Mass Diffusion Process Research Articles

Mass Diffusion Coefficients of Cellulose Acetate Butyrate in Methyl Ethyl Ketone Solutions at Temperatures between (293 and 323) K and Mass Fractions from 0.05 to 0.60 Using the Soret Forced Rayleigh Scattering Method

The binary mass diffusion coefficients of cellulose acetate butyrate in methyl ethyl ketone solutions (CAB + MEK) have been measured under atmospheric pressure at temperatures from (293 to 323) K and mass fractions from 0.05 to 0.6. The present experimental apparatus is based on the Soret forced Rayleigh scattering method (S-FRSM), which utilizes the Soret effect to create periodic spatial concentration modulation of micrometer-order fringe spacing in a sample binary liquid mixture due to the absorption of an optical interference grating generated by two intersecting heating laser beams. The decay of the concentration modulation by the mass diffusion process is monitored by the diffraction of a probing laser beam. This method provides several advantages in comparison with conventional techniques such as Taylor dispersion or diaphragm cells; namely, a single measurement can be performed within a short time [(10−3 to 10−2) s], with small temperature and concentration changes (ΔT < 10−2 K and Δc < 10−5) usin...

Mixture segregation by an inertial cavitation bubble

Pressure diffusion is a mass diffusion process forced by pressure gradients. It has the ability to segregate two species of a mixture, driving the densest species toward high pressure zones, but requires very large pressure gradients to become noticeable. An inertial cavitation bubble develops large pressure gradients in its vicinity, especially as the bubble rebounds at the end of its collapse, and it is therefore expected that a liquid mixture surrounding such a bubble would become segregated. Theory developed in an earlier paper shows that this is indeed the case for sufficiently large molecules or nano-particles. The main theoretical results are recalled and a possible implication of this segregation phenomenon on the well-known cavitation-enhanced crystals nucleation is proposed.

A thermodynamic model for electrical current induced damage

Electromigration-induced damage, which is in principal an irreversible mass diffusion under high current density, has been a concern for VLSI design for a long time. Miniaturization of electronic device sizes down to nano-scale will make electromigration a concern for all conducting components. This paper uses thermodynamics, statistical mechanics and mass transport (diffusion) principals to propose a model for electromigration process and a damage evolution model to quantify the degradation in microelectronics (and micro electromechanical system) solder joints subjected to high current densities. Entropy production in the system is used as a damage metric. The irreversible thermodynamic damage model utilized in this work has previously been successfully applied to thermo-mechanical fatigue of microelectronic solder joints. In this paper we extend this model to electromigration-induced degradation. Electromigration process is modeled by the atomic vacancy flux (mass diffusion) process. The proposed unified model is compared with several existing analytical and empirical models. A comparison of the damage evolution model proposed in here agrees well with empirical models proposed in the literature.

Time-dependent behavior of gas absorption in lubricant oil

Gas absorption behavior in liquid with time has been studied by applying a simple mathematical model. The model is based on a one-dimensional mass diffusion process due to the concentration difference in dissolving gas. In order to examine the model validity, selected experimental data in the literature have been analyzed with the present model. The model has faithfully reproduced the experimental transient behavior of dissolving gases, and physically meaningful model parameters, diffusion constant and solubility limit, have been obtained for dissolving gas (water and refrigerant) in various lubricant oils. The validity and the significance of the model are discussed.

Modelling of volatile organic compounds emission from dry building materials

A numerical and an analytical model were developed to predict the volatile organic compound (VOC) emission rate from dry building materials. Both models consider the mass diffusion process within the material and the mass convection and diffusion processes in the boundary layer. All the parameters, the mass diffusion coefficient of the material, the material/air partition coefficient, and the mass transfer coefficient of the air can be either found in the literature or calculated using known principles. The predictions of the models were validated at two levels: with experimental results from the specially designed test and with predictions made by a CFD model. The results indicated that there was generally good agreement between the model predictions, the experimental results, and the CFD results. The analytical and numerical models then were used to investigate the impact of air velocity on emission rates from dry building materials. Results showed that the impact of air velocity on the VOC emission rate increased as the VOC diffusion coefficient of the material increased. For the material with a diffusion coefficient >10 −10 m 2/ s , the VOC emission rate increased as the velocity increased; air velocity had significant effect on the VOC emission. For the material with a VOC diffusion coefficient <10 −10 m 2/ s , the VOC emission rate increased as the velocity increased only in the short-term; <24 h . In the medium to long-term time range, the VOC emission rate decreased slightly as the air velocity increased; velocity did not have much impact on these materials. Furthermore, the study also found that the VOC concentration distribution within the material; the VOC emission rate and the VOC concentration in the air were linearly proportional to the initial concentration. However, the normalized emitted mass was not a function of the initial concentration: it was a function of the properties of the VOC and the material.

Extinction thickness in the SHS flame propagation in two-layered composite medium

Extinction of the self-propagating high-temperature synthesis (SHS) flame in a condensed composite medium, consisting of adjacent layers of reactants and inert, has been analyzed for the synthesis of functionally graded materials (FGMs), which are anticipated to be useful in future space applications. The essential heterogeneous nature of the SHS flame propagation is appropriately described and the effects of the particle size on the combustion and/or extinction behavior are capture. The analysis, based on the temperature sensitivity of the mass diffusion process in the condensed phase, yields the extinction thickness due to heat transfer to the neighboring inert layer. The study further identifies the extinction thickness as function of the system parameters, which include the mixture ratio, the degree of dilution, the particle size, the representative length of the specimen cross section, and the initial temperature. It is demonstrated that the extinction thickness strongly depends on the particle radius, increasing with increasing particle size, due to the reduced heat generation rate at the particle surfaces. It is also shown that the thickness of the heat of combustion. Furthermore, it is found that preheating can be quite effective in reducing the extinction thickness when there exist restriction in reducing the particle size for the production of composite materials.

Modelling of volatile organic compounds emission from dry building materials

A numerical and an analytical model were developed to predict the volatile organic compound (VOC) emission rate from dry building materials. Both models consider the mass diffusion process within the material and the mass convection and diffusion processes in the boundary layer. All the parameters, the mass diffusion coefficient of the material, the material/air partition coefficient, and the mass transfer coefficient of the air can be either found in the literature or calculated using known principles. The predictions of the models were validated at two levels: with experimental results from the specially designed test and with predictions made by a CFD model. The results indicated that there was generally good agreement between the model predictions, the experimental results, and the CFD results. The analytical and numerical models then were used to investigate the impact of air velocity on emission rates from dry building materials. Results showed that the impact of air velocity on the VOC emission rate increased as the VOC diffusion coefficient of the material increased. For the material with a diffusion coefficient > 10 −10 m 2/ s , the VOC emission rate increased as the velocity increased; air velocity had significant effect on the VOC emission. For the material with a VOC diffusion coefficient < 10 −10 m 2/ s , the VOC emission rate increased as the velocity increased only in the short term; < 24 h . In the medium- to long-term time range, the VOC emission rate decreased slightly as the air velocity increased; velocity did not have much impact on these materials. Furthermore, the study also found that the VOC concentration distribution within the material; the VOC emission rate and the VOC concentration in the air were linearly proportional to the initial concentration. However, the normalized emitted mass was not a function of the initial concentration: it was a function of the properties of the VOC and the material.

Modelling of Coupled Heat and Moisture Transfer in Grain Kernels by Modified Luikov’s Equations

The existing heat and mass transfer models are based on the Luikov’s equations. In these equations the mass diffusion process is driven by the moisture gradients. This approximation can lead to inaccurate predictions of the dehydrations processes if the body is non-isotropic. In the proposed model the Luikov’s equations have been rewritten using the capillary potential gradients. Furthermore, the advised calculation method makes it possible to determine the equilibrium moisture contents in the biological material where measurements are practically impossible. The suggested heat and mass transfer model gives more accurate and more sophisticated results from physical point of view then the existing ones.

Modeling of gas dynamics for a laser-generated plasma: propagation into low-pressure gases

The physical phenomena involved during three-dimensional axisymmetric laser-induced plasma expansion into background gas are numerically studied. For this purpose, a multispecies hydrodynamic model is developed which considers the effects of mass and ambipolar diffusions, thermal conduction, viscosity, and nonequilibrium conditions for ionization. This model is applied to describe quantitatively the Si plasma plume expansion into Ar or He gases. It is shown that the mechanism of plasma expansion depends critically on both the pressure and mass of the background gas. The shock front expansion is found to be strongly correlated with ion dynamics. A pronounced difference between heavy-particle and electron temperatures indicates a persistent lack of equilibrium between the heavy particle and the electron in the plasma plume expansion. The Si atoms of the rarefied plume are essentially driven by the backward-moving background gas as a result of a mass diffusion process. It is also noted that the diffusion processes are only important in the last expansion stage, and are less significant in the first stage. Therefore, it is shown that a computation which does not include diffusion effects (Euler equations) can adequately describe only the earliest stage of plasma expansion into background gas. The ability of the Navier-Stokes hydrodynamic multispecies model to predict the key role of the background gas type (Ar, He) and pressure is demonstrated.

Influence of Heat Transfer on the Kinetic Process Involved during the Adsorption of Soluble Organic Substances on to Porous Polymeric Sorbents

During adsorption from the gaseous phase on to solid sorbents, it is known that heat transfer generally induces a mass transfer process. The present investigation was concerned with the solution of some questions relating to the heat transfer phenomenon during adsorption from the aqueous phase. In so doing, the thermodynamic and kinetic characteristics of the adsorption of benzene derivatives from aqueous solution by polymeric sorbents, i.e. Polysorb 60/100 and sample G-5, have been studied using the method of statistical moments for calculating the heat diffusion contribution to the general mass diffusion process. This method consists of the mathematical analysis of the temperature dependence of the kinetic diffusion curves on the basis of a linear adsorption isotherm. The contribution of the kinetics of heat transfer to the first sum of the moment of the kinetic curve may be defined as: [Formula: see text] where Mlq is that part of the first moment which represents heat diffusion and MID is the diffusion part of the first moment. The results obtained for the different systems investigated show the existence of a heat transfer effect on the kinetic adsorption process. This effect which retards the heat transfer process may be expressed in terms of the final rate of heat dispersion. The external contribution of heat transfer to the general mass transfer has been evaluated as 3–11% for various research systems. It has been shown that the evaluated contribution of the heat transfer is larger during adsorption by hydrophilic polymeric sorbents than when hydrophobic ones are employed. This fact may be connected with the different chemical composition and density of the sorbents.

Experimental investigation of mass transfer in a grid-generated turbulent flow using combined optical methods

The aim of this paper is to provide some significant experimental results for the mass diffusion process from a point source in a quasi-isotropic homogeneous turbulent field generated by means of a grid. Experimental data for the mean, the fluctuating concentration fields, and the turbulent mass flux, which is the cross-correlation between concentration and velocity, are provided. Two combined optical non-intrusive methods, laser-induced fluorescence and laser Doppler velocimetry, have been used to measure simultaneously and instantaneously the concentration of the passive contaminant and the velocity of the flow. The experimental results are compared with a theoretical development, including the concept of turbulent diffusivity. An experimental determination of the turbulent diffusivity is also performed.

Isochoric heat capacity Cv at the critical point of SF6 under micro- and earth-gravity

Abstract As a consequence of the diverging compressibility, earth-bound experiments near the gas-liquid critical point suffer extremely from the strong influence of gravity. Caloric measurements, in particular of the heat capacity Cv, are inevitably affected by local changes of the density throughout the volume. Experimental results thus rather represent some integral average over all density and temperature variations than a thermodynamic point of state. The first measurements of Cv under micro-gravity conditions for the fluid SF6 near the critical state conducted during the German Spacelab Mission D1 in Oct./Nov. 1985 are reported here. Due to the surprising μg-results, the influence of gravity and equilibration have subsequently been investigated. By numerical simulation of the equilibration process, it became evident that the flattening of the Cv-curves observed could be caused by a non-uniform mass distribution and the slow mass diffusion process.

Prediction of the Mixture Effect On Boiling in Vertical Thermosyphon Reboilers

Abstract The present study has investigated the effect of mixtures on the nucleate boiling contribution to flow boiling inside vertical tubes at low vapor qualities, operating conditions typical of vertical thermosyphon reboilers. The mass diffusion process created by the composition difference between the vapor and liquid phases was found to impede the boiling process and substantially reduce the nucleate boiling heat transfer contribution to flow boiling in mixtures. Two widely quoted flow boiling mixture correction factors were tested against a published set of experimental data for ethanol/cyclohexane mixtures and were determined to be only partially reliable. Instead, several theoretically based nucleate pool boiling mixture correlations were shown to be accurate for flow boiling conditions and are recommended for design use.

Study of the [formula omitted] ratios of light and heavy fragments from collisions of 129Xe, 132Xe and 132Xe with 197Au near the interaction barrier

The reactions of 761 MeV 129Xe ions, 764 MeV 132Xe ions and 787 MeV 136Xe ions with thick 197Au targets were investigated with radiochemical techniques. From the relative shift of the N/ Z ratios observed with the different Xe projectiles a characteristic time of the order of 10 −22 sec is estimated for the complete relaxation of the charge asymmetry mode. The most probable N/ Z ratios deviate considerably from the N/ Zratio of the composite system. Apparently, in the mass diffusion process a continuous readjustment of 〈 N/ Z〉 values takes place which minimizes the potential energy of the two separating fragments. The inclusion of shell corrections at low excitation energies and corrections for the breaking of nucleon pairs in the transfer process are shown to be essential in the potential energy calculations. These results, together with evidence for small widths in the N/ Z distributions indicate strong correlations between proton and neutron exchanges in the damped collision process.

Studies of particulate plume diffusion over laboratory wind-generated water waves

A numerical simulation of the turbulent mass diffusion process from an elevated, continuous point source over a wind-disturbed water surface is described. The diffusion equation, with models for turbulent diffusivities, in the boundary layer over water waves was solved with a successive-over-relaxation finite difference scheme. In the numerical computation, measured quantities of flow conditions such as mean velocities, turbulent intensities and boundary layer thickness were used. To improve computational efficiency, a variable grid system was used. The grid system was designed to expand with the spread of the diffusing plume. The water surface was viewed, in the mean, as a flat surface with influences of the wavy surface implicitly incorporated into the turbulent diffusivities. The diffusivities are functions of the turbulent intensities, the boundary layer thickness, and the scale of the phenomenon. The numerical solutions were compared with experimental results of particle concentration measurements obtained with an optical system ( Liu and Karaki, 1972a) in a wind-water tunnel at Colorado State University. With the net mean convection properly corrected for the effects of the particle fall velocity, streamline displacements in a developing boundary layer, and secondary flow (in the experimental facility), general agreements were observed between numerical solutions and corresponding experimental results.