Mass Transfer Direction Research Articles

Steady-State Performance of a Small-Scale Liquid-to-Air Membrane Energy Exchanger for Different Heat and Mass Transfer Directions, and Liquid Desiccant Types and Concentrations: Experimental and Numerical Data

A liquid-to-air membrane energy exchanger (LAMEE) is an energy exchanger that allows heat and moisture transfer between air and salt solution flows through a semipermeable membrane. For the first time, a novel small-scale single-panel LAMEE test facility is used to experimentally investigate the effect of the direction of heat and mass transfers for the air and salt solution flows, and the effect of different salt solution types and concentrations on the LAMEE effectiveness. The data for steady-state effectiveness of the LAMEE are compared to the simulation results of a numerical model. Two studies are conducted; first a study based on different heat and mass transfer directions (four test cases), and second a study focused on the influence of solution types and concentration on LAMEE performance. For the first study, NTU = 3 and four different heat capacity ratios (i.e., Cr* = 1, 3, 5, 7) are used, with a LiCl salt solution in the exchanger. Mass and energy balances for all the test cases and the repeatability of the experimental data for the air cooling and dehumidifying test case show that the experimental data are repeatable and within an acceptable uncertainty range. The results show increasing effectiveness with increasing Cr*, and good agreement between the numerical and experimental results for both air cooling and dehumidifying and air heating and humidifying test cases. In the second study, two different salt solutions (i.e., LiCl and MgCl2), and three different concentrations for the LiCl solution (i.e., 25%, 30%, and 35%) are selected to investigate the effect of different salt solution types and concentrations on the performance of the LAMEE. A maximum difference of 10% is obtained for the LAMEE total effectiveness data with the different salt solution types and concentrations. The results show that both the salt solution type and concentration affect the LAMEE effectiveness, and changing the concentration is one way to control the supply air outlet humidity ratio.

Experiment and finite element method analysis mass erosion and transfer of Ag/La2NiO4-based electrical contacts during operation

A uniform transient temperature field model of electrical contacts operation was found by analyzing the process of closing arc → constriction resistance Joule heat → breaking arc. Essential parameters of Ag/La2NiO4 electrical contact material for transient temperature field calculation were obtained through tests of electrical contact experimental instrument under 18 V DC in different currents, other correlation experiments, and calculation analysis. The finite element method was applied to solve the transient temperature field, and the features and distribution of the transient temperature field were obtained. The condition of material erosion and mass transfer can be forecasted by those calculation results. It is beneficial to research about the lifetime of Ag/La2NiO4 electrical material. The two curves of current with product of maximum molten pool volume and lifetime of molten pool for break arc and close arc crossed between 20 and 25 A. Those curves are related with the mass transfer curves. Because the mass transfer was directly affected by molten pool volume and molten pool lifetime, the direction of mass transfer can be forecasted. The direction of mass transfer began to change from anode to cathode after current was larger than 20 A. These are consistent with the experimental results.

Effect of hypotonic and hypertonic solutions on impregnation of curcuminoids in coconut slices

The immersion of solid foods into the surrounding hypotonic or hypertonic solution was explored as a method to infuse curcuminoids in coconut slices without altering its matrix. The rate of mass transfer of moisture, solid and curcuminoid with or without application of ultrasound was studied for the surrounding solutions of sucrose (12.5%) and/or sodium chloride (2.5 and 5.0%) consisting of curcuminoids. The highest diffusion coefficient of curcuminoids (1.78×10−10 m2/s) was found to be in a situation, when curcuminoids were dissolved in 2.5% sodium chloride solution, which was further enhanced by the application of ultrasound to 1.81×10−10 m2/s. The direction of moisture and solute mass transfer was dependent on the osmotic pressure of the surrounding solution as well as the osmotic pressure in the coconut slices. The extent and rate of mass transfer can be varied by varying the type and concentration of solutes in the surrounding solution. Industrial relevance: The knowledge provided by this work may be useful for impregnation of bioactive compounds in solid foods without altering their natural matrix. The extent and rate of infusion of bioactive compounds can be changed by varying the type of surrounding solution from hypotonic to hypertonic solution. Further, the application of external field such as ultrasound can result in enhanced mass transfer of bioactive compounds. This technique may be helpful in producing foods with enriched bioactive compounds, besides providing diversified products in terms of taste and nutrition

An Experimental Study of Liquid-Liquid Microflow Pattern Maps Accompanied with Mass Transfer

This paper presents the experimental results of liquid-liquid microflows in a coaxial microfluidic device with mass transfer. Three working systems were n-butanol + phosphoric acid (PA) + water, methyl isobutyl ketone (MIBK) + PA + water, 30% kerosene in tri-n-butylphosphate (TBP) + PA + water. The direction and intensity of mass transfer were adjusted by adding PA in one of two phases mutual saturated in advance. When PA transferred from the organic phase to the aqueous phase, tiny aqueous droplets may generate inside the organic phase by mass transfer inducement to form a new W/O/W flow pattern directly on some special cases. Once the PA concentration was very high, violent Marangoni effect could be observed to throw part of organic phase out of droplets as tail. The interphase transfer of PA could expand the jetting flow region, in particular for systems with low or medium interfacial tension and when the mass transfer direction was from the aqueous phase to the organic phase.

Prediction of mass transfer coefficients in a pulsed disc and doughnut extraction column

AbstractA study of the mass transfer performance for a pulsed disc and doughnut extraction column has been presented for a range of operating conditions. The mass transfer performance has been investigated for both directions of mass transfer. This study has examined the mass transfer coefficients which has incorporated the effects of back‐mixing in the continuous phase. The effect of operating variables including pulsation intensity and dispersed and continuous phase velocities on volumetric overall mass transfer coefficient has been investigated. The experiments showed that mixer‐settler, transition and emulsion regimes exist in the column depending on the pulse characteristics. In the present work, effective diffusivity is substituted for molecular diffusivity in the Gröber equation for estimation of overall mass transfer coefficients. The enhancement factor is determined experimentally and there from a single empirical correlation is derived for prediction of enhancement factor in terms of Reynolds number, holdup and Eötvös number for all operating regimes and each mass transfer direction. The experimental results are in very good agreement with the values calculated by the proposed equation. © 2011 Canadian Society for Chemical Engineering

Mass transfer performance in pulsed disc and doughnut extraction columns

Mass transfer performance is presented for a 76 mm diameter pulsed disc and doughnut extraction column for the toluene-acetone-water system. The experiments were carried out for both mass transfer directions. The mass transfer data are interpreted in terms of the axial diffusion model, thus accounting for continuous phase axial dispersion. The effect of operating parameters on the overall volumetric mass transfer coefficients has been investigated. The results show that the column performance increases with an increase in pulsation intensity. At high pulsation intensity, however, the overall volumetric mass transfer coefficient decreases due to the production of very fine dispersed droplets. It was also found that the column performance decreases with both an increase in dispersed phase velocity and a decrease in continuous phase velocity. An empirical correlation for prediction of the continuous phase overall mass transfer coefficient is derived in terms of the overall Sherwood number, Reynolds number and dispersed phase holdup for each mass transfer direction. The prediction of continuous phase overall mass transfer coefficients from the presented correlations is in good agreement with experimental data.

The influence of nanoparticles on hydrodynamic characteristics and mass transfer performance in a pulsed liquid–liquid extraction column

With respect to the influence of nanoparticles on mass transfer characteristics, limited number of studies available in the literature, deal primarily with gas–liquid systems. In this work, mass transfer performance and hydrodynamic characteristics including static and dynamic dispersed phase hold-ups of nanofluids have been investigated for pulsed liquid–liquid extraction column (PLLEC). The nanofluids used were prepared by dispersing SiO 2 nanoparticles of 0.01, 0.05 and 0.1 volume percent with two different hydrophobicities in kerosene as base fluid using ultrasonication. UV–vis spectrophotometer was also used for evaluation of the nanofluids stability. The results were compared with conditions of no-nanoparticles in the dispersed phase and in the absence of mass transfer effect (no acetic acid as solute). Different pulsation intensities were maintained for the fixed mass flow rates of dispersed ( Q d) and continuous ( Q c) phases (with ratio Q c/ Q d = 1.2) with mass transfer direction being made from the dispersed phase to the continuous one. The results indicate that in the presence of the nanofluids, static and dynamic dispersed phase hold-ups increased by 23–398%, and 23–257%, respectively, while mass transfer performance was enhanced by 4–60%.

Osmotic dehydration assisted impregnation of curcuminoids in coconut slices

Osmotic treatment was explored as a method to infuse curcuminoids in coconut slices. The rate of mass transfer of moisture, solid and curcuminoids with or without application of ultrasound were studied over a range of concentration of osmotic solutions (0–50%). The diffusion coefficient of curcuminoids was 1.64 × 10 −10 m 2/s, when water was used in place of osmotic solute which was further enhanced by the application of ultrasound to 1.87 × 10 −10 m 2/s. Increase in the concentration of osmotic solution beyond 25% resulted in reversal in the direction of moisture and solid mass transfer. Ultrasound treatment resulted in higher moisture and solid mass transfer due to the breaking of cell structure as revealed by microstructure examination. HPLC analysis revealed that all the curcuminoids (curcumin, demethoxycurcumin and bisdemethoxycurcumin) were infused into the coconut matrix. The present study concluded that osmotic dehydration is a feasible technology for impregnation of functional ingredients into foods without altering its matrix.

Mass transfer enhancement at deformable droplets due to Marangoni convection

One of the key design parameters in liquid/liquid extraction is the mass transfer coefficient. A complex list of parameters including fluid dynamics, drop size distribution, chemical properties of the involved species, local interfacial instabilities (Marangoni convection) is required in order to determine the transient evolution of the mass transfer coefficient. The influence of Marangoni convection on single drop mass transfer cannot yet be described in an analytical manner, and empirical correlations available in literature fail to predict the mass transfer process. In the present study, experimental investigations on deformable single droplets in the toluene/acetone/water system are presented which shows strong interfacial instabilities. Parameters varied are the drop diameter, the initial solute concentration and the mass transfer direction. Experimental results are compared with the well-known models by Kronig and Brink and Handlos and Baron. The Kronig and Brink model cannot describe Marangoni dominated systems, but comparisons reveal the influence of deformation on the mass transfer enhancement. In contrary, with a slight modification to the Handlos and Baron model, the mean droplet concentration of the transferred component was successfully modelled as a function of Fourier number.

Investigation of multicomponent mass transfer in liquid–liquid extraction systems at microscale

A theoretical study of multicomponent mass transfer in liquid–liquid extraction systems at microscale is carried out using the standard extraction system water/toluene/acetone/MIPK. We focus on the diffusional interactions between the transferred components, the so-called cross effects, and investigate the conditions at which these effects can significantly influence multicomponent mass transfer behaviour at microscale. For this purpose, a rigorous mathematical model is developed based on the Stefan–Maxwell equations. Another, less rigorous model that does not consider cross effects is built up using effective diffusion coefficients. The latter model is used as a reference, because such models are widely used for the description of multicomponent mass transfer in conventional macroscopic devices. Both models are implemented into a commercial CFD software. The comparison of the simulation results obtained by both approaches permits the impact of cross-effects to be estimated. Microchannel dimensions and the contact time of the two immiscible phases, which flow countercurrently, are varied over a large range. Furthermore, different mass transfer directions are examined. It is found that the cross effects can considerably influence mass transfer behaviour and hence extraction performance at small-scale microchannel dimensions and sufficiently large contact times. The intensity of this influence largely depends on the component transfer direction.

The results of two-point experiments on the estimation of the urban anthropogenic effect on the characteristics of atmospheric transparency

To estimate the anthropogenic effect of the city of Tomsk on the measurements of the aerosol optical thickness (AOT) and the columnar water vapor of the atmosphere in the eastern suburb of Tomsk (Akademgorodok), two issues are discussed: (1) the comparative analysis of the data of simultaneous measurements in the suburban zone and at the background region (∼60-km distance), and (2) the dependence of the aerosol turbidity in the suburb on the air mass transfer direction. In addition to the spectral atmospheric AOT, we also considered two AOT components: fine and coarse aerosol. It is noted that variations of the atmospheric turbidity characteristics are mainly caused by synoptic-scale processes and manifest themselves similarly in urban and background regions. During the summertime, the AOT and columnar water vapor of the atmosphere in the two abovementioned regions are statistically indistinguishable, indicating the absence of the anthropogenic urban effect. During the cold period, the suburban zone may be characterized by higher atmospheric turbidity, seemingly due to the inversion accumulation of aerosol. The dependence of the AOT on the wind direction has the following features: (1) overall, the largest aerosol turbidity is observed during winds blowing from the southern sector; (2) during the cold period, the fine AOT component is, on average, 14% higher in cases of air mass transfer from the direction of the city (from the west and northwest directions); and (3) the coarse AOT component is slightly higher during westward air transfer than during an eastward one.

Modelling mass transfer coefficient for liquid-liquid extraction with the interface adsorption of hydroxyl ions

A combined model was used for prediction of overall mass transfer coefficient of drops in the liquid-liquid extraction process, prone to the deleterious effect of adsorbed hydroxyl ions onto the interface. The importance is due to the use of different pH waters as aqueous phase. The work is based on single drop experiments with a chemical system of toluene-acetone-water where the pH of the continuous aqueous phase was within the range 5.5–8, appropriate to most industrial waters, and can lead to rigid behavior of circulating drops. The combined model in conjunction with the correlation developed here for the ratio of interfacial velocity to drop terminal velocity that links the film mass transfer coefficients of both sides can be used satisfactorily for design purposes. This model gives a maximum relative deviation of less than ±10% for the mass transfer directions of dispersed to continuous phase and vice versa.

Mass transfer coefficients in a pulsed packed extraction column

The volumetric overall mass transfer coefficients have been measured in a pulsed packed extraction column using diffusion model for the toluene/acetone/water system. The experiments were carried out for both mass transfer directions. The effects of operational variables such as pulsation intensity and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The experimental findings indicate that pulsation intensity and mass transfer direction have great influence on volumetric overall mass transfer coefficient. Significant, but weaker, are the effects of continuous and dispersed phase flow rates. The experimental results obtained in the present work are compared with some other types of extraction columns. Finally, two empirical correlations for prediction of the continuous phase overall mass transfer coefficient is derived in terms of Sherwood and Reynolds numbers. Good agreement between prediction and experiments was found for all operating conditions that were investigated.

Interfacial instability of growing drop: Experimental study and conceptual analysis

Capillary pressure experiments were performed at the water/hexane interface including adsorption and mass exchange of hexanol under different conditions. The results from growing drop experiments show that instabilities due to Marangoni convection not only depend on the same parameters as have been reported for quasi-static interfaces, such as direction of mass transfer, distribution coefficient and ratio of diffusion coefficients, but also on the experimental conditions such as dispersed phase flow rate, capillary tip size, size of growing drop and its lifetime. Based on a new flow expansion model for mass transfer, a new approach is presented for data analysis, which includes the various parameters effecting interfacial instabilities. The proposed analysis considers the overall mass transfer coefficient ratio ( k 1/ k 2) which includes diffusion and convection effects instead of the pure ratio of diffusivities ( D 1/ D 2) under the condition of growing drops. The proposed analysis is verified on the basis of capillary pressure measurements.

Impact of Marangoni instabilities on the fluid dynamic behaviour of organic droplets

Marangoni instabilities in dispersed liquid/liquid systems occur if the local solute concentration varies over the interface. The additional shear stress at the interface between a droplet and an ambient phase generates complex convection patterns which increase temporarily the global drag coefficient of the drop and thus retard the drop rise velocity. When Marangoni effects get weaker, the shear forces decrease and the drop reaccelerates. In the present experimental study, the transient drop rise velocity has been intensely investigated in the system toluene ( d )/acetone ( s )/water ( c ) for different initial solute concentrations and different drop diameters. Both mass transfer directions have been considered. The reacceleration time as an indicator of the end of Marangoni dominance can be expressed as a function of drop diameter and initial solute concentration.

Mass transfer enhancement through Marangoni instabilities during single drop formation

The impact of Marangoni convection on the extraction efficiency during the drop formation stage is investigated in the system toluene/acetone/water for different initial solute concentrations and different drop diameters. Both mass transfer directions of the solute have been considered. Marangoni instabilities are supposed to increase the internal mixing and thus enhance mass transfer coefficients. Experimental results show a strong dependency on the mass transfer direction. The amount of solute extracted is between 19% and 55%. The total transferred mass M A increases with drop diameter and initial concentration. Present models from the literature which predict extraction efficiencies do not take into account interfacial effects like Marangoni convection. A correlation is proposed introducing an effective diffusivity which depends on the initial solute concentration. The diffusivity factor increases linearly with initial solute concentration and is more sensitive in the mass transfer direction c → d.

EXPERIMENTAL INVESTIGATION OF PHASE INVERSION OF LIQUID-LIQUID SYSTEMS IN A SPRAY EXTRACTION COLUMN

An experimental study of the phase inversion behavior of liquid-liquid dispersion has been conducted in a spray extraction column for systems of toluene / water, n-hexane/water, CCl4/water, toluene /water + glycerol (25 % wt), toluene + CCl4 (25 % wt) / water and toluene / acetic acid (5 % wt)/water. The effects of physical properties, mass transfer and column geometry on phase inversion have been investigated. The results show that the dispersed phase hold up sufficient for phase inversion increases in o/w dispersion and decreases in w/o dispersion by increasing interfacial tension. Also, it was found that by increasing the viscosity of aqueous phase, dispersed phase hold up decreases at phase inversion point in both o/w and w/o dispersions. The tendency to phase inversion increases in o/w dispersion with an increase in density difference of two phases. It was observed that dispersed phase hold up at phase inversion point decreases in the presence of mass transfer, when the direction of mass transfer is from dispersed phase to continuous phase. The results show that dispersed phase holdup increases with drop size at phase inversion point and column diameter has an important effect on phase inversion because of wall effect.

Mass Transfer Performance in Karr Reciprocating Plate Extraction Columns

A study of the hydrodynamic and mass transfer performance for Karr reciprocating plate extraction columns has been presented for a range of operating conditions and column diameters of 50, 100, and 450 mm. Although the use of Karr columns has been widespread for many years for a range of important applications, the need for more reliable methods for predicting the performance and scale-up of such columns continues to be a matter of significant importance. The present study has examined the hydrodynamic performance in terms of the dispersed phase hold up and droplet size distribution and mass transfer performance which has incorporated the effects of backmixing in the continuous phase. Work was initially carried out in a 50 mm diameter laboratory scale Karr column using the system 10 v/v% tributyl phosphate/kerosene (continuous)−phenol−water (dispersed) where hydrodynamic and mass transfer performance was analyzed for both directions of mass transfer. Using these data, models were investigated and developed to predict performance over a range of operating conditions. An alternative system consisting of an organic solvent (continuous)−phenolic alkaloid−aqueous caustic (dispersed) was also studied, using both 100 and 450 mm diameter Karr columns. These data were used to validate the hydrodynamic and mass transfer performance models developed for the phenol system in the 50 mm diameter column. Dispersed phase holdup data were found to fit the correlation presented by Kumar and Hartland [Ind. Eng. Chem. Res. 1995, 34, 3925−3940], and the drop size distribution also agreed with the relationship presented by Kumar and Hartland [Ind. Eng. Chem. Res. 1996, 35, 2682−2695] within reasonable accuracy. The mass transfer performance results indicated that the continuous phase controlled the mass transfer rate, and thus, column design was simplified by assuming that the overall mass transfer coefficient can be obtained using a standard mass transfer correlation for the continuous phase. The current mass transfer results were found to be best predicted by a refitted form of the overall mass transfer coefficient correlation developed by Harikrishnan et al. [Chem. Eng. J. 1994, 54, 7−16].

Stage efficiency of Hanson mixer-settler extraction column

Stage efficiency of a pilot plant Hanson mixer-settler extraction column with seven stages was measured by using toluene-acetone-water system. The experiments were carried out for both mass transfer directions. The effects of agitation speed, flow ratio, total throughput and solute concentration on stage efficiency were investigated and found to be significant. The comparison of investigated column with some other type of extractors showed that the stage efficiency of this column is high, while its throughput is small. Finally an empirical correlation was proposed for prediction of stage efficiency and very good agreement between experimental data and calculated values was obtained.

Controllable Preparation of Nanoparticles by Drops and Plugs Flow in a Microchannel Device

Well controlled two-liquid-phase flows in a T-junction microchannel device have been realized. The system of H2SO4 and BaCl2, respectively, in two phases to form BaSO4 nanoparticles was used as a probe to characterize the microscale two-phase flow and transport conditions of a system with interphase mass transfer and chemical reaction. Nanoparticles with narrow size and good dispersibility were produced through drops or plugs flow in the microdevice. As a novel work, the influence of mass transfer and chemical reaction on interfacial tension and flow patterns was discussed based on the experiments. At the same time, the effect of the two-phase flow patterns on the nanoparticle size was also discussed. It was found that the increase of the amount of mass transfer and chemical reaction could change the flow patterns from plugs flow to drops flow. The drop diameter or plug length could be changed in a wide range. Accordingly, a new parameter of mu(0)u(c)/gamma(0)/Q(d) was defined to distinguish the flow patterns. The prepared nanoparticles ranged in size from 10 to 40 nm. Apparently, the particle size decreased with the increase of the drop diameter or plug length. Reasons were discussed based on the mass transfer direction and speed in drops and plugs flow patterns.