Goemans, M.G.E.; Gloyna, E.F.; Buelow, S.J.
1996-04-01
Molecular diffusion coefficients of lithium-, sodium-, potassium-, cesium-, calcium-, and strontium nitrate in subcritical water were determined by analysis of Taylor dispersion profiles. Pressures ranged from 300 to 500 bar at temperatures ranging from 25{degrees}C to 300{degrees}C. The reported diffusion values were determined at infinite dilution. Molecular diffusion coefficients were 10 to 20 times faster in near-critical subcritical water than in water at ambient temperature and pressure (ATP). These findings implied that the diffusion rates were more liquid like than they were gas like, hence experimental results were correlated with diffusion models for liquids. The subcritical diffusion data presented in this work, and supercritical diffusion results published elsewhere were correlated with hydrodynamic diffusion equations. Both the Wilke-Chang correlation and the Stokes-Einstein equation yielded predictions within 10% of the experimental results if the structure of the diffusing species could be estimated. The effect of the increased diffusion rates on mass transfer rates in supercritical water oxidation applications was quantified, with emphasis on heterogeneous oxidation processes. This study and results published elsewhere showed that diffusion limited conditions are much more likely to be encountered in SCWO processes than commonly acknowledged.
Diffusion mass transfer in ionic materials under intense electron irradiation
NASA Astrophysics Data System (ADS)
Bochkarev, I. G.; Ghyngazov, S. A.; Frangulyan, T. S.; Petrova, A. B.; Chernyavskii, A. V.
2017-01-01
The results of studies on the impact of an electron beam with the energy of 1-2 MeV on diffusion processes in materials with ionic bonds are presented in the paper. Used electron beam intensity is allowed to provide heating of the material to temperatures of 1600 K. Diffusion of Na, Mg, Al ions into single crystals KBr in the temperature range 573-883 K, Al ions in the NiO-AlO system at 1373-1573 K, was studied. Diffusion annealing carried out under thermal and radiation-thermal heating of the samples. Then diffusion coefficients were determined. It was found stimulating action of irradiation on diffusion processes of Mg, Al ions in Kbr and Al ions in the NiO-Al2O3 system, which consists in increasing the diffusion coefficients at radiation-thermal annealing. The observed effect is achieved by increasing the effective rate of diffusion jumps.
Bhattacharjee, C.; Datta, S.
1999-08-01
An unsteady-state mass transfer model has been developed which takes into account the variation of diffusivity with solute concentration in the boundary layer. The main aim of this model is to study the effect of variation of diffusivity on membrane surface concentration as well as on the concentration profile prevailing within the boundary layer. Experimental data generated in this study have been used to validate the model. The resulting complex nonlinear partial differential equation has been solved by a numerical technique. The developed model is also capable of simulating volumetric flux and the permeate volume collected at any time under specified operating conditions. The simulated results show excellent fitting of the present model with variable diffusivity consideration when compared with experimental data. On the other hand, prediction based on constant diffusivity deviates considerably, indicating the importance of consideration of variable diffusivity in unsteady-state batch ultrafiltration.
Kinetics of diffusive decomposition in the case of several mass transfer mechanisms
NASA Astrophysics Data System (ADS)
Alexandrov, D. V.
2017-01-01
An analytical description of the final stage of diffusive decomposition leaning upon the Slezov theory is developed for several mass transfer mechanisms. The process of formation and relaxation of the crystal size distribution function from the initial ripening stage to its final state corresponding to the universal distribution is studied. The boundary points of a transition region responsible for the tails of the distribution functions on the right of the relevant stopping points are found analytically. The explicit time-dependent analytical expressions for the distribution function and particle growth rates are derived with allowance for the plausible mechanisms of mass transfer.
NASA Astrophysics Data System (ADS)
Ogorzalek Loo, Rachel R.; Mitchell, Charles; Stevenson, Tracy I.; Loo, Joseph A.; Andrews, Philip C.
1997-12-01
Diffusive transfer was examined as a blotting method to transfer proteins from polyacrylamide gels to membranes for ultraviolet matrix-assisted laser desorption ionization (MALDI) mass spectrometry. The method is well-suited for transfers from isoelectric focusing (IEF) gels. Spectra have been obtained for 11 pmol of 66 kDa albumin loaded onto an IEF gel and subsequently blotted to polyethylene. Similarly, masses of intact carbonic anhydrase and hemoglobin were obtained from 14 and 20 pmol loadings. This methodology is also compatible with blotting high molecular weight proteins, as seen for 6 pmol of the 150 kDa monoclonal antibody anti-[beta]-galactosidase transferred to Goretex. Polypropylene, Teflon, Nafion and polyvinylidene difluoride (PVDF) also produced good spectra following diffusive transfer. Only analysis from PVDF required that the membrane be kept wet prior to application of matrix. Considerations in mass accuracy for analysis from large-area membranes with continuous extraction and delayed extraction were explored, as were remedies for surface charging. Vapor phase CNBr cleavage was applied to membrane-bound samples for peptide mapping.
Lichtenberg, Mads; Nørregaard, Rasmus Dyrmose; Kühl, Michael
2017-03-01
The role of hyaline hairs on the thallus of brown algae in the genus Fucus is long debated and several functions have been proposed. We used a novel motorized set-up for two-dimensional and three-dimensional mapping with O2 microsensors to investigate the spatial heterogeneity of the diffusive boundary layer (DBL) and O2 flux around single and multiple tufts of hyaline hairs on the thallus of Fucus vesiculosus. Flow was a major determinant of DBL thickness, where higher flow decreased DBL thickness and increased O2 flux between the algal thallus and the surrounding seawater. However, the topography of the DBL varied and did not directly follow the contour of the underlying thallus. Areas around single tufts of hyaline hairs exhibited a more complex mass-transfer boundary layer, showing both increased and decreased thickness when compared with areas over smooth thallus surfaces. Over thallus areas with several hyaline hair tufts, the overall effect was an apparent increase in the boundary layer thickness. We also found indications for advective O2 transport driven by pressure gradients or vortex shedding downstream from dense tufts of hyaline hairs that could alleviate local mass-transfer resistances. Mass-transfer dynamics around hyaline hair tufts are thus more complex than hitherto assumed and may have important implications for algal physiology and plant-microbe interactions.
NASA Technical Reports Server (NTRS)
Kleinman, Leonid S.; Red, X. B., Jr.
1995-01-01
An algorithm has been developed for time-dependent forced convective diffusion-reaction having convection by a recirculating flow field within the drop that is hydrodynamically coupled at the interface with a convective external flow field that at infinity becomes a uniform free-streaming flow. The concentration field inside the droplet is likewise coupled with that outside by boundary conditions at the interface. A chemical reaction can take place either inside or outside the droplet, or reactions can take place in both phases. The algorithm has been implemented, and for comparison results are shown here for the case of no reaction in either phase and for the case of an external first order reaction, both for unsteady behavior. For pure interphase mass transfer, concentration isocontours, local and average Sherwood numbers, and average droplet concentrations have been obtained as a function of the physical properties and external flow field. For mass transfer enhanced by an external reaction, in addition to the above forms of results, we present the enhancement factor, with the results now also depending upon the (dimensionless) rate of reaction.
NASA Technical Reports Server (NTRS)
Kleinman, Leonid S.; Reed, X. B., Jr.
1995-01-01
An algorithm has been developed for the forced convective diffusion-reaction problem for convection inside and outside a droplet by a recirculating flow field hydrodynamically coupled at the droplet interface with an external flow field that at infinity becomes a uniform streaming flow. The concentration field inside the droplet is likewise coupled with that outside by boundary conditions at the interface. A chemical reaction can take place either inside or outside the droplet or reactions can take place in both phases. The algorithm has been implemented and results are shown here for the case of no reaction and for the case of an external first order reaction, both for unsteady behavior. For pure interphase mass transfer, concentration isocontours, local and average Sherwood numbers, and average droplet concentrations have been obtained as a function of the physical properties and external flow field. For mass transfer enhanced by an external reaction, in addition to the above forms of results, we present the enhancement factor, with the results now also depending upon the (dimensionless) rate of reaction.
Gilbert, Dorothea; Jakobsen, Hans H; Winding, Anne; Mayer, Philipp
2014-04-15
The environmental chemodynamics of hydrophobic organic chemicals (HOCs) are often rate-limited by diffusion in stagnant boundary layers. This study investigated whether motile microorganisms can act as microbial carriers that enhance mass transfer of HOCs through diffusive boundary layers. A new experimental system was developed that allows (1) generation of concentration gradients of HOCs under the microscope, (2) exposure and direct observation of microorganisms in such gradients, and (3) quantification of HOC mass transfer. Silicone O-rings were integrated into a Dunn chemotaxis chamber to serve as sink and source for polycyclic aromatic hydrocarbons (PAHs). This resulted in stable concentration gradients in water (>24 h). Adding the model organism Tetrahymena pyriformis to the experimental system enhanced PAH mass transfer up to hundred-fold (benzo[a]pyrene). Increasing mass transfer enhancement with hydrophobicity indicated PAH co-transport with the motile organisms. Fluorescence microscopy confirmed such transport. The effective diffusivity of T. pyriformis, determined by video imaging microscopy, was found to exceed molecular diffusivities of the PAHs up to four-fold. Cell-bound PAH fractions were determined to range from 28% (naphthalene) to 92% (pyrene). Motile microorganisms can therefore function as effective carriers for HOCs under diffusive conditions and might significantly enhance mobility and availability of HOCs.
NASA Astrophysics Data System (ADS)
He, Ping; Ghoniem, Ahmed F.
2017-03-01
Mixing of partially miscible fluids plays an important role in many physical and chemical processes. The modeling complexities lie in the tight coupling of the multiphase flow, heat transfer and multicomponent mass transfer, as well as diffusions across the phase interface. We present a sharp interface method for modeling such process. The non-ideal equation of state is used to compute the fluid properties such as density, fugacity and enthalpy, and to predict phase equilibrium composition. The phase interface location is tracked using the phase propagation velocity. A third-order one-sided finite difference scheme using a variable grid size according to the interface location is utilized to discretize the partial derivatives immediately next to the interface, while a second-order central scheme is used for the bulk of fluids. An optimization method, the Nelder-Mead method, is applied to search for (1) the phase compositions on both sides of the interface, and (2) the phase propagation velocity based on the coupling of the multicomponent phase equilibrium and the species' balance across the interface. The temperature at the interface is determined by the energy balance. Numerical results are used to demonstrate the convergence of our method and show its capability to simulate the mixing of multicomponent partially miscible fluids.
A diffusion-kinetic model for pulverized-coal combustion and heat-and-mass transfer in a gas stream
E.A. Boiko; S.V. Pachkovskii
2008-12-15
A diffusion-kinetic model for pulverized-coal combustion and heat-and-mass transfer in a gas stream is proposed, and the results of numerical simulation of the burnout dynamics of Kansk-Achinsk coals in the pulverized state at different treatment conditions and different model parameters are presented. The mathematical model describes the dynamics of thermochemical conversion of solid organic fuels with allowance for complex physicochemical phenomena of heat-and-mass exchange between coal particles and the gaseous environment.
NASA Technical Reports Server (NTRS)
Srivastava, R.; Rosner, D. E.
1979-01-01
A rational approach to the correlation of boundary layer mass transport rates, applicable to many commonly encountered laminar flow conditions with thermal diffusion and/or variable properties, is outlined. The correlation scheme builds upon already available constant property blowing/suction solutions by introducing appropriate correction factors to account for the additional ('pseudo' blowing and source) effects identified with variable properties and thermal diffusion. Applications of the scheme to the particular laminar boundary layer mass transfer problems considered herein (alkali and transition metal compound vapor transport) indicates satisfactory accuracy up to effective blowing factors equivalent to about one third of the 'blow off' value. As a useful by-product of the variable property correlation, we extend the heat-mass transfer analogy, for a wide range of Lewis numbers, to include variable property effects.
Heat transfer, diffusion, and evaporation
NASA Technical Reports Server (NTRS)
Nusselt, Wilhelm
1954-01-01
Although it has long been known that the differential equations of the heat-transfer and diffusion processes are identical, application to technical problems has only recently been made. In 1916 it was shown that the speed of oxidation of the carbon in iron ore depends upon the speed with which the oxygen of the combustion air diffuses through the core of gas surrounding the carbon surface. The identity previously referred to was then used to calculate the amount of oxygen diffusing to the carbon surface on the basis of the heat transfer between the gas stream and the carbon surface. Then in 1921, H. Thoma reversed that procedure; he used diffusion experiments to determine heat-transfer coefficients. Recently Lohrisch has extended this work by experiment. A technically very important application of the identity of heat transfer and diffusion is that of the cooling tower, since in this case both processes occur simultaneously.
Evaluating Technology Transfer and Diffusion.
ERIC Educational Resources Information Center
Bozeman, Barry; And Others
1988-01-01
Four articles discuss the evaluation of technology transfer and diffusion: (1) "Technology Transfer at the U.S. National Laboratories: A Framework for Evaluation"; (2) "Application of Social Psychological and Evaluation Research: Lessons from Energy Information Programs"; (3) "Technology and Knowledge Transfer in Energy R and D Laboratories: An…
NASA Astrophysics Data System (ADS)
Bao, Cheng; Jiang, Zeyi; Zhang, Xinxin
2016-08-01
Following the previous work on comparing performance of Fickian, Stefan-Maxwell and dusty-gas model for mass transfer in single fuel system, this article is focused on the electrochemistry and transport in the anode of solid oxide fuel cell using H2sbnd H2Osbnd COsbnd CO2sbnd N2 hybrid fuel. Under the standard framework of the dusty-gas model combined with the Butler-Volmer equation, it carries out a macroscopic area-specific modeling work. More specifically, two variables of hydrogen current fraction and enhancement factor are well defined and solved for the electrochemical co-oxidation of H2 and CO, and the diffusion equivalent circuit model is introduced to describe more comprehensively the resistance of mass transfer including molecular/Knudsen diffusion and surface diffusion. The model has been validated well in full region of Vsbnd I performance of an experimental anode-supported button cell. An approximate analytical solution of the hydrogen current fraction is also presented for explicit computation. Comparison between the results by different approaches for the effective diffusivity shows the importance of right mass-transfer modeling.
Espinal-Ruiz, Mauricio; Restrepo-Sánchez, Luz-Patricia; Narváez-Cuenca, Carlos-Eduardo
2016-10-15
The effect of high (HMP) and low (LMP) methoxylated pectins (2%w/w) on the rate and extent of the mass transfer of monosaccharides, amino acids, and a corn oil-in-water emulsion across a cellulose membrane was evaluated. A sigmoidal response kinetic analysis was used to calculate both the diffusion coefficients (rate) and the amount of nutrients transferred through the membrane (extent). In all cases, except for lysine, HMP was more effective than LMP in inhibiting both the rate and extent of the mass transfer of nutrients through the membrane. LMP and HMP, e.g., reduced 1.3 and 3.0times, respectively, the mass transfer rate of glucose, as compared to control (containing no pectin), and 1.3 and 1.5times, respectively, the amount of glucose transferred through the membrane. Viscosity, molecular interactions, and flocculation were the most important parameters controlling the mass transfer of electrically neutral nutrients, electrically charged nutrients, and emulsified lipids, respectively.
NASA Astrophysics Data System (ADS)
Zhang, Zhijun; Gao, Jingxin; Zhang, Shiwei
2016-10-01
A frozen phase transition model is developed to investigate the heat and mass transfer of a single water droplet during the vacuum freezing process. The model is based on the diffusion-controlled evaporation mechanism and phase transition characteristics. The droplet vacuum freezing process can be divided into three stages according to the droplet states and the time order. It includes the evaporation freezing stage, the isothermal freezing stage and the sublimation freezing stage. A numerical calculation is performed, and the result is analysed. The effects of the vacuum chamber pressure, initial droplet diameter and initial droplet temperature on the heat and mass transfer characteristics at each stage are studied. The droplet experiences supercooling breakdown at the end of the evaporation freezing stage before the isothermal freezing stage begins. The temperature is transiently raised as a result of the supercooling breakdown phenomenon, whose effects on the freezing process and freezing parameters are considered.
Zhang, Zhijun; Gao, Jingxin; Zhang, Shiwei
2016-10-14
A frozen phase transition model is developed to investigate the heat and mass transfer of a single water droplet during the vacuum freezing process. The model is based on the diffusion-controlled evaporation mechanism and phase transition characteristics. The droplet vacuum freezing process can be divided into three stages according to the droplet states and the time order. It includes the evaporation freezing stage, the isothermal freezing stage and the sublimation freezing stage. A numerical calculation is performed, and the result is analysed. The effects of the vacuum chamber pressure, initial droplet diameter and initial droplet temperature on the heat and mass transfer characteristics at each stage are studied. The droplet experiences supercooling breakdown at the end of the evaporation freezing stage before the isothermal freezing stage begins. The temperature is transiently raised as a result of the supercooling breakdown phenomenon, whose effects on the freezing process and freezing parameters are considered.
Zhang, Zhijun; Gao, Jingxin; Zhang, Shiwei
2016-01-01
A frozen phase transition model is developed to investigate the heat and mass transfer of a single water droplet during the vacuum freezing process. The model is based on the diffusion-controlled evaporation mechanism and phase transition characteristics. The droplet vacuum freezing process can be divided into three stages according to the droplet states and the time order. It includes the evaporation freezing stage, the isothermal freezing stage and the sublimation freezing stage. A numerical calculation is performed, and the result is analysed. The effects of the vacuum chamber pressure, initial droplet diameter and initial droplet temperature on the heat and mass transfer characteristics at each stage are studied. The droplet experiences supercooling breakdown at the end of the evaporation freezing stage before the isothermal freezing stage begins. The temperature is transiently raised as a result of the supercooling breakdown phenomenon, whose effects on the freezing process and freezing parameters are considered. PMID:27739466
Daneyko, Anton; Hlushkou, Dzmitry; Baranau, Vasili; Khirevich, Siarhei; Seidel-Morgenstern, Andreas; Tallarek, Ulrich
2015-08-14
In recent years, chromatographic columns packed with core-shell particles have been widely used for efficient and fast separations at comparatively low operating pressure. However, the influence of the porous shell properties on the mass transfer kinetics in core-shell packings is still not fully understood. We report on results obtained with a modeling approach to simulate three-dimensional advective-diffusive transport in bulk random packings of monosized core-shell particles, covering a range of reduced mobile phase flow velocities from 0.5 up to 1000. The impact of the effective diffusivity of analyte molecules in the porous shell and the shell thickness on the resulting plate height was investigated. An extension of Giddings' theory of coupled eddy dispersion to account for retention of analyte molecules due to stagnant regions in porous shells with zero mobile phase flow velocity is presented. The plate height equation involving a modified eddy dispersion term excellently describes simulated data obtained for particle-packings with varied shell thickness and shell diffusion coefficient. It is confirmed that the model of trans-particle mass transfer resistance of core-shell particles by Kaczmarski and Guiochon [42] is applicable up to a constant factor. We analyze individual contributions to the plate height from different mass transfer mechanisms in dependence of the shell parameters. The simulations demonstrate that a reduction of plate height in packings of core-shell relative to fully porous particles arises mainly due to reduced trans-particle mass transfer resistance and transchannel eddy dispersion.
Mass Transfer Cooling Near The Stagnation Point
NASA Technical Reports Server (NTRS)
Roberts, Leonard
1959-01-01
A simplified analysis is made of mass transfer cooling, that is, injection of a foreign gas, near the stagnation point for two-dimensional and axisymmetric bodies. The reduction in heat transfer is given in terms of the properties of the coolant gas and it is shown that the heat transfer may be reduced considerably by the introduction of a gas having appropriate thermal and diffusive properties. The mechanism by which heat transfer is reduced is discussed.
NASA Astrophysics Data System (ADS)
Glaus, M. A.; Aertsens, M.; Appelo, C. A. J.; Kupcik, T.; Maes, N.; Van Laer, L.; Van Loon, L. R.
2015-09-01
Enhanced mass transfer rates have been frequently observed in diffusion studies with alkaline and earth alkaline elements in compacted clay minerals and clay rocks. Whether this phenomenon - often termed surface diffusion - is also relevant for more strongly sorbing species is an open question. We therefore investigated the diffusion of Sr2+, Co2+ and Zn2+ in compacted illite with respect to variations of the concentration of the background electrolyte, pH and carbonate. New experimental techniques were developed in order to avoid artefacts stemming from the confinement of the clay sample. A distinct dependence of the effective diffusion coefficients on the concentration of the background electrolyte was observed for all three elements. A similar correlation was found for the sorption distribution ratio (Rd) derived from tracer breakthrough in the case of Sr2+, while this dependence was much weaker for Co2+ and Zn2+. Model calculations using Phreeqc resulted in a good agreement with the experimental data when it was assumed that the cationic species, present in the electrical double layer (EDL) of the charged clay surface, are mobile. Species bound to the specific surface complexation sites at the clay edges were assumed to be immobile. An assessment of the mobility of the type of cationic elements studied here in argillaceous media thus requires an analysis of their distribution among specifically sorbed surface species and species in the EDL. The normal approach of deriving unknown effective diffusion coefficients from reference values of an uncharged water tracer may significantly underestimate the mobility of metal cations in argillaceous media.
Davila-Guzman, Nancy E; Cerino-Córdova, Felipe J; Soto-Regalado, Eduardo; Loredo-Cancino, Margarita; Loredo-Medrano, José A; García-Reyes, Refugio B
2016-08-01
In this study, amberlite XAD-16 (XAD-16) bed column system was used to remove ferulic acid (FA) from aqueous solutions. Laboratory-scale column experiments were conducted in downflow fixed bed at initial FA concentration of 1 g/L, initial pH 3, and 25°C. The performance of the adsorbent bed under different flow rates (1.3-7.7 mL/min) was studied. The bed utilization efficiency was in the range of 64.64-72.21% at the studied flow rates. A mass transfer model considering both axial dispersion and intraparticle diffusion was developed to predict the breakthrough curves of FA adsorption on XAD-16. This model predicted the experimental data better than Bohart-Adams model and Thomas model, based on the low deviation between predicted and experimental data. The axial dispersion coefficient value varied from 6.45 × 10(-6) to 1.10 × 10(-6) m(2)/s at flow rate from 1.3 to 7.7 mL/min, whereas the intraparticle diffusion coefficient was 1.04 × 10(-10) m(2)/s, being this last resistance the rate-limiting step. In conclusion, axial dispersion and intraparticle diffusion phenomena play the major role in predicting the adsorption of FA onto XAD-16 in fixed-bed columns.
NASA Astrophysics Data System (ADS)
Abdel-Rahman, Gamal M.
2010-06-01
In this paper, the thermal-diffusion and magnetic field effects on a stagnation point flowing over a flat stretching surface have been obtained and studied numerically with the variation of the viscosity under the Soret and Dufour's effects. The governing continuity, momentum, energy and concentration equations are converted into a system of non-linear ordinary differential equations by means of similarity transformation. The resulting system of coupled non-linear ordinary differential equations is solved numerically. Numerical results were presented for velocity, temperature and concentration profiles for different parameters of the problem as radiation parameter, magnetic field parameter, porous medium parameter, endothermic chemical reaction, heat source parameter, stretching parameter, the Soret and Dufour number and other. Also the effects of the pertinent parameters on the skin friction, the rate of heat and mass transfer are obtained and discussed numerically and illustrated graphically.
NASA Technical Reports Server (NTRS)
Gokoglu, S. A.; Santoro, G. J.
1985-01-01
Two sets of experiments have been performed to be able to predict the convective diffusion heat/mass transfer rates to a cylindrical target whose height and diameter are comparable to, but less than, the diameter of the circular cross-stream jet, thereby simulating the same geometric configuration as a typical burner rig test specimen located in the cross-stream of the combustor exit nozzle. The first set exploits the naphthalene sublimation technique to determine the heat/mass transfer coefficient under isothermal conditions for various flow rates (Reynolds numbers). The second set, conducted at various combustion temperatures and Reynolds numbers, utilized the temperature variation along the surface of the above-mentioned target under steady-state conditions to estimate the effect of cooling (dilution) due to the entrainment of stagnant room temperature air. The experimental information obtained is used to predict high temperature, high velocity corrosive salt vapor deposition rates in burner rigs on collectors that are geometrically the same. The agreement with preliminary data obtained from Na2SO4 vapor deposition experiments is found to be excellent.
NASA Technical Reports Server (NTRS)
Gokoglu, S. A.; Santoro, G. J.
1986-01-01
Two sets of experiments have been performed to be able to predict the convective diffusion heat/mass transfer rates to a cylindrical target whose height and diameter are comparable to, but less than, the diameter of the circular cross-stream jet, thereby simulating the same geometric configuration as a typical burner rig test specimen located in the cross-stream of the combustor exit nozzlle. The first set exploits the naphthalene sublimation technique to detetermine the heat/mass transfer coefficient under isothermal conditions for various flow rates (Reynolds numbers). The second set, conducted at various combustion temperatures and Reynolds numbers, utilized the temperature variation along the surface of the above-mentioned target under steady-state conditions to estimate the effect of cooling (dilution) due to the entrainment of stagnant room temperature air. The experimental information obtained is used to predict high temperature, high velocity corrosive salt vapor deposition rates in burner rigs on collectors that are geometrically the same. The agreement with preliminary data obtained from Na2S04 vapor deposition experiments is found to be excellent.
Geochemical Speciation Mass Transfer
1985-12-01
PHREEQC is designed to model geochemical reactions. Based on an ion association aqueous model, PHREEQC can calculate pH, redox potential, and mass transfer as a function of reaction progress. It can be used to describe geochemical processes for both far-field and near-field performance assessment and to evaluate data acquisition needs and test data. It can also calculate the composition of solutions in equilibrium with multiple phases. The data base, including elements, aqueous species, and mineral phases, is independent of the program and is completely user-definable. PHREEQC requires thermodynamic data for each solid, gaseous, or dissolved chemical species being modeled. The two data bases, PREPHR and DEQPAK7, supplied with PHREEQC are for testing purposes only and should not be applied to real problems without first being carefully examined. The conceptual model embodied in PHREEQC is the ion-association model of Pearson and Noronha. In this model a set of mass action equations are established for each ion pair (and controlling solid phases when making mass transfer calculations) along with a set of mass balance equations for each element considered. These sets of equations are coupled using activity coefficient values for each aqueous species and solved using a continued fraction approach for the mass balances combined with a modified Newton-Raphson technique for all other equations. The activity coefficient expressions in PHREEQC include the extended Debye-Huckel, WATEQ Debye-Huckel, and Davies equations from the original United States Geological Survey version of the program. The auxiliary preprocessor program PHTL, which is derived from EQTL, converts EQ3/6 thermodynamic data to PHREEQC format so that the two programs can be compared. PHREEQC can be used to determine solubility limits on the radionuclides present in the waste form. These solubility constraints may be input to the WAPPA leach model.
NASA Astrophysics Data System (ADS)
Touhid Hossain, M. M.; Afruz-Zaman, Md.; Rahman, Fouzia; Hossain, M. Arif
2013-09-01
In this study the thermal diffusion effect on the steady laminar free convection flow and heat transfer of viscous incompressible MHD electrically conducting fluid above a vertical porous surface is considered under the influence of an induced magnetic field. The governing non-dimensional equations relevant to the problem, containing the partial differential equations, are transformed by usual similarity transformations into a system of coupled non-linear ordinary differential equations and will be solved analytically by using the perturbation technique. On introducing the non-dimensional concept and applying Boussinesq's approximation, the solutions for velocity field, temperature distribution and induced magnetic field to the second order approximations are obtained for large suction with different selected values of the established dimensionless parameters. The influences of these various establish parameters on the velocity and temperature fields and on the induced magnetic fields are exhibited under certain assumptions and are studied graphically in the present analysis. It is observed that the effects of thermal-diffusion and large suction have great importance on the velocity, temperature and induced magnetic fields and mass concentration for several fluids considered, so that their effects should be taken into account with other useful parameters associated. It is also found that the dimensionless Prandtl number, Grashof number, Modified Grashof number and magnetic parameter have an appreciable influence on the concerned independent variables.
Mass Transfer with Chemical Reaction.
ERIC Educational Resources Information Center
DeCoursey, W. J.
1987-01-01
Describes the organization of a graduate course dealing with mass transfer, particularly as it relates to chemical reactions. Discusses the course outline, including mathematics models of mass transfer, enhancement of mass transfer rates by homogeneous chemical reaction, and gas-liquid systems with chemical reaction. (TW)
Soldatov, A A
2012-01-01
Effect of hypoosmotic conditions of medium on oxygen regime of skeletal muscles of the stenohalin goby Gobius cobitus Pallas was studied under conditions of experiment. The control fish group was maintained at 12-14 %o, the experimental one - at 4.8-5.6 per thousand. Duration of the experiment - 44-45 days, water temperature - 15 +/- 1 degrees C, photoperiod - 12 day/12 night. It was established that under conditions of external hypoosmia there occurred hydration of the goby skeletal muscles and a decrease of their diffusion capability with respect to oxygen. The latter was accompanied by the tissue P(O2) decrease, which is indicated by low values of P(O2) in the venous blood outflowing from muscles. For the first 14-16 days of adaptation to the hypoosmotic medium there were restricted processes of mass transfer and oxygen utilization, which was associated with a decrease of the voluminous tissue blood flow and the blood oxygen concentration. These changes occurred on the background of the blood plasma hydration and a decrease of the number of circulated erythrocytes, and then they were completely compensated.
Thermal /Soret/ diffusion effects on interfacial mass transport rates
NASA Technical Reports Server (NTRS)
Rosner, D. E.
1980-01-01
It is shown that thermal (Soret) diffusion significantly alters convective mass transport rates and important transition temperatures in highly nonisothermal flow systems involving the transport of 'heavy' species (vapors or particles). Introduction of the Soret transport term is shown to result in mass transfer effects similar to those of 'suction' and a homogeneous chemical 'sink'. It is pointed out that this analogy provides a simple method of correlating and predicting thermal diffusion effects in the abovementioned systems.
Yasin, Muhammad; Park, Shinyoung; Jeong, Yeseul; Lee, Eun Yeol; Lee, Jinwon; Chang, In Seop
2014-10-01
This study proposed a submerged hollow fibre membrane bioreactor (HFMBR) system capable of achieving high carbon monoxide (CO) mass transfer for applications in microbial synthesis gas conversion systems. Hydrophobic polyvinylidene fluoride (PVDF) membrane fibres were used to fabricate a membrane module, which was used for pressurising CO in water phase. Pressure through the hollow fibre lumen (P) and membrane surface area per unit working volume of the liquid (A(S)/V(L)) were used as controllable parameters to determine gas-liquid volumetric mass transfer coefficient (k(L)a) values. We found a k(L)a of 135.72 h(-1) when P was 93.76 kPa and AS/VL was fixed at 27.5m(-1). A higher k(L)a of 155.16 h(-1) was achieved by increasing AS/VL to 62.5m(-1) at a lower P of 37.23 kPa. Practicality of HFMBR to support microbial growth and organic product formation was assessed by CO/CO2 fermentation using Eubacterium limosum KIST612.
Diffuse mass transport in a porous medium
NASA Astrophysics Data System (ADS)
Ho, F. G.
1981-08-01
Variational methods are used to investigate the problems of diffusive mass transport in a porous medium. Calculations of the effective diffusivities are performed for a model pore structure generated by randomly placed, freely overlapping solid spheres all of the same radius. Effects of the tortuosity of the diffusion paths are considered. Numerical evaluations are used to test some approximate engineering models. For gaseous transition region diffusion the mean free path kinetic theory is used to derive a variational upper bound on the effective transition region diffusivity. For the simultaneous liquid or gas phase Fickian bulk diffusion in the void and Fickian surface diffusion on the pore wall surface, an analytical expression for effective diffusion coefficient is obtained and compared with the usual engineering model of parallel surface and void diffusion. The simultaneous gaseous transition region diffusion in the void and the Fickian surface diffusion on the pore wall surface are examined numerically.
Limiting current technique in the research of mass/heat transfer in nanofluid
NASA Astrophysics Data System (ADS)
Wilk, J.; Grosicki, S.
2016-09-01
In the paper the authors focused on the application of the electrochemical limiting diffusion current technique to the study of mass transfer in nanofluid flow. As mass and heat transfer are analogical phenomena, analysing mass transfer helps understand heat transfer processes in nanofluids. The paper begins with a short review of the available literature on the subject followed by the authors' results of mass transfer coefficient measurements and the conclusions concerning mass/heat transfer enhancement in nanofluids.
Mass transfer in corrugated membranes
NASA Astrophysics Data System (ADS)
Gronda, Ann Mclaughry
Research on the chemical and physical structure of membranes has failed to overcome the inverse relationship between selectivity and permeability. While this permeability is partially responsible for the rate of separation, the geometry of the membrane contributes significantly to this rate. In this work, we focused on the system geometry by examining the effect of corrugations on the rate of membrane separations. We developed a theory to describe mass transport in corrugations and to predict the effectiveness of corrugated membranes. To verify this theory, membranes with millimeter-sized corrugations were made. Pervaporation experiments with highly permeable and less permeable solutes showed excellent agreement with the theory. Based on the membrane geometry and permeability, the effectiveness factor and the flux enhancement can be quantified by a modified Thiele analysis. We used this theory to examine the effect of small corrugations on the mass transfer of both liquids and gases across membranes, including the effects of free convection, membrane supports, and Knudsen diffusion. In systems with a liquid feed, corrugations are promising only for very impermeable solutes. In gases, corrugations are more effective, especially when supported by a porous structure. We attempted to make smaller corrugations in two ways. The more promising method is phase-inversion of diblock copolymers. These diblocks were dissolved in a solvent, made into a thin film, and immersed in a liquid that was a nonsolvent for the majority block and a solvent for the minority block. In this way, we attempted to draw the minority block to the surface of an undulating structure created by the phase inversion. Ideally, the minority block would be selective and the majority block would be highly permeable or porous. Scanning electron microscopy showed promising structures made from polystyrene-polyisoprene and polyacrylonitrile-polyethylene oxide. The other, less promising, attempt at making
Mass Transfer and Rheology of Fiber Suspensions
NASA Astrophysics Data System (ADS)
Wang, Jianghui
Rheological and mass transfer properties of non-Brownian fiber suspensions are affected by fiber characteristics, fiber interactions, and processing conditions. In this thesis we develop several simulation methods to study the dynamics of single fibers in simple shear flow, as well as the rheology and mass transfer of fiber suspensions. Isolated, rigid, neutrally-buoyant, non-Brownian, slightly curved, nonchiral fibers in simple shear flow of an incompressible Newtonian fluid at low Reynolds number can drift steadily in the gradient direction without external forces or torques. The average drift velocity and direction depend on the fiber aspect ratio, curvature and initial orientation. The drift results from the coupling of rotational and translational dynamics, and the combined effects of flipping, scooping, and spinning motions of the fiber. Irreversible fiber collisions in the suspensions cause shear-induced diffusion. The shear-induced self-diffusivity of dilute suspensions of fibers increases with increasing concentration and increasing static friction between contacts. The diffusivities in both the gradient and vorticity directions are larger for suspensions of curved fibers than for suspensions of straight fibers. For suspensions of curved fibers, significant enhancements in the diffusivity in the gradient direction are attributed to fiber drift in the gradient direction. The shear-induced self-diffusivity of concentrated suspensions of fibers increases with increasing concentration before fiber networks or flocs are formed, after which the diffusivity decreases with increasing concentration. The diffusivity increases with increasing fiber equilibrium bending angle, effective stiffness, coefficient of static friction, and rate of collisions. The specific viscosity of fiber suspensions increases with increasing fiber curvature, friction coefficient between mechanical contacts, and solids concentration. The specific viscosity increases linearly with
Lu, W.J.; Chou, I.-Ming; Burruss, R.C.; Yang, M.Z.
2006-01-01
A new method was developed for in situ study of the diffusive transfer of methane in aqueous solution under high pressures near hydrate formation conditions within an optical capillary cell. Time-dependent Raman spectra of the solution at several different spots along the one-dimensional diffusion path were collected and thus the varying composition profile of the solution was monitored. Diffusion coefficients were estimated by the least squares method based on the variations in methane concentration data in space and time in the cell. The measured diffusion coefficients of methane in water at the liquid (L)-vapor (V) stable region and L-V metastable region are close to previously reported values determined at lower pressure and similar temperature. This in situ monitoring method was demonstrated to be suitable for the study of mass transfer in aqueous solution under high pressure and at various temperature conditions and will be applied to the study of nucleation and dissolution kinetics of methane hydrate in a hydrate-water system where the interaction of methane and water would be more complicated than that presented here for the L-V metastable condition. ?? 2006 Society for Applied Spectroscopy.
Lu, W J; Chou, I M; Burruss, R C; Yang, M Z
2006-02-01
A new method was developed for in situ study of the diffusive transfer of methane in aqueous solution under high pressures near hydrate formation conditions within an optical capillary cell. Time-dependent Raman spectra of the solution at several different spots along the one-dimensional diffusion path were collected and thus the varying composition profile of the solution was monitored. Diffusion coefficients were estimated by the least squares method based on the variations in methane concentration data in space and time in the cell. The measured diffusion coefficients of methane in water at the liquid (L)-vapor (V) stable region and L-V metastable region are close to previously reported values determined at lower pressure and similar temperature. This in situ monitoring method was demonstrated to be suitable for the study of mass transfer in aqueous solution under high pressure and at various temperature conditions and will be applied to the study of nucleation and dissolution kinetics of methane hydrate in a hydrate-water system where the interaction of methane and water would be more complicated than that presented here for the L-V metastable condition.
Forced convective heat transfer in curved diffusers
NASA Technical Reports Server (NTRS)
Rojas, J.; Whitelaw, J. H.; Yianneskis, M.
1987-01-01
Measurements of the velocity characteristics of the flows in two curved diffusers of rectangular cross section with C and S-shaped centerlines are presented and related to measurements of wall heat transfer coefficients along the heated flat walls of the ducts. The velocity results were obtained by laser-Doppler anemometry in a water tunnel and the heat transfer results by liquid crystal thermography in a wind tunnel. The thermographic technique allowed the rapid and inexpensive measurement of wall heat transfer coefficients along flat walls of arbitrary boundary shapes with an accuracy of about 5 percent. The results show that an increase in secondary flow velocities near the heated wall causes an increase in the local wall heat transfer coefficient, and quantify the variation for maximum secondary-flow velocities in a range from 1.5 to 17 percent of the bulk flow velocity.
Mass transfer mechanism in hydrophilic interaction chromatography.
Gritti, Fabrice; Guiochon, Georges
2013-08-09
The mass transfer mechanism in HILIC was investigated in depth. The reduced heights equivalent to a theoretical plate (HETP) of five low molecular weigh compounds with retention factors of -0.05 (slight exclusion from the surface due to the presence of a water-rich layer in which naphthalene is insoluble) to 3.64 were measured at room temperature for a 4.6mm×100mm column packed with 3.5μm 140Å XBridge HILIC particles in a wide range of flow velocities. The mobile phase was a buffered acetonitrile-water mixture (92.5/7.5, v/v). Using a physically reliable model of effective diffusion in binary composite media (Torquato's model), the longitudinal diffusion and solid-liquid mass transfer resistance reduced HETP terms were measured. The reduced short-range eddy dispersion HETP was taken from the literature data. The long-range reduced HETP was directly measured from the subtraction of these HETP terms to the overall HETP measured from moment analysis. In contrast to RPLC, the plots of the reduced HETP versus the reduced velocity depend weakly on the retention factor, due to the constant, low intra-particle diffusivity observed in HILIC. So, the reduced longitudinal diffusion HETP is smaller and the reduced solid-liquid mass transfer resistance HETP is larger in HILIC than in RPLC. Whereas border effects can be concealed in RPLC for retained analytes due to fast radial equilibration across the column diameter, a residual long-range eddy dispersion term persists in 4.6mm I.D. HILIC columns, even at very slow flow rates. Experiments show that the minor differences in the long-range eddy dispersion term between analytes having different retention factors is directly correlated to the reciprocal of their bulk diffusion coefficient. The performance of HILIC columns packed with fine particles is then more sensitive to the inlet sample distribution and to the outlet sample collection than RPLC columns due to the relatively poor radial mixing controlled by lateral diffusion.
Mass transfer between binary stars
NASA Technical Reports Server (NTRS)
Modisette, J. L.; Kondo, Y.
1980-01-01
The transfer of mass from one component of a binary system to another by mass ejection is analyzed through a stellar wind mechanism, using a model which integrates the equations of motion, including the energy equation, with an initial static atmosphere and various temperature fluctuations imposed at the base of the star's corona. The model is applied to several situations and the energy flow is calculated along the line of centers between the two binary components, in the rotating frame of the system, thereby incorporating the centrifugal force. It is shown that relatively small disturbances in the lower chromosphere or photosphere can produce mass loss through a stellar wind mechanism, due to the amplification of the disturbance propagating into the thinner atmosphere. Since there are many possible sources of the disturbance, the model can be used to explain many mass ejection phenomena.
NASA Technical Reports Server (NTRS)
Santoro, G. J.; Gokoglu, S. A.
1986-01-01
The application of a recently formulated vapor transport theory to predict deposition rates of corrosive salts from alkali-seeded combustion gases of a small-capacity, high-velocity, atmospheric-pressure burner rig was hampered by the relatively large dimensions of the cylindrical deposit collector compared to the diameter of the combustion gas stream. The relative dimensions lead to a highly nonadiabatic combustion gas flow around the collector and necessitate two series of experiments. In the first series, mass transfer coefficients are determined by utilizing the naphthalene sublimation technique. The second series of experiments determines the dilution effect on the sodium species concentrations due to the entrainment of ambient air. This second series involves the measurement of the temperature variation along the surface of the collector under steady state conditions. Vapor deposition rates are determined exploiting this information and the results are found to compare favorably with experimentally obtained rates.
NASA Astrophysics Data System (ADS)
Kandasamy, R.; Jeyabalan, C.; Sivagnana Prabhu, K. K.
2016-02-01
This article examines the influence of thermophoresis, Brownian motion of the nanoparticles with variable stream conditions in the presence of magnetic field on mixed convection heat and mass transfer in the boundary layer region of a semi-infinite porous vertical plate in a nanofluid under the convective boundary conditions. The transformed boundary layer ordinary differential equations are solved numerically using Maple 18 software with fourth-fifth order Runge-Kutta-Fehlberg method. Numerical results are presented both in tabular and graphical forms illustrating the effects of these parameters with magnetic field on momentum, thermal, nanoparticle volume fraction and solutal concentration boundary layers. The numerical results obtained for the velocity, temperature, volume fraction, and concentration profiles reveal interesting phenomenon, some of these qualitative results are presented through plots. It is interesting to note that the magnetic field plays a dominant role on nanofluid flow under the convective boundary conditions.
NASA Technical Reports Server (NTRS)
Santoro, G. J.; Gokoglu, S. A.
1988-01-01
The application of a recently formulated vapor transport theory to predict deposition rates of corrosive salts from alkali-seeded combustion gases of a small-capacity, high-velocity, atmospheric-pressure burner rig was hampered by the relatively large dimensions of the cylindrical deposit collector compared to the diameter of the combustion gas stream. The relative dimensions lead to a highly nonadiabatic combustion gas flow around the collector and necessitate two series of experiments. In the first series, mass transfer coefficients are determined by utilizing the naphthalene sublimation technique. The second series of experiments determines the dilution effect on the sodium species concentrations due to the entrainment of ambient air. This second series involves the measurement of the temperature variation along the surface of the collector under steady state conditions. Vapor deposition rates are determined exploiting this information and the results are found to compare favorably with experimentally obtained rates.
Reimus, Paul W
2010-12-08
A semi-analytical model was developed to conduct rapid scoping calculations of responses of thermally degrading and diffusing tracers in multi-well tracer tests in enhanced geothermal systems (EGS). The model is based on an existing Laplace transform inversion model for solute transport in dual-porosity media. The heat- and mass-transfer calculations are decoupled and conducted sequentially, taking advantage of the fact that heat transfer between fractures and the rock matrix is much more rapid than mass transfer and therefore mass transfer will effectively occur in a locally isothermal system (although the system will be nonisothermal along fracture flow pathways, which is accounted for by discretizing the flow pathways into multiple segments that have different temperature histories). The model takes advantage of the analogies between heat and mass transfer, solving the same governing equations with k{sub m}/({rho}C{sub p}){sub w} being substituted for {phi}D{sub m} in the equation for fracture transport and k{sub m}/({rho}C{sub p}){sub m} being subsituted for D{sub m} in the equation for matrix transport; where k = thermal conductivity (cal/cm-s-K), {rho} = density (g/cm{sup 3}), C{sub p} = heat capacity (at constant pressure) (cal/g-K), {phi} = matrix porosity, and D = tracer diffusion coefficient (cm{sup 2}/s), with the subscripts w and m referring to water and matrix, respectively. A significant advantage of the model is that it executes in a fraction of second on a single-CPU personal computer, making it very amenable for parameter estimation algorithms that involve repeated runs to find global minima. The combined thermal-mass transport model was used to evaluate the ability to estimate when thermal breakthrough would occur in a multi-well EGS configuration using thermally degrading tracers. Calculations were conducted to evaluate the range of values of Arrhenius parameters, A and E{sub {alpha}} (pre-exponential factor, 1/s, and activation energy, cal
PHREEQC. Geochemical Speciation Mass Transfer
Parkhurst, D.L.
1995-01-01
PHREEQC is designed to model geochemical reactions. Based on an ion association aqueous model, PHREEQC can calculate pH, redox potential, and mass transfer as a function of reaction progress. It can be used to describe geochemical processes for both far-field and near-field performance assessment and to evaluate data acquisition needs and test data. It can also calculate the composition of solutions in equilibrium with multiple phases. The data base, including elements, aqueous species, and mineral phases, is independent of the program and is completely user-definable. PHREEQC requires thermodynamic data for each solid, gaseous, or dissolved chemical species being modeled. The two data bases, PREPHR and DEQPAK7, supplied with PHREEQC are for testing purposes only and should not be applied to real problems without first being carefully examined. The conceptual model embodied in PHREEQC is the ion-association model of Pearson and Noronha. In this model a set of mass action equations are established for each ion pair (and controlling solid phases when making mass transfer calculations) along with a set of mass balance equations for each element considered. These sets of equations are coupled using activity coefficient values for each aqueous species and solved using a continued fraction approach for the mass balances combined with a modified Newton-Raphson technique for all other equations. The activity coefficient expressions in PHREEQC include the extended Debye-Huckel, WATEQ Debye-Huckel, and Davies equations from the original United States Geological Survey version of the program. The auxiliary preprocessor program PHTL, which is derived from EQTL, converts EQ3/6 thermodynamic data to PHREEQC format so that the two programs can be compared. PHREEQC can be used to determine solubility limits on the radionuclides present in the waste form. These solubility constraints may be input to the WAPPA leach model.
Efficient Heat and Mass Transfer Formulations for Oil Shale Retorting
NASA Astrophysics Data System (ADS)
Parker, J. C.; Zhang, F.
2007-12-01
A mathematical model for oil shale retorting is described that considers kerogen pyrolysis, oil coking, residual carbon gasification, carbonate mineral decomposition, water-gas shift, and phase equilibria reaction. Reaction rate temperature-dependence is described by Arrhenius kinetics. Fractured rock is modeled as a bi-continuum consisting of fracture porosity in which advective and dispersive gas and heat transport occur, and rock matrix in which diffusive mass transport and thermal conduction occur. Heat transfer between fracture and matrix regions is modeled either by a partial differential equation for spherical conduction or by a linear first-order heat transfer formulation. Mass transfer is modeled in an analogous manner or assuming local equilibrium. First-order mass and heat transfer coefficients are computed by a theoretical model from fundamental rock matrix properties. The governing equations are solved using a 3-D finite element formulation. Simulations of laboratory retort experiments and hypothetical problems indicated thermal disequilibrium to be the dominant factor controlling retort reactions. Simulation accuracy was unaffected by choice of mass transfer formulation. However, computational effort to explicitly simulate diffusive mass transfer in the rock matrix increased computational effort by more than an order of magnitude compared with first-order mass transfer or equilibrium analyses. A first-order heat transfer approximation of thermal conduction can be used without significant loss of accuracy if the block size and/or heating rate are not too large, as quantified by a proposed dimensionless heating rate.
Hsieh, Chiu-Lan; Peng, Chiung-Chi; Lin, Li-Yun; Cheng, Yu-Ting; Chen, Kuan-Chou; Peng, Robert Y
2009-01-01
The chorioallantoic membrane (CAM) assays have been intensively used to determine angiogenesis and anti-angiogenesis of medicines. In view of bioactivity, this technique should be performed with kinetic control regime in chicken embryos. Whether the dosages ever used had satisfied this requirement, we explored by mathematical analysis. A diffusion-in-egg model was established to describe several medicinal diffusions in egg white that involved the instantaneous transient kinetic behavior, the diffusion of medicines in capping volume (the volume from the air sac to the interface of egg yolk). By reviewing the diffusion of various compounds including the cited and the experimentals in this work, we conclude that all the CAM assays ever cited were performed under diffusion control regime rather than kinetic control, which may bring forth deviations caused by a diversity of constitutes in egg white through various medicine-protein interactions.
Mass transfer from bypassed zones during gas injection
Burger, J.E.; Mohanty, K.K.
1995-12-31
Gasflooding in oil reservoirs leads to bypassing of the oil due to gravitational, viscous and/or heterogeneity effects. The bypassed oil can be recovered by the flowing solvent by pressure-driven, gravity-driven, dispersion/diffusion-driven and capillarity-driven crossflow/mass transfer. It is difficult to represent all of these mechanisms explicitly in large-scale simulations. In this work, we have studied the effect of the orientation of the bypassed region and the enrichment of the solvent on the mass transfer. Laboratory-scale mass transfer and coreflood experiments were conducted. Numerical simulation was used to identify the role of the different mechanisms. Results indicate that the mass transfer is the least for the vertical orientation, intermediate for the inverted orientation and the highest for the horizontal orientation. The mass transfer increases with enrichment for all orientations. Liquid phase diffusion controls vertical orientation mass transfer for the fluids studied. Phase behavior determines the liquid phase saturation. Capillary pumping does not contribute to the mass transfer of oil because the interfacial tension decreases towards the flowing region. Gravity-driven flow contributes the most to the mass transfer in the horizontal and the inverted orientations. The gravity-driven flow, however, is impeded by the capillarity whose magnitude decreases with solvent enrichment. Oil recovery in the horizontal gasfloods is nonmonotonic with enrichment for this fluid system in an almost homogeneous Berea core. Multiphase flow in the near-miscible floods leads to less gravity override compared to the FCM floods. In the heterogeneous core studied, the heterogeneity is very strong and the capillary forces do not prevent bypassing. The capillary forces, in fact, reduce oil recovery by diminishing mass transfer from the bypassed regions.
Transport phenomena of crystal growth—heat and mass transfer
NASA Astrophysics Data System (ADS)
Rudolph, Peter
2010-07-01
Selected fundamentals of transport processes and their importance for crystal growth are given. First, principal parameters and equations of heat and mass transfer, like thermal flux, radiation and diffusion are introduced. The heat- and mass- balanced melt-solid and solution-solid interface velocities are derived, respectively. The today's significance of global numeric simulation for analysis of thermo-mechanical stress and related dislocation dynamics within the growing crystal is shown. The relation between diffusion and kinetic regime is discussed. Then, thermal and solutal buoyancy-driven and Marangoni convections are introduced. Their important interplay with the diffusion boundary layer, component and particle incorporation as well as morphological interface stability is demonstrated. Non-steady crystallization phenomena (striations) caused by convective fluctuations are considered. Selected results of global 3D numeric modeling are shown. Finally, advanced methods to control heat and mass transfer by external forces, such as accelerated container rotation, ultrasonic vibration and magnetic fields are discussed.
Mass transfer in a geologic environment
Zavoshy, S.J.; Chambre, P.L.; Pigford, T.H.
1984-11-01
A new analytical solution is presented that predicts the rate of dissolution of species from a waste package surrounded by a wet porous medium. By equating the rate of diffusive mass transfer into the porous rock to the rate of liquid-surface chemical reaction, an analytical solution for the time-dependent dissolution rate and the time-dependent concentration of dissolved species at the waste surface is obtained. From these results it is shown that for most of the important species in a package of radioactive waste the surface liquid quickly reaches near-saturation concentrations and the dissolution rate can be predicted by the simpler theory that assumes saturation concentrations in the surface liquid. 26 refs., 3 figs., 1 tab.
Heat and mass transfer in flames
NASA Technical Reports Server (NTRS)
Faeth, G. M.
1986-01-01
Heat- and mass-transfer processes in turbulent diffusion flames are discussed, considering turbulent mixing and the structure of single-phase flames, drop processes in spray flames, and nonluminous and luminous flame radiation. Interactions between turbulence and other phenomena are emphasized, concentrating on past work of the author and his associates. The conserved-scalar formalism, along with the laminar-flamelet approximation, is shown to provide reasonable estimates of the structure of gas flames, with modest levels of empiricism. Extending this approach to spray flames has highlighted the importance of drop/turbulence interactions; e.g., turbulent dispersion of drops, modification of turbulence by drops, etc. Stochastic methods being developed to treat these phenomena are yielding encouraging results.
Diffusion Of Mass In Evaporating Multicomponent Drops
NASA Technical Reports Server (NTRS)
Bellan, Josette; Harstad, Kenneth G.
1992-01-01
Report summarizes study of diffusion of mass and related phenomena occurring in evaporation of dense and dilute clusters of drops of multicomponent liquids intended to represent fuels as oil, kerosene, and gasoline. Cluster represented by simplified mathematical model, including global conservation equations for entire cluster and conditions on boundary between cluster and ambient gas. Differential equations of model integrated numerically. One of series of reports by same authors discussing evaporation and combustion of sprayed liquid fuels.
Dynamical mass transfer in cataclysmic binaries
NASA Technical Reports Server (NTRS)
Melia, Fulvio; Lamb, D. Q.
1987-01-01
When a binary comes into contact and mass transfer begins, orbital angular momentum is stored in the accretion disk until the disk couples tidally to the binary system. Taam and McDermott (1987) have suggested that this leads to unstable dynamical mass transfer in many cataclysmic variables in which mass transfer would otherwise be stable, and that it explains the gap between 2 and 3 h in the orbital period distribution of these systems. Here the consequences of this hypothesis for the evolution of cataclysmic binaries are explored. It is found that systems coming into contact longward of the period gap undergo one or more episodes of dynamical mass transfer.
How We Make Mass Transfer Seem Difficult.
ERIC Educational Resources Information Center
Cussler, E. L.
1984-01-01
Indicates that teaching of mass transfer can be improved by: (1) using a single, simple definition of mass transfer coefficients; (2) altering use of analogies; and (3) repeatedly stressing differences between mathematical models used for chemical reactions and the actual chemistry of these reactions. Examples for undergraduate/graduate courses…
A Simple Experiment for Mass Transfer.
ERIC Educational Resources Information Center
Rodriguez, Jesus M.; Henriquez, Vicente; Macias-Machin, Agustin
1998-01-01
Presents an experiment in which students use laboratory data to calculate the interphase mass transfer coefficient for a fluid passed over a sphere and obtain correlations for solid-gas mass transfer. Students develop a realistic mathematical model to describe the sublimation process. (DDR)
Binary stars: Mass transfer and chemical composition
NASA Technical Reports Server (NTRS)
Lambert, D. L.
1982-01-01
It is noted that mass exchange (and mass loss) within a binary system should produce observable changes in the surface chemical composition of both the mass losing and mass gaining stars as a stellar interior exposed to nucleosyntheses is uncovered. Three topics relating mass exchange and/or mass loss to nucleosynthesis are sketched: the chemical composition of Algol systems; the accretion disk of a cataclysmic variable fed by mass from a dwarf secondary star; and the hypothesis that classical Ba II giants result from mass transfer from a more evolved companion now present as a white dwarf.
The effects of dual-domain mass transfer on the tritium-helium-3 dating method.
Neumann, Rebecca B; Labolle, Eric M; Harvey, Charles F
2008-07-01
Diffusion of tritiated water (referred to as tritium) and helium-3 between mobile and immobile regions in aquifers (mass transfer) can affect tritium and helium-3 concentrations and hence tritium-helium-3 (3H/3He) ages that are used to estimate aquifer recharge and groundwater residence times. Tritium and helium-3 chromatographically separate during transport because their molecular diffusion coefficients differ. Simulations of tritium and helium-3 transport and diffusive mass transfer along stream tubes show that mass transfer can shift the 3H/3He age of the tritium and helium-3 concentration ([3H + 3He]) peak to dates much younger than the 1963 peak in atmospheric tritium. Furthermore, diffusive mass-transfer can cause the 3H/3He age to become younger downstream along a stream tube, even as the mean water-age must increase. Simulated patterns of [3H + 3He] versus 3H/3He age using a mass transfer model appear consistent with a variety of field data. These results suggest that diffusive mass transfer should be considered, especially when the [3H + 3He] peak is not well defined or appears younger than the atmospheric peak. 3H/3He data provide information about upstream mass-transfer processes that could be used to constrain mass-transfer models; however, uncritical acceptance of 3H/3He dates from aquifers with immobile regions could be misleading.
Theory of exciton transfer and diffusion in conjugated polymers
Barford, William; Tozer, Oliver Robert
2014-10-28
We describe a theory of Förster-type exciton transfer between conjugated polymers. The theory is built on three assumptions. First, we assume that the low-lying excited states of conjugated polymers are Frenkel excitons coupled to local normal modes, and described by the Frenkel-Holstein model. Second, we assume that the relevant parameter regime is ℏω < J, i.e., the adiabatic regime, and thus the Born-Oppenheimer factorization of the electronic and nuclear degrees of freedom is generally applicable. Finally, we assume that the Condon approximation is valid, i.e., the exciton-polaron wavefunction is essentially independent of the normal modes. The resulting expression for the exciton transfer rate has a familiar form, being a function of the exciton transfer integral and the effective Franck-Condon factors. The effective Franck-Condon factors are functions of the effective Huang-Rhys parameters, which are inversely proportional to the chromophore size. The Born-Oppenheimer expressions were checked against DMRG calculations, and are found to be within 10% of the exact value for a tiny fraction of the computational cost. This theory of exciton transfer is then applied to model exciton migration in conformationally disordered poly(p-phenylene vinylene). Key to this modeling is the assumption that the donor and acceptor chromophores are defined by local exciton ground states (LEGSs). Since LEGSs are readily determined by the exciton center-of-mass wavefunction, this theory provides a quantitative link between polymer conformation and exciton migration. Our Monte Carlo simulations indicate that the exciton diffusion length depends weakly on the conformation of the polymer, with the diffusion length increasing slightly as the chromophores became straighter and longer. This is largely a geometrical effect: longer and straighter chromophores extend over larger distances. The calculated diffusion lengths of ∼10 nm are in good agreement with experiment. The spectral
Discrete diffusion Monte Carlo for frequency-dependent radiative transfer
Densmore, Jeffrey D; Kelly, Thompson G; Urbatish, Todd J
2010-11-17
Discrete Diffusion Monte Carlo (DDMC) is a technique for increasing the efficiency of Implicit Monte Carlo radiative-transfer simulations. In this paper, we develop an extension of DDMC for frequency-dependent radiative transfer. We base our new DDMC method on a frequency-integrated diffusion equation for frequencies below a specified threshold. Above this threshold we employ standard Monte Carlo. With a frequency-dependent test problem, we confirm the increased efficiency of our new DDMC technique.
Ozone mass transfer and kinetics experiments
Bollyky, L.J.; Beary, M.M.
1981-12-01
Experiments were conducted at the Hanford Site to determine the most efficient pH and temperature levels for the destruction of complexants in Hanford high-level defense waste. These complexants enhance migration of radionuclides in the soil and inhibit the growth of crystals in the evaporator-crystallizer. Ozone mass transfer and kinetics tests have been outlined for the determination of critical mass transfer and kinetics parameters of the ozone-complexant reaction.
Simultaneous heat and mass transfer in a porous medium
NASA Astrophysics Data System (ADS)
Siang, H.
1981-11-01
Based upon the principle of irreversible thermodynamics, the macroscopic conservation laws of mass, momentum and energy, and equilibrium sorption of the porous concrete system, a set of basic equations for simultaneous mass and heat transfer is developed. An implicit finite difference technique is employed to solve this set of nonlinear partial differential equations. Numerical examples, using the theory developed, are illustrated to deepen the general understanding of the drying, thermal characteristics and related phenomena of hydrated concrete. The developed theoretical model is made nondimensional and an order of magnitude analysis is performed to elucidate the transport phenomenum of heat and mass occurring in a concrete body. In addition to diffusion, both the capillary and evaporation-condensation mechanisms, which are strongly affected by the topology of the porous concrete system, are important in the heat and mass transfer processes.
Educational Policy Diffusion and Transfer: The Case of Armenia
ERIC Educational Resources Information Center
Karakhanyan, Susanna; van Veen, Klaas; Bergen, Theo
2011-01-01
This paper explores the quality of the implementation of the West European Bologna reforms in higher education in a post-soviet country. This process of policy diffusion is analysed using concepts of policy diffusion/transfer and innovation literature, attempting to combine both streams of literature. Despite strong motivation to improve the…
Mass transfer cycles in cataclysmic variables
NASA Technical Reports Server (NTRS)
King, A. R.; Frank, J.; Kolb, U.; Ritter, H.
1995-01-01
It is well known that in cataclysmic variables the mass transfer rate must fluctuate about the evolutionary mean on timescales too long to be directly observable. We show that limit-cycle behavior can occur if the radius change of the secondary star is sensitive to the instantaneous mass transfer rate. The only reasonable way in which such a dependence can arise is through irradiation of this star by the accreting component. The system oscillates between high states, in which irradiation causes slow expansion of the secondary and drives an elevated transfer rate, and low states, in which this star contracts.
Calculating Mass Diffusion in High-Pressure Binary Fluids
NASA Technical Reports Server (NTRS)
Bellan, Josette; Harstad, Kenneth
2004-01-01
A comprehensive mathematical model of mass diffusion has been developed for binary fluids at high pressures, including critical and supercritical pressures. Heretofore, diverse expressions, valid for limited parameter ranges, have been used to correlate high-pressure binary mass-diffusion-coefficient data. This model will likely be especially useful in the computational simulation and analysis of combustion phenomena in diesel engines, gas turbines, and liquid rocket engines, wherein mass diffusion at high pressure plays a major role.
Rates of mass, momentum, and energy transfer at the magnetopause
NASA Technical Reports Server (NTRS)
Hill, T. W.
1979-01-01
Empirical estimates of the global rates of transfer of solar wind mass, tangential momentum, and energy at the Earth's magnetopause are presented for comparison against model estimates based on the four principal mechanisms that have been proposed to explain such transfer. The comparisons, although not quite conclusive, strongly favor a model that incorporates some combination of direct magnetic connection and anomalous cross field diffusion. An additional global constraint, the rate at which magnetic flux is cycled through the magnetospheric convection system, strongly suggests that direct magnetic connection plays a significant if not dominant role in the solar wind/magnetosphere interaction.
Varakin, A I; Mazur, V V; Arkhipova, N V; Serianov, Iu V
2009-01-01
Mathematical models of the transfer of charged macromolecules have been constructed on the basis of the classical equations of electromigration diffusion of Helmholtz-Smolukhovskii, Goldman, and Goldman-Hodgkin-Katz. It was shown that ion transfer in placental (mimicking lipid-protein barriers) and muscle barriers occurs by different mechanisms. In placental barriers, the electromigration diffusion occurs along lipid-protein channels formed due to the conformational deformation of phospholipid and protein molecules with the coefficients of diffusion D = (2.6-3.6) x 10(-8) cm2/s. The transfer in muscle barriers is due to the migration across charged interfibrillar channels with the negative diffusion activation energy, which is explained by changes in the structure of muscle fibers and expenditures of thermal energy for the extrusion of Cl- from channel walls with the diffusion coefficient D = (6.0-10.0) x 10(-6) cm2/s.
Thermodynamic evaluation of mass diffusion in ionic mixtures
Kagan, Grigory; Tang, Xian-Zhu
2014-02-15
The thermodynamic technique of Landau and Lifshitz originally developed for inter-species diffusion in a binary neutral gas mixture is extended to a quasi-neutral plasma with two ion species. It is shown that, while baro- and electro-diffusion coefficients depend on the choice of the thermodynamic system, prediction for the total diffusive mass flux is invariant.
Transfer number in fine bubble diffused aeration systems.
Capela, S; Roustan, M; Héduit, A
2001-01-01
On the basis of full-scale data from 58 clean water tests performed in 26 activated sludge tanks equipped with fine bubble diffusers and of a theoretical approach, it can be stated that fine bubble aeration systems with total floor coverage arrangement provide higher kLa values and the lowest spiral liquid circulation. An efficiency criterion for oxygen transfer (NT) was defined on the basis of the dimensional analysis. The transfer number NT allows us to take account of the impact of vertical liquid circulation movements on oxygen transfer. The values of NT calculated from the results of full scale nonsteady-state clean water tests vary from 5.3 x 10(-5) to 9.1 x 10(-5) and are directly dependent upon the arrangement of air diffusers. It has been shown that the highest transfer numbers corresponded to the total floor coverage arrangement and the average calculated NT values is 7.7 x 10(-5), independently of the diffuser density and of the gas velocity, over the ranges studied. The lowest transfer numbers are obtained when the diffusers are located in separate grids, and the transfer number is reduced with increasing air flow rate.
An Entrance Region Mass Transfer Experiment.
ERIC Educational Resources Information Center
Youngquist, G. R.
1979-01-01
This paper describes an experiment designed to reveal the consequences of the development of a concentration boundary layer. The rate of a mass transfer limited electrochemical reaction is measured and used to obtain the dependence of average Sherwood number on Reynolds number and entrance length. (Author/BB)
Overall Heat and Mass Transfer Coefficient of Water Vapor Adsorption
NASA Astrophysics Data System (ADS)
Hamamoto, Yoshinori; Mori, Hideo; Godo, Masazumi; Miura, Kunio; Watanabe, Yutaka; Ishizawa, Toshihiko; Takatsuka, Takeshi
A fundamental investigation was performed to develop a compact and simple desiccant ventilation unit which is one of the main components of a novel energy saving air-conditioning system. Water vapor in the air is adsorbed and/or desorbed to be controlled the humidity of supply air through a unit of an adsorbent rotor. A numerical simulation helps to understand the phenomena of heat and mass transfer in the rotor block. Overall transfer coefficients were estimated by performing both experiment and calculation. It was examined that the transient overall equivalent heat and mass transfer coefficient was not constant. It seems that both film fluid and diffusion resistance govern the coefficients in the block, and the influence of air flow on the time averaged coefficients is estimated by a considering the laminar forced convection from a flat plate. There is little difference of the coefficient between adsorption and desorption process. The correlation and fitting parameters are presented for prediction of the overall heat and mass transfer coefficients. The estimation accuracy was improved.
Zhu, H; Imai, T; Tani, K; Ukita, M; Sekine, M; Higuchi, T; Zhang, Z J
2007-05-01
Surface transfer and bubble transfer both contribute significantly to oxygen transfer in a diffused aeration system. In the present study, liquid-film-forming apparatus is successfully developed on a laboratory scale to improve considerably the surface transfer via the unique liquid film transfer technique. The experimental results show that the volumetric mass transfer coefficient for liquid-film-forming apparatus alone is found to be as much as 5.3 times higher than that for water surface and that the total volumetric mass transfer coefficient for liquid film aeration system increases by 37 % in comparison with conventional aeration system. Additionally, by tuning finely the structural parameters of the liquid-film-forming apparatus, it can also lead to high dissolved oxygen water with the dissolved oxygen percent saturation greater than 90 %. More importantly, this result is accomplished by simply offering a single-pass aeration at the depth as shallow as 26 cm. As a result, the objective of economical energy consumption in diffused aeration systems can be realized by lowering the aeration depth without sacrificing the aeration efficiency.
Orbital Transfer Vehicle Engine Technology High Velocity Ratio Diffusing Crossover
NASA Technical Reports Server (NTRS)
Lariviere, Brian W.
1992-01-01
High speed, high efficiency head rise multistage pumps require continuous passage diffusing crossovers to effectively convey the pumped fluid from the exit of one impeller to the inlet of the next impeller. On Rocketdyne's Orbital Transfer Vehicle (OTV), the MK49-F, a three stage high pressure liquid hydrogen turbopump, utilizes a 6.23 velocity ratio diffusing crossover. This velocity ratio approaches the diffusion limits for stable and efficient flow over the operating conditions required by the OTV system. The design of the high velocity ratio diffusing crossover was based on advanced analytical techniques anchored by previous tests of stationary two-dimensional diffusers with steady flow. To secure the design and the analytical techniques, tests were required with the unsteady whirling characteristics produced by an impeller. A tester was designed and fabricated using a 2.85 times scale model of the MK49-F turbopumps first stage, including the inducer, impeller, and the diffusing crossover. Water and air tests were completed to evaluate the large scale turbulence, non-uniform velocity, and non-steady velocity on the pump and crossover head and efficiency. Suction performance tests from 80 percent to 124 percent of design flow were completed in water to assess these pump characteristics. Pump and diffuser performance from the water and air tests were compared with the actual MK49-F test data in liquid hydrogen.
Orbital transfer vehicle engine technology high velocity ratio diffusing crossover
NASA Astrophysics Data System (ADS)
Lariviere, Brian W.
1992-12-01
High speed, high efficiency head rise multistage pumps require continuous passage diffusing crossovers to effectively convey the pumped fluid from the exit of one impeller to the inlet of the next impeller. On Rocketdyne's Orbital Transfer Vehicle (OTV), the MK49-F, a three stage high pressure liquid hydrogen turbopump, utilizes a 6.23 velocity ratio diffusing crossover. This velocity ratio approaches the diffusion limits for stable and efficient flow over the operating conditions required by the OTV system. The design of the high velocity ratio diffusing crossover was based on advanced analytical techniques anchored by previous tests of stationary two-dimensional diffusers with steady flow. To secure the design and the analytical techniques, tests were required with the unsteady whirling characteristics produced by an impeller. A tester was designed and fabricated using a 2.85 times scale model of the MK49-F turbopumps first stage, including the inducer, impeller, and the diffusing crossover. Water and air tests were completed to evaluate the large scale turbulence, non-uniform velocity, and non-steady velocity on the pump and crossover head and efficiency. Suction performance tests from 80 percent to 124 percent of design flow were completed in water to assess these pump characteristics. Pump and diffuser performance from the water and air tests were compared with the actual MK49-F test data in liquid hydrogen.
Batch uptake of lysozyme: effect of solution viscosity and mass transfer on adsorption.
Wright, P R; Muzzio, F J; Glasser, B J
1998-01-01
In this study, solid-phase adsorption by macroporous and hyper-diffusive resins was investigated in a batch uptake adsorption system to quantify solid-phase diffusion rates as a function of bulk phase viscosity. The performance of chromatographic resins used for adsorption of proteins is dependent on several factors including solid and liquid-phase diffusivity, boundary layer mass transfer, and intraparticle mass transfer effects. Understanding these effects is critical to process development and optimization of both packed and fluidized bed adsorption systems. The macroporous resin used here was Streamline SP, and the hyper-diffusive resin was S-HyperD LS. Both have been frequently used in fluidized bed adsorption of proteins; however, factors that affect uptake rates of these media are not well quantified. Adsorption isotherms were well represented by an empirical fit of a Langmuir isotherm. Solid-phase diffusion coefficients obtained from simulations were in agreement with other models for macroporous and hyper-diffusive particles. S-HyperD LS in the buffer system had the highest uptake rate, but increased bulk phase viscosity decreased the rate by approximately 50%. Increases in bulk phase viscosity increased film mass transfer effects, and uptake was observed to be a strong function of the film mass transfer coefficient. Uptake by Streamline SP particles was slower than S-HyperD in buffer, due to a greater degree of intraparticle mass transfer resistance. The effect of increased film mass transfer resistance coupled with intraparticle mass transfer resistances at an increased bulk phase viscosity resulted in a decrease of 80% in the uptake rate by Streamline SP relative to S-HyperD.
Gillot, S; Capela-Marsal, S; Roustan, M; Héduit, A
2005-04-01
The standard oxygenation performances of fine bubble diffused aeration systems in clean water, measured in 12 cylindrical tanks (water depth from 2.4 to 6.1m), were analysed using dimensional analysis. A relationship was established to estimate the scale-up factor for oxygen transfer, the transfer number (N(T)) The transfer number, which is written as a function of the oxygen transfer coefficient (k(L)a(20)), the gas superficial velocity (U(G)), the kinematic viscosity of water (nu) and the acceleration due to gravity (g), has the same physical meaning as the specific oxygen transfer efficiency. N(T) only depends on the geometry of the tank/aeration system [the total surface of the perforated membrane (S(p)), the surface of the tank (S) or its diameter (D), the total surface of the zones covered by the diffusers ("aerated area", S(a)) and the submergence of the diffusers (h)]. This analysis allowed to better describe the mass transfer in cylindrical tanks. Within the range of the parameters considered, the oxygen transfer coefficient (k(L)a(20)) is an increasing linear function of the air flow rate. For a given air flow rate and a given tank surface area, k(L)a(20) decreases with the water depth (submergence of the diffusers). For a given water depth, k(L)a(20) increases with the number of diffusers, and, for an equal number of diffusers, with the total area of the zones covered by the diffusers. The latter result evidences the superiority of the total floor coverage over an arrangement whereby the diffusers are placed on separate grids. The specific standard oxygen transfer efficiency is independent of the air flow rate and the water depth, the drop in the k(L)a(20) being offset by the increase of the saturation concentration. For a given tank area, the impact of the total surface of the perforated membrane (S(p)) and of the aerated area (S(a)) is the same as on the oxygen transfer coefficient.
Proton Transfer Reaction Ion Trap Mass Spectrometer
Prazeller, Peter; Palmer, Peter T.; Boscaini, Elena; Jobson, B Tom T.; Alexander, M. Lizabeth
2003-06-11
Proton transfer reaction mass spectrometry is a relatively new field that has attracted a great deal of interest in the last few years. This technique uses H₃Oþ as a chemical ionization (CI) reagent to measure volatile organic compounds (VOCs) in the parts per billion by volume (ppbv) to parts per trillion by volume (pptv) range. Mass spectra acquired with a proton transfer reaction mass spectrometer (PTR-MS) are simple because proton transfer chemical ionization is ‘soft’ and results in little or no fragmentation. Unfortunately, peak identification can still be difficult due to isobaric interferences. A possible solution to this problem is to couple the PTR drift tube to an ion trap mass spectrometer (ITMS). The use of an ITMS is appealing because of its ability to perform MS/MS and possibly distinguish between isomers and other isobars. Additionally, the ITMS duty cycle is much higher than that of a linear quadrupole so faster data acquisition rates are possible that will allow for detection of multiple compounds. Here we present the first results from a proton transfer reaction ion trap mass spectrometer (PTR-ITMS). The aim of this study was to investigate ion injection and storage efficiency of a simple prototype instrument in order to estimate possible detection limits of a second-generation instrument. Using this prototype a detection limit of 100 ppbv was demonstrated. Modifications are suggested that will enable further reduction in detection limits to the low-ppbv to high-pptv range. Furthermore, the applicability of MS/MS in differentiating between isobaric species was determined. MS/MS spectra of the isobaric compounds methyl vinyl ketone (MVK) and methacrolein (MACR) are presented and show fragments of different mass making differentiation possible, even when a mixture of both species is present in the same sample. However, MS/MS spectra of acetone and propanal produce fragments with the same molecular masses but with different intensity ratios
The diffusion approximation. An application to radiative transfer in clouds
NASA Technical Reports Server (NTRS)
Arduini, R. F.; Barkstrom, B. R.
1976-01-01
It is shown how the radiative transfer equation reduces to the diffusion equation. To keep the mathematics as simple as possible, the approximation is applied to a cylindrical cloud of radius R and height h. The diffusion equation separates in cylindrical coordinates and, in a sample calculation, the solution is evaluated for a range of cloud radii with cloud heights of 0.5 km and 1.0 km. The simplicity of the method and the speed with which solutions are obtained give it potential as a tool with which to study the effects of finite-sized clouds on the albedo of the earth-atmosphere system.
Predicting heat and mass transfer in fractured porous media (Invited)
NASA Astrophysics Data System (ADS)
Geiger, S.; Cortis, A.; Emmanuel, S.
2010-12-01
Fractures are abundant in the subsurface and affect many relevant single- and multi-phase transport processes such as gas and oil extraction, contaminant transport, or geothermal reservoir engineering. However, making reliable predictions of heat and mass transfer in fractured porous media is an outstanding challenge due to its multi-scale nature and the orders-of-magnitude varations in transport rates. Direct high-resolution simulations provide fundamental insights into the local advective and diffusive transport processes in fractured porous media. However, this approach is intractable for inverse simulations because of its high computational requirements. Continuous Time Random Walks on the other hand are a viable alternative and general way to model heat and mass transfer in structurally complex and multi-scale geological media, particularly for inverse problems. But they do not offer the same insights into local transport processes as direct numerical simulations. Here we combine both approaches to simulate the detailed transport processes occurring during heat and mass transfer in fractured porous media and analyse how these affect the breakthrough curves used to calibrate the Continuous Time Random Walks. We show that heat transport in fractured porous media can be anomalous, i.e. characterised by early breakthrough and long tailing, like it is well known for solute transport. We also demonstrate that a careful analysis of the solute breakthrough curves can yield insights into the heterogeneity of the fracture pattern and the transport occurring between fracture and matrix as well as within the matrix and fractures.
Personalized recommendation based on preferential bidirectional mass diffusion
NASA Astrophysics Data System (ADS)
Chen, Guilin; Gao, Tianrun; Zhu, Xuzhen; Tian, Hui; Yang, Zhao
2017-03-01
Recommendation system provides a promising way to alleviate the dilemma of information overload. In physical dynamics, mass diffusion has been used to design effective recommendation algorithms on bipartite network. However, most of the previous studies focus overwhelmingly on unidirectional mass diffusion from collected objects to uncollected objects, while overlooking the opposite direction, leading to the risk of similarity estimation deviation and performance degradation. In addition, they are biased towards recommending popular objects which will not necessarily promote the accuracy but make the recommendation lack diversity and novelty that indeed contribute to the vitality of the system. To overcome the aforementioned disadvantages, we propose a preferential bidirectional mass diffusion (PBMD) algorithm by penalizing the weight of popular objects in bidirectional diffusion. Experiments are evaluated on three benchmark datasets (Movielens, Netflix and Amazon) by 10-fold cross validation, and results indicate that PBMD remarkably outperforms the mainstream methods in accuracy, diversity and novelty.
Geoelectrical Measurement of Multi-Scale Mass Transfer Parameters
Day-Lewis, Frederick; Singha, Kamini; Haggerty, Roy; Johnson, Tim; Binley, Andrew; Lane, John
2014-01-16
measure mass transfer in-situ and estimate multi-scale and spatially variable mass-transfer parameters. The current lack of such techniques results in large parameter uncertainty, which in turn translates into enormous prediction uncertainty and cost to DOE. In this project, we considered three hydrogeophysical approaches for providing information about mass-transfer parameters: (1) the combination of electrical-resistivity tomography (ERT) and ionic tracer experiments to explore rates of exchange and relative mobile and immobile porosities; (2) complex resistivity (CR) measurements to infer the distribution of diffusive length scales active in a porous medium; and (3) nuclear magnetic resonance (NMR) to estimate mobile and immobile porosity.
The electronic transfer of information and aerospace knowledge diffusion
NASA Technical Reports Server (NTRS)
Pinelli, Thomas E.; Bishop, Ann P.; Barclay, Rebecca O.; Kennedy, John M.
1992-01-01
Increasing reliance on and investment in information technology and electronic networking systems presupposes that computing and information technology will play a motor role in the diffusion of aerospace knowledge. Little is known, however, about actual information technology needs, uses, and problems within the aerospace knowledge diffusion process. The authors state that the potential contributions of information technology to increased productivity and competitiveness will be diminished unless empirically derived knowledge regarding the information-seeking behavior of the members of the social system - those who are producing, transferring, and using scientific and technical information - is incorporated into a new technology policy framework. Research into the use of information technology and electronic networks by U.S. aerospace engineers and scientists, collected as part of a research project designed to study aerospace knowledge diffusion, is presented in support of this assertion.
A microscale turbine driven by diffusive mass flux.
Yang, Mingcheng; Liu, Rui; Ripoll, Marisol; Chen, Ke
2015-10-07
An external diffusive mass flux is shown to be able to generate a mechanical torque on a microscale object based on anisotropic diffusiophoresis. In light of this finding, we propose a theoretical prototype micro-turbine driven purely by diffusive mass flux, which is in strong contrast to conventional turbines driven by convective mass flows. The rotational velocity of the proposed turbine is determined by the external concentration gradient, the geometry and the diffusiophoretic properties of the turbine. This scenario is validated by performing computer simulations. Our finding thus provides a new type of chemo-mechanical response which could be used to exploit existing chemical energies at small scales.
Proton Transfer Reaction Ion Trap Mass Spectrometer
Prazeller, Peter; Palmer, Peter T.; Boscaini, Elena; Jobson, B Tom; Alexander, M. Lizabeth
2003-07-07
Proton Transfer Reaction Mass Spectrometry (PTR-MS) is a relatively new field that has attracted a great deal of interest in the last several years. This technique uses H3O+ as a chemical ionization (CI) agent for measuring volatile organic compounds (VOCs) in the parts per billion by volume (ppbv) - parts per trillion by volume (pptv) range. PTR-MS mass spectra are simple because the ionization method of proton transfer is “soft”, resulting in little or no fragmentation. Unfortunately, the simplicity of the mass spectra can cause problems in peak identification due to isobaric interferences. A possible solution to this problem is to couple the PTR drift tube to an ion trap mass spectrometer (ITMS). ITMS is appealing because of the ability to perform MS/MS and possibly distinguish between isomers and other isobars. Additionally, the ITMS duty cycle is much higher than that of a linear quadrupole so faster data acquisition rates can be realized for detection of multiple compounds. We present here the first results from a Proton Transfer Reaction Ion Trap Mass Spectrometer (PTR-ITMS). The aim of this study was to investigate ion injection and storage efficiency of a simple prototype interface in order to estimate possible detection limits of a second generation instrument. Using this prototype a detection limit of 100 ppbv was demonstrated for the PTR-ITMS. Modifications are suggested that will enable further reduction in detection limits to the low ppbv to pptv range. Furthermore the applicability of MS/MS to differentiate between isobaric species was determined. MS/MS spectra of the isobaric compounds methyl vinyl ketone (MVK) and methacrolein (MACR) are presented and show fragments of different mass making a differentiation possible even when a mixture of both species is present in the same sample. MS/MS spectra of acetone and propanal produce fragments with the same molecular weight but different ratios, allowing quantitative distinction only if one species
43 CFR 3106.4-3 - Mass transfers.
Code of Federal Regulations, 2012 CFR
2012-10-01
... 43 Public Lands: Interior 2 2012-10-01 2012-10-01 false Mass transfers. 3106.4-3 Section 3106.4-3... or Otherwise § 3106.4-3 Mass transfers. (a) A mass transfer may be utilized in lieu of the provisions... large number of Federal leases to the same transferee. (b) Three originally executed copies of the...
43 CFR 3106.4-3 - Mass transfers.
Code of Federal Regulations, 2013 CFR
2013-10-01
... 43 Public Lands: Interior 2 2013-10-01 2013-10-01 false Mass transfers. 3106.4-3 Section 3106.4-3... or Otherwise § 3106.4-3 Mass transfers. (a) A mass transfer may be utilized in lieu of the provisions... large number of Federal leases to the same transferee. (b) Three originally executed copies of the...
43 CFR 3106.4-3 - Mass transfers.
Code of Federal Regulations, 2014 CFR
2014-10-01
... 43 Public Lands: Interior 2 2014-10-01 2014-10-01 false Mass transfers. 3106.4-3 Section 3106.4-3... or Otherwise § 3106.4-3 Mass transfers. (a) A mass transfer may be utilized in lieu of the provisions... large number of Federal leases to the same transferee. (b) Three originally executed copies of the...
43 CFR 3106.4-3 - Mass transfers.
Code of Federal Regulations, 2011 CFR
2011-10-01
... 43 Public Lands: Interior 2 2011-10-01 2011-10-01 false Mass transfers. 3106.4-3 Section 3106.4-3... or Otherwise § 3106.4-3 Mass transfers. (a) A mass transfer may be utilized in lieu of the provisions... large number of Federal leases to the same transferee. (b) Three originally executed copies of the...
Turbulent mass transfer through a flat shear-free surface
NASA Astrophysics Data System (ADS)
Magnaudet, Jacques; Calmet, Isabelle
2006-04-01
Mass transfer through the flat shear-free surface of a turbulent open-channel flow is investigated over a wide range of Schmidt number (1 ≤ Sc ≤ 200) by means of large-eddy simulations using a dynamic subgrid-scale model. In contrast with situations previously analysed using direct numerical simulation, the turbulent Reynolds number Re is high enough for the near-surface turbulence to be fairly close to isotropy and almost independent of the structure of the flow in the bottom region (the statistics of the velocity field are identical to those described by I. Calmet & J. Magnaudet J. Fluid Mech. vol. 474, 2003, p. 355). The main statistical features of the concentration field are analysed in connection with the structure of the turbulent motion below the free surface, characterized by a velocity macroscale u and an integral length scale L. All near-surface statistical profiles are found to be Sc-independent when plotted vs. the dimensionless coordinate Sc({1) / 2}yu/nu (y is the distance to the surface and nu is the kinematic viscosity). Mean concentration profiles are observed to be linear throughout an inner diffusive sublayer whose thickness is about one Batchelor microscale, i.e. LSc({) - 1 / 2 }Re({) - 3 / 4}. In contrast, the concentration fluctuations are found to reach their maximum near the edge of the outer diffusive layer which scales as LSc({) - 1 / 2}Re({) - 1 / 2}. Instantaneous views of the near-surface isovalues of the concentration and vertical velocity are used to reveal the influence of the Schmidt number. In particular, it is observed that at high Schmidt number, the tiny concentration fluctuations that subsist in the diffusive sublayer just mirror the divergence of the two-component surface velocity field. Co-spectra of concentration and vertical velocity fluctuations indicate that the main contribution to the turbulent mass flux is provided by eddies whose horizontal size is close to L, which strongly supports the view that the mass
Kinetic study of the mass transfer of bovine serum albumin in anion-exchange chromatography.
Miyabe, K; Guiochon, G
2000-01-14
A kinetic study was made on the mass transfer phenomena of bovine serum albumin (BSA) in two different anion-exchange columns (Resource-Q and TSK-GEL-DEAE-5PW). The analysis of the concentration dependence of the lumped mass transfer rate coefficient (km,L) provided the information about the kinetics of the several mass transfer processes in the columns and the anion exchangers, i.e., the axial dispersion, the fluid-to-particle mass transfer, the intraparticle diffusion, and the adsorption/desorption. In the Resource-Q column, the intraparticle diffusion had a dominant contribution to the band broadening compared with those of the other processes. The surface diffusion coefficient (Ds) of BSA showed a positive concentration dependence, by which the linear dependence of km,L on the BSA concentration seemed to be interpreted. On the other hand, in the TSK-GEL-DEAE-5PW column, the contribution of the adsorption/desorption was also important and almost same as that due to the intraparticle diffusion. There are some differences between the intrinsic properties of the mass transfer kinetics inside the two anion exchangers. It was likely that the positive concentration dependence of Ds was explained by the heterogeneous surface model.
A mass transfer model for VOC emission from silage
NASA Astrophysics Data System (ADS)
Hafner, Sasha D.; Montes, Felipe; Rotz, C. Alan
2012-07-01
Silage has been shown to be an important source of emissions of volatile organic compounds (VOCs), which contribute to the formation of ground-level ozone. Measurements have shown that environmental conditions and silage properties strongly influence emission rates, making it difficult to assess the contribution of silage in VOC emission inventories. In this work, we present an analytical convection-diffusion-dispersion model for predicting emission of VOCs from silage. It was necessary to incorporate empirical relationships from wind tunnel trials for the response of mass transfer parameters to surface air velocity and silage porosity. The resulting model was able to accurately predict the effect of temperature on ethanol emission in wind tunnel trials, but it over-predicted alcohol and aldehyde emission measured using a mass balance approach from corn silage samples outdoors and within barns. Mass balance results confirmed that emission is related to gas-phase porosity, but the response to air speed was not clear, which was contrary to wind tunnel results. Mass balance results indicate that alcohol emission from loose silage on farms may approach 50% of the initial mass over six hours, while relative losses of acetaldehyde will be greater.
Self-diffusion of vibrational states: Impact on the heat transfer in hypersonic flows
NASA Astrophysics Data System (ADS)
Josyula, E.; Kustova, E. V.; Vedula, P.
2014-12-01
In the present paper, the influence of self-diffusion of vibrationally excited states on the fluid dynamics and surface heat transfer in an axisymmetric Mach 7.2 air flow past a sphere-cone is discussed. Two models for state-to-state transport properties are considered: a simplified model using the Eucken's relation for thermal conductivity and Fick's law for diffusion velocities with the constant Lewis number, and a rigorous kinetic theory based model for the calculation of state-specific thermal conductivity, diffusion and thermal diffusion coefficients. The simplified model is applied for the flowfield simulation to avoid high computational costs. For the application of the accurate kinetic theory approach, a post-processing procedure is used. Inclusion of self-diffusion results in an increase in the surface heat flux of up to 6.5% upstream of a shoulder region. Thermal conductivity is found to be the primary contributor to surface heat flux; the influence of mass and thermal diffusion is found to be negligible. Self-diffusion has a considerably greater influence in decreasing heat flux in the downstream regions far from stagnation point.
Simultaneous Heat and Mass Transfer Model for Convective Drying of Building Material
NASA Astrophysics Data System (ADS)
Upadhyay, Ashwani; Chandramohan, V. P.
2016-06-01
A mathematical model of simultaneous heat and moisture transfer is developed for convective drying of building material. A rectangular brick is considered for sample object. Finite-difference method with semi-implicit scheme is used for solving the transient governing heat and mass transfer equation. Convective boundary condition is used, as the product is exposed in hot air. The heat and mass transfer equations are coupled through diffusion coefficient which is assumed as the function of temperature of the product. Set of algebraic equations are generated through space and time discretization. The discretized algebraic equations are solved by Gauss-Siedel method via iteration. Grid and time independent studies are performed for finding the optimum number of nodal points and time steps respectively. A MATLAB computer code is developed to solve the heat and mass transfer equations simultaneously. Transient heat and mass transfer simulations are performed to find the temperature and moisture distribution inside the brick.
Interrupted Binary Mass Transfer in Star Clusters
NASA Astrophysics Data System (ADS)
Leigh, Nathan W. C.; Geller, Aaron M.; Toonen, Silvia
2016-02-01
Binary mass transfer (MT) is at the forefront of some of the most exciting puzzles of modern astrophysics, including SNe Ia, gamma-ray bursts, and the formation of most observed exotic stellar populations. Typically, the evolution is assumed to proceed in isolation, even in dense stellar environments such as star clusters. In this paper, we test the validity of this assumption via the analysis of a large grid of binary evolution models simulated with the SeBa code. For every binary, we calculate analytically the mean time until another single or binary star comes within the mean separation of the mass-transferring binary, and compare this timescale to the mean time for stable MT to occur. We then derive the probability for each respective binary to experience a direct dynamical interruption. The resulting probability distribution can be integrated to give an estimate for the fraction of binaries undergoing MT that are expected to be disrupted as a function of the host cluster properties. We find that for lower-mass clusters (≲ {10}4 {M}⊙ ), on the order of a few to a few tens of percent of binaries undergoing MT are expected to be interrupted by an interloping single, or more often binary, star, over the course of the cluster lifetime, whereas in more massive globular clusters we expect \\ll 1% to be interrupted. Furthermore, using numerical scattering experiments performed with the FEWBODY code, we show that the probability of interruption increases if perturbative fly-bys are considered as well, by a factor ˜2.
Effects of Rate-Limited Mass Transfer on Modeling Vapor Intrusion with Aerobic Biodegradation.
Chen, Yiming; Hou, Deyi; Lu, Chunhui; Spain, Jim C; Luo, Jian
2016-09-06
Most of the models for simulating vapor intrusion accept the local equilibrium assumption for multiphase concentration distributions, that is, concentrations in solid, liquid and vapor phases are in equilibrium. For simulating vapor transport with aerobic biodegradation controlled by counter-diffusion processes, the local equilibrium assumption combined with dual-Monod kinetics and biomass decay may yield near-instantaneous behavior at steady state. The present research investigates how predicted concentration profiles and fluxes change as interphase mass transfer resistances are increased for vapor intrusion with aerobic biodegradation. Our modeling results indicate that the attenuation coefficients for cases with and without mass transfer limitations can be significantly different by orders of magnitude. Rate-limited mass transfer may lead to larger overlaps of contaminant vapor and oxygen concentrations, which cannot be simulated by instantaneous reaction models with local equilibrium mass transfer. In addition, the contaminant flux with rate-limited mass transfer is much smaller than that with local equilibrium mass transfer, indicating that local equilibrium mass transfer assumption may significantly overestimate the biodegradation rate and capacity for mitigating vapor intrusion through the unsaturated zone. Our results indicate a strong research need for field tests to examine the validity of local equilibrium mass transfer, a widely accepted assumption in modeling vapor intrusion.
Early solar mass loss, element diffusion, and solar oscillation frequencies
Guzik, J.A.; Cox, A.N.
1994-07-01
Swenson and Faulkner, and Boothroyd et al. investigated the possibility that early main-sequence mass loss via a stronger early solar wind could be responsible for the observed solar lithium and beryllium depiction. This depletion requires a total mass loss of {approximately}0.1 M{circle_dot}, nearly independent of the mass loss timescale. We have calculated the evolution and oscillation frequencies of solar models including helium and element diffusion, and such early solar mass loss. We show that extreme mass loss of 1 M{circle_dot} is easily ruled out by the low-degree p-modes that probe the solar center and sense the steeper molecular weight gradient produced by the early phase of more rapid hydrogen burning. The effects on central structure are much smaller for models with an initial mass of 1.1 M{circle_dot} and exponentially-decreasing mass loss irate with e-folding timescale 0.45 Gyr. While such mass loss slightly worsens the agreement between observed and calculated low-degree modes, the observational uncertainties of several tenths of a microhertz weaken this conclusion. Surprisingly, the intermediate-degree modes with much smaller observational uncertainties that probe the convection zone bottom prove to be the key to discriminating between models: The early mass loss phase decreases the total amount of helium and heavier elements diffused from the convection zone, and the extent of the diffusion produced composition gradient just below the convection zone, deteriorating the agreement with observed frequencies for these modes. Thus it appears that oscillations can also rule out this smaller amount of gradual early main-sequence mass loss in the young Sun. The mass loss phase must be confined to substantially under a billion years, probably 0.5 Gyr or less, to simultaneously solve the solar Li/Be problem and avoid discrepancies with solar oscillation frequencies.
Drop oscillation and mass transfer in alternating electric fields
Carleson, T.E.; Yang, W.
1991-05-30
After the second annual progress report to DOE in July 1990, we continued the experimental work for another liquid system. The mathematical model was also improved to include secondary effects due to drop deformation and charge redistribution on the deformed drop surface. Originally, we planned to study a mass transfer process after the hydrodynamic modelling. Due to difficulty in measuring drop concentration during oscillations, we decided to study a heat transfer process instead. Using the analogy between the mass transfer and the heat transfer, we can easily extend the results for the heat transfer study to the mass transfer problem.
Reacting viscous-shock-layer solutions with multicomponent diffusion and mass injection
NASA Technical Reports Server (NTRS)
Moss, J. N.
1974-01-01
Numerical solutions of the viscous-shock-layer equation where the chemistry is treated as being either frozen, equilibrium, or nonequilibrium are presented. Also the effects of the diffusion model, surface catalysis, and mass injection on surface transport and flow parameters are considered. The flow is treated as a mixture of five inert and thermally perfect species. The viscous-shock-layer equations are solved by using an implicit-difference scheme. All calculations are for hyperboloids with included angles of 20 and 45. The flight conditions are those for various altitudes and velocities in the earth's atmosphere. Data are presented to show the effects of the chemical models; diffusion models; surface catalysis; and mass injection of air on heat transfer; skin friction; shock standoff distance; wall pressure distribution; and tangential velocity, temperature, and species profiles. The results show that an equilibrium analysis can substantially overpredict the heat-transfer rates for flow conditions experienced by earth-orbital entry vehicles. Moreover, at such conditions surface catalysis significantly influences heat-transfer and flow-field properties. If a binary rather than a multicomponent diffusion model is assumed, negligible errors in most flow properties result. Quantitative results are presented that show the effect of mass injection on flow properties within and downstream of the injection region.
Thermophoretically augmented mass transfer rates to solid walls across laminar boundary layers
NASA Technical Reports Server (NTRS)
Gokoglu, S. A.; Rosner, D. E.
1986-01-01
Predictions of mass transfer (heavy vapor and small particle deposition) rates to solid walls, including the effects of thermal (Soret) diffusion ('thermophoresis' for small particles), are made by numerically solving the two-dimensional self-similar forced convection laminar boundary-layer equations with variable properties, covering the particle size range from vapor molecules up to the size threshold for inertial (dynamical nonequilibrium) effects. The effect of thermophoresis is predicted to be particularly important for submicron particle deposition on highly cooled solid surfaces, with corresponding enhancement factors at atmospheric conditions being over a thousand-fold at T(w)/T(e) equal to about 0.6. As a consequence of this mass transfer mechanism, the particle size dependence of the mass transfer coefficient to a cooled wall will be much weaker than for the corresponding case of isothermal capture by Brownian-convective diffusion.
Coste, P.; Bestion, D.
1995-09-01
This paper presents a simple modelling of mass diffusion effects on condensation. In presence of noncondensable gases, the mass diffusion near the interface is modelled using the heat and mass transfer analogy and requires normally an iterative procedure to calculate the interface temperature. Simplifications of the model and of the solution procedure are used without important degradation of the predictions. The model is assessed on experimental data for both film condensation in vertical tubes and direct contact condensation in horizontal tubes, including air-steam, Nitrogen-steam and Helium-steam data. It is implemented in the Cathare code, a french system code for nuclear reactor thermal hydraulics developed by CEA, EDF, and FRAMATOME.
Diffusion and phase change characterization by mass spectrometry
NASA Technical Reports Server (NTRS)
Koslin, M. E.; White, F. A.
1979-01-01
The high temperature diffusion of trace elements in metals and alloys was investigated. Measurements were made by high sensitivity mass spectrometry in which individual atoms were detected, and quantitative data was obtained for zircaloy-2, 304 stainless steel, and tantalum. Additionally, a mass spectrometer was also an analytical tool for determining an allotropic phase change for stainless steel at 955 C, and a phase transition region between 772 C and 1072 C existing for zircaloy-2. Diffusion rates were measured in thin (0.001" (0.0025 cm) and 0.0005" (0.0013 cm)) ribbons which were designed as high temperature thermal ion sources, with the alkali metals as naturally occurring impurities. In the temperature and pressure regime where diffusion measurements were made, the solute atoms evaporated from the ribbon filaments when the impurities diffused to the surface, with a fraction of these impurity atoms ionized according to the Langmuir-Saha relation. The techniques developed can be applied to many other alloys important to space vehicles and supersonic transports; and, with appropriate modifications, to the diffusion of impurities in composites.
Methods and problems in heat and mass transfer
NASA Astrophysics Data System (ADS)
Kotliar, Iakov Mikhailovich; Sovershennyi, Viacheslav Dmitrievich; Strizhenov, Dmitrii Sergeevich
The book focuses on the mathematical methods used in heat and mass transfer problems. The theory, statement, and solution of some problems of practical importance in heat and mass transfer are presented, and methods are proposed for solving algebraic, transcendental, and differential equations. Examples of exact solutions to heat and mass transfer equations are given. The discussion also covers some aspects of the development of a mathematical model of turbulent flows.
Tube-side mass transfer for hollow fibre membrane contactors operated in the low Graetz range.
Wang, C Y; Mercer, E; Kamranvand, F; Williams, L; Kolios, A; Parker, A; Tyrrel, S; Cartmell, E; McAdam, E J
2017-02-01
Transformation of the tube-side mass transfer coefficient derived in hollow fibre membrane contactors (HFMC) of different characteristic length scales (equivalent diameter and fibre length) has been studied when operated in the low Graetz range (Gz<10). Within the low Gz range, mass transfer is generally described by the Graetz problem (Sh=3.67) which assumes that the concentration profile comprises a constant shape over the fibre radius. In this study, it is experimentally evidenced that this assumption over predicts mass transfer within the low Graetz range. Furthermore, within the low Gz range (below 2), a proportional relationship between the experimentally determined mass transfer coefficient (Kov ) and the Graetz number has been identified. For Gz numbers below 2, the experimental Sh number approached unity, which suggests that mass transfer is strongly dependent upon diffusion. However, within this diffusion controlled region of mass transfer, tube-side fluid velocity remained important. For Gz numbers above 2, Sh could be satisfactorily described by extension to the Lévêque solution, which can be ascribed to the constrained growth of the concentration boundary layer adjacent to the fibre wall. Importantly this study demonstrates that whilst mass transfer in the low Graetz range does not explicitly conform to either the Graetz problem or classical Lévêque solution, it is possible to transform the experimentally derived overall mass transfer coefficient (Kov ) between characteristic length scales (dh and L). T h is was corroborated by comparison of the empirical relationship determined in this study (Sh=0.36Gz) with previously published studies operated in the low Gz range. This analysis provides important insight for process design when slow tube-side flows, or low Schmidt numbers (coincident with gases) constrain operation of hollow fibre membrane contactors to the low Gz range.
NASA Technical Reports Server (NTRS)
Pollmann, Konrad W.; Stodieck, Louis S.; Luttges, Marvin W.
1994-01-01
Microgravity can provide a diffusion-dominated environment for double-diffusion and diffusion-reaction experiments otherwise disrupted by buoyant convection or sedimentation. In sliding solvent diffusion cells, a diffusion interface between two liquid columns is achieved by aligning two offset sliding wells. Fluid in contact with the sliding lid of the cavities is subjected to an applied shear stress. The momentum change by the start/stop action of the well creates an additional hydrodynamical force. In microgravity, these viscous and inertial forces are sufficiently large to deform the diffusion interface and induce hydrodynamic transfer between the wells. A series of KC-135 parabolic flight experiments were conducted to characterize these effects and establish baseline data for microgravity diffusion experiments. Flow visualizations show the diffusion interface to be deformed in a sinusoidal fashion following well alignment. After the wells were separated again in a second sliding movement, the total induced liquid transfer was determined and normalized by the well aspect ratio. The normalized transfer decreased linearly with Reynolds number from 3.3 to 4.0% (w/v) for Re = 0.4 (Stokes flow) to a minimum of 1.0% for Re = 23 to 30. Reynolds numbers that provide minimum induced transfers are characterized by an interface that is highly deformed and unsuitable for diffusion measurements. Flat diffusion interfaces acceptable for diffusion measurements are obtained with Reynolds numbers on the order of 7 to 10. Microgravity experiments aboard a sounding rocket flight verified counterdiffusion of different solutes to be diffusion dominated. Ground control experiments showed enhanced mixing by double-diffusive convection. Careful selection of experimental parameters improves initial conditions and minimizes induced transfer rates.
Mass transfer and transport in a geologic environment
Chambre, P.L.; Pigford, T.H.; Lee, W.W.L.; Ahn, J.; Kajiwara, S.; Kim, C.L.; Kimura, H.; Lung, H.; Williams, W.J.; Zavoshy, S.J.
1985-04-01
This report is in a continuing series of reports that present analytic solutions for the dissolution and hydrogeologic transport of radionuclides from geologic repositories of nuclear waste. Previous reports have dealt mainly with radionuclide transport in the far-field, away from the effects of the repository. In the present report, the emphasis is on near-field processes, the transfer and transport of radionuclides in the vicinity of the waste packages. The primary tool used in these analyses is mass transfer theory from chemical engineering. The thrust of our work is to develop methods for predicting the performance of geologic repositories. The subjects treated in the present report are: radionuclide transport from a spherical-equivalent waste form through a backfill; analysis of radionuclide transport through a backfill using a non-linear sorption isotherm; radionuclide transport from a prolate spheroid-equivalent waste form with a backfill; radionuclide transport from a spherical-equivalent waste form through a backfill, where the solubility, diffusivity and retardation coefficients are temperature dependent; a coupled near-field, far-field analysis where dissolution and migration rates are temperature dependent; transport of radionuclides from a point source in a three-dimensional flow field; and a general solution for the transport of radioactive chains in geologic media. There are several important results from the numerical evaluations. First, radioactive decay, higher sorption in the rock and the backfill steepens the gradient for mass transfer, and lead to higher dissolution rates. This is contrary to what was expected by some other workers, but is shown clearly in the analytical solutions. Second, the backfill serves to provide sorption sites so that there is a delay in the arrival of radionuclides in the rock, although this effect is not so important for the steady-state transport of long-lived radionuclides.
NASA Technical Reports Server (NTRS)
Deissler, Robert G
1955-01-01
The expression for eddy diffusivity from a previous analysis was modified in order to account for the effect of kinematic viscosity on the turbulence in the region close to a wall. By using the modified expression, good agreement was obtained between predicted and experimental results for heat and mass transfer at Prandtl and Schmidt numbers between 0.5 and 3000. The effects of length-to-diameter ratio and of variable viscosity were also investigated for a wide range of Prandtl numbers.
Probing mass transfer in mesoporous faujasite-type zeolite nanosheet assemblies.
Mehlhorn, Dirk; Inayat, Alexandra; Schwieger, Wilhelm; Valiullin, Rustem; Kärger, Jörg
2014-06-06
Pulsed field gradient nuclear magnetic resonance (NMR) diffusion studies are performed by using cyclohexane to probe transport properties in a NaX-type zeolite with a hierarchical pore structure (house-of-cards-like assemblies of mesoporous nanosheets), which is compared with a purely microporous sample. With guest loadings chosen to ensure saturation of the micropores, and the meso- and macropores left essentially unoccupied, guest diffusion is shown to be enhanced by almost one order of magnitude, even at room temperature. Diffusivity enhancement is further increased with increasing temperature, which may, therefore, be unambiguously attributed to the contribution of mass transfer in the meso- and macropores.
Neutrino diffusion and mass ejection in protoneutron stars
Almeida, L. G.; Rodrigues, H.; Portes, D. Jr.; Duarte, S. B.
2010-11-15
We discuss the mass ejection mechanism induced by diffusion of neutrino during the early stage of the protoneutron star cooling. A dynamical calculation is employed in order to determine the amount of matter ejected and the remnant compact object mass. An equation of state considering hadronic and quark phases for the stellar dense matter was used to solve the whole time evolution of the system during the cooling phase. The initial neutrino population was obtained by considering beta equilibrium in the dense stellar matter with confined neutrinos, in the very early period of the deleptonic stage of the nascent pulsar. For specified initial configurations of the protoneutron star, we solve numerically the set of equations of motion together with neutrino diffusion through the dense stellar medium.
Image quality transfer and applications in diffusion MRI.
Alexander, Daniel C; Zikic, Darko; Ghosh, Aurobrata; Tanno, Ryutaro; Wottschel, Viktor; Zhang, Jiaying; Kaden, Enrico; Dyrby, Tim B; Sotiropoulos, Stamatios N; Zhang, Hui; Criminisi, Antonio
2017-03-03
This paper introduces a new computational imaging technique called image quality transfer (IQT). IQT uses machine learning to transfer the rich information available from one-off experimental medical imaging devices to the abundant but lower-quality data from routine acquisitions. The procedure uses matched pairs to learn mappings from low-quality to corresponding high-quality images. Once learned, these mappings then augment unseen low quality images, for example by enhancing image resolution or information content. Here, we demonstrate IQT using a simple patch-regression implementation and the uniquely rich diffusion MRI data set from the human connectome project (HCP). Results highlight potential benefits of IQT in both brain connectivity mapping and microstructure imaging. In brain connectivity mapping, IQT reveals, from standard data sets, thin connection pathways that tractography normally requires specialised data to reconstruct. In microstructure imaging, IQT shows potential in estimating, from standard "single-shell" data (one non-zero b-value), maps of microstructural parameters that normally require specialised multi-shell data. Further experiments show strong generalisability, highlighting IQT's benefits even when the training set does not directly represent the application domain. The concept extends naturally to many other imaging modalities and reconstruction problems.
Instability of mass transfer in a planet-star system
NASA Astrophysics Data System (ADS)
Jia, Shi; Spruit, H. C.
2017-02-01
We show that the angular momentum exchange mechanism governing the evolution of mass-transferring binary stars does not apply to Roche lobe filling planets, because most of the angular momentum of the mass-transferring stream is absorbed by the host star. Apart from a correction for the difference in specific angular momentum of the stream and the centre of mass of the planet, the orbit does not expand much on Roche lobe overflow. We explore the conditions for dynamically unstable Roche lobe overflow as a function of planetary mass and mass and radius (age) of host star and equation of state of planet. For a Sun-like host, gas giant planets in a range of mass and entropy can undergo dynamical mass transfer. Examples of the evolution of the mass transfer process are given. Dynamic mass transfer of rocky planets depends somewhat sensitively on equation of state used. Silicate planets in the range 1 < Mp < 10 M⊕ typically go through a phase of dynamical mass transfer before settling to slow overflow when their mass drops to less than 1 M⊕.
A mass transfer model of bauxite formation
Soler, J.M.; Lasaga, A.C.
1996-12-01
The formation of bauxite due to weathering of a granitic protolith has been simulated by means of a one-dimensional flow and reaction model based on the mass transfer principle. The model couples mineral dissolution and precipitation reactions, speciation in solution, and advective solute transport in a porous medium. A very important aspect of the modeling study is the use of mineral reaction rates determined experimentally in the laboratory. The important effects of solution saturation state and pH have been incorporated into the kinetic rate laws governing the heterogeneous reactions. The values of these parameters have been obtained from the scientific literature to guarantee that realistic reaction rates are used in the simulations. Albite and quartz are the minerals that make up the parent rock in the model. Gibbsite, kaolinite, and a Na-mica (as a surrogate for smectite) are the secondary minerals that have been taken into account. Long-term simulations (>1 Ma) have been run, and the formation of a bauxitic profile, with an upper gibbsite-rich and a lower kaolinite-rich zone, is predicted. In early stages of the process (up to a few hundreds of thousands of years), both gibbsite and kaolinite precipitate directly from solution as a consequence of albite dissolution. In later stages, the bulk of gibbsite precipitation derives from the incongruent dissolution of kaolinite, while kaolinite precipitation is still caused by the dissolution of albite. This is also reflected by the formation of two reaction fronts in the profile. These results are compared with weathering sequences from the Los Pijiguaos bauxite deposit, Venezuela. The overlap between the gibbsite and kaolinite zones and the replacement of kaolinite by gibbsite are consistent with model calculations. 59 refs., 22 figs., 1 tab.
NASA Technical Reports Server (NTRS)
Rosner, D. E.
1985-01-01
The effects of Soret diffusion (for vapors) and thermophoresis (for particles) are illustrated using recent optical experiments and boundary layer computations. Mass transfer rate augmentations of up to a factor of 1000 were observed and predicted for submicron-particle capture by cooled solid surfaces, while mass transfer suppressions of more than 10 to the -10th-fold were predicted for 'overheated' surfaces. It is noted that the results obtained are of interest in connection with such technological applications as fly-ash capture in power generation equipment and glass droplet deposition in optical-waveguide manufacture.
Diffusion-weighted magnetic resonance imaging in cystic renal masses
Balyemez, Fikret; Aslan, Ahmet; Inan, Ibrahim; Ayaz, Ercan; Karagöz, Vildan; Özkanli, Sıdıka Şeyma; Acar, Murat
2017-01-01
Introduction: We aimed to introduce the diagnostic value of diffusion-weighted (DWI) magnetic resonance imaging (MRI) for distinguishing benign and malignant renal cystic masses. Methods: Abdominal DWI-MRIs of patients with Bosniak categories 2F, 3, and 4 cystic renal masses were evaluated retrospectively. Cystic masses were assigned as benign or malignant according to histopathological or followup MRI findings and compared with apparent diffusion coefficient (ADC) values. Results: There were 30 patients (18 males and 12 females, mean age was 59.23 ± 12.08 years [range 38–83 years]) with cystic renal masses (eight Bosniak category 2F, 12 Bosniak category 3, 10 Bosniak category 4). Among them, 14 cysts were diagnosed as benign and 16 as malignant by followup imaging or histopathological findings. For the malignant lesions, the mean ADC values were lower than for benign lesions (p=0.001). An ADC value of ≤2.28 ×10−6 mm2/s or less had a sensitivity of 75% and a specificity of 92.86% for detecting malignancy. Conclusions: ADC can improve the diagnostic performance of MRI in the evaluation of complex renal cysts when used together with conventional MRI sequences. PMID:28163806
Numerical study on heat and mass transfer in hygroscopic rotor during sorption process
NASA Astrophysics Data System (ADS)
Shin, Hyun-Geun; Park, Il Seouk
2016-06-01
Recently, interest in hygroscopic dehumidifiers has rapidly increased in the indoor environment industry because of their potential contribution to the development of hybrid (refrigerating + hygroscopic) dehumidifiers. Heat and mass transport phenomena such as adsorption and desorption, and their complex interactions occur in a desiccant rotor, which comprises many small hygroscopic channels. This study numerically investigated the conjugated heat and mass transfers in a channel modeled with the flow and porous desiccant regions, where only ordinary and surface diffusions (excluding Knudsen diffusion) during the sorption processes were considered. The change in the dehumidification performance depending on operating conditions such as the rotor's rotating speed, air flow rate, and adsorption-desorption ratio, was examined under various working environments. The temporal and spatial variations in the temperature, vapor mass fraction, and liquid water mass fraction in the channel were considered in detail. The closely linked heat and mass transports were clarified for a better understanding of the sorption processes in the desiccant rotor.
Numerical study on heat and mass transfer in hygroscopic rotor during sorption process
NASA Astrophysics Data System (ADS)
Shin, Hyun-Geun; Park, Il Seouk
2017-02-01
Recently, interest in hygroscopic dehumidifiers has rapidly increased in the indoor environment industry because of their potential contribution to the development of hybrid (refrigerating + hygroscopic) dehumidifiers. Heat and mass transport phenomena such as adsorption and desorption, and their complex interactions occur in a desiccant rotor, which comprises many small hygroscopic channels. This study numerically investigated the conjugated heat and mass transfers in a channel modeled with the flow and porous desiccant regions, where only ordinary and surface diffusions (excluding Knudsen diffusion) during the sorption processes were considered. The change in the dehumidification performance depending on operating conditions such as the rotor's rotating speed, air flow rate, and adsorption-desorption ratio, was examined under various working environments. The temporal and spatial variations in the temperature, vapor mass fraction, and liquid water mass fraction in the channel were considered in detail. The closely linked heat and mass transports were clarified for a better understanding of the sorption processes in the desiccant rotor.
Influence of drying air parameters on mass transfer characteristics of apple slices
NASA Astrophysics Data System (ADS)
Beigi, Mohsen
2016-10-01
To efficiently design both new drying process and equipment and/or to improve the existing systems, accurate values of mass transfer characteristics are necessary. The present study aimed to investigate the influence of drying air parameters (i.e. temperature, velocity and relative humidity) on effective diffusivity and convective mass transfer coefficient of apple slices. The Dincer and Dost model was used to determine the mass transfer characteristics. The obtained Biot number indicated that the moisture transfer in the apple slices was controlled by both internal and external resistance. The effective diffusivity and mass transfer coefficient values obtained to be in the ranges of 7.13 × 10-11-7.66 × 10-10 and 1.46 × 10-7-3.39 × 10-7 m s-1, respectively and the both of them increased with increasing drying air temperature and velocity, and decreasing relative humidity. The validation of the model showed that the model predicted the experimental drying curves of the samples with a good accuracy.
NASA Astrophysics Data System (ADS)
Ghanbarian, Davoud; Baraani Dastjerdi, Mojtaba; Torki-Harchegani, Mehdi
2016-05-01
An accurate understanding of moisture transfer parameters, including moisture diffusivity and moisture transfer coefficient, is essential for efficient mass transfer analysis and to design new dryers or improve existing drying equipments. The main objective of the present study was to carry out an experimental and theoretical investigation of mushroom slices drying and determine the mass transfer characteristics of the samples dried under different conditions. The mushroom slices with two thicknesses of 3 and 5 mm were dried at air temperatures of 40, 50 and 60 °C and air flow rates of 1 and 1.5 m s-1. The Dincer and Dost model was used to determine the moisture transfer parameters and predict the drying curves. It was observed that the entire drying process took place in the falling drying rate period. The obtained lag factor and Biot number indicated that the moisture transfer in the samples was controlled by both internal and external resistance. The effective moisture diffusivity and the moisture transfer coefficient increased with increasing air temperature, air flow rate and samples thickness and varied in the ranges of 6.5175 × 10-10 to 1.6726 × 10-9 m2 s-1 and 2.7715 × 10-7 to 3.5512 × 10-7 m s-1, respectively. The validation of the Dincer and Dost model indicated a good capability of the model to describe the drying curves of the mushroom slices.
Observing Mass Transfer in a Neglected Interacting Binary Star
NASA Astrophysics Data System (ADS)
Reed, Phillip A.
2011-05-01
The eclipsing and interacting binary star R Arae is a very interesting system that has unfortunately been neglected. The few spectroscopic studies of the system report badly blended absorption lines that indicate mass transfer, but until now there has been no orbital period study to conclusively show a real period change resulting from mass transfer. In this study, new data are combined with those found in the available literature and in the database of the American Association of Variable Star Observers to construct the first ephemeris curve for R Ara, which spans more than a century since its discovery in 1894. Average orbital period change and conservative mass transfer rates are presented.
Effect of mass transfer resistance on the Lineweaver-Burk plots for flocculating microorganisms.
Ngian, K F; Lin, S H; Martin, W R
1977-12-01
It is shown that the mass transfer resistance can significantly distort the linearity of the Lineweaver-Burk plot of the kinetic data for a microbial culture which forms aggregates. For small flocs, the linearity of the Lineweaver-Burk plot is largely retained, but a different slope and intercept will be obtained compared with flocs free from mass transfer resistance. For large flocs, the Lineweaver-Burk plot shows pronounced curvature at high limiting substrate concentrations. Hence, if the true intrinsic kinetic parameters are to be extracted from a highly flocculating microbial culture, sufficient agitation has to be provided to remove the effect of mass transfer resistance. If the behavior of the flocculating microbial culture is to be explored, additional values for some physical parameters, such as the effective diffusion coefficient of the substrate in floc, the floc density, and the mean floc radius, are needed.
Left upper lobe mass and diffuse reticular-nodular infiltrate.
Jackson, H D; Carney, K J; Knautz, M A; Tenholder, M F
1994-06-01
We encountered a clinical problem in a young man who presented with a left upper lobe mass and a diffuse reticular-nodular infiltrate. We thought we had appropriately applied Murphy's Law (the famed bank robber who "went where the money is"), and Ockham's Razor (the philosopher William of Ockham [1285 to 1349]-"Entities are not to be multiplied beyond necessity") as we rapidly diagnosed the lung mass with computed tomography, scintigraphy, and fine-needle aspiration. However, when his invaluable previous chest radiographs arrived, bronchoscopy with transbronchial biopsy, bronchoalveolar lavage, brushings, and postbronchoscopy sputum revealed the more ominous diagnosis in this patient. This case illustrates the complementary nature of current imaging and bronchoscopy techniques; but, even more importantly, it demonstrates the value of the history coupled with the previous radiograph. Even an unusual case can provide lessons in cost containment.
Effect of vapor-phase mass transfer on aquifer restoration
Miller, C.T.; Staes, E.G.
1992-02-01
Volatile organic chemicals (VOC) are a frequent source of groundwater contamination in North Carolina and throughout the United States and other developed countries. The work is considered a subset of the general multiphase flow and transport problem: fluid flow and contaminant transport in the gas phase of the unsaturated zone. The specific purpose of the work was to investigate gas-phase (VOC) transport phenomena at the field scale to assess the relative importance of operative transport phenomena. A field research site was established at an active fire training area on Pope Air Force Base. Monitoring of groundwater flow and gas-phase contaminant distributions was accomplished as a function of three spatial dimensions and time. These distributions are reported and interpreted with respect to the current level of understanding of gas-phase transport phenomena. Consideration is given to advective transport, diffusive transport, interphase mass transfer, and multicomponent effects. Numerical modeling is used to evaluate expected steady-state contaminant distributions in the unsaturated zone and to assess relative time scales of operative transport processes. Reasonable agreement is achieved between model simulations and observed concentration distributions in the field, with a dominant vertical transport component shown in both predicted and observed contaminant distributions.
Mass transfer coefficients determination from linear gradient elution experiments.
Pfister, David; Morbidelli, Massimo
2015-01-02
A procedure to estimate mass transfer coefficients in linear gradient elution chromatography is presented and validated by comparison with experimental data. Mass transfer coefficients are traditionally estimated experimentally through the van Deemter plot, which represents the HETP as a function of the fluid velocity. Up to now, the HETP was obtained under isocratic elution conditions. Unfortunately, isocratic elution experiments are often not suitable for large biomolecules which suffer from severe mass transfer hindrances. Yamamoto et al. were the first to propose a semi-empirical equation to relate HETPs measured from linear gradient elution experiments to those obtained under isocratic conditions [7]. Based on his pioneering work, the approach presented in this work aims at providing an experimental procedure supported by simple equations to estimate reliable mass transfer parameters from linear gradient elution chromatographic experiments. From the resolution of the transport model, we derived a rigorous analytical expression for the HETP in linear gradient elution chromatography.
Correlation of liquid-film cooling mass transfer data.
NASA Technical Reports Server (NTRS)
Gater, R. A.; L'Ecuyer, M. R.
1972-01-01
An empirical correlation proposed by Gater and Ecuyer (1970) for liquid-film cooling mass transfer, accounting for film roughness and entrainment effects, is extended to include liquid films of arbitrary length. A favorable comparison between the predicted results and the experimental data of Kinney et al. (1952) and Emmons and Warner (1964) shows the utility of the mass transfer correlation for predictions over a wide range of experimental parameters.
Influence of pluronic F68 on oxygen mass transfer.
Sieblist, Christian; Jenzsch, Marco; Pohlscheidt, Michael
2013-01-01
Pluronic F68 is one of the most used shear protecting additives in cell culture cultivations. It is well known from literature that such surface-active surfactants lower the surface tension at the gas-liquid interface, which influences the mass transfer. In this study, the effect of Pluronic F68 on oxygen mass transfer in aqueous solutions was examined. Therefore, the gassing in/gassing out method and bubble size measurements were used. At low concentrations of 0.02 g/L, a 50% reduction on mass transfer was observed for all tested spargers and working conditions. An explanation of the observed effects by means of Higbie's penetration or Dankwerts surface renewal theory was applied. It could be demonstrated that the suppressed movement of the bubble surface layer is the main cause for the significant drop down of the kL a-values. For Pluronic F68 concentrations above 0.1 g/L, it was observed that it comes to changes in bubble appearance and bubble size strongly dependent on the sparger type. By using the bubble size measurement data, it could be shown that only small changes in mass transfer coefficient (kL ) take place above the critical micelle concentration. Further changes on overall mass transfer at higher Pluronic F68 concentrations are mainly based on increasing of gas holdup and, more importantly, by increasing of the surface area available for mass transfer.
Local Mass and Heat Transfer on a Turbine Blade Tip
Jin, P.; Goldstein, R. J.
2003-01-01
Locmore » al mass and heat transfer measurements on a simulated high-pressure turbine blade-tip surface are conducted in a linear cascade with a nonmoving tip endwall, using a naphthalene sublimation technique. The effects of tip clearance (0.86–6.90% of chord) are investigated at various exit Reynolds numbers (4–7 × 10 5 ) and turbulence intensities (0.2 and 12.0%). The mass transfer on the tip surface is significant along its pressure edge at the smallest tip clearance. At the two largest tip clearances, the separation bubble on the tip surface can cover the whole width of the tip on the second half of the tip surface. The average mass-transfer rate is highest at a tip clearance of 1.72% of chord. The average mass-transfer rate on the tip surface is four and six times as high as on the suction and the pressure surface, respectively. A high mainstream turbulence level of 12.0% reduces average mass-transfer rates on the tip surface, while the higher mainstream Reynolds number generates higher local and average mass-transfer rates on the tip surface.« less
Micro-scale mass-transfer variations during electrodeposition
Sutija, D.P.
1991-08-01
Results of two studies on micro-scale mass-transfer enhancement are reported: (1) Profiled cross-sections of striated zinc surfaces deposited in laminar channel flow were analyzed with fast-fourier transforms (FFT) to determine preferred striation wavelengths. Striation frequency increases with current density until a minimum separation between striae of 150 {mu}m is reached. Beyond this point, independent of substrate used, striae meld together and form a relatively smooth, nodular deposit. Substrates equipped with artificial micron-sized protrusions result in significantly different macro-morphology in zinc deposits. Micro-patterned electrodes (MPE) with hemispherical protrusions 5 {mu}m in diameter yield thin zinc striae at current densities that ordinarily produce random nodular deposits. MPEs with artificial hemi-cylinders, 2.5 {mu}m in height and spaced 250 {mu}m apart, form striae with a period which matches the spacing of micron-sized ridges. (2) A novel, corrosion-resistant micromosaic electrode was fabricated on a silicon wafer. Measurements of mass-transport enhancement to a vertical micromosaic electrode caused by parallel bubble streams rising inside of the diffusion boundary-layer demonstrated the presence of two co-temporal enhancement mechanisms: surface-renewal increases the limiting current within five bubble diameters of the rising column, while bubble-induced laminar flows cause weaker enhancement over a much broader swath. The enhancement caused by bubble curtains is predicted accurately by linear superposition of single-column enhancements. Two columns of smaller H{sub 2} bubbles generated at the same volumetric rate as a single column of larger bubbles cause higher peak and far-field enhancements. 168 refs., 96 figs., 6 tabs.
Application of Lattice Boltzmann Methods in Complex Mass Transfer Systems
NASA Astrophysics Data System (ADS)
Sun, Ning
Lattice Boltzmann Method (LBM) is a novel computational fluid dynamics method that can easily handle complex and dynamic boundaries, couple local or interfacial interactions/reactions, and be easily parallelized allowing for simulation of large systems. While most of the current studies in LBM mainly focus on fluid dynamics, however, the inherent power of this method makes it an ideal candidate for the study of mass transfer systems involving complex/dynamic microstructures and local reactions. In this thesis, LBM is introduced to be an alternative computational method for the study of electrochemical energy storage systems (Li-ion batteries (LIBs) and electric double layer capacitors (EDLCs)) and transdermal drug design on mesoscopic scale. Based on traditional LBM, the following in-depth studies have been carried out: (1) For EDLCs, the simulation of diffuse charge dynamics is carried out for both the charge and the discharge processes on 2D systems of complex random electrode geometries (pure random, random spheres and random fibers). Steric effect of concentrated solutions is considered by using modified Poisson-Nernst-Plank (MPNP) equations and compared with regular Poisson-Nernst-Plank (PNP) systems. The effects of electrode microstructures (electrode density, electrode filler morphology, filler size, etc.) on the net charge distribution and charge/discharge time are studied in detail. The influence of applied potential during discharging process is also discussed. (2) For the study of dendrite formation on the anode of LIBs, it is shown that the Lattice Boltzmann model can capture all the experimentally observed features of microstructure evolution at the anode, from smooth to mossy to dendritic. The mechanism of dendrite formation process in mesoscopic scale is discussed in detail and compared with the traditional Sand's time theories. It shows that dendrite formation is closely related to the inhomogeneous reactively at the electrode-electrolyte interface
Geoelectrical Measurement of Multi-Scale Mass Transfer Parameters
Day-Lewis, Frederick David; Singha, Kamini; Johnson, Timothy C.; Haggerty, Roy; Binley, Andrew; Lane, John W.
2014-11-25
Mass transfer affects contaminant transport and is thought to control the efficiency of aquifer remediation at a number of sites within the Department of Energy (DOE) complex. An improved understanding of mass transfer is critical to meeting the enormous scientific and engineering challenges currently facing DOE. Informed design of site remedies and long-term stewardship of radionuclide-contaminated sites will require new cost-effective laboratory and field techniques to measure the parameters controlling mass transfer spatially and across a range of scales. In this project, we sought to capitalize on the geophysical signatures of mass transfer. Previous numerical modeling and pilot-scale field experiments suggested that mass transfer produces a geoelectrical signature—a hysteretic relation between sampled (mobile-domain) fluid conductivity and bulk (mobile + immobile) conductivity—over a range of scales relevant to aquifer remediation. In this work, we investigated the geoelectrical signature of mass transfer during tracer transport in a series of controlled experiments to determine the operation of controlling parameters, and also investigated the use of complex-resistivity (CR) as a means of quantifying mass transfer parameters in situ without tracer experiments. In an add-on component to our grant, we additionally considered nuclear magnetic resonance (NMR) to help parse mobile from immobile porosities. Including the NMR component, our revised study objectives were to: 1. Develop and demonstrate geophysical approaches to measure mass-transfer parameters spatially and over a range of scales, including the combination of electrical resistivity monitoring, tracer tests, complex resistivity, nuclear magnetic resonance, and materials characterization; and 2. Provide mass-transfer estimates for improved understanding of contaminant fate and transport at DOE sites, such as uranium transport at the Hanford 300 Area. To achieve our objectives, we implemented a 3
Koyama, Shigeru; Yu, Jian; Ishibashi, Akira
1999-07-01
In the face of the phase-out of HCFC22 for its effect on globe environment, the alternative refrigerant has been paid attention in the refrigeration and heat pump industry. In the present stage, it is found that any pure refrigerant is not a good substitute of HCFC22 for the system in use. The authors have to use binary or ternary refrigerant mixtures as the substitute to meet industrial requirement. But until now, although the heat transfer characteristics of the refrigerant mixtures can be measured in experiments and predicted in some degree, the mass transfer characteristics in condensation process, which is a main part in most systems, can not be clarified by both experimental and theoretical methods. In the present study a non-equilibrium model for condensation of binary refrigerant mixtures inside a horizontal microfin tube is proposed. In this model it is assumed that the phase equilibrium is only established at the vapor-liquid interface, while the bulk vapor and the bulk liquid are in non-equilibrium in the same cross section. The mass transfer characteristic in vapor core is obtained from the analogy between mass and momentum transfer. In the liquid layer, the mass fraction distribution is neglected, but the mass transfer coefficient is treated as infinite that can keep a finite value for the mass transfer rate in liquid phase. From the calculation results compared with the experimental ones for the condensation of HFC134a/HCFC123 and HCFC22/CFC114 mixtures, it is found that the calculated heat flux distribution along the tube axis is in good agreement with that of experiment, and the calculated values of condensing length agree well with the experimental ones. Using the present model, the local mass faction distribution, the diffusion mass transfer rate and the mass transfer characteristics in both vapor and liquid phase are demonstrated. From these results, the effect of mass transfer resistance on condensation heat transfer characteristics for binary
Mass transfer between debris discs during close stellar encounters
NASA Astrophysics Data System (ADS)
Jílková, Lucie; Hamers, Adrian S.; Hammer, Michael; Portegies Zwart, Simon
2016-04-01
We study mass transfers between debris discs during stellar encounters. We carried out numerical simulations of close flybys of two stars, one of which has a disc of planetesimals represented by test particles. We explored the parameter space of the encounters, varying the mass ratio of the two stars, their pericentre and eccentricity of the encounter, and its geometry. We find that particles are transferred to the other star from a restricted radial range in the disc and the limiting radii of this transfer region depend on the parameters of the encounter. We derive an approximate analytic description of the inner radius of the region. The efficiency of the mass transfer generally decreases with increasing encounter pericentre and increasing mass of the star initially possessing the disc. Depending on the parameters of the encounter, the transfer particles have a specific distribution in the space of orbital elements (semimajor axis, eccentricity, inclination, and argument of pericentre) around their new host star. The population of the transferred particles can be used to constrain the encounter through which it was delivered. We expect that many stars experienced transfer among their debris discs and planetary systems in their birth environment. This mechanism presents a formation channel for objects on wide orbits of arbitrary inclinations, typically having high eccentricity but possibly also close to circular (eccentricities of about 0.1). Depending on the geometry, such orbital elements can be distinct from those of the objects formed around the star.
Secular dynamics in hierarchical three-body systems with mass loss and mass transfer
Michaely, Erez; Perets, Hagai B.
2014-10-20
Recent studies have shown that secular evolution of triple systems can play a major role in the evolution and interaction of their inner binaries. Very few studies explored the stellar evolution of triple systems, and in particular the mass-loss phase of the evolving stellar components. Here we study the dynamical secular evolution of hierarchical triple systems undergoing mass loss. We use the secular evolution equations and include the effects of mass loss and mass transfer, as well as general relativistic effects. We present various evolutionary channels taking place in such evolving triples, and discuss both the effects of mass loss and mass transfer in the inner binary system, as well as the effects of mass loss/transfer from an outer third companion. We discuss several distinct types/regimes of triple secular evolution, where the specific behavior of a triple system can sensitively depend on its hierarchy and the relative importance of classical and general relativistic effects. We show that the orbital changes due to mass-loss and/or mass-transfer processes can effectively transfer a triple system from one dynamical regime to another. In particular, mass loss/transfer can both induce and quench high-amplitude (Lidov-Kozai) variations in the eccentricity and inclination of the inner binaries of evolving triples. They can also change the system dynamics from an orderly periodic behavior to a chaotic one, and vice versa.
Internal mass transfer in hollow fiber supported liquid membranes
Urtiaga, A.M.; Irabien, J.A. )
1993-03-01
The study of mass transfer in hollow fiber supported liquid membranes is justified by a large number of separation processes. The analysis starts from the definition of an overall permeability coefficient which is a lumped parameter of a particular system and process conditions which gathers both mass transfer and operation parameters. By applying the film theory the contribution of the interfacial mass-transfer coefficient due to the inner boundary layer and the contribution of the supported liquid membrane permeability coefficient can be separated and analyzed. The study yields overall permeability coefficients that can be compared with those expected from hollow fiber design equations suggested earlier. The second approach considers the continuity mass conservation equation and the associated boundary conditions for the solute in the inner fluid. The analysis by means of the fundamental equations separates the effects of the operation variables such as the hydrodynamic conditions and length and diameter of the fibers from the mass-transfer properties of the system, described by the wall Sherwood number. The scope of the present work is to compare both methods of describing a hollow fiber supported liquid membrane module, analyzing the influence of the internal mass transfer on the design of such systems. In the experimental system under consideration, the simultaneous separation-concentration of phenol from aqueous solutions with hollow fiber supported liquid membrane modules is performed. The influence of the flow rate of the inner aqueous phase on the phenol separation rate has been studied.
Monolithic supports with unique geometries and enhanced mass transfer.
Stuecker, John Nicholas; Ferrizz, Robert Matthew; Cesarano, Joseph, III; Miller, James Edward
2004-01-01
The catalytic combustion of natural gas has been the topic of much research over the past decade. Interest in this technology results from a desire to decrease or eliminate the emissions of harmful nitrogen oxides (NOX) from gas turbine power plants. A low-pressure drop catalyst support, such as a ceramic monolith, is ideal for this high-temperature, high-flow application. A drawback to the traditional honeycomb monoliths under these operating conditions is poor mass transfer to the catalyst surface in the straight-through channels. 'Robocasting' is a unique process developed at Sandia National Laboratories that can be used to manufacture ceramic monoliths with alternative 3-dimensional geometries, providing tortuous pathways to increase mass transfer while maintaining low pressure drops. This report details the mass transfer effects for novel 3-dimensional robocast monoliths, traditional honeycomb-type monoliths, and ceramic foams. The mass transfer limit is experimentally determined using the probe reaction of CO oxidation over a Pt / {gamma}-Al{sub 2}O{sub 3} catalyst, and the pressure drop is measured for each monolith sample. Conversion versus temperature data is analyzed quantitatively using well-known dimensionless mass transfer parameters. The results show that, relative to the honeycomb monolith support, considerable improvement in mass transfer efficiency is observed for robocast samples synthesized using an FCC-like geometry of alternating rods. Also, there is clearly a trade-off between enhanced mass transfer and increased pressure drop, which can be optimized depending on the particular demands of a given application.
NASA Astrophysics Data System (ADS)
Vandadi, Vahid; Jafari Kang, Saeed; Masoud, Hassan
2016-06-01
In the study of convective heat and mass transfer from a particle, key quantities of interest are usually the average rate of transfer and the mean distribution of the scalar (i.e., temperature or concentration) at the particle surface. Calculating these quantities using conventional equations requires detailed knowledge of the scalar field, which is available predominantly for problems involving uniform scalar and flux boundary conditions. Here we derive a reciprocal relation between two diffusing scalars that are advected by oppositely driven Stokes or potential flows whose streamline configurations are identical. This relation leads to alternative expressions for the aforementioned average quantities based on the solution of the scalar field for uniform surface conditions. We exemplify our results via two applications: (i) heat transfer from a sphere with nonuniform boundary conditions in Stokes flow at small Péclet numbers and (ii) extension of Brenner's theorem for the invariance of heat transfer rate to flow reversal.
DIFFUSING INNOVATIONS: Implementing the Technology Transfer Act of 1986.
2007-11-02
resources 6. D Improved quality of R&D products 7. D Better transfer and utilization of technology 8. D Other (please specify) Questions 24-30...Views on the Legislation’s Effectiveness Views on Improvements to Technology Transfer Examples of Successful and Unsuccessful Transfer Attempts...Service reserach centers designated by the agency - The FAA Technology Center, Tumer-Fairbank Research Center, and Coast Guard Research Development
Chemical mass transfer in magmatic processes
NASA Astrophysics Data System (ADS)
Ghiorso, Mark S.; Carmichael, Ian S. E.
1985-07-01
. Calculations suggest that in order to generate a silica rich residuum and the characteristic iron enrichment trend during the fractional crystallization of a tholeiitic basalt, the magma must crystallize esentially along f_{{text{O}}_{text{2}} } buffer. This buffered state can be maintained by exchange of oxygen (via hydrogen diffusion) between the magma and the surrounding country rocks or by magmatic oxidation-reduction equilibria. Additional calculations indicate the possibility that oxygen exchange may be unnecessary if the magma contains sufficient sulfur to maintain the system along an S2/SO2 oxygen buffer during the initial stages of crystallization.
A Simplified Mass-Transfer Model for Visual Pigments in Amphibian Retinal-Cone Outer Segments
Weber, Paul W.; Howle, Laurens E.; Murray, Mark M.; Corless, Joseph M.
2011-01-01
When radiolabeled precursors and autoradiography are used to investigate turnover of protein components in photoreceptive cone outer segments (COSs), the labeled components—primarily visual pigment molecules (opsins)—are diffusely distributed along the COS. To further assess this COS labeling pattern, we derive a simplified mass-transfer model for quantifying the contributions of advective and diffusive mechanisms to the distribution of opsins within COSs of the frog retina. Two opsin-containing regions of the COS are evaluated: the core axial array of disks and the plasmalemma. Numerical solutions of the mass-transfer model indicate three distinct stages of system evolution. In the first stage, plasmalemma diffusion is dominant. In the second stage, the plasmalemma density reaches a metastable state and transfer between the plasmalemma and disk region occurs, which is followed by an increase in density that is qualitatively similar for both regions. The final stage consists of both regions slowly evolving to the steady-state solution. Our results indicate that autoradiographic and cognate approaches for tracking labeled opsins in the COS cannot be effective methodologies for assessing new disk formation at the base of the COS. PMID:21281566
Kuśba, Jósef; Li, Li; Gryczynski, Ignacy; Piszczek, Grzegorz; Johnson, Michael; Lakowicz, Joseph R
2002-01-01
We describe measurements of lateral diffusion in membranes using resonance energy transfer. The donor was a rhenium (Re) metal-ligand complex lipid, which displays a donor decay time near 3 micros. The long donor lifetime resulted in an ability to measure lateral diffusion coefficient below 10(-8) cm(2)/s. The donor decay data were analyzed using a new numerical algorithm for calculation of resonance energy transfer for donors and acceptors randomly distributed in two dimensions. An analytical solution to the diffusion equation in two dimensions is not known, so the equation was solved by the relaxation method in Laplace space. This algorithm allows the donor decay in the absence of energy transfer to be multiexponential. The simulations show that mutual lateral diffusion coefficients of the donor and acceptor on the order of 10(-8) cm(2)/s are readily recovered from the frequency-domain data with donor decay times on the microsecond timescale. Importantly, the lateral diffusion coefficients and acceptor concentrations can be recovered independently despite correlation between these parameters. This algorithm was tested and verified using the donor decays of a long lifetime rhenium lipid donor and a Texas red-lipid acceptor. Lateral diffusion coefficients ranged from 4.4 x 10(-9) cm(2)/s in 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DMPG) at 10 degrees C to 1.7 x 10(-7) cm(2)/s in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) at 35 degrees C. These results demonstrated the possibility of direct measurements of lateral diffusion coefficients using microsecond decay time luminophores. PMID:11867452
Curvature dependence of the interfacial heat and mass transfer coefficients
NASA Astrophysics Data System (ADS)
Glavatskiy, K. S.; Bedeaux, D.
2014-03-01
Nucleation is often accompanied by heat transfer between the surroundings and a nucleus of a new phase. The interface between two phases gives an additional resistance to this transfer. For small nuclei the interfacial curvature is high, which affects not only equilibrium quantities such as surface tension, but also the transport properties. In particular, high curvature affects the interfacial resistance to heat and mass transfer. We develop a framework for determining the curvature dependence of the interfacial heat and mass transfer resistances. We determine the interfacial resistances as a function of a curvature. The analysis is performed for a bubble of a one-component fluid and may be extended to various nuclei of multicomponent systems. The curvature dependence of the interfacial resistances is important in modeling transport processes in multiphase systems.
FEHM: finite element heat and mass transfer code
Zyvoloski, G.; Dash, Z.; Kelkar, S.
1988-03-01
The finite element heat and mass (FEHM) transfer code is a computer code developed to simulate geothermal and hot dry rock reservoirs. It is also applicable to natural-state studies of geothermal systems and ground-water flow. It solves the equations of heat and mass transfer for multiphase flow in porous and permeable media using the finite element method. The code also has provisions for a noncoupled tracer; that is, the tracer solutions do not affect the heat and mass transfer solutions. It can simulate two-dimensional, two-dimensional radial, or three-dimensional geometries. A summary of the equations in the model, the numerical solution procedure, and model verification and validation are provided in this report. A user's guide and sample problems are included in the appendices. 17 refs., 10 figs., 4 tabs.
Agitating mass transfer with a warped disc's shadow
NASA Astrophysics Data System (ADS)
Cambier, H.
2015-10-01
For compact objects fed by Roche lobe overflow, accretion-generated X-rays irradiating the donor star can alter gas flow towards the Lagrange point thus varying mass transfer. The latest work specific to this topic consists of simple yet insightful two-dimensional hydrodynamics simulations stressing the role of global flow. To explore how a time-varying disc shadow affects mass transfer, I generalize the geometry, employ a robust hydrodynamics solver, and use phase space analysis near the nozzle to include coriolis lift there. Without even exposing the nozzle, a warped disc's shadow can drive mass transfer cycles by shifting the equatorial edges of the irradiation patches in turns: drawing in denser ambient gas before sweeping it into the nozzle. Other important effects remain missing in two-dimensional models, which I discuss along with prospects for more detailed yet efficient models.
Bell, J H; Hand, L A
2005-04-21
The growth rate of a crystal in a supersaturated solution is limited by both reaction kinetics and the local concentration of solute. If the local mass transfer coefficient is too low, concentration of solute at the crystal-solution interface will drop below saturation, leading to a defect in the growing crystal. Here, mass transfer coefficients are calculated for a rotating crystal growing in a supersaturated solution of potassium diphosphate (KDP) in water. Since mass transfer is difficult to measure directly, the heat transfer coefficient of a scale model crystal in water is measured using temperature-sensitive paint (TSP). To the authors' knowledge this is the first use of TSP to measure temperatures in water. The corresponding mass transfer coefficient is then calculated using the Chilton- Colburn analogy. Measurements were made for three crystal sizes at two running conditions each. Running conditions include periodic reversals of rotation direction. Heat transfer coefficients were found to vary significantly both across the crystal faces and over the course of a rotation cycle, but not from one face to another. Mean heat transfer coefficients increased with both crystal size and rotation rate. Computed mass transfer coefficients were broadly in line with expectations from the full-scale crystal growth experiments. Additional experiments show that continuous rotation of the crystal results in about a 30% lower heat transfer compared to rotation with periodic reversals. The continuous rotation case also shows a periodic variation in heat transfer coefficient of about 15%, with a period about 1/20th of the rotation rate.
Mass transfer apparatus and method for separation of gases
Blount, Gerald C.
2015-10-13
A process and apparatus for separating components of a source gas is provided in which more soluble components of the source gas are dissolved in an aqueous solvent at high pressure. The system can utilize hydrostatic pressure to increase solubility of the components of the source gas. The apparatus includes gas recycle throughout multiple mass transfer stages to improve mass transfer of the targeted components from the liquid to gas phase. Separated components can be recovered for use in a value added application or can be processed for long-term storage, for instance in an underwater reservoir.
NASA Technical Reports Server (NTRS)
Gokoglu, Suleyman A.; Rosner, Daniel E.
1986-01-01
A formulation previously developed to predict and correlate the thermophoretically-augmented submicron particle mass transfer rate to cold surfaces is found to account for the thermophoretically reduced particle mass transfer rate to overheated surfaces such that thermophoresis brings about a 10-decade reduction below the convective mass transfer rate expected by pure Brownian diffusion and convection alone. Thermophoretic blowing is shown to produce effects on particle concentration boundary-layer (BL) structure and wall mass transfer rates similar to those produced by real blowing through a porous wall. The applicability of the correlations to developing BL-situations is demonstrated by a numerical example relevant to wet-steam technology.
Flow-Dependent Mass Transfer May Trigger Endothelial Signaling Cascades
Vandrangi, Prashanthi; Sosa, Martha; Shyy, John Y.-J.; Rodgers, Victor G. J.
2012-01-01
It is well known that fluid mechanical forces directly impact endothelial signaling pathways. But while this general observation is clear, less apparent are the underlying mechanisms that initiate these critical signaling processes. This is because fluid mechanical forces can offer a direct mechanical input to possible mechanotransducers as well as alter critical mass transport characteristics (i.e., concentration gradients) of a host of chemical stimuli present in the blood stream. However, it has recently been accepted that mechanotransduction (direct mechanical force input), and not mass transfer, is the fundamental mechanism for many hemodynamic force-modulated endothelial signaling pathways and their downstream gene products. This conclusion has been largely based, indirectly, on accepted criteria that correlate signaling behavior and shear rate and shear stress, relative to changes in viscosity. However, in this work, we investigate the negative control for these criteria. Here we computationally and experimentally subject mass-transfer limited systems, independent of mechanotransduction, to the purported criteria. The results showed that the negative control (mass-transfer limited system) produced the same trends that have been used to identify mechanotransduction-dominant systems. Thus, the widely used viscosity-related shear stress and shear rate criteria are insufficient in determining mechanotransduction-dominant systems. Thus, research should continue to consider the importance of mass transfer in triggering signaling cascades. PMID:22558132
Fuel cell collector plates with improved mass transfer channels
Gurau, Vladimir; Barbir, Frano; Neutzler, Jay K.
2003-04-22
A fuel cell collector plate can be provided with one or more various channel constructions for the transport of reactants to the gas diffusion layer and the removal of water therefrom. The outlet channel can be arranged to have a reduced volume compared to the inlet channel, in both interdigitated and discontinuous spiral applications. The land width between an inlet channel and outlet channel can be reduced to improved mass flow rate in regions of deleted reactant concentrations. Additionally or alternatively, the depth of the inlet channel can be reduced in the direction of flow to reduce the diffusion path as the concentration of reactant is reduced.
Drop mass transfer in a microfluidic chip compared to a centrifugal contactor
Nemer, Martin B.; Roberts, Christine C.; Hughes, Lindsey G.; ...
2014-06-13
A model system was developed for enabling a multiscale understanding of centrifugal-contactor liquid–liquid extraction.The system consisted of Nd(III) + xylenol orange in the aqueous phase buffered to pH =5.5 by KHP, and dodecane + thenoyltrifluroroacetone (HTTA) + tributyphosphate (TBP) in the organic phase. Diffusion constants were measured for neodymium in both the organic and aqueous phases, and the Nd(III) partition coefficients were measured at various HTTA and TBP concentrations. A microfluidic channel was used as a high-shear model environment to observe mass-transfer on a droplet scale with xylenol orange as the aqueous-phase metal indicator; mass-transfer rates were measured quantitatively inmore » both diffusion and reaction limited regimes on the droplet scale. Lastly, the microfluidic results were comparable to observations made for the same system in a laboratory scale liquid–liquid centrifugal contactor, indicating that single drop microfluidic experiments can provide information on mass transfer in complicated flows and geometries.« less
Drop mass transfer in a microfluidic chip compared to a centrifugal contactor
Nemer, Martin B.; Roberts, Christine C.; Hughes, Lindsey G.; Wyatt, Nicholas B.; Brooks, Carlton F.; Rao, Rekha
2014-06-13
A model system was developed for enabling a multiscale understanding of centrifugal-contactor liquid–liquid extraction.The system consisted of Nd(III) + xylenol orange in the aqueous phase buffered to pH =5.5 by KHP, and dodecane + thenoyltrifluroroacetone (HTTA) + tributyphosphate (TBP) in the organic phase. Diffusion constants were measured for neodymium in both the organic and aqueous phases, and the Nd(III) partition coefficients were measured at various HTTA and TBP concentrations. A microfluidic channel was used as a high-shear model environment to observe mass-transfer on a droplet scale with xylenol orange as the aqueous-phase metal indicator; mass-transfer rates were measured quantitatively in both diffusion and reaction limited regimes on the droplet scale. Lastly, the microfluidic results were comparable to observations made for the same system in a laboratory scale liquid–liquid centrifugal contactor, indicating that single drop microfluidic experiments can provide information on mass transfer in complicated flows and geometries.
Mass-transfer properties of insulin on core-shell and fully porous stationary phases.
Lambert, Nándor; Kiss, Ibolya; Felinger, Attila
2014-10-31
The mass-transfer properties of three superficially-porous packing materials, with 2.6 and 3.6μm particle and 1.9, 2.6, and 3.2μm inner core diameter, respectively, were investigated and compared with those of fully porous packings with similar particle properties. Several sources of band spreading in the chromatographic bed have been identified and studied according to the general rate model of chromatography. Besides the axial dispersion in the stream of the mobile phase, and the external mass transfer resistance, the intraparticle diffusion was studied in depth. The first absolute and the second central moments of the peaks of human insulin, over a wide range of mobile phase velocities were measured and used for the calculation of the mass-transfer coefficients. The experimental data were also analyzed using the stochastic or molecular dynamic model of Giddings and Eyring. The dissimilarities of the mass-transfer observed in the different columns were identified and evaluated.
A hybrid transport-diffusion model for radiative transfer in absorbing and scattering media
NASA Astrophysics Data System (ADS)
Roger, M.; Caliot, C.; Crouseilles, N.; Coelho, P. J.
2014-10-01
A new multi-scale hybrid transport-diffusion model for radiative transfer is proposed in order to improve the efficiency of the calculations close to the diffusive regime, in absorbing and strongly scattering media. In this model, the radiative intensity is decomposed into a macroscopic component calculated by the diffusion equation, and a mesoscopic component. The transport equation for the mesoscopic component allows to correct the estimation of the diffusion equation, and then to obtain the solution of the linear radiative transfer equation. In this work, results are presented for stationary and transient radiative transfer cases, in examples which concern solar concentrated and optical tomography applications. The Monte Carlo and the discrete-ordinate methods are used to solve the mesoscopic equation. It is shown that the multi-scale model allows to improve the efficiency of the calculations when the medium is close to the diffusive regime. The proposed model is a good alternative for radiative transfer at the intermediate regime where the macroscopic diffusion equation is not accurate enough and the radiative transfer equation requires too much computational effort.
N-body Simulation of Binary Star Mass Transfer
NASA Astrophysics Data System (ADS)
Hutyra, Taylor; Sumpter, William
2017-01-01
Over 70% of the stars in our galaxy are multiple star systems, many of which are two stars that orbit around a common center of mass. The masses of the individual stars can be found using Newton’s and Kepler’s Laws. This allows astronomers to use these systems as astrophysical laboratories to study properties and processes of stars and galaxies. Among the many types observed, the dynamics of contact systems are the most interesting because they exhibit mass transfer, which changes the composition and function of both stars. The process by which this mass exchange takes place is not well understood. The lack of extensive mass transfer analysis, inadequate theoretical models, and the large time scale of this process are reasons for our limited understanding. In this work, a model was made to give astronomers a method for gaining a deeper knowledge and visual intuition of how the mass transfer between binary stars takes place. We have built the foundations for a simulation of arbitrary systems, which we plan to elaborate on in the future to include thermodynamics and nuclear processes.
TWIN BINARIES: STUDIES OF STABILITY, MASS TRANSFER, AND COALESCENCE
Lombardi, J. C.; Holtzman, W.; Gearity, K.; Dooley, K. L.; Kalogera, V.; Rasio, F. A.
2011-08-20
Motivated by suggestions that binaries with almost equal-mass components ('twins') play an important role in the formation of double neutron stars and may be rather abundant among binaries, we study the stability of synchronized close and contact binaries with identical components in circular orbits. In particular, we investigate the dependency of the innermost stable circular orbit on the core mass, and we study the coalescence of the binary that occurs at smaller separations. For twin binaries composed of convective main-sequence stars, subgiants, or giants with low-mass cores (M{sub c} {approx}< 0.15M, where M is the mass of a component), a secular instability is reached during the contact phase, accompanied by a dynamical mass transfer instability at the same or at a slightly smaller orbital separation. Binaries that come inside this instability limit transfer mass gradually from one component to the other and then coalesce quickly as mass is lost through the outer Lagrangian points. For twin giant binaries with moderate to massive cores (M{sub c} {approx}> 0.15M), we find that stable contact configurations exist at all separations down to the Roche limit, when mass shedding through the outer Lagrangian points triggers a coalescence of the envelopes and leaves the cores orbiting in a central tight binary. In addition to the formation of binary neutron stars, we also discuss the implications of our results for the production of planetary nebulae with double degenerate central binaries.
Multiscale computations of mass accumulation effect on mass transfer in bubbly flow
NASA Astrophysics Data System (ADS)
Aboulhasanzadeh, Bahman; Tryggvason, Gretar
2014-11-01
Mass transfer in bubbly flow generally takes place on a much smaller length and time scale than the length and time scale of the momentum flow, resulting in a thin mass boundary layer around the bubbles. We developed a multiscale model to solve a boundary layer equation for the mass boundary layer next to the bubble interface, assuming zero mass concentration in the far field, which couples with the rest of domain using a source/sink term. Here, we extend our model to account for non-zero concentration next to the mass boundary layer. Comparison of simple case studies in 1D and 2D problems show good agreement between the fully resolved solution and the solution on a much coarser grid using our model. We study the effect of mass accumulation in a domain and also the effect of bubble moving into the wake of another bubble on the mass transfer. This study was funded by NSF Grant CBET-1132410.
Evaporation from flowing channels ( mass-transfer formulas).
Fulford, J.M.; Sturm, T.W.
1984-01-01
Stability-dependent and Dalton-type mass transfer formulas are determined from experimental evaporation data in ambient and heated channels and are shown to have similar performance in prediction of evaporation. The formulas developed are compared with those proposed by other investigators for lakes and flowing channels. -from ASCE Publications Information
Dissociation and Mass Transfer Coefficients for Ammonia Volatilization Models
Technology Transfer Automated Retrieval System (TEKTRAN)
Process-based models are being used to predict ammonia emissions from manure sources, but their accuracy has not been fully evaluated for cattle manure. Laboratory trials were conducted to measure the dissociation and mass transfer coefficients for ammonia volatilization from media of buffered ammon...
LUT observations of the mass-transferring binary AI Dra
NASA Astrophysics Data System (ADS)
Liao, Wenping; Qian, Shengbang; Li, Linjia; Zhou, Xiao; Zhao, Ergang; Liu, Nianping
2016-06-01
Complete UV band light curve of the eclipsing binary AI Dra was observed with the Lunar-based Ultraviolet Telescope (LUT) in October 2014. It is very useful to adopt this continuous and uninterrupted light curve to determine physical and orbital parameters of the binary system. Photometric solutions of the spot model are obtained by using the W-D (Wilson and Devinney) method. It is confirmed that AI Dra is a semi-detached binary with secondary component filling its critical Roche lobe, which indicates that a mass transfer from the secondary component to the primary one should happen. Orbital period analysis based on all available eclipse times suggests a secular period increase and two cyclic variations. The secular period increase was interpreted by mass transfer from the secondary component to the primary one at a rate of 4.12 ×10^{-8}M_{⊙}/yr, which is in agreement with the photometric solutions. Two cyclic oscillations were due to light travel-time effect (LTTE) via the presence of two cool stellar companions in a near 2:1 mean-motion resonance. Both photometric solutions and orbital period analysis confirm that AI Dra is a mass-transferring binary, the massive primary is filling 69 % of its critical Roche lobe. After the primary evolves to fill the critical Roche lobe, the mass transfer will be reversed and the binary will evolve into a contact configuration.
Atmospheric composition affects heat- and mass-transfer processes
NASA Technical Reports Server (NTRS)
Blakely, R. L.; Nelson, W. G.
1970-01-01
For environmental control system functions sensitive to atmospheric composition, components are test-operated in helium-oxygen and nitrogen-oxygen mixtures, pure oxygen, and air. Transient heat- and mass-transfer tests are conducted for carbon dioxide adsorption on molecular sieve and for water vapor adsorption on silica gel.
Transient natural convection heat and mass transfer in crystal growth
NASA Technical Reports Server (NTRS)
Han, Samuel S.
1988-01-01
A numerical analysis of transient combined heat and mass transfer across a rectangular cavity is performed by a numerical method based on the SIMPLE algorithm. The physical parameters are selected to represent a range of possible crystal growth in solutions. Numerical results are compared with available experimental data to confirm the accuracy of the results. Good qualitative agreements are obtained for the average mass transfer rate across the cavity. Also, qualitative agreements are observed for the global development of thermal and solute fields. It is found that the thermal and solute fields become highly oscillatory when the thermal and solute Grashof numbers are large. Oscillations are probably caused by a number of different instability mechanisms. By reducing the gravity some of these instabilities were made to disappear at the lower Grashof numbers. Transient temperature and solute distribution near the crystal growing surface are highly non-uniform at the higher Grashof numbers. These non-uniformities are less severe in the reduced gravity environments but still exist. The effects of convection on the rate of average mass transfer are more than one order of magnitude higher than those of conduction in the range of Grashof numbers studied. Dependency of mass transfer rate on the Grashof number indicates that the convection effects many not be negligible even in the microgravity environments for the range of parameters investigated.
A Course in Advanced Topics in Heat and Mass Transfer.
ERIC Educational Resources Information Center
Shaeiwitz, Joseph A.
1983-01-01
A three or four semester-hour graduate course was designed to provide basic instruction in heat/mass transfer topics relevant to chemical engineering problems and to train students to develop mathematical descriptions for new situations encountered in problem-solving. Course outline and list of references used in the course are provided. (JM)
Transient natural convection heat and mass transfer in crystal growth
NASA Technical Reports Server (NTRS)
Han, Samuel S.
1990-01-01
A numerical analysis of transient combined heat and mass transfer across a rectangular cavity is performed. The physical parameters are selected to represent a range of possible crystal growth in solutions. Good agreements with measurement data are observed. It is found that the thermal and solute fields become highly oscillatory when the thermal and solute Grashof numbers are large.
Saponification reaction system: a detailed mass transfer coefficient determination.
Pečar, Darja; Goršek, Andreja
2015-01-01
The saponification of an aromatic ester with an aqueous sodium hydroxide was studied within a heterogeneous reaction medium in order to determine the overall kinetics of the selected system. The extended thermo-kinetic model was developed compared to the previously used simple one. The reaction rate within a heterogeneous liquid-liquid system incorporates a chemical kinetics term as well as mass transfer between both phases. Chemical rate constant was obtained from experiments within a homogeneous medium, whilst the mass-transfer coefficient was determined separately. The measured thermal profiles were then the bases for determining the overall reaction-rate. This study presents the development of an extended kinetic model for considering mass transfer regarding the saponification of ethyl benzoate with sodium hydroxide within a heterogeneous reaction medium. The time-dependences are presented for the mass transfer coefficient and the interfacial areas at different heterogeneous stages and temperatures. The results indicated an important role of reliable kinetic model, as significant difference in k(L)a product was obtained with extended and simple approach.
Laser ablation sample transfer for mass spectrometry imaging.
Park, Sung-Gun; Murray, Kermit K
2015-01-01
Infrared laser ablation sample transfer (IR-LAST) is a novel ambient sampling technique for mass spectrometry. In this technique, a pulsed mid-IR laser is used to ablate materials that are collected for mass spectrometry analysis; the material can be a solid sample or deposited on a sample target. After collection, the sample can be further separated or analyzed directly by mass spectrometry. For IR-LAST sample transfer tissue imaging using MALDI mass spectrometry, a tissue section is placed on a sample slide and material transferred to a target slide by scanning the tissue sample under a focused laser beam using transmission-mode (back side) IR laser ablation. After transfer, the target slide is analyzed using MALDI imaging. The spatial resolution is approximately 400 μm and limited by the spread of the laser desorption plume. IR-LAST for MALDI imaging provides several new capabilities including ambient sampling, area to spot concentration of ablated material, multiple ablation and analysis from a single section, and direct deposition on matrix-free nanostructured targets.
Modelling of heat and mass transfer processes in neonatology.
Ginalski, Maciej K; Nowak, Andrzej J; Wrobel, Luiz C
2008-09-01
This paper reviews some of our recent applications of computational fluid dynamics (CFD) to model heat and mass transfer problems in neonatology and investigates the major heat and mass transfer mechanisms taking place in medical devices such as incubators and oxygen hoods. This includes novel mathematical developments giving rise to a supplementary model, entitled infant heat balance module, which has been fully integrated with the CFD solver and its graphical interface. The numerical simulations are validated through comparison tests with experimental results from the medical literature. It is shown that CFD simulations are very flexible tools that can take into account all modes of heat transfer in assisting neonatal care and the improved design of medical devices.
Turbulent mass transfer in the furnace of high output boilers
Noskievic, P.; Kolat, P.; Novacek, A.
1995-12-31
The up-to-date identification methods for the evaluation of combustion process quality provide a picture of what is taking place in the furnace. The Energetics Department of VSB-TU Ostrava concentrates its attention on untraditional methods which proceed from an analysis of turbulent transfer phenomena, especially the transfer of mass in the furnace of pulverized boilers. Particularly in the region of burners, this mass transfer influences the quality of the combustion process as well as the formation of solid and gaseous emissions. Measurements of combustion aerodynamics in the furnace of high output boilers are part of the Czech Clean Coal Technology program. A complex approach to these problems could lead to a decrease of pollutants released.
Effect of numerical diffusion on the water mass transformation in eddy-resolving models
NASA Astrophysics Data System (ADS)
Urakawa, L. Shogo; Hasumi, Hiroyasu
2014-02-01
This study investigates the effect of numerical diffusion associated with advection schemes on water mass transformation in an eddy-resolving model. The effect of numerical diffusion is evaluated as a residual between the total water mass transformation and the explicit water mass transformation: the former is calculated as the sum of meridional streamfunction and the temporal change rate of an isopycnal surface depth, and the latter is directly calculated with the use of the tendency equation of density. This method is used for investigating a dependency of numerical diffusion on explicit diffusivity. It is found that idealized channel experiments are categorized into three regimes according to a magnitude of explicit diffusivity: numerical diffusion, transitional, and explicit diffusion regimes. The numerical diffusion regime is defined as the regime where explicit diffusion changes do not significantly impact the solution. The magnitude of numerical diffusion is independent of the explicit diffusivity there. In the transitional regime, explicit (numerical) diffusion works more (less) with higher explicit diffusivity. Explicit and numerical diffusions are comparably important there. The explicit diffusion becomes significantly large and the numerical diffusion is almost negligible in the explicit diffusion regime. The total diffusion effect on water mass transformation there is considerably larger than those in the two other regimes. Two experiments are conducted with a Southern Ocean model under a realistic configuration. These belong to the numerical diffusion and transitional regimes. The model becomes a little too diffusive in the latter experiment. This result and results of channel experiments indicate that it is not an adequate option for a realistic Southern Ocean simulation that we adopt a diffusion coefficient in the explicit diffusion regime in order to reduce levels of numerical diffusion. It indicates that numerical diffusion is inevitable for eddy
Heat and mass transfer at adiabatic evaporation of binary zeotropic solutions
NASA Astrophysics Data System (ADS)
Makarov, M. S.; Makarova, S. N.
2016-01-01
Results of numerical simulation of heat and mass transfer in a laminar flow of three-component gas at adiabatic evaporation of binary solutions from a flat plate are presented. The studies were carried out for the perfect solution of ethanol/methanol and zeotrope solutions of water/acetone, benzene/acetone, and ethanol/acetone. The liquid-vapor equilibrium is described by the Raoult law for the ideal solution and Carlson-Colburn model for real solutions. The effect of gas temperature and liquid composition on the heat and diffusion flows, and temperature of vapor-gas mixture at the interface is analyzed. The formula for calculating the temperature of the evaporation surface for the binary liquid mixtures using the similarity of heat and mass transfer was proposed. Data of numerical simulations are in a good agreement with the results of calculations based on the proposed dependence for all examined liquid mixtures in the considered range of temperatures and pressures.
Effect of protein molecular weight on the mass transfer in protein mixing
NASA Astrophysics Data System (ADS)
Asad, Ahmed; Chai, Chuan; Wu, JiangTao
2012-03-01
The mixing of protein solutions with that of precipitating agents is very important in protein crystallization experiments. In this work, the interferometry images were recorded during the mixing of two proteins with different molecular weights: lysozyme of ˜14.6 kDa, trypsin of ˜23.3 kDa and pepsin of ˜34.8 kDa were placed in a Mach-Zehnder interferometer. The protein molecular weight dependence on the competition of the transport process and kinetics at the interface was studied. The concentration profiles of protein solutions were calculated to analyze the mass transfer during the mixing process. It was observed that the mass transfer process is more efficient during the mixing of proteins with higher molecular weights. In addition, the more rapid concentration changes above the interface suggest that convection may dominate the diffusion. The phenomenon of convection is higher in the protein solutions with higher molecular weight.
NASA Astrophysics Data System (ADS)
Torki-Harchegani, Mehdi; Ghanbarian, Davoud; Sadeghi, Morteza
2015-08-01
To design new dryers or improve existing drying equipments, accurate values of mass transfer parameters is of great importance. In this study, an experimental and theoretical investigation of drying whole lemons was carried out. The whole lemons were dried in a convective hot air dryer at different air temperatures (50, 60 and 75 °C) and a constant air velocity (1 m s-1). In theoretical consideration, three moisture transfer models including Dincer and Dost model, Bi- G correlation approach and conventional solution of Fick's second law of diffusion were used to determine moisture transfer parameters and predict dimensionless moisture content curves. The predicted results were then compared with the experimental data and the higher degree of prediction accuracy was achieved by the Dincer and Dost model.
Mass and heat transfer model of Tubular Solar Still
Ahsan, Amimul; Fukuhara, Teruyuki
2010-07-15
In this paper, a new mass and heat transfer model of a Tubular Solar Still (TSS) was proposed incorporating various mass and heat transfer coefficients taking account of the humid air properties inside the still. The heat balance of the humid air and the mass balance of the water vapor in the humid air were formulized for the first time. As a result, the proposed model enabled to calculate the diurnal variations of the temperature, water vapor density and relative humidity of the humid air, and to predict the hourly condensation flux besides the temperatures of the water, cover and trough, and the hourly evaporation flux. The validity of the proposed model was verified using the field experimental results carried out in Fukui, Japan and Muscat, Oman in 2008. The diurnal variations of the calculated temperatures and water vapor densities had a good agreement with the observed ones. Furthermore, the proposed model can predict the daily and hourly production flux precisely. (author)
NASA Technical Reports Server (NTRS)
Pinelli, Thomas E.; Bishop, Ann P.; Barclay, Rebecca O.; Kennedy, John M.
1992-01-01
Increasing reliance on and investment in information technology and electronic networking systems presupposes that computing and information technology will play a major role in the diffusion of aerospace knowledge. Little is known, however, about actual information technology needs, uses, and problems within the aerospace knowledge diffusion process. The authors state that the potential contributions of information technology to increased productivity and competitiveness will be diminished unless empirically derived knowledge regarding the information-seeking behavior of the members of the social system - those who are producing, transferring, and using scientific and technical information - is incorporated into a new technology policy framework. Research into the use of information technology and electronic networks by U.S. aerospace engineers and scientists, collected as part of a research project designed to study aerospace knowledge diffusion, is presented in support of this assertion.
Modelling heat and mass transfer in a membrane-based air-to-air enthalpy exchanger
NASA Astrophysics Data System (ADS)
Dugaria, S.; Moro, L.; Del, D., Col
2015-11-01
The diffusion of total energy recovery systems could lead to a significant reduction in the energy demand for building air-conditioning. With these devices, sensible heat and humidity can be recovered in winter from the exhaust airstream, while, in summer, the incoming air stream can be cooled and dehumidified by transferring the excess heat and moisture to the exhaust air stream. Membrane based enthalpy exchangers are composed by different channels separated by semi-permeable membranes. The membrane allows moisture transfer under vapour pressure difference, or water concentration difference, between the two sides and, at the same time, it is ideally impermeable to air and other contaminants present in exhaust air. Heat transfer between the airstreams occurs through the membrane due to the temperature gradient. The aim of this work is to develop a detailed model of the coupled heat and mass transfer mechanisms through the membrane between the two airstreams. After a review of the most relevant models published in the scientific literature, the governing equations are presented and some simplifying assumptions are analysed and discussed. As a result, a steady-state, two-dimensional finite difference numerical model is setup. The developed model is able to predict temperature and humidity evolution inside the channels. Sensible and latent heat transfer rate, as well as moisture transfer rate, are determined. A sensitive analysis is conducted in order to determine the more influential parameters on the thermal and vapour transfer.
Secondary Ion Mass Spectrometry for Mg Tracer Diffusion: Issues and Solutions
Tuggle, Jay; Giordani, Andrew; Kulkarni, Nagraj S; Warmack, Robert J Bruce; Coffey, Kevin; Sohn, Yong Ho; HunterJr., Jerry
2014-01-01
A Secondary Ion Mass Spectrometry (SIMS) method has been developed to measure stable Mg isotope tracer diffusion. This SIMS method was then used to calculate Mg self- diffusivities and the data was verified against historical data measured using radio tracers. The SIMS method has been validated as a reliable alternative to the radio-tracer technique for the measurement of Mg self-diffusion coefficients and can be used as a routine method for determining diffusion coefficients.
Body mass scaling of passive oxygen diffusion in endotherms and ectotherms
Gillooly, James F.; Gomez, Juan Pablo; Mavrodiev, Evgeny V.; Rong, Yue; McLamore, Eric S.
2016-01-01
The area and thickness of respiratory surfaces, and the constraints they impose on passive oxygen diffusion, have been linked to differences in oxygen consumption rates and/or aerobic activity levels in vertebrates. However, it remains unclear how respiratory surfaces and associated diffusion rates vary with body mass across vertebrates, particularly in relation to the body mass scaling of oxygen consumption rates. Here we address these issues by first quantifying the body mass dependence of respiratory surface area and respiratory barrier thickness for a diversity of endotherms (birds and mammals) and ectotherms (fishes, amphibians, and reptiles). Based on these findings, we then use Fick’s law to predict the body mass scaling of oxygen diffusion for each group. Finally, we compare the predicted body mass dependence of oxygen diffusion to that of oxygen consumption in endotherms and ectotherms. We find that the slopes and intercepts of the relationships describing the body mass dependence of passive oxygen diffusion in these two groups are statistically indistinguishable from those describing the body mass dependence of oxygen consumption. Thus, the area and thickness of respiratory surfaces combine to match oxygen diffusion capacity to oxygen consumption rates in both air- and water-breathing vertebrates. In particular, the substantially lower oxygen consumption rates of ectotherms of a given body mass relative to those of endotherms correspond to differences in oxygen diffusion capacity. These results provide insights into the long-standing effort to understand the structural attributes of organisms that underlie the body mass scaling of oxygen consumption. PMID:27118837
Body mass scaling of passive oxygen diffusion in endotherms and ectotherms.
Gillooly, James F; Gomez, Juan Pablo; Mavrodiev, Evgeny V; Rong, Yue; McLamore, Eric S
2016-05-10
The area and thickness of respiratory surfaces, and the constraints they impose on passive oxygen diffusion, have been linked to differences in oxygen consumption rates and/or aerobic activity levels in vertebrates. However, it remains unclear how respiratory surfaces and associated diffusion rates vary with body mass across vertebrates, particularly in relation to the body mass scaling of oxygen consumption rates. Here we address these issues by first quantifying the body mass dependence of respiratory surface area and respiratory barrier thickness for a diversity of endotherms (birds and mammals) and ectotherms (fishes, amphibians, and reptiles). Based on these findings, we then use Fick's law to predict the body mass scaling of oxygen diffusion for each group. Finally, we compare the predicted body mass dependence of oxygen diffusion to that of oxygen consumption in endotherms and ectotherms. We find that the slopes and intercepts of the relationships describing the body mass dependence of passive oxygen diffusion in these two groups are statistically indistinguishable from those describing the body mass dependence of oxygen consumption. Thus, the area and thickness of respiratory surfaces combine to match oxygen diffusion capacity to oxygen consumption rates in both air- and water-breathing vertebrates. In particular, the substantially lower oxygen consumption rates of ectotherms of a given body mass relative to those of endotherms correspond to differences in oxygen diffusion capacity. These results provide insights into the long-standing effort to understand the structural attributes of organisms that underlie the body mass scaling of oxygen consumption.
Mass transfer of large molecules through collagen and collagen-silica hybrid membranes
NASA Astrophysics Data System (ADS)
Jofre-Lora, Pedro
Diabetes is a growing concern in the United States and around the world that must be addressed through new treatment options. Current standard treatment options of diabetes are limiting and have tremendous impacts on patient's lives. Emerging therapies, such as the implantation of encapsulated islets, are promising treatment options, but have not yet materialized due to unsolved problems with material properties. Hybrid silica-collagen membranes address some of these unsolved problems and are a promising material for cell encapsulation. However, the mass transfer properties of large molecules, such as insulin, TNF-alpha, IL1beta, and other important proteins in the etiology of diabetes, through these hybrid membranes are poorly characterized. In order to begin characterizing these properties, a device was constructed to accurately and efficiently measure the mass transfer of other similar large molecules, fluorescein isothiocyanate dextrans (FITC-dextran), through collagen-silica hybrid membranes. The device was used to measure diffusion coefficients of 4, 20, 40, and 150 kDa FITC-dextrans through non-silicified and silicified samples of 200 and 1000 Pa porcine skin collagen. Diffusion coefficients were found to be in the 10-7-10-6 cm2s -1 range, which is in agreement with previously published data for similar molecules through similar hydrogels. The effects of collagen stiffness, FITC-dextran molecular weight, and silicification treatment on diffusion were investigated. It was found that collagen stiffness and FITC-dextran molecular weight had a negative correlation with diffusion, whereas silicification treatment had no global impact on diffusion. The device created, and the results of this preliminary investigation, can be used to develop collagen-silica hybrid membranes as an alternative material for cell encapsulation in a forward-design manner.
Subgrid models for mass and thermal diffusion in turbulent mixing
Sharp, David H; Lim, Hyunkyung; Li, Xiao - Lin; Gilmm, James G
2008-01-01
We are concerned with the chaotic flow fields of turbulent mixing. Chaotic flow is found in an extreme form in multiply shocked Richtmyer-Meshkov unstable flows. The goal of a converged simulation for this problem is twofold: to obtain converged solutions for macro solution features, such as the trajectories of the principal shock waves, mixing zone edges, and mean densities and velocities within each phase, and also for such micro solution features as the joint probability distributions of the temperature and species concentration. We introduce parameterized subgrid models of mass and thermal diffusion, to define large eddy simulations (LES) that replicate the micro features observed in the direct numerical simulation (DNS). The Schmidt numbers and Prandtl numbers are chosen to represent typical liquid, gas and plasma parameter values. Our main result is to explore the variation of the Schmidt, Prandtl and Reynolds numbers by three orders of magnitude, and the mesh by a factor of 8 per linear dimension (up to 3200 cells per dimension), to allow exploration of both DNS and LES regimes and verification of the simulations for both macro and micro observables. We find mesh convergence for key properties describing the molecular level of mixing, including chemical reaction rates between the distinct fluid species. We find results nearly independent of Reynolds number for Re 300, 6000, 600K . Methodologically, the results are also new. In common with the shock capturing community, we allow and maintain sharp solution gradients, and we enhance these gradients through use of front tracking. In common with the turbulence modeling community, we include subgrid scale models with no adjustable parameters for LES. To the authors' knowledge, these two methodologies have not been previously combined. In contrast to both of these methodologies, our use of Front Tracking, with DNS or LES resolution of the momentum equation at or near the Kolmogorov scale, but without resolving the
Bai, Dongsheng; Zhang, Diwei; Zhang, Xianren; Chen, Guangjin
2015-01-01
Gas hydrates could show an unexpected high stability at conditions out of thermodynamic equilibrium, which is called the self-preservation effect. The mechanism of the effect for methane hydrates is here investigated via molecular dynamics simulations, in which an NVT/E method is introduced to represent different levels of heat transfer resistance. Our simulations suggest a coupling between the mass transfer resistance and heat transfer resistance as the driving mechanism for self-preservation effect. We found that the hydrate is initially melted from the interface, and then a solid-like water layer with temperature-dependent structures is formed next to the hydrate interface that exhibits fractal feature, followed by an increase of mass transfer resistance for the diffusion of methane from hydrate region. Furthermore, our results indicate that heat transfer resistance is a more fundamental factor, since it facilitates the formation of the solid-like layer and hence inhibits the further dissociation of the hydrates. The self-preservation effect is found to be enhanced with the increase of pressure and particularly the decrease of temperature. Kinetic equations based on heat balance calculations is also developed to describe the self-preservation effect, which reproduces our simulation results well and provides an association between microscopic and macroscopic properties. PMID:26423519
NASA Astrophysics Data System (ADS)
Bai, Dongsheng; Zhang, Diwei; Zhang, Xianren; Chen, Guangjin
2015-10-01
Gas hydrates could show an unexpected high stability at conditions out of thermodynamic equilibrium, which is called the self-preservation effect. The mechanism of the effect for methane hydrates is here investigated via molecular dynamics simulations, in which an NVT/E method is introduced to represent different levels of heat transfer resistance. Our simulations suggest a coupling between the mass transfer resistance and heat transfer resistance as the driving mechanism for self-preservation effect. We found that the hydrate is initially melted from the interface, and then a solid-like water layer with temperature-dependent structures is formed next to the hydrate interface that exhibits fractal feature, followed by an increase of mass transfer resistance for the diffusion of methane from hydrate region. Furthermore, our results indicate that heat transfer resistance is a more fundamental factor, since it facilitates the formation of the solid-like layer and hence inhibits the further dissociation of the hydrates. The self-preservation effect is found to be enhanced with the increase of pressure and particularly the decrease of temperature. Kinetic equations based on heat balance calculations is also developed to describe the self-preservation effect, which reproduces our simulation results well and provides an association between microscopic and macroscopic properties.
Mass Transfer via Low Velocity Impacts into Regolith
NASA Astrophysics Data System (ADS)
Jarmak, Stephanie; Colwell, Josh E.; Brisset, Julie; Dove, Adrienne
2016-10-01
The study of low velocity collisions (<1 m/s) is essential to understand the growth and formation of aggregates in a number of environments in planetary systems. The Collisions Into Dust Experiment (COLLIDE) and Physics of Regolith Impacts in Microgravity Experiment (PRIME) experiments produced observations of mass transfer from regolith onto an impactor at these velocities in microgravity. We have subsequently carried out ground-based experiments in which a cm-scale sphere impacts and rebounds from a bed of granular material in 1-g laboratory conditions at low impact speeds with the aid of a spring. This allows impacts at v<1 m/s and ensures rebound of the impactor, with the spring providing enough force to overcome gravity. Preliminary results from an impact of a brass impactor into sand (200-500 μm) produced a monolayer of granular material onto the impactor, but the grains are not cohesive enough to allow a significant mass transfer under these conditions. Further experiments with a range of regolith properties, impactor composition and surface properties, impact velocities, and atmospheric conditions will be performed in the laboratory to study the effects of each of these properties on the contact transfer of regolith onto the impactor. Further microgravity experiments with PRIME and in a small drop tower are planned to then study bulk mass transfer with conditions informed by the ground-based experiments. Impacts with the COLLIDE and PRIME microgravity experiments showed mass transfer at speeds < 40 cm/s into JSC-1 lunar regolith simulant and quartz sand targets. We will present the free-fall and laboratory results and implications for the collisional evolution of dust, pebbles and boulders in the protoplanetary disk as well as particles in planetary ring systems.
Evaporative Mass Transfer Behavior of a Complex Immiscible Liquid
McColl, Colleen M.; Johnson, Gwynn R.; Brusseau, Mark L.
2010-01-01
A series of laboratory experiments was conducted with a multiple-component immiscible liquid, collected from the Picillo Farm Superfund Site in Rhode Island, to examine liquid-vapor mass-transfer behavior. The immiscible liquid, which comprises solvents, oils, pesticides, PCBs, paint sludges, explosives, and other compounds, was characterized using gas chromatography and gas chromatography/mass spectrometry to determine mole fractions of selected constituents. Batch experiments were conducted to evaluate equilibrium phase-partitioning behavior. Two sets of air-stripping column studies were conducted to examine the mass-transfer dynamics of five selected target compounds present in the immiscible-liquid mixture. One set of column experiments was designed to represent a system with free-phase immiscible liquid present; the other was designed to represent a system with a residual phase of immiscible liquid. Initial elution behavior of all target components generally appeared to be ideal for both systems, as the initial vapor-phase concentrations were similar to vapor-phase concentrations measured for the batch experiment and those estimated using Raoult’s law (incorporating the immiscible-liquid composition data). Later-stage removal of 1,2-dichlorobenzene appeared to be rate limited for the columns containing free-phase immiscible liquid and no porous medium. Conversely, evaporative mass transfer appeared to be ideal throughout the experiment conducted with immiscible liquid distributed relatively uniformly as a residual phase within a sandy porous medium. PMID:18614196
Mass transfer limitations in protein separations using ion-exchange membranes.
Sarfert, F T; Etzel, M R
1997-03-07
Sorption of bovine serum albumin to commercial 150-micron pore size membranes was measured in batch and flow experiments. For residence times of 2-40 min, early and broad breakthrough curves and broad asymmetric elution peaks were observed that depended strongly on flow-rate. System dispersion could not explain the flow-rate dependence. Breakthrough and elution curves were analyzed using new models that included Langmuir sorption, convection and diffusion. From the analysis, film mass transfer resistance was found to be the rate-limiting factor. The maximum allowable pore size that eliminates this limitation was calculated for different molecular weight solutes.
Law Jr., C.G.; Pierini, P.; Newman, J.
1980-07-01
Experimental data and theoretical calculations are presented for the mass-transfer rate to rotating disks and rotating rings when laminar, transition, and fully developed turbulent flow exist upon different portions of the surface. Good agreement of data and the model is obtained for rotating disks and relatively thick rotating rings. Results of the calculations for thin rings generally exceed the experimental data measured in transition and turbulent flow. A y{sup +{sup 3}} form for the eddy diffusivity is used to fit the data. No improvement is noticed with a form involving both y{sup +{sup 3}} and y{sup +{sup 3}}.
Mass transfer and magnetic braking in Sco X-1
NASA Astrophysics Data System (ADS)
Pavlovskii, K.; Ivanova, N.
2016-02-01
Sco X-1 is a low-mass X-ray binary (LMXB) that has one of the most precisely determined set of binary parameters such as the mass accretion rate, companions mass ratio and the orbital period. For this system, as well as for a large fraction of other well-studied LMXBs, the observationally-inferred mass accretion rate is known to strongly exceed the theoretically expected mass transfer (MT) rate. We suggest that this discrepancy can be solved by applying a modified magnetic braking prescription, which accounts for increased wind mass-loss in evolved stars compared to main sequence stars. Using our MT framework based on MESA, we explore a large range of binaries at the onset of the MT. We identify the subset of binaries for which the MT tracks cross the Sco X-1 values for the mass ratio and the orbital period. We confirm that no solution can be found for which the standard magnetic braking can provide the observed accretion rates, while wind-boosted magnetic braking can provide the observed accretion rates for many progenitor binaries that evolve to the observed orbital period and mass ratio.
Mass-transfer in close binary and their companions
NASA Astrophysics Data System (ADS)
Liao, Wenping; Qian, Shengbang; Zhu, Liying; Li, Linjia
2016-07-01
Secular and/or cyclical orbital period variations of close binaries can be derived by analyzing the (O-C) diagram. The secular variations are usually explained as mass transfer between components, while the most plausible explanation of the cyclic period changes is the light-travel time effect (LTTE) through the presence of a third body. Mass transfer and additional companions in close binary systems are important for understanding the formation and evolution of the systems. Here, UV light curves of several close binaries based on the Lunar-based Ultraviolet Telescope (LUT) observations are presented and analyzed with the Wilson-Devinney (W-D) method. Then, based on those light-curve solutions and new analysis of the orbital period variations, the multiplicity, geometrical structure and evolution state of targets are discussed.
Chemical separations by bubble-assisted interphase mass-transfer.
Boyd, David A; Adleman, James R; Goodwin, David G; Psaltis, Demetri
2008-04-01
We show that when a small amount of heat is added close to a liquid-vapor interface of a captive gas bubble in a microchannel, interphase mass-transfer through the bubble can occur in a controlled manner with only a slight change in the temperature of the fluid. We demonstrate that this method, which we refer to as bubble-assisted interphase mass-transfer (BAIM), can be applied to interphase chemical separations, e.g., simple distillation, without the need for high temperatures, vacuum, or active cooling. Although any source of localized heating could be used, we illustrate BAIM with an all-optical technique that makes use of the plasmon resonance in an array of nanoscale metal structures that are incorporated into the channel to produce localized heating of the fluid when illuminated by a stationary low-power laser.
Geoelectrical inference of mass transfer parameters using temporal moments
Day-Lewis, F. D.; Singha, K.
2008-01-01
We present an approach to infer mass transfer parameters based on (1) an analytical model that relates the temporal moments of mobile and bulk concentration and (2) a bicontinuum modification to Archie's law. Whereas conventional geochemical measurements preferentially sample from the mobile domain, electrical resistivity tomography (ERT) is sensitive to bulk electrical conductivity and, thus, electrolytic solute in both the mobile and immobile domains. We demonstrate the new approach, in which temporal moments of collocated mobile domain conductivity (i.e., conventional sampling) and ERT-estimated bulk conductivity are used to calculate heterogeneous mass transfer rate and immobile porosity fractions in a series of numerical column experiments. Copyright 2008 by the American Geophysical Union.
Jensen, Malene Ringkjøbing; Kristensen, Søren M; Led, Jens J
2007-03-01
The NMR saturation transfer experiment is widely used to characterize exchange processes in proteins that take place on the ms-s timescale. However, spin diffusion effects are inherently associated with the saturation transfer experiment and may overshadow the effect of the exchange processes of interest. As shown here, the effects from spin diffusion and exchange processes can be separated by varying the field strength of the saturation pulse, thereby allowing correct exchange rates to be obtained. The method is demonstrated using the hydrogen exchange process in the protein Escherichia coli thioredoxin as an example.
Mass transfer ways of ultraviolet printing ink ingredients into foodstuffs.
Jung, T; Simat, T J; Altkofer, W
2010-07-01
The case of isopropylthioxanthone (ITX) showed conclusively that the ingredients of ultraviolet printing inks may migrate into packaged foodstuffs. For multilayered materials like beverage cartons, the only way that mass transfer can occur is by the so-called set-off effect. In contrast, in the case of rigid plastics like yoghurt cups, two other methods of mass transfer, permeation and gas phase, have to be considered. In cooperation with producers of ink, plastic cups and yoghurt, a project was conducted in order to elucidate the mass transfer of ink ingredients. In addition, the influence of storage time and the age of ultraviolet lamps on the migration level was examined. The suitability of 50% ethanol as a simulant for yoghurt was also tested. ITX was chosen as a model migrant, as it is easily detectable. Furthermore, the migration of two other substances, the photo-initiator 2-methyl-4'-(methylthio)-2-morpholinopropiophenone (MTMP) and the amine synergist ethyl-4-(dimethylamino)benzoate (EDAB), which may be used in combination with ITX, was studied. Before being filled with yoghurt or 50% ethanol, the printed cups were stored under different contact conditions, with and without contact between the inner layer and the printed surfaces, in order to distinguish between the possible mass transfer ways. All analyses were performed by means of high performance liquid chromatography with diode array and fluorescence detection (HPLC-DAD/FLD). It was shown that contamination with ITX and EDAB occurs via set-off and that the degree of migration increases with lamp age and storage time of the unfilled cups. Migration of MTMP was not detectable. The results show that besides the careful selection of the appropriate raw materials for printing ink, a close monitoring of the process also plays a major role in migration control. In addition, the results proved that 50% ethanol is a suitable simulant for yoghurt.
Vaporization of Graphitic Materials at High Mass Transfer Rates
1976-03-01
graphite 2. Carbon sublimation 3. High temperature carbon response 4. Sublimation kinetics |ITR\\CT fCanllim an rararaa «14a II nacaaaair an« Htnlllr *r...8217»’» numbmi) iThe thermochemical sublimation response of ATJ-S graphite in both low and high mass transfer convective environments was studied... sublimation effects com- pared to JANAF equilibrium sublimation predictions. Extrapolation of the inferred kinetic sublimation effects to the high
Combined heat and mass transfer device for improving separation process
Tran, Thanh Nhon
1999-01-01
A two-phase small channel heat exchange matrix simultaneously provides for heat transfer and mass transfer between the liquid and vapor phases of a multi-component mixture at a single, predetermined location within a separation column, significantly improving the thermodynamic efficiency of the separation process. The small channel heat exchange matrix is composed of a series of channels having a hydraulic diameter no greater than 5.0 millimeters for conducting a two-phase coolant. In operation, the matrix provides the liquid-vapor contacting surfaces within the separation column, such that heat and mass are transferred simultaneously between the liquid and vapor phases. The two-phase coolant allows for a uniform heat transfer coefficient to be maintained along the length of the channels and across the surface of the matrix. Preferably, a perforated, concave sheet connects each channel to an adjacent channel to facilitate the flow of the liquid and vapor phases within the column and to increase the liquid-vapor contacting surface area.
Combined heat and mass transfer device for improving separation process
Tran, T.N.
1999-08-24
A two-phase small channel heat exchange matrix simultaneously provides for heat transfer and mass transfer between the liquid and vapor phases of a multi-component mixture at a single, predetermined location within a separation column, significantly improving the thermodynamic efficiency of the separation process. The small channel heat exchange matrix is composed of a series of channels having a hydraulic diameter no greater than 5.0 millimeters for conducting a two-phase coolant. In operation, the matrix provides the liquid-vapor contacting surfaces within the separation column, such that heat and mass are transferred simultaneously between the liquid and vapor phases. The two-phase coolant allows for a uniform heat transfer coefficient to be maintained along the length of the channels and across the surface of the matrix. Preferably, a perforated, concave sheet connects each channel to an adjacent channel to facilitate the flow of the liquid and vapor phases within the column and to increase the liquid-vapor contacting surface area. 12 figs.
Heat and mass transfer in volcano-hydrothermal systems
NASA Astrophysics Data System (ADS)
Scott, S. W.
2015-12-01
Hydrothermal systems re-distribute heat and mass derived from subsurface magma bodies over large temporal and spatial scales. Numerical models of fluid flow and heat transfer provide a quantitative basis for understanding the thermo-hydrological structure and transient behavior of volcano-hydrothermal systems. At the brittle-ductile transition around a magma body, the rate of conductive heat transfer from the impermeable intrusion is balanced by the rate of advective heat transfer by the fluid. Using the Complex Systems Modeling Platform (CSMP++) to model fluid flow up to near-magmatic conditions, we examine the effect of geologic factors such as host rock permeability, magma emplacement depth, the temperature conditions of the brittle-ductile transition, and rock/magma thermal conductivity on the rates of heat and mass transfer around magma bodies. Additionally, we investigate the role of these factors on the thermo-hydrological structure of the hydrothermal system, including patterns of phase separation, gravity-driven phase segregation, and fluid mixing. Passive tracers are included in the fluid flow models to simulate the input of magmatic volatiles into hydrothermal fluids and their fractionation between the liquid and vapor phases. Ultimately, we compare our model results against measured heat and gas fluxes from volcano-hydrothermal systems to help inform the interpreation of these measurements.
NASA Astrophysics Data System (ADS)
Watkins, James; Gupta, Ravi; Ramachandrarao, Vijay
2001-03-01
Diffusion coefficients of molecular probes in CO2-swollen polystyrene films were measured in situ using high-pressure fluorescence nonradiative energy transfer (NRET). Specifically, the diffusivities of decacyclene and BPEA (9,10- bis phenyl ethnyl Anthracene), relatively large fluorescence acceptor probes, were determined in real time using pyrene-labeled polystyrene as the corresponding energy donor in carbon dioxide-plasticized films. Decacyclene diffusivities were measured at 65 and 80 C and carbon dioxide pressures ranging from 62 to 144 bar, conditions near and well above the previously reported, solvent-depressed glass transition of polystyrene. Decacyclene diffusivity shows an increase of over 5 orders of magnitude upon CO2 sorption relative to the PS glass at ambient pressure and equivalent temperatures. BPEA exhibits similar behavior but diffuses about an order of magnitude faster than decacyclene in CO2 plasticized polystyrene under similar conditions.
Mass transfer controlled by fracturing in micritic carbonate rocks
NASA Astrophysics Data System (ADS)
Richard, James; Coulon, Michel; Gaviglio, Patrick
2002-05-01
The fractured Coniacian chalk from the Omey area (Paris Basin, France) displays strong evidence of modifications controlled by brittle deformation. Fracturing is associated with important changes in pore space (decrease in total porosity and pore interconnection, change in distribution of pore access diameters and capillary characteristics), nannofacies (gradual evolution from a point-contact fabric to a welded, interlocked or coalescent fabric) and chemical composition (Sr concentration decrease). These modifications result from fluid-rock interaction that control significant mass transfer (percentage of secondary calcite >50%). Sr is a remarkable indicator of these mass transfers. Sr analyses allowed us to prove that the deformed zone (26.7 m) is wider than the fractured zone (11.3 m). They also indicate that the footwall block is less affected than the hanging wall block. A physicochemical model of the deformation mechanism is proposed. It shows that a cyclic process of fracturing controls the temporal evolution of the fluid saturation and fluid pressure and, consequently, the mass transfer.
Mass transfer and oxidation kinetics in an in situ ozone generator.
Mathews, A P; Panda, K K; Ananthi, S; Padmanabhan, K
2004-01-01
An in situ ozone generator design based on a novel type of corona discharge tube construction was tested to examine enhancements in mass transfer and ozonation efficiency over conventional systems. In this design, the discharge gap is kept juxtaposed to the tubular pathway through which the treatment fluid is passed. A porous inner electrode tube is employed in the discharge tube, and the generated ozone diffuses through this porous tube and dissolves and reacts with the contaminants in the fluid that is being treated. The inner porous ceramic tube is grounded while the outer glass electrode is positively charged for corona discharge. Oxidation studies conducted on Reactive Blue 19 dye indicate that the time required for 90% color removal is about half that of a conventional ozone generation and bubble diffusion system at the same ozone dosage.
Rational design of mass diffusion metamaterial concentrators based on coordinate transformations
NASA Astrophysics Data System (ADS)
Restrepo-Flórez, Juan Manuel; Maldovan, Martin
2016-08-01
Recent advances in coordinate transformations of Fick's equation have paved the way for the design of metamaterial devices that can manipulate mass diffusion flux. The control of diffusion paths has a great potential for the design of novel catalytic and separation systems in chemical and biomolecular engineering. In order to explore these new applications, it is necessary to understand mass diffusion in coordinate transformation metamaterial devices. In this work, we present a comprehensive study on the impact of structure and material properties on the resultant physical properties of mass concentrator metamaterial shells. The concentration gradient at the core, the total mass flow rate towards the core, and the disturbance of the external concentration field are systematically examined in order to provide guidelines for the rational design and fabrication of metamaterial mass concentrators. A practical case is also presented where the concentration of oxygen diffusing in a polymeric system is studied.
Kim, Hyunjung; Guiochon, Georges A
2005-08-01
The parameters of the thermodynamics and mass transfer kinetics of the structural analogues (L-enantiomers) of the template were measured on an Fmoc-L-tryptophan (Fmoc-L-Trp) imprinted polymer, at different temperatures. The equilibrium isotherm data and the overloaded band profiles of these compounds were measured at temperatures of 298, 313, 323, and 333 K. The isotherm data were modeled. The thermodynamic functions of the different adsorption sites were derived from the isotherm parameters, using van't Hoff plots. The mass transfer parameters were derived by comparing the experimental peak profiles and profiles calculated using the lumped pore diffusion (POR) model for chromatography. These data show that (1) the strength between the substrate molecules and the MIP increases with increasing number of functional groups on the substrates; (2) enthalpy is the driving force for the affinity of the substrates for the MIP; (3) surface diffusion is the dominant mass transfer mechanism of the substrates through the porous MIP. For those substrate molecules that have the same stereochemistry as the template, the energetic surface heterogeneity needs to be incorporated into the surface diffusion coefficients. Heterogeneous surface diffusivities decrease with increasing affinity of the substrates for the MIP.
The adsorption and mass-transfer process of cationic red X-GRL dye on natural zeolite.
Tian, Jingjing; Guan, Junfang; Gao, Huimin; Wen, Yafei; Ren, Zijie
2016-01-01
The adsorption behavior of natural zeolite was studied in order to determine the adsorption capacity and mass-transfer process of cationic red X-GRL (C(18)H(21)BrN(6)) onto the adsorbent. The adsorption tests to determine both the uptake capacity and the mass-transfer process at equilibrium were performed under batch conditions, which showed rapid uptake in general for the initial 5 min, corresponding to 92% total removal. The equilibrium adsorption capacity value (q(e,cal)) in pseudo-second-order kinetics was 13.51 mg/g at 293 K and the whole adsorption process was governed by physical adsorption with an endothermic, endothermic spontaneous nature. Adsorption tests indicated that the zeolite has great potential as an alternative low-cost material in the treatment of X-GRL drainage. However, the mass-transfer process to determine the rate-controlling steps showed that both film diffusion and pore diffusion were important in controlling the adsorption rate. The adsorption process was governed by film diffusion while pore diffusion was poor because the X-GRL molecules could not penetrate into the zeolite easily. The X-GRL molecules were only adsorbed on the external surface of the zeolite. Hence, to improve the adsorption capacity of natural zeolite further, modification to expand its micropores is necessary.
Prak, Dianne J Luning
2008-05-01
A key component to predicting the success of utilizing surfactants to enhance the removal of organic liquids from soil system is quantifying micellar solubilization kinetics. In this study, a flow reactor was employed to investigate the influence of surfactant ethoxylate chain length on the rates of solubilization of octane, decane, and dodecane in micellar solutions of a homologous series of purified dodecyl alcohol ethoxylates. Effluent concentration data were fit using a finite element model utilizing a linear-driving-force model to represent mass transfer at the interface. For flow rates between 0.1 and 2 ml min(-1), mass transfer coefficients ranged from 5 x 10(-8) to 7 x 10(-7)m s(-1) and did not vary in a systematic way with either solute structure or surfactant ethoxylate chain length and were lower than those found in pure water. Correlations developed for the Sherwood number based on diffusion coefficients of surfactant micelles containing organic material (organic-laden micelle) exhibit a velocity dependence similar to that found for systems based on aqueous diffusion. These results suggest that under gentle flowing conditions, the mass transfer is limited by diffusion of the organic-laden micelle. Although these trends are specific for this experimental system, the results demonstrate the importance of selecting the proper diffusion coefficient when modeling surfactant solubilization processes.
Mass transfer model for two-layer TBP oxidation reactions
Laurinat, J.E.
1994-09-28
To prove that two-layer, TBP-nitric acid mixtures can be safely stored in the canyon evaporators, it must be demonstrated that a runaway reaction between TBP and nitric acid will not occur. Previous bench-scale experiments showed that, at typical evaporator temperatures, this reaction is endothermic and therefore cannot run away, due to the loss of heat from evaporation of water in the organic layer. However, the reaction would be exothermic and could run away if the small amount of water in the organic layer evaporates before the nitric acid in this layer is consumed by the reaction. Provided that there is enough water in the aqueous layer, this would occur if the organic layer is sufficiently thick so that the rate of loss of water by evaporation exceeds the rate of replenishment due to mixing with the aqueous layer. This report presents measurements of mass transfer rates for the mixing of water and butanol in two-layer, TBP-aqueous mixtures, where the top layer is primarily TBP and the bottom layer is comprised of water or aqueous salt solution. Mass transfer coefficients are derived for use in the modeling of two-layer TBP-nitric acid oxidation experiments. Three cases were investigated: (1) transfer of water into the TBP layer with sparging of both the aqueous and TBP layers, (2) transfer of water into the TBP layer with sparging of just the TBP layer, and (3) transfer of butanol into the aqueous layer with sparging of both layers. The TBP layer was comprised of 99% pure TBP (spiked with butanol for the butanol transfer experiments), and the aqueous layer was comprised of either water or an aluminum nitrate solution. The liquid layers were air sparged to simulate the mixing due to the evolution of gases generated by oxidation reactions. A plastic tube and a glass frit sparger were used to provide different size bubbles. Rates of mass transfer were measured using infrared spectrophotometers provided by SRTC/Analytical Development.
Modelling mass and heat transfer in nano-based cancer hyperthermia.
Nabil, M; Decuzzi, P; Zunino, P
2015-10-01
We derive a sophisticated mathematical model for coupled heat and mass transport in the tumour microenvironment and we apply it to study nanoparticle delivery and hyperthermic treatment of cancer. The model has the unique ability of combining the following features: (i) realistic vasculature; (ii) coupled capillary and interstitial flow; (iii) coupled capillary and interstitial mass transfer applied to nanoparticles; and (iv) coupled capillary and interstitial heat transfer, which are the fundamental mechanisms governing nano-based hyperthermic treatment. This is an improvement with respect to previous modelling approaches, where the effect of blood perfusion on heat transfer is modelled in a spatially averaged form. We analyse the time evolution and the spatial distribution of particles and temperature in a tumour mass treated with superparamagnetic nanoparticles excited by an alternating magnetic field. By means of numerical experiments, we synthesize scaling laws that illustrate how nano-based hyperthermia depends on tumour size and vascularity. In particular, we identify two distinct mechanisms that regulate the distribution of particle and temperature, which are characterized by perfusion and diffusion, respectively.
Mass transfer in a flow past a non-porous catalyst sphere
NASA Astrophysics Data System (ADS)
Sun, Bo; Tenneti, Sudheer; Subramaniam, Shankar
2015-11-01
Mass transfer in a flow past a particle with a surface chemical reaction occurs in applications involving catalytic reaction. This type of the mass transfer problem has been analyzed by solving the convection-diffusion equation for Stokes flow (Acrivos et al., 1962) or flow at low Reynolds number (Taylor 1963, Gupalo et al., 1972). The objective of this study is to extend our understanding of this mass transfer problem to higher Reynolds number (up to 100) and assemblies of several particles by using particle-resolved direct numerical simulation (PR-DNS) of gas-solid flow. A uniform flow past a non-porous spherical particle with a first-order surface reaction is simulated. The non-dimensional reaction rate constant is the important parameter in the single particle case. The PR-DNS results at low Reynolds number for a single particle are first compared with 2D analytical solutions for concentration fields and the Sherwood number. Finally, the dependence of the concentration field on the non-dimensional reaction rate constant, and comparison of PR-DNS results with other Sherwood number correlations that use the Reynolds analogy to adapt Nusselt number correlations (which do not explicitly account for surface reactions) are explored at high Reynolds number. CBET 1034307, CBET 1336941.
Modelling mass and heat transfer in nano-based cancer hyperthermia
Nabil, M.; Decuzzi, P.; Zunino, P.
2015-01-01
We derive a sophisticated mathematical model for coupled heat and mass transport in the tumour microenvironment and we apply it to study nanoparticle delivery and hyperthermic treatment of cancer. The model has the unique ability of combining the following features: (i) realistic vasculature; (ii) coupled capillary and interstitial flow; (iii) coupled capillary and interstitial mass transfer applied to nanoparticles; and (iv) coupled capillary and interstitial heat transfer, which are the fundamental mechanisms governing nano-based hyperthermic treatment. This is an improvement with respect to previous modelling approaches, where the effect of blood perfusion on heat transfer is modelled in a spatially averaged form. We analyse the time evolution and the spatial distribution of particles and temperature in a tumour mass treated with superparamagnetic nanoparticles excited by an alternating magnetic field. By means of numerical experiments, we synthesize scaling laws that illustrate how nano-based hyperthermia depends on tumour size and vascularity. In particular, we identify two distinct mechanisms that regulate the distribution of particle and temperature, which are characterized by perfusion and diffusion, respectively. PMID:26587251
Mass Transfer Model of Desulfurization in the Electroslag Remelting Process
NASA Astrophysics Data System (ADS)
Hou, Dong; Jiang, Zhou-Hua; Dong, Yan-Wu; Li, Yang; Gong, Wei; Liu, Fu-Bin
2017-02-01
Experimental and theoretical studies have been carried out to investigate the effects of the slag on desulfurization during the electroslag remelting (ESR) process with a focus of developing a mass transfer model to understand the mechanism of desulfurization. Stainless steel 1Cr21Ni5Ti was used as the electrode and remelted with two different kinds of slags using a 50-kg ESR furnace. The contents of sulfur along the axial direction of product ingots were analyzed. It was found that the sulfur content of 350 ppm in the electrode is reduced to 71 to 95 ppm in the ingot by remelting with the slag containing 5 wt pct of CaO, and lowered more to 47 to 59 ppm with another slag having 20 wt pct CaO. On the basis of the penetration and film theories, the theoretical model developed in this work well elucidates the kinetics of desulfurization revealing the mechanism of sulfur transfer during the ESR process. The calculation results obtained from the model agree well with the experimental results. The model indicates that when sulfur content in electrode is given, there is a corresponding minimum value of sulfur content in the ingot due to the kinetics limit. This lowest sulfur content cannot be further reduced even with increasing L S (sulfur distribution coefficient between metal and slag phases) or decreasing sulfur content in the slag. Constant addition of extra amount of CaO to the molten slag with the increase of sulfur content in the slag during the remelting process can improve the macrosegregation of sulfur distributed along the axial direction of ESR ingots. Since the rate-determining steps of the sulfur mass transfer lie in the metal phase, adding calcium as deoxidizer can change mass transfer of sulfur and thus promote desulfurization further during the ESR process.
Heat and mass transfer and hydrodynamics in swirling flows (review)
NASA Astrophysics Data System (ADS)
Leont'ev, A. I.; Kuzma-Kichta, Yu. A.; Popov, I. A.
2017-02-01
Research results of Russian and foreign scientists of heat and mass transfer in whirling flows, swirling effect, superficial vortex generators, thermodynamics and hydrodynamics at micro- and nanoscales, burning at swirl of the flow, and technologies and apparatuses with the use of whirling currents for industry and power generation were presented and discussed at the "Heat and Mass Transfer in Whirling Currents" 5th International Conference. The choice of rational forms of the equipment flow parts when using whirling and swirling flows to increase efficiency of the heat-power equipment and of flow regimes and burning on the basis of deep study of the flow and heat transfer local parameters was set as the main research prospect. In this regard, there is noticeable progress in research methods of whirling and swirling flows. The number of computational treatments of swirling flows' local parameters has been increased. Development and advancement of the up to date computing models and national productivity software are very important for this process. All experimental works are carried out with up to date research methods of the local thermoshydraulic parameters, which enable one to reveal physical mechanisms of processes: PIV and LIV visualization techniques, high-speed and infrared photography, high speed registration of parameters of high-speed processes, etc. There is a problem of improvement of researchers' professional skills in the field of fluid mechanics to set adequately mathematics and physics problems of aerohydrodynamics for whirling and swirling flows and numerical and pilot investigations. It has been pointed out that issues of improvement of the cooling system and thermal protection effectiveness of heat-power and heat-transfer equipment units are still actual. It can be solved successfully using whirling and swirling flows as simple low power consumption exposing on the flow method and heat transfer augmentation.
A reciprocal theorem for convective heat and mass transfer in Stokes and potential flows
NASA Astrophysics Data System (ADS)
Masoud, Hassan; Vandadi, Vahid; Jafari Kang, Saeed
2016-11-01
In the study of convective heat and mass transfer from a particle, key quantities of interest are usually the average rate of transfer and the mean distribution of the scalar (i.e., temperature or concentration) at the particle surface. Calculating these quantities using conventional equations requires detailed knowledge of the scalar field, which is available predominantly for problems involving uniform scalar and flux boundary conditions. Here, we derive a reciprocal relation between two diffusing scalars that are advected by oppositely driven Stokes or potential flows whose streamline configurations are identical. This relation leads to alternative expressions for the aforementioned average quantities based on the solution of the scalar field for uniform surface conditions.
Yao, Yi; Berkowitz, Max L. E-mail: ykanai@unc.edu; Kanai, Yosuke E-mail: ykanai@unc.edu
2015-12-28
The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na{sup +} and K{sup +} ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications.
NASA Astrophysics Data System (ADS)
Yao, Yi; Berkowitz, Max L.; Kanai, Yosuke
2015-12-01
The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na+ and K+ ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications.
Yao, Yi; Berkowitz, Max L; Kanai, Yosuke
2015-12-28
The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na(+) and K(+) ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications.
Jimenez, Mélanie; Dietrich, Nicolas; Grace, John R; Hébrard, Gilles
2014-07-01
Powerful techniques, based on the Planar Laser Induced Fluorescence (PLIF) technique, are deployed to locally visualize and quantify the impact of surfactants in wastewaters on hydrodynamics and oxygen mass transfer. Bubble diameter, aspect ratio, rise velocity, contamination angle, as well as flux, flux density, liquid side mass transfer and diffusion coefficients of transferred oxygen are determined based on these techniques applied in the wake of rising bubbles of diameter 1 mm and through planar gas/liquid interfaces. The initial experiments were performed in demineralized water containing small amounts of surfactant. Different concentrations of surfactant were added to finally reach the Critical Micelle Concentration (CMC). Bubbles have classically been found to be more spherical with a reduced rise velocity in the presence of surfactants up to the CMC. Above the CMC, these hydrodynamic characteristics were found to be almost constant, although the oxygen mass transfer decreased due to the presence of surfactants. Experimental results were markedly lower than predicted by the well-known Frössling equation with rigid surfaces. This is believed to be caused by a barrier of surfactants hindering the oxygen mass transfer at the interface. Similar hindrance of oxygen mass transfer applies to waters from sewage plants (filtered raw water and treated water), making accurate design of aeration tanks difficult.
ERIC Educational Resources Information Center
Ottoson, Judith M.
2009-01-01
Five knowledge-for-action theories are summarized and compared in this chapter for their evaluation implications: knowledge utilization, diffusion, implementation, transfer, and translation. Usually dispersed across multiple fields and disciplines, these theories are gathered here for a common focus on knowledge and change. Knowledge in some form…
PAHs and organic matter partitioning and mass transfer from coal tar particles to water
Karim Benhabib; Marie-Odile Simonnot; Michel Sardin
2006-10-01
The coal tar found in contaminated soils of former manufactured gas plants and coking plants acts as a long-term source of PAHs. Organic carbon and PAH transfer from coal tar particles to water was investigated with closed-looped laboratory column experiments run at various particle sizes and temperatures. Two models were derived. The first one represented the extraction process at equilibrium and was based on a linear partitioning of TOC and PAHs between coal tar and water. The partition coefficient was derived as well as the mass of extractable organic matter in the particles. The second model dealt with mass transfer. Particle diffusion was the limiting step; organic matter diffusivity in the coal tar was then computed in the different conditions. A good consistency was obtained between experimental and computed results. Hence, the modeling of PAH migration in contaminated soils at the field scale requires taking into account coal tar as the source-term for PAH release. 28 refs., 5 figs., 3 tabs.
Effects of mass transfer between Martian satellites on surface geology
NASA Astrophysics Data System (ADS)
Nayak, Michael; Nimmo, Francis; Udrea, Bogdan
2016-03-01
Impacts on planetary bodies can lead to both prompt secondary craters and projectiles that reimpact the target body or nearby companions after an extended period, producing so-called "sesquinary" craters. Here we examine sesquinary cratering on the moons of Mars. We model the impact that formed Voltaire, the largest crater on the surface of Deimos, and explore the orbital evolution of resulting high-velocity ejecta across 500 years using four-body physics and particle tracking. The bulk of mass transfer to Phobos occurs in the first 102 years after impact, while reaccretion of ejecta to Deimos is predicted to continue out to a 104 year timescale (cf. Soter, S. [1971]. Studies of the Terrestrial Planets. Cornell University). Relative orbital geometry between Phobos and Deimos plays a significant role; depending on the relative true longitude, mass transfer between the moons can change by a factor of five. Of the ejecta with a velocity range capable of reaching Phobos, 25-42% by mass reaccretes to Deimos and 12-21% impacts Phobos. Ejecta mass transferred to Mars is <10%. We find that the characteristic impact velocity of sesquinaries on Deimos is an order of magnitude smaller than those of background (heliocentric) hypervelocity impactors and will likely result in different crater morphologies. The time-averaged flux of Deimos material to Phobos can be as high as 11% of the background (heliocentric) direct-to-Phobos impactor flux. This relatively minor contribution suggests that spectrally red terrain on Phobos (Murchie, S., Erard, S. [1996]. Icarus 123, 63-86) is not caused by Deimos material. However the high-velocity ejecta mass reaccreted to Deimos from a Voltaire-sized impact is comparable to the expected background mass accumulated on Deimos between Voltaire-size events. Considering that the high-velocity ejecta contains only 0.5% of the total mass sent into orbit, sesquinary ejecta from a Voltaire-sized impact could feasibly resurface large parts of the Moon
Conjugate heat and mass transfer in the lattice Boltzmann equation method
Li, LK; Chen, C; Mei, RW; Klausner, JF
2014-04-22
An interface treatment for conjugate heat and mass transfer in the lattice Boltzmann equation method is proposed based on our previously proposed second-order accurate Dirichlet and Neumann boundary schemes. The continuity of temperature (concentration) and its flux at the interface for heat (mass) transfer is intrinsically satisfied without iterative computations, and the interfacial temperature (concentration) and their fluxes are conveniently obtained from the microscopic distribution functions without finite-difference calculations. The present treatment takes into account the local geometry of the interface so that it can be directly applied to curved interface problems such as conjugate heat and mass transfer in porous media. For straight interfaces or curved interfaces with no tangential gradient, the coupling between the interfacial fluxes along the discrete lattice velocity directions is eliminated and thus the proposed interface schemes can be greatly simplified. Several numerical tests are conducted to verify the applicability and accuracy of the proposed conjugate interface treatment, including (i) steady convection-diffusion in a channel containing two different fluids, (ii) unsteady convection-diffusion in the channel, (iii) steady heat conduction inside a circular domain with two different solid materials, and (iv) unsteady mass transfer from a spherical droplet in an extensional creeping flow. The accuracy and order of convergence of the simulated interior temperature (concentration) field, the interfacial temperature (concentration), and heat (mass) flux are examined in detail and compared with those obtained from the "half-lattice division" treatment in the literature. The present analysis and numerical results show that the half-lattice division scheme is second-order accurate only when the interface is fixed at the center of the lattice links, while the present treatment preserves second-order accuracy for arbitrary link fractions. For curved
Conjugate heat and mass transfer in the lattice Boltzmann equation method.
Li, Like; Chen, Chen; Mei, Renwei; Klausner, James F
2014-04-01
An interface treatment for conjugate heat and mass transfer in the lattice Boltzmann equation method is proposed based on our previously proposed second-order accurate Dirichlet and Neumann boundary schemes. The continuity of temperature (concentration) and its flux at the interface for heat (mass) transfer is intrinsically satisfied without iterative computations, and the interfacial temperature (concentration) and their fluxes are conveniently obtained from the microscopic distribution functions without finite-difference calculations. The present treatment takes into account the local geometry of the interface so that it can be directly applied to curved interface problems such as conjugate heat and mass transfer in porous media. For straight interfaces or curved interfaces with no tangential gradient, the coupling between the interfacial fluxes along the discrete lattice velocity directions is eliminated and thus the proposed interface schemes can be greatly simplified. Several numerical tests are conducted to verify the applicability and accuracy of the proposed conjugate interface treatment, including (i) steady convection-diffusion in a channel containing two different fluids, (ii) unsteady convection-diffusion in the channel, (iii) steady heat conduction inside a circular domain with two different solid materials, and (iv) unsteady mass transfer from a spherical droplet in an extensional creeping flow. The accuracy and order of convergence of the simulated interior temperature (concentration) field, the interfacial temperature (concentration), and heat (mass) flux are examined in detail and compared with those obtained from the "half-lattice division" treatment in the literature. The present analysis and numerical results show that the half-lattice division scheme is second-order accurate only when the interface is fixed at the center of the lattice links, while the present treatment preserves second-order accuracy for arbitrary link fractions. For curved
Influence of mass transfer on bubble plume hydrodynamics.
Lima Neto, Iran E; Parente, Priscila A B
2016-03-01
This paper presents an integral model to evaluate the impact of gas transfer on the hydrodynamics of bubble plumes. The model is based on the Gaussian type self-similarity and functional relationships for the entrainment coefficient and factor of momentum amplification due to turbulence. The impact of mass transfer on bubble plume hydrodynamics is investigated considering different bubble sizes, gas flow rates and water depths. The results revealed a relevant impact when fine bubbles are considered, even for moderate water depths. Additionally, model simulations indicate that for weak bubble plumes (i.e., with relatively low flow rates and large depths and slip velocities), both dissolution and turbulence can affect plume hydrodynamics, which demonstrates the importance of taking the momentum amplification factor relationship into account. For deeper water conditions, simulations of bubble dissolution/decompression using the present model and classical models available in the literature resulted in a very good agreement for both aeration and oxygenation processes. Sensitivity analysis showed that the water depth, followed by the bubble size and the flow rate are the most important parameters that affect plume hydrodynamics. Lastly, dimensionless correlations are proposed to assess the impact of mass transfer on plume hydrodynamics, including both the aeration and oxygenation modes.
Kim, Hyunjung; Kaczmarski, Krzysztof; Guiochon, Georges A
2006-03-01
The equilibrium isotherm and the intraparticle mass transfer kinetics of the enantiomers of the template were investigated on an Fmoc-L-tryptophan (Fmoc-L-Trp) imprinted polymer at different pHs and water concentrations in acetonitrile/aqueous buffer mobile phases. The equilibrium isotherm data were measured using frontal analysis at 25 {+-} 2 C. The adsorption energy distribution was found to be trimodal, with narrow modes. Consistent with this distribution, the adsorption data were modeled using a tri-Langmuir isotherm equation and the best estimates of the isotherm parameters were determined. The intraparticle mass transfer parameters were derived by comparing the profiles of experimental overloaded bands and the profiles calculated using the isotherm model and the lumped pore diffusion (POR) model of chromatography. These results showed that different adsorption and mass transfer mechanisms exist in mobile phases made of acetonitrile/aqueous buffer and of acetonitrile/acetic acid solutions.
Counter-extrapolation method for conjugate interfaces in computational heat and mass transfer.
Le, Guigao; Oulaid, Othmane; Zhang, Junfeng
2015-03-01
In this paper a conjugate interface method is developed by performing extrapolations along the normal direction. Compared to other existing conjugate models, our method has several technical advantages, including the simple and straightforward algorithm, accurate representation of the interface geometry, applicability to any interface-lattice relative orientation, and availability of the normal gradient. The model is validated by simulating the steady and unsteady convection-diffusion system with a flat interface and the steady diffusion system with a circular interface, and good agreement is observed when comparing the lattice Boltzmann results with respective analytical solutions. A more general system with unsteady convection-diffusion process and a curved interface, i.e., the cooling process of a hot cylinder in a cold flow, is also simulated as an example to illustrate the practical usefulness of our model, and the effects of the cylinder heat capacity and thermal diffusivity on the cooling process are examined. Results show that the cylinder with a larger heat capacity can release more heat energy into the fluid and the cylinder temperature cools down slower, while the enhanced heat conduction inside the cylinder can facilitate the cooling process of the system. Although these findings appear obvious from physical principles, the confirming results demonstrates the application potential of our method in more complex systems. In addition, the basic idea and algorithm of the counter-extrapolation procedure presented here can be readily extended to other lattice Boltzmann models and even other computational technologies for heat and mass transfer systems.
Cho, Yeo-Myoung; Werner, David; Moffett, Kevan B; Luthy, Richard G
2010-08-01
Advective porewater movement and molecular diffusion are important factors affecting the mass transfer of hydrophobic organic compounds (HOCs) in marsh and mudflat sediments. This study assessed porewater movement in an intertidal mudflat in South Basin adjacent to Hunters Point Shipyard, San Francisco, CA, where a pilot-scale test of sorbent amendment assessed the in situ stabilization of polychlorinated biphenyls (PCBs). To quantify advective porewater movement within the top 0-60 cm sediment layer, we used temperature as a tracer and conducted heat transport analysis using 14-day data from multidepth sediment temperature logging stations and one-dimensional heat transport simulations. The best-fit conditions gave an average Darcy velocity of 3.8cm/d in the downward vertical direction for sorbent-amended sediment with a plausible range of 0 cm/d to 8 cm/d. In a limiting case with no net advection, the best-fit depth-averaged mechanical dispersion coefficient was 2.2x10(-7) m2/s with a range of 0.9x10(-7) m2/s to 5.6x10(-7) m2/s. The Peclet number for PCB mobilization showed that molecular diffusion would control PCB mass transfer from sediment to sorbent particles for the case of uniform distribution of sorbent. However, the advective flow and mechanical dispersion in the test site would significantly benefit the stabilization effect of heterogeneously distributed sorbent by acting to smooth out the heterogeneities and homogenizing pollutant concentrations across the entire bioactive zone. These measurements and modeling techniques on intertidal sediment porewater transport could be useful for the development of more reliable mass transfer models for the prediction of contaminant release within the sediment bed, the movement of HOCs in the intertidal aquatic environment, and in situ sequestration by sorbent addition.
Kristi Christensen; Veronica Rutledge; Troy Garn
2011-09-01
In support of the Nuclear Energy Advanced Modeling Simulation Safeguards and Separations (NEAMS SafeSep) program, the Idaho National Laboratory (INL) worked in collaboration with Los Alamos National Laboratory (LANL) to further a modeling effort designed to predict mass transfer behavior for selected metal species between individual dispersed drops and a continuous phase in a two phase liquid-liquid extraction (LLE) system. The purpose of the model is to understand the fundamental processes of mass transfer that occur at the drop interface. This fundamental understanding can be extended to support modeling of larger LLE equipment such as mixer settlers, pulse columns, and centrifugal contactors. The work performed at the INL involved gathering the necessary experimental data to support the modeling effort. A custom experimental apparatus was designed and built for performing drop contact experiments to measure mass transfer coefficients as a function of contact time. A high speed digital camera was used in conjunction with the apparatus to measure size, shape, and velocity of the drops. In addition to drop data, the physical properties of the experimental fluids were measured to be used as input data for the model. Physical properties measurements included density, viscosity, surface tension and interfacial tension. Additionally, self diffusion coefficients for the selected metal species in each experimental solution were measured, and the distribution coefficient for the metal partitioning between phases was determined. At the completion of this work, the INL has determined the mass transfer coefficient and a velocity profile for drops rising by buoyancy through a continuous medium under a specific set of experimental conditions. Additionally, a complete set of experimentally determined fluid properties has been obtained. All data will be provided to LANL to support the modeling effort.
Numerical modelling of shear-dependent mass transfer in large arteries
NASA Astrophysics Data System (ADS)
Rappitsch, Gerhard; Perktold, Karl; Pernkopf, Elisabeth
1997-10-01
A numerical scheme for the simulation of blood flow and transport processes in large arteries is presented. Blood flow is described by the unsteady 3D incompressible Navier-Stokes equations for Newtonian fluids; solute transport is modelled by the advection-diffusion equation. The resistance of the arterial wall to transmural transport is described by a shear-dependent wall permeability model. The finite element formulation of the Navier-Stokes equations is based on an operator-splitting method and implicit time discretization. The streamline upwind/Petrov-Galerkin (SUPG) method is applied for stabilization of the advective terms in the transport equation and in the flow equations. A numerical simulation is carried out for pulsatile mass transport in a 3D arterial bend to demonstrate the influence of arterial flow patterns on wall permeability characteristics and transmural mass transfer. The main result is a substantial wall flux reduction at the inner side of the curved region.
Irudayaraj, J.; Wu, Y.
1996-05-01
Luikov`s system of partial differential equations for heat, mass and pressure transfer was applied to describe the drying process in a capillary porous body. A two dimensional finite element model were formulated to solve the system of equations. The simulated results agreed very well with the exact solutions. The finite element model was then used to study the sensitivity of the parameters in Luikov`s heat, mass and pressure transfer system, and to estimate the key parameters identified (the coefficient of moisture conductivity, k{sub m}, and the ratio of vapor diffusion to total diffusion, {epsilon}) for Norway spruce. The finite element model was further used for the prediction of temperature, moisture and pressure variation during drying of Norway spruce. Laboratory experiments were conducted to measure the temperature and moisture content of a Norway spruce sample during drying. The predicted results showed good agreement with the experimental results.
Direct geoelectrical evidence of mass transfer at the laboratory scale
Swanson, Ryan D.; Singha, Kamini; Day-Lewis, Frederick D.; Binley, Andrew; Keating, Kristina; Haggerty, Roy
2012-01-01
Previous field-scale experimental data and numerical modeling suggest that the dual-domain mass transfer (DDMT) of electrolytic tracers has an observable geoelectrical signature. Here we present controlled laboratory experiments confirming the electrical signature of DDMT and demonstrate the use of time-lapse electrical measurements in conjunction with concentration measurements to estimate the parameters controlling DDMT, i.e., the mobile and immobile porosity and rate at which solute exchanges between mobile and immobile domains. We conducted column tracer tests on unconsolidated quartz sand and a material with a high secondary porosity: the zeolite clinoptilolite. During NaCl tracer tests we collected nearly colocated bulk direct-current electrical conductivity (σb) and fluid conductivity (σf) measurements. Our results for the zeolite show (1) extensive tailing and (2) a hysteretic relation between σf and σb, thus providing evidence of mass transfer not observed within the quartz sand. To identify best-fit parameters and evaluate parameter sensitivity, we performed over 2700 simulations of σf, varying the immobile and mobile domain and mass transfer rate. We emphasized the fit to late-time tailing by minimizing the Box-Cox power transformed root-mean square error between the observed and simulated σf. Low-field proton nuclear magnetic resonance (NMR) measurements provide an independent quantification of the volumes of the mobile and immobile domains. The best-fit parameters based on σf match the NMR measurements of the immobile and mobile domain porosities and provide the first direct electrical evidence for DDMT. Our results underscore the potential of using electrical measurements for DDMT parameter inference.
Direct geoelectrical evidence of mass transfer at the laboratory scale
NASA Astrophysics Data System (ADS)
Swanson, Ryan D.; Singha, Kamini; Day-Lewis, Frederick D.; Binley, Andrew; Keating, Kristina; Haggerty, Roy
2012-10-01
Previous field-scale experimental data and numerical modeling suggest that the dual-domain mass transfer (DDMT) of electrolytic tracers has an observable geoelectrical signature. Here we present controlled laboratory experiments confirming the electrical signature of DDMT and demonstrate the use of time-lapse electrical measurements in conjunction with concentration measurements to estimate the parameters controlling DDMT, i.e., the mobile and immobile porosity and rate at which solute exchanges between mobile and immobile domains. We conducted column tracer tests on unconsolidated quartz sand and a material with a high secondary porosity: the zeolite clinoptilolite. During NaCl tracer tests we collected nearly colocated bulk direct-current electrical conductivity (σb) and fluid conductivity (σf) measurements. Our results for the zeolite show (1) extensive tailing and (2) a hysteretic relation between σf and σb, thus providing evidence of mass transfer not observed within the quartz sand. To identify best-fit parameters and evaluate parameter sensitivity, we performed over 2700 simulations of σf, varying the immobile and mobile domain and mass transfer rate. We emphasized the fit to late-time tailing by minimizing the Box-Cox power transformed root-mean square error between the observed and simulated σf. Low-field proton nuclear magnetic resonance (NMR) measurements provide an independent quantification of the volumes of the mobile and immobile domains. The best-fit parameters based on σf match the NMR measurements of the immobile and mobile domain porosities and provide the first direct electrical evidence for DDMT. Our results underscore the potential of using electrical measurements for DDMT parameter inference.
Solid lubricant mass contact transfer technology usage for vacuum ball bearings longevity increasing
NASA Astrophysics Data System (ADS)
Arzymatov, B.; Deulin, E.
2016-07-01
A contact mass transfer technological method of solid lubricant deposition on components of vacuum ball bearings is presented. Physics-mathematical model of process contact mass transfer is being considered. The experimental results of ball bearings covered with solid lubricant longevity in vacuum are presented. It is shown that solid lubricant of contact mass transfer method deposition is prospective for ball bearing longevity increasing.
Transient mass transfer at the rotating disk electrode.
NASA Technical Reports Server (NTRS)
Nanis, L.; Klein, I.
1972-01-01
Transient mass transfer at the rotating disk has been investigated theoretically and experimentally for cathodic reduction of ferricyanide in the redox system ferricyanide-ferrocyanide with potassium hydroxide supporting electrolyte. It has been shown that overpotential-time predictions for the rotating disk are fitted very well for decay (current interruption) but poorly for build-up following switching on of constant current. As an explanation for this behavior, attention is directed to the inadequacy of the assumption that a radially independent concentration profile exists at the disk surface just at the start of galvanostatic current passage.
Evaluation of the Effect of Gravity Force on Transient Mass Diffusion Fields
NASA Astrophysics Data System (ADS)
Komiya, Atsuki; Maruyama, Shigenao
In this study, the relationship between gravitational force and diffusion phenomena in aque-ous solutions is discussed. The microgravity environment gives a high quality crystal growth condition which produces high quality medicines or foods. In this condition, a natural con-vection can be neglected and diffusion phenomenon without convection is observed. The mass diffusion coefficient is one of the most important thermophysical properties to investigate that mass transport system. However, the available experimental data of mass diffusion coefficients in microgravity conditions is not enough. Because it is quite a few opportunity that exper-iments can be conducted using facilities which produce microgravity environment for a long time. Then we have developed an observation system of small transient diffusion fields within 20 seconds. The experimental apparatus is composed of phase shifting interferometer, special designed signal processing unit and recorder. The mechanism of test cell used in this study has a unique performance that the transient diffusion fields can be produced continuously with no change of solutions and cell. Therefore this system can be applied to short-time microgravity experiment which is generated by the parabolic flight of an airplane. By using this system, the transient diffusion field of Sodium Chloride (NaCl) solution in microgravity conditions could be clearly observed and the mass diffusion coefficient was estimated from the obtained data. In microgravity condition, the transient diffusion fields have different appearances from the normal gravity condition. A slight acceleration governs the transient diffusion fields because of no density difference, so vibrations applied the apparatus disturb the transient diffusion fields. The measured mass diffusion coefficient has been estimated as a smaller value compared with ones under normal gravity condition. Using the airplane as a facility, not only microgravity condition but also 0.8G, 1
Gas stream in Algol. [mass transfer in binary star systems
NASA Technical Reports Server (NTRS)
Cugier, H.; Chen, K.-Y.
1977-01-01
Additional absorption features in the red wings of the Mg II resonance lines near 2800 A are found in observations of Algol made from the Copernicus satellite. The absorption features were clearly seen only during a part of the primary eclipse, in the phase interval 0.90-0.03. The observations are interpreted as being produced by a stream of matter flowing from Algol B in the direction of Algol A. The measured Doppler shifts of the features give the value of 150 km/s as the characteristic velocity of matter in the stream. The mass transfer connected with the stream is estimated to be of the order of 10 to the -13th power solar mass per year.
Perturbations and dynamics of reaction-diffusion systems with mass conservation.
Kuwamura, Masataka; Morita, Yoshihisa
2015-07-01
In some reaction-diffusion systems where the total mass of their components is conserved, solutions with initial values near a homogeneous equilibrium converge to a simple localized pattern (spike) after exhibiting Turing-like patterns near the equilibrium for appropriate diffusion coefficients. In this study, we investigate the perturbed reaction-diffusion systems of such conserved systems. We show that a reaction-diffusion model with a globally stable homogeneous equilibrium can exhibit large amplitude Turing-like patterns in the transient dynamics. Moreover, we propose a three-component model, which exhibits an alternating repetition of spatially (almost) homogeneous oscillations and large amplitude Turing-like patterns.
Modeling of heat and mass transfer in lateritic building envelopes
NASA Astrophysics Data System (ADS)
Meukam, Pierre; Noumowe, Albert
2005-12-01
The aim of the present work is to investigate the behavior of building envelopes made of local lateritic soil bricks subjected to different climatic conditions. The building envelopes studied in this work consist of lateritic soil bricks with incorporation of natural pozzolan or sawdust in order to obtain small thermal conductivity and low-density materials. In order to describe coupled heat and moisture transfer in wet porous materials, the coupled equations were solved by the introduction of diffusion coefficients. A numerical model HMtrans, developed for prediction of heat and moisture transfer in multi-layered building components, was used to simulate the temperature, water content and relative humidity profiles within the building envelopes. The results allow the prediction of the duration of the exposed building walls to the local weather conditions. They show that the durability of building envelopes made of lateritic soil bricks with incorporation of natural pozzolan or sawdust is not strongly affected by the climatic conditions in tropical and equatorial areas.
Macro- to Nanoscale Heat and Mass Transfer: The Lagging Behavior
NASA Astrophysics Data System (ADS)
Ghazanfarian, Jafar; Shomali, Zahra; Abbassi, Abbas
2015-07-01
The classical model of the Fourier's law is known as the most common constitutive relation for thermal transport in various engineering materials. Although the Fourier's law has been widely used in a variety of engineering application areas, there are many exceptional applications in which the Fourier's law is questionable. This paper gathers together such applications. Accordingly, the paper is divided into two parts. The first part reviews the papers pertaining to the fundamental theory of the phase-lagging models and the analytical and numerical solution approaches. The second part wrap ups the various applications of the phase-lagging models including the biological materials, ultra-high-speed laser heating, the problems involving moving media, micro/nanoscale heat transfer, multi-layered materials, the theory of thermoelasticity, heat transfer in the material defects, the diffusion problems we call as the non-Fick models, and some other applications. It is predicted that the interest in the field of phase-lagging heat transport has grown incredibly in recent years because they show good agreement with the experiments across a wide range of length and time scales.
Transformed Fourier and Fick equations for the control of heat and mass diffusion
Guenneau, S.; Petiteau, D.; Zerrad, M.; Amra, C.; Puvirajesinghe, T.
2015-05-15
We review recent advances in the control of diffusion processes in thermodynamics and life sciences through geometric transforms in the Fourier and Fick equations, which govern heat and mass diffusion, respectively. We propose to further encompass transport properties in the transformed equations, whereby the temperature is governed by a three-dimensional, time-dependent, anisotropic heterogeneous convection-diffusion equation, which is a parabolic partial differential equation combining the diffusion equation and the advection equation. We perform two dimensional finite element computations for cloaks, concentrators and rotators of a complex shape in the transient regime. We precise that in contrast to invisibility cloaks for waves, the temperature (or mass concentration) inside a diffusion cloak crucially depends upon time, its distance from the source, and the diffusivity of the invisibility region. However, heat (or mass) diffusion outside cloaks, concentrators and rotators is unaffected by their presence, whatever their shape or position. Finally, we propose simplified designs of layered cylindrical and spherical diffusion cloaks that might foster experimental efforts in thermal and biochemical metamaterials.
Heat and Mass Diffusions in the Absorption of Water Vapor by Aqueous Solution of Lithium Bromide
NASA Astrophysics Data System (ADS)
Kashiwagi, Takao; Kurosaki, Yasuo; Nikai, Isao
The recent development of absorption-type heat pump is highly essential from the viewpoint of extracting the effective energy from waste heat or solar energy. To increase the efficiency of energy conversion, it is important to improve the performance of absorbers. The objective of this paper is to obtain an increased understanding of the fine mechanisms of vapor absorption. A system combining holographic interferometry wity thermometry is adopted to observe the progress of one-dimensional water vapor absorption by aqueous solution of lithium bromide (LiBr) and also to measure the unsteady temperature and concentration distributions in the absorption process. The experiments are carried out under the condition that the solution surface is exposed to the saturated water vapor at reduced pressure, and the effects of LiBr mass concentration on absorption mechanism are examined in the concentration range 20-60 mass%. The interference fringes are analyzed to distinguish between the layers of heat conduction and mass diffusion. The temperature and concentration distributions thus determined experimentally are compared with numerical solutions obtained by the equations for unsteady heat conduction and mass diffusion taking into consideration the effect of heat by dilution, to give reasonable values of mass diffusivity hitherto remaining unknown. Especially in the range of 40-60 mass%, the mass diffusivity decreases extremely with the increase of mass concentration of LiBr and it falls down to 0.7-0.8×10-9 m2/s in case of 60 mass% solution.
L. Pan; Y. Seol; G. Bodvarsson
2004-04-29
The dual-continuum random-walk particle tracking approach is an attractive simulation method for simulating transport in a fractured porous medium. In order to be truly successful for such a model, however, the key issue is to properly simulate the mass transfer between the fracture and matrix continua. In a recent paper, Pan and Bodvarsson (2002) proposed an improved scheme for simulating fracture-matrix mass transfer, by introducing the concept of activity range into the calculation of fracture-matrix particle-transfer probability. By comparing with analytical solutions, they showed that their scheme successfully captured the transient diffusion depth into the matrix without any additional subgrid (matrix) cells. This technical note presents an expansion of their scheme to cases in which significant water flow through the fracture-matrix interface exists. The dual-continuum particle tracker with this new scheme was found to be as accurate as a numerical model using a more detailed grid. The improved scheme can be readily incorporated into the existing particle-tracking code, while still maintaining the advantage of needing no additional matrix cells to capture transient features of particle penetration into the matrix.
An advanced model of heat and mass transfer in the protective clothing - verification
NASA Astrophysics Data System (ADS)
Łapka, P.; Furmański, P.
2016-09-01
The paper presents an advanced mathematical and numerical models of heat and mass transfer in the multi-layers protective clothing and in elements of the experimental stand subjected to either high surroundings temperature or high radiative heat flux emitted by hot objects. The model included conductive-radiative heat transfer in the hygroscopic porous fabrics and air gaps as well as conductive heat transfer in components of the stand. Additionally, water vapour diffusion in the pores and air spaces as well as phase transition of the bound water in the fabric fibres (sorption and desorption) were accounted for. The thermal radiation was treated in the rigorous way e.g.: semi-transparent absorbing, emitting and scattering fabrics were assumed a non-grey and all optical phenomena at internal or external walls were modelled. The air was assumed transparent. Complex energy and mass balance as well as optical conditions at internal or external interfaces were formulated in order to find exact values of temperatures, vapour densities and radiation intensities at these interfaces. The obtained highly non-linear coupled system of discrete equation was solve by the in-house iterative algorithm which was based on the Finite Volume Method. The model was then successfully partially verified against the results obtained from commercial software for simplified cases.
Toptygin, Dmitri; Chin, Alexander F; Hilser, Vincent J
2015-10-01
Intrinsically disordered protein regions and many other biopolymers lack the three-dimensional structure that could be determined by X-ray crystallography or NMR, which encourages the application of alternative experimental methods. Time-resolved resonance energy transfer data are often used to measure distances between two fluorophores attached to a flexible biopolymer. This is complicated by the rotational and translational diffusion of the fluorophores and by nonmonoexponential donor decay in the absence of the acceptor. Equation I(DA)(t) = I(D)(t)·F(t) is derived here, which is applicable regardless of whether I(D)(t) is monoexponential. I(D)(t) and I(DA)(t) are the δ-excitation donor emission decays in the absence and in the presence of the acceptor; F(t) contains information about energy transfer, donor-acceptor distance distribution, and diffusion dynamics. It is shown that in the absence of rotational and translational diffusion, F(t) is a continuous distribution of exponentials, whereas in the presence of rotational and translational diffusion, F(t) is a sum of discrete exponentials. For each case it is shown how F(t) is related to the distance distribution. Experimental data obtained with a flexible tetradecapeptide in aqueous solution clearly demonstrate that F(t) is a sum of discrete exponential terms. A partial differential equation describing resonance energy transfer in the presence of both rotational and translational diffusion of the donor and acceptor tethered to the ends of a semiflexible chain is solved in this work using a combination of analytical and numerical methods; the solution is used to fit time-resolved emission of the donor, which makes it possible to determine the model parameters: contour length, persistence length, and the end-to-end translational diffusion coefficient.
NASA Astrophysics Data System (ADS)
Nikkhou, Fatemeh; Keshavarz, Peyman; Ayatollahi, Shahab; Jahromi, Iman Raoofi; Zolghadr, Ali
2015-04-01
CO2 gas injection is known as one of the most popular enhanced oil recovery techniques for light and medium oil reservoirs, therefore providing an acceptable mass transfer mechanism for CO2-oil systems seems necessary. In this study, interfacial mass transfer coefficient has been evaluated for CO2-normal heptane and CO2-normal hexadecane systems using equilibrium and dynamic interfacial tension data, which have been measured using the pendant drop method. Interface mass transfer coefficient has been calculated as a function of temperature and pressure in the range of 313-393 K and 1.7-8.6 MPa, respectively. The results showed that the interfacial resistance is a parameter that can control the mass transfer process for some CO2-normal alkane systems, and cannot be neglected. Additionally, it was found that interface mass transfer coefficient increased with pressure. However, the variation of this parameter with temperature did not show a clear trend and it was strongly dependent on the variation of diffusivity and solubility of CO2 in the liquid phase.
Gorpas, Dimitris; Andersson-Engels, Stefan
2012-12-01
The solution of the forward problem in fluorescence molecular imaging strongly influences the successful convergence of the fluorophore reconstruction. The most common approach to meeting this problem has been to apply the diffusion approximation. However, this model is a first-order angular approximation of the radiative transfer equation, and thus is subject to some well-known limitations. This manuscript proposes a methodology that confronts these limitations by applying the radiative transfer equation in spatial regions in which the diffusion approximation gives decreased accuracy. The explicit integro differential equations that formulate this model were solved by applying the Galerkin finite element approximation. The required spatial discretization of the investigated domain was implemented through the Delaunay triangulation, while the azimuthal discretization scheme was used for the angular space. This model has been evaluated on two simulation geometries and the results were compared with results from an independent Monte Carlo method and the radiative transfer equation by calculating the absolute values of the relative errors between these models. The results show that the proposed forward solver can approximate the radiative transfer equation and the Monte Carlo method with better than 95% accuracy, while the accuracy of the diffusion approximation is approximately 10% lower.
A new characterization of the turbulent diapycnal diffusivities of mass and momentum in the ocean
NASA Astrophysics Data System (ADS)
Salehipour, H.; Peltier, W. R.; Whalen, C. B.; MacKinnon, J. A.
2016-04-01
The diapycnal diffusivity of mass supported by turbulent events in the ocean interior plays a fundamental role in controlling the global overturning circulation. The conventional representation of this diffusivity, due to Osborn (1980), assumes a constant mixing efficiency. We replace this methodology by a generalized-Osborn formula which involves a mixing efficiency that varies nonmonotonically with at least two nondimensional variables. Using these two variables, we propose dynamic parameterizations for mixing efficiency and turbulent Prandtl number (the latter quantifies the ratio of momentum to mass diapycnal diffusivities) based on the first synthesis of an extensive direct numerical simulation of inhomogeneously stratified shear-induced turbulence. Data from Argo floats are employed to demonstrate the extent of the spatial and statistical variability to be expected in both the diapycnal diffusivities of mass and momentum. We therefore suggest that previous estimates of these important characteristics of the global ocean require reconsideration.
Transfer of diffuse astronomical light and airglow in scattering Earth atmosphere
NASA Astrophysics Data System (ADS)
Hong, S. S.; Kwon, S. M.; Park, Y.-S.; Park, C.
1998-06-01
To understand an observed distribution of atmospheric diffuse light (ADL) over an entire meridian, we have solved rigorously, with the quasi-diffusion method, the problem of radiative transfer in an anisotropically scattering spherical atmosphere of the earth. In addition to the integrated starlight and the zodiacal light we placed a narrow layer of airglow emission on top of the scattering earth atmosphere. The calculated distribution of the ADL brightness over zenith distance shows good agreement with the observed one. The agreement can be utilized in deriving the zodiacal light brightness at small solar elongations from the night sky brightness observed at large zenith distances.
Acoustic Streaming and Heat and Mass Transfer Enhancement
NASA Technical Reports Server (NTRS)
Trinh, E. H.; Gopinath, A.
1996-01-01
A second order effect associated with high intensity sound field, acoustic streaming has been historically investigated to gain a fundamental understanding of its controlling mechanisms and to apply it to practical aspects of heat and mass transfer enhancement. The objectives of this new research project are to utilize a unique experimental technique implementing ultrasonic standing waves in closed cavities to study the details of the generation of the steady-state convective streaming flows and of their interaction with the boundary of ultrasonically levitated near-spherical solid objects. The goals are to further extend the existing theoretical studies of streaming flows and sample interactions to higher streaming Reynolds number values, for larger sample size relative to the wavelength, and for a Prandtl and Nusselt numbers parameter range characteristic of both gaseous and liquid host media. Experimental studies will be conducted in support to the theoretical developments, and the crucial impact of microgravity will be to allow the neglect of natural thermal buoyancy. The direct application to heat and mass transfer in the absence of gravity will be emphasized in order to investigate a space-based experiment, but both existing and novel ground-based scientific and technological relevance will also be pursued.
Hornblendite delineates zones of mass transfer through the lower crust
Daczko, Nathan R.; Piazolo, Sandra; Meek, Uvana; Stuart, Catherine A.; Elliott, Victoria
2016-01-01
Geochemical signatures throughout the layered Earth require significant mass transfer through the lower crust, yet geological pathways are under-recognized. Elongate bodies of basic to ultrabasic rocks are ubiquitous in exposures of the lower crust. Ultrabasic hornblendite bodies hosted within granulite facies gabbroic gneiss of the Pembroke Valley, Fiordland, New Zealand, are typical occurrences usually reported as igneous cumulate hornblendite. Their igneous features contrast with the metamorphic character of their host gabbroic gneiss. Both rock types have a common parent; field relationships are consistent with modification of host gabbroic gneiss into hornblendite. This precludes any interpretation involving cumulate processes in forming the hornblendite; these bodies are imposter cumulates. Instead, replacement of the host gabbroic gneiss formed hornblendite as a result of channeled high melt flux through the lower crust. High melt/rock ratios and disequilibrium between the migrating magma (granodiorite) and its host gabbroic gneiss induced dissolution (grain-scale magmatic assimilation) of gneiss and crystallization of mainly hornblende from the migrating magma. The extent of this reaction-replacement mechanism indicates that such hornblendite bodies delineate significant melt conduits. Accordingly, many of the ubiquitous basic to ultrabasic elongate bodies of the lower crust likely map the ‘missing’ mass transfer zones. PMID:27546342
Hornblendite delineates zones of mass transfer through the lower crust.
Daczko, Nathan R; Piazolo, Sandra; Meek, Uvana; Stuart, Catherine A; Elliott, Victoria
2016-08-22
Geochemical signatures throughout the layered Earth require significant mass transfer through the lower crust, yet geological pathways are under-recognized. Elongate bodies of basic to ultrabasic rocks are ubiquitous in exposures of the lower crust. Ultrabasic hornblendite bodies hosted within granulite facies gabbroic gneiss of the Pembroke Valley, Fiordland, New Zealand, are typical occurrences usually reported as igneous cumulate hornblendite. Their igneous features contrast with the metamorphic character of their host gabbroic gneiss. Both rock types have a common parent; field relationships are consistent with modification of host gabbroic gneiss into hornblendite. This precludes any interpretation involving cumulate processes in forming the hornblendite; these bodies are imposter cumulates. Instead, replacement of the host gabbroic gneiss formed hornblendite as a result of channeled high melt flux through the lower crust. High melt/rock ratios and disequilibrium between the migrating magma (granodiorite) and its host gabbroic gneiss induced dissolution (grain-scale magmatic assimilation) of gneiss and crystallization of mainly hornblende from the migrating magma. The extent of this reaction-replacement mechanism indicates that such hornblendite bodies delineate significant melt conduits. Accordingly, many of the ubiquitous basic to ultrabasic elongate bodies of the lower crust likely map the 'missing' mass transfer zones.
Gas Blowing: Mass Transfer in Gas and Melt
NASA Astrophysics Data System (ADS)
Sortland, Øyvind Sunde; Tangstad, Merete
2014-09-01
Metallurgical routes for solar grade silicon production are being developed as alternatives to chemical processes for their potential to achieve cost reductions, increased production volume, and reduced environmental and safety concerns. An important challenge in the development of metallurgical routes relates to the higher impurity concentrations in the silicon product, particularly for boron and other elements that are not efficiently segregated in solidification techniques. The reactive gas refining process is studied for its potential to remove boron below the solar grade silicon target concentration in a single step by blowing steam and hydrogen gas jets onto the melt surface. Boron in a silicon melt is extracted to HBO gas in parallel to active oxidation of silicon. The literature is not unified regarding the rate determining step in this process. Relevant theories and equations for gas blowing in induction furnaces are combined and used to explain mass transfer in experiments. Mass transfer in the melt and gas is investigated by comparing resistance and induction heating of the melt, and varying gas flow rate, crucible diameter, diameter of the gas lance, and the position of the gas lance above the melt surface. The rate of boron removal is found to increase with increasing gas flow rate and crucible diameter. A relatively high fraction of the reactive gas is utilized in the process, and supply of steam in the bulk gas is the only identified rate determining step.
Hornblendite delineates zones of mass transfer through the lower crust
NASA Astrophysics Data System (ADS)
Daczko, Nathan R.; Piazolo, Sandra; Meek, Uvana; Stuart, Catherine A.; Elliott, Victoria
2016-08-01
Geochemical signatures throughout the layered Earth require significant mass transfer through the lower crust, yet geological pathways are under-recognized. Elongate bodies of basic to ultrabasic rocks are ubiquitous in exposures of the lower crust. Ultrabasic hornblendite bodies hosted within granulite facies gabbroic gneiss of the Pembroke Valley, Fiordland, New Zealand, are typical occurrences usually reported as igneous cumulate hornblendite. Their igneous features contrast with the metamorphic character of their host gabbroic gneiss. Both rock types have a common parent; field relationships are consistent with modification of host gabbroic gneiss into hornblendite. This precludes any interpretation involving cumulate processes in forming the hornblendite; these bodies are imposter cumulates. Instead, replacement of the host gabbroic gneiss formed hornblendite as a result of channeled high melt flux through the lower crust. High melt/rock ratios and disequilibrium between the migrating magma (granodiorite) and its host gabbroic gneiss induced dissolution (grain-scale magmatic assimilation) of gneiss and crystallization of mainly hornblende from the migrating magma. The extent of this reaction-replacement mechanism indicates that such hornblendite bodies delineate significant melt conduits. Accordingly, many of the ubiquitous basic to ultrabasic elongate bodies of the lower crust likely map the ‘missing’ mass transfer zones.
Parallel Mass Transfer Simulation of Nanoparticles Using Nonblocking Communications
NASA Astrophysics Data System (ADS)
Chantrapornchai (Phonpensri), Chantana; Dolwithayakul, Banpot; Gorlatch, Sergei
This paper presents experiences and results obtained in optimizing parallelization of the mass transfer simulation in the High Gradient Magnetic Separation (HGMS) of nanoparticles using nonblocking communication techniques in the point-to-point and collective model. We study the dynamics of mass transfer statistically in terms of particle volume concentration and the continuity equation, which is solved numerically by using the finite-difference method to compute concentration distribution in the simulation domain at a given time. In the parallel simulation, total concentration data in the simulation domain are divided row-wise and distributed equally to a group of processes. We propose two parallel algorithms based on the row-wise partitioning: algorithms with nonblocking send/receive and nonblocking scatter/gather using the NBC library. We compare the performance of both versions by measuring their parallel speedup and efficiency. We also investigate the communication overhead in both versions. Our results show that the nonblocking collective communication can improve the performance of the simulation when the number of processes is large.
Proton transfer mass spectrometry studies of peroxy radicals
NASA Astrophysics Data System (ADS)
Hanson, D.; Orlando, J.; Noziere, B.; Kosciuch, E.
2004-12-01
A laminar flow reactor coupled to a proton transfer mass spectrometer utilizing H3O+.(H2O)n cluster ions is described. Experiments involving the Cl-atom initiated oxidation of organic species (cyclohexane, cyclopentane, ethane, methane) were performed in the flow reactor and detection of the peroxyl radicals and other oxidation products are discussed. The detection sensitivities for the RO2 radicals (R = cyclohexyl, ethyl, and methyl) were estimated. The sensitivities are consistent with a fast rate (coefficient ~10-9 cm3 molecule-1 s-1) for the proton transfer reaction between many RO2 species and water-proton clusters. The effect of the presence of water vapor in the ion drift region (IDR) on the detection sensitivity for RO2 was investigated. The detection of the methyl and ethyl peroxy radical species was adversely affected by water vapor however, that for the cylcohexyl peroxy radical was much less affected. The cyclohexyl- and cyclopentyl-peroxy radicals were reacted with NO and the products so formed were probed with proton transfer from water molecules. Products identified include a wide array of mono-, di-, and tri-functional species containing peroxyl, alcoholic, carbonyl, nitrate, and peroxynitrate functional groups. These products are shown to be in accord with the current state of knowledge on the oxidation of cyclopentane and cyclohexane.
Heat and mass transfer with condensation in capillary porous bodies.
Larbi, Salah
2014-01-01
The purpose of this present work is related to wetting process analysis caused by condensation phenomena in capillary porous material by using a numerical simulation. Special emphasis is given to the study of the mechanism involved and the evaluation of classical theoretical models used as a predictive tool. A further discussion will be given for the distribution of the liquid phase for both its pendular and its funicular state and its consequence on diffusion coefficients of the mathematical model used. Beyond the complexity of the interaction effects between vaporisation-condensation processes on the gas-liquid interfaces, the comparison between experimental and numerical simulations permits to identify the specific contribution and the relative part of mass and energy transport parameters. This analysis allows us to understand the contribution of each part of the mathematical model used and to simplify the study.
Optimal-mass-transfer-based estimation of glymphatic transport in living brain
NASA Astrophysics Data System (ADS)
Ratner, Vadim; Zhu, Liangjia; Kolesov, Ivan; Nedergaard, Maiken; Benveniste, Helene; Tannenbaum, Allen
2015-03-01
It was recently shown that the brain-wide cerebrospinal fluid (CSF) and interstitial fluid exchange system designated the `glymphatic pathway' plays a key role in removing waste products from the brain, similarly to the lymphatic system in other body organs . It is therefore important to study the flow patterns of glymphatic transport through the live brain in order to better understand its functionality in normal and pathological states. Unlike blood, the CSF does not flow rapidly through a network of dedicated vessels, but rather through para-vascular channels and brain parenchyma in a slower time-domain, and thus conventional fMRI or other blood-flow sensitive MRI sequences do not provide much useful information about the desired flow patterns. We have accordingly analyzed a series of MRI images, taken at different times, of the brain of a live rat, which was injected with a paramagnetic tracer into the CSF via the lumbar intrathecal space of the spine. Our goal is twofold: (a) find glymphatic (tracer) flow directions in the live rodent brain; and (b) provide a model of a (healthy) brain that will allow the prediction of tracer concentrations given initial conditions. We model the liquid flow through the brain by the diffusion equation. We then use the Optimal Mass Transfer (OMT) approach to derive the glymphatic flow vector field, and estimate the diffusion tensors by analyzing the (changes in the) flow. Simulations show that the resulting model successfully reproduces the dominant features of the experimental data. Keywords: inverse problem, optimal mass transport, diffusion equation, cerebrospinal fluid flow in brain, optical flow, liquid flow modeling, Monge Kantorovich problem, diffusion tensor estimation
Isotopic mass-dependence of noble gas diffusion coefficients inwater
Bourg, I.C.; Sposito, G.
2007-06-25
Noble gas isotopes are used extensively as tracers inhydrologic and paleoclimatic studies. These applications requireknowledge of the isotopic mass (m) dependence of noble gas diffusioncoefficients in water (D), which has not been measured but is estimatedusing experimental D-values for the major isotopes along with an untestedrelationship from kinetic theory, D prop m-0.5. We applied moleculardynamics methods to determine the mass dependence of D for four noblegases at 298 K, finding that D prop m-beta with beta<0.2, whichrefutes the kinetic theory model underlying all currentapplications.
Munasinghe, Pradeep Chaminda; Khanal, Samir Kumar
2010-01-01
Lignocellulosic biomass such as agri-residues, agri-processing by-products, and energy crops do not compete with food and feed, and is considered to be the ideal renewable feedstocks for biofuel production. Gasification of biomass produces synthesis gas (syngas), a mixture primarily consisting of CO and H(2). The produced syngas can be converted to ethanol by anaerobic microbial catalysts especially acetogenic bacteria such as various clostridia species.One of the major drawbacks associated with syngas fermentation is the mass transfer limitation of these sparingly soluble gases in the aqueous phase. One way of addressing this issue is the improvement in reactor design to achieve a higher volumetric mass transfer coefficient (k(L)a). In this study, different reactor configurations such as a column diffuser, a 20-μm bulb diffuser, gas sparger, gas sparger with mechanical mixing, air-lift reactor combined with a 20-μm bulb diffuser, air-lift reactor combined with a single gas entry point, and a submerged composite hollow fiber membrane (CHFM) module were employed to examine the k(L) a values. The k(L) a values reported in this study ranged from 0.4 to 91.08 h(-1). The highest k(L) a of 91.08 h(-1) was obtained in the air-lift reactor combined with a 20-μm bulb diffuser, whereas the reactor with the CHFM showed the lowest k(L) a of 0.4 h(-1). By considering both the k(L) a value and the statistical significance of each configuration, the air-lift reactor combined with a 20-μm bulb diffuser was found to be the ideal reactor configuration for carbon monoxide mass transfer in an aqueous phase.
Monodisperse droplet generation for microscale mass transfer studies
NASA Astrophysics Data System (ADS)
Roberts, Christine; Rao, Rekha; Grillet, Anne; Jove-Colon, Carlos; Brooks, Carlton; Nemer, Martin
2011-11-01
Understanding interfacial mass transport on a droplet scale is essential for modeling liquid-liquid extraction processes. A thin flow-focusing microfluidic channel is evaluated for generating monodisperse liquid droplets for microscale mass transport studies. Surface treatment of the microfluidic device allows creation of both oil in water and water in oil emulsions, facilitating a large parameter study of viscosity and flow rate ratios. The unusually thin channel height promotes a flow regime where no droplets form. Through confocal microscopy, this regime is shown to be highly influenced by the contact angle of the liquids with the channel. Drop sizes are found to scale with a modified capillary number. Liquid streamlines within the droplets are inferred by high speed imagery of microparticles dispersed in the droplet phase. Finally, species mass transfer to the droplet fluid is quantitatively measured using high speed imaging. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85.
Mass transfer during osmotic dehydration of celery stalks in a batch osmo-reactor
NASA Astrophysics Data System (ADS)
Sareban, M.; Abbasi Souraki, B.
2017-03-01
In this study, dehydration behavior of bulk of celery stalks, during osmotic drying in a limited volume of salt solution, was investigated. Experiments were carried out in the three initial solution concentrations of 10, 18 and 25 % (w/w) and at the three temperatures of 35, 45 and 55 °C. The volume ratio of the fruit to the solution was considered 1:3. A two-parameter model was used for prediction of kinetics of mass transfer and values of equilibrium moisture loss and solid gain. Moisture and salt effective diffusivities in celery stalks were estimated by fitting the experimental data of moisture loss and solute gain to the analytical solution of Fick's second law of diffusion. The analytical model was solved by defining a partition factor, K, assuming that the concentration of solute just within the surface of the material is K times that in the solution. Results showed that moisture and salt effective diffusivities and equilibrium values of moisture loss and solute gain increased with increasing the temperature and solution concentration. Results showed a good agreement between the two parameter model (with mean relative error of 4.016 % for moisture loss and 5.977 % for solid gain), analytical solution of Fick's second law (with mean relative error of 8.924 % for moisture loss and 9.164 % for solid gain) and experimental data.
Mass transfer during osmotic dehydration of celery stalks in a batch osmo-reactor
NASA Astrophysics Data System (ADS)
Sareban, M.; Abbasi Souraki, B.
2016-07-01
In this study, dehydration behavior of bulk of celery stalks, during osmotic drying in a limited volume of salt solution, was investigated. Experiments were carried out in the three initial solution concentrations of 10, 18 and 25 % (w/w) and at the three temperatures of 35, 45 and 55 °C. The volume ratio of the fruit to the solution was considered 1:3. A two-parameter model was used for prediction of kinetics of mass transfer and values of equilibrium moisture loss and solid gain. Moisture and salt effective diffusivities in celery stalks were estimated by fitting the experimental data of moisture loss and solute gain to the analytical solution of Fick's second law of diffusion. The analytical model was solved by defining a partition factor, K, assuming that the concentration of solute just within the surface of the material is K times that in the solution. Results showed that moisture and salt effective diffusivities and equilibrium values of moisture loss and solute gain increased with increasing the temperature and solution concentration. Results showed a good agreement between the two parameter model (with mean relative error of 4.016 % for moisture loss and 5.977 % for solid gain), analytical solution of Fick's second law (with mean relative error of 8.924 % for moisture loss and 9.164 % for solid gain) and experimental data.
A multi-compartment mass transfer model applied to building vapor intrusion
NASA Astrophysics Data System (ADS)
Murphy, Brian L.; Chan, Wanyu R.
2011-12-01
We develop a systematic approach to model steady-state advective and diffusive fluxes, as well as phase changes, between multi-media environmental compartments. The approach results in four simple rules for constructing mass transfer coefficients. Results are analogous to electrical circuit theory with resistors, including variable resistors or potentiometers, in parallel and series. This general approach lends itself particularly well to vapor intrusion calculations where there are multi-media compartments involving groundwater, soil, and air. In addition to showing that the model reduces to the well-known Johnson & Ettinger model in limiting cases, we illustrate its simplicity and ease of use with several examples: (1) an example of how multiple partition coefficients collapse into a single partition coefficient illustrated by a three-phase problem involving tar, water, and air, (2) determination of when the presence of a basement significantly lowers first floor exposures, and (3) addition of diffusion in the saturated zone to the model to investigate whether the resistance associated with this compartment can be neglected. We conclude that if the water table is truly steady, this resistance would be very significant. Therefore, a vapor intrusion model that neglects both water table fluctuations and diffusion in groundwater is ignoring important physical phenomena.
Image Reconstruction for Diffuse Optical Tomography Based on Radiative Transfer Equation
Han, Bo; Tang, Jinping
2015-01-01
Diffuse optical tomography is a novel molecular imaging technology for small animal studies. Most known reconstruction methods use the diffusion equation (DA) as forward model, although the validation of DA breaks down in certain situations. In this work, we use the radiative transfer equation as forward model which provides an accurate description of the light propagation within biological media and investigate the potential of sparsity constraints in solving the diffuse optical tomography inverse problem. The feasibility of the sparsity reconstruction approach is evaluated by boundary angular-averaged measurement data and internal angular-averaged measurement data. Simulation results demonstrate that in most of the test cases the reconstructions with sparsity regularization are both qualitatively and quantitatively more reliable than those with standard L2 regularization. Results also show the competitive performance of the split Bregman algorithm for the DOT image reconstruction with sparsity regularization compared with other existing L1 algorithms. PMID:25648064
Ozturk, S S; Palsson, B O; Thiele, J H
1989-02-05
Dynamic reaction diffusion models were used to analyze the consequences of aggregation for syntrophic reactions in methanogenic ecosystems. Flocs from a whey digestor were used to measure all model parameters under the in situ conditions of a particular defined biological system. Fermentation simulations without adjustable parameters could precisely predict the kinetics of H(2) gas production of digestor flocs during syntrophic methanogenesis from ethanol. The results demonstrated a kinetic compartmentalization of H(2) metabolism inside the flocs. The interspecies electron transfer reaction was mildly diffusion controlled. The H(2) gas profiles across the flocs showed high H (2) concentrations inside the flocs at any time. Simulations of the syntrophic metabolism at low substrate concentrations such as in digestors or sediments showed that it is impossible to achieve high H(2) gas turnovers at simultaneously low steady-state H(2) concentrations. This showed a mechanistic contradiction in the concept of postulated low H(2) microenvironments for the anaerobic digestion process. The results of the computer experiments support the conclusion that syntrophic H(2) production may only be a side reaction of H(2) independent interspecies electron transfer in methanogenic ecosystems.
Modeling of Heat and Mass Transfer in Fusion Welding
Zhang, Wei
2011-01-01
In fusion welding, parts are joined together by melting and subsequent solidification. Although this principle is simple, complex transport phenomena take place during fusion welding, and they determine the final weld quality and performance. The heat and mass transfer in the weld pool directly affect the size and shape of the pool, the solidification microstructure, the formation of weld defects such as porosity and humping, and the temperature distribution in the fusion zone and heat-affected zone (HAZ). Furthermore, the temperature evolution affects the kinetics and extent of various solid-state phase transformations, which in turn determine the final weld microstructure and mechanical properties. The formation of residual stresses and distortion originates from the thermal expansion and contraction during welding heating and cooling, respectively.
Mass transfer effects on the transmission of bubble screens
NASA Astrophysics Data System (ADS)
Fuster, Daniel; Bergamasco, Luca
2016-11-01
In this work we investigate, theoretically and numerically, the reflection and transmission properties of bubble screens excited by pressure wave pulses. We use modified expressions for the bubble resonance frequency and the damping factor in order to capture the influence of mass transfer on the reflection-transmission coefficients. In addition to the influence of variables such as the bubble radius and the averaged inter-bubble distance, the analysis reveals that in conditions close to the saturation line there exists a regime where the heat transport surrounding the bubble plays an important role on the bubble's response also influencing the reflection properties of the bubble screen. The linear analysis allows us to predict the critical vapor content beyond which liquid heat's transport controls the dynamic response of the bubbles. Numerical simulations show that these effects become especially relevant in the nonlinear regime. ANR Cachmap.
Hydromagnetic free convection flow with Hall effect and mass transfer
NASA Astrophysics Data System (ADS)
Sahoo, Prasan Kumar
2016-02-01
The study of magnetohydrodynamics (MHD) deals with the flow of an electrically conducting fluid in the presence of an electromagnetic field, which has many applications in astrophysics, geophysics and engineering. Objective of the present study in this paper is to consider the effect of dissipation and Hall current on the MHD free convection flow with mass transfer in a porous vertical channel. An exact solution of the governing equations is obtained by solving the complex variables. The effect of Hall parameter (m), Hartmann number (M), and Concentration parameter (Sc) on the velocity and temperature of the fluid is studied. Simulation results show that the shear stress of primary and secondary velocity for the lower plate increases with increase in the strength of Hall parameter (m) and decreases with increase in Hartmann number (M) and concentration parameter (Sc).
Mass transfer in binary X-ray systems
NASA Technical Reports Server (NTRS)
Mccray, R.; Hatchett, S.
1975-01-01
The influence of X-ray heating on gas flows in binary X-ray systems is examined. A simple estimate is obtained for the evaporative wind flux from a stellar atmosphere due to X-ray heating which agrees with numerical calculations by Alme and Wilson (1974) but disagrees with calculations by Arons (1973) and by Basko and Sunyaev (1974) for the Her X-1/HZ Her system. The wind flux is sensitive to the soft X-ray spectrum. The self-excited wind mechanism does not work. Mass transfer in the Hercules system probably occurs by flow of the atmosphere of HZ Her through the gravitational saddle point of the system. The accretion gas stream is probably opaque with atomic density of not less than 10 to the 15th power per cu cm and is confined to a small fraction of 4(pi) steradians. Other binary X-ray systems are briefly discussed.
Mass Transfer and Light Time Effect Studies for AU Serpentis
NASA Astrophysics Data System (ADS)
Amin, S. M.
2015-02-01
The orbital period changes of theWUMa eclipsing binary AU Ser are studied using the (O-C) method. We conclude that the period variation is due to mass transfer from the primary star to the secondary one at a very low and decreasing rate dP/dt = -8.872 × 10-8, superimposed on the sinusoidal variation due to a third body orbiting the binary with period 42.87 ± 3.16 years, orbital eccentricity e = 0.52±0.12 and a longitude of periastron passage ! = 133.7±15. On studying the magnetic activity, we have concluded that the Applegate mechanism failed to describe the cycling variation of the (O-C) diagram of AU Ser.
Spectral diffusion and drift: single chromophore and en masse.
Lubchenko, Vassiliy; Silbey, Robert J
2007-02-14
We develop a systematic description of spectral diffusion of ideal chromophores interacting with incoherently relaxing two-state, localized environmental degrees of freedom ("spins") for general initial environment configurations. We remedy the existing, incomplete treatments by formulating the problem in terms of the proper correlation function and by obtaining an accurate solution for generic aperiodic arrangements of environmental spins, nearly free of the customary simplifying assumptions on the multiparticle spin coordinate distribution. We report and estimate, for the first time, the effects of the drift and distortion of a narrow spectral line that arise when the line is not in the center of the inhomogeneous band. While the drift turns out to be modest in most ensemble measurements, accounting for its effects is imperative in analyzing single chromophore spectral jumps, to which end the authors propose a novel experiment. Further, we argue that by employing a sufficiently large chromophore one can decouple the concentration of the fluctuating centers from the strength of their interaction with the chromophore. Finally, the additional line broadening, owing to a distribution of the central chromophore frequencies, is evaluated. Upper estimates for an analogous broadening stemming from a nonequilibrium environment are made.
Devices with extended area structures for mass transfer processing of fluids
TeGrotenhuis, Ward E.; Wegeng, Robert S.; Whyatt, Greg A.; King, David L.; Brooks, Kriston P.; Stenkamp, Victoria S.
2009-04-21
A microchannel device includes several mass transfer microchannels to receive a fluid media for processing at least one heat transfer microchannel in fluid communication with a heat transfer fluid defined by a thermally conductive wall, and at several thermally conductive fins each connected to the wall and extending therefrom to separate the mass transfer microchannels from one another. In one form, the device may optionally include another heat transfer microchannel and corresponding wall that is positioned opposite the first wall and has the fins and the mass transfer microchannels extending therebetween.
Drop oscillation and mass transfer in alternating electric fields. Progress report
Carleson, T.E.; Yang, W.
1991-05-30
After the second annual progress report to DOE in July 1990, we continued the experimental work for another liquid system. The mathematical model was also improved to include secondary effects due to drop deformation and charge redistribution on the deformed drop surface. Originally, we planned to study a mass transfer process after the hydrodynamic modelling. Due to difficulty in measuring drop concentration during oscillations, we decided to study a heat transfer process instead. Using the analogy between the mass transfer and the heat transfer, we can easily extend the results for the heat transfer study to the mass transfer problem.
Heat and mass transfer from a supercritical LOX spray
NASA Astrophysics Data System (ADS)
Chegini, H.; Chaturvedi, S. K.; Kondic, N.
1991-12-01
The injection, evaporation and diffusion of liquid oxygen in a high pressure airstream in a parallel wall mixing channel is analyzed and computationally solved. The droplet evaporation in the supercritical environment is treated by a nonisothermal droplet heat transfer model which accounts for the finite thermal conductivity of oxygen droplets and the gas film. The nonideal gas effects in the gas phase are modeled by the Redlich-Kwong equation of state. The mixture density and enthalpy are determined by applying the ideal-solution limit which is shown to be valid for the prevailing conditions. The coupled dynamics of droplet and gas phases is calculated by solving numerically the Navier-Stokes equations in two dimensions. The turbulence effects are modeled by a two equation (k-epsilon) model. The results show that the nonideal gas behavior prevails over a large portion of the mixing channel. Furthermore, the injected liquid oxygen droplets achieve critical temperature very quickly, and as a result they evaporate in the vicinity of the injection point. The effects of injection angle on oxygen mixing characteristics is also investigated.
Asplund, S.
1996-01-01
Catalyst aging by coke formation has been studied for the selective hydrogenation of acetylene in the presence of excess ethylene on supported palladium catalysts. Deposited coke was found to have a substantial influence on the effective diffusivity, which decreased about one order of magnitude during 100 h of operation. As has been observed previously the selectivity for the undesired ethane was higher on aged catalysts, while the activity for acetylene hydrogenation was almost constant. These effects, however, were strongly dependent on the catalyst particle size, although the behaviour of fresh catalysts was unaffected by mass transfer limitations. When the catalyst used was Pd/{alpha}-Al{sub 2}O{sub 3} the change in selectivity with aging could be explained solely as a consequence of the increased diffusion resistance. The mass transfer effects were important also on Pd/{gamma}-Al{sub 2}O{sub 3}, but on this catalyst there was an additional increase in ethane selectivity that could not be attributed to diffusion limitations. Calculations and experimental tests showed that the observed phenomena are relevant also for the shell-type catalysts normally used industrially. The coke formation itself was about four to five times faster on Pd/{gamma}-Al{sub 2}O{sub 3} compared to the {alpha}-Al{sub 2}O{sub 3}-supported catalyst. The coke was generally concentrated towards the pellet periphery showing the influence of diffusion resistance also on the coke-forming reactions. 27 refs., 10 figs., 5 tabs.
Mass Transfer of Nickel-Base Alloy Covered Electrode During Shielded Metal Arc Welding
NASA Astrophysics Data System (ADS)
Qin, Renyao; He, Guo
2013-03-01
The mass transfer in shielded metal arc welding of a group of nickel-base alloy covered electrodes according to AWS specification A5.11-A5.11M was investigated by directly measuring their deposited metal compositions. The results indicate that the chromium mass-transfer coefficient is in the range of 86 to 94 pct, iron in the range of 82 to 89 pct, manganese in the range of 60 to 73 pct, niobium in the range of 44 to 56 pct, and silicon in the range of 41 to 47 pct. The metal mass-transfer coefficient from the core wire is markedly higher than that from the coating. The basicity of slag, the metal contents in the flux coating, and the welding current together affect the mass transfer. As the basicity of slag increases, the mass-transfer coefficients of Mn, Fe, and Cr slightly increase, but those of Nb and Si decrease significantly. As the niobium and manganese contents increase in the coating, their mass-transfer coefficients also increase. However, iron is different. The content of iron in the coating in the range of 8 to 20 wt pct results in the optimal effective mass transfer. The lower, or higher, iron content leads to lower mass-transfer coefficient. As the welding current increases, the mass-transfer coefficients of niobium and manganese decrease, but chromium and silicon increase. Iron has the lowest mass-transfer coefficient when welded under the operating current of 100 A.
Mass transfer and free convection through a porous medium by the presence of a rotating fluid
NASA Astrophysics Data System (ADS)
Raptis, A.
1983-04-01
An analytical examination of steady, free convective flow and mass transfer through a porous medium bounded by a vertical porous plate in the case of a rotating fluid with a constant angular velocity and a constant temperature at the plate is presented. The fluid is assumed incompressible and viscous, and governing equations are defined for continuity, momentum, energy, and diffusion. Boundary conditions are configured to include the constant heat flux, the species concentration at the plate, and the suction velocity. The primary and secondary velocities were determined for different values of the modified Grashof number, Eckman number, and a permeability parameter. Increases in the Eckman number were accompanied by decreases in the primary velocity, which increased with increases in the permeability parameter or the modified Grashof number. The same was verified for the secondary velocity.
NASA Astrophysics Data System (ADS)
Wu, Yixiang; Zou, Xingfu
2016-10-01
Mass action and standard incidence are two major infection mechanisms in modelling spread of infectious diseases. Spatial heterogeneity plays an important role in spread of infectious diseases, and hence, motivates and advocates diffusive models for disease dynamics. By analyzing a diffusive SIS model with the standard incidence infection mechanism, some recent works [2,12] have investigated the asymptotical profiles of the endemic steady state for large and small diffusion rates, and the results show that controlling the diffusion rate of the susceptible individuals can help eradicate the infection, while controlling the diffusion rate of the infectious individuals cannot. This paper aims to reveal the difference between the two infection mechanisms in a spatially heterogeneous environment. To this end, we consider a diffusive SIS model of the same structure but with the mass action infection adopted, and explore the asymptotic profiles of the endemic steady state for small and large diffusion rates. It turns out that the new model poses some new challenges due to the nonlocal term in the equilibrium problem and the unboundedness of the nonlinear term. Our results on this new model reveal some fundamental differences between the two transmission mechanisms in such spatial models, which may provide some implications on disease modelling and controls.
Leith, S.D.; Reddy, M.M.; Irez, W.F.; Heymans, M.J.
1996-01-01
The pore structure of Salem limestone is investigated, and conclusions regarding the effect of the pore geometry on modeling moisture and contaminant transport are discussed based on thin section petrography, scanning electron microscopy, mercury intrusion porosimetry, and nitrogen adsorption analyses. These investigations are compared to and shown to compliment permeability and capillary pressure measurements for this common building stone. Salem limestone exhibits a bimodal pore size distribution in which the larger pores provide routes for convective mass transfer of contaminants into the material and the smaller pores lead to high surface area adsorption and reaction sites. Relative permeability and capillary pressure measurements of the air/water system indicate that Salem limestone exhibits high capillarity end low effective permeability to water. Based on stone characterization, aqueous diffusion and convection are believed to be the primary transport mechanisms for pollutants in this stone. The extent of contaminant accumulation in the stone depends on the mechanism of partitioning between the aqueous and solid phases. The described characterization techniques and modeling approach can be applied to many systems of interest such as acidic damage to limestone, mass transfer of contaminants in concrete and other porous building materials, and modeling pollutant transport in subsurface moisture zones.
Bio-inspired Murray materials for mass transfer and activity.
Zheng, Xianfeng; Shen, Guofang; Wang, Chao; Li, Yu; Dunphy, Darren; Hasan, Tawfique; Brinker, C Jeffrey; Su, Bao-Lian
2017-04-06
Both plants and animals possess analogous tissues containing hierarchical networks of pores, with pore size ratios that have evolved to maximize mass transport and rates of reactions. The underlying physical principles of this optimized hierarchical design are embodied in Murray's law. However, we are yet to realize the benefit of mimicking nature's Murray networks in synthetic materials due to the challenges in fabricating vascularized structures. Here we emulate optimum natural systems following Murray's law using a bottom-up approach. Such bio-inspired materials, whose pore sizes decrease across multiple scales and finally terminate in size-invariant units like plant stems, leaf veins and vascular and respiratory systems provide hierarchical branching and precise diameter ratios for connecting multi-scale pores from macro to micro levels. Our Murray material mimics enable highly enhanced mass exchange and transfer in liquid-solid, gas-solid and electrochemical reactions and exhibit enhanced performance in photocatalysis, gas sensing and as Li-ion battery electrodes.
Center of mass velocity during diffusion: Comparisons of fluid and kinetic models
NASA Astrophysics Data System (ADS)
Vold, Erik; Yin, Lin; Taitano, William; Molvig, Kim; Albright, B. J.
2016-11-01
We examine the diffusion process between two ideal gases mixing across an initial discontinuity by comparing fluid and kinetic model results and find several similarities between ideal gases and plasma transport. Binary diffusion requires a net zero species mass flux in the Lagrange frame to assure momentum conservation in collisions. Diffusion between ideal gases is often assumed to be isobaric and isothermal which requires constant molar density. We show this condition exists only in the lab frame at late times (many collision times) after a pressure transient relaxes. The sum of molar flux across an initial discontinuity is non-zero for species of differing atomic masses resulting in a pressure perturbation. The results show three phases of mixing: a pressure discontinuity forms across the initial interface (times of a few collisions), pressure perturbations propagate away from the mix region (time scales of an acoustic transit) and at late times characteristic of the diffusion process, the pressure relaxes leaving a non-zero center of mass flow velocity. The center of mass velocity associated with the outward propagating pressure waves is required to conserve momentum in the rest frame. Implications are considered in multi-species diffusion numerics and in applications. Work performed under the auspices of the U.S. DOE by the LANS, LLC, Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396. Funding provided by the Advanced Simulation and Computing (ASC) Program.
Numerical simulations of heat and mass transfer at ablating surface in hypersonic flow
NASA Astrophysics Data System (ADS)
Bocharov, A. N.; Golovin, N. N.; Petrovskiy, V. P.; Teplyakov, I. O.
2015-11-01
The numerical technique was developed to solve heat and mass transfer problem in 3D hypersonic flow taking into account destruction of thermal protection system. Described technique was applied for calculation of heat and mass transfer in sphere-cone shaped body. The data on temperature, heat flux and mass flux were obtained.
Uncluttering graph layouts using anisotropic diffusion and mass transport.
Frishman, Yaniv; Tal, Ayellet
2009-01-01
Many graph layouts include very dense areas, making the layout difficult to understand. In this paper, we propose a technique for modifying an existing layout in order to reduce the clutter in dense areas. A physically inspired evolution process based on a modified heat equation is used to create an improved layout density image, making better use of available screen space. Using results from optimal mass transport problems, a warp to the improved density image is computed. The graph nodes are displaced according to the warp. The warp maintains the overall structure of the graph, thus limiting disturbances to the mental map, while reducing the clutter in dense areas of the layout. The complexity of the algorithm depends mainly on the resolution of the image visualizing the graph and is linear in the size of the graph. This allows scaling the computation according to required running times. It is demonstrated how the algorithm can be significantly accelerated using a graphics processing unit (GPU), resulting in the ability to handle large graphs in a matter of seconds. Results on several layout algorithms and applications are demonstrated.
NASA Astrophysics Data System (ADS)
Tecklenburg, Jan; Neuweiler, Insa; Carrera, Jesus; Dentz, Marco
2016-05-01
We study modeling of two-phase flow in highly heterogeneous fractured and porous media. The flow behaviour is strongly influenced by mass transfer between a highly permeable (mobile) fracture domain and less permeable (immobile) matrix blocks. We quantify the effective two-phase flow behavior using a multirate rate mass transfer (MRMT) approach. We discuss the range of applicability of the MRMT approach in terms of the pertinent viscous and capillary diffusion time scales. We scrutinize the linearization of capillary diffusion in the immobile regions, which allows for the formulation of MRMT in the form of a non-local single equation model. The global memory function, which encodes mass transfer between the mobile and the immobile regions, is at the center of this method. We propose two methods to estimate the global memory function for a fracture network with given fracture and matrix geometry. Both employ a scaling approach based on the known local memory function for a given immobile region. With the first method, the local memory function is calculated numerically, while the second one employs a parametric memory function in form of truncated power-law. The developed concepts are applied and tested for fracture networks of different complexity. We find that both physically based parameter estimation methods for the global memory function provide predictive MRMT approaches for the description of multiphase flow in highly heterogeneous porous media.
Pore-scale supercritical CO2 dissolution and mass transfer under drainage conditions
NASA Astrophysics Data System (ADS)
Chang, Chun; Zhou, Quanlin; Oostrom, Mart; Kneafsey, Timothy J.; Mehta, Hardeep
2017-02-01
Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO2 (scCO2) and a prolonged depletion of residual scCO2. In this study, pore-scale scCO2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO2 into the sandstone-analogue pore network initially saturated by water without dissolved CO2 (dsCO2). During the experiments, time-lapse images of dye intensity, reflecting water pH, were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO2 dissolution and phase equilibrium occurs when scCO2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes - scCO2 dissolution at phase interfaces and diffusion of dsCO2 at the pore scale (10-100 μm) observed after scCO2 bubble invasion into water-filled pores without pore throat constraints - are relatively fast. The overall slow dissolution of scCO2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. This finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded
Lordgooei, M.; Sagen, J.; Rood, M.J.; Rostam-Abadi, M.
1998-01-01
A new activated-carbon fiber-cloth (ACFC) adsorber coupled with an electrothermal regenerator and a cryogenic condenser was designed and developed to efficiently capture and recover toxic chemical vapors (TCVs) from simulated industrial gas streams. The system was characterized for adsorption by ACFC, electrothermal desorption, and cryogenic condensation to separate acetone and methyl ethyl ketone from gas streams. Adsorption dynamics are numerically modeled to predict system characteristics during scale-up and optimization of the process in the future. The model requires diffusivities of TCVs into an activated-carbon fiber (ACF) as an input. Effective diffusivities of TCVs into ACFs were modeled as a function of temperature, concentration, and pore size distribution. Effective diffusivities for acetone at 65 ??C and 30-60 ppmv were measured using a chromatography method. The energy factor for surface diffusion was determined from comparison between the experimental and modeled effective diffusivities. The modeled effective diffusivities were used in a dispersive computational model to predict mass transfer zones of TCVs in fixed beds of ACFC under realistic conditions for industrial applications.
NASA Technical Reports Server (NTRS)
Moss, J. N.
1971-01-01
Numerical solutions are presented for the viscous shocklayer equations where the chemistry is treated as being either frozen, equilibrium, or nonequilibrium. Also the effects of the diffusion model, surface catalyticity, and mass injection on surface transport and flow parameters are considered. The equilibrium calculations for air species using multicomponent: diffusion provide solutions previously unavailable. The viscous shock-layer equations are solved by using an implicit finite-difference scheme. The flow is treated as a mixture of inert and thermally perfect species. Also the flow is assumed to be in vibrational equilibrium. All calculations are for a 45 deg hyperboloid. The flight conditions are those for various altitudes and velocities in the earth's atmosphere. Data are presented showing the effects of the chemical models; diffusion models; surface catalyticity; and mass injection of air, water, and ablation products on heat transfer; skin friction; shock stand-off distance; wall pressure distribution; and tangential velocity, temperature, and species profiles.
Reaction-diffusion systems in natural sciences and new technology transfer
NASA Astrophysics Data System (ADS)
Keller, André A.
2012-12-01
Diffusion mechanisms in natural sciences and innovation management involve partial differential equations (PDEs). This is due to their spatio-temporal dimensions. Functional semi-discretized PDEs (with lattice spatial structures or time delays) may be even more adapted to real world problems. In the modeling process, PDEs can also formalize behaviors, such as the logistic growth of populations with migration, and the adopters’ dynamics of new products in innovation models. In biology, these events are related to variations in the environment, population densities and overcrowding, migration and spreading of humans, animals, plants and other cells and organisms. In chemical reactions, molecules of different species interact locally and diffuse. In the management of new technologies, the diffusion processes of innovations in the marketplace (e.g., the mobile phone) are a major subject. These innovation diffusion models refer mainly to epidemic models. This contribution introduces that modeling process by using PDEs and reviews the essential features of the dynamics and control in biological, chemical and new technology transfer. This paper is essentially user-oriented with basic nonlinear evolution equations, delay PDEs, several analytical and numerical methods for solving, different solutions, and with the use of mathematical packages, notebooks and codes. The computations are carried out by using the software Wolfram Mathematica®7, and C++ codes.
The influence of state-to-state kinetics on diffusion and heat transfer behind shock waves
Kunova, O.; Kustova, E.; Mekhonoshina, M.; Nagnibeda, E.
2014-12-09
In the paper, the influence of vibrational and chemical kinetics on heat transfer and diffusion in hypersonic flows of N{sub 2}/N mixture in the relaxation zone behind shock waves is studied on the basis of the state-to-state kinetic theory approach. The results of calculations of vibrational level populations ni, gas temperature T, total energy flux q, diffusion velocities of molecules at different vibrational states V{sub i} and atoms V{sub a} in the relaxation zone behind a shock front are presented for the free stream Mach number M = 10, 15. The contribution of different dissipative processes to the total energy flux is estimated for various flow conditions. The impact of non-equilibrium vibrational distributions in the free stream on molecular level populations and transport properties in the relaxation zone is shown.
Direct Geoelectrical Evidence of Mass Transfer at the Lab scale
NASA Astrophysics Data System (ADS)
Swanson, R. D.; Singha, K.; Day-Lewis, F. D.; Keating, K.; Binley, A.; Clifford, J.; Haggerty, R.
2011-12-01
At many field sites, anomalous tailing behavior-- a long, slow decrease of solute concentration in time-- is observed yet cannot be explained with the advection-dispersion model. One explanation for this commonly observed behavior is the exchange of solute between mobile and immobile domains; however, direct experimental observations of this controlling process remain elusive. Circumstantial evidence for a less-mobile phase is typically inferred from tailing behavior observed in fluid samples of the mobile phase. Electrical methods provide a measure of the total solutes in both the immobile and mobile domain and therefore have been hypothesized to provide, in combination with fluid sampling, direct experimental evidence for a less-mobile and mobile model, yet experimental evidence is needed to support this claim. Here, we conduct column solute tracer tests and measure both electrical resistivity and fluid conductivity on unconsolidated, well-sorted sand in addition to fine and coarse fractions of the porous zeolite clinoptilolite. We examine nearly co-located time-lapse standard fluid conductivity and bulk apparent resistivity measurements to identify solute exchange between multiple domains at the lab scale. Our results show extensive tailing behavior in both fluid and bulk electrical conductivity measurements in the zeolite but not in sand, providing evidence for a mobile-immobile framework. Transport parameters are estimated by minimizing the root-mean-square error between the observed and simulated fluid conductivity in COMSOL Multiphysics. These best-fit parameters support our claims of mass transfer occurring in the zeolite columns and provide the first direct electrical evidence of dual-domain mass transport at the lab scale.
Fick's second law transformed: one path to cloaking in mass diffusion
Guenneau, S.; Puvirajesinghe, T. M.
2013-01-01
Here, we adapt the concept of transformational thermodynamics, whereby the flux of temperature is controlled via anisotropic heterogeneous diffusivity, for the diffusion and transport of mass concentration. The n-dimensional, time-dependent, anisotropic heterogeneous Fick's equation is considered, which is a parabolic partial differential equation also applicable to heat diffusion, when convection occurs, for example, in fluids. This theory is illustrated with finite-element computations for a liposome particle surrounded by a cylindrical multi-layered cloak in a water-based environment, and for a spherical multi-layered cloak consisting of layers of fluid with an isotropic homogeneous diffusivity, deduced from an effective medium approach. Initial potential applications could be sought in bioengineering. PMID:23536540
Zaikowski, Lori; Mauro, Gina; Bird, Matthew; Karten, Brianne; Asaoka, Sadayuki; Wu, Qin; Cook, Andrew R; Miller, John R
2015-06-18
Photoexcitation of conjugated poly-2,7-(9,9-dihexylfluorene) polyfluorenes with naphthylimide (NI) and anthraquinone (AQ) electron-acceptor end traps produces excitons that form charge transfer states at the end traps. Intramolecular singlet exciton transport to end traps was examined by steady state fluorescence for polyfluorenes of 17-127 repeat units in chloroform, dimethylformamide (DMF), tetrahydrofuran (THF), and p-xylene. End traps capture excitons and form charge transfer (CT) states at all polymer lengths and in all solvents. The CT nature of the end-trapped states is confirmed by their fluorescence spectra, solvent and trap group dependence, and DFT descriptions. Quantum yields of CT fluorescence are as large as 46%. This strong CT emission is understood in terms of intensity borrowing. Energies of the CT states from onsets of the fluorescence spectra give the depths of the traps which vary with solvent polarity. For NI end traps, the trap depths are 0.06 (p-xylene), 0.13 (THF), and 0.19 eV (CHCl3). For AQ, CT fluorescence could be observed only in p-xylene where the trap depth is 0.27 eV. Quantum yields, emission energies, charge transfer energies, solvent reorganization, and vibrational energies were calculated. Fluorescence measurements on chains >100 repeat units indicate that end traps capture ∼50% of the excitons, and that the exciton diffusion length is LD = 34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains. The efficiency of exciton capture depends on chain length but not on trap depth, solvent polarity, or which trap group is present.
Zaikowski, Lori; Mauro, Gina; Bird, Matthew; Karten, Brianne; Asaoka, Sadayuki; Wu, Qin; Cook, Andrew R.; Miller, John R.
2014-12-22
Photoexcitation of conjugated poly-2,7-(9,9-dihexylfluorene) polyfluorenes with naphthylimide (NI) and anthraquinone (AQ) electron-acceptor end traps produces excitons that form charge transfer states at the end traps. Intramolecular singlet exciton transport to end traps was examined by steady state fluorescence for polyfluorenes of 17 to 127 repeat units in chloroform, dimethylformamide (DMF), tetrahydrofuran (THF), and p-xylene. End traps capture excitons and form charge transfer (CT) states at all polymer lengths and in all solvents. The CT nature of the end-trapped states is confirmed by their fluorescence spectra, solvent and trap group dependence and DFT descriptions. Quantum yields of CT fluorescence are as large as 46%. This strong CT emission is understood in terms of intensity borrowing. Energies of the CT states from onsets of the fluorescence spectra give the depths of the traps which vary with solvent polarity. For NI end traps the trap depths are 0.06 (p-xylene), 0.13 (THF) and 0.19 eV (CHCl_{3}). For AQ, CT fluorescence could be observed only in p-xylene where the trap depth is 0.27 eV. Quantum yields, emission energies, charge transfer energies, solvent reorganization and vibrational energies were calculated. Fluorescence measurements on chains >100 repeat units indicate that end traps capture ~50% of the excitons, and that the exciton diffusion length L_{D} =34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains. As a result, the efficiency of exciton capture depends on chain length, but not on trap depth, solvent polarity or which trap group is present.
Zaikowski, Lori; Mauro, Gina; Bird, Matthew; ...
2014-12-22
Photoexcitation of conjugated poly-2,7-(9,9-dihexylfluorene) polyfluorenes with naphthylimide (NI) and anthraquinone (AQ) electron-acceptor end traps produces excitons that form charge transfer states at the end traps. Intramolecular singlet exciton transport to end traps was examined by steady state fluorescence for polyfluorenes of 17 to 127 repeat units in chloroform, dimethylformamide (DMF), tetrahydrofuran (THF), and p-xylene. End traps capture excitons and form charge transfer (CT) states at all polymer lengths and in all solvents. The CT nature of the end-trapped states is confirmed by their fluorescence spectra, solvent and trap group dependence and DFT descriptions. Quantum yields of CT fluorescence are asmore » large as 46%. This strong CT emission is understood in terms of intensity borrowing. Energies of the CT states from onsets of the fluorescence spectra give the depths of the traps which vary with solvent polarity. For NI end traps the trap depths are 0.06 (p-xylene), 0.13 (THF) and 0.19 eV (CHCl3). For AQ, CT fluorescence could be observed only in p-xylene where the trap depth is 0.27 eV. Quantum yields, emission energies, charge transfer energies, solvent reorganization and vibrational energies were calculated. Fluorescence measurements on chains >100 repeat units indicate that end traps capture ~50% of the excitons, and that the exciton diffusion length LD =34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains. As a result, the efficiency of exciton capture depends on chain length, but not on trap depth, solvent polarity or which trap group is present.« less
Heat and mass transfer in unsaturated porous media. Final report
Childs, S.W.; Malstaff, G.
1982-02-01
A preliminary study of heat and water transport in unsaturated porous media is reported. The project provides background information regarding the feasibility of seasonal thermal energy storage in unconfined aquifers. A parametric analysis of the factors of importance, and an annotated bibliography of research findings pertinent to unconfined aquifer thermal energy storage (ATES) are presented. This analysis shows that heat and mass transfer of water vapor assume dominant importance in unsaturated porous media at elevated temperature. Although water vapor fluxes are seldom as large as saturated medium liquid water fluxes, they are important under unsaturated conditions. The major heat transport mechanism for unsaturated porous media at temperatures from 50 to 90/sup 0/C is latent heat flux. The mechanism is nonexistent under saturated conditions but may well control design of unconfined aquifer storage systems. The parametric analysis treats detailed physical phenomena which occur in the flow systems study and demonstrates the temperature and moisture dependence of the transport coefficients of importance. The question of design of an unconfined ATES site is also addressed by considering the effects of aquifer temperature, depth to water table, porous medium flow properties, and surface boundary conditions. Recommendations are made for continuation of this project in its second phase. Both scientific and engineering goals are considered and alternatives are presented.
Biological conversion of synthesis gas. Mass transfer/kinetic studies
Klasson, K.T.; Basu, R.; Johnson, E.R.; Clausen, E.C.; Gaddy, J.L.
1992-03-01
Mass transfer and kinetic studies were carried out for the Rhodospirillum rubrum and Chlorobium thiosulfatophilum bacterial systems. R. rubrum is a photosynthetic anaerobic bacterium which catalyzes the biological water gas shift reaction: CO + H{sub 2}0 {yields} CO{sub 2} + H{sub 2}. C. thiosulfatophilum is also a H{sub 2}S and COS to elemental sulfur. The growth of R. rubrum may be satisfactorily carried out at 25{degree} and 30{degree}C, while CO uptake and thus the conversion of CO best occurs at temperatures of either 30{degree}, 32{degree} or 34{degree}C. The rate of conversion of COs and H{sub 2}O to CO{sub 2} and H{sub 2}S may be modeled by a first order rate expression. The rate constant at 30{degree}C was found to be 0.243 h{sup {minus}1}. The growth of C. thiosulfatophilum may be modeled in terms of incoming light intensity using a Monod equation: {mu} = {sub 351} + I{sub o}/{sup 0.152}I{sub o}. Comparisons of the growth of R. rubrum and C. thiosulfatophilum shows that the specific growth rate of C. thiosulfatophilum is much higher at a given light intensity.
Myung, Jaewook; Kim, Minkyu; Pan, Ming; Criddle, Craig S; Tang, Sindy K Y
2016-05-01
Methane is a low-cost feedstock for the production of polyhydroxyalkanoate biopolymers, but methanotroph fermentations are limited by the low solubility of methane in water. To enhance mass transfer of methane to water, vigorous mixing or agitation is typically used, which inevitably increases power demand and operational costs. This work presents a method for accelerating methane mass transfer without agitation by growing methanotrophs in water-in-oil emulsions, where the oil has a higher solubility for methane than water does. In systems without agitation, the growth rate of methanotrophs in emulsions is five to six times that of methanotrophs in the medium-alone incubations. Within seven days, cells within the emulsions accumulate up to 67 times more P3HB than cells in the medium-alone incubations. This is achieved due to the increased interfacial area of the aqueous phase, and accelerated methane diffusion through the oil phase.
Effects of dynamic disorder on exciton migration: Quantum diffusion, coherences, and energy transfer
NASA Astrophysics Data System (ADS)
Dutta, Rajesh; Bagchi, Biman
2016-10-01
We study excitation transfer and migration in a one-dimensional lattice characterized by dynamic disorder. The diagonal and off-diagonal energy disorders arise from the coupling of system and bath. We consider both same bath (when baths are spatially correlated) and independent bath (when baths are completely uncorrelated) limits. In the latter case, all diagonal and off-diagonal bath coupling elements fluctuate independently of each other and the dynamics is complicated. We obtain time dependent population distribution by solving Kubo's quantum stochastic Liouville equation. In the Markovian limit, both energy transfer dynamics and mean square displacement of the exciton behave the similar way in same and independent bath cases. However, these two baths can give rise to a markedly different behavior in the non-Markovian limit. We note that previously only the same bath case has been studied in the non-Markovian limit. The other main results of our study include the following. (i) For an average, non-zero off-diagonal coupling value J, exciton migration remains coherent in same bath case even at long times while it becomes incoherent in independent bath case in the Markovian limit. (ii) Coherent transfer is manifested in an oscillatory behavior of the energy transfer dynamics accompanied by faster-than diffusive spread of the exciton from the original position. (iii) Agreement with available analytical expression of mean squared displacement is good in Markovian limit for independent bath (off-diagonal fluctuation) case but only qualitative in non-Markovian limit for which no complete analytical solution is available. (iv) We observe transition from coherent to incoherent transport in independent bath (diagonal fluctuation) case when the bath is made progressively more Markovian. We present an analytical study that shows coherence to propagate through excited bath states. (v) The correlation time of the bath plays a unique role in dictating the diffusive spread
Impact of NAPL architecture on interphase mass transfer: A pore network study
NASA Astrophysics Data System (ADS)
Agaoglu, Berken; Scheytt, Traugott; Copty, Nadim K.
2016-09-01
Interphase mass transfer in porous media is commonly modeled using Sherwood number expressions that are developed in terms of fluid and porous medium properties averaged over some representative elementary volume (REV). In this work the influence of sub-grid scale properties on interphase mass transfer was investigated using a two-dimensional pore network model. The focus was on assessing the impact of (i) NAPL saturation, (ii) interfacial area (iii) NAPL spatial distribution at the pore scale, (iv) grain size heterogeneity, (v) REV or domain size and (vi) pore scale heterogeneity of the porous media on interphase mass transfer. Variability of both the mass transfer coefficient that explicitly accounts for the interfacial area and the mass transfer coefficient that lumps the interfacial area was examined. It was shown that pore scale NAPL distribution and its orientation relative to the flow direction have significant impact on flow bypassing and the interphase mass transfer coefficient. This results in a complex non-linear relationship between interfacial area and the REV-based interphase mass transfer rate. Hence, explicitly accounting for the interfacial area does not eliminate the uncertainty of the mass transfer coefficient. It was also shown that, even for explicitly defined flow patterns, changing the domain size over which the mass transfer process is defined influences the extent of NAPL bypassing and dilution and, consequently, the interphase mass transfer. It was also demonstrated that the spatial variability of pore scale parameters such as pore throat diameters may result in different rates of interphase mass transfer even for the same pore size distribution index.
Radiation Heat Transfer Between Diffuse-Gray Surfaces Using Higher Order Finite Elements
NASA Technical Reports Server (NTRS)
Gould, Dana C.
2000-01-01
This paper presents recent work on developing methods for analyzing radiation heat transfer between diffuse-gray surfaces using p-version finite elements. The work was motivated by a thermal analysis of a High Speed Civil Transport (HSCT) wing structure which showed the importance of radiation heat transfer throughout the structure. The analysis also showed that refining the finite element mesh to accurately capture the temperature distribution on the internal structure led to very large meshes with unacceptably long execution times. Traditional methods for calculating surface-to-surface radiation are based on assumptions that are not appropriate for p-version finite elements. Two methods for determining internal radiation heat transfer are developed for one and two-dimensional p-version finite elements. In the first method, higher-order elements are divided into a number of sub-elements. Traditional methods are used to determine radiation heat flux along each sub-element and then mapped back to the parent element. In the second method, the radiation heat transfer equations are numerically integrated over the higher-order element. Comparisons with analytical solutions show that the integration scheme is generally more accurate than the sub-element method. Comparison to results from traditional finite elements shows that significant reduction in the number of elements in the mesh is possible using higher-order (p-version) finite elements.
Direct estimation of mass flow and diffusion of nitrogen compounds in solution and soil.
Oyewole, Olusegun Ayodeji; Inselsbacher, Erich; Näsholm, Torgny
2014-02-01
Plant nutrient uptake from soil is mainly governed by diffusion and transpirationally induced mass flow, but the current methods for assessing the relative importance of these processes are indirect. We developed a microdialysis method using solutions of different osmotic potentials as perfusates to simulate diffusion and mass flow processes, and assessed how induced mass flow affected fluxes of nitrogen (N) compounds in solution and in boreal forest soil. Varying the osmotic potential of perfusates induced vertical fluxes in the direction of the dialysis membranes at rates of between 1 × 10(-8) and 3 × 10(-7) m s(-1) , thus covering the estimated range of water velocities perpendicular to root surfaces and induced by transpiration. Mass flow increased N fluxes in solution but even more so in soil. This effect was explained by an indirect effect of mass flow on rates of diffusive fluxes, possibly caused by the formation of steeper gradients in concentrations of N compounds from membrane surfaces out in the soil. Our results suggest that transpiration may be an essential driver of plant N acquisition.
An analysis of three dimensional diffusion in a representative arterial wall mass transport model.
Denny, William J; O'Connell, Barry M; Milroy, John; Walsh, Michael T
2013-05-01
The development and use of drug eluting stents has brought about significant improvements in reducing in-stent restenosis, however, their long term presence in the artery is still under examination due to restenosis reoccurring. Current studies focus mainly on stent design, coatings and deployment techniques but few studies address the issue of the physics of three dimensional mass transport in the artery wall. There is a dearth of adequate validated numerical mass transport models that simulate the physics of diffusion dominated drug transport in the artery wall whilst under compression. A novel experimental setup used in a previous study was adapted and an expansion of that research was carried out to validate the physics of three dimensional diffusive mass transport into a compressed porous media. This study developed a more sensitive method for measuring the concentration of the species of interest. It revalidated mass transport in the radial direction and presented results which highlight the need for an evaluation of the governing equation for transient diffusive mass transport in a porous media, in its current form, to be carried out.
NASA Astrophysics Data System (ADS)
Landel, Julien R.; Thomas, Amalia; McEvoy, Harry; Dalziel, Stuart B.
2015-11-01
We investigate the convective mass transfer of dilute passive tracers contained in small viscous drops into a submerging falling film. This problem has applications in industrial cleaning, domestic dishwashers, and decontamination of hazardous material. The film Peclet number is very high, whereas the drop Peclet number varies from 0.1 to 1. The characteristic transport time in the drop is much larger than in the film. We model the mass transfer using an analogy with Newton's law of cooling. This empirical model is supported by an analytical model solving the quasi-steady two-dimensional advection-diffusion equation in the film that is coupled with a time-dependent one-dimensional diffusion equation in the drop. We find excellent agreement between our experimental data and the two models, which predict an exponential decrease in time of the drop concentration. The transport characteristic time is related to the drop diffusion time scale, as diffusion within the drop is the limiting process. Our theoretical model not only predicts the well-known relationship between the Sherwood number and the external Reynolds number in the case of a well-mixed drop Sh ~ Re1/3, it also predicts a correction in the case of a non-uniform drop concentration. The correction depends on Re, the film Schmidt number, the drop aspect ratio and the diffusivity ratio between the two phases. This prediction is in good agreement with experimental data. This material is based upon work supported by the Defense Threat Reduction Agency under Contract No. HDTRA1-12-D-0003-0001.
Nitrogen mass transfer models for plasma-based low-energy ion implantation
Zheng, Bocong; Wang, Kesheng; Zhang, Zhipeng; Che, Honglong; Lei, Mingkai
2015-03-15
The nitrogen mass transfer process in plasma-based low-energy ion implantation (PBLEII) is theoretically and experimentally studied in order to explore the process mechanism of PBLEII and therefore to optimize the apparatus design and the process conditions. An electron cyclotron resonance (ECR) microwave discharge generates the nitrogen plasma with a high density of 10{sup 11}–10{sup 12} ions/cm{sup 3}, which diffuses downstream to the process chamber along the divergent magnetic field. The nitrogen ions in the plasma implant into the surface and transport to the matrix of an austenitic stainless steel under the low negative pulsed bias of −2 kV at a process temperature of 400 °C. A global plasma model is used to simulate the ECR microwave plasma discharge for a range of working pressures and microwave powers. The fluid models are adopted to calculate the plasma downstream diffusion, the sheath expansion and the low-energy ion implantation on the surface. A nonlinear kinetic discrete model is established to describe the nitrogen transport in the austenitic stainless steel and the results are compared with the experimental measurements. Under an average implantation current density of 0.3–0.6 mA/cm{sup 2}, the surface nitrogen concentration in the range from 18.5 to 29 at. % is a critical factor for the nitrogen transport in the AISI 304 austenitic stainless steel by PBLEII, which accelerates the implanted nitrogen diffusion inward up to 6–12 μm during a nitriding time of 4 h.
Kinetic study on external mass transfer in high performance liquid chromatography system.
Miyabe, Kanji; Kawaguchi, Yuuki; Guiochon, Georges
2010-04-30
External mass transfer coefficients (k(f)) were measured for a column packed with fully porous C(18)-silica spherical particles (50.6 microm in diameter), eluted with a methanol/water mixture (70/30, v/v). The pulse response and the peak-parking methods were used. Profiles of elution peaks of alkylbenzene homologues were recorded at flow rates between 0.2 and 2.0 mL min(-1). Peak-parking experiments were conducted under the same conditions, to measure intraparticle and pore diffusivity, and surface diffusion coefficients. Finally, the values of k(f) for these compounds at 298 K were derived from the first and second moments of the elution peaks by subtracting the contribution of intraparticle diffusion to band broadening. As a result, the Sherwood number (Sh) was measured under such conditions that the Reynolds (Re) and the Schmidt numbers (Sc) varied from 0.004 to 0.05 and from 1.8x10(3) to 2.7x10(3), respectively. We found that Sh is proportional to Re(alpha) and Sc(beta) and that the correlation between these three nondimensional parameters is almost the same as those given by conventional literature equations. The values of alpha and beta were close to those in the literature correlations, between 0.26 and 0.41 and between 0.31 and 0.36, respectively. The use of the Wilson-Geankoplis equation to estimate k(f) values entails a relative error of ca. 15%. So, conventional literature correlations provide correct estimates of k(f) in HPLC systems, even for particle sizes of the order of a micrometer.
NASA Astrophysics Data System (ADS)
Hansen, A. C.; Foslien, W. E.
2015-09-01
The microstructure of a dry alpine snowpack is a dynamic environment where microstructural evolution is driven by seasonal density profiles and weather conditions. Notably, temperature gradients on the order of 10-20 K m-1, or larger, are known to produce a faceted snow microstructure exhibiting little strength. However, while strong temperature gradients are widely accepted as the primary driver for kinetic growth, they do not fully account for the range of experimental observations. An additional factor influencing snow metamorphism is believed to be the rate of mass transfer at the macroscale. We develop a mixture theory capable of predicting macroscale deposition and/or sublimation in a snow cover under temperature gradient conditions. Temperature gradients and mass exchange are tracked over periods ranging from 1 to 10 days. Interesting heat and mass transfer behavior is observed near the ground, near the surface, as well as immediately above and below dense ice crusts. Information about deposition (condensation) and sublimation rates may help explain snow metamorphism phenomena that cannot be accounted for by temperature gradients alone. The macroscale heat and mass transfer analysis requires accurate representations of the effective thermal conductivity and the effective mass diffusion coefficient for snow. We develop analytical models for these parameters based on first principles at the microscale. The expressions derived contain no empirical adjustments, and further, provide self consistent values for effective thermal conductivity and the effective diffusion coefficient for the limiting cases of air and solid ice. The predicted values for these macroscale material parameters are also in excellent agreement with numerical results based on microscale finite element analyses of representative volume elements generated from X-ray tomography.
Yuan, Yi; Wang, Lei; Amemiya, Shigeru
2004-09-15
Chronoamperometry was carried out at liquid/liquid interfaces supported at the tip of micropipet electrodes for direct determination of the diffusion coefficient of a species in the outer solution. The diffusion coefficient was used for subsequent determination of the transferred charges per species from the diffusion-limited steady-state current. A large tip resistance of the micropipets causes prolonged charging current so that the faradic current can be measured accurately only at a long-time regime (typically t > 5 ms). At the same time, the long-time current response at the interfaces surrounded by a thin glass wall of the pipets is enhanced by diffusion of the species from behind the pipet tip. Therefore, numerical simulations of the long-time chronoamperometric response were carried out using the finite element method for accurate determination of diffusion coefficients. Validity of the simulation results was confirmed by studying simple transfer of tetraethylammonium ion. The technique was applied for transfer/adsorption reactions of the natural polypeptide protamine and also for Ca2+ and Mg2+ transfers facilitated by ionophore ETH 129. With the diffusion coefficient of protamine determined to be (1.2 +/- 0.1) x 10(-6) cm(2)/s, the ionic charge transferred by each protamine molecule was obtained as +20 +/- 1, which is close to the excess positive charge of protamine. Also, the diffusion coefficient of ETH 129 was determined to demonstrate that each ionophore molecule transfers +0.67 and +1 charge per Ca2+ and Mg2+ transfer, respectively, which corresponds to formation of 1:3 and 1:2 complexes with the respective ions.
Simulation of a fast diffuse optical tomography system based on radiative transfer equation
NASA Astrophysics Data System (ADS)
Motevalli, S. M.; Payani, A.
2016-12-01
Studies show that near-infrared (NIR) light (light with wavelength between 700nm and 1300nm) undergoes two interactions, absorption and scattering, when it penetrates a tissue. Since scattering is the predominant interaction, the calculation of light distribution in the tissue and the image reconstruction of absorption and scattering coefficients are very complicated. Some analytical and numerical methods, such as radiative transport equation and Monte Carlo method, have been used for the simulation of light penetration in tissue. Recently, some investigators in the world have tried to develop a diffuse optical tomography system. In these systems, NIR light penetrates the tissue and passes through the tissue. Then, light exiting the tissue is measured by NIR detectors placed around the tissue. These data are collected from all the detectors and transferred to the computational parts (including hardware and software), which make a cross-sectional image of the tissue after performing some computational processes. In this paper, the results of the simulation of an optical diffuse tomography system are presented. This simulation involves two stages: a) Simulation of the forward problem (or light penetration in the tissue), which is performed by solving the diffusion approximation equation in the stationary state using FEM. b) Simulation of the inverse problem (or image reconstruction), which is performed by the optimization algorithm called Broyden quasi-Newton. This method of image reconstruction is faster compared to the other Newton-based optimization algorithms, such as the Levenberg-Marquardt one.
Development of a correlation for aqueous-vapor phase mass transfer in porous media
NASA Astrophysics Data System (ADS)
Szatkowski, Andrew; Imhoff, Paul T.; Miller, Cass T.
1995-03-01
In many situations vapor-phase extraction procedures (e.g., soil venting, air sparging, and bioventing) may be suitable methods for remediating porous media contaminated by volatile organic compounds. This has led to increased study of operative processes in these systems, including aqueous-vapor phase mass transfer. Past work has shown the importance of the flow regime on this process, but a quantitative estimate of mass-transfer coefficients is lacking, especially for systems not confounded by uncertainties involving interfacial area between the phases. An experimental investigation was conducted to isolate the resistance to aqueous-vapor phase mass transfer at the phase boundary, using an ideal porous medium system. Mass-transfer coefficients were measured for toluene for a wide range of Reynolds numbers. An empirical model was fit to the data in dimensionless form. The mass-transfer model was coupled with an available interfacial area model, yielding a dimensionless expression for the mass-transfer rate coefficient. This expression was used to compare results from this work to three other experimental studies reported in the literature. These comparisons showed that for experiments where infiltrating water flowed uniformly within the porous medium, the predicted mass-transfer coefficients were within a factor of 5 of the measured coefficients. Mass transfer was significantly slower than the rate predicted, using the results from this work, in experiments where infiltrating water flowed nonuniformly.
Optimizing SVE Remediation With Subsurface Flow and Mass Transfer Measurements
NASA Astrophysics Data System (ADS)
Spansky, M. C.; Riha, B. D.; Rossabi, J.; Hyde, W. K.; Dixon, K. L.; Nichols, R. L.
2002-05-01
The 5.9-acre A-Area Miscellaneous Rubble Pile (ARP) at the DOE Savannah River Site (SRS) was created in the 1950s as a general disposal area. An aerial photograph from 1953 shows evidence of disposal activities; however, the exact materials disposed and dates of operation at ARP remain unknown. Within the larger ARP unit exists an approximately 2-acre T-shaped trench filled with ash debris to a depth of 10-14 feet. Soil sampling analysis of the ARP trench indicates the presence of the volatile organic compounds (VOCs) trichloroethelyne (TCE) and tetrachloroetheylene (PCE). TCE and PCE contamination in the trench has the potential to migrate and poses a groundwater contamination risk. Several remediation options have been considered at ARP to date. The first, passive soil vapor extraction (PSVE), uses barometric pressure fluctuations to create a differential pressure between subsurface soil vapors and the atmosphere. Five wells were installed along the axes of the ARP trench. Differential pressure in the wells was monitored to determine the potential for PSVE. Results showed that the ash formation was too shallow and permeable to create pressure gradients sufficient for effective PSVE. The addition of a temporary cap over the formation did little to improve the differential pressure. Two pumping tests were subsequently conducted at the ARP trench. Air was pumped from two separate wells and drawdowns recorded at three observation wells. Data from the tests were used to model permeability of the ash unit and to estimate the zone of influence for the proposed active soil vapor extraction (SVE) system. Results indicate a high permeability for the ash. Contaminant concentrations were monitored with a portable infrared photoacoustic multigas monitor during continuous, pulsed, and variable flow rate scenarios. The concentration and flow data were used to evaluate mass transfer limitations of the system and to optimize the full-scale SVE remediation.
High fidelity radiative heat transfer models for high-pressure laminar hydrogen-air diffusion flames
NASA Astrophysics Data System (ADS)
Cai, Jian; Lei, Shenghui; Dasgupta, Adhiraj; Modest, Michael F.; Haworth, Daniel C.
2014-11-01
Radiative heat transfer is studied numerically for high-pressure laminar H2-air jet diffusion flames, with pressure ranging from 1 to 30 bar. Water vapour is assumed to be the only radiatively participating species. Two different radiation models are employed, the first being the full spectrum k-distribution model together with conventional Radiative Transfer Equation (RTE) solvers. Narrowband k-distributions of water vapour are calculated and databased from the HITEMP 2010 database, which claims to retain accuracy up to 4000 K. The full-spectrum k-distributions are assembled from their narrowband counterparts to yield high accuracy with little additional computational cost. The RTE is solved using various spherical harmonics methods, such as P1, simplified P3 (SP3) and simplified P5 (SP5). The resulting partial differential equations as well as other transport equations in the laminar diffusion flames are discretized with the finite-volume method in OpenFOAM®. The second radiation model is a Photon Monte Carlo (PMC) method coupled with a line-by-line spectral model. The PMC absorption coefficient database is derived from the same spectroscopy database as the k-distribution methods. A time blending scheme is used to reduce PMC calculations at each time step. Differential diffusion effects, which are important in laminar hydrogen flames, are also included in the scalar transport equations. It was found that the optically thin approximation overpredicts radiative heat loss at elevated pressures. Peak flame temperature is less affected by radiation because of faster chemical reactions at high pressures. Significant cooling effects are observed at downstream locations. As pressure increases, the performance of RTE models starts to deviate due to increased optical thickness. SPN models perform only marginally better than P1 because P1 is adequate except at very high pressure.
Boscaini, Elena; Alexander, M. Lizabeth; Prazeller, Peter; Mark, T. D.
2004-12-15
A membrane introduction proton transfer reaction mass spectrometry (MI-PTRMS) has been employed for the characterisation of a polydimethylsiloxane (PDMS) membrane. For this purpose the diffusion and partition coefficients (which serves as a measure for solubility) have been determined experimentally for different classes of chemical compounds both non-polar and polar species, i.e. aromatics, alcohols, ketones. It turned out that not only polar compounds exhibit strong interaction with a hydrophobic membrane such as the PDMS, but also non polar compounds as trimethylbenzene or propylbenzene which bear a relevant number of methyl groups or an alkyl chain show strong interaction with a PDMS membrane. Stronger interaction analyte-membrane leads to a slower diffusion coefficient and larger partition coefficient. The effect of the temperature on the diffusion coefficient and partition coefficient is also investigated. At higher temperature diffusion becomes faster and solubility lower. Permeability is calculated from diffusion and partition coefficients and activation energy are derived from corresponding Arrhenius plots. The MI-PTRMS system shows detection limits in the order of tens of pptv and it’s linear over five orders of magnitude.
Yih, K.A.
1999-04-01
Coupled heat and mass transfer (or double-diffusion) driven by buoyancy, due to temperature and concentration variations in a saturated porous medium, has several important applications in geothermal and geophysical engineering such as the migration of moisture through the air contained in fibrous insulation, the extraction of geothermal energy, underground disposal of nuclear wastes, and the spreading of chemical contaminants through water-saturated soil. Here, the heat and mass transfer characteristics of free convection about a permeable horizontal cylinder embedded in porous media under the coupled effects of thermal and mass diffusion are numerically analyzed. The surface of the horizontal cylinder is maintained at a uniform wall temperature and uniform wall concentration. The transformed governing equations are obtained and solved by Keller box method. Numerical results for the dimensionless temperature profiles, the dimensionless concentration profiles, the Nusselt number and the Sherwood number are presented. Increasing the buoyancy ratio N and the transpiration parameter f{sub w} increases the Nusselt number and the Sherwood number. For thermally assisting flow, when Lewis number Le increases, the Nusselt (Sherwood) number decreases (increases). Whereas, for thermally opposing flow, both the Nusselt number and the Sherwood number increase with increasing the Lewis number.
Yih, K.A.
1997-03-01
Effect of transpiration velocity on the heat and mass transfer characteristics of mixed convection about a permeable vertical plate embedded in a saturated porous medium under the coupled effects of thermal and mass diffusion is numerically analyzed. The plate is maintained at a uniform temperature and species concentration with constant transpiration velocity. The transformed governing equations are solved by Keller box method. Numerical results for the local Nusselt number and local Sherwood number are presented. In general, it has been found for thermally assisted flow that the local surface heat and mass transfer rates increase owing to suction of fluid. This trend reversed for blowing of fluid. It is apparent that the Lewis number has a pronounced effect on the local Sherwood number than it does on the local Nusselt number. Increasing the Lewis number decreases (increases) the local heat (mass) transfer rate.
Yologlu, Zeynel; Aydin, Hasan; Alp, Nalan A.; Aribas, Bilgin K.; Kizilgoz, Volkan; Arda, Kemal
2016-01-01
Objective To demonstrate the diagnostic potentials of MRI, diffusion weighted imaging (DWI), and apparent diffusion coefficient (ADC) mapping in the detection of parotid masses correlated to the histopathological results. Methods Study design was retrospective. Fifteen patients with parotid gland masses were included as the study group and contralateral normal parotis glands of same patients were taken as the control group. Patients with bilateral parotid gland tumors were excluded, 7 right-sided and 8 left-sided parotid masses were included in the research. The study took place at the Department of Radiology, Ankara, Turkey, between May 2012 and September 2014. Results Apparent diffusion coefficient measurements of 15 parotis tumors in 1000 and 750 sec/mm2 b-values with comparison to the contralateral normal gland parenchyma were demonstrated. Neurofibromas was predicted as the highest, and lipomas as the lowest ADC values. Pleomorphic adenomas, Warthin’s tumor, and normal parotid parenchyma indicate significant statistical differences from each other on the basis of mean ADC values (p<0.05). Conclusion The DWI and ADC mapping of parotis gland could aid in the differential diagnosis of benign and malignant masses. PMID:27874161
Mass-loading and diffusion-loss rates of the Io plasma torus
NASA Technical Reports Server (NTRS)
Shemansky, D. E.
1980-01-01
Limits to the mass-loading and diffusion-loss rates of ions in the Io plasma torus have been calculated on the assumption that observed optical emissions are controlled by electron-ion collisions. Calculations of the yield of emission from the vicinity of Io limit the mass-loading rate to the order of 10 to the 27th per s for S II or O II, on the grounds that electron-excited emissions associated with the location of Io have not been observed in the optical spectrum. This mass-loading limit is dependent on the assumptions that Io is the source of torus particles and that most of the neutral atoms are converted to ions within 1 R(J) of Io. According to the calculations presented below, the observed partitioning of sulfur ion species in the hot torus at the time of Voyager 1 encounter indicates that the diffusion-loss time of the ions is of the order of 1/D = 100 days. The two results limiting the mass-loading and diffusion-loss rates are compatible and suggest that the energy required to maintain the observed radiated power cannot be supplied by acceleration of ions formed at Io in Jupiter's rotating magnetic field.
Impact of kinetic mass transfer on free convection in a porous medium
NASA Astrophysics Data System (ADS)
Lu, Chunhui; Shi, Liangsheng; Chen, Yiming; Xie, Yueqing; Simmons, Craig T.
2016-05-01
We investigate kinetic mass transfer effects on unstable density-driven flow and transport processes by numerical simulations of a modified Elder problem. The first-order dual-domain mass transfer model coupled with a variable-density-flow model is employed to describe transport behavior in porous media. Results show that in comparison to the no-mass-transfer case, a higher degree of instability and more unstable system is developed in the mass transfer case due to the reduced effective porosity and correspondingly a larger Rayleigh number (assuming permeability is independent on the mobile porosity). Given a constant total porosity, the magnitude of capacity ratio (i.e., immobile porosity/mobile porosity) controls the macroscopic plume profile in the mobile domain, while the magnitude of mass transfer timescale (i.e., the reciprocal of the mass transfer rate coefficient) dominates its evolution rate. The magnitude of capacity ratio plays an important role on the mechanism driving the mass flux into the aquifer system. Specifically, for a small capacity ratio, solute loading is dominated by the density-driven transport, while with increasing capacity ratio local mass transfer dominated solute loading may occur at later times. At significantly large times, however, both mechanisms contribute comparably to solute loading. Sherwood Number could be a nonmonotonic function of mass transfer timescale due to complicated interactions of solute between source zone, mobile zone and immobile zone in the top boundary layer, resulting in accordingly a similar behavior of the total mass. The initial assessment provides important insights into unstable density-driven flow and transport in the presence of kinetic mass transfer.
Mass dependence of the Soret coefficient for atomic diffusion in condensed matter.
Yu, Wei-Feng; Lin, Zheng-Zhe; Ning, Xi-Jing
2013-06-01
Particle diffusion in condensed matters driven by thermal gradient, the so-called Ludwig-Soret effect, has been investigated for about 160 years, but up to the present, seldom do theories on atomic level understand a series of puzzles in relevant experiments. In this work, we derived an expression of Soret coefficient for atomic diffusion in condensed matter from a single atom statistic model with relevant parameters expressed in terms of atomic mass and the potential profile felt by the guest atom without empirical parameters. The reality of the model was strictly tested by molecular dynamics simulations, especially the result for He atom diffusing on graphene sheet, which suggests the Soret effect may be used to separate (3)He from (4)He.
Effect of NAPL Source Morphology on Mass Transfer in the Vadose Zone.
Petri, Benjamin G; Fučík, Radek; Illangasekare, Tissa H; Smits, Kathleen M; Christ, John A; Sakaki, Toshihiro; Sauck, Carolyn C
2015-01-01
The generation of vapor-phase contaminant plumes within the vadose zone is of interest for contaminated site management. Therefore, it is important to understand vapor sources such as non-aqueous-phase liquids (NAPLs) and processes that govern their volatilization. The distribution of NAPL, gas, and water phases within a source zone is expected to influence the rate of volatilization. However, the effect of this distribution morphology on volatilization has not been thoroughly quantified. Because field quantification of NAPL volatilization is often infeasible, a controlled laboratory experiment was conducted in a two-dimensional tank (28 cm × 15.5 cm × 2.5 cm) with water-wet sandy media and an emplaced trichloroethylene (TCE) source. The source was emplaced in two configurations to represent morphologies encountered in field settings: (1) NAPL pools directly exposed to the air phase and (2) NAPLs trapped in water-saturated zones that were occluded from the air phase. Airflow was passed through the tank and effluent concentrations of TCE were quantified. Models were used to analyze results, which indicated that mass transfer from directly exposed NAPL was fast and controlled by advective-dispersive-diffusive transport in the gas phase. However, sources occluded by pore water showed strong rate limitations and slower effective mass transfer. This difference is explained by diffusional resistance within the aqueous phase. Results demonstrate that vapor generation rates from a NAPL source will be influenced by the soil water content distribution within the source. The implications of the NAPL morphology on volatilization in the context of a dynamic water table or climate are discussed.
Huang, Chong; Radabaugh, Jeffrey P.; Aouad, Rony K.; Lin, Yu; Gal, Thomas J.; Patel, Amit B.; Valentino, Joseph; Shang, Yu; Yu, Guoqiang
2015-01-01
Abstract. Knowledge of tissue blood flow (BF) changes after free tissue transfer may enable surgeons to predict the failure of flap thrombosis at an early stage. This study used our recently developed noncontact diffuse correlation spectroscopy to monitor dynamic BF changes in free flaps without getting in contact with the targeted tissue. Eight free flaps were elevated in patients with head and neck cancer; one of the flaps failed. Multiple BF measurements probing the transferred tissue were performed during and post the surgical operation. Postoperative BF values were normalized to the intraoperative baselines (assigning “1”) for the calculation of relative BF change (rBF). The rBF changes over the seven successful flaps were 1.89±0.15, 2.26±0.13, and 2.43±0.13 (mean±standard error), respectively, on postoperative days 2, 4, and 7. These postoperative values were significantly higher than the intraoperative baseline values (p<0.001), indicating a gradual recovery of flap vascularity after the tissue transfer. By contrast, rBF changes observed from the unsuccessful flaps were 1.14 and 1.34, respectively, on postoperative days 2 and 4, indicating less flow recovery. Measurement of BF recovery after flap anastomosis holds the potential to act early to salvage ischemic flaps. PMID:26187444
NASA Astrophysics Data System (ADS)
Huang, Chong; Radabaugh, Jeffrey P.; Aouad, Rony K.; Lin, Yu; Gal, Thomas J.; Patel, Amit B.; Valentino, Joseph; Shang, Yu; Yu, Guoqiang
2015-07-01
Knowledge of tissue blood flow (BF) changes after free tissue transfer may enable surgeons to predict the failure of flap thrombosis at an early stage. This study used our recently developed noncontact diffuse correlation spectroscopy to monitor dynamic BF changes in free flaps without getting in contact with the targeted tissue. Eight free flaps were elevated in patients with head and neck cancer; one of the flaps failed. Multiple BF measurements probing the transferred tissue were performed during and post the surgical operation. Postoperative BF values were normalized to the intraoperative baselines (assigning "1") for the calculation of relative BF change (rBF). The rBF changes over the seven successful flaps were 1.89±0.15, 2.26±0.13, and 2.43±0.13 (mean±standard error), respectively, on postoperative days 2, 4, and 7. These postoperative values were significantly higher than the intraoperative baseline values (p<0.001), indicating a gradual recovery of flap vascularity after the tissue transfer. By contrast, rBF changes observed from the unsuccessful flaps were 1.14 and 1.34, respectively, on postoperative days 2 and 4, indicating less flow recovery. Measurement of BF recovery after flap anastomosis holds the potential to act early to salvage ischemic flaps.
Huang, Chong; Radabaugh, Jeffrey P; Aouad, Rony K; Lin, Yu; Gal, Thomas J; Patel, Amit B; Valentino, Joseph; Shang, Yu; Yu, Guoqiang
2015-07-01
Knowledge of tissue blood flow (BF) changes after free tissue transfer may enable surgeons to predict the failure of flap thrombosis at an early stage. This study used our recently developed noncontact diffuse correlation spectroscopy to monitor dynamic BF changes in free flaps without getting in contact with the targeted tissue. Eight free flaps were elevated in patients with head and neck cancer; one of the flaps failed. Multiple BF measurements probing the transferred tissue were performed during and post the surgical operation. Postoperative BF values were normalized to the intraoperative baselines (assigning "1") for the calculation of relative BF change (rBF). The rBF changes over the seven successful flaps were 1.89 ± 0.15, 2.26 ± 0.13, and 2.43 ± 0.13 (mean ± standard error), respectively, on postoperative days 2, 4, and 7. These postoperative values were significantly higher than the intraoperative baseline values (p<0.001), indicating a gradual recovery of flap vascularity after the tissue transfer. By contrast, rBF changes observed from the unsuccessful flaps were 1.14 and 1.34, respectively, on postoperative days 2 and 4, indicating less flow recovery. Measurement of BF recovery after flap anastomosis holds the potential to act early to salvage ischemic flaps.
Miyabe, Kanji; Guiochon, G. |
1999-07-01
The experimental results of a previous study of the mass transfer kinetics of bovine serum albumin (BSA) in ion-exchange chromatography under nonlinear conditions are reevaluated. The analysis of the concentration dependence of the lumped mass-transfer rate coefficient (k{sub m,L}) provides information on the kinetics of axial dispersion, fluid-to-particle mass transfer, intraparticle mass transfer, and adsorption/desorption. The new analysis shows that the contribution of intraparticle mass transfer is the dominant one. Similar to k{sub m,L}, the surface diffusivity (D{sub s}) of BSA increases with increasing concentration. The linear concentration dependence of k{sub m,L} seems to originate in a similar dependence of D{sub s}. The use of a heterogeneous-surface model for the anion-exchange resin provides an explanation of the positive concentration dependence of D{sub s}. This work illustrates how frontal analysis data can be used for a detailed investigation of the kinetics of mass transfer between the phases of a chromatographic column, in addition to its conventional use in the determination of the thermodynamic characteristics of the phase equilibrium.
Mass transfer of terpenes through a silicone rubber membrane in a liquid-liquid contacting system.
Boontawan, Apichat; Stuckey, David C
2005-01-01
Terpenoids are important compounds for the fragrance industry, and recently, biocatalytic methods have been developed to produce them from cheap monoterpenes, such as alpha-pinene oxide. The biotransformation of alpha-pinene oxide using resting cells of Pseudomonas fluorescens NCIMB 11671 produces isonovalal (cis-2-methyl-5-isopropylhexa-2,5-dienal), which is a fragrance. However, this biotransformation has technical problems including the following: alpha-pinene oxide undergoes autoxidation in water and light; it is hydrophobic and relatively toxic to the biocatalyst; and it suffers from product inhibition. Therefore, removal of isonovalal as it is formed should reduce its toxicity and increase volumetric productivity and production yield. Aqueous-organic two-phase (AOTP) systems can be used in the biotransformation of hydrophobic substrates and can protect biocatalysts from toxic substrates and products. However, the formation of stable emulsions makes further downstream processing and continuous operation difficult. One solution to these problems is to use a solid-phase membrane between the aqueous and organic phases in a Membrane Bioreactor for Biotransformation (MBB). Since there are no data in the literature on the behavior of terpenes and terpenoids with solid-phase membranes, or their mass transfer behavior, the objective of this work was to measure these parameters for a wide range of compounds so as to be able to design an MBB, and to gain a greater understanding of their behavior in these types of systems. Organic/aqueous (P (org) (aq)) and membrane/aqueous (P (mem) (aq)) partition coefficients were measured first, and subsequently used to quantify the overall mass transfer coefficients (k(ov)). The overall mass transfer coefficient (k(ov)) of alpha-pinene oxide through the membrane was found to be 2.5 x 10(-5) m x s(-1) using thicknesses of both 250 and 1,000 microm. Extraction kinetics were successfully described using a resistance-in-series model and
Leung, Juliana Y; Srinivasan, Sanjay
2016-09-01
Modeling transport process at large scale requires proper scale-up of subsurface heterogeneity and an understanding of its interaction with the underlying transport mechanisms. A technique based on volume averaging is applied to quantitatively assess the scaling characteristics of effective mass transfer coefficient in heterogeneous reservoir models. The effective mass transfer coefficient represents the combined contribution from diffusion and dispersion to the transport of non-reactive solute particles within a fluid phase. Although treatment of transport problems with the volume averaging technique has been published in the past, application to geological systems exhibiting realistic spatial variability remains a challenge. Previously, the authors developed a new procedure where results from a fine-scale numerical flow simulation reflecting the full physics of the transport process albeit over a sub-volume of the reservoir are integrated with the volume averaging technique to provide effective description of transport properties. The procedure is extended such that spatial averaging is performed at the local-heterogeneity scale. In this paper, the transport of a passive (non-reactive) solute is simulated on multiple reservoir models exhibiting different patterns of heterogeneities, and the scaling behavior of effective mass transfer coefficient (Keff) is examined and compared. One such set of models exhibit power-law (fractal) characteristics, and the variability of dispersion and Keff with scale is in good agreement with analytical expressions described in the literature. This work offers an insight into the impacts of heterogeneity on the scaling of effective transport parameters. A key finding is that spatial heterogeneity models with similar univariate and bivariate statistics may exhibit different scaling characteristics because of the influence of higher order statistics. More mixing is observed in the channelized models with higher-order continuity. It
NASA Astrophysics Data System (ADS)
Leung, Juliana Y.; Srinivasan, Sanjay
2016-09-01
Modeling transport process at large scale requires proper scale-up of subsurface heterogeneity and an understanding of its interaction with the underlying transport mechanisms. A technique based on volume averaging is applied to quantitatively assess the scaling characteristics of effective mass transfer coefficient in heterogeneous reservoir models. The effective mass transfer coefficient represents the combined contribution from diffusion and dispersion to the transport of non-reactive solute particles within a fluid phase. Although treatment of transport problems with the volume averaging technique has been published in the past, application to geological systems exhibiting realistic spatial variability remains a challenge. Previously, the authors developed a new procedure where results from a fine-scale numerical flow simulation reflecting the full physics of the transport process albeit over a sub-volume of the reservoir are integrated with the volume averaging technique to provide effective description of transport properties. The procedure is extended such that spatial averaging is performed at the local-heterogeneity scale. In this paper, the transport of a passive (non-reactive) solute is simulated on multiple reservoir models exhibiting different patterns of heterogeneities, and the scaling behavior of effective mass transfer coefficient (Keff) is examined and compared. One such set of models exhibit power-law (fractal) characteristics, and the variability of dispersion and Keff with scale is in good agreement with analytical expressions described in the literature. This work offers an insight into the impacts of heterogeneity on the scaling of effective transport parameters. A key finding is that spatial heterogeneity models with similar univariate and bivariate statistics may exhibit different scaling characteristics because of the influence of higher order statistics. More mixing is observed in the channelized models with higher-order continuity. It
NASA Astrophysics Data System (ADS)
Kriaa, Wassim; Bejaoui, Salma; Mhiri, Hatem; Le Palec, Georges; Bournot, Philippe
2014-02-01
In this study, we developed a two-dimensional Computational Fluid Dynamics (CFD) model to simulate dynamic structure and heat and mass transfer of a vertical ceramic tiles dryer (EVA 702). The carrier's motion imposed the choice of a dynamic mesh based on two methods: "spring based smoothing" and "local remeshing". The dryer airflow is considered as turbulent ( Re = 1.09 × 105 at the dryer inlet), therefore the Re-Normalization Group model with Enhanced Wall Treatment was used as a turbulence model. The resolution of the governing equation was performed with Fluent 6.3 whose capacities do not allow the direct resolution of drying problems. Thus, a user defined scalar equation was inserted in the CFD code to model moisture content diffusion into tiles. User-defined functions were implemented to define carriers' motion, thermo-physical properties… etc. We adopted also a "two-step" simulation method: in the first step, we follow the heat transfer coefficient evolution (Hc). In the second step, we determine the mass transfer coefficient (Hm) and the features fields of drying air and ceramic tiles. The found results in mixed convection mode (Fr = 5.39 at the dryer inlet) were used to describe dynamic and thermal fields of airflow and heat and mass transfer close to the ceramic tiles. The response of ceramic tiles to heat and mass transfer was studied based on Biot numbers. The evolutions of averages temperature and moisture content of ceramic tiles were analyzed. Lastly, comparison between experimental and numerical results showed a good agreement.
Kim, Hyunjung; Guiochon, Georges
2005-12-02
The parameters of the thermodynamics and mass transfer kinetics of the structural analogues (L-enantiomers) of the template were measured on an Fmoc-L-tryptophan (Fmoc-L-Trp) imprinted polymer, at different temperatures. The equilibrium isotherm data and the overloaded band profiles of these compounds were measured at temperatures of 298, 313, 323, and 333 K. The isotherm data were modeled. The thermodynamic functions of the different adsorption sites were derived from the isotherm parameters, using van't Hoff plots. The mass transfer parameters were derived by comparing the experimental peak profiles and profiles calculated using the lumped pore diffusion (POR) model for chromatography. These data show that (1) the strength between the substrate molecules and the MIP increases with increasing number of functional groups on the substrates; (2) enthalpy is the driving force for the affinity of the substrates for the MIP; (3) surface diffusion is the dominant mass transfer mechanism of the substrates through the porous MIP. For those substrate molecules that have the same stereochemistry as the template, the energetic surface heterogeneity needs to be incorporated into the surface diffusion coefficients. Heterogeneous surface diffusivities decrease with increasing affinity of the substrates for the MIP.
Solute mass transfer from near field to far field in a HLWR experiment at real scale.
NASA Astrophysics Data System (ADS)
Buil, B.; Peña, J.; Gómez, P.; Garralón, A.; Turrero, M. J.; Sánchez, L.; Durán, J. M.
2009-04-01
The FEBEX experiment located in Grimsel (Switzerland) is a 1:1 simulation of a high level waste disposal facility in crystalline rock according to the Spanish concept: two electrical heaters of dimension and weight equivalent to those of the real canisters were installed concentrically with the drift and simulated the thermal effect of the wastes and surrounded by a clay barrier constructed from highly-compacted bentonite blocks. This experiment started in 1996 and the external rim of bentonite is saturated with the granitic water. The difference between the chemical gradients generated by the bentonite porewater and the granitic water made possible the movement of solute into the geosphere. The experiment reproduces in the most realistic conditions, all the processes affecting the radionuclide migration in a HLWR. Two boreholes parallel to the axis of the FEBEX drift were drilled in granite relatively close to the bentonite surface (20 and 60cm) in order to highlight the solute migration mechanisms in crystalline host rock, influenced by the presence of the bentonite buffer and by the geochemical gradients generated at the bentonite/granite interface. After three years of periodic water sampling campaigns in those boreholes, the chemical composition of waters reveal that there is an appreciable increase of Na and Cl concentration in time in the waters sampled from the borehole located at 20cm from the bentonite surface. On the other hand, the Na/Cl ratio in waters is similar to the Na/Cl ratio in the bentonite porewater. For this reason Cl and Na are considered as the main natural tracers indicating the mass transfer process between the bentonite porewater and the granite. A diffusion transport modelling (PHREEQC) was used to describe the mass transfer process. The results show that the Cl and Na concentration in the granitic waters is the result of a diffusive transport from the bentonite to the granite, with a calculated De≈ 5,0E-11 m2/s. These results could
Barrier heights of hydrogen-transfer reactions with diffusion quantum monte carlo method.
Zhou, Xiaojun; Wang, Fan
2017-04-30
Hydrogen-transfer reactions are an important class of reactions in many chemical and biological processes. Barrier heights of H-transfer reactions are underestimated significantly by popular exchange-correlation functional with density functional theory (DFT), while coupled-cluster (CC) method is quite expensive and can be applied only to rather small systems. Quantum Monte-Carlo method can usually provide reliable results for large systems. Performance of fixed-node diffusion quantum Monte-Carlo method (FN-DMC) on barrier heights of the 19 H-transfer reactions in the HTBH38/08 database is investigated in this study with the trial wavefunctions of the single-Slater-Jastrow form and orbitals from DFT using local density approximation. Our results show that barrier heights of these reactions can be calculated rather accurately using FN-DMC and the mean absolute error is 1.0 kcal/mol in all-electron calculations. Introduction of pseudopotentials (PP) in FN-DMC calculations improves efficiency pronouncedly. According to our results, error of the employed PPs is smaller than that of the present CCSD(T) and FN-DMC calculations. FN-DMC using PPs can thus be applied to investigate H-transfer reactions involving larger molecules reliably. In addition, bond dissociation energies of the involved molecules using FN-DMC are in excellent agreement with reference values and they are even better than results of the employed CCSD(T) calculations using the aug-cc-pVQZ basis set. © 2017 Wiley Periodicals, Inc.
Ungerman, Andrew J; Heindel, Theodore J
2007-01-01
This study compares the power demand and gas-liquid volumetric mass transfer coefficient, kLa, in a stirred tank reactor (STR) (T = 0.211 m) using different impeller designs and schemes in a carbon monoxide-water system, which is applicable to synthesis gas (syngas) fermentation. Eleven different impeller schemes were tested over a range of operating conditions typically associated with the "after large cavity" region (ALC) of a Rushton-type turbine (D/T = 0.35). It is found that the dual Rushton-type impeller scheme exhibits the highest volumetric mass transfer rates for all operating conditions; however, it also displays the lowest mass transfer performance (defined as the volumetric mass transfer coefficient per unit power input) for all conditions due to its high power consumption. Dual impeller schemes with an axial flow impeller as the top impeller show improved mass transfer rates without dramatic increases in power draw. At high gas flow rates, dual impeller schemes with a lower concave impeller have kLa values similar to those of the Rushton-type dual impeller schemes but show improved mass transfer performance. It is believed that the mass transfer performance can be further enhanced for the bottom concave impeller schemes by operating at conditions beyond the ALC region defined for Rushton-type impellers because the concave impeller can handle higher gas flow rates prior to flooding.
Tracking polymer diffusion in a wet latex film with fluorescence resonance energy transfer.
Haley, Jeffrey C; Liu, Yuanqin; Winnik, Mitchell A; Demmer, David; Haslett, Tom; Lau, Willie
2007-08-01
We describe an instrument to measure the polymer interdiffusion between donor-labeled and acceptor-labeled latex polymers in a partially wet latex film with fluorescence resonance energy transfer (FRET). It is possible to temporarily arrest the drying process of a wet latex film by sealing the film in an airtight chamber. In our approach, we measure donor fluorescence decays from 0.5 mm diameter spots at various positions across an arrested latex film with time-correlated single photon counting. We interpret the resulting decays with a Monte Carlo simulation of the FRET process and extract information about the extent of polymer diffusion as a function of position on the film. These results enable us to determine the extent of polymer interdiffusion as a function of distance from the wet-dry edge in the latex film. To highlight this device's ability to capture the rapid early stages of latex interdiffusion, we report results from an acrylate copolymer latex.
Bankston, Theresa E; Stone, Melani C; Carta, Giorgio
2008-04-25
This work provides the theoretical foundation and a range of practical application examples of a recently developed method to measure protein mass transfer in adsorbent particles using refractive index-based optical microscopy. A ray-theoretic approach is first used to predict the behavior of light traveling through a particle during transient protein adsorption. When the protein concentration gradient in the particle is sharp, resulting in a steep refractive index gradient, the rays bend and intersect, thereby concentrating light in a sharp ring that marks the position of the adsorption front. This behavior is observed when mass transfer is dominated by pore diffusion and the adsorption isotherm is highly favorable. Applications to protein cation-exchange, hydrophobic interaction, and affinity adsorption are then considered using, as examples, the three commercial, agarose-based stationary phases SP-Sepharose-FF, Butyl Sepharose 4FF, and MabSelect. In all three cases, the method provides results that are consistent with measurements based on batch adsorption and previously published data confirming its utility for the determination of protein mass transfer kinetics under a broad range of practically relevant conditions.
Li, Chunyan; Wagner, Michael; Lackner, Susanne; Horn, Harald
2016-05-01
Imaging and modeling are two major approaches in biofilm research to understand the physical and biochemical processes involved in biofilm development. However, they are often used separately. In this study we combined these two approaches to investigate substrate mass transfer and mass flux. Cross-sectional biofilm images were acquired by means of optical coherence tomography (OCT) for biofilms grown on carriers. A 2D biofilm model was developed incorporating OCT images as well as a simplified biofilm geometry serving as structural templates. The model incorporated fluid flow, substrate transfer and biochemical conversion of substrates and simulated the hydrodynamics surrounding the biofilm structure as well as the substrate distribution. The method allowed detailed analysis of the hydrodynamics and mass transfer characteristics at the micro-scale. Biofilm activity with respect to substrate fluxes was compared among different combinations of flow, substrate availability and biomass density. The combined approach revealed that higher substrate fluxes at heterogeneous biofilm surface under two conditions: pure diffusion and when high flow velocity along the biofilms surface renders the whole liquid-biofilm interface to be highly active. In-between the two conditions the substrate fluxes across the surface of smooth biofilm geometry were higher than that of the heterogeneous biofilms.
Sherman, Brent J.; Rochelle, Gary T.
2016-12-16
Explanations for the mass transfer behavior of 2-amino-2-methyl-1-propanol (AMP) are conflicting, despite extensive study of the amine for CO_{2} capture. At equilibrium, aqueous AMP reacts with CO_{2} to give bicarbonate in a 1:1 ratio. While this is the same stoichiometry as a tertiary amine, the reaction rate of AMP is 100 times faster. This work aims to explain the mass transfer behavior of AMP, specifically the stoichiometry and kinetics. An eNRTL thermodynamic model was used to regress wetted-wall column mass transfer data with two activity-based reactions: formation of carbamate and formation of bicarbonate. Data spanned 40–100 C and 0.15–0.60 mol CO_{2}/mol alk). The fitted carbamate rate constant is three orders of magnitude greater than the bicarbonate rate constant. Rapid carbamate formation explains the kinetics, while the stoichiometry is explained by the carbamate reverting in the bulk liquid to allow CO_{2} to form bicarbonate. Understanding the role of carbamate formation and diffusion in hindered amines enables optimizing solvent amine concentration by balancing viscosity and free amine concentration. Furthermore, this improves absorber design for CO_{2} capture.
Sherman, Brent J.; Rochelle, Gary T.
2016-12-16
Explanations for the mass transfer behavior of 2-amino-2-methyl-1-propanol (AMP) are conflicting, despite extensive study of the amine for CO2 capture. At equilibrium, aqueous AMP reacts with CO2 to give bicarbonate in a 1:1 ratio. While this is the same stoichiometry as a tertiary amine, the reaction rate of AMP is 100 times faster. This work aims to explain the mass transfer behavior of AMP, specifically the stoichiometry and kinetics. An eNRTL thermodynamic model was used to regress wetted-wall column mass transfer data with two activity-based reactions: formation of carbamate and formation of bicarbonate. Data spanned 40–100 C and 0.15–0.60 molmore » CO2/mol alk). The fitted carbamate rate constant is three orders of magnitude greater than the bicarbonate rate constant. Rapid carbamate formation explains the kinetics, while the stoichiometry is explained by the carbamate reverting in the bulk liquid to allow CO2 to form bicarbonate. Understanding the role of carbamate formation and diffusion in hindered amines enables optimizing solvent amine concentration by balancing viscosity and free amine concentration. Furthermore, this improves absorber design for CO2 capture.« less
Oxygen profiles in egg masses predicted from a diffusion-reaction model.
Woods, H Arthur; Moran, Amy L
2008-03-01
We developed a novel diffusion-reaction model to describe spatial and temporal changes in oxygen concentrations in gelatinous egg masses containing live, respiring embryos. We used the model in two ways. First, we constructed artificial egg masses of known metabolic density using embryos of the Antarctic sea urchin Sterechnius neumayeri, measured radial oxygen profiles at two temperatures, and compared our measurements to simulated radial oxygen profiles generated by the model. We parameterized the model by measuring the radius of the artificial masses, metabolic densities (=embryo metabolic rate x embryo density) and oxygen diffusion coefficients at both ambient (-1.5 degrees C) or slightly warmer (+1.5-2 degrees C) temperatures. Simulated and measured radial oxygen profiles were similar, indicating that the model captured the major biological features determining oxygen distributions. Second, we used the model to analyze sources of error in step-change experiments for determining oxygen diffusion coefficients (D), and to determine the suitability of simpler, analytical equations for estimating D. Our analysis indicated that embryo metabolism can lead to large (several-fold) overestimates of D if the analytical equation is fitted to step-down-traces of central oxygen concentration (i.e. external oxygen concentration stepped from some high value to zero). However, good estimates of D were obtained from step-up-traces. We used these findings to estimate D in egg masses of three species of nudibranch molluscs: two Antarctic species (Tritonia challengeriana and Tritoniella belli; -1.5 and +2 degrees C) and one temperate Pacific species (Tritonia diomedea; 12 and 22 degrees C). D for all three species was approximately 8 x 10(-6) cm(2) s(-1), and there was no detectable effect of temperature on estimated D. For the Antarctic species, D in egg masses was 70-90% of its value in seawater of similar temperature.
The Experimental Analysis of Local Heat and Mass Transfer Data for Vertical Falling Film Absorption
Keyhani, M.; Miller, W.A.
1999-11-14
In pure heat transfer, specifications of effectiveness, fluid properties, and flows enable calculation of the heat exchanger area. In the case of falling film absorption, a simultaneous heat and mass transfer governs the performance of the absorber. The exchange of mass across the liquid-vapor interface involves the generation of heat. The heat effects associated with the mass exchange increase the temperature, which affects the equilibrium state of the pressure and composition and in turn affects the mass. The falling film flow rate coupled to the physical properties of kinematic viscosity and surface tension govern the flow regime of a vertical falling film. Wavy-laminar, roll-wave laminar, and turbulent flows will develop convective contributions that can enhance the transfer of mass into the film. The combined interaction of all these factors makes the absorption process very difficult to analyze and predict. A study of simultaneous heat and mass transfer was therefore conduct ed on a vertical falling film absorber to better understand the mechanisms driving the heat and mass transfer processes. Falling films are characteristically unstable, and a wavy-laminar flow was observed during the experimental study. The wavy flow further complicates the problem; therefore, only limited information is known about the temperature and concentration profiles along the length of the absorber that describe the local heat and mass transfer rates.
Rahmanseresht, Sheema; Ramos, Kieran P.; Gamari, Ben D.; Goldner, Lori S.; Milas, Peker
2015-05-11
Fluorescence resonance energy transfer (FRET) from individual, dye-labeled RNA molecules confined in freely-diffusing attoliter-volume aqueous droplets is carefully compared to FRET from unconfined RNA in solution. The use of freely-diffusing droplets is a remarkably simple and high-throughput technique that facilitates a substantial increase in signal-to-noise for single-molecular-pair FRET measurements. We show that there can be dramatic differences between FRET in solution and in droplets, which we attribute primarily to an altered pH in the confining environment. We also demonstrate that a sufficient concentration of a non-ionic surfactant mitigates this effect and restores FRET to its neutral-pH solution value. At low surfactant levels, even accounting for pH, we observe differences between the distribution of FRET values in solution and in droplets which remain unexplained. Our results will facilitate the use of nanoemulsion droplets as attoliter volume reactors for use in biophysical and biochemical assays, and also in applications such as protein crystallization or nanoparticle synthesis, where careful attention to the pH of the confined phase is required.
NASA Astrophysics Data System (ADS)
Rahmanseresht, Sheema; Milas, Peker; Ramos, Kieran P.; Gamari, Ben D.; Goldner, Lori S.
2015-05-01
Fluorescence resonance energy transfer (FRET) from individual, dye-labeled RNA molecules confined in freely-diffusing attoliter-volume aqueous droplets is carefully compared to FRET from unconfined RNA in solution. The use of freely-diffusing droplets is a remarkably simple and high-throughput technique that facilitates a substantial increase in signal-to-noise for single-molecular-pair FRET measurements. We show that there can be dramatic differences between FRET in solution and in droplets, which we attribute primarily to an altered pH in the confining environment. We also demonstrate that a sufficient concentration of a non-ionic surfactant mitigates this effect and restores FRET to its neutral-pH solution value. At low surfactant levels, even accounting for pH, we observe differences between the distribution of FRET values in solution and in droplets which remain unexplained. Our results will facilitate the use of nanoemulsion droplets as attoliter volume reactors for use in biophysical and biochemical assays, and also in applications such as protein crystallization or nanoparticle synthesis, where careful attention to the pH of the confined phase is required.
Mass transfer in a 1370 C (2500 F) lithium thermal convection loop
NASA Technical Reports Server (NTRS)
Scheuermann, C. M.
1974-01-01
Experimental results from a test to evaluate interstitial element mass transfer effects on T-111, ASTAR 811C, and ASTAR 1211C after 5000 hours in flowing lithium at 1370 C (2500 F) are presented. No gross corrosion effects were observed. However, hafnium and nitrogen transfer to cooler regions within the loop were noted. Oxygen was in general removed from test specimens, but there was no evidence to indicate that it was a major factor in the mass transfer process. Carbon and hydrogen transfer were not detected.
Bassani, Ilaria; Kougias, Panagiotis G; Angelidaki, Irini
2016-12-01
Biological biogas upgrading coupling CO2 with external H2 to form biomethane opens new avenues for sustainable biofuel production. For developing this technology, efficient H2 to liquid transfer is fundamental. This study proposes an innovative setup for in-situ biogas upgrading converting the CO2 in the biogas into CH4, via hydrogenotrophic methanogenesis. The setup consisted of a granular reactor connected to a separate chamber, where H2 was injected. Different packing materials (rashig rings and alumina ceramic sponge) were tested to increase gas-liquid mass transfer. This aspect was optimized by liquid and gas recirculation and chamber configuration. It was shown that by distributing H2 through a metallic diffuser followed by ceramic sponge in a separate chamber, having a volume of 25% of the reactor, and by applying a mild gas recirculation, CO2 content in the biogas dropped from 42 to 10% and the final biogas was upgraded from 58 to 82% CH4 content.
A Consistent Treatment of TKE and Scalar Variance in an Eddy Diffusivity Mass Flux Scheme
NASA Astrophysics Data System (ADS)
Pressel, Kyle; Schneider, Tapio; Teixeira, Joao; Lam, Remi; Tan, Zhihong; Kaul, Colleen; Suselj, Kay; Witek, Marcin; Matheou, George
2013-04-01
Eddy Diffusivity Mass Flux (EDMF) schemes have shown significant utility in parameterizing boundary layer turbulent fluxes and as a basis for unifying the parameterization of boundary layer turbulence and clouds. EDMF schemes are based upon an updraft/environment decomposition of turbulent fluxes. A steady state bulk updraft model is used to represent the updraft, or mass flux, portion of the decomposed fluxes, while the environment component is represented with an eddy diffusivity closure. Typically, the eddy diffusivity closure is formulated as a 1.5 order closure requiring the solution of a prognostic equation for the turbulent kinetic energy (TKE). To date, however, EDMF schemes have not been formulated in a manner that formally separates the TKE in the environment from that in updraft. We present a new EDMF parameterization that respects the updraft/environment decomposition more formally. Orthogonally decomposing the TKE into updraft and environment components allows the eddy diffusivity closure for the environmental fluxes to be based on a prognostic equation for the environmental TKE. The updrafts interact with the environment by entraining environmental TKE and detraining mean updraft kinetic energy. The environmental TKE is then used to compute the environmental eddy diffusivity. We argue that an EDMF scheme formulated in this manner is more energetically and conceptually consistent. This formalism is then extended to provide a consistent parameterization of scalar variances. Applying this new formalism has several benefits. First, it removes the need to include the updraft buoyancy flux in the TKE equation, hence conceptually simplifying the EDMF scheme. Second, under relaxation of the requirement that updrafts occupy only a small area fraction, the environmental TKE obeys the limit that as updraft area fraction goes to unity the environmental TKE goes to zero. This second benefit has clear advantages for extension of the EDMF framework to scale
Numerical calculations of mass transfer flow in semi-detached binary systems. [of stars
NASA Technical Reports Server (NTRS)
Edwards, D. A.; Pringle, J. E.
1987-01-01
The details of the mass transfer flow near the inner Lagrangian point in a semidetached binary system are numerically calculated. A polytropic equation of state with n = 3/2 is used. The dependence of the mass transfer rate on the degree to which the star overfills its Roche lobe is calculated, and good agreement with previous analytic estimates is found. The variation of mass transfer rate which occurs if the binary system has a small eccentricity is calculated and is used to cast doubt on the model for superhumps in dwarf novae proposed by Papaloizou and Pringle (1979).
Model of Mass Transfer in Liquid-Liquid Extraction in a Turbulent Forward Flow
NASA Astrophysics Data System (ADS)
Laptev, A. G.; Farakhov, T. M.; Dudarovskaya, O. G.
2015-01-01
A mathematical description of the process of mass transfer in a continuous phase in the turbulent motion of two mutually insoluble liquids has been obtained on the basis of an assigned law of damping of turbulent pulsations in the boundary layer. The basic parameters of the model have been found in terms of the hydraulic resistance of a droplet in motion. Consideration has been given to the use of the mathematical mass-transfer model in apparatuses with mixing devices. Agreement has been shown between results of calculation of mass-transfer coefficients and experimental data.
Matar, H; Larner, J; Kansagra, S; Atkinson, K L; Skamarauskas, J T; Amlot, R; Chilcott, R P
2014-06-01
The efficient removal of contaminants from the outer surfaces of the body can provide an effective means of reducing adverse health effects associated with incidents involving the accidental or deliberate release of hazardous materials. Showering with water is frequently used by first responders as a rapid method of mass casualty decontamination (MCD). However, there is a paucity of data on the generic effectiveness and safety of aqueous decontamination systems. To address these issues, we have developed a new in vitro skin diffusion cell system to model the conditions of a common MCD procedure ("ladder pipe system"). The new diffusion cell design incorporates a showering nozzle, an air sampling port for measurement of vapour loss and/aerosolisation, adjustable (horizontal to vertical) skin orientation and a circulating manifold system (to maintain a specified flow rate, temperature and pressure of shower water). The dermal absorption characteristics of several simulants (Invisible Red S, curcumin and methyl salicylate) measured with the new in vitro model were in good agreement with previous in vitro and in vivo studies. Moreover, these initial studies have indicated that whilst flow rate and water temperature are important factors for MCD, the presence of clothing during showering may (under certain circumstances) cause transfer and spreading of contaminants to the skin surface.
Ooshima, H.; Harano, Y.
1983-01-01
Taking the hydrolysis of sucrose by invertase immobilized on anion-exchange resin as an example, the effects of mass-transfer resistance on the apparent stability of immobilized enzyme (IME) and the optimal policy for an IME reaction in a fixed-bed reactor have been studied theoretically and experimentally. The following results were obtained: 1) The effect of mass-transfer resistance on the effective deactivation rate of IME is summarized in two parameters concerning the intraparticle diffusion alphap and the interparticle alphaf. 2) At a constant processed amount of raw materials, there exists an optimal flow rate of reaction fluid to enhance the reactor performance while the mass-transfer resistance shifts the optimal point. 3) The intrinsic deactivation rate of IME has been estimated from the relationship between the fractional conversion at the reactor outlet and the operation time. (Refs. 12).
2010-01-01
Background Published studies of the past decades have established that mass transfer across the dialyzer membrane is governed by diffusion, convection and osmosis. While the former is independent of the pressure in the liquids, the latter two are pressure dependent and are enhanced when the pressure difference across the membrane is increased. The goal of the present study is to examine the impact of pulsatile flow on the transport phenomena across the membrane of a high-flux dialyzer in a wearable artificial kidney (WAK) with a novel single small battery-operated pulsatile pump that drives both the blood and dialysate in a counter-phased manner, maximizing the trans-membrane pressure. Methods Both in-vitro experimental and numerical tools are employed to compare the performance of the pulsatile WAK dialyzer with a traditional design of a single-channel roller blood pump together with a centrifugal pump that drives the dialysate flow. The numerical methods utilize the axisymmetric Navier-Stokes and mass transfer equations to model the flow in the fibers of the dialyzer. Results While diffusion is still the dominating transport regime, the WAK pump enhances substantially the trans-membrane pressure and thus increases mass convection that might be as high as 30% of the overall transfer. This increase is obtained due to the design of the pulsatile WAK pump that increases ultrafiltration by increasing the trans-membrane pressure. Conclusions The experimental and numerical results revealed that when pumping at similar flow rates, a small battery-operated pulsatile pump provides clearances of urea and creatinine similar as or better than a large heavy AC-powered roller pump. PMID:20497572
NASA Astrophysics Data System (ADS)
Harikrishnan, L.; Maiya, M. P.; Tiwari, S.; Wohlfeil, A.; Ziegler, F.
2009-10-01
In this paper the heat and mass transfer characteristics of a horizontal tube absorber for the mixture R134a/DMAC in terms of experimentally gained heat and mass transfer coefficients are presented. The heat transfer coefficient is mainly dependent on the solution’s mass flow rate. The mass transfer coefficient is strongly related to the subcooling of the solution. The data are compared to experimental absorption characteristics of water into aqueous lithium bromide in an absorption chiller. The mass transfer coefficients are of similar size whereas the heat transfer coefficients are about one order of magnitude smaller for R134a-DMAC.
Mass transfer in supercritical fluids instancing selected fluids in supercritical carbon dioxide
NASA Astrophysics Data System (ADS)
Hu, Miao; Benning, Rainer; Delgado, Antonio; Ertunc, Oezguer
The research interests lie in a deeper understanding of the mechanisms of diffusion and nucle-ation of organic solutes in near-and supercritical state of a solvent, which count as important means of mass transfer in the process engineering industry. The use of supercritical fluids in industrial processes, such as extraction and particle handling, has become a more and more popular method. Take a closer look at the two processes one would find that there are obviously two sub-processes involved in each of the process, namely the diffusion/nucleation as well as a phase transition procedure. Because of the operational limitations in the practice, this phase transition can-not be neglected. So it is also included in the theoretical approach. Classically to deduce conclusions from experiment results, mathematical/physical models outlining property changes and summarizing characteristics of the two processes are expected. In order to become an insight of these phenomena from the origin, and also to serve as a fundamental attribute for the numerical simulation later, the theories of statistical thermodynamics are adopted here as a proper means to describe the behaviors of the two processes. As the diffusion coefficients of the samples in our case are only of an order of approx. 10-8m2s-1, it can be assumed that the processes are in equilibrium (local changes are neglectably small), a model can be built on a general macroscopic approach for equilibrium systems, namely the Boltzmann-Gibbs distri-bution. And some rather general methods e.g. linear response theory can be applied. But as the transfer phenomena are genuinely not equilibrium systems, from this aspect a model can also be built based on the microscopic description -the kinetic theory of the behaviors of the particles of this non-equilibrium system. The characteristics under compensated gravity are also to be considered in the models. The differences and constraints between the models are to be compared and
NASA Astrophysics Data System (ADS)
Istrate, A. G.; Marchant, P.; Tauris, T. M.; Langer, N.; Stancliffe, R. J.; Grassitelli, L.
2016-10-01
A large number of extremely low-mass helium white dwarfs (ELM WDs) have been discovered in recent years. The majority of them are found in close binary systems suggesting they are formed either through a common-envelope phase or via stable mass transfer in a low-mass X-ray binary (LMXB) or a cataclysmic variable (CV) system. Here, we investigate the formation of these objects through the LMXB channel with emphasis on the proto-WD evolution in environments with different metallicities. We study for the first time the combined effects of rotational mixing and element diffusion (e.g. gravitational settling, thermal and chemical diffusion) on the evolution of proto-WDs and on the cooling properties of the resulting WDs. We present state-of-the-art binary stellar evolution models computed with MESA for metallicities of Z = 0.02, 0.01, 0.001 and 0.0002, producing WDs with masses between 0.16-0.45 M⊙. Our results confirm that element diffusion plays a significant role in the evolution of proto-WDs that experience hydrogen shell flashes. The occurrence of these flashes produces a clear dichotomy in the cooling timescales of ELM WDs, which has important consequences e.g. for the age determination of binary millisecond pulsars. In addition, we confirm that the threshold mass at which this dichotomy occurs depends on metallicity. Rotational mixing is found to counteract the effect of gravitational settling in the surface layers of young, bloated ELM proto-WDs and therefore plays a key role in determining their surface chemical abundances, i.e. the observed presence of metals in their atmospheres. We predict that these proto-WDs have helium-rich envelopes through a significant part of their lifetime. This is of great importance as helium is a crucial ingredient in the driving of the κ-mechanism suggested for the newly observed ELM proto-WD pulsators. However, we find that the number of hydrogen shell flashes and, as a result, the hydrogen envelope mass at the beginning of
NASA Astrophysics Data System (ADS)
Leclerc, Monique Y.; Schuepp, Peter H.; Thurtell, George W.
1986-03-01
This paper reports on forced-convection mass transfer from isolated discs on rectangular plates as well as hemispheres on realistic fluttering leaves. An electrochemical method was used where the convective transfer of ions to the test electrode (the droplet or the wet spot) in an electrolytic flow system was measured as a function of flow rates, sizes of discs and hemispheres. Measurements showed that the local transfer coefficient for uniformly transferring plates varied as expected while the transfer from isolated discs on plates was much less a function of the distance from the leading edge. An expression to describe the transfer coefficient for an isolated disc as a function of distance from the leading edge was determined. An expression describing the transfer from hemispherical drops on fluttering leaves was derived and compared with the predictions from transfer theory for a sphere in free space.
Implications of rate-limited mass transfer for aquifer storage and recovery.
Culkin, Sean L; Singha, Kamini; Day-Lewis, Frederick D
2008-01-01
Pressure to decrease reliance on surface water storage has led to increased interest in aquifer storage and recovery (ASR) systems. Recovery efficiency, which is the ratio of the volume of recovered water that meets a predefined standard to total volume of injected fluid, is a common criterion of ASR viability. Recovery efficiency can be degraded by a number of physical and geochemical processes, including rate-limited mass transfer (RLMT), which describes the exchange of solutes between mobile and immobile pore fluids. RLMT may control transport behavior that cannot be explained by advection and dispersion. We present data from a pilot-scale ASR study in Charleston, South Carolina, and develop a three-dimensional finite-difference model to evaluate the impact of RLMT processes on ASR efficiency. The modeling shows that RLMT can explain a rebound in salinity during fresh water storage in a brackish aquifer. Multicycle model results show low efficiencies over one to three ASR cycles due to RLMT degrading water quality during storage; efficiencies can evolve and improve markedly, however, over multiple cycles, even exceeding efficiencies generated by advection-dispersion only models. For an idealized ASR model where RLMT is active, our simulations show a discrete range of diffusive length scales over which the viability of ASR schemes in brackish aquifers would be hindered.
Impact of plant shoot architecture on leaf cooling: a coupled heat and mass transfer model
Bridge, L. J.; Franklin, K. A.; Homer, M. E.
2013-01-01
Plants display a range of striking architectural adaptations when grown at elevated temperatures. In the model plant Arabidopsis thaliana, these include elongation of petioles, and increased petiole and leaf angles from the soil surface. The potential physiological significance of these architectural changes remains speculative. We address this issue computationally by formulating a mathematical model and performing numerical simulations, testing the hypothesis that elongated and elevated plant configurations may reflect a leaf-cooling strategy. This sets in place a new basic model of plant water use and interaction with the surrounding air, which couples heat and mass transfer within a plant to water vapour diffusion in the air, using a transpiration term that depends on saturation, temperature and vapour concentration. A two-dimensional, multi-petiole shoot geometry is considered, with added leaf-blade shape detail. Our simulations show that increased petiole length and angle generally result in enhanced transpiration rates and reduced leaf temperatures in well-watered conditions. Furthermore, our computations also reveal plant configurations for which elongation may result in decreased transpiration rate owing to decreased leaf liquid saturation. We offer further qualitative and quantitative insights into the role of architectural parameters as key determinants of leaf-cooling capacity. PMID:23720538
Multi-layer onion drying: Study of mass and heat transfer mechanism and quality evaluation
NASA Astrophysics Data System (ADS)
Asiah, N.; Djaeni, M.
2015-12-01
Drying is one of methods to prolong storage life of onion. The outer layer of onion has kept dry around 12% of moisture content or below to retain the freshness of its inside part. The model of multi layers onion drying is very important to predict the water and temperature transport during dying process. In this case, one dimensional partial equation was used for predicting moisture distribution in the onion layer. To support the study, the onion drying was performed at various temperatures ranging of 40-50 °C. Then the attribute quality (quercetin content) of dried onion was analysed. The experimental data was to validate the value of water diffusivity and mass transfer coefficient used in the model. Results showed that the model can predict moisture distribution in each layer of onion. Moreover, based on the average moisture content during the drying, the model result closed to experiment data with accuracy of R2 0.970-0.999. The model was useful to estimate the drying time of outer layer to the desired level. Besides that, the quality evaluation showed that after 2 hours drying process, quercetin content can be retained.
Heat and mass transfer in combustion - Fundamental concepts and analytical techniques
NASA Technical Reports Server (NTRS)
Law, C. K.
1984-01-01
Fundamental combustion phenomena and the associated flame structures in laminar gaseous flows are discussed on physical bases within the framework of the three nondimensional parameters of interest to heat and mass transfer in chemically-reacting flows, namely the Damkoehler number, the Lewis number, and the Arrhenius number which is the ratio of the reaction activation energy to the characteristic thermal energy. The model problems selected for illustration are droplet combustion, boundary layer combustion, and the propagation, flammability, and stability of premixed flames. Fundamental concepts discussed include the flame structures for large activation energy reactions, S-curve interpretation of the ignition and extinctin states, reaction-induced local-similarity and non-similarity in boundary layer flows, the origin and removal of the cold boundary difficulty in modeling flame propagation, and effects of flame stretch and preferential diffusion on flame extinction and stability. Analytical techniques introduced include the Shvab-Zeldovich formulation, the local Shvab-Zeldovich formulation, flame-sheet approximation and the associated jump formulation, and large activation energy matched asymptotic analysis. Potentially promising research areas are suggested.
Assessment of interfacial mass transfer in water-unsaturated soils during vapor extraction.
Hoeg, S; Schöler, H F; Warnatz, J
2004-10-01
This paper presents results of a numerical investigation of soil vapor extraction (SVE) systems at the laboratory scale. The SVE technique is used to remove volatile chlorinated hydrocarbons (VCHC) from the water-unsaturated soil zone. The developed numerical model solves equations of flow, transport and interfacial mass transfer regarding an isothermal n-component and three-phase system. The mathematical model is based on a simple pore network and phase distribution model and designed to be scaled by a characteristic length. All mathematical expressions are structured into VCHC specific and VCHC non-specific parameters. Furthermore, indicators are introduced that help to separate thermodynamic equilibrium from thermodynamic non-equilibrium domains and to determine the controlling physical parameters. For numerical solution, the system of partial differential equations is discretized by a finite volume method and an implicit Euler time stepping scheme. Computational effort is reduced notably through techniques that enable spatial and temporal adaptivity, through a standard multigrid method as well as through a problem-oriented sparse-matrix storage concept. Computations are carried out in two dimensions regarding the laboratory experiment of Fischer et al. [Water Resour. Res. 32 (12) 1996 3413]. By varying the characteristic length scale of the pore network and phase distribution model, it is shown that the experimental gas phase concentrations cannot be explained only by the volatility and diffusivity of the VCHC. The computational results suggest a sorption process whose significance grows with the aqueous activity of the less or non-polar organic compounds.
Xie, Yuliang; Chindam, Chandraprakash; Nama, Nitesh; Yang, Shikuan; Lu, Mengqian; Zhao, Yanhui; Mai, John D.; Costanzo, Francesco; Huang, Tony Jun
2015-01-01
We investigated bubble oscillation and its induced enhancement of mass transfer in a liquid-liquid extraction process with an acoustically-driven, bubble-based microfluidic device. The oscillation of individually trapped bubbles, of known sizes, in microchannels was studied at both a fixed frequency, and over a range of frequencies. Resonant frequencies were analytically identified and were found to be in agreement with the experimental observations. The acoustic streaming induced by the bubble oscillation was identified as the cause of this enhanced extraction. Experiments extracting Rhodanmine B from an aqueous phase (DI water) to an organic phase (1-octanol) were performed to determine the relationship between extraction efficiency and applied acoustic power. The enhanced efficiency in mass transport via these acoustic-energy-assisted processes was confirmed by comparisons against a pure diffusion-based process. PMID:26223474
NASA Astrophysics Data System (ADS)
Xie, Yuliang; Chindam, Chandraprakash; Nama, Nitesh; Yang, Shikuan; Lu, Mengqian; Zhao, Yanhui; Mai, John D.; Costanzo, Francesco; Huang, Tony Jun
2015-07-01
We investigated bubble oscillation and its induced enhancement of mass transfer in a liquid-liquid extraction process with an acoustically-driven, bubble-based microfluidic device. The oscillation of individually trapped bubbles, of known sizes, in microchannels was studied at both a fixed frequency, and over a range of frequencies. Resonant frequencies were analytically identified and were found to be in agreement with the experimental observations. The acoustic streaming induced by the bubble oscillation was identified as the cause of this enhanced extraction. Experiments extracting Rhodanmine B from an aqueous phase (DI water) to an organic phase (1-octanol) were performed to determine the relationship between extraction efficiency and applied acoustic power. The enhanced efficiency in mass transport via these acoustic-energy-assisted processes was confirmed by comparisons against a pure diffusion-based process.
NASA Astrophysics Data System (ADS)
Illangasekare, T. H.; Frippiat, C. C.; Zyvoloski, G. A.
2007-12-01
A significant body of knowledge exists on separates processes of thermal and mass transport in granular and fractured subsurface formations. However, the need to simulate these processes in a fully coupled way has become necessary to deal with problems associated with long-term-storage of nuclear waste, and the development of new technologies for subsurface remediation. Another emerging area for research is associated with the development of technologies for in situ extraction of underground resources. Numerical models that couple thermal and mass transport processes will play a crucial role in understanding the fundamental processes associated with these new technologies, as well as in making predictions on how complex subsurface systems are expected to behave. It is our hypothesis that heat transport will have a significant impact on distributions of solute concentration, through temperature-dependent dissolution and precipitation, and temperature-dependent rate-limited diffusive transfer of solutes in fractured or highly heterogeneous media. A number of issues related to the validity of existing numerical tools that capture these processes, and their application to field systems through up-scaling need to be investigated. With this overall goal in mind, in this preliminary study, we explore the effect of the variability of subsurface properties on heat and mass transport using simulations conducted using an existing multiphase model. The finite-element code FEHM (Finite-Element Heat and Mass transport code) used in this study was developed at Los Alamos National Laboratory. This code allows for the coupled simulation of flow, heat and mass transport, accounting for density effects and dissolution and/or precipitation reactions. Our analysis is based on two- and three-dimensional simulations using synthetic data sets. Heterogeneous facies distributions are generated according to Markov Chain transition probability models. A distributed source of constant
Tabares Velasco, P. C.
2011-04-01
This presentation discusses estimating heat and mass transfer processes in green roof systems: current modeling capabilities and limitations. Green roofs are 'specialized roofing systems that support vegetation growth on rooftops.'
NASA Astrophysics Data System (ADS)
Zhong, Hongying; Zhang, Juan; Tang, Xuemei; Zhang, Wenyang; Jiang, Ruowei; Li, Rui; Chen, Disong; Wang, Peng; Yuan, Zhiwei
2017-02-01
Monitoring of interfacial electron transfer (ET) in situ is important to understand the ET mechanism and designing efficient photocatalysts. We describe herein a mass spectrometric approach to investigate the ultrafast transfer of photoelectrons that are generated by ultraviolet irradiation on surfaces of semiconductor nanoparticles or crystalline facets. The mass spectrometric approach can not only untargetedly detect various intermediates but also monitor their reactivity through associative or dissociative photoelectron capture dissociation, as well as electron detachment dissociation of adsorbed molecules. Proton-coupled electron transfer and proton-uncoupled electron transfer with radical initiated polymerization or hydroxyl radical abstraction have been unambiguously demonstrated with the mass spectrometric approach. Active crystalline facets of titanium dioxide for photocatalytic degradation of juglone and organochlorine dichlorodiphenyltrichloroethane are visualized with mass spectrometry imaging based on ion scanning and spectral reconstruction. This work provides a new technique for studying photo-electric properties of various materials.
Spanwise mass transfer variations on a cylinder in 'nominally' uniform crossflow
NASA Technical Reports Server (NTRS)
Mayle, R. E.; Marziale, M.
1982-01-01
Mass transfer experiments on a circular cylinder in a 'nominally' uniform crossflow are described. Experiments were conducted at the tunnel's turbulence level and with a woven-wire turbulence screen. In both cases spanwise and circumferential mass transfer measurements were made. Without the turbulence screen, the results were found to be spanwise independent and agreed quite well with both theory and the result of others. In addition to the mass transfer measurements, spanwise traverse measurements of the mean velocity and turbulence quantities in the incident flow were made and showed that the screen produced a small-amplitude spanwise periodic perturbation in the incident flow. Although this perturbation was only one quarter of a percent in the mean velocity and buried in the stream's turbulence, disproportionately large spanwise variations of 15 percent were found in the mass transfer rate.
The mechanism of thermal-gradient mass transfer in the sodium hydroxide-nickel system
NASA Technical Reports Server (NTRS)
May, Charles E
1958-01-01
"Thermal-gradient mass transfer" was investigated in the molten sodium hydroxide-nickel system. Possible mechanisms (physical, electrochemical, and chemical) are discussed in terms of experimental and theoretical evidence. Experimental details are included in appendixes.
Small chamber tests were conducted to experimentally determine the overall mass transfer coefficient for pollutant emissions from still water under simulated indoor-residential or occupational-environmental conditions. Fourteen tests were conducted in small environmental chambers...
Improving mass transfer to soften tissues by pulsed electric fields: fundamentals and applications.
Puértolas, E; Luengo, E; Álvarez, I; Raso, J
2012-01-01
The mass transfer phenomenon occurs in many operations of the food industry with the purpose of obtaining a given substance of interest, removing water from foods, or introducing a given substance into the food matrix. Pretreatments that modify the permeability of the cell membranes, such as grinding, heating, or enzymatic treatment, enhance the mass transfer. However, these techniques may require a significant amount of energy and can cause losses of valuable food compounds. Pulsed electric field (PEF) technology is a nonthermal processing method that causes permeabilization of cell membranes using low energy requirements and minimizing quality deterioration of the food compounds. Many practical applications of PEF for enhancing mass transfer in the food industry have been investigated. The purpose of this chapter is to give an overview of the state of the art of application of PEF for improving mass transfer in the food industry.
Simoes, P.C.; Matos, H.A.; Carmelo, P.J.; Gomes de Azevedo, E.; Nunes da Ponte, M. . Faculdade de Ciencias e Tecnologia)
1995-02-01
Supercritical fluid extraction (SFE) is an alternative separation method to more conventional processes such as liquid extraction and distillation. However, up to now, few works have been devoted to the investigation of the efficiency of countercurrent packed columns under supercritical conditions from a mass transfer point of view. Mass transfer in a countercurrent column, filled with structured gauze packing, was measured for the separation of a mixture of terpenes (d-limonene/1,8-cineole) by supercritical carbon dioxide, at 313 and 318 K and pressures up to 9 MPa. The extraction efficiency was determined in terms of the overall mass transfer coefficient. Operating lines for this process had an appreciable curvature due to a high miscibility of the two contacting phases. The real slope of these lines had to be estimated. Available mass transfer models for packed columns predicted efficiencies diverging to a great extent from the experimental results.
Zhong, Hongying; Zhang, Juan; Tang, Xuemei; Zhang, Wenyang; Jiang, Ruowei; Li, Rui; Chen, Disong; Wang, Peng; Yuan, Zhiwei
2017-01-01
Monitoring of interfacial electron transfer (ET) in situ is important to understand the ET mechanism and designing efficient photocatalysts. We describe herein a mass spectrometric approach to investigate the ultrafast transfer of photoelectrons that are generated by ultraviolet irradiation on surfaces of semiconductor nanoparticles or crystalline facets. The mass spectrometric approach can not only untargetedly detect various intermediates but also monitor their reactivity through associative or dissociative photoelectron capture dissociation, as well as electron detachment dissociation of adsorbed molecules. Proton-coupled electron transfer and proton-uncoupled electron transfer with radical initiated polymerization or hydroxyl radical abstraction have been unambiguously demonstrated with the mass spectrometric approach. Active crystalline facets of titanium dioxide for photocatalytic degradation of juglone and organochlorine dichlorodiphenyltrichloroethane are visualized with mass spectrometry imaging based on ion scanning and spectral reconstruction. This work provides a new technique for studying photo-electric properties of various materials. PMID:28224986
Galinada, Wilmer; Kaczmarski, Krzysztof; Guiochon, Georges A
2005-09-01
The effect of microwave irradiation on the kinetics of mass transfer in reversed-phase liquid chromatography (RPLC) was studied by measuring its influence on the band profile of propylbenzene in a C{sub 18}-silica column eluted with an aqueous solution of methanol and placed inside a microwave oven. The elution peaks were measured by the pulse-response method, under linear conditions. The amount of microwave energy induced into the column was varied based on the microwave input power. The experimental data were analyzed using the conventional method of moment analysis and the lumped pore diffusion model. With input powers of 15 and 30 W, the effluent temperatures were 25 {+-} 1 and 30 {+-} 1 C, respectively. The effect of microwave irradiation on the mass transfer of the studied solute was determined by comparing the band profiles obtained under the same experimental conditions, at the same temperature, with and without irradiation. The values of the intraparticle diffusion coefficient, D{sub e}, measured with microwave irradiation were ca. 20% higher than those obtained without irradiation. Derived from the method of moments, the values of D{sub e} at 15 W (25 {+-} 1 C) and 0 W (25 {+-} 1 C) were 8.408 x 10{sup -6} cm{sup 2} s{sup -1} and 6.947 x 10{sup -6} cm{sup 2} s{sup -1}, respectively, while these values at 30 W (30 {+-} 1 C) and 0 W (30 {+-} 1 C) were 9.389 x 10{sup -6} cm{sup 2} s{sup -1} and 7.848 x 10{sup -6} cm{sup 2} s{sup -1}, respectively. The values of the surface diffusivity, D{sub S}, also increased with increasing power of the microwave irradiation. It is assumed that the increase in intraparticle diffusion for propylbenzene was caused by the molecular excitation of the organic modifier that has a higher dielectric loss than the solute. The values of D{sub e} were also analyzed and determined using the POR model. There was an excellent agreement between the results of the two independent methods. These preliminary results suggest that microwave
The response of a dwarf nova disc to real mass transfer variations
NASA Astrophysics Data System (ADS)
Schreiber, M. R.; Gänsicke, B. T.; Hessman, F. V.
2000-06-01
We present simulations of dwarf nova outbursts taking into account realistic variations of the mass loss rate from the secondary. The mass transfer variation has been derived from 20 years of visual monitoring and from X-ray observations covering various accretion states of the discless cataclysmic variable AM Herculis. We find that the outburst behaviour of a fictitious dwarf nova with the same system parameters as AM Her is strongly influenced by these variations of the mass loss rate. Depending on the mass loss rate, the disc produces either long outbursts, a cycle of one long outburst followed by two short outbursts, or only short outbursts. The course of the transfer rate dominates the shape of the outbursts because the mass accreted during an outburst cycle roughly equals the mass transferred from the secondary over the outburst interval. Only for less than 10% of the simulated time, when the mass transfer rate is nearly constant, the disc is in a quasi-stationary state during which it periodically repeats the same cycle of outbursts. Consequently, assuming that the secondary stars in non-magnetic CV's do not differ from those in magnetic ones, our simulation indicates that probably all dwarf novae are rarely in a stationary state and are constantly adjusting to the prevailing value of the mass transfer rate from the secondary.
Li, Ming; Ding, Jianhua; Gu, Haiwei; Zhang, Yan; Pan, Susu; Xu, Ning; Chen, Huanwen; Li, Hongmei
2013-01-01
By using silver cations (Ag⁺) as the ionic reagent in reactive extractive electrospray ionization mass spectrometry (EESI-MS), the concentrations of acetonitrile in exhaled breath samples from the volunteers including active smokers, passive smokers, and non-smokers were quantitatively measured in vivo, without any sample pretreatment. A limit of detection (LOD) and relative standard deviation (RSD) were 0.16 ng/L and 3.5% (n = 8), respectively, for the acetonitrile signals in MS/MS experiments. Interestingly, the concentrations of acetonitrile in human breath continuously increased for 1-4 hours after the smoker finished smoking and then slowly decreased to the background level in 7 days. The experimental data of a large number of (> 165) samples indicated that the inhaled acetonitrile is excreted most likely by facilitated diffusion, instead of simple diffusion reported previously for other volatile compounds.
On the Effective Thermal Conductivity of Frost Considering Mass Diffusion and Eddy Convection
NASA Technical Reports Server (NTRS)
Kandula, Max
2010-01-01
A physical model for the effective thermal conductivity of water frost is proposed for application to the full range of frost density. The proposed model builds on the Zehner-Schlunder one-dimensional formulation for porous media appropriate for solid-to-fluid thermal conductivity ratios less than about 1000. By superposing the effects of mass diffusion and eddy convection on stagnant conduction in the fluid, the total effective thermal conductivity of frost is shown to be satisfactorily described. It is shown that the effects of vapor diffusion and eddy convection on the frost conductivity are of the same order. The results also point out that idealization of the frost structure by cylindrical inclusions offers a better representation of the effective conductivity of frost as compared to spherical inclusions. Satisfactory agreement between the theory and the measurements for the effective thermal conductivity of frost is demonstrated for a wide range of frost density and frost temperature.
Das, Abanti; Bhalla, Ashu S; Sharma, Raju; Kumar, Atin; Sharma, Meher; Gamanagatti, Shivanand; Thakar, Alok; Sharma, Suresh
2016-01-01
Diffusion weighted imaging (DWI) evolved as a complementary tool to morphologic imaging by offering additional functional information about lesions. Although the technique utilizes movement of water molecules to characterize biological tissues in terms of their cellularity, there are other factors related to the histological constitution of lesions which can have a significant bearing on DWI. Benign lesions with atypical histology including presence of lymphoid stroma, inherently increased cellularity or abundant extracellular collagen can impede movement of water molecules similar to malignant tissues and thereby, show restricted diffusion. Knowledge of these atypical entities while interpreting DWI in clinical practice can avoid potential misdiagnosis. This review aims to present an imaging spectrum of such benign neck masses which, owing to their distinct histology, can show discordant behavior on DWI. PMID:26981226
Gondrexon, N; Cheze, L; Jin, Y; Legay, M; Tissot, Q; Hengl, N; Baup, S; Boldo, P; Pignon, F; Talansier, E
2015-07-01
This paper aims to illustrate the interest of ultrasound technology as an efficient technique for both heat and mass transfer intensification. It is demonstrated that the use of ultrasound results in an increase of heat exchanger performances and in a possible fouling monitoring in heat exchangers. Mass transfer intensification was observed in the case of cross-flow ultrafiltration. It is shown that the enhancement of the membrane separation process strongly depends on the physico-chemical properties of the filtered suspensions.
Calculation of Post-Closure Natural Convection Heat and Mass Transfer in Yucca Mountain Drifts
S. Webb; M. Itamura
2004-03-16
Natural convection heat and mass transfer under post-closure conditions has been calculated for Yucca Mountain drifts using the computational fluid dynamics (CFD) code FLUENT. Calculations have been performed for 300, 1000, 3000, and 10,000 years after repository closure. Effective dispersion coefficients that can be used to calculate mass transfer in the drift have been evaluated as a function of time and boundary temperature tilt.
Simultaneous heat and mass transfer from a two-dimensional, partially liquid-covered surface
Tao, Y.X.; Kaviany, M. )
1991-11-01
Simultaneous heat and mass transfer from partially liquid-covered surfaces is examined experimentally using a surface made of cylinders with the voids filled with liquid. The steady-state evaporation rate, surface temperature of the liquid and exposed solid, and location of meniscus are measured for various ambient air velocities and temperatures. Using these, the authors examine the effect of the extent to which the liquid covers the surface on the evaporation mass transfer rate resulting from the convective heat transfer from the ambient gas to this surface. The results show strong Bond and Reynolds number effects. For small Bond and Reynolds numbers, the presence of dry (exposed solid) surface does not influence the mass transfer rate. As the Bond or Reynolds number increases, a critical liquid coverage is found below which the mass transfer begins to decrease. Heat transfer from the exposed solid to the liquid is also examined using the measured surface temperature, a conduction model, and an estimate of the liquid and solid surface areas (using a static formation for the liquid meniscus). The results show that at the liquid surface an analogy between heat and mass transfer does not exist.
Mitigating diffuse phosphorus transfer from agriculture according to cost and efficiency.
Haygarth, P M; Apsimon, H; Betson, M; Harris, D; Hodgkinson, R; Withers, P J A
2009-01-01
Potential options for mitigating phosphorus (P) transfer from agriculture to water in England and Wales (E&W) were collated across a range of farm systems to assess their potential effectiveness in reducing mass of P transferred and potential cost (pounds sterling [ pound]) to the farming industry. A simple model framework (called PEASE) incorporating a number of assumptions was used to identify 15 methods for mitigating inputs of P to agricultural systems, 19 methods for preventing mobilization of P, and six methods for controlling the transport of P to streams. The scope for largest reductions in P inputs was to grassland and horticulture. Potential reductions in P mobilization were up to 1.2 kg P ha(-1). Reductions in P transfer associated with transport mitigation were larger than those associated with input and mobilization methods (up to 2.2 kg P ha(-1)). The largest estimated reductions were achieved by installing buffer zones and constructed wetlands, the former being very cost effective ( pound3-5 kg(-1) P saved). Plots of cost curves helped identify where the combined and cumulative P transfer reductions were attainable; these were approximately 0.2 kg ha(-1) for uplands, 0.6 kg ha(-1) for outdoor pigs, 0.9 kg ha(-1) for intensive dairy, and 2.2 kg ha(-1) for arable examples. We concluded that established catchment-scale evidence for mitigation is sparse, especially for specific farm systems in E&W. Sensitivities and uncertainties in the approach, especially associated with expert coefficients, are noted. This approach is nonetheless considered useful for prioritizing where and how best options might be most effectively targeted for least cost but greatest benefit.
NASA Astrophysics Data System (ADS)
Cvetkovic, Vladimir; Fiori, Aldo; Dagan, Gedeon
2016-04-01
The driving mechanism of contaminant transport in aquifers is groundwater flow, which is controlled by boundary conditions and heterogeneity of hydraulic properties. In this work we show how hydrodynamics and mass transfer can be combined in a general analytical manner to derive a physically-based (or process-based) residence time distribution for a given integral scale of the hydraulic conductivity; the result can be applied for a broad class of linear mass transfer processes. The derived tracer residence time distribution is a transfer function with parameters to be inferred from combined field and laboratory measurements. It is scalable relative to the correlation length and applicable for an arbitrary statistical distribution of the hydraulic conductivity. Based on the derived residence time distribution, the coefficient of variation and skewness of contaminant residence time are illustrated assuming a log-normal hydraulic conductivity distribution and first-order mass transfer. We show that for a low Damkohler number the coefficient of variation is more strongly influenced by mass transfer than by heterogeneity, whereas skewness is more strongly influenced by heterogeneity. The derived physically-based residence time distribution for solute transport in heterogeneous aquifers is particularly useful for studying natural attenuation of contaminants. We illustrate the relative impacts of high heterogeneity and a generalised (non-Fickian) multi-rate mass transfer on natural attenuation defined as contaminant mass loss from injection to a downstream compliance boundary.
Recovery efficiency of aquifer storage and recovery (ASR) with mass transfer limitation
NASA Astrophysics Data System (ADS)
Lu, Chunhui; Du, Pengfei; Chen, Yiming; Luo, Jian
2011-08-01
Aquifer storage and recovery (ASR) is an effective strategy for water resources management and has been widely used in many contaminated and saline aquifers. However, its recovery efficiency (RE) may be significantly affected by mass transfer limitations. A numerical model is developed to simulate ASR performance by combining the convergent and divergent dispersion models with a first-order mass transfer model. By analyzing the concentration history at the pumping well, we obtain simple and effective relationships for investigating ASR efficiency under various mass transfer parameters, including capacity ratio and mass transfer timescale, and operational parameters, including injection durations and well-pumping rates. On the basis of such relationships, one can conveniently determine whether a site with mass transfer limitations is appropriate or not for ASR and how many ASR cycles are required for achieving a positive RE. Results indicate that the immobile domain may function as a contaminant source or sink or both during the recovery phase and RE usually improves with well-flow rate, the decrease of capacity ratio, and the ASR cycles. However, RE is a nonmonotonic function of the mass transfer timescale and the injection duration. A critical timescale is given for quantifying this nonmonotonic behavior. When the injection period is greater than such a critical value, increasing injection period results in a higher RE. Contrarily, when the injection period is less than the critical value, increasing the injection period may even yield a lower RE.
Interfacial mass transfer to a cylinder endwall during spin-up/spin-down
NASA Technical Reports Server (NTRS)
Larrousse, Mark F.; Wilcox, William R.
1990-01-01
The local rate of mass transfer to the bottom endwall of a large aspect ratio cylinder was measured during spin-up/spin-down. The local mass transfer rate was a strong function radial position along the endwall. At the center during spin-up from rest, the maximum enhancement in mass transfer occurred after the Ekman time scale and before the viscous time scale. At the center during spin-down to rest, a stagnation vortex formed, causing the mass transfer rate to decay and then increase back to the original value of the order of the viscous time scale. Away from the center a much more complicated pattern was observed, but spin-up and spin-down were similar. Two peaks in mass transfer rate occurred for an Ekman number over 0.0074. Alternating spin-up and spin-down with a short period caused the center of the endwall to experience a nearly sinusoidal variation in mass transfer with the frequency equal to the forcing frequency. Near the edge the frequency was twice the forcing frequency.
Drop oscillation and mass transfer in alternating electric fields
Carleson, T.E.
1992-06-24
In certain cases droplet direct contact heat transfer rates can be significantly enhanced by the application of an alternating electric field. This field can produce shape oscillations in a droplet which will enhance mixing. The theoretical evaluation of the effect of the interaction of the field with drop charge on the hydrodynamics has been completed for small amplitude oscillations. Previous work with a zero order perturbation method was followed up with a first order perturbation method to evaluate the effect of drop distortion on drop charge and field distribution. The first order perturbation results show secondary drop oscillations of four modes and two frequencies in each mode. The most significant secondary oscillation has the same mode and frequency as the second mode oscillation predicted from the first order perturbation work. The resonant frequency of all oscillations decrease with increasing electric field strength and drop charge. Work is currently underway to evaluate the heat transfer enhancement from an applied alternating electric field.
Turbulent heat and mass transfers across a thermally stratified air-water interface
NASA Technical Reports Server (NTRS)
Papadimitrakis, Y. A.; Hsu, Y.-H. L.; Wu, J.
1986-01-01
Rates of heat and mass transfer across an air-water interface were measured in a wind-wave research facility, under various wind and thermal stability conditions (unless otherwise noted, mass refers to water vapor). Heat fluxes were obtained from both the eddy correlation and the profile method, under unstable, neutral, and stable conditions. Mass fluxes were obtained only under unstable stratification from the profile and global method. Under unstable conditions the turbulent Prandtl and Schmidt numbers remain fairly constant and equal to 0.74, whereas the rate of mass transfer varies linearly with bulk Richardson number. Under stable conditions the turbulent Prandtl number rises steadily to a value of 1.4 for a bulk Richardson number of about 0.016. Results of heat and mass transfer, expressed in the form of bulk aerodynamic coefficients with friction velocity as a parameter, are also compared with field data.
Orbital Evolution of Mass-transferring Eccentric Binary Systems. II. Secular Evolution
NASA Astrophysics Data System (ADS)
Dosopoulou, Fani; Kalogera, Vicky
2016-07-01
Finite eccentricities in mass-transferring eccentric binary systems can be explained by taking into account the mass loss and mass transfer processes that often occur in these systems. These processes can be treated as perturbations of the general two-body problem. The time-evolution equations for the semimajor axis and the eccentricity derived from perturbative methods are generally phase-dependent. The osculating semimajor axis and eccentricity change over the orbital timescale and are not easy to implement in binary evolution codes like MESA. However, the secular orbital element evolution equations can be simplified by averaging over the rapidly varying true anomalies. In this paper, we derive the secular time-evolution equations for the semimajor axis and the eccentricity for various mass loss/transfer processes using either the adiabatic approximation or the assumption of delta-function mass loss/transfer at periastron. We begin with the cases of isotropic and anisotropic wind mass loss. We continue with conservative and non-conservative non-isotropic mass ejection/accretion (including Roche-Lobe-Overflow) for both point-masses and extended bodies. We conclude with the case of phase-dependent mass accretion. Comparison of the derived equations with similar work in the literature is included and an explanation of the existing discrepancies is provided.
Mass transfer during ice particle collisions in planetary rings
NASA Technical Reports Server (NTRS)
Mcdonald, J. S. B.; Hatzes, A.; Bridges, F.; Lin, D. N. C.
1989-01-01
Experimental results are presented from laboratory environment simulations of the ice particle collisional properties defining the structure and dynamical evolution of planetary rings. It is inferred from these data that there is a dependence of the interacting volume on the impact velocity. Although the volume fraction exchanged during a collision is small, the net amount of material transferred can be substantially smaller. Attention is given to the implications of these determinations for planetary ring structure and evolution.
Estimation of cauliflower mass transfer parameters during convective drying
NASA Astrophysics Data System (ADS)
Sahin, Medine; Doymaz, İbrahim
2017-02-01
The study was conducted to evaluate the effect of pre-treatments such as citric acid and hot water blanching and air temperature on drying and rehydration characteristics of cauliflower slices. Experiments were carried out at four different drying air temperatures of 50, 60, 70 and 80 °C with the air velocity of 2.0 m/s. It was observed that drying and rehydration characteristics of cauliflower slices were greatly influenced by air temperature and pre-treatment. Six commonly used mathematical models were evaluated to predict the drying kinetics of cauliflower slices. The Midilli et al. model described the drying behaviour of cauliflower slices at all temperatures better than other models. The values of effective moisture diffusivities ( D eff ) were determined using Fick's law of diffusion and were between 4.09 × 10-9 and 1.88 × 10-8 m2/s. Activation energy was estimated by an Arrhenius type equation and was 23.40, 29.09 and 26.39 kJ/mol for citric acid, blanch and control samples, respectively.
Estimation of cauliflower mass transfer parameters during convective drying
NASA Astrophysics Data System (ADS)
Sahin, Medine; Doymaz, İbrahim
2016-05-01
The study was conducted to evaluate the effect of pre-treatments such as citric acid and hot water blanching and air temperature on drying and rehydration characteristics of cauliflower slices. Experiments were carried out at four different drying air temperatures of 50, 60, 70 and 80 °C with the air velocity of 2.0 m/s. It was observed that drying and rehydration characteristics of cauliflower slices were greatly influenced by air temperature and pre-treatment. Six commonly used mathematical models were evaluated to predict the drying kinetics of cauliflower slices. The Midilli et al. model described the drying behaviour of cauliflower slices at all temperatures better than other models. The values of effective moisture diffusivities (D eff ) were determined using Fick's law of diffusion and were between 4.09 × 10-9 and 1.88 × 10-8 m2/s. Activation energy was estimated by an Arrhenius type equation and was 23.40, 29.09 and 26.39 kJ/mol for citric acid, blanch and control samples, respectively.
NASA Technical Reports Server (NTRS)
Weidner, John W.; Fedkiw, Peter S.
1991-01-01
A means is presented to account for the effect of ohmic, mass-transfer, and kinetic resistances on linear-sweep voltammograms by modeling a pore in a porous matrix as a cylindrical-pore electrode, and solving the mass and charge conservation equations in the context of this geometry for the simply redox reaction O + ne(-) yield R where both O and R are soluble species. Both analytical and numerical techniques are used to solve the governing equations. The calculated peak currents and potentials are correlated by empirical formulas to the measurable parameters: sweep rate, concentration of the redox species, diffusion coefficient, conductivity of the electrolyte, and pore dimensions. Using the correlations, a methodology is established for determining if the redox reaction kinetics are irreversible or reversible (Nernstian). If the reaction is irreversible, it is shown how the standard rate constant and the transfer coefficient may be extracted from linear-sweep voltammetry data, or, if the reaction is reversible, how the number of electrons transferred may be deduced.
Mass Conservation in Modeling Moisture Diffusion in Multi-Layer Carbon Composite Structures
NASA Technical Reports Server (NTRS)
Nurge, Mark A.; Youngquist, Robert C.; Starr, Stanley O.
2009-01-01
Moisture diffusion in multi-layer carbon composite structures is difficult to model using finite difference methods due to the discontinuity in concentrations between adjacent layers of differing materials. Applying a mass conserving approach at these boundaries proved to be effective at accurately predicting moisture uptake for a sample exposed to a fixed temperature and relative humidity. Details of the model developed are presented and compared with actual moisture uptake data gathered over 130 days from a graphite epoxy composite sandwich coupon with a Rohacell foam core.
Isotopic mass-dependence of metal cation diffusion coefficients in liquid water
Bourg, I.C.; Richter, F.M.; Christensen, J.N.; Sposito, G.
2009-01-11
Isotope distributions in natural systems can be highly sensitive to the mass (m) dependence of solute diffusion coefficients (D) in liquid water. Isotope geochemistry studies routinely have assumed that this mass dependence either is negligible (as predicted by hydrodynamic theories) or follows a kinetic-theory-like inverse square root relationship (D {proportional_to} m{sup -0.5}). However, our recent experimental results and molecular dynamics (MD) simulations showed that the mass dependence of D is intermediate between hydrodynamic and kinetic theory predictions (D {proportional_to} m{sup -{beta}} with 0 {<=} {beta} < 0.2 for Li{sup +}, Cl{sup -}, Mg{sup 2+}, and the noble gases). In this paper, we present new MD simulations and experimental results for Na{sup +}, K{sup +}, Cs{sup +}, and Ca{sup 2+} that confirm the generality of the inverse power-law relation D {proportional_to} m{sup -{beta}}. Our new findings allow us to develop a general description of the influence of solute valence and radius on the mass dependence of D for monatomic solutes in liquid water. This mass dependence decreases with solute radius and with the magnitude of solute valence. Molecular-scale analysis of our MD simulation results reveals that these trends derive from the exponent {beta} being smallest for those solutes whose motions are most strongly coupled to solvent hydrodynamic modes.
NASA Astrophysics Data System (ADS)
Stoyanov, Dimitar M.; Marciniak, Michael A.; Meola, Joseph
2015-09-01
The sensitivity of hyper-spectral remote sensing to the directional reflectance of surfaces was studied using both laboratory and field measurements. Namely, the effects of the specular- and diffuse-reflectance properties of a set of eight samples, ranging from high to low in both total reflectance and specularity, on diffuse-only and diffusespecular radiative transfer models in the long-wave infrared (LWIR, 7-14-μm wavelength) were studied. The samples were measured in the field as a set of eight panels, each in two orientations, with surface normal pointing toward zenith and tipped at 45° from zenith. The field-collected data also included down-welling spectral sky radiance at several angles from zenith to the horizon, ground spectral radiance, panel spectral radiances in both orientations, Infragold® spectral radiances in both orientations near each panel location, and panel temperatures. Laboratory measurements included spectral hemispherical, specular and diffuse directional reflectance (HDR, SDR and DDR) for each sample for several reflectance angles with respect to the surface normal. The diffuse-only radiative transfer model used the HDR data, while the diffuse-specular model used the SDR and DDR data. Both calculated spectral reflected and self-emitted radiances for each panel, using the field-collected sky radiance data to avoid uncertainties associated with atmospheric models. The modeled spectral radiances were then compared to the field-collected values to quantify differences in moving from an HDR-based model to an SDR/DDR model in the LWIR for a variety of surface-reflectance types.
Development of Turbulent Diffusion Transfer Algorithms to Estimate Lake Tahoe Water Budget
NASA Astrophysics Data System (ADS)
Sahoo, G. B.; Schladow, S. G.; Reuter, J. E.
2012-12-01
The evaporative loss is a dominant component in the Lake Tahoe hydrologic budget because watershed area (813km2) is very small compared to the lake surface area (501 km2). The 5.5 m high dam built at the lake's only outlet, the Truckee River at Tahoe City can increase the lake's capacity by approximately 0.9185 km3. The lake serves as a flood protection for downstream areas and source of water supply for downstream cities, irrigation, hydropower, and instream environmental requirements. When the lake water level falls below the natural rim, cessation of flows from the lake cause problems for water supply, irrigation, and fishing. Therefore, it is important to develop algorithms to correctly estimate the lake hydrologic budget. We developed a turbulent diffusion transfer model and coupled to the dynamic lake model (DLM-WQ). We generated the stream flows and pollutants loadings of the streams using the US Environmental Protection Agency (USEPA) supported watershed model, Loading Simulation Program in C++ (LSPC). The bulk transfer coefficients were calibrated using correlation coefficient (R2) as the objective function. Sensitivity analysis was conducted for the meteorological inputs and model parameters. The DLM-WQ estimated lake water level and water temperatures were in agreement to those of measured records with R2 equal to 0.96 and 0.99, respectively for the period 1994 to 2008. The estimated average evaporation from the lake, stream inflow, precipitation over the lake, groundwater fluxes, and outflow from the lake during 1994 to 2008 were found to be 32.0%, 25.0%, 19.0%, 0.3%, and 11.7%, respectively.
Experimental Investigations of Heat and Mass Transfer in Microchannel Heat-Transfer Elements
NASA Astrophysics Data System (ADS)
Konovalov, D. A.
2016-05-01
The present work seeks to develop and investigate experimentally microchannel heat-exchange apparatuses of two designs: with porous elements manufactured from titanium and copper, and also based on the matrix of filamentary silicon single crystals under operating conditions with high heat loads, unsteadiness, and nonlinear flow of the coolant. For experimental investigations, the authors have developed and manufactured a unique test bench allowing tests of the developed heat-transfer elements in unsteady operating regimes. The performed experimental investigations have made it possible to obtain criterial dependences of the heat-transfer coefficient on the Reynolds and Prandtl numbers and to refine the values of viscous and inertial coefficients. It has been established that microchannel heat-transfer elements based on silicon single crystals, which make it possible to remove a heat flux above 100 W/cm2, are the most efficient. For porous heat-transfer elements, the best result was attained for wedge-shaped copper samples. According to investigation results, the authors have considered the issues of optimization of thermal and hydraulic characteristics of the heat-transfer elements under study. In the work, the authors have given examples of practical use of the developed heat-transfer elements for cooling systems of radioelectronic equipment.
Final Report: Geoelectrical Measurement of Multi-Scale Mass Transfer Parameters
Haggerty, Roy; Day-Lewis, Fred; Singha, Kamini; Johnson, Timothy; Binley, Andrew; Lane, John
2014-03-20
Mass transfer affects contaminant transport and is thought to control the efficiency of aquifer remediation at a number of sites within the Department of Energy (DOE) complex. An improved understanding of mass transfer is critical to meeting the enormous scientific and engineering challenges currently facing DOE. Informed design of site remedies and long-term stewardship of radionuclide-contaminated sites will require new cost-effective laboratory and field techniques to measure the parameters controlling mass transfer spatially and across a range of scales. In this project, we sought to capitalize on the geophysical signatures of mass transfer. Previous numerical modeling and pilot-scale field experiments suggested that mass transfer produces a geoelectrical signature—a hysteretic relation between sampled (mobile-domain) fluid conductivity and bulk (mobile + immobile) conductivity—over a range of scales relevant to aquifer remediation. In this work, we investigated the geoelectrical signature of mass transfer during tracer transport in a series of controlled experiments to determine the operation of controlling parameters, and also investigated the use of complex-resistivity (CR) as a means of quantifying mass transfer parameters in situ without tracer experiments. In an add-on component to our grant, we additionally considered nuclear magnetic resonance (NMR) to help parse mobile from immobile porosities. Including the NMR component, our revised study objectives were to: 1. Develop and demonstrate geophysical approaches to measure mass-transfer parameters spatially and over a range of scales, including the combination of electrical resistivity monitoring, tracer tests, complex resistivity, nuclear magnetic resonance, and materials characterization; and 2. Provide mass-transfer estimates for improved understanding of contaminant fate and transport at DOE sites, such as uranium transport at the Hanford 300 Area. To achieve our objectives, we implemented a 3
NASA Technical Reports Server (NTRS)
Castillo, J. L.; Garcia-Ybarra, P. L.; Rosner, D. E.
1991-01-01
The stability of solid planar growth from a binary vapor phase with a condensing species dilute in a carrier gas is examined when the ratio of depositing to carrier species molecular mass is large and the main diffusive transport mechanism is thermal diffusion. It is shown that a deformation of the solid-gas interface induces a deformation of the gas phase isotherms that increases the thermal gradients and thereby the local mass deposition rate at the crests and reduces them at the valleys. The initial surface deformation is enhanced by the modified deposition rates in the absence of appreciable Fick/Brownian diffusion and interfacial energy effects.
Mass Transfer Limited Enhanced Bioremediation at Dnapl Source Zones: a Numerical Study
NASA Astrophysics Data System (ADS)
Kokkinaki, A.; Sleep, B. E.
2011-12-01
The success of enhanced bioremediation of dense non-aqueous phase liquids (DNAPLs) relies on accelerating contaminant mass transfer from the organic to the aqueous phase, thus enhancing the depletion of DNAPL source zones compared to natural dissolution. This is achieved by promoting biological activity that reduces the contaminant's aqueous phase concentration. Although laboratory studies have demonstrated that high reaction rates are attainable by specialized microbial cultures in DNAPL source zones, field applications of the technology report lower reaction rates and prolonged remediation times. One possible explanation for this phenomenon is that the reaction rates are limited by the rate at which the contaminant partitions from the DNAPL to the aqueous phase. In such cases, slow mass transfer to the aqueous phase reduces the bioavailability of the contaminant and consequently decreases the potential source zone depletion enhancement. In this work, the effect of rate limited mass transfer on bio-enhanced dissolution of DNAPL chlorinated ethenes is investigated through a numerical study. A multi-phase, multi-component groundwater transport model is employed to simulate DNAPL mass depletion for a range of source zone scenarios. Rate limited mass transfer is modeled by a linear driving force model, employing a thermodynamic approach for the calculation of the DNAPL - water interfacial area. Metabolic reductive dechlorination is modeled by Monod kinetics, considering microbial growth and self-inhibition. The model was utilized to identify conditions in which mass transfer, rather than reaction, is the limiting process, as indicated by the bioavailability number. In such cases, reaction is slower than expected, and further increase in the reaction rate does not enhance mass depletion. Mass transfer rate limitations were shown to affect both dechlorination and microbial growth kinetics. The complex dynamics between mass transfer, DNAPL transport and distribution, and
Numerical Simulation of Heat and Mass Transfer in an Ejection Apparatus
NASA Astrophysics Data System (ADS)
Kologrivov, M. M.; Buzovskii, V. P.
2016-01-01
The results of numerical simulation of heat and mass transfer in an ejection apparatus during condensation of vapor-gas mixture components on cold brine droplets are presented. The local parameters of working flows were determined by solving a system of differential heat transfer equations with account for the hydrodynamic pattern. Calculations were carried out on the assumption that the liquid spray is directed horizontally. The Stefan formula has been derived with reference to a spherical coordinate system. The results of calculation of heat and mass transfer rates with and without regard for steam condensation jointly with hydrocarbon vapors are compared and analyzed. Estimation of the effect exerted by the apparatus and drip pan walls on the general process of heat and mass transfer was carried out. The results of simulation made it possible to quantitatively estimate the influence of the adopted thickness of the diffusional boundary layer on the vapor-air mixture cooling effect.
Stability of coaxial jets confined in a tube with heat and mass transfer
NASA Astrophysics Data System (ADS)
Mohanta, Lokanath; Cheung, Fan-Bill; Bajorek, Stephen M.
2016-02-01
A linear temporal stability of coaxial confined jets in a vertical tube involving heat and mass transfer at the interface is presented in this paper. A potential flow analysis that includes the effect of viscosity at the interface is performed in analyzing the stability of the system. Film boiling in a vertical tube gives rise to the flow configuration explored in this work. The effects of various non-dimensional parameters on the growth rate and the neutral curve are discussed. The heat transfer at the interface has been characterized by introducing a heat flux ratio between the conduction heat flux and the evaporation heat flux. Viscous forces and the heat and mass transfer at the interface are found to stabilize the flow both in the capillary instability region and Kelvin-Helmholtz instability region. Increasing heat and mass transfer at the interface stabilizes the flow to small as well as very large wave numbers.
Seasonal changes of thermal diffusivity and their effect on heat transfer in soils
NASA Astrophysics Data System (ADS)
Dedecek, Petr; Correia, Antonio; Safanda, Jan; Cermak, Vladimir; Rajver, Dusan; Pechacova, Blanka
2016-04-01
The aim of the work is to describe the effects of seasonal changes of thermal diffusivity (TD) on the thermal regime in shallow subsurface soils. The long term temperature series from observatories at Prague (Czechia), Evora (Portugal) and Malence (Slovenia) were processed by newly improved code which enables a detailed calculation of time changes of TD of the soils. To determine the effect of climate warming of the recent years and to describe the possible effect of TD changes on the temperature-depth profiles, time dependent numerical models were computed. In the case of Evora, the effect of the TD changes on mean annual temperatures was confirmed. This observatory is located on bare sandy surface and TD in the upper soil layer significantly decreases (up to 50%) in summer months. It is due to local climate, which is typical by alternating winter/wet and summer/dry periods. The negative temperature gradient in the depth of 2-5 cm increases with TD decreasing, the coefficient of determination is 0.6 (2012). The TD decreasing during the summer months substitutes the effect of vegetation and controls the heat transfer to the subsurface. The climate in Prague and Malence is typical by rainy/snowy periods during the whole year and effect of TD changes in bare sandy soils is only short-term, or even insignificant under grassy surfaces.
A grey diffusion acceleration method for time-dependent radiative transfer calculations
Nowak, P.F.
1991-07-01
The equations of thermal radiative transfer describe the emission, absorption and transport of photons in a material. As photons travel through the material they are absorbed and re-emitted in a Planckian distribution characterized by the material temperature. As a result of these processes, the material can change resulting in a change in the Planckian emission spectrum. When the coupling between the material and radiation is strong, as occurs when the material opacity or the time step is large, standard iterative techniques converge very slowly. As a result, nested iterative algorithms have been applied to the problem. One algorithm, is to use multifrequency DSA to accelerate the convergence of the multifrequency transport iteration and a grey transport acceleration (GTA) followed by a single group DSA. Here we summarize a new method which uses a grey diffusion equation (GDA) to directly solve the multifrequency transport (S{sub N}) problem. Results of Fourier analysis for both the continuous and discretized equations are discussed and the computational efficiency of GDA is compared with the DSA and GTA nested algorithms. 5 refs., 1 fig., 1 tab.
NASA Astrophysics Data System (ADS)
Masson, J.; Chabrier, G.; Hennebelle, P.; Vaytet, N.; Commerçon, B.
2016-03-01
Angular momentum transport and the formation of rotationally supported structures are major issues in our understanding of protostellar core formation. Whereas purely hydrodynamical simulations lead to large Keplerian disks, ideal magnetohydrodynamics (MHD) models yield the opposite result, with essentially no disk formation. This stems from the flux-freezing condition in ideal MHD, which leads to strong magnetic braking. In this paper, we provide a more accurate description of the evolution of the magnetic flux redistribution by including resistive terms in the MHD equations. We focus more particularly on the effect of ambipolar diffusion on the properties of the first Larson core and its surrounding structure, exploring various initial magnetisations and magnetic field versus rotation axis orientations of a 1 M⊙ collapsing prestellar dense core. We used the non-ideal magnetohydrodynamics version of the adaptive mesh refinement code RAMSES to carry out these calculations. The resistivities required to calculate the ambipolar diffusion terms were computed using a reduced chemical network of charged, neutral, and grain species. Including ambipolar diffusion leads to the formation of a magnetic diffusion barrier (also known as the decoupling stage) in the vicinity of the core, which prevents accumulation of magnetic flux in and around the core and amplification of the field above 0.1 G. The mass and radius of the first Larson core, however, remain similar between ideal and non-ideal MHD models. This diffusion plateau, preventing further amplification of the field and reorganising the field topology, has crucial consequences for magnetic braking processes, allowing the formation of disk structures. Magnetically supported outflows launched in ideal MHD models are weakened or even disappear when using non-ideal MHD. In contrast to ideal MHD calculations, misalignment between the initial rotation axis and the magnetic field direction does not significantly affect the
The Binary Mass Transfer Origin of the Red Blue Straggler Sequence in M30
NASA Astrophysics Data System (ADS)
Xin, Y.; Ferraro, F. R.; Lu, P.; Deng, L.; Lanzoni, B.; Dalessandro, E.; Beccari, G.
2015-03-01
Two separated sequences of blue straggler stars (BSSs) have been revealed by Ferraro et al. in the color-magnitude diagram (CMD) of the Milky Way globular cluster M30. Their presence has been suggested to be related to the two BSS formation channels (namely, collisions and mass transfer in close binaries) operating within the same stellar system. The blue sequence was indeed found to be well reproduced by collisional BSS models. In contrast, no specific models for mass-transfer BSSs were available for an old stellar system like M30. Here we present binary evolution models, including case-B mass transfer and binary merging, specifically calculated for this cluster. We discuss in detail the evolutionary track of a 0.9 + 0.5 M ⊙ binary, which spends approximately 4 Gyr in the BSS region of the CMD of a 13 Gyr old cluster. We also run Monte Carlo simulations to study the distribution of mass-transfer BSSs in the CMD and to compare it with the observational data. Our results show that (1) the color and magnitude distribution of synthetic mass-transfer BSSs defines a strip in the CMD that nicely matches the observed red-BSS sequence, thus providing strong support to the mass-transfer origin for these stars; (2) the CMD distribution of synthetic BSSs never attains the observed location of the blue-BSS sequence, thus reinforcing the hypothesis that the latter formed through a different channel (likely collisions); (3) most (~60%) of the synthetic BSSs are produced by mass-transfer models, while the remaining <40% requires the contribution from merger models.
Flipping the thin film model: Mass transfer by hyporheic exchange in gaining and losing streams
NASA Astrophysics Data System (ADS)
McCluskey, Alexander H.; Grant, Stanley B.; Stewardson, Michael J.
2016-10-01
The exchange of mass between a stream and its hyporheic zone, or "hyporheic exchange," is central to many important ecosystem services. In this paper we show that mass transfer across the streambed by linear mechanisms of hyporheic exchange in a gaining or losing stream can be represented by a thin film model in which (a) the mass transfer coefficient is replaced with the average Darcy flux of water downwelling into the sediment and (b) the driving force for mass transfer is "flipped" from normal to the surface (concentration difference across a boundary layer) to parallel to the surface (concentration difference across downwelling and upwelling zones). Our analysis is consistent with previously published analytical, computational, and experimental studies of hyporheic exchange in the presence of stream-groundwater interactions, and links stream network, advection-dispersion, and stochastic descriptions of solute fate and transport in rivers.
An immersed boundary method for mass transfer across permeable moving interfaces
NASA Astrophysics Data System (ADS)
Gong, Xiaobo; Gong, Zhaoxin; Huang, Huaxiong
2014-12-01
In this paper, we present an immersed boundary method for mass transfer across permeable deformable moving interfaces interacting with the surrounding fluids. One of the key features of our method is the introduction of the mass flux as an independent variable, governed by a non-standard vector transport equation. The flux equation, coupled with the mass transport and the fluid flow equations, allows for a natural implementation of an immersed boundary algorithm when the flux across the interfaces is proportional to the jump in concentration. As an example, the oxygen transfer from red blood cells in a capillary vessel is used to illustrate the applicability of the proposed method. We show that our method is capable of handling multi-physics problems involving fluid-structure interaction with multiple deformable moving interfaces and (interfacial) mass transfer simultaneously.
NASA Astrophysics Data System (ADS)
Zannouni, K.; El Abrach, H.; Dhahri, H.; Mhimid, A.
2016-12-01
The present paper reports a numerical study to investigate the drying of rectangular gypsum sample based on a diffusive model. Both vertical and low sides of the porous media are treated as adiabatic and impermeable surfaces plate. The upper face of the plate represents the permeable interface. The energy equation model is based on the local thermal equilibrium assumption between the fluid and the solid phases. The lattice Boltzmann method (LBM) is used for solving the governing differential equations system. The obtained numerical results concerning the moisture content and the temperature within a gypsum sample were discussed. A comprehensive analysis of the influence of the mass transfer coefficient, the convective heat transfer coefficient, the external temperature, the relative humidity and the diffusion coefficient on macroscopic fields are also investigated. They all presented results in this paper and obtained in the stable regime correspond to time superior than 4000 s. Therefore the numerical error is inferior to 2%. The experimental data and the descriptive information of the approach indicate an excellent agreement between the results of our developed numerical code based on the LBM and the published ones.
Zhang, Chuan; Zhang, Huan; Zhang, Zhiping; Jiao, Youzhou; Zhang, Quanguo
2014-02-05
In this work, effects of mass transfer and light intensity on performance of substrate biodegradation by cell-immobilized photosynthetic bacteria were investigated within an annular fiber-illuminating bioreactor (AFIBR). In AFIBR, stable biofilm of photosynthetic bacteria was generated on the surface of side-glowing optical fiber to provide sufficient light supply and uniform light distribution in cell-immobilized zone for continuous substrate biodegradation during hydrogen production process. To optimize operation parameters for substrate degradation, a two-dimensional mass transfer model based on experimental data to describe coupled processes of substrate transfer and biodegradation in biofilm with substrate diffusion and convection in bulk flow region was proposed. Investigations on influences of substrate concentration, flow rate and light intensity were carried out. It was showed that the optimum operational parameters for the substrate degradation in the AFIBR are: 10g/l substrate concentration, 100ml/h flow rate and 3.1W/m(2) light intensity.
NASA Astrophysics Data System (ADS)
Neculae, Adrian P.; Otte, Andreas; Curticapean, Dan
2013-03-01
In the brain-cell microenvironment, diffusion plays an important role: apart from delivering glucose and oxygen from the vascular system to brain cells, it also moves informational substances between cells. The brain is an extremely complex structure of interwoven, intercommunicating cells, but recent theoretical and experimental works showed that the classical laws of diffusion, cast in the framework of porous media theory, can deliver an accurate quantitative description of the way molecules are transported through this tissue. The mathematical modeling and the numerical simulations are successfully applied in the investigation of diffusion processes in tissues, replacing the costly laboratory investigations. Nevertheless, modeling must rely on highly accurate information regarding the main parameters (tortuosity, volume fraction) which characterize the tissue, obtained by structural and functional imaging. The usual techniques to measure the diffusion mechanism in brain tissue are the radiotracer method, the real time iontophoretic method and integrative optical imaging using fluorescence microscopy. A promising technique for obtaining the values for characteristic parameters of the transport equation is the direct optical investigation using optical fibers. The analysis of these parameters also reveals how the local geometry of the brain changes with time or under pathological conditions. This paper presents a set of computations concerning the mass transport inside the brain tissue, for different types of cells. By measuring the time evolution of the concentration profile of an injected substance and using suitable fitting procedures, the main parameters characterizing the tissue can be determined. This type of analysis could be an important tool in understanding the functional mechanisms of effective drug delivery in complex structures such as the brain tissue. It also offers possibilities to realize optical imaging methods for in vitro and in vivo
Brantley, P S
2006-08-08
The double spherical harmonics angular approximation in the lowest order, i.e. double P{sub 0} (DP{sub 0}), is developed for the solution of time-dependent non-equilibrium grey radiative transfer problems in planar geometry. Although the DP{sub 0} diffusion approximation is expected to be less accurate than the P{sub 1} diffusion approximation at and near thermodynamic equilibrium, the DP{sub 0} angular approximation can more accurately capture the complicated angular dependence near a non-equilibrium radiation wave front. In addition, the DP{sub 0} approximation should be more accurate in non-equilibrium optically thin regions where the positive and negative angular domains are largely decoupled. We develop an adaptive angular technique that locally uses either the DP{sub 0} or P{sub 1} flux-limited diffusion approximation depending on the degree to which the radiation and material fields are in thermodynamic equilibrium. Numerical results are presented for two test problems due to Su and Olson and to Ganapol and Pomraning for which semi-analytic transport solutions exist. These numerical results demonstrate that the adaptive P{sub 1}-DP{sub 0} diffusion approximation can yield improvements in accuracy over the standard P{sub 1} diffusion approximation, both without and with flux-limiting, for non-equilibrium grey radiative transfer.
Brantley, P S
2005-12-13
The double spherical harmonics angular approximation in the lowest order, i.e. double P{sub 0} (DP{sub 0}), is developed for the solution of time-dependent non-equilibrium grey radiative transfer problems in planar geometry. Although the DP{sub 0} diffusion approximation is expected to be less accurate than the P{sub 1} diffusion approximation at and near thermodynamic equilibrium, the DP{sub 0} angular approximation can more accurately capture the complicated angular dependence near a non-equilibrium radiation wave front. In addition, the DP{sub 0} approximation should be more accurate in non-equilibrium optically thin regions where the positive and negative angular domains are largely decoupled. We develop an adaptive angular technique that locally uses either the DP{sub 0} or P{sub 1} flux-limited diffusion approximation depending on the degree to which the radiation and material fields are in thermodynamic equilibrium. Numerical results are presented for two test problems due to Su and Olson and to Ganapol and Pomraning for which semi-analytic transport solutions exist. These numerical results demonstrate that the adaptive P{sub 1}-DP{sub 0} diffusion approximation can yield improvements in accuracy over the standard P{sub 1} diffusion approximation, both without and with flux-limiting, for non-equilibrium grey radiative transfer.
A 17-billion-solar-mass black hole in a group galaxy with a diffuse core.
Thomas, Jens; Ma, Chung-Pei; McConnell, Nicholas J; Greene, Jenny E; Blakeslee, John P; Janish, Ryan
2016-04-21
Quasars are associated with and powered by the accretion of material onto massive black holes; the detection of highly luminous quasars with redshifts greater than z = 6 suggests that black holes of up to ten billion solar masses already existed 13 billion years ago. Two possible present-day 'dormant' descendants of this population of 'active' black holes have been found in the galaxies NGC 3842 and NGC 4889 at the centres of the Leo and Coma galaxy clusters, which together form the central region of the Great Wall--the largest local structure of galaxies. The most luminous quasars, however, are not confined to such high-density regions of the early Universe; yet dormant black holes of this high mass have not yet been found outside of modern-day rich clusters. Here we report observations of the stellar velocity distribution in the galaxy NGC 1600--a relatively isolated elliptical galaxy near the centre of a galaxy group at a distance of 64 megaparsecs from Earth. We use orbit superposition models to determine that the black hole at the centre of NGC 1600 has a mass of 17 billion solar masses. The spatial distribution of stars near the centre of NGC 1600 is rather diffuse. We find that the region of depleted stellar density in the cores of massive elliptical galaxies extends over the same radius as the gravitational sphere of influence of the central black holes, and interpret this as the dynamical imprint of the black holes.
Volumetric vs Mass Velocity in Analyzing Convective-Diffusive Transport Processes in Liquids
NASA Astrophysics Data System (ADS)
Brenner, Howard
2000-11-01
Because mass rather than volume is preserved in fluid-mechanical problems involving density changes, a natural predilection exists for quantifying convective-diffusive transport phenomena in terms of a velocity field based upon mass, rather than volume. Indeed, in the classic BSL "Transport Phenomena" textbook, but a single reference exists even to the very concept of a volume velocity, and even then it is relegated to a homework assignment. However, especially when dealing with transport in fluids in which the mass density of the conserved property being transported (e.g., chemical species, internal energy, etc.) is independent of the prevailing pressure, as is largely true in the case of liquids, overwhelming advantages exist is preferring the volume velocity over the more ubiquitous and classical mass velocity. In a generalization of ideas pioneered by D. D. Joseph and co-workers, we outline the reasons for this volumetric velocity preference in a broad general context by identifying a large class of physical problems whose solutions are rendered more accessible by exploiting this unconventional velocity choice.
Orbital Evolution of Mass-transferring Eccentric Binary Systems. I. Phase-dependent Evolution
NASA Astrophysics Data System (ADS)
Dosopoulou, Fani; Kalogera, Vicky
2016-07-01
Observations reveal that mass-transferring binary systems may have non-zero orbital eccentricities. The time evolution of the orbital semimajor axis and eccentricity of mass-transferring eccentric binary systems is an important part of binary evolution theory and has been widely studied. However, various different approaches to and assumptions on the subject have made the literature difficult to comprehend and comparisons between different orbital element time evolution equations not easy to make. Consequently, no self-consistent treatment of this phase has ever been included in binary population synthesis codes. In this paper, we present a general formalism to derive the time evolution equations of the binary orbital elements, treating mass loss and mass transfer as perturbations of the general two-body problem. We present the self-consistent form of the perturbing acceleration and phase-dependent time evolution equations for the orbital elements under different mass loss/transfer processes. First, we study the cases of isotropic and anisotropic wind mass loss. Then, we proceed with non-isotropic ejection and accretion in a conservative as well as a non-conservative manner for both point masses and extended bodies. We compare the derived equations with similar work in the literature and explain the existing discrepancies.
Effect of electric fields on mass transfer to droplets. Final report
Carleson, T.E.; Budwig, R.
1994-02-01
During the six year funding period, the effects of a direct and alternating field upon single drop hydrodynamics and mass transfer were evaluated both experimentally and theoretically. Direct current field effects upon drop size, velocity and mass transfer rates were also observed for multiple drops formed in a three stage sieve tray column. Drop size, velocity, and mass transfer rates were measured experimentally and compared to simple models for direct current electric fields. Agreement between theory and experiment was found for drop charge, size, and velocity. Drop mass transfer coefficients were substantially larger than theoretical predictions while extraction efficiencies were moderately higher. Drop distortion and oscillation were observed and are thought to result in the experimentally observed higher values. For alternating current fields, drop flow streamlines and oscillations were measured and found to compare well with predictions from a solved mathematical model. In addition, equipment was constructed to determine mass transfer rates to oscillating drops. Concentration profiles in still and oscillating drops were measured and qualitatively compared to theoretical predictions.
The Momentum Transfer and Target Mass Dependence of the
NASA Astrophysics Data System (ADS)
Boberg, Paul Richard
In order to study some of the exclusive structure and reaction dynamics in the quasi elastic region, (e,e ^' p) measurements on ^{12}C and ^{63 }Cu were performed. These measurements attempt to isolate the nuclear reaction mechanism contribution from the off shell e-p cross section. We performed measurements at five three-momentum transfer |vec {rm q}| for each target, varying |vec{rm q} | by changing the electron scattering angle theta_{rm e^' }. The measurements were performed at the MIT -Bates Linear Accelerator Center. The measurements were compared with Impulse Approximation (IA) predictions, providing quantitative tests of the approximations involved. The measurements for the p-shells were emphasized: the ^{12}C 1p-shell and the ^{63}Cu 2p-shell. For both targets, missing energy spectra were extract up to 50 MeV. The data from the second major shell regions, the ^{12}C s-shell and the ^{63}Cu f-s shell, were also compared with IA predictions. Finally, the ^{12}C results were compared with existing ^{12}C(e,e ^' p) results.
Modeling of turbulence effects on the heat and mass transfer of evaporating sprays
NASA Astrophysics Data System (ADS)
Madhanabharatam, Balasubramanyam
A large diversity of two-phase gas-liquid flows of both scientific and practical interest involves the evaporation of near spherical liquid droplets in high temperature turbulent environments. Current numerical modeling approaches are predominantly focused towards the effects of continuous phase (gas phase) turbulence on the evaporation rates of liquid fuel sprays during the evaporation process, failing to account for the inherent turbulence present in the dispersed phase (liquid phase), due to the injection of sprays at high velocities. Existing models accounting for internal turbulence effects use Direct Numerical Simulations and Large Eddy Simulations that are computationally intensive. This research provides an alternative phenomenological approach of modeling droplet internal turbulence effects through the mass and heat transfer between the droplet surface and the external gas phase within a thin film inside the droplet. This finite conductivity (F-C) model was based on the two-temperature film theory, where the turbulence characteristics of the droplet are used to estimate the effective thermal diffusivity (alphaeff) within the droplet phase. The alphaeff is estimated from the physical properties of the flow within the droplet rather than from a 'curve-fit' as done conventionally. The results of the one-way coupled study indicated that the equilibrium drop temperature predictions were higher than calculations by the infinite conductivity (I-C) model. The liquid internal turbulence has a considerable effect on the diffusivity in the primary atomization regime. The thermal boundary layer was found to be substantially thick initially, decreasing quickly to a small value, exhibiting a reasonable physical trend. The two-way coupled studies (CFD) indicated that the F-C model, slowed down the evaporation process, produced larger droplets and longer tip penetration lengths during the initial stages of injection. For a jet in a supersonic cross-flow, results indicated
Intraparticle heat and mass transfer characteristics of silica-gel/water vapor adsorption
Yamamoto, Eri; Watanabe, Fujio; Hasatani, Masanobu
1999-07-01
Recently, highly efficient energy utilization systems which extensively employ adsorption phenomena such as pressure swing adsorption, heat storage, adsorption heat pump, etc. are being regarded as one of the countermeasures for environmental issues such as green house effect and ozone layer destruction. An Adsorption Heat Pump (AHP) has been investigated as one of the important techniques via which cold heat energy is obtained from waste thermal energy below 373K without using electricity and CFCs. An AHP normally consists of an adsorber and an evaporator/condenser and cold heat energy is generated by latent heat of evaporation during adsorption process. For realizing the AHP technology, it has been pointed out that the development of an adsorber with optimum heat and mass transfer characteristics is essentially important. In this study, experimental studies were carried out which was based on the data of temperature inside the adsorbent particle and adsorptivity profiles at the adsorption/desorption process by volumetric method. To clarify adsorption mechanism relatively large silica-gel particle (7 mm f) was used. Temperature distribution in the particle is determined at the center, at one half radius in the radial direction and at the surface by using very thin (30 mm f) thermocouples. The temperatures at these points simultaneously increase/decrease as soon as the adsorption/desorption started, reached their respective maximum/minimum values and then return to initial temperature. The temperature profiles for the adsorption process show that the temperature at the surface is initially slightly higher than the other two points. All three points reached their respective maximum temperature at the same time with the temperature at the center point the highest and at the surface the lowest. The temperature profiles during the desorptive process are almost exactly the opposite to that of the adsorption process. This shows that the adsorption phenomena can take
Mass-transfer limitations for nitrate removal in a uranium-contaminated aquifer.
Luo, Jian; Cirpka, Olaf A; Wu, Weimin; Fienen, Michael N; Jardine, Philip M; Mehlhorn, Tonia L; Watson, David B; Criddle, Craig S; Kitanidis, Peter K
2005-11-01
A field test on in situ subsurface bioremediation of uranium(VI) is underway at the Y-12 National Security Complex in the Oak Ridge Reservation, Oak Ridge, TN. Nitrate has a high concentration at the site, which prevents U(VI) reduction, and thus must be removed. An acidic-flush strategy for nitrate removal was proposed to create a treatment zone with low levels of accessible nitrate. The subsurface at the site contains highly interconnected fractures surrounded by matrix blocks of low permeability and high porosity and is therefore subject to preferential flow and matrix diffusion. To identify the heterogeneous mass transfer properties, we performed a novel forced-gradient tracer test, which involved the addition of bromide, the displacement of nitrate, and the rebound of nitrate after completion of pumping. The simplest conceptualization consistent with the data is that the pore-space consists of a single mobile domain, as well as a fast and a slowly reacting immobile domain. The slowly reacting immobile domain (shale matrix) constitutes over 80% of the pore volume and acts as a long-term reservoir of nitrate. According to simulations, the nitrate stored in the slowly interacting immobile domain in the fast flow layer, at depths of about 12.2-13.7 m, will be reduced by an order of magnitude over a period of about a year. By contrast, the mobile domain rapidly responds to flushing, and a low average nitrate concentration can be maintained if the nitrate is removed as soon as it enters the mobile domain. A field-scale experiment in which the aquifer was flushed with acidic solution confirmed our understanding of the system. For the ongoing experiments on microbial U(VI) reduction, nitrate concentrations must be low in the mobile domain to ensure U(VI) reducing conditions. We therefore conclude that the nitrate leaching out of the immobile pore space must continuously be removed by in situ denitrification to maintain favorable conditions.
A NUMERICAL METHOD FOR STUDYING SUPER-EDDINGTON MASS TRANSFER IN DOUBLE WHITE DWARF BINARIES
Marcello, Dominic C.; Tohline, Joel E. E-mail: tohline@phys.lsu.edu
2012-04-01
We present a numerical method for the study of double white dwarf (DWD) binary systems at the onset of super-Eddington mass transfer. We incorporate the physics of ideal inviscid hydrodynamical flow, Newtonian self-gravity, and radiation transport on a three-dimensional uniformly rotating cylindrical Eulerian grid. Care has been taken to conserve the key physical quantities such as angular momentum and energy. Our new method conserves total energy to a higher degree of accuracy than other codes that are presently being used to model mass transfer in DWD systems. We present the results of verification tests and simulate the first 20 + orbits of a binary system of mass ratio q 0.7 at the onset of dynamically unstable direct impact mass transfer. The mass transfer rate quickly exceeds the critical Eddington limit by many orders of magnitude, and thus we are unable to model a trans-Eddington phase. It appears that radiation pressure does not significantly affect the accretion flow in the highly super-Eddington regime. An optically thick common envelope forms around the binary within a few orbits. Although this envelope quickly exceeds the spatial domain of the computational grid, the fraction of the common envelope that exceeds zero gravitational binding energy is extremely small, suggesting that radiation-driven mass loss is insignificant in this regime. It remains to be seen whether simulations that capture the trans-Eddington phase of such flows will lead to the same conclusion or show that substantial material gets expelled.
Neff, Diane; Simons, Jack
2010-01-28
Earlier work from this group has suggested that, in electron capture and electron-transfer mass spectrometry experiments on positively charged gas-phase samples of polypeptides, the initial electron attachment event most likely occurs at one of the peptide's positively charged sites (e.g., protonated side chains), although electron attachment can occur at a disulfide or amide site ca. 1-10% of the time. Focusing on the 90-99% dominant channel in which initial electron attachment occurs at a positive site, this paper addresses to what extent and over what distances electron transfer can take place from a positively charged site to a disulfide sigma* or amide pi* orbital, because it is thought that it is through such orbitals that disulfide or N-C(alpha) backbone bond cleavage occurs. Ab initio electronic structure calculations show that, as long as an SS sigma* (or OCN pi*) orbital experiences sufficient Coulomb stabilization from proximal positively charged groups, there are a myriad of excited Rydberg states located on positive sites that are able to induce such intrapeptide electron transfer. Computational data show that the transfer rates decay exponentially with distance for a given Rydberg orbital. An analytical model is developed that allows us to estimate the rates of Rydberg-to-valence and Rydberg-to-Rydberg electron transfers as functions of the Rydberg orbitals' n quantum numbers. This model suggests that transfer can occur over very long distances at rates that are more than competitive with the rates of radiationless relaxation within the manifold of Rydberg states (the latter processes eventually terminate the electron-transfer process an thus the disulfide or N-C(alpha) bond cleavages), and it gives formulas for how these rates depend on n (and thus the radial span of the Rydberg orbitals).
Hustedt, E J; Beth, A H
2001-12-01
Computational methods have been developed to model the effects of constrained or restricted amplitude uniaxial rotational diffusion (URD) on saturation transfer electron paramagnetic resonance (ST-EPR) signals observed from nitroxide spin labels. These methods, which have been developed to model the global rotational motion of intrinsic membrane proteins that can interact with the cytoskeleton or other peripheral proteins, are an extension of previous work that described computationally efficient algorithms for calculating ST-EPR spectra for unconstrained URD (Hustedt and Beth, 1995, Biophys. J. 69:1409-1423). Calculations are presented that demonstrate the dependence of the ST-EPR signal (V'(2)) on the width (Delta) of a square-well potential as a function of the microwave frequency, the correlation time for URD, and the orientation of the spin-label with respect to the URD axis. At a correlation time of 10 micros, the V'(2) signal is very sensitive to Delta in the range from 0 to 60 degrees, marginally sensitive from 60 degrees to 90 degrees, and insensitive beyond 90 degrees. Sensitivity to Delta depends on the correlation time for URD with higher sensitivity to large values of Delta at the shorter correlation times, on the microwave frequency, and on the orientation of the spin-label relative to the URD axis. The computational algorithm has been incorporated into a global nonlinear least-squares analysis approach, based upon the Marquardt-Levenberg method (Blackman et al., 2001, Biophys. J. 81:3363-3376). This has permitted determination of the correlation time for URD and the width of the square-well potential by automated fitting of experimental ST-EPR data sets obtained from a spin-labeled membrane protein and provided a new automated method for analysis of data obtained from any system that exhibits restricted amplitude URD.
Effect of impeller geometry on gas-liquid mass transfer coefficients in filamentous suspensions.
Dronawat, S N; Svihla, C K; Hanley, T R
1997-01-01
Volumetric gas-liquid mass transfer coefficients were measured in suspensions of cellulose fibers with concentrations ranging from 0 to 20 g/L. The mass transfer coefficients were measured using the dynamic method. Results are presented for three different combinations of impellers at a variety of gassing rates and agitation speeds. Rheological properties of the cellulose fibers were also measured using the impeller viscometer method. Tests were conducted in a 20 L stirred-tank fermentor and in 65 L tank with a height to diameter ratio of 3:1. Power consumption was measured in both vessels. At low agitation rates, two Rushton turbines gave 20% better performance than the Rushton and hydrofoil combination and 40% better performance than the Rushton and propeller combination for oxygen transfer. At higher agitation rates, the Rushton and hydrofoil combination gave 14 and 25% better performance for oxygen transfer than two Rushton turbines and the Rushton and hydrofoil combination, respectively.
Distribution and mass transfer of dissolved oxygen in a multi-habitat membrane bioreactor.
Tang, Bing; Qiu, Bing; Huang, Shaosong; Yang, Kanghua; Bin, Liying; Fu, Fenglian; Yang, Huiwen
2015-04-01
This work investigated the DO distribution and the factors influencing the mass transfer of DO in a multi-habitat membrane bioreactor. Through the continuous measurements of an on-line automatic system, the timely DO values at different zones in the bioreactor were obtained, which gave a detailed description to the distribution of oxygen within the bioreactor. The results indicated that the growth of biomass had an important influence on the distribution of oxygen. As the extension of operational time, the volumetric oxygen mass transfer coefficient (kLa) was generally decreased. With the difference in DO values, a complex environment combining anoxic and oxic state was produced within a single bioreactor, which provided a fundamental guarantee for the total removal of TN. Aeration rate, the concentration and apparent viscosity of MLSS have different influences on kLa, but adjusting the viscosity is a feasible method to improve the mass transfer of oxygen in the bioreactor.
Temperature-difference-driven mass transfer through the vapor from a cold to a warm liquid.
Struchtrup, Henning; Kjelstrup, Signe; Bedeaux, Dick
2012-06-01
Irreversible thermodynamics provides interface conditions that yield temperature and chemical potential jumps at phase boundaries. The interfacial jumps allow unexpected transport phenomena, such as the inverted temperature profile [Pao, Phys. Fluids 14, 306 (1971)] and mass transfer from a cold to a warm liquid driven by a temperature difference across the vapor phase [Mills and Phillips, Chem. Phys. Lett. 372, 615 (2002)]. Careful evaluation of the thermodynamic laws has shown [Bedeaux et al., Physica A 169, 263 (1990)] that the inverted temperature profile is observed for processes with a high heat of vaporization. In this paper, we show that cold to warm mass transfer through the vapor from a cold to a warm liquid is only possible when the heat of evaporation is sufficiently small. A necessary criterium for the size of the mass transfer coefficient is given.
Occupational hot exposures: a review of heat and mass transfer theory.
Galbraith, G H; McLean, R C; Stewart, D
1989-01-01
The assessment and control of hot working environments is based on an appraisal of the thermal interaction between an individual and the surroundings. This paper examines in detail the processes of convection, radiation and evaporation which constitute the principal mechanisms for this interaction. The defining equations are discussed with particular attention given to the appropriate numerical values of body heat and mass transfer coefficients. The use of the heat-mass transfer analogy for the prediction of the mass transfer coefficient is introduced and verified. Finally, recommendations are given as to the most appropriate set of energy exchange equations for use in the analysis of high-temperature environments. The physiological criteria involved in hot working conditions, and the generation of a suitable assessment procedure based on the energy exchange equations, are the subject of a companion paper.
Evaporation in relation to CO 2 concentration: Analysis of mass transfer coefficient
NASA Astrophysics Data System (ADS)
Ojha, C. S. P.; Yasuda, Hiroshi; Rao, Surampalli; Abd Elbasit, Mohamed A. M.; Kumar, Manoj
2011-11-01
In this study, the potential of mass transfer approach in estimating evaporation changes under different CO 2 levels are evaluated using data from controlled chamber experiments in which radiation and wind velocity were kept constant and temperature and relative humidity profiles were varied in different patterns along with CO 2 concentration. Currently, FAO procedure lists three approaches to compute air vapour pressure based on temperature and relative humidity profiles. In this study, the impact of using different procedures of estimating air vapour pressure is examined to assess the use of mass transfer approach for estimating evaporation. To achieve this, a part of the data is used to calibrate mass transfer coefficient which is subsequently used to project evaporation for future states. Accordingly, strategies are ranked for their potential in estimating evaporation. The effect of evaporation rate is compared at 400 ppm and 600 ppm CO 2 level. It has been observed that the evaporation rate is more pronounced at higher CO 2 level.
A Novel Model for the Mass Transfer of Articular Cartilage: Rolling Depression Load Device
NASA Astrophysics Data System (ADS)
Fan, Zhenmin; Zhang, Chunqiu; Liu, Haiying; Xu, Baoshan; Li, Jiang; Gao, Lilan
The mass transfer is one of important aspects to maintain the physiological activity proper of tissue, specially, cartilage cannot run without mechanical environment. The mechanical condition drives nutrition in and waste out in the cartilage tissue, the change of this process plays a key role for biological activity. Researchers used to adopt compression to study the mass transfer in cartilage, here we firstly establish a new rolling depression load (RDL) device, and also put this device into practice. The device divided into rolling control system and the compression adjusting mechanism. The rolling control system makes sure the pure rolling and uniform speed of roller applying towards cultured tissue. The compression adjusting mechanism can realize different compressive magnitudes and uniform compression. Preliminary test showed that rolling depression load indeed enhances the process of mass transfer articular cartilage.
Stagnation point flow and mass transfer with chemical reaction past a stretching/shrinking cylinder.
Najib, Najwa; Bachok, Norfifah; Arifin, Norihan Md; Ishak, Anuar
2014-02-26
This paper is about the stagnation point flow and mass transfer with chemical reaction past a stretching/shrinking cylinder. The governing partial differential equations in cylindrical form are transformed into ordinary differential equations by a similarity transformation. The transformed equations are solved numerically using a shooting method. Results for the skin friction coefficient, Schmidt number, velocity profiles as well as concentration profiles are presented for different values of the governing parameters. Effects of the curvature parameter, stretching/shrinking parameter and Schmidt number on the flow and mass transfer characteristics are examined. The study indicates that dual solutions exist for the shrinking cylinder but for the stretching cylinder, the solution is unique. It is observed that the surface shear stress and the mass transfer rate at the surface increase as the curvature parameter increases.
Effect of Reynolds number on flow and mass transfer characteristics of a 90 degree elbow
NASA Astrophysics Data System (ADS)
Fujisawa, Nobuyuki; Ikarashi, Yuya; Yamagata, Takayuki; Taguchi, Syoichi
2016-11-01
The flow and mass transfer characteristics of a 90 degree elbow was studied experimentally by using the mass transfer measurement by plaster dissolution method, the surface flow visualization by oil film method and stereo PIV measurement. The experiments are carried out in a water tunnel of a circular pipe of 56mm in diameter with a working fluid of water. The Reynolds number was varied from 30000 to 200000. The experimental result indicated the change of the mass transfer coefficient distribution in the elbow with increasing the Reynolds number. This phenomenon is further examined by the surface flow visualization and measurement of secondary flow pattern in the elbow, and the results showed the suggested change of the secondary flow pattern in the elbow with increasing the Reynolds numbers.
NASA Astrophysics Data System (ADS)
Hollenbeck, K. J.; Harvey, C. F.; Haggerty, R.; Werth, C. J.
1999-04-01
Mass transfer between aquifer material and groundwater is often modeled as first-order rate-limited sorption or diffusive exchange between mobile zones and immobile zones with idealized geometries. Recent improvements in experimental techniques and advances in our understanding of pore-scale heterogeneity demonstrate that two (or even a few) rate coefficients are insufficient in many cases. Here, we investigate a piece-wise linear model for a continuous distribution of rate coefficients, that has several advantages over previously used `statistical' distribution models (with functional form from gamma or lognormal PDF's): (1) distributions of arbitrary, even bimodal, shapes can be represented; (2) linear estimation methods can be applied to determine the distribution from experimental data; (3) the uncertainty in the distribution can be determined for each of its sections; and (4) the relationship between the time scales of available data and those of estimatable mass transfer processes can be investigated. A statistical model refinement algorithm is presented that reduces the number of parameters (sections of the piece-wise linear model) to the admissible minimum. We show that purging experiments allow estimation of a wider zone of the rate distribution than do batch experiments, and hence will provide predictions that are accurate over a wider range of time scales. Finally, in an application to TCE gas-purging desorption data, the piece-wise linear rate-distribution model has a higher probability of being adequate than those using a gamma or lognormal distribution or a single rate coefficient.
Racault, Y; Stricker, A-E; Husson, A; Gillot, S
2011-01-01
Oxygen transfer in biological wastewater treatment processes with high sludge concentration, such as membrane bioreactor (MBR), is an important issue. The variation of alpha-factor versus mixed liquor suspended solids (MLSS) concentration was investigated in a full scale MBR plant under process conditions, using mass balances. Exhaustive data from the Supervisory Control And Data Acquisition (SCADA) and from additional online sensors (COD, DO, MLSS) were used to calculate the daily oxygen consumption (OC) using a non-steady state mass balance for COD and total N on a 24-h basis. To close the oxygen balance, OC has to match the total oxygen transfer rate (OTRtot) of the system, which is provided by fine bubble (FB) diffusers in the aeration tank and coarse bubbles (CB) in separate membrane tanks. First assessing OTR(CB) then closing the balance OC = OTRtot allowed to calculate OTR(FB) and to fit an exponential relationship between OTR(FB) and MLSS. A comparison of the alpha-factor obtained by this balance method and by direct measurements with the off-gas method on the same plant is presented and discussed.
Hay, Michael B.; Stoliker, Deborah L.; Davis, James A.; Zachara, John M.
2011-01-01
Although "intragranular" pore space within grain aggregates, grain fractures, and mineral surface coatings may contain a relatively small fraction of the total porosity within a porous medium, it often contains a significant fraction of the reactive surface area, and can thus strongly affect the transport of sorbing solutes. In this work, we demonstrate a batch experiment procedure using tritiated water as a high-resolution diffusive tracer to characterize the intragranular pore space. The method was tested using uranium-contaminated sediments from the vadose and capillary fringe zones beneath the former 300A process ponds at the Hanford site (Washington). Sediments were contacted with tracers in artificial groundwater, followed by a replacement of bulk solution with tracer-free groundwater and the monitoring of tracer release. From these data, intragranular pore volumes were calculated and mass transfer rates were quantified using a multirate first-order mass transfer model. Tritium-hydrogen exchange on surface hydroxyls was accounted for by conducting additional tracer experiments on sediment that was vacuum dried after reaction. The complementary ("wet" and "dry") techniques allowed for the simultaneous determination of intragranular porosity and surface area using tritium. The Hanford 300A samples exhibited intragranular pore volumes of ~1% of the solid volume and intragranular surface areas of ~20%–35% of the total surface area. Analogous experiments using bromide ion as a tracer yielded very different results, suggesting very little penetration of bromide into the intragranular porosity.
Hay, M.B.; Stoliker, D.L.; Davis, J.A.; Zachara, J.M.
2011-01-01
Although "intragranular" pore space within grain aggregates, grain fractures, and mineral surface coatings may contain a relatively small fraction of the total porosity within a porous medium, it often contains a significant fraction of the reactive surface area, and can thus strongly affect the transport of sorbing solutes. In this work, we demonstrate a batch experiment procedure using tritiated water as a high-resolution diffusive tracer to characterize the intragranular pore space. The method was tested using uranium-contaminated sediments from the vadose and capillary fringe zones beneath the former 300A process ponds at the Hanford site (Washington). Sediments were contacted with tracers in artificial groundwater, followed by a replacement of bulk solution with tracer-free groundwater and the monitoring of tracer release. From these data, intragranular pore volumes were calculated and mass transfer rates were quantified using a multirate first-order mass transfer model. Tritium-hydrogen exchange on surface hydroxyls was accounted for by conducting additional tracer experiments on sediment that was vacuum dried after reaction. The complementary ("wet" and "dry") techniques allowed for the simultaneous determination of intragranular porosity and surface area using tritium. The Hanford 300A samples exhibited intragranular pore volumes of ???1% of the solid volume and intragranular surface areas of ???20%-35% of the total surface area. Analogous experiments using bromide ion as a tracer yielded very different results, suggesting very little penetration of bromide into the intragranular porosity. Copyright 2011 by the American Geophysical Union.
Cheung, M C; Wolfbauer, G; Albers, J J
1996-09-27
Human plasma phospholipid transfer protein (PLTP) has been shown to facilitate the transfer of phospholipid from liposomes or isolated very low and low density lipoproteins to high density lipoproteins. Its activity in plasma and its physiological function are presently unknown. To elucidate the role of PLTP in lipoprotein metabolism and to delineate factors that may affect the rate of phospholipid transfer between lipoproteins, we determined the plasma phospholipid mass transfer rate (PLTR) in 16 healthy adult volunteers and assessed its relationship to plasma lipid levels, and to phospholipid transfer activity (PLTA) and cholesteryl ester transfer activity (CETA) measured by radioassays. The plasma PLTR in these subjects was 27.2 +/- 11.8 nmol/ml per h at 37 degrees C (mean +/- S.D.), and their PLTA and CETA were 13.0 +/- 1.7 mumol/ml per h and 72.8 +/- 15.7 nmol/ml per h, respectively. Plasma PLTR was correlated directly with total, non-HDL, and HDL triglyceride (rs = 0.76, P < 0.001), total and non-HDL phospholipid (rs > 0.53, P < 0.05), and inversely with HDL free cholesterol (rs = -0.54, P < 0.05), but not with plasma PLTA and CETA. When 85% to 96% of the PLTA in plasma was removed by polyclonal antibodies against recombinant human PLTP, phospholipid mass transfer from VLDL and LDL to HDL was reduced by 50% to 72%, but 80% to 100% of CETA could still be detected. These studies demonstrate that PLTP plays a major role in facilitating the transfer of phospholipid between lipoproteins, and suggest that triglyceride is a significant modulator of intravascular phospholipid transport. Furthermore, most of the PLTP and CETP in human plasma is associated with different particles. Plasma PLTA and CETA were also measured in mouse, rat, hamster, guinea pig, rabbit, dog, pig, and monkey. Compared to human, PLTA in rat and mouse was significantly higher and in rabbit and guinea pig was significantly lower while the remaining animal species had PLTA similar to humans. No
NASA Astrophysics Data System (ADS)
Ohmori, Hiroko; Iwai, Hiroshi
2015-07-01
A time-dependent 2-D numerical simulation was performed on a solid oxide iron-air battery (SOIAB) to reveal the fundamental characteristics of this new system. The SOIAB is a rechargeable battery consisting of a solid oxide electrochemical cell (SOEC) and iron as a redox metal. A simple battery configuration was employed assuming a system with a small capacity. A simulation model for a unit element was developed considering heat and mass transfer in the system, taking both electrochemical and redox reactions into account. The numerical results showed the spatial and temporal changes in the temperature field in the charge and discharge operations, which were due to the combined effects of heat generation/absorption by the electrochemical and redox reactions and heat exchange with the air supplied through convective heat transfer. As the reaction rates are functions of the local temperature, the predicted results show the importance of considering the heat transfer phenomena in this system. It was also found that the active reaction region in the redox metal evolves with time. The nonuniform distribution of iron utilization is affected by the effective gas diffusion coefficients in the porous redox metal, and consequently the change in the current density distribution in the SOEC.
NASA Astrophysics Data System (ADS)
Viesca, R. C.
2015-12-01
Subsurface fluid injection is often followed by observations of an enlarging cloud of microseismicity. The cloud's diffusive growth is thought to be a direct response to the diffusion of elevated pore fluid pressure reaching pre-stressed faults, triggering small instabilities; the observed high rates of this growth are interpreted to reflect a relatively high permeability of a fractured subsurface [e.g., Shapiro, GJI 1997]. We investigate an alternative mechanism for growing a microseismic cloud: the elastic transfer of stress due to slow, aseismic slip on a subset of the pre-existing faults in this damaged subsurface. We show that the growth of the slipping region of the fault may be self-similar in a diffusive manner. While this slip is driven by fluid injection, we show that, for critically stressed faults, the apparent diffusion of this slow slip may quickly exceed the poroelastically driven diffusion of the elevated pore fluid pressure. Under these conditions, microseismicity can be first triggered by the off-fault stress perturbation due to the expanding region of slip on principal faults. This provides an alternative interpretation of diffusive growth rates in terms of the subsurface stress state rather than an enhanced hydraulic diffusivity. That such aseismic slip may occur, outpace fluid diffusion, and in turn trigger microseismic events, is also suggested by on- and near-fault observations in past and recently reported fluid injection experiments [e.g., Cornet et al., PAGEOPH 1997; Guglielmi et al., Science 2015]. The model of injection-induced slip assumes elastic off-fault behavior and a fault strength determined by the product of a constant friction coefficient and the local effective normal stress. The sliding region is enlarged by the pore pressure increase resolved on the fault plane. Remarkably, the rate of self-similar expansion may be determined by a single parameter reflecting both the initial stress state and the magnitude of the pore pressure
NASA Astrophysics Data System (ADS)
Jin, Shi; Lu, Hanqing
2017-04-01
In this paper, we develop an Asymptotic-Preserving (AP) stochastic Galerkin scheme for the radiative heat transfer equations with random inputs and diffusive scalings. In this problem the random inputs arise due to uncertainties in cross section, initial data or boundary data. We use the generalized polynomial chaos based stochastic Galerkin (gPC-SG) method, which is combined with the micro-macro decomposition based deterministic AP framework in order to handle efficiently the diffusive regime. For linearized problem we prove the regularity of the solution in the random space and consequently the spectral accuracy of the gPC-SG method. We also prove the uniform (in the mean free path) linear stability for the space-time discretizations. Several numerical tests are presented to show the efficiency and accuracy of proposed scheme, especially in the diffusive regime.
NASA Astrophysics Data System (ADS)
Fujii, Hiroyuki; Okawa, Shinpei; Yamada, Yukio; Hoshi, Yoko
2014-11-01
Numerical modeling of light propagation in random media has been an important issue for biomedical imaging, including diffuse optical tomography (DOT). For high resolution DOT, accurate and fast computation of light propagation in biological tissue is desirable. This paper proposes a space-time hybrid model for numerical modeling based on the radiative transfer and diffusion equations (RTE and DE, respectively) in random media under refractive-index mismatching. In the proposed model, the RTE and DE regions are separated into space and time by using a crossover length and the time from the ballistic regime to the diffusive regime, ρDA 10 / μt‧ and tDA 20 / v μt‧ where μt‧ and v represent a reduced transport coefficient and light velocity, respectively. The present model succeeds in describing light propagation accurately and reduces computational load by a quarter compared with full computation of the RTE.
Mass and momentum transfer across solid-fluid boundaries in the lattice-Boltzmann method.
Yin, Xuewen; Le, Guigao; Zhang, Junfeng
2012-08-01
Mass conservation and momentum transfer across solid-fluid boundaries have been active topics through the development of the lattice-Boltzmann method. In this paper, we review typical treatments to prevent net mass transfer across solid-fluid boundaries in the lattice-Boltzmann method, and argue that such efforts are in general not necessary and could lead to incorrect results. Carefully designed simulations are conducted to examine the effects of normal boundary movement, tangential density gradient, and lattice grid resolution. Our simulation results show that the global mass conservation can be well satisfied even with local unbalanced mass transfer at boundary nodes, while a local mass conservation constraint can produce incorrect flow and pressure fields. These simulations suggest that local mass conservation, at either a fluid or solid boundary node, is not only an unnecessary consequence to maintain the global mass conservation, but also harmful for meaningful simulation results. In addition, the concern on the momentum addition and reduction associated with status-changing nodes is also not technically necessary. Although including this momentum addition or reduction has no direct influence on flow and pressure fields, the incorrect fluid-particle interaction may affect simulation results of particulate suspensions.
Mass transfer studies of Geobacter sulfurreducens biofilms on rotating disk electrodes.
Babauta, Jerome T; Beyenal, Haluk
2014-02-01
Electrochemical impedance spectroscopy has received significant attention recently as a method to measure electrochemical parameters of Geobacter sulfurreducens biofilms. Here, we use electrochemical impedance spectroscopy to demonstrate the effect of mass transfer processes on electron transfer by G. sulfurreducens biofilms grown in situ on an electrode that was subsequently rotated. By rotating the biofilms up to 530 rpm, we could control the microscale gradients formed inside G. sulfurreducens biofilms. A 24% increase above a baseline of 82 µA could be achieved with a rotation rate of 530 rpm. By comparison, we observed a 340% increase using a soluble redox mediator (ferrocyanide) limited by mass transfer. Control of mass transfer processes was also used to quantify the change in biofilm impedance during the transition from turnover to non-turnover. We found that only one element of the biofilm impedance, the interfacial resistance, changed significantly from 900 to 4,200 Ω under turnover and non-turnover conditions, respectively. We ascribed this change to the electron transfer resistance overcome by the biofilm metabolism and estimate this value as 3,300 Ω. Additionally, under non-turnover, the biofilm impedance developed pseudocapacitive behavior indicative of bound redox mediators. Pseudocapacitance of the biofilm was estimated at 740 µF and was unresponsive to rotation of the electrode. The increase in electron transfer resistance and pseudocapacitive behavior under non-turnover could be used as indicators of acetate limitations inside G. sulfurreducens biofilms.
Solis, Kyle Jameson; Martin, James E.
2012-11-01
Isothermal magnetic advection is a recently discovered method of inducing highly organized, non-contact flow lattices in suspensions of magnetic particles, using only uniform ac magnetic fields of modest strength. The initiation of these vigorous flows requires neither a thermal gradient nor a gravitational field and so can be used to transfer heat and mass in circumstances where natural convection does not occur. These advection lattices are comprised of a square lattice of antiparallel flow columns. If the column spacing is sufficiently large compared to the column length, and the flow rate within the columns is sufficiently large, then one wouldmore » expect efficient transfer of both heat and mass. Otherwise, the flow lattice could act as a countercurrent heat exchanger and only mass will be efficiently transferred. Although this latter case might be useful for feeding a reaction front without extracting heat, it is likely that most interest will be focused on using IMA for heat transfer. In this paper we explore the various experimental parameters of IMA to determine which of these can be used to control the column spacing. These parameters include the field frequency, strength, and phase relation between the two field components, the liquid viscosity and particle volume fraction. We find that the column spacing can easily be tuned over a wide range, to enable the careful control of heat and mass transfer.« less
Tribological behavior of a friction couple functioning with selective mass transfer
NASA Astrophysics Data System (ADS)
Ilie, Filip
2016-06-01
Experimental researches on different lubricated friction couples, have confirmed that it is useful to investigate thermodynamic processes which are unstable in lubricant and on the friction couples surfaces in the first stage of the friction process. This presupposes that, in operating conditions, physical-chemical processes which are favourable to friction, such as: polymerization, formation of colloids, formation of other active substances at the contact surfaces and of other compounds with low resistance to shear take place. Friction in such conditions takes place with selective mass transfer, and it is used there where the friction of the mixed and adherence layers is not safe enough, or the durability of the friction couples is not assured. The selective mass transfer allows the transfer of some elements of the materials in contact from one surface to the other, covering them with a thin, superficial layer, with superior properties at minimal friction and wear. The aim of this paper is to analyse the physical-chemical factors and the proper processes for achieving the selective mass transfer for the couple steel/bronze, which in optimal conditions, forms a thin layer of copper on the contact surfaces areas. Also, it presents some studies and researches concerning the tribological behaviour of the surfaces of a friction couple with linear contact (roll/roll) which operates with selective mass transfer, tested on Amsler tribometer.
Solis, Kyle Jameson; Martin, James E.
2012-11-01
Isothermal magnetic advection is a recently discovered method of inducing highly organized, non-contact flow lattices in suspensions of magnetic particles, using only uniform ac magnetic fields of modest strength. The initiation of these vigorous flows requires neither a thermal gradient nor a gravitational field and so can be used to transfer heat and mass in circumstances where natural convection does not occur. These advection lattices are comprised of a square lattice of antiparallel flow columns. If the column spacing is sufficiently large compared to the column length, and the flow rate within the columns is sufficiently large, then one would expect efficient transfer of both heat and mass. Otherwise, the flow lattice could act as a countercurrent heat exchanger and only mass will be efficiently transferred. Although this latter case might be useful for feeding a reaction front without extracting heat, it is likely that most interest will be focused on using IMA for heat transfer. In this paper we explore the various experimental parameters of IMA to determine which of these can be used to control the column spacing. These parameters include the field frequency, strength, and phase relation between the two field components, the liquid viscosity and particle volume fraction. We find that the column spacing can easily be tuned over a wide range, to enable the careful control of heat and mass transfer.
Tribological behavior of a friction couple functioning with selective mass transfer
NASA Astrophysics Data System (ADS)
Ilie, Filip
2017-02-01
Experimental researches on different lubricated friction couples, have confirmed that it is useful to investigate thermodynamic processes which are unstable in lubricant and on the friction couples surfaces in the first stage of the friction process. This presupposes that, in operating conditions, physical-chemical processes which are favourable to friction, such as: polymerization, formation of colloids, formation of other active substances at the contact surfaces and of other compounds with low resistance to shear take place. Friction in such conditions takes place with selective mass transfer, and it is used there where the friction of the mixed and adherence layers is not safe enough, or the durability of the friction couples is not assured. The selective mass transfer allows the transfer of some elements of the materials in contact from one surface to the other, covering them with a thin, superficial layer, with superior properties at minimal friction and wear. The aim of this paper is to analyse the physical-chemical factors and the proper processes for achieving the selective mass transfer for the couple steel/bronze, which in optimal conditions, forms a thin layer of copper on the contact surfaces areas. Also, it presents some studies and researches concerning the tribological behaviour of the surfaces of a friction couple with linear contact (roll/roll) which operates with selective mass transfer, tested on Amsler tribometer.
On the role of mass diffusion and fluid dynamics in the dissipation of chunk mix
Cloutman, L D
1999-03-01
When numerically simulating multicomponent turbulent flows, subgrid-scale diffusion of chemical species requires closure. This mixing of chemical species at the molecular level dissipates concentration uctuations, which limits possible demixing and affects other pro- cesses such as energy transport and reaction rates at the subgrid level. We discuss some of the physical processes that reduce small chunks of a heavy material in a light gas or plasma to a mixture at the atomic level. Preliminary direct numerical simulations of these processes are presented using the dissipation of small spheres of heavy gas in a light gas as an archetypal process in turbulent micromixing in multicomponent ows, including classical uid instabilities and shock ejecta. We use a detailed approach for the diffusion process, directly solving the Stefan-Maxwell equations for the mass fluxes. We discuss the dissipa- tion of a 24µm sphere of xenon in helium in three different flow regimes, and we present suggestions for future work intended as input to improved subgrid-scale turbulence models.
Effective diffusivity and mass flux across the sediment-water interface in streams
NASA Astrophysics Data System (ADS)
Grant, Stanley B.; Stewardson, Michael J.; Marusic, Ivan
2012-05-01
The exchange of water between a stream and its hyporheic zone (defined as the sediment beneath and immediately adjacent to a stream) underpins many ecological and hydrological functions in turbulent streams. Hyporheic exchange can be parameterized in terms of an effective diffusion coefficient Deffand considerable effort has gone into developing process-based models and empirical correlations for predicting the value of this transport parameter. In this paper we demonstrate previous laboratory estimates forDeffcan be biased by as much as a factor of 10, due to errors in the equations and/or ambiguities in the variables used to reduce data from transient tracer experiments in flow-through and recirculating flumes. After correcting these problems, an analysis of 93 previously published flume experiments revealsDeffdepends on properties of the tracer (molecular diffusivity), flow field (shear velocity, kinematic viscosity), and sediment bed (permeability and depth). The shear velocity depends implicitly on the Darcy-Weisbach friction factor, which captures the influence of bed roughness and bed forms on hyporheic exchange in both laboratory and field studies. The dependence ofDeffon sediment bed depth is consistent with the hypothesis that coherent turbulence in the water column drives mass transport across the sediment-water interface. Furthermore, the dependence ofDeff on sediment bed depth raises the possibility that hyporheic exchange rates measured in the laboratory are not representative of hyporheic exchange rates in the field.
Brantley, P S
2005-06-06
The double spherical harmonics angular approximation in the lowest order, i.e. double P{sub 0} (DP{sub 0}), is developed for the solution of time-dependent non-equilibrium grey radiative transfer problems in planar geometry. The standard P{sub 1} angular approximation represents the angular dependence of the radiation specific intensity using a linear function in the angular domain -1 {le} {mu} {le} 1. In contrast, the DP{sub 0} angular approximation represents the angular dependence as isotropic in each half angular range -1 {le} {mu} < 0 and 0 < {mu} {le} 1. Neglecting the time derivative of the radiation flux, both the P{sub 1} and DP{sub 0} equations can be written as a single diffusion equation for the radiation energy density. Although the DP{sub 0} diffusion approximation is expected to be less accurate than the P{sub 1} diffusion approximation at and near thermodynamic equilibrium, the DP{sub 0} angular approximation can more accurately capture the complicated angular dependence near the non-equilibrium wave front. We develop an adaptive angular technique that locally uses either the DP{sub 0} or the P{sub 1} diffusion approximation depending on the degree to which the radiation and material fields are in thermodynamic equilibrium. Numerical results are presented for a test problem due to Su and Olson for which a semi-analytic transport solution exists. The numerical results demonstrate that the adaptive P{sub 1}-DP{sub 0} diffusion approximation can yield improvements in accuracy over the standard P{sub 1} diffusion approximation for non-equilibrium grey radiative transfer.
Mass fractionation of noble gases in diffusion-limited hydrodynamic hydrogen escape
NASA Technical Reports Server (NTRS)
Zahnle, Kevin; Pollack, James B.; Kasting, James F.
1990-01-01
The theory of mass fractionation by hydrogen is presently extended to atmospheres in which hydrogen is not the major constituent. This theoretical framework is applied to three different cases. In the first, it is shown that the fractionation of terrestrial atmospheric neon with respect to mantle neon is explainable as a consequence of diffusion-limited hydrogen escape from a steam atmosphere toward the end of the accretion process. In the second, the anomalously high Ar-38/Ar-36 ratio of Mars is shown to be due to hydrodynamic fractionation by a vigorously escaping and very pure hydrogen wind. In the last case, it is speculated that the currently high Martian D/H ratio emerged during the hydrodynamic escape phase which fractionated Ar.
Mathematical modeling of non-stationary heat and mass transfer in disperse systems
NASA Astrophysics Data System (ADS)
Ermakova, L. A.; Krasnoperov, S. Y.; Kalashnikov, S. N.
2016-09-01
The work describes mathematical model of non-stationary heat and mass transfer processes in dispersed environment, taking into account the phase transition; presents the results of numeric modelling for conditions of direct reduction in high-temperature reducing atmosphere, corresponding to the direct reduction in the jet-emulsion unit according to the principles of self-organization. The method was developed for calculation of heat and mass transfer of the aggregate of iron material particles in accordance with the given distribution law.
Magnetohydrodynamic Flow and Mass Transfer of a Jeffery Fluid over a Nonlinear Stretching Surface
NASA Astrophysics Data System (ADS)
Hayat, Tasawar; Qasim, Muhammad; Abbas, Zaheer; Hendi, Awatif A.
2010-12-01
This paper investigates the magnetohydrodynamic (MHD) boundary layer flow of a Jeffery fluid induced by a nonlinearly stretching sheet with mass transfer. The relevant system of partial differential equations has been reduced into ordinary differential equations by employing the similarity transformation. Series solutions of velocity and concentration fields are developed by using the homotopy analysis method (HAM). Effects of the various parameters such as Hartman number, Schmidt number, and chemical reaction parameter on velocity and concentration fields are discussed by presenting graphs. Numerical values of the mass transfer coefficient are also tabulated and analyzed.
NASA Astrophysics Data System (ADS)
Mobile, Michael; Widdowson, Mark; Stewart, Lloyd; Nyman, Jennifer; Deeb, Rula; Kavanaugh, Michael; Mercer, James; Gallagher, Daniel
2016-04-01
Better estimates of non-aqueous phase liquid (NAPL) mass, its persistence into the future, and the potential impact of source reduction are critical needs for determining the optimal path to clean up sites impacted by NAPLs. One impediment to constraining time estimates of source depletion is the uncertainty in the rate of mass transfer between NAPLs and groundwater. In this study, an innovative field test is demonstrated for the purpose of quantifying field-scale NAPL mass transfer coefficients (klN) within a source zone of a fuel-contaminated site. Initial evaluation of the test concept using a numerical model revealed that the aqueous phase concentration response to the injection of clean groundwater within a source zone was a function of NAPL mass transfer. Under rate limited conditions, NAPL dissolution together with the injection flow rate and the radial distance to monitoring points directly controlled time of travel. Concentration responses observed in the field test were consistent with the hypothetical model results allowing field-scale NAPL mass transfer coefficients to be quantified. Site models for groundwater flow and solute transport were systematically calibrated and utilized for data analysis. Results show klN for benzene varied from 0.022 to 0.60 d- 1. Variability in results was attributed to a highly heterogeneous horizon consisting of layered media of varying physical properties.
NASA Astrophysics Data System (ADS)
Karyakin, Yu. E.; Pletnev, A. A.; Fedorovich, E. D.
2017-01-01
The paper describes in brief the heat and mass transfer processes in the transfer of spent nuclear fuel of the RBMK-100 reactor from "wet" to "dry" cask storage. The algorithms are described and the results are presented of the "through" calculation of the heat and mass transfer processes in ampoules and in a metal-concrete cask at various stages of spent nuclear fuel management.
A 17-billion-solar-mass black hole in a group galaxy with a diffuse core
NASA Astrophysics Data System (ADS)
Thomas, Jens; Ma, Chung-Pei; McConnell, Nicholas J.; Greene, Jenny E.; Blakeslee, John P.; Janish, Ryan
2016-04-01
Quasars are associated with and powered by the accretion of material onto massive black holes; the detection of highly luminous quasars with redshifts greater than z = 6 suggests that black holes of up to ten billion solar masses already existed 13 billion years ago. Two possible present-day ‘dormant’ descendants of this population of ‘active’ black holes have been found in the galaxies NGC 3842 and NGC 4889 at the centres of the Leo and Coma galaxy clusters, which together form the central region of the Great Wall—the largest local structure of galaxies. The most luminous quasars, however, are not confined to such high-density regions of the early Universe; yet dormant black holes of this high mass have not yet been found outside of modern-day rich clusters. Here we report observations of the stellar velocity distribution in the galaxy NGC 1600—a relatively isolated elliptical galaxy near the centre of a galaxy group at a distance of 64 megaparsecs from Earth. We use orbit superposition models to determine that the black hole at the centre of NGC 1600 has a mass of 17 billion solar masses. The spatial distribution of stars near the centre of NGC 1600 is rather diffuse. We find that the region of depleted stellar density in the cores of massive elliptical galaxies extends over the same radius as the gravitational sphere of influence of the central black holes, and interpret this as the dynamical imprint of the black holes.
Thermal compression waves. 2: Mass adjustment and vertical transfer of the total energy
NASA Astrophysics Data System (ADS)
Nicholls, Melville E.; Pielke, Roger A.
1994-01-01
A fully compressible model is used to simulate the mass adjustment that occurs in response to a prescribed heat source. Results illustrate the role that thermal compression waves have in this process. The vertical mass transport associated with compression waves decreases rapidly with height. Most of the mass transport occurs in the horizontal, with the vertical structure of the disturbance similar to that of a Lamb wave. The vertical transfer of total energy in a thermally driven mixed layer is also examined. It is shown that the upward transport of total energy is accomplished by a compression effect rather than by the exchange of warm and cold air by buoyant thermals. Model results are analyzed to determine budgets of total energy, mass and entropy. It is demonstrated that buoyant thermals are predominantly responsible for a transfer of entropy, rather than total energy. In the light of these results the notion of 'heat transport' in a fluid is discussed.
Divyashri, Gangaraju; Prapulla, Siddalingaiya Gurudatt
2015-03-01
Gamma-aminobutyric acid (GABA) production by free and Ca-alginate encapsulated cells of Enterococcus faecium CFR 3003 was investigated. Mass transfer rates characterizing the GABA production process using encapsulated cells were investigated. Experiments were performed to investigate external film and internal pore diffusion mass transfer rates. The Damkohler and Thiele analysis provides a good description of external film and internal pore diffusion resistances, respectively. The experiments revealed that the external film effects could be neglected but the process is affected to the greater extent by internal mass transfer effects and was found to be the principal rate-controlling step. Protective effect of encapsulation on cell survivability was tested under digestive environment, when challenged to salivary α-amylase, simulated gastric fluid and intestinal fluid. Viability of encapsulated cells was significantly higher under simulated gastro-intestinal conditions and could produce higher GABA than those observed with free cells. The results indicate that the Ca-alginate encapsulated probiotics could effectively be delivered to the colonic site for effective inhibitory action.
NASA Astrophysics Data System (ADS)
Wang, Y.; Shu, C.; Shao, J. Y.; Wu, J.; Niu, X. D.
2015-06-01
In this work a mass-conserved diffuse interface method is proposed for simulating incompressible flows of binary fluids with large density ratio. In the method, a mass correction term is introduced into the Cahn-Hilliard equation to compensate the mass losses or offset the mass increases caused by the numerical and modeling diffusion. Since the mass losses or increases are through the phase interfaces and at each time step, their values are very small, to keep mass conservation, mass sources or sinks are introduced and uniformly distributed in the volume of diffuse layer. With the uniform distribution, the mass correction term representing mass sources or sinks is derived analytically by applying mass conservation principle. By including the mass correction, the modified Cahn-Hilliard equation is solved by the fifth-order upwind scheme to capture the phase field of the bindery fluids. The flow field is simulated by the newly-developed multiphase lattice Boltzmann flux solver [20]. The proposed approach is validated by simulating the Laplace law, the merging of two bubbles, Rayleigh-Taylor instability and bubble rising under gravity with density ratio of 1000 and viscosity ratio of 100. Numerical results of interface shapes and flow properties agree well with both analytical solutions and benchmark data in the literature. Numerical results also show that the mass is well-conserved in all cases considered. In addition, it is demonstrated that the mass correction term at each time step is in the order of 10-4 ∼10-5, which is a small number compared with the magnitude of order parameter.
Garrido-Baserba, Manel; Sobhani, Reza; Asvapathanagul, Pitiporn; McCarthy, Graham W; Olson, Betty H; Odize, Victory; Al-Omari, Ahmed; Murthy, Sudhir; Nifong, Andrea; Godwin, Johnnie; Bott, Charles B; Stenstrom, Michael K; Shaw, Andrew R; Rosso, Diego
2017-03-15
This research systematically studied the behavior of aeration diffuser efficiency over time, and its relation to the energy usage per diffuser. Twelve diffusers were selected for a one year fouling study. Comprehensive aeration efficiency projections were carried out in two WRRFs with different influent rates, and the influence of operating conditions on aeration diffusers' performance was demonstrated. This study showed that the initial energy use, during the first year of operation, of those aeration diffusers located in high rate systems (with solids retention time - SRT-less than 2 days) increased more than 20% in comparison to the conventional systems (2 > SRT). Diffusers operating for three years in conventional systems presented the same fouling characteristics as those deployed in high rate processes for less than 15 months. A new procedure was developed to accurately project energy consumption on aeration diffusers; including the impacts of operation conditions, such SRT and organic loading rate, on specific aeration diffusers materials (i.e. silicone, polyurethane, EPDM, ceramic). Furthermore, it considers the microbial colonization dynamics, which successfully correlated with the increase of energy consumption (r(2):0.82 ± 7). The presented energy model projected the energy costs and the potential savings for the diffusers after three years in operation in different operating conditions. Whereas the most efficient diffusers provided potential costs spanning from 4900 USD/Month for a small plant (20 MGD, or 74,500 m(3)/d) up to 24,500 USD/Month for a large plant (100 MGD, or 375,000 m(3)/d), other diffusers presenting less efficiency provided spans from 18,000USD/Month for a small plant to 90,000 USD/Month for large plants. The aim of this methodology is to help utilities gain more insight into process mechanisms and design better energy efficiency strategies at existing facilities to reduce energy consumption.
On the stream-accretion disk interaction - Response to increased mass transfer rate
NASA Technical Reports Server (NTRS)
Dgani, Ruth; Livio, Mario; Soker, Noam
1989-01-01
The time-dependent interaction between the stream of mass from the inner Lagrangian point and the accretion disk, resulting from an increasing mass transfer rate is calculated. The calculation is fully three-dimensional, using a pseudoparticle description of the hydrodynamics. It is demonstrated that the results of such calculations, when combined with specific observations, have the potential of both determining essential parameters, such as the viscosity parameter alpha, and can distinguish between different models of dwarf nova eruptions.
NASA Technical Reports Server (NTRS)
Curry, D. M.; Cox, J. E.
1972-01-01
Coupled nonlinear partial differential equations describing heat and mass transfer in a porous matrix are solved in finite difference form with the aid of a new iterative technique (the strongly implicit procedure). Example numerical results demonstrate the characteristics of heat and mass transport in a porous matrix such as a charring ablator. It is emphasized that multidimensional flow must be considered when predicting the thermal response of a porous material subjected to nonuniform boundary conditions.
Jiao, Anjun; Zhang, Yuwen; Ma, Hongbin; Critser, John
2009-03-01
Heat and mass transfer in a circular tube subject to the boundary condition of the third kind is investigated. The closed form of temperature and concentration distributions, the local Nusselt number based on the total external heat transfer and convective heat transfer inside the tube, as well as the Sherwood number were obtained. The effects of Lewis number and Biot number on heat and mass transfer were investigated.
Ding, Mingqiang; Jiang, Xiaowu; Peng, Jinying; Zhang, Lifen; Cheng, Zhenping; Zhu, Xiulin
2015-03-01
A concept based on diffusion-regulated phase-transfer catalysis (DRPTC) in an aqueous-organic biphasic system with copper-mediated initiators for continuous activator regeneration is successfully developed for atom transfer radical polymerization (ICAR ATRP) (termed DRPTC-based ICAR ATRP here), using methyl methacrylate (MMA) as a model monomer, ethyl α-bromophenylacetate (EBrPA) as an initiator, and tris(2-pyridylmethyl)amine (TPMA) as a ligand. In this system, the monomer and initiating species in toluene (organic phase) and the catalyst complexes in water (aqueous phase) are simply mixed under stirring at room temperature. The trace catalyst complexes transfer into the organic phase via diffusion to trigger ICAR ATRP of MMA with ppm level catalyst content once the system is heated to the polymerization temperature (75 °C). It is found that well-defined PMMA with controlled molecular weights and narrow molecular weight distributions can be obtained easily. Furthermore, the polymerization can be conducted in the presence of limited amounts of air without using tedious degassed procedures. After cooling to room temperature, the upper organic phase is decanted and the lower aqueous phase is reused for another 10 recycling turnovers with ultra low loss of catalyst and ligand loading. At the same time, all the recycled catalyst complexes retain nearly perfect catalytic activity and controllability, indicating a facile and economical strategy for catalyst removal and recycling.
Effect of acoustic streaming on the mass transfer from a sublimating sphere
NASA Astrophysics Data System (ADS)
Kawahara, N.; Yarin, A. L.; Brenn, G.; Kastner, O.; Durst, F.
2000-04-01
The effect of the acoustic streaming on the mass transfer from the surface of a sphere positioned in an ultrasonic acoustic levitator is studied both experimentally and theoretically. Acoustic levitation using standing ultrasonic waves is an experimental tool for studying the heat and mass transfer from small solid or liquid samples, because it allows an almost steady positioning of a sample at a fixed location in space. However, the levitator introduces some difficulties. One of the main problems with acoustic levitation is that an acoustic streaming is induced near the sample surface, which affects the heat and mass transfer rates, as characterized by increased Nusselt and Sherwood numbers. The transfer rates are not uniform along the sample surface, and the aim of the present study is to quantify the spatial Sherwood number distribution over the surface of a sphere. The experiments are based on the measurement of the surface shape of a sphere layered with a solid substance as a function of time using a charge-coupled device (CCD) camera with backlighting. The sphere used in this research is a glass sphere layered with a volatile solid substance (naphthalene or camphor). The local mass transfer from the surface both with and without an ultrasonic acoustic field is investigated in order to evaluate the effect of the acoustic streaming. The experimental results are compared with predictions following from the theory outlined [A. L. Yarin, M. Pfaffenlehner, and C. Tropea, J. Fluid Mech. 356, 65 (1998); A. L. Yarin, G. Brenn, O. Kastner, D. Rensink, and C. Tropea, ibid. 399, 151 (1999)] which describes the acoustic field and the resulting acoustic streaming, and the mass transfer at the surface of particles and droplets located in an acoustic levitator. The results are also compared with the experimental data and with the theoretical predictions of Burdukov and Nakoryakov [J. Appl. Mech. Tech. Phys. 6, 51 (1965)], which are valid only in the case of spherical
Effect of laminar and turbulent fluid flow on mass transfer in some electrochemical systems
NASA Astrophysics Data System (ADS)
Chen, Qian
2000-10-01
The influence of fluid flow on electrode-shape change that results from electrodeposition in the presence of a model leveling agent is simulated and discussed. The treatment is more rigorous than past studies in that flow and concentration fields are recalculated as the electrode shape changes. It is shown that uncertainties due to approximate treatments of fluid flow may be as significant as existing discrepancies between experiment and theory. The mass transfer characteristics of a turbulent slot jet impinging normally on a target wall are examined using numerical simulations. Fluid flow is modeled using the k-turbulence model of Wilcox [1]. The computations are validated against existing experimental fluid flow, heat transfer and mass transfer data. The range of Reynolds numbers examined is from 450 to 20,000 with Prandtl or Schmidt numbers from 1 to 2,400. The distance of the target plate from the slot jet varies between 2 to 8 times the slot jet width. The study reveals computational aspects that are unique to the solution of flow and mass transfer problems with the combination of high Schmidt numbers and turbulent flows. A low order "coherent structure" near-wall flow model first proposed by Chapman and Kuhn [2] is used to obtain the near-wall fluid flow field. This flow field is then used to compute high Schmidt number mass transfer for a turbulent boundary layer flow. It is shown that useful insight can be obtained into high Schmidt number mass transfer for a turbulent fluid flow using this model. The boundary conditions for this near-wall field for more complicated flow or geometries may be obtained either from experimental turbulent velocity and frequency data or from a k-o type of turbulence model.
Heat and mass transfer models to understand the drying mechanisms of a porous substrate.
Songok, Joel; Bousfield, Douglas W; Gane, Patrick A C; Toivakka, Martti
2016-02-01
While drying of paper and paper coatings is expensive, with significant energy requirements, the rate controlling mechanisms are not currently fully understood. Two two-dimensional models are used as a first approximation to predict the heat transfer during hot air drying and to evaluate the role of various parameters on the drying rates of porous coatings. The models help determine the structural limiting factors during the drying process, while applying for the first time the recently known values of coating thermal diffusivity. The results indicate that the thermal conductivity of the coating structure is not the controlling factor, but the drying rate is rather determined by the thermal transfer process at the structure surface. This underlines the need for ensuring an efficient thermal transfer from hot air to coating surface during drying, before considering further measures to increase the thermal conductivity of porous coatings.
NASA Astrophysics Data System (ADS)
Kneafsey, T. J.; Chang, C.; Zhou, Q.; Oostrom, M.; Wietsma, T. W.; Yu, Q.
2015-12-01
Dissolution trapping of supercritical CO2 (scCO2) is usually modeled by assuming instantaneous scCO2 dissolution and equilibrium phase partitioning. Our recent core-scale imbibition experiments show a prolonged depletion of residual scCO2 by dissolution, implying a non-equilibrium mechanism. In our 2D sandstone-analogue micromodel experimental study, pore-scale scCO2 dissolution was inferred from imaging (1) drainage using a pH-sensitive water dye and (2) imbibition using a scCO2 dye. The drainage experiment was conducted by injecting scCO2 into the dissolved-CO2 (dsCO2)-free water-filled pore network. The time-lapse images of non-uniform dye intensities indicating varying pH show that dsCO2 concentration varies from zero to solubility in individual pores and pore clusters and the average concentration gradually increases with time. The different rates of dissolution in different pores/clusters can be attributed to (1) fast scCO2 dissolution at scCO2-water interfaces, (2) rate-limited mass transfer due to limited interface areas, and (3) a transition from rate-limited to diffusion-limited mass transfer, revealed by detailed analysis on selected pores and pore clusters. The imbibition experiments conducted by injecting deionized water at different rates show (1) water flow in channels bypassing scCO2 at high residual saturations, (2) subsequent, slow scCO2 depletion by dissolution and mass transfer as effluent dsCO2 concentration varies from 0.06% to 4.44% of solubility, and (3) creation of new water flow paths by dissolution, enhancing scCO2 depletion by coupled displacement and dissolution. Both the drainage and imbibitions experiments indicate non-equilibrium scCO2 dissolution in the centimeter-scale pore network over 4.5 hours and up to 14 hours, respectively. The pore-scale imaging can help better understand the effects of pore-throat characteristics on scCO2 dissolution and mass transfer during drainage and imbibition and the interplay between displacement and
Models for mass transfer effects in semi-fuel cells and for a silver-zinc battery
NASA Astrophysics Data System (ADS)
Venkatraman, Murali Sankar
Semi-Fuel Cells (SFCs) and Silver-Zinc batteries have been recognized as batteries for high power applications. For channel flow between two parallel plates, featured in SFCs, obstacles may take the form of ordered asymmetrical porous nets. The net controls the spacing between the two electrode plates. The effect of the inert insulating net and its geometry on the heat and mass transfer characteristics in such a system is presented. The governing equations for momentum, continuity, and energy are solved in a three-dimensional domain using a commercial computational fluid dynamics software for fully developed flow with constant temperature boundary conditions. The local Nusselt number is calculated from the resulting temperature distribution. This net also affects the limiting current distribution in an SFC operating at limiting current because it disrupts the parabolic laminar flow velocity distribution. Hence, the current density distribution is obtained from the Nusselt number distribution through a heat and mass transfer analogy. The location, spacing, and number of the longitudinal and transverse ribs of the net are shown to affect the local and average current density distributions and Nusselt numbers on each of the two electrode plates. The results show that transverse ribs have a greater effect and that the enhancements of the average current density of 250% can be obtained for a spacing of 0.94 x 10-3 m with greater than 16 transverse ribs. A silver-zinc battery shows similar mass transfer limitations while discharged at moderate to high discharge rates. A one-dimensional mathematical model consisting of a negative (zinc) electrode, separator, and positive (silver) electrode, has been developed to study the performance and thermal behavior of the silver-zinc cell during discharge. The physical phenomena described here are reaction kinetics, mass transfer and heat generation. The analysis includes finite matrix conductivities (thermal and electrical
Mass fractionation of noble gases in diffusion-limited hydrodynamic hydrogen escape.
Zahnle, K; Kasting, J F; Pollack, J B
1990-01-01
Mass fractionation by hydrodynamic hydrogen escape is a promising mechanism for explaining the observed elemental and isotopic abundance patterns in terrestrial planet atmospheres. Previous work has considered only pure hydrogen winds. Here, the theory of mass fractionation by hydrogen escape is extended to atmospheres in which hydrogen is not the only major constituent. Analytical solutions are derived for cases in which all relevant atmospheric constituents escape; both analytical and numerical solutions are obtained for cases in which important heavy constituents are retained. In either case the fractionation patterns that result can differ significantly from those produced by pure hydrogen winds. Three applications of the theory are discussed: (1) The observed fractionation of terrestrial atmospheric neon with respect to mantle neon can be explained as a by-product of diffusion-limited hydrogen escape from a steam atmosphere toward the end of accretion. (2) The anomalously high Martian (SNC) 38Ar/36Ar ratio is attributed to hydrodynamic fractionation by a vigorously escaping, nearly pure hydrogen wind. (3) It is possible that the present high Martian D/H ratio was established during the same hydrodynamic escape phase that fractionated argon, but the predicted degree of D/H enrichment is sensitive to other, less well constrained parameters.
Diffuse supernova neutrinos: oscillation effects, stellar cooling and progenitor mass dependence
Lunardini, Cecilia; Tamborra, Irene E-mail: tamborra@mpp.mpg.de
2012-07-01
We estimate the diffuse supernova neutrino background (DSNB) using the recent progenitor-dependent, long-term supernova simulations from the Basel group and including neutrino oscillations at several post-bounce times. Assuming multi-angle matter suppression of collective effects during the accretion phase, we find that oscillation effects are dominated by the matter-driven MSW resonances, while neutrino-neutrino collective effects contribute at the 5–10% level. The impact of the neutrino mass hierarchy, of the time-dependent neutrino spectra and of the diverse progenitor star population is 10% or less, small compared to the uncertainty of at least 25% of the normalization of the supernova rate. Therefore, assuming that the sign of the neutrino mass hierarchy will be determined within the next decade, the future detection of the DSNB will deliver approximate information on the MSW-oscillated neutrino spectra. With a reliable model for neutrino emission, its detection will be a powerful instrument to provide complementary information on the star formation rate and for learning about stellar physics.
Interface Dynamics of a Metastable Mass-Conserving Spatially Extended Diffusion
NASA Astrophysics Data System (ADS)
Berglund, Nils; Dutercq, Sébastien
2016-01-01
We study the metastable dynamics of a discretised version of the mass-conserving stochastic Allen-Cahn equation. Consider a periodic one-dimensional lattice with N sites, and attach to each site a real-valued variable, which can be interpreted as a spin, as the concentration of one type of metal in an alloy, or as a particle density. Each of these variables is subjected to a local force deriving from a symmetric double-well potential, to a weak ferromagnetic coupling with its nearest neighbours, and to independent white noise. In addition, the dynamics is constrained to have constant total magnetisation or mass. Using tools from the theory of metastable diffusion processes, we show that the long-term dynamics of this system is similar to a Kawasaki-type exchange dynamics, and determine explicit expressions for its transition probabilities. This allows us to describe the system in terms of the dynamics of its interfaces, and to compute an Eyring-Kramers formula for its spectral gap. In particular, we obtain that the spectral gap scales like the inverse system size squared.
Ultra-diffuse Galaxies in Clusters and the Field: Masses and Stellar Populations
NASA Astrophysics Data System (ADS)
Romanowsky, Aaron; Laine, Seppo; Krick, Jessica; van Dokkum, Pieter; Villaume, Alexa; Brodie, Jean
2016-08-01
Ultra-diffuse galaxies (UDGs) were recognized only last year as a novel class of galaxies, with luminosities like dwarfs but sizes like giants. Although some UDGs appear to be just unusually extended dwarfs, others show evidence of being very different and unexpected: their dark matter halos are overmassive by factors of ~10, with one UDG even being arguably a 'failed Milky Way.' These exotic galaxies might be a byproduct of environmental processes within galaxy clusters, but UDGs have also now been found in the field. It is crucial for understanding their origins to test if UDGs have the same properties in cluster and field environments. Here we propose studying the stellar populations (ages and metallicities) of seven UDGs using Spitzer/IRAC 3.6- and 4.5-micron imaging combined with optical photometry, along with mass estimation of three of the UDGs using HST/ACS imaging to provide globular cluster number counts and colors (proxies for halo mass). This ultra low surface brightness photometry in the near infrared, on an important new class of galaxies, could become a legacy result from the Spitzer mission.
NASA Astrophysics Data System (ADS)
Imhoff, Paul T.; Jaffé, Peter R.
1994-09-01
Gas-water phase mass transfer was examined in a homogeneous sand with both the gas and water phase mobile: water was infiltrated from the top of the sand column while benzene-laden air flowed upward from the bottom. Mass-transfer limitations for this situation may be important for applications of bioventing, where water and nutrients are added at the ground surface simultaneously with induced air movement to carry oxygen and volatile organics to microbial populations. Gas- and water-phase samples indicate that gas-water phase mass transfer was sufficiently fast that equilibrium between gas and water phases was achieved at all sampling locations within the porous medium. Lower-bound estimates for the gas-water mass-transfer rate coefficient show that mass transfer was at least 10-40 times larger than predictions made from an empirical model developed for gas-water phase mass transfer in an identical porous medium. A water-phase tracer test demonstrates that water flow was much more uniform in this study than in those earlier experiments, which is a likely explanation for the differing rates of gas-water phase mass transfer. It is hypothesized that the liquid distribution in previous laboratory experiments was less uniform because of preferential flow paths due to wetting front instabilities. Gas-water phase mass-transfer rate coefficients reported in this investigation are for an ideal situation of uniform water infiltration: mass-transfer rates in field soils are expected to be significantly smaller.
Samin, Adib; Lahti, Erik; Zhang, Jinsuo
2015-08-15
Cyclic voltammetry is a powerful tool that is used for characterizing electrochemical processes. Models of cyclic voltammetry take into account the mass transport of species and the kinetics at the electrode surface. Analytical solutions of these models are not well-known due to the complexity of the boundary conditions. In this study we present closed form analytical solutions of the planar voltammetry model for two soluble species with fast electron transfer and equal diffusivities using the eigenfunction expansion method. Our solution methodology does not incorporate Laplace transforms and yields good agreement with the numerical solution. This solution method can be extended to cases that are more general and may be useful for benchmarking purposes.
Keefe, D H; Bulen, J C; Campbell, S L; Burns, E M
1994-01-01
The diffuse-field pressure transfer function from a reverberant field to the ear canal of human infants, ages 1, 3, 6, 12, and 24 months, has been measured from 125-10700 Hz. The source was a loudspeaker using pink noise, and the diffuse-field pressure and the ear-canal pressure were simultaneously measured using a spatial averaging technique in a reverberant room. The results in most subjects show a two-peak structure in the 2-6-kHz range, corresponding to the ear-canal and concha resonances. The ear-canal resonance frequency decreases from 4.4 kHz at age 1 month to 2.9 kHz at age 24 months. The concha resonance frequency decreases from 5.5 kHz at age 1 month to 4.5 kHz at age 24 months. Below 2 kHz, the diffuse-field transfer function shows effects due to the torsos of the infant and parent, and varies with how the infant is held. Comparisons are reported of the diffuse-field absorption cross section for infants relative to adults. This quantity is a measure of power absorbed by the middle ear from a diffuse sound field, and large differences are observed in infants relative to adults. The radiation efficiencies of the infant and the adult ear are small at low frequencies, near unity at midfrequencies, and decrease at higher frequencies. The process of ear-canal development is not yet complete at age 24 months. The results have implications for experiments on hearing in infants.
Mass transfer coefficient in ginger oil extraction by microwave hydrotropic solution
NASA Astrophysics Data System (ADS)
Handayani, Dwi; Ikhsan, Diyono; Yulianto, Mohamad Endy; Dwisukma, Mandy Ayulia
2015-12-01
This research aims to obtain mass transfer coefficient data on the extraction of ginger oil using microwave hydrotropic solvent as an alternative to increase zingiberene. The innovation of this study is extraction with microwave heater and hydrotropic solvent,which able to shift the phase equilibrium, and the increasing rate of the extraction process and to improve the content of ginger oil zingiberene. The experiment was conducted at the Laboratory of Separation Techniques at Chemical Engineering Department of Diponegoro University. The research activities carried out in two stages, namely experimental and modeling work. Preparation of the model postulated, then lowered to obtain equations that were tested and validated using data obtained from experimental. Measurement of experimental data was performed using microwave power (300 W), extraction temperature of 90 ° C and the independent variable, i.e.: type of hydrotropic, the volume of solvent and concentration in order, to obtain zingiberen levels as a function of time. Measured data was used as a tool to validate the postulation, in order to obtain validation of models and empirical equations. The results showed that the mass transfer coefficient (Kla) on zingiberene mass transfer models ginger oil extraction at various hydrotropic solution attained more 14 ± 2 Kla value than its reported on the extraction with electric heating. The larger value of Kla, the faster rate of mass transfer on the extraction process. To obtain the same yields, the microwave-assisted extraction required one twelfth time shorter.
Dissociation and ammonia mass transfer from ammonium solution and dairy cattle manure
Technology Transfer Automated Retrieval System (TEKTRAN)
Process-based models are being used to predict ammonia (NH**3) emissions from manure sources, but their accuracy has not been fully evaluated for cattle manure. Laboratory trials were conducted to measure the dissociation and mass transfer coefficient for NH**3 volatilization from media of buffered ...
Oxygen mass transfer and scale-up studies in baffled roller bioreactors.
Nikakhtari, H; Song, W; Nemati, M; Hill, G A
2014-02-01
Oxygen mass transfer was studied in conventional, bead mill and baffled roller bioreactors. Using central composite rotational design, impacts of size, rotation speed and working volume on the oxygen mass transfer were evaluated. Baffled roller bioreactor outperformed its conventional and bead mill counterparts, with the highest k(L)a obtained in these configurations being 0.58, 0.19, 0.41 min(-1), respectively. Performances of the bead mill and baffled roller bioreactor were only comparable when a high bead loading (40%) was applied. Regardless of configuration increase in rotation speed and decrease in working volume improved the oxygen mass transfer rate. Increase in size led to enhanced mass transfer and higher k(L)a in baffled roller bioreactor (0.49 min(-1) for 2.2 L and 1.31 min(-1) for 55 L bioreactors). Finally, the experimentally determined k(L)a in the baffled roller bioreactors of different sizes fit reasonably well to an empirical correlation describing the k(L)a in terms of dimensionless numbers.
A Laboratory Experiment for Measuring Solid-Liquid Mass Transfer Parameters
ERIC Educational Resources Information Center
Dapia, Sonia; Vila, Carlos; Dominguez, Herminia; Parajo, Juan Carlos
2004-01-01
The lab experiment described starts from the principles developed by Sensel and Myers, but the experimental procedure are modified to provide a more reliable experiment assessment. The mass transfer equation is solved and all the involved parameters are calculated by a simple, numerical method.
A mass transfer model of ethanol emission from thin layers of corn silage
Technology Transfer Automated Retrieval System (TEKTRAN)
A mass transfer model of ethanol emission from thin layers of corn silage was developed and validated. The model was developed based on data from wind tunnel experiments conducted at different temperatures and air velocities. Multiple regression analysis was used to derive an equation that related t...
Technology Transfer Automated Retrieval System (TEKTRAN)
An empirical correlation of volumetric mass transfer coefficient was developed for a pilot scale internal-loop rectangular airlift bioreactor that was designed for biotechnology. The empirical correlation combines classic turbulence theory, Kolmogorov’s isotropic turbulence theory with Higbie’s pen...
Mass Transfer Testing of a 12.5-cm Rotor Centrifugal Contactor
D. H. Meikrantz; T. G. Garn; J. D. Law; N. R. Mann; T. A. Todd
2008-09-01
TRUEX mass transfer tests were performed using a single stage commercially available 12.5 cm centrifugal contactor and stable cerium (Ce) and europium (Eu). Test conditions included throughputs ranging from 2.5 to 15 Lpm and rotor speeds of 1750 and 2250 rpm. Ce and Eu extraction forward distribution coefficients ranged from 13 to 19. The first and second stage strip back distributions were 0.5 to 1.4 and .002 to .004, respectively, throughout the dynamic test conditions studied. Visual carryover of aqueous entrainment in all organic phase samples was estimated at < 0.1 % and organic carryover into all aqueous phase samples was about ten times less. Mass transfer efficiencies of = 98 % for both Ce and Eu in the extraction section were obtained over the entire range of test conditions. The first strip stage mass transfer efficiencies ranged from 75 to 93% trending higher with increasing throughput. Second stage mass transfer was greater than 99% in all cases. Increasing the rotor speed from 1750 to 2250 rpm had no significant effect on efficiency for all throughputs tested.
The influence of the HGMF on mass-charge transfer in gravisensing cells.
Kondrachuk, A; Belyavskaya, N
2001-07-01
The present work is focused on the influence of the high-gradient-magnetic field (HGMF) on spatial distribution of ion fluxes along the roots (a), cytoplasmic streaming (b), and the processes of plant cell growth connected with intracellular mass and charge transfer (c).
Mass transfer in thin films under counter-current gas: experiments and numerical study
NASA Astrophysics Data System (ADS)
Lucquiaud, Mathieu; Lavalle, Gianluca; Schmidt, Patrick; Ausner, Ilja; Wehrli, Marc; O Naraigh, Lennon; Valluri, Prashant
2016-11-01
Mass transfer in liquid-gas stratified flows is strongly affected by the waviness of the interface. For reactive flows, the chemical reactions occurring at the liquid-gas interface also influence the mass transfer rate. This is encountered in several technological applications, such as absorption units for carbon capture. We investigate the absorption rate of carbon dioxide in a liquid solution. The experimental set-up consists of a vertical channel where a falling film is sheared by a counter-current gas flow. We measure the absorption occurring at different flow conditions, by changing the liquid solution, the liquid flow rate and the gas composition. With the aim to support the experimental results with numerical simulations, we implement in our level-set flow solver a novel module for mass transfer taking into account a variant of the ghost-fluid formalism. We firstly validate the pure mass transfer case with and without hydrodynamics by comparing the species concentration in the bulk flow to the analytical solution. In a final stage, we analyse the absorption rate in reactive flows, and try to reproduce the experimental results by means of numerical simulations to explore the active role of the waves at the interface.
Demonstrating the Effect of Interphase Mass Transfer in a Transparent Fluidized Bed Reactor
ERIC Educational Resources Information Center
Saayman, Jean; Nicol, Willie
2011-01-01
A demonstration experiment is described that employs the ozone decomposition reaction at ambient conditions on Fe2O3 impregnated Fluidized Catalytic Cracking (FCC) catalyst. Using a two-dimensional see-through column the importance of interphase mass transfer is clearly illustrated by the significant difference in ozone conversion between the…
Mass Transfer Study of Chlorine Dioxide Gas Through Polymeric Packaging Materials
Technology Transfer Automated Retrieval System (TEKTRAN)
A continuous system for measuring the mass transfer of gaseous chlorine dioxide (ClO2), a strong oxidizing agent and used in food and pharmaceutical packaging, through 10 different types of polymeric packaging material was developed utilizing electrochemical sensor as a detector. Permeability, diff...
Numerical Problems and Agent-Based Models for a Mass Transfer Course
ERIC Educational Resources Information Center
Murthi, Manohar; Shea, Lonnie D.; Snurr, Randall Q.
2009-01-01
Problems requiring numerical solutions of differential equations or the use of agent-based modeling are presented for use in a course on mass transfer. These problems were solved using the popular technical computing language MATLABTM. Students were introduced to MATLAB via a problem with an analytical solution. A more complex problem to which no…
Mixing and mass transfer in a pilot scale U-loop bioreactor.
Petersen, Leander A H; Villadsen, John; Jørgensen, Sten B; Gernaey, Krist V
2017-02-01
A system capable of handling a large volumetric gas fraction while providing a high gas to liquid mass transfer is a necessity if the metanotrophic bacterium Methylococcus capsulatus is to be used in single cell protein (SCP) production. In this study, mixing time and mass transfer coefficients were determined in a 0.15 m(3) forced flow U-loop fermenter of a novel construction. The effect on the impeller drawn power when a gas was introduced into the system was also studied. Mixing time decreased and mass transfer increased with increasing volumetric liquid flow rate and specific power input. This happened also for a large volume fraction of the gas, which was shown to have only minor effect on the power drawn from the pump impeller. Very large mass transfer coefficients, considerably higher than those obtainable in an STR and previous tubular loop reactors, could be achieved in the U-loop fermenter equipped with static mixers at modest volumetric liquid and gas flow rates. Biotechnol. Bioeng. 2017;114: 344-354. © 2016 Wiley Periodicals, Inc.
Effect of laminar unsteady fluid flows on mass transfer in electrochemical systems
NASA Astrophysics Data System (ADS)
Shehata, Ahmed Kamal
1999-11-01
A numerical study of mass transfer in steady as well as unsteady two-dimensional laminar channel flows is investigated. When a circular cylinder is suspended in a steady flow stream, the flow becomes unsteady and oscillates periodically for Reynolds numbers, Re, between 200 and 800 (where Re is based on the channel height) due to the formation of the Karman vortex street. This well- characterized unsteady periodic flow is utilized to study mass transfer rates at different positions downstream of the blocking cylinder. The study consisted of mass transfer to a channel wall and mass transfer to the bottom surface of rectangular cavities, of different depth/width ratios. All investigated positions, including cavity position, are located downstream of the blocking cylinder. The study also included the mass transfer to a channel wall in a steady fully-developed flow when a hemi-cylindrical bump is located at the lower wall. The results of the numerical simulations are then compared to the experimental data. The numerical and experimental results are found to be generally in good agreement. Structured multi-block grids are utilized for the fluid flow simulations. It is shown that grids can be created differently with different block topologies. Solution accuracy is shown to be strongly affected by the shape as well as the densities of the resulting grids. The finite element method is used to simulate the fluid flow while for the concentration field a procedure based on the finite volume method is used. The strength of the flow at the cavity mouth was found to scale linearly with wall shear in the absence of the cavity for steady channel flow. The flow at the cavity mouth was also found to be independent of the cavity depth for both steady and unsteady flows. Based on these observations it is possible to predict cavity flows and cavity mass transfer without computing the flow in the entire channel plus cavity domain when studying different cavity aspect ratios. A
About Mass Transfer in Capillaries of Biological Systems under Influence of Vibrations
NASA Astrophysics Data System (ADS)
Prisniakov, K.
Vibrations accompany the flight of the manned spacecraft both at a stage of a orbital injection to an orbit, and during long flights (as noise), rendering undesirable physiological influence on crew, reducing serviceability and creating constant discomfort. The report represents attempt to predict a state of the cosmonaut in conditions of influence of vibrations for the period of start and stay in Space, being based on researches of mass transfer processes in capillary systems. For this purpose the original researches on heat and mass transfer processes with evaporation of liquids in capillary - porous structures in conditions of vibration actions and changes of a direction of action of gravitation are generalized. Report demonstrates the existence of modes at which increased or lowered mass transfer is achieved on border of separation "liquid - gas". The possible mechanism of influence of vibrations on evaporation of a liquid in capillaries is examined. The magnitudes of frequencies and amplitudes are submitted at which minimax characteristics are observed. The opportunity of application of the developed mathematical model of heat and mass transfer in capillary - porous structures to forecasting influence of vibrations for biological processes in capillaries of alive essences is analyzed. Such approach is justified on the mechanical nature of harmful influence of vibrations on an organism of the person. In addition the range of vibration frequencies which arise during space flights, corresponds to own resonant frequencies of a human body and his separate organs. Comparison of these resonant frequencies of a body of the person (5-80 Hertz) with vibration frequencies of optimum modes of heat and mass transfer in capillary - porous structures (20-40 Hertz) is shown their ranges of coverage. It gives the basis to assume existence of similar effects in capillaries of human body. It is supposed, that the difficulty of breath, change of a rhythm of breath, the subsequent
Mass transfer to reactive boundaries from steady three-dimensional flows in microchannels
NASA Astrophysics Data System (ADS)
Kirtland, Joseph D.; McGraw, Gregory J.; Stroock, Abraham D.
2006-07-01
This paper presents a numerical study of the effect of transverse secondary flows on mass transfer to reactive boundaries in microchannels. The geometry considered is relevant to surface catalyzed reactions, fuel cells, biochemical sensors, and other microreactor applications. The 3D flows that we consider approximate flows that are experimentally achievable through topographical patterning of one wall of a microchannel, as in the Staggered Herringbone Mixer (SHM) and similar geometries. We simulate a mass transfer process using passive tracers to model reactive solute molecules in a Stokes flow (Reynolds number, Re =0) over a range of Péclet number, 102⩽Pe⩽105, with instantaneous kinetics at the reactive boundary. Our simulation allows for the evaluation of the local Sherwood number produced by a uniaxial Poiseuille flow and several chaotic and nonchaotic 3D flows. In chaotic flows, the local Sherwood number evolves in a simple manner that shares features with the classic Graetz solution for transfer from a uniaxial pipe flow: an entrance region with cube-root scaling in the Graetz number and a constant asymptotic value. This "Modified Graetz" behavior also differs in important ways from the standard case: the entrance length is Pe independent and the asymptotic rate of transfer is Pe dependent and potentially much greater than in the uniaxial case. We develop a theoretical model of the transfer process; the predictions of this model compare well with simulation results. We use our results to develop a correlation for the mass transfer in laminar channel flows, to elucidate the importance of chaos in defining transfer in these flows, and to provide design rules for microreactors with a single reactive wall.
Bibliography on augmentation of convective heat and mass transfer-II
Bergles, A.E.; Nirmalan, V.; Junkhan, G.H.; Webb, R.L.
1983-12-01
Heat transfer augmentation has developed into a major specialty area in heat transfer research and development. This report presents and updated bibliography of world literature on augmentation. The literature is classified into passive augmentation techniques, which require no external power, and active techniques, which do require external power. The fifteen techniques are grouped in terms of their applications to the various modes of heat transfer. Mass transfer is included for completeness. Key words are included with each citation for technique/mode identification. The total number of publications cited is 3045, including 135 surveys of various techniques and 86 papers on performance evaluation of passive techniques. Patents are not included, as they are the subject of a separate bibliographic report.
Impact of heat and mass transfer on combustion of a fuel particle in CFB boilers
Palchonok, G.I.; Breitholtz, C.; Thunman, H.; Leckner, B.
1997-12-31
High excess temperatures of burning coal particles, up to 600 K, have been measured with a two-color pyrometer in the transport zone of a CFB boiler at a rather low average oxygen concentration of about 6%. To understand this phenomenon, a model of heat and mass transfer between a burning char particle and its surrounding has been developed, based on measured heat transfer coefficients and the estimated slip velocity of a char particle. The gas-convective and radiative mechanisms of heat transfer were found to dominate in the core of the transport zone of a CFB furnace. The gas-convective transfer rate was 1.5 times as high as in a single-phase flow. Model calculations show that particles between 0.3 and 3 mm could have as high a temperature as the measured ones, provided that there is a highly non-uniform oxygen distribution over the furnace cross-section.
3D modelling of coupled mass and heat transfer of a convection-oven roasting process.
Feyissa, Aberham Hailu; Gernaey, Krist V; Adler-Nissen, Jens
2013-04-01
A 3D mathematical model of coupled heat and mass transfer describing oven roasting of meat has been developed from first principles. The proposed mechanism for the mass transfer of water is modified and based on a critical literature review of the effect of heat on meat. The model equations are based on a conservation of mass and energy, coupled through Darcy's equations of porous media - the water flow is mainly pressure-driven. The developed model together with theoretical and experimental assessments were used to explain the heat and water transport and the effect of the change in microstructure (permeability, water binding capacity and elastic modulus) that occur during the meat roasting process. The developed coupled partial differential equations were solved by using COMSOL Multiphysics®3.5 and state variables are predicted as functions of both position and time. The proposed mechanism was partially validated by experiments in a convection oven where temperatures were measured online.
Netcher, Andrea C; Duranceau, Steven J
2016-03-01
In surface water treatment, ultrafiltration (UF) membranes are widely used because of their ability to supply safe drinking water. Although UF membranes produce high-quality water, their efficiency is limited by fouling. Improving UF filtrate productivity is economically desirable and has been attempted by incorporating sustainable biofiltration processes as pretreatment to UF with varying success. The availability of models that can be applied to describe the effectiveness of biofiltration on membrane mass transfer are lacking. In this work, UF water productivity was empirically modeled as a function of biofilter feed water quality using either a quadratic or Gaussian relationship. UF membrane mass transfer variability was found to be governed by the dimensionless mass ratio between the alkalinity (ALK) and dissolved organic carbon (DOC). UF membrane productivity was optimized when the biofilter feed water ALK to DOC ratio fell between 10 and 14.