Correlation of high-pressure thermal conductivity,viscosity, and diffusion coefficients for n-alkanes

Thermal conductivity, viscosity, and self-diffusion coefficient data for liquid n-alkanes are satisfactorily correlated simultaneously by a method based on the hard-sphere theory of transport properties. Universal curves are developed for the reduced transport properties ^*, ^*, and D ^* as a function of the reduced volume. A consistent set of equations is derived for the characteristic volume and for the parameters R , R , and R _D, introduced to account for the nonsphericity and roughness of the molecules. The temperature range of the above scheme extends from 110 to 370 K, and the pressure range up to 650 MPa.     

A boundary value technique for the solution of some diffusion equations with concentration-dependent diffusion coefficients

A boundary value method is applied to the problem of diffusion equations with concentration-dependent diffusion coefficients. The resulting non-linear system of difference equations is solved with exceptional speed by using a form of the Gauss elimination method. This method of solving problems with a semi-infinite domain was found to be more accurate and up to ten times faster than initial value techniques.     

Isotopic fractionation during diffusion of transition metal ions in solution

Isotope ratios and elemental concentrations were measured in aqueous solutions sampled at varying distances from sources of Fe or Zn ions. The measurements reveal fractionation of isotopes resulting from pure diffusion in solution. Our data demonstrate that diffusion alone can cause changes in (56)Fe/(54)Fe and (66)Zn/(64)Zn isotope ratios in excess of -0.3 per thousand. These findings thus confirm previous suspicions that transport processes contribute to observed variations in isotopic compositions. Diffusion must therefore be considered when attempting to make inferences from isotope measurements on samples originating from aqueous systems where concentration gradients may develop.     

Determination of diffusion coefficients of glycerol and glucose from starch based thermoplastic compounds on simulated physiological solution

Blends of corn starch with poly(ethylene-vinylalcohol) copolymer (SEVA-C) have been studied and reported as biodegradable. These materials are known to be sensitive to enzymatic action, evidencing a degradation of the starch phase in -amylase assays. However, from the physical-chemical point of view the degradation of the blend is mainly associated with the leaching of glycerol, since other compounds are not released and no carbohydrates were found in the degradation solution. Based on these results, the present work attempts to determinate the respective diffusion coefficients. Four different experiments were performed, using samples with different thicknesses that were immersed in a simulated physiological solution. High performance liquid chromatography (HPLC) was used to separate the sugar derivatives and glycerol from the degradation solutions. The obtained data were fitted to an empirical model to allow the estimation of the diffusion coefficient for glycerol and glucose, based on the analytical solution for Ficks law of diffusion, and a good agreement was found (R² 1). The glycerol leaches quickly out during the first few days of immersion, stabilizing thereafter, presenting greater diffusion coefficients for thicker samples. As the quantity of saccharides in the solution remains almost invariable along the experiments, this work also confirms that the degradation process is difficult without the action of enzymes.     

Prediction of the temperature dependence of binary diffusion coefficients of gaseous systems from thermal diffusion factors and diffusion coefficients at 300 K

Data are presented which enable binary diffusion coefficients and their concentration dependences to be predicted from diffusion coefficients and thermal diffusion factors at 300 K. The results up to 2000 K are compared with corresponding values derived from the complication of Mason and Marrero. Paper dedicated to Professor Edward A. Mason.     

Fluorescence correlation spectroscopy with patterned photoexcitation for measuring solution diffusion coefficients of robust fluorophores

Patterned fluorescence correlation spectroscopy is developed as a new technique for measuring diffusion coefficients of photostable fluorescent probe molecules. In this method, interference between two intersecting, coherent laser beams creates an excitation fringe pattern from which fluorescence emission is monitored. Spontaneous concentration fluctuations of fluorescent molecules within the excitation volume are detected as excess noise on a fluorescence transient; concentration fluctuations are driven primarily by diffusion of these molecules between interference fringes although contributions from photobleaching and diffusion over the entire pattern dimensions can also be observed. Autocorrelation of the fluorescence transient allows analysis of the temporal characteristics of the fluctuations, which were used to determine solution diffusion coefficients; the method was applied to study the diffusion of Rhodamine 6G (R6G) in water/methanol solutions containing added electrolyte and in pure ethanol. The method can be used to characterize the diffusive transport of fluorescently labeled species, which is an important issue in designing small-volume detection experiments.     

Thermodynamic analysis of diffusion coefficients

An analysis is presented of the process of diffusion of a multicomponent fluid through a solid porous medium. It is shown that there are conditions in which the diffusion fluxes vanish, and for which the multicomponent system may be replaced by a one-component system in aerodynamic problems.     

Vapor-liquid activity coefficients for methanol and ethanol from heat of solution data: application to steam-methane reforming

This paper presents equations and curves to calculate vapor-liquid phase equilibria for methanol and ethanol in dilute aqueous solution as a function of temperature, using activity coefficients at infinite dilution. These thermodynamic functions were originally derived to assess the distribution of by-product contaminants in the process condensate and the steam-system deaerator of a hydrogen plant [Paper ENV-00-171 presented at the NPRA 2000 Environmental Conference, San Antonio, TX, 10-12 September 2000], but have general applicability to other systems as well. The functions and calculation method described here are a necessary piece of an overall prediction technique to estimate atmospheric emissions from the deaerator-vent when the process condensate is recycled as boiler feed water (BFW) make-up.Having such an estimation technique is of particular significance at this time because deaerator-vent emissions are already coming under regulatory scrutiny in California [Emissions from Hydrogen Plant Process Vents, Adopted 21 January 2000] followed closely elsewhere in the US, and eventually worldwide. The overall technique will enable a permit applicant to estimate environmental emissions to comply with upcoming regulations, and a regulatory agency to evaluate those estimates. It may also be useful to process engineers as a tool to estimate contaminant concentrations and flow rates in internal process streams such as the steam-generating system. Metallurgists and corrosion engineers might be able to use the results for materials selection.     

Determination of heat liberation coefficients within a channel by solution of the converse thermal conductivity problem

A method is presented for determination of local heat liberation coefficients, based on numerical solution of the two-dimensional converse thermal conductivity problem.Translated from Inzhenerno-Fizieheskii Zhurnal, Vol. 56, No. 3, pp. 391–395, March, 1989.     

Non-constant distribution coefficients from experimental data: Theoretical

Techniques were developed for calculating the distribution coefficient k from experimental data for directional crystallization and zone melting. Simplifying assumptions such as constant k and constant zone length were $\text{not}$ made. Error analyses were performed to determine the optimal calculation methods.     

Effective thermal conductivity coefficients of a grainy medium

An exact solution is presented for the problem of determination of effective thermal conductivity coefficients of a composite medium with regularly spaced spherical grains.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 2, pp. 336–344, February, 1981.     

Removal of lead ions from solution by phosphosilicate glass

A new, selective and sensitive on-site spectrophotometric method for the determination of antimony at trace level in water, soil and dust samples of Central India has been demonstrated. It is based on the color reaction of Sb(III) with I⁻ ions in the presence of a cationic surfactant cetylpyridinium chloride (CPC) in acidic media, and subsequent extraction of the complex with N-phenylbenzimidoylthiourea (PBITU) into chloroform to give a yellow colored complex. The value of apparent molar absorptivity of the complex in the terms of Sb is (7.84) × 10⁴ l mol⁻¹ cm⁻¹ at 440 nm. The detection limit of the method is 5 ng ml⁻¹. In addition, the present method is free from interferences of all metal ions that are associated during the determination of antimony in environmental samples.     

Calculation of diffusion coefficients for dense gases

Calculated values of mutual gas diffusion coefficients are compared to values measured by the laser interferometry method.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 3, pp. 438–442, March, 1988.     

Partial analytical solution of a model used for measuring oxygen diffusion coefficients of polymer films by luminescence quenching

Many aspects of optical chemical sensor design would benefit from a better knowledge of the diffusion properties of the analyte in the polymer host. The response times of such sensors to a step change of analyte concentration are of vital interest for many applications of fast-responding sensors. Further, the diffusion properties govern their quenching behavior and their sensitivity. A method for determination of the diffusion constant of oxygen in polymers has been developed and used by several groups in the past. The underlying mathematical model for luminescence quenching by molecules of a gas in a single sensing layer on an impermeable support has not yet been completely derived in an analytical form and still uses tedious numerical methods. We present a partial analytical solution to the problem of modeling the time dependence of luminescence generated by in- or out-diffusion of a gaseous quencher in a polymer film in which a luminophor is immobilized and offer a suitable method to predict sensor response times.     

Temperature dependence of the diffusion coefficients of gases

The use of empirical power laws to calculate the diffusion coefficients of gases is considered. The method of similitude is used to obtain generalized relations which permit the calculation of the diffusion coefficients of gases in temperature ranges not covered by experiment.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 3, pp. 530–534, September, 1969.     

Molecular dynamics simulation to assess the effect of temperature on diffusion coefficients of different ions and water molecules in C-S-H

Diffusion is a particle transportation process beginning from one point of a system to another through random molecular motion. This process depends on various parameters like temperature, concentration gradient, and particle size. The objective of this article is to assess the variation of diffusion coefficients of water molecules, chloride and sodium ions against different temperatures in calcium silicate hydrates (C-S-H) through molecular dynamics simulation. A uniform sodium chloride solution is modeled between cement hydrate layers with no concentration gradient. In such a solution, temperature could affect diffusion process in a significant manner. The two most important crystalline mineral analogues of C-S-H, tobermorite and jennite, are applied in this simulation. Diffusion coefficients of different ions and water molecules are found in different temperatures. It is revealed that diffusion coefficient is higher at high temperatures. Activation energies of chloride and sodium ions transport in cement hydrates are calculated through Arrhenius law. Output values of diffusion coefficients and activation energies are compared to previous experimental and simulation results in the related literature. A multi-scale analysis is run to estimate the penetration depth of \(\mbox{Cl}^{-}\) ions in cement paste through Fick’s second law.     

An analytical method of calculating variable diffusion coefficients

An analytical method of calculating variable diffusion coefficients has been developed. The Boltzmann-Matano graphical method used up to now has certain disadvantages which restrict the acuracy of the evaluated diffusion coefficients. Due to these disadvantages, the accuracy of this method is restricted even more when diffusion coefficients are determined in an area of low concentration of the diffused species of atom. The reliability of the analytical expression obtained in the present investigation has been verified experimentally by comparing the results obtained with those of the graphical method. On the basis of this comparison the analytical method can claim an accuracy better than, or at least equal to, that of the graphical method.     

Seafloor temperature and conductivity data from Stefansson Sound, Alaska

Overconsolidated sediments, seasonal seafloor freezing, and ice-bonded permafrost are unique features in shallow arctic coastal waters. They are related to low seawater temperatures and varying salinities. Seabed temperatures can be less than −1.0°C for much of the year, with noticeable warming occurring only during the summer months. Observations from recent deployment of three instruments in Stefansson Sound and data from an earlier deployment, which included sites in Harrison Bay, showed decreasing mean annual seafloor temperatures with increasing water depth, ranging from −0.9°C in 4.4 m of water to −1.6°C in 14 m of water. Salinities also varied seasonally, with noticeable freshening developing during the summer and highly uniform values occurring during the winter. Periodic temperature and salinity measurements at sites in Stefansson Sound, made during August 1987 and August 1989, also helped verify the data obtained with the seabottom instruments.Seasonal freezing of the seabed can begin in late September and may noticeably change its engineering properties. In areas of coarse-grained sediments, ice bonding and strengthening of the seabed can result. In areas of fine-grained sediments it appears that seasonal freezing of the seafloor can cause overconsolidation of the seabed sediments. This densification process can result in a significant permanent increase in strength.     

The diffusion of ions through water-saturated cement

The interdiffusion of l^? and Cl^? ions and the tracer diffusion of Cs⁺ ions in watersaturated Ordinary Portland Cement have been measured at 30° C as a function of water/ cement ratio at fabrication. The diffusion was strongly influenced by the water/cement ratio in an approximately exponential manner and the Cs⁺ ions were significantly less mobile than the other ions. Diffusion measurements and electrical conductivity measurements have also been made as a function of temperature and reveal that significant irreversible changes in pore structure were induced on heating. The implications of the observations for the diffusion mechanism and the probable pore structure of the cement paste are discussed.