Obtained Mass Transfer Coefficients Research Articles

Crystal growth and resistivity modulation of n-type phosphorus-doped cast mono-like silicon

Resistivity tailing seriously reduces the production of phosphorus-doped n-type cast mono-like silicon (CM-Si) ingots and increases costs. However, it is believed that a uniform axial dopant profile can be efficiently obtained by adjusting furnace pressure to enhance phosphorus evaporation at the ingot top due to high saturated vapor pressure of phosphorus in molten silicon. To increase the resistivity at the ingot top, we compared the growth of n-type cast mono-like silicon ingots under normal and reduced pressure. Ingots quality was characterized, and resistivity distribution was measured and discussed. The fitting results of resistivity suggest that Scheil’s equation which describes the solute redistribution during the non-equilibrium solidification process of the crystals can be used to calculate theoretical resistivity distribution of lightly phosphorus-doped ingots under normal furnace pressure (600 mbar), but it need to be modified in depressurization process. The modified results shows that the physical growth under reduced pressure is a coupling result of evaporation and segregation, of which a model to calculate the mass transfer coefficients of phosphorus in silicon is established. The obtained mass transfer coefficients illustrate that the transfer of phosphorus through gas phase to external environment is the controlling step, and depressurization can enhance the evaporation of phosphorus to a certain extent by increasing the total mass transfer coefficient. This work is supposed to pave an economy-effective way to fabricating n-type CM-Si ingots with homogenized axial resistivity profile in industry.

Mass transfer during transient condensate vaporization: Experimental and modeling study

The gas condensate reservoirs, which are a major source of energy, usually experience an unwanted phenomenon called liquid drop-out. Gas injection as a proven effective remedy is generally employed to diminish the liquid loss. The condensate recovery by gas injection is typically estimated by assuming local equilibrium. This assumption is not valid in porous media when the limited contact area, high velocity, and low residence time are involved, particularly in near-wellbore region. In this study, we attempt to calculate mass transfer coefficient of the gas condensate systems in porous media at the transient state. Hence, a number of experiments are performed where the tests include three injection gases (CO2, N2, and CH4), three liquid types as condensate components (C5, C6, and C7), and three mean grain sizes (150–300 μm) within a wide range of gas velocity (0.00472–0.0283 cm/s). The experiments are modeled numerically and analytically based on the effluent concentrations. The obtained mass transfer coefficients are then employed to introduce new models such that Sherwood number (Sh) is correlated to Peclet (Pe) and Schmidt (Sc) numbers, and other physical/operational parameters. Based on a systematic sensitivity analysis as well as the modeling results, both analytical and numerical modeling approaches are promising and viable. The statistical parameters are calculated to be 97.13% (R2) and 0.0044 (mean squared error or MSE) for the analytical method, and 97.33% (R2) and 0.00303 (MSE) for the numerical solution, confirming the accuracy and reliability of the employed models. The mass transfer coefficients are then fitted well using three correlations with R2 values of 95.29%, 97.04%, and 96.73%, and absolute relative deviation or ARD magnitudes of 13.22%, 11.73%, and 11.44%. The new proposed correlations can be simply implemented in numerical/analytical modeling and commercial software packages to obtain the non-equilibrium mass transfer coefficients of components in the gas phase. The sensitivity analysis also reveals that condensate shrinkage has a significant effect on the amount of mass transfer and vaporization. Methane shows a relatively higher potential to strip the liquid condensate in comparison with other gases in the experiments. Among the liquid hydrocarbons, pentane has a higher tendency to evaporate into the flowing gas phase, followed by hexane and heptane. It is also found that porous system cases with larger mean grain size offer more suitable conditions for enhancement of mass transfer. The findings of this study can help to better understand the mass transfer during gas injection in gas condensate reserves under transient condition.

Mass transfer at the confining wall of an electrochemical cell in annular flow with a rotating central rod

ABSTRACT An electrochemical method (limiting current technique) was used to obtain mass transfer coefficient (k L) in a flow reactor in which the coaxial inner cylindrical rod was rotated at different revolutions per minute (rpm). The effect of liquid velocity, rpm and rod diameter on the liquid-wall mass transfer coefficient was investigated. It was observed that at any given rpm, the k L increased with the liquid velocity. Rotation of the central rod was found to further augment the coefficient. Augmentations were found to be more significant at small liquid velocities. The effect of central (annular) rod diameter was also studied and the k L data were correlated using Colburn j-factor format.

Технологічні особливості капсулювання гранульованих добрив плівкою на основі модифікованого ПЕТФ

Проаналізовано взаємодію твердої дисперсної фази, рідкого плівкоутворювача та повітря під час капсулювання гранульованих мінеральних добрив. Показано, що на поверхні частинки відбувається передача тепла від повітря до розчину плівкоутворювача і видалення розчинника у середовище газової фази. Оцінено вплив гідродинаміки, тепло- та масообміну на процес капсулювання амонійної селітри та нітроамофоски в апараті псевдозрідженого стану плівками, які складаються з модифікованого поліетилентерефталату, гідролізного лігніну та цеоліту. Встановлено, що визначальним технологічним параметром процесу капсулювання є швидкість повітря, за якої шар твердого матеріалу буде перебувати у стані стійкого псевдозрідження. Теоретичним методом розраховано швидкість повітря в апараті для капсулювання аміачної селітри 5,6 м/с та нітроамофоски 6,1 м/с. Проведено аналітично-експериментальні дослідження тепломасообміну під час капсулювання гранульованих добрив у апараті псевдозрідженого стану циліндричного типу періодичної дії за встановлених гідродинамічних режимів. Отримано експериментальні залежності температури повітря від висоти шару досліджуваних мінеральних добрив за витрати плівкоутворювача 1∙10-4 кг/с, 3∙10-4 кг/с і 5∙10-4 кг/с з використанням 7-канального інтелектуального перетворювача, який дав змогу одночасно фіксувати температуру в семи точках з виводом інформації на ПК. Графічним методом за кутом нахилу температурних кривих встановлено значення коефіцієнтів тепловіддачі α під час капсулювання аміачної селітри 135,7 Вт/(м2К) і нітроамофоски 118,3 Вт/(м2К). Для плівкоутворювального розчину, який складався із етилацетату 87 % (мас), модифікованого ПЕТФ 10 % (мас), гідролізного лігніну 3 % (мас) визначено коефіцієнти масовіддачі β під час капсулювання аміачної селітри 0,251 м/с і нітроамофоски 0,198 м/с. На підставі отриманих коефіцієнтів масовіддачі встановлено максимальну витрату плівкоутворювача Pmax (104кг/с∙кг добрив): аміачна селітра – 20,512, нітроамофоски – 22,857. За отриманими технологічними параметрами здійснено капсулювання досліджуваних добрив. За характером кінетичних кривих вивільнення компонентів із капсульованих частинок аміачної селітри і нітроамофоски встановлено, що за визначеними технологічними параметрами отримано мінеральні добрива із прогнозованими властивостями.

Mass transfer from freely rising microbubbles in aqueous solutions of surfactant or salt

Microbubbles are used in many applications. One of the major advantages of using microbubbles is to improve the mass transfer of gases to the bulk phase. In this study, mass transfer from single microbubbles that rise in ultrapure water and aqueous solutions of surfactants (SDS, Pluronic F68) or salt (NaCl) was investigated. The rising and dissolution behaviors of single air microbubbles were observed using a high-speed imaging technique by which the rising velocity, UB, and the mass transfer coefficient, kL, were optically evaluated. We found that the rising velocity of microbubbles obeys Stokes’ law, indicating that the surface of the microbubbles used in this study is immobile, despite their rising in ultrapure water. The obtained mass transfer coefficients were in good agreement with those predicted by Ranz and Marshall’s correlation for the Sherwood number, Sh. Using the two correlations for UB and Sh, a theoretical model that describes the mass transfer from a microbubble was constructed. The proposed model can predict the dissolution of single microbubbles rising in ultrapure water and aqueous solutions with an accuracy of ±10% in terms of dissolution time.

EKSTRAKSI FLAVONOID DARI BAYAM MERAH (Alternanthera Amoena Voss)

Red spinach ( Alternanthera Amoena Voss ) contains antioxidant compounds such as betalain, karatenoid, vitamin C and flavonoids. Antioxidant compounds serve to neutralize free radicals in the body, so that the body is protected from degenerative diseases. The separation of flavonoid compounds from red spinach is carried out by using extraction process. This study aims to obtain mass transfer coefficient (Kc) in red spinach extraction process and study the relationship between agitation speed with mass transfer coefficient, and antioxidant activity of the flavonoids obtained. The relationship of Kc and agitation speed is expressed in an equation of Sherwood Number (Sh). Red spinach that had been cut to the square sized (1 x 1 cm) was extracted by using aquadest in an agitated vessel at a temperature of 60 o C and agitation speed of 100 rpm, 200 rpm and 300 rpm. Every 5 minutes sample was taken and its total flavonoid was measured using a UV-VIS spectrophotometer at 415 nm. The extraction process terminated after the equilibrium condition had been reached. The conclusion obtained from this study is the value of Kc increases along with the increasing of agitation speed and equation of sherwood number (Sh) for this extraction is Sh = 240,6154Re 0,6195 .

Theoretical estimation of mass transfer coefficients in solution crystallization

Generally, diffusion through film thickness is used for correlating data in the industrial crystallization processes. Furthermore, mass transfer is an important phenomenon in most chemical processes and studies involving determination of mass transfer coefficients are necessary for a better estimation of equipment performance. Solid-liquid mass transfer coefficients in stirred systems have received substantial attention in the past due to their practical applications. In contrast, little information is available on solid-liquid mass transfer in crystallization systems, despite the importance of crystallization. In this work, an expression for the mass transfer coefficients in solution crystallization has been developed based on the Stefan problem formulation. The model is able to predict a finite mass transfer coefficient when the layer thickness vanishes. The obtained mass transfer coefficients agree with previously reported experimental data. Furthermore, it is found that the stagnant film for mass transfer has oscillatory behavior, and this behavior is a function of residence time.

Adsorption Characteristics of Activated Carbon for the Reclamation of Colored Effluents Containing Orange G and New Solid–Liquid Phase Equilibrium Model

Adsorption characteristics of activated carbon for the removal of orange G, an acid dye from aqueous solutions, have been investigated. The effect of initial dye concentration, temperature, and pH on the removal of orange G was investigated. The removal of orange G decreased from 95% to 82%, when the pH was increased from 2 to 12. The study of the effect of temperature and associated thermodynamic properties revealed the process of removal of dye is exothermic and spontaneous. Kinetic and mass transfer studies of the process were also carried out. The experimental data were used to develop a new solid–liquid phase equilibrium isotherm model. The average absolute relative deviation of the experimental data from the proposed model equation was 5.68%. In order to scale up the batch process for the removal of orange G, the concentration versus time data were analyzed to obtain mass transfer coefficient. The liquid-phase volumetric mass transfer coefficient (kLapL) was found to decrease from 0.008057 to 0.0028...

Possibilities of the Use of the Electrolytic Technique for the Investigations of Mass/Heat Transfer in Nanofluid

In the paper the author presents the possibilities of the application of the electrolytic technique for the investigation of heat transfer coefficients in channels with nanofluids. The electrolytic technique called the limiting current method enables to obtain mass transfer coefficients on the basis of the electrochemical processes and the laws governing these physical phenomena. The exemplary graph presenting the limiting currents values resulting from the experiment is shown in Fig. 1. These are the voltammograms at different Reynolds numbers and the ion concentration Cb. Heat transfer coefficients can be calculated using the correlations describing the analogy of mass and heat transfer processes. Some cases of the possible application of the electrolytic technique and factors influencing the mass transfer experiment including the state of the electroactive surface, change in ion concentration and thickness of the diffusion layer are discussed in [1]. In this work the author focused on the mass transfer experiment with the application of the nanofluid. Special properties of the nanofluid should be taken into account in the investigations. The paper presents the preliminary results of the experiment with nanofluid in the annular channel.

Characterisation of Mass Transfer in Frontal Nanofiltration Equipment and Development of a Simple Correlation

This aim of this work was to investigate the effects of mass transfer in three commercially available frontal nanofiltration systems (Amicon, Sterlitech and Membranology) using the rejection of uncharged poly ethylene glycol (molecular weight 3400) at different pressures and stirrer speeds using a 4000 MWCO membrane. The real rejection was calculated from the observed rejection using the infinite rejection method and a comparison was made between experimentally obtained mass transfer coefficients and those obtained from commonly used ultrafiltration theory. A new mass transfer correlation was proposed that is more appropriate to account for the increased mass transfer effects observed with the larger pressures of nanofiltration. This new correlation is defined as NSh = j(NRe)n (NSc)0.33(1+(Jv/wr)x) is only a minor modification to existing theory and has an accuracy suitable for engineering design purposes.

Effect of channel size on mass transfer during liquid–liquid plug flow in small scale extractors

In this paper the effect of channel size on the mass transfer characteristics of liquid–liquid plug flow was investigated for capillaries with internal diameter ranging from 0.5 to 2mm. The extraction of {UO2}2+ ions from nitric acid solutions into TBP/IL mixtures, relevant to spent nuclear fuel reprocessing, was studied for different residence times, dispersed phase fractions, and mixture velocities. It was found that extraction efficiencies increased as the channel size decreased. For a given channel length and for all channel sizes, an increase in mixture velocity decreased the extraction efficiency. The overall mass transfer coefficients (kLα) for all channels varied between 0.049 and 0.29s−1 and decreased as the channel size increased. The evolution of the kLα along the extraction channel showed a decreasing trend for all the channel sizes. The experimentally obtained mass transfer coefficients were compared with existing models for liquid–liquid and gas–liquid segmented flows from the literature. The results showed good agreement with the empirical correlation proposed for a liquid–liquid system. A finite element model was developed that solved the velocity and concentration fields in the channel for both phases considering a unit cell (one plug and one slug) with periodic boundary conditions at the inlet and the outlet. The model used experimental data for the geometric characteristics of the plug flow and predicted reasonably well the experimentally measured extraction efficiencies (with mean relative error of 11%).

Numerical and experimental analysis of composite fouling in corrugated plate heat exchangers

This paper provides a numerical and experimental analysis on precipitation and particulate fouling in corrugated plate heat exchangers with different geometric parameters which are plate height, plate spacing, and plate angle. The Realizable κ–ε model with non-equilibrium wall functions is used in the 3D numerical simulation considering the realistic geometries of the flow channel to obtained Nusselt number and wall shear stress, while Von-Karman analogy is used to obtain mass transfer coefficient. Numerical analysis is verified by experimental study. The predicted influence of fluid velocity in fouling resistance is compatible with experimental data that it can help to optimize the design of plate heat exchangers. This investigation significantly simplifies the fouling analysis of complex flow fields and can be used to assess the fouling potential of corrugated plate heat exchangers.

Particulate fouling and composite fouling assessment in corrugated plate heat exchangers

Experimental and theoretical investigations of water-side fouling have been performed inside four corrugated plate heat exchangers. They have different geometric parameters, such as plate height, plate spacing, and plate angle. Fouling experiments including particulate fouling tests and composite particulate and precipitation fouling tests have been performed. The tests are primarily focused on the effects of concentration and average velocity. Scanning electron microscope (SEM) was used to investigate the microscopic structures of composite fouling. Heat transfer coefficients and friction factors have been obtained in clean tests. The plate heat exchanger with the largest de and height to pitch ratio shows the best anti-fouling performance. The Von-Karman analogy was used to obtain mass transfer coefficient to develop appropriate semi-theoretical fouling correlations; The wall shear stress is obtained from the pressure drop. The model predictions agree well with experimental data.

Verification and Validation of Evaluation Procedures for Local Wall Thinning Due to Flow-Accelerated Corrosion and Liquid Droplet Impingement

A six-step evaluation procedures have been proposed to evaluate the local wall thinning due to flow-accelerated corrosion (FAC) and that due to liquid droplet impingement (LDI). Corrosive conditions were calculated with a N2H4-O2 reaction analysis code. Precise flow turbulence at major parts of the system was analyzed with the three-dimensional computational flow dynamics code to obtain mass transfer coefficients at structure surfaces. Then, wall thinning rates were calculated with the coupled model of electrochemical analysis and oxide layer growth analysis by applying the corrosive conditions and the mass transfer coefficients.To apply computer simulation codes for wall thinning due to FAC and LDI to evaluate residual life and the effectiveness of countermeasures, accuracy and applicability of the codes were confirmed based on verification and validation processes. From comparison of the calculated wall thinning rates due to FAC with hundreds of measured results for secondary piping of an actual pressurized water reactor plant, it was confirmed that the calculated wall thinning rates agreed with the measured ones within a factor of 2 and the accuracy of the evaluation model for residual pipe wall thickness after 1 year of operation had an error of <20%. Finally, just the FAC simulation code was applied to evaluate the effects of oxygen injection into the feedwater line.From comparison of the calculated wall thinning rates due to LDI with measured results for vent lines of an actual boiling water reactor plant, it was confirmed that the calculated local wall thinning rates agreed with the measured ones within about a factor of 2, though there were still some outside that region.

English

To obtain mass transfer coefficients of three baby food mixtures on cereal basis in a tunnel dryer, Bi-G drying correlation can be used. Experimental moisture content values for three mixtures at three different air temperatures (60, 80 and 100&deg;C) and air velocities (0.5, 1.0 and 1.5 m/s) during tunnel drying were collected. Effective moisture diffusivities coefficients were calculated in two ways and for mixtures 1, 2 and 3 and ranged between 1.51 &times; 10-8&nbsp;to 52.7 &times; 10-8&nbsp;m2/s, 1.05 &times; 10-8&nbsp;to 64.9 &times; 10-8&nbsp;m2/s and 0.107 &times; 10-8&nbsp;to 53.1 &times; 10-8&nbsp;m2/s, respectively. At lower drying temperature, moisture diffusivities values calculated in two ways agreed better than at higher temperature. The influence of baby food composition on mass transfer parameters was observed. &nbsp; Key words:&nbsp;Baby food, exponential drying model, mass transfer coefficients, tunnel drying.

IONIC MASS TRANSFER IN THREE-PHASE FLUIDIZED BEDS IN THE PRESENCE OF DISC PROMOTERS

Three-phase fluidized beds have wide applications in process industries. The present investigation is carried out to identify the enhancement of ionic mass transfer coefficients due to the presence of a disc promoter in a three-phase fluidized bed. A diffusion-controlled electrode reaction—reduction of ferricyanide ion—was employed to obtain mass transfer coefficient data. The mass transfer coefficient data were obtained by varying the geometric variables of the disc promoter (disc diameter, disc spacing) and dynamic variables (superficial liquid velocity, superficial gas velocity). The effect of particle diameter was also investigated. The investigations revealed that the mass transfer coefficients were enhanced with decreased disc spacing, increased disc diameter, increased superficial gas velocity, increased superficial liquid velocity, and increased particle diameter.

Evaluation Methods for Corrosion Damage of Components in Cooling Systems of Nuclear Power Plants by Coupling Analysis of Corrosion and Flow Dynamics (IV) Comparison of Wall Thinning Rates Calculated with the Coupled Model of Static Electrochemical Analysis and Dynamic Double Oxide Layer Analysis and Their Values Measured at a PWR Plant

In order to confirm applicability and accuracy of FAC evaluation methods based on the coupled FAC model of static electrochemical analysis and dynamic oxide layer growth analysis, wall thinning rates calculated with the proposed methods were compared with those measured for the secondary piping of a PWR plant. Distributions of flow velocity and temperature along the whole system were calculated with 1D and 2D computational flow dynamics (CFD) codes and corrosive conditions were calculated with a N2H4-O2 reaction analysis code. Precise flow turbulence at major parts of the system was analyzed with 3D CFD codes to obtain mass transfer coefficients at structure surfaces. Then, wall thinning rates were calculated with the coupled FAC model by applying the mass transfer coefficients. Comparison of the calculated and measured results led to the following conclusions. 1) Structures with complicated geometry in the plant, e.g., the pair of a bend pipe and a valve, could be simplified as a combination of pipes for the calculation. 2) Flow distribution calculated with 3D CFD codes for a large-scale piping system could be extrapolated to those at the very surface of the piping to obtain a precise distribution of mass transfer coefficients at the region of interest. 3) Wall thinning rates calculated by applying the obtained mass transfer coefficients agreed with the measured rates within a factor of 2. 4) The effects of flow turbulence were transferred through a distance of more than 5 times the pipe diameter from the original turbulent point, but the effects on wall thinning rate were negligibly small.

Evaluation Methods for Corrosion Damage of Components in Cooling Systems of Nuclear Power Plants by Coupling Analysis of Corrosion and Flow Dynamics (IV)

In order to confirm applicability and accuracy of FAC evaluation methods based on the coupled FAC model of static electrochemical analysis and dynamic oxide layer growth analysis, wall thinning rates calculated with the proposed methods were compared with those measured for the secondary piping of a PWR plant. Distributions of flow velocity and temperature along the whole system were calculated with 1D and 2D computational flow dynamics (CFD) codes and corrosive conditions were calculated with a N2H4-O2 reaction analysis code. Precise flow turbulence at major parts of the system was analyzed with 3D CFD codes to obtain mass transfer coefficients at structure surfaces. Then, wall thinning rates were calculated with the coupled FAC model by applying the mass transfer coefficients. Comparison of the calculated and measured results led to the following conclusions. 1) Structures with complicated geometry in the plant, e.g., the pair of a bend pipe and a valve, could be simplified as a combination of pipes for the calculation. 2) Flow distribution calculated with 3D CFD codes for a large-scale piping system could be extrapolated to those at the very surface of the piping to obtain a precise distribution of mass transfer coefficients at the region of interest. 3) Wall thinning rates calculated by applying the obtained mass transfer coefficients agreed with the measured rates within a factor of 2. 4) The effects of flow turbulence were transferred through a distance of more than 5 times the pipe diameter from the original turbulent point, but the effects on wall thinning rate were negligibly small.

MULTI-SCALE MASS TRANSFER MODEL FOR GAS-SOLID TWO-PHASE FLOW

ABSTRACT This article is devoted to analyzing the mass transfer in heterogeneous gas-solid flow by means of structure and process decomposition. A multi-scale mass transfer model was developed on the basis of the hydrodynamics calculated from the so-called EMMS model. This resulted in the predictions of the steady-state two-dimensional concentration distributions of sublimated substance as well as total mass transfer coefficient for circular concurrent gas-solid contactors. The predictions were validated by experimentally measured (via an on-line HP GC-MS system) axial concentration distributions of sublimated naphthalene in air in a circulating fluidized bed riser 3.0 m in height and 72 mm in diameter. The experiment also obtained mass transfer coefficients comparable to theoretical predictions under conditions with various gas velocities, solid circulation rates, particle sizes, and active material fractions in the particles. Both the theoretical and experimental results demonstrated that the heterogeneous flow structure prevailing in the concurrent gas-solid flow greatly influenced the flow's mass transfer.

Reductive extraction kinetics of actinide and lanthanide elements in molten chloride and liquid cadmium system

Abstract For the development of reductive extraction process, the rate of extraction of actinide and lanthanide elements was measured in a two-phase system of molten LiCl–KCl eutectic salt and liquid cadmium at 723–873 K. The mass transfer coefficient of the elements was evaluated by applying a film theory. The obtained mass transfer coefficients were found to be as high as expected in the present system. In some cases, however, it was found that the rate of reductive extraction was affected possibly by the solubility of the solute elements in the metal phase.