diffusive mass transfer
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Reliable mathematical models are important tools for design/optimization of haemo-filtration modules. For a specific module, such a model requires knowledge of fluid- mechanical and mass transfer parameters, which have to be determined through experimental data representative of the usual countercurrent operation. Attempting to determine all these parameters, through measured/external flow-rates and pressures, combined with the inherent inaccuracies of pressure measurements, creates an ill-posed problem (as recently shown). The novel systematic methodology followed herein, demonstrated for Newtonian fluids, involves specially designed experiments, allowing first the independent reliable determination of fluid-mechanical parameters. In this paper, the method is further developed, to determine the complete mass transfer module-characteristics; i.e., the mass transfer problem is modelled/solved, employing the already fully-described flow field. Furthermore, the model is validated using new/detailed experimental data on concentration profiles of a typical solute (urea) in counter-current flow. A single intrinsic-parameter value (i.e., the unknown effective solute-diffusivity in the membrane) satisfactorily fits all data. Significant insights are also obtained regarding the relative contributions of convective and diffusive mass-transfer. This study completes the method for reliable module simulation in Newtonian-liquid flow and provides the basis for extension to plasma/blood haemofiltration, where account should be also taken of oncotic-pressure and membrane-fouling effects.

Особенность состояния системы жидкость–твердое тело в метастабильном растворе вещества состоит в том, что она (система) претерпевает два фазовых превращения в вакуум-аппарате (ВА) – кристаллообразование и растворение, требующие экспериментального изучения и описания в силу их важности при совершенствовании технологии производства кристаллического сахара. Однако и теоретическое обоснование фазовых превращений в метастабильном растворе разработано недостаточно. В статье предпринята попытка количественно поставить и решить проблему учета возникающего при проведении обработки метастабильного сахарсодержащего раствора повышения температуры в результате конденсации молекул на центре концентрации при пересыщении в ВА. В качестве основы численного моделирования поставленной задачи использовали программные продукты информационной среды Mathcad. С использованием модели диффузионного массопереноса сахарозы в пересыщенном растворе к затравке был разработан алгоритм расчета зависимости массы сахарозы от времени проведения процесса кристаллизации. На примере сахарозы дана оценка влияния физического фактора – выделяющейся при кристаллообразовании теплоты на расчет теплового баланса и производительности ВА. The peculiarity of the state of the liquid-solid system in a metastable solution of a substance is that it (the system) undergoes two phase transformations in a vacuum apparatus (VA) – crystal formation and dissolution, requiring experimental study and description due to their importance in improving the technology of production of crystalline sugar. However the theoretical justification of phase transformations in a metastable solution has not been sufficiently developed. The article attempts to quantify and solve the problem of taking into account the temperature increase that occurs during the processing of a metastable sugar-containing solution as a result of condensation of molecules at the concentration center during supersaturation in VA. Software products of the Mathcad information environment were used as the basis for numerical modeling of the task. Using a model of diffusive mass transfer of sucrose in a supersaturated solution to the seed, an algorithm was developed for calculating the dependence of the sucrose mass on the time of the crystallization process. On the example of sucrose, an assessment of the influence of a physical factor – the heat released during crystallization on the calculation of the thermal balance and the productivity of the VA is given.

In the present study, convective diffusive mass transfer is considered, along with effects of particle drag under the influence of a magnetic field concerning drug delivery in the presence of the catheter. A concentric annular region is created by the presence of a catheter, and the effects of which on mass transfer are considered. A model on the hydrodynamics of the fluid, blood flow, and convective diffusive mass transfer of the species is presented. Here, an attempt is made to analyze a drug delivery method for delivering a drug to a specific site in the body and for this analysis, considered a channel bounded by the tissue region where the drug is targeted. The magnetic field induces pulsatile flow, which affects the mass transfer. The graphs predict that the mass transfer increases from the lumen region to the tissue region. Peclet number and magnetic parameter are the parameters that significantly affect carrying drugs towards the tissue. The results are well agreed with the physical phenomena of the problem as well as many biomedical applications.

Abstract During gas injection in ultra-tight fractured reservoirs, molecular diffusion can play a dominant role in the mass transfer process and enhance recovery by extracting oil components from matrix and delaying gas breakthrough. There has been a growing interest from scholars and operators to study the effect of diffusive mass transfer on the potential incremental recovery from CO2 and rich gas injection. However, many fundamental questions pertaining to the physics of multicomponent multiphase flow and transport are still left unanswered. This paper aims to improve the understanding of multicomponent diffusive mass transfer between matrix and fracture blocks through experimental and modeling work. Displacement experiments were carried out using analog fluids and mesoporous medium to effectively isolate and study the relevant physical mechanisms at play. The experiments were performed in packed columns utilizing silica-gel particles that have internal porosity. The particle size is 40-70 micron with highly controlled internal pore size of 6 nm that makes up approximately 50% of the overall porosity. The quaternary analog fluids system consists of Water, Methanol, Isopropanol, and Isooctane, was used because it mimics the phase behavior of CO2, Methane, Butane and Dodecane mixtures at 2,280 psi and 100°C. Our selection of the analog fluid system and porous medium allowed us to investigate matrix-fracture fluid exchange as observed during an enhanced recovery operation in an ultra-tight fractured system. The effluents from these displacement experiments served as the basis for our analysis of diffusive mass transfer. The role of molecular diffusion in the displacement experiments was investigated by first performing separate diffusion experiments to obtain diffusion coefficients for all relevant binary mixtures. Infinite dilution diffusion coefficients were measured for all binary mixtures and then used to model binary and multicomponent diffusion coefficients over the whole composition range. The accuracy of this approach was determined by performing additional binary diffusion experiments over a broader range of compositions. The displacement experiments were simulated using an in-house simulator and excellent agreement was obtained: The extensive experimental/modeling work related to the diffusion coefficients of the analog fluid system was used in interpreting the diffusive mass transfer between the matrix (stagnant) and fracture (flowing) domains via a 1D linear model. The presented work provides new insights into the role of diffusive mass transfer in ultra-tight fractured systems and builds a framework to highlight the critical data needed to effectively characterize and simulate recovery from such complex geological settings.

Abstract The gas content is one of the important factors in cavitation, which may increase the pressure inside the cavity through the diffusive mass transfer of the dissolved gas into the cavity. In the present study, we try to directly measure the cavity pressure inside the sheet cavity at the throat of a converging-diverging nozzle. Then the influences of the flow velocity and the gas content (amount of dissolved oxygen) on the gas partial pressure are investigated. It is found that, even in low gas content level, the cavity pressure is slightly but apparently higher than the saturated vapor pressure, indicating the presence of gas partial pressure. It is observed that the gas partial pressure in significantly developed cavitation is almost constant regardless of the flow velocity but slightly increases against the increase of the saturation level of dissolved gas. It is also found that the gas partial pressure inside cavity depends on the degree of cavitation development; the gas partial pressure decreases with the development of cavitation.

<p>The Late Silurian Moine Thrust Zone (MTZ) of the NW Highlands of Scotland has long been fundamental to the understanding of the nature and processes that occur during thrust tectonics in the upper continental crust. This complex imbrication zone formed during final Scandian stages of the Caledonian orogeny when collision of Baltica and Laurentia led to WNW-ESE tectonic foreshortening of >100km. The MTZ juxtaposed greenschist to amphibolite facies Neoproterozoic metamorphic rocks of the Moine Supergroup over sequences of little metamorphosed Cambro-Ordovician and Neoproterozoic sedimentary rocks and their Neoarchean to Paleoproterozoic gneissic basement in a zone ranging from <1km to >20km wide.</p><p>The mechanical problems represented by thrust wedges being transported over such great distances without losing their internal cohesion has highlighted the role played by detachment structures and the need for mechanisms that create significant weakening along basal detachments that allow overthrusts to accommodate major horizontal displacements in the shallow crust. Field studies and use of section balancing techniques have highlighted that a substantial proportion of the displacement seems to be accommodated along detachments that follow specific stratigraphic levels.</p><p>Other than the Moine Thrust Mylonites and the mylonitised parts of the Cambrian Quartzites, relatively little is known about the grain scale deformation and potential weakening processes that have occurred in other parts of the MTZ. New lithological descriptions of the fault rocks and sedimentary protoliths observed in the Assynt, Durness and Eriboll areas are presented here and provide detailed microstructural evidence for the long-term weakening mechanisms that were operating at the time. These mechanisms are consistently related to the onset of grain size reduction, triggered by both chemical enhanced and geometric processes. These include feldspar alteration to fine phyllosilicates associated with cataclasis and dynamic recrystallization of quartz.</p><p>Pressure solution, evidenced by changes in the shape of minerals along cleavage surfaces and the presence of dissolution seams and caps, is widespread throughout the studied rock sequences. The profuse occurrence of this grain-scale mechanism makes it very likely that syn-deformational fluid-influx lead to the destruction of load bearing microstructural frameworks and the development of interconnected weak layers due to alteration, explaining the occurrence of detachments within impure layers of the predominantly quartzose Pipe Rock and Salterella Grit members. The progressive development of these interconnecting fine-grained weak layers resulting from incongruent diffusive mass transfer is enhanced in the more mineralogically heterogeneous units of the Cambro-Ordovician sedimentary sequence (in particular, Fucoid Beds dolomitic siltstones and Durness limestones) explaining the consistently observed slip localization in these horizons.</p>

<p>Micro-cracks in fault damage zones can heal through diffusive mass transfer driven by differences in chemical potential, with rates controlled by temperature and pressure. The diffusion of pore fluid pressure in fault damage zones accelerates mass diffusion and assists healing processes. In this work, we use fluid flow model coupled with heat transfer and crack healing to investigate, through different scenarios, the role of subsurface warm fluid migration, along damage zones, in enhancing healing and re-shaping the fault permeability structure. Our results show that if the flow communication exists between the bed and only one side of the damage zone and not the other side, it leads to an asymmetric permeability structure caused by healing in the side circulated by fluids (ex: Rapolano geothermal area, Italy). Another scenario is when the damage zone adjacent to the fault core is not the interval with the highest permeability, as conventionally expected, which is the case of the Alpine Fault, New Zealand. As shown by our simulations, this can be due to healing by diffusive mass transfer, favored by the localized high geothermal gradients and the upward fluid migration through the fault relay structure.</p>