Простая теория многокомпонентной диффузии и моделирование горения стехиометрической смеси H-=SUB=-2-=/SUB=-/O-=SUB=-2-=/SUB=-

A theory of multicomponent diffusion based on Fick's law is proposed, where, when writing the Maxwell-Stephen equations, a multicomponent mixture is represented as consisting of two components: the isolated substance and all the others with average characteristics. The number of diffusion coefficients is significantly reduced, the method for their calculation is indicated, and they strongly depend on the concentration of the mixture components. Based on the results of this theory, the combustion of an H2/O2 mixture with an equivalence ratio equal to unity was simulated. For each component, great chemical work is carried out with alternating signs, but in total they partially destroy each other. Also, in the chemical reaction zone, there is a strong change in the stoichiometric ratio of the H2 and O2 components.

Conditions for Consistency of Equations of Nonlinear Diffusion in Complex Systems with Thermodynamic Constraints

The paper proposes relations between the coefficients of nonlinear diffusion in complex systems within the framework of the mechanism approach of Ya. I. Frenkel for matching equations with thermodynamic constraints. Three conditions for limiting the microdescription of a complex system have been identified the fulfillment of which ensures the thermodynamically correct behavior of the equations of nonlinear multicomponent diffusion.

Potential Uranium Migration within the Geochemical Gradient of the Opalinus Clay System at the Mont Terri

Transport properties of potential host rocks for nuclear waste disposal are typically determined in laboratory or in-situ experiments under geochemically controlled and constant conditions. Such a homogeneous assumption is no longer applicable on the host rock scale as can be seen from the pore water profiles of the potential host rock Opalinus Clay at Mont Terri (Switzerland). The embedding aquifers are the hydro-geological boundaries, that established gradients in the 210 m thick low permeable section through diffusive exchange over millions of years. Present-day pore water profiles were confirmed by a data-driven as well as by a conceptual scenario. Based on the modelled profiles, the influence of the geochemical gradient on uranium migration was quantified by comparing the distances after one million years with results of common homogeneous models. Considering the heterogeneous system, uranium migrated up to 24 m farther through the formation depending on the source term position within the gradient and on the partial pressure of carbon dioxide pCO2 of the system. Migration lengths were almost equal for single- and multicomponent diffusion. Differences can predominantly be attributed to changes in the sorption capacity, whereby pCO2 governs how strong uranium migration is affected by the geochemical gradient. Thus, the governing parameters for uranium migration in the Opalinus Clay can be ordered in descending priority: pCO2, geochemical gradients, mineralogical heterogeneity.

Analytical solution of diffusion equations in multicomponent systems when applying diffusion coatings

For multicomponent coatings, analytical equations are obtained that take into account the diffusion coefficients in the concentration equations. It is shown, that to solve the problem of multicomponent diffusion in a solid solution containing substitutional elements and interstitial elements, it is advisable to use the equations for the concentrations of chemical elements. Keywords: multicomponent coating, solid solution, concentration, diffusion coefficient, analytical solution [email protected]

Numerical Calculation of the Diffusion Process in Multicomponent Hydrocarbon Gas Mixtures

Knowledge of the laws of diffusion is necessary in the description, design and calculation of the mass transfer process in the production, operation and transportation of gaseous fuels. In this article, the calculation of diffusion processes for five natural hydrocarbon gas mixtures into the air was carried out. The effective diffusion coefficients and matrix coefficients of multicomponent diffusion were determined. Also the advantages of using effective coefficients in the description of mass transfer were shown.

An Improved Multicomponent Diffusion Model for Compositional Simulation of Fractured Unconventional Reservoirs

Summary Most simulators currently use the advection/diffusion model (ADM), where the total flux comprises Darcian advection and Fickian diffusion. However, significant errors can arise, especially for modeling diffusion processes in fractured unconventional reservoirs, if diffusion is modeled by the conventional Fick’s law using molar concentration. Hence, we propose an improved multicomponent diffusion model for fractured reservoirs to better quantify the multiphase multicomponent transport across the fracture/matrix interface. We first give a modified formulation of the Maxwell-Stefan (MS) equation to model the multicomponent diffusion driven by the chemical potential gradients. A physics-based modification is proposed for the ADM in fractured reservoirs, where fracture, matrix, and their interface are represented by three different yet interconnected flow domains to honor the flux continuity at the fracture/matrix interface. The added interface using a more representative fluid saturation and composition of the interface can hence better capture the transient mass fluxes between fracture and matrix. The proposed approach is also implemented in an in-house compositional simulator. The multicomponent diffusion model is validated with both intraphase and interphase diffusion experiments. Then, the improved model for fracture/matrix interaction is compared with a fine-grid model. The proposed multiple interacting continua (MINC) model with three continua (MINC3) can better match the fine-grid model’s result than the double-porosity (DP) model, which only obtains a fair match at an early time. Then, we simulate a gas huff ‘n’ puff (HnP) well in the Permian Basin to investigate the effect of diffusion within the fractured tight oil reservoir. The simulation reveals that diffusion has a minor effect on the performance of depletion when oil is the dominant phase. For gas HnP, the simulation neglecting diffusion will underestimate the oil recovery factor (RF) but overestimate the gas rate. The DP approach tends to overestimate the RF of heavy components but leads to a similar cumulative oil RF compared with MINC3. With the diffusion included in the simulation, gas HnP performance becomes more sensitive to the soaking time than the model without diffusion. Although increasing the soaking time will lead to a higher RF after considering diffusion, the incremental oil is not sufficiently large to justify a prolonged soaking time.

RECENT TRENDS IN OSMOTIC DEHYDRATION OF FRUITS: A REVIEW

The marvel of expulsion of water from lower solvent concentration to higher concentration by a semi-perimeable membrane is osmotic dehydration, resulting in equilibrium state on both sides of the membrane. As it decreases the water activity of fruits. It is found to be most widely used application for preserving food materials. Due to colour, scent, nutritional constituents and flavour compound retention value, osmotic dehydration is favoured over other methods. Drying, shower drying, freezedrying, solidifying, vacuum packing, canning, syrup conservation (osmotic dehydration), sugar crystallization, nourishment illumination and the addition of preservatives or inert gases such as carbon dioxide are typical methods of applying these processes. The solutes used in osmotic parchedness are ordinarily sugar syrup with fruit slices or 3d shapes, and salt (sodium chloride) or vegetable brine. This can be the method of multicomponent diffusion. Water moves from fruits or vegetables to the solution in this process and certain fruit and vegetable components such as minerals, vitamins, fruit acids, etc also pass into the solution along with water to the fruits and vegetables, sugar and salt migrate. Examples that are considered are Gooseberry Murabbas (Aonla), apples, sweets, candies of Different fruits and vegetables, including pethas, parwal, Osmosis-made sweets in sugar syrup are the most popular items of commercial value available in the market made from fruits. It is processed in a brine solution before drying in pickles made from raw mango. In brine, various vegetables are handled to lower their moisture content

Multicomponent diffusion in atmospheric aerosol particles

Condensed phase mass transport in single aerosol particles is investigated using a linear quadrupole electrodynamic balance (LQ-EDB) and the Maxwell–Stefan (MS) framework.