, isooctane/1-hexanol/CTAB reverse micellar system without nanoparticles, and isooctane/1-hexanol/CTAB reverse micellar system with nanoparticles. Results of modeling and optimization of the gas-liquid systems under nonequilibrium interface condition, using pressure decay data show that the presence of surfactants and nanoparticles leads to decreased gas diffusion coefficient; while increased interface mass transfer resistance due to presence of aqueous droplets and nanoparticles as well as lower solubility of CO in the light oil are the results of applying these additives, which limits their application. The obtained CO diffusion coefficients for isooctane/1-hexanol, reverse micellar system without nanoparticles, and reverse micellar system with nanoparticles are 8.5550×10, 8.2216×10, and 8.1114×10 m/s, respectively. [ABSTRACT FROM AUTHOR]

Mass transfer performance is studied in a tall, thin, and low plate free area liquid pulsed sieve-plate extraction column. The 5.0 cm internal diameter column consists of eighty sieve plates with percent free area of only 13.5. The effects of pulsation intensity (product of amplitude and frequency) and dispersed phase velocity are studied on the extraction efficiency of the column for the acetic acid-kerosene-water system. A mass transfer correlation for the measurement of overall mass transfer coefficient is developed that best-fits the experimental data obtained in the present study. Mathematical analysis of the column is carried out that shows the insignificance of axial diffusivities in the column. [ABSTRACT FROM AUTHOR]

Mass transfer coefficient data were computed from measured limiting current values obtained at point electrodes fixed flush with the inner wall of an outer cylinder of three phase fluidized bed electrochemical reactor in the presence of an angled disc internal. Nitrogen was used as gas phase. Glass balls of different diameters were used as solid phase. The liquid phase was an electrolyte that belonged to the ferricyanide-ferrocyanide redox system. Enhancement in mass transfer coefficient obtained in the case of three-phase fluidized bed in the presence of angled disc internal was upto 14 fold in comparison with the homogeneous flow of electrolyte in plain pipe. The mass transfer coefficient data thus obtained were found to increase with increasing gas velocity, pitch and disc diameter. An increase in disc angle resulted in a decrease in the mass transfer coefficient. The influence of liquid velocity, promoter rod diameter and particle diameter on mass transfer coefficient was found to be insignificant. The entire mass transfer coefficient data obtained in the present study were subjected to regression analysis and useful correlation equation was obtained. [ABSTRACT FROM AUTHOR]

An experimental chemical method for determining the kinetic characteristics (volumetric mass transfer coefficient and rate constant of a second-order reaction) of gas-liquid ozone reactions in a bubble column reactor is described. The calculation formulas are substantiated, and the ranges of values of the experimental factors that determine the method's limits of applicability are found. The conditions under which the boundary-value problem of a gas-liquid ozone reaction of the second order can be reduced to a problem of a pseudo-first order reaction allowing an analytical solution are revealed. [ABSTRACT FROM AUTHOR]

The possibility of obtaining analytical estimates in a diffusion approximation of the times needed by nonequilibrium small bodies to relax to their equilibrium states based on knowledge of the mass transfer coefficient is considered. This coefficient is expressed as the product of the self-diffusion coefficient and the thermodynamic factor. A set of equations for the diffusion transport of mixture components is formulated, characteristic scales of the size of microheterogeneous phases are identified, and effective mass transfer coefficients are constructed for them. Allowing for the developed interface of coexisting and immiscible phases along with the porosity of solid phases is discussed. This approach can be applied to the diffusion equalization of concentrations of solid mixture components in many physicochemical systems: the mutual diffusion of components in multicomponent systems (alloys, semiconductors, solid mixtures of inert gases) and the mass transfer of an absorbed mobile component in the voids of a matrix consisting of slow components or a mixed composition of mobile and slow components (e.g., hydrogen in metals, oxygen in oxides, and the transfer of molecules through membranes of different natures, including polymeric). [ABSTRACT FROM AUTHOR]

Comparative analysis of three kinds of boundary condition for solution of the diffusion equation in a mathematical model of vacuum carburizing (low-pressure one) is performed for plotting the carbon concentration curves in carbon and alloy steels. With allowance for the special features of mass transfer in formation of the diffusion layer and for the effect of control factors of the carburizing process, the mass transfer coefficient in the equation of the boundary condition of the third kind is evaluated with the help of parametric equations. [ABSTRACT FROM AUTHOR]

A new numerically efficient simulator for dual layer catalysts is implemented and its performance is demonstrated using the example of the dual layer ammonia oxidation catalyst. For the solution of the radial mass balances, each washcoat layer is represented by a single volume element and the diffusive mass fluxes into and within the washcoat are computed based on the concept of the internal mass transfer coefficients. The performance of the new simulator is compared against a reference simulator that fully resolves the concentration profiles in the washcoat. For a steady state test case, the error introduced by the new solution scheme is below 2 % for all relevant exhaust components. For a transient test case, the deviations become more significant. For the simulation of a WHTC, the maximum deviation in the NH outlet concentration is 23.3 %, whereas the cumulated NH emissions deviate by 10.6 %.With the new simulator, the 1800 s of the transient WHTC cycle can be simulated within 53 s on a standard laptop, 30 times faster than real time. [ABSTRACT FROM AUTHOR]

The use of dissolved sulphur from gaseous phase was tested for its ability to precipitate platinum ions in chloride system with alterations in the parameters such as metal ion concentration, hydrochloric acid concentration, pressure and temperature. The precipitation process was analysed on the basis of mass transfer coefficient, diffusivity models and also by absorption kinetic models. The maximum physical and reactive absorption capacity for sulphur dioxide was found to be 0.015 and 0.018 mol/L, respectively, at 298.15 K and 1.125 bars in a short contact time of 10 min. Based on the sulphur dioxide solubility data in gas-liquid system for both physical and reactive absorption conditions, the introduction of sulphur atoms in the chloride system was achieved. The mass transfer coefficients obtained for all metal ions were in the range 0.10-0.26 min, while the diffusivity of SO at different temperatures and pressures was found to be in the range (2.36-3.43) × 10 and (1.36-2.22) × 10 ms, respectively. Thermodynamic parameters such as the changes in Gibbs free energy, enthalpy and entropy were also evaluated. The results indicated that the precipitation of platinum and base metals in gas-liquid (G-L) chloride system was an endothermic process. [ABSTRACT FROM AUTHOR]

The aim of the paper is to model the permeate flux during reverse osmosis (RO) of a highly concentrated glucose solution using the osmotic pressure model. Such a model accounts for the effect of the concentration polarization phenomenon on the permeate flux. To apply this model the viscosity, the osmotic pressure of solution and the diffusion coefficient of glucose were estimated. Using mathematical simulation software, the values of mass transfer coefficient for different concentrations of glucose (5, 10, 15 and 20 wt%) and at different feed flow rate were determined. The experimental permeate flux values conducted on flat RO membranes (Type HR-99) agreed well with the values calculated by the osmotic pressure model, as shown by statistical analysis. [ABSTRACT FROM AUTHOR]

Three designs of a gas-liquid ejection apparatus were developed: with a long ejector, a gas-liquid jet and a short ejector, and a combined one with a multi-tiered ejector. The effectiveness of the gas-liquid apparatuses was determined by the sulfite method. From the results of experimental studies it was found that the gas-liquid ejection apparatus with a multi-tiered ejector is considerably more effective than the others. [ABSTRACT FROM AUTHOR]

Erosion-corrosion experiments of copper elbow were performed by acidified dichromate. Mass transfer coefficient inside 90° copper elbow has been investigated. The results showed that the mass transfer coefficient increases as solution velocity increases in both cases of one- and two-phase flow. The mass transfer coefficient can be related to the solution velocity in case one-phase flow by the following equations: In case of liquid-solid flow In case of liquid-gas flow The importance of these equations is to understand and predict erosion corrosion inside 90 copper elbow. [ABSTRACT FROM AUTHOR]

Present study exhibits an experimental examination of mass transfer coefficient and evaporative effectiveness of a falling film evaporator. Further, a statistical replica is extended in order to have optimal controlling parameters viz. non-dimensional enthalpy potential, film Reynolds number of cooling water, Reynolds number of air and relative humidity of up-streaming air. The models not only give an optimal solution but also help in establishing a correlation among controlling parameters. In this context, response surface methodology is employed by aid of design of experiment approach. Later, the response surface curves are studied using ANOVA. Finally, the relations established are confirmed experimentally to validate the models. The relations thus established are beneficent in furtherance of designing evaporators. Additionally, the present study is among the first attempts to reveal the effect of humidity on the performance of falling film evaporator. [ABSTRACT FROM AUTHOR]

We did an experimental study on ammonia absorption in a spray tower. The kinetic characteristics of droplets were investigated by considering the forces acting on a droplet. The gas-phase mass transfer coefficient was deduced with the Colburn analogy method. A simplified model for predicting NH capture with a spray tower has been presented based on mass transfer and ionic equilibrium, which was successfully validated against experimental data. The influences and the sensitivity analysis of main operating parameters on the absorption efficiency were analyzed. As the most sensitive parameter, the mean droplet diameter was obtained by fitting experimental data with an empirical correlation. The distributions of two typical process parameters along the absorber were also simulated. Decreasing the pH value of absorbent is an effective but restrictive way to strengthen the mass transfer rate on account of insufficient liquid-side resistance. [ABSTRACT FROM AUTHOR]

The problem of nonstationary diffusion of the target component to a phase that is external relative to the surface of a cylindrical body has been formulated and solved analytically. From the found solution the dependences have been obtained for calculating the instantaneous mass transfer coefficient and the phase-contact-time mean mass transfer coefficient, on the basis of which the process of extraction of technological pollutants from fibrous materials has been analyzed. [ABSTRACT FROM AUTHOR]

Biological conversion of methane gas has been attracting considerable recent interest. However, methanotropic bioreactor is limited by low solubility of methane gas in aqueous solution. Although a large mass transfer coefficient of methane in water could possibly overcome this limitation, no dissolved methane probe in aqueous environment is commercially available. We have developed a reactor enabling the measurement of aqueous phase methane concentration and mass transfer coefficient (ka). The feasibility of the new reactor was demonstrated by measuring ka values as a function of spinning rate of impeller and flow rate of methane gas. Especially, at spinning rate of 300 rpm and flow rate of 3.0 L/min, a large ka value of 102.9 h was obtained. [ABSTRACT FROM AUTHOR]

Application of microreactor systems could be the next break-through in the intensification of chemical and biochemical processes. The common flow regime for organic solvent-aqueous phase two-phase systems is a segmented flow. Internal circulations in segments cause high mass transfer and conversion. We analyzed slug flow in seven systems of organic solvents and aqueous phase. To analyze how slug lengths in tested systems depend on linear velocity and physical and chemical properties of used organic solvents, regression models were proposed. It was shown that models based on linearization of approximation by potentials give low correlation for slug length prediction; however, application of an essential nonlinear model of multiple layer perceptron (MLP) neural network gives high correlation with R=0.9. General sensitivity analysis was applied for the MLP neural network model, which showed that 80% of variance in slug length for the both phases is accounted for the viscosity and density of the organic phases; 10% is accounted by surface tension of the organic phase, while molecular masses and flow rates each account for 5%. For defined geometry of microreactor, mass transfer has been determined by carrying out the neutralization experiment with NaOH where acetic acid diffuses from organic phase (hexane) into aqueous phase. Estimated mass transfer coefficients were in the range ka=4,652-1,9807 h. [ABSTRACT FROM AUTHOR]

The possibility of a change in the desorption kinetics of an adsorbate from an adsorbent granule is demonstrated with use of solid-electrolyte cells. A description of the experimental bench created for measurement of kinetic curves is given for adsorbate adsorption from an adsorbent granule. Results of test changes in the kinetic curves are presented for oxygen desorption from a granule of a carbon-molecular sieve (UMS-1). [ABSTRACT FROM AUTHOR]