Diffusion Flow Research Articles

Dispersion with a pinch of salt

Ding (J. Fluid Mech., vol. 970, 2023, A27) analysed the dispersion of a multicomponent electrolyte solution flowing through a channel. An inequality in ionic diffusion coefficients induces a spontaneous electric field that leads to nonlinear coupling of species fluxes. Ding presented an effective equation for the long-time evolution of the ionic concentration distributions, which revealed novel features compared with the classic case of an uncharged solute. This work highlights the rich physics of ion diffusion and electro-migration in non-uniform flows.

Microvascular proliferation is associated with high tumour blood flow by mpMRI and disease progression in primary prostate cancer

Active angiogenesis may be assessed by immunohistochemistry using Nestin, a marker of newly formed vessels, combined with Ki67 for proliferating cells. Here, we studied microvascular proliferation by Nestin-Ki67 co-expression in prostate cancer, focusing on relations to quantitative imaging parameters from anatomically matched areas obtained by preoperative mpMRI, clinico-pathological features and prognosis. Tumour slides from 67 patients (radical prostatectomies) were stained for Nestin-Ki67. Proliferative microvessel density (pMVD) and presence of glomeruloid microvascular proliferation (GMP) were recorded. From mpMRI, forward volume transfer constant (Ktrans), reverse volume transfer constant (kep), volume of EES (ve), blood flow, and apparent diffusion coefficient (ADC) were obtained. High pMVD was associated with high blood flow (p = 0.008) and low ADC (p = 0.032). High Ktrans, kep, and blood flow were associated with high Gleason score. High pMVD, GMP, and low ADC were associated with most adverse clinico-pathological factors. Regarding prognosis, high pMVD, Ktrans, kep, and low ADC were associated with reduced biochemical recurrence-free- and metastasis-free survival (p ≤ 0.044) and high blood flow with reduced time to biochemical- and clinical recurrence (p < 0.026). In multivariate analyses however, microvascular proliferation was a stronger predictor compared with blood flow. Indirect, dynamic markers of angiogenesis from mpMRI and direct, static markers of angiogenesis from immunohistochemistry may aid in the stratification and therapy planning of prostate cancer patients.

Radiative heat transport of Cattaneo‐Christov double diffusive Casson nanofluid flow between two rotating disks with Hall current and activation energy

AbstractThe present research uncovers the mathematical exploration of the magnetohydrodynamic radiative Casson nanofluid flow produced due to stretching and coaxially rotating surfaces of two disks inside a non‐Darcy porous medium under the dominance of the diacritic Hall current and heat generation. The energy field is displayed under the dominance of radiative and dissipative heat transport by involving the consequences of distinctive nonlinear thermal radiation, viscous dissipation, and Joule heating. The present study overcomes the barrier of heat and mass transport by annexing Cattaneo‐Christov double diffusion effects. The current exploration shows the characteristics of the concentration field due to arising chemical reaction incited by activation energy. A substantive mathematical problem is modeled by assigning nonlinear partial differential equations together with convective boundary conditions. A compatible similarity transformation comprised in the current study is exerted to produce a set of nonlinear ordinary differential equations with competent boundary conditions. The resulting mathematical model is numerically solved via dispensing the SLM. The present article deals with an in‐depth exploration of diagnostic flow parameters' attributes against the flow field and efficient physical quantities with the help of distinctive graphs and tables. As per the current investigation, the energy field becomes potent due to enhancing the stretching of each of the disks. Besides, augmenting the thermophoretic diffusion and chemical reaction boosts diluting the concentration of nanoparticles. The flow along the radial direction gets controlled near the upper disk under the increasing influence of the Hall current, intensity of the magnetic field, and stretching rate of the lower disk. On the other hand, the enlarging Casson parameter, rotation parameter, and stretching parameter for the lower disk lead to controlling the flow along the radial direction adjacent to the lower disk. Apart from that, the intense effects of the stretching rate of the upper disk and rotation rein axial flow throughout the flow region.

Evolution mechanism of unsteady internal flow of an ultra-high head pump-turbine in pump mode

In this study, the unsteady flow of an ultra-high-head model pump turbine in pump mode is numerically investigated, revealing the evolution mechanism of unsteady flow diffusion and propagation. Under high-flow-rate and high-efficiency conditions, stable flow separation occurs in the channel of the stay vanes. As the flow rate decreases, the flow separation gradually spreads in the radial direction and expands from the stay vanes to the guide vanes. This causes a partial blockage in the channel of the guide vanes. Meanwhile, the flow separation gradually switches from stable to unstable with a low-frequency rotation (about 4.8 % of the impeller rotational frequency) in the circumferential direction. In addition, the correlation between the hump characteristics and unsteady flow is discussed. For an ultra-high-head pump turbine, the unstable flow initiates at static operating conditions from the pump performance curve with negative slope, which is significantly different from medium and low-head pump turbines.

Chemolithoautotrophic Organic Matter Contributions to Subterranean Food Webs Dominated by Filter-feeders

Chemolithoautotrophic Organic Matter Contributions to Subterranean Food Webs Dominated by Filter-feeders

Order-preserving fuzzy transform for singular boundary value problems of polytropic gas flow and sewage diffusion

We describe a fuzzy transform method to analyze two-point singular and non-singular boundary value problems with high-order solution accuracies. This framework implements a fuzzy transform that approximates solutions with fourth-order accuracy at the interior mesh points. The fuzzy components and the triangular base function are locally arranged with a three-point linear combination of solution values. This yields a tri-diagonal Jacobian matrix that can be easily computed in a space-time efficient manner. Since a linear system relates solution values and fuzzy components, it is easy to obtain solution approximations via fuzzy components by a tri-diagonal matrix inversion. In addition to the numerical solution, it is easy to determine an approximate analytic solution using a cubic spline interpolating polynomial from the data available with fuzzy components. The error estimates for approximate analytical solutions and numerical solutions are obtained by integrated absolute error and maximum absolute errors. The new mechanism is analyzed for convergence using matrix theory. Several linear and nonlinear equations of practical importance related to sewage diffusion and polytropic gas flow models are simulated to corroborate the new scheme's utility and fourth-order convergence. Mathematics subject classification03B80, 65L10, 65L12

Nanosheets array-induced nanofluidic channels toward efficient primary batteries-coordinated textiles

Flexible hygroelectric generators (HEGs) that derive affordable and sustainable electricity power from omnipresent moisture are promising candidates for smart textile electronics. However, the desired compatibility of high output current and continuous operating voltage is still challenging for wearable HEGs to meet the ever-increasing nanotechnological requirements. Herein, we rationally design and finely synthesize conductive carbonized silk fabrics with in situ growth of SnO/SnO2 nanosheet arrays, which are successfully employed to fabricate high-efficiency wearable HEGs with a maximal power density of 26.66 μW·cm−2 by sandwiching with MXene/cotton fabrics and Al electrodes. Impressively, the vertically interlaced SnO/SnO2 nanosheet arrays supply abundant nanofluidic channels for rapid water diffusive flow with a high flow potential. Combined with the excellent moisture absorption and retention of MXene/cotton textiles, these prepared HEGs process sustained voltage and current outputs of 0.932 V and 0.434 mA over 20,000 s. These flexible HEGs are capable of application in self-powered sensors and micro power supplies, delivering a fresh strategy for the rational design of high-performance and sustainable textile-based electronics.

Lateral heat flux reduction using a lock-in thermography compensation method

The naturally diffusive heat flow in solids often results in differences in surface temperatures. Active thermography (AT) exploits such differences to gain information on the internal structure, morphology, or geometry of technical components or biological specimens. In contrast to sound or light waves, thermal waves are lossy; consequently, it is difficult to interpret measured 2D temperature fields. Most AT evaluation methods are based on 1D approaches, and measured 3D heat fluxes are frequently not considered, which is why edges, small features, or gradients are often blurred. Herein, we present a method for reducing the local temperature gradients at feature areas and minimizing the induced lateral heat flux in optical lock-in thermography (LT) measurements through spatial- and temporal-structured heating. The vanishing lateral gradients convert the problem into a 1D problem, which can be adequately solved by the LT approach. The proposed compensation method can bypass the blind frequency of LT and make the inspection largely independent of the excitation frequency. Furthermore, the edge sharpness and separability of features are improved, ultimately improving the feature-detection efficiency.

A novel bound water occurrence model for tight sandstone

Understanding the occurrence state and microscopic distribution of bound water, as well as the factors governing bound water saturation and its impact on natural gas flow within nano-scaled pore networks, holds significant importance for reservoir evaluation, productivity prediction, and production. However, the complexity of pore structure poses a challenge in quantitatively characterizing these aspects, and currently, no effective method exists to achieve this characterization. This study takes the Bashijiqike tight sandstone of the Kuqa Depression of the Tarim Basin as an example; by integrating physical property test, XRD, microscopic observation with casting thin section and SEM, HPMI, NMR, and NMR-supervised gas-charging experiment, proposed a novel bound water occurrence model to depict the microscopic distribution of bound water in nano-scaled pore space. Furthermore, the impact of bound water on gas-flowing behaviors was thoroughly examined and the complex relationships between bound water saturation and reservoir macroscopic and microscopic parameters were explored. In addition, based on the grey relational analysis, the critical controlling factor on bound water saturation were screened out.The bound water in the pore space of tight sandstone comprises two components: capillary-bound water within small pores (<rcutoff) and restricted (by pore/throat < rcutoff) large pores, layered water-film within large pores (>rcutoff). The water-film within large pores is non-uniform, non-isothick, and low in content. During gas charing to reservoirs, the water-film thickness decreased gradually as the charging force increased,with a minimum thickness ranging from 0.10 to 3.72 nm. Water-film accounted for 1.75% to 22.96% of the total bound water content, with an average of 7.28%. In contrast to previous studies,we found that water-film had a negligible impact on the minimum pore/throat radius for gas charging, with only an increase of 0.7 nm. However, it significantly altered the physical characteristics, reducing gas permeability from 46.11% to 97.84%, with an average reduction of 78.37%. Furthermore, a water-film effectively eradicated the slip effect, leading to the prevalence of Darcy and diffusion flow as the primary mechanisms for gas seepage. At low pressure, diffusion flow prevails, whereas Darcy flow dominates at high pressure. I/S-mixed layer and illite exert the most significant influence on bound water saturation.

Impact of roof shape on indoor gaseous pollutant level for natural ventilation buildings in a street canyon: Numerical simulation

Introduction: Coupling the indoor and outdoor airflow of roadside buildings in a street canyon, the impact of flat and triangular roofs on indoor air pollutant concentration and ventilation rates of naturally ventilated buildings is studied using numerical simulation methods.&#x0D; Materials and methods: The flow and pollutant diffusion control equations are solved by using ANSYS Fluent. In simulation, RNG k-ε turbulence model is adopted. The numerical model is validated using the three-dimensional street canyon test data from the wind tunnel experiment at University of Karlsruhe.&#x0D; Results: The flow and pollutant concentration distributions under different roof shapes are obtained. The ventilation rates with different air flow resistances and pollution level indoors are provided.&#x0D; Conclusion: Ventilation direction through windows of roadside buildings determines the level of indoor air polluted by vehicle emissions in street canyon. When the building main height equals to the width of the street, flat roofs make the indoor concentration basically consistent with that near the external walls of the canyon. The higher the triangular roofs, the higher the ventilation rate and the lower the indoor concentration. The ventilation rate is influenced not only by roofs, but also by the floor location and indoor ventilation resistance.v

Two-time level finite-difference method for solving the downstream diffusion for flow between Parallel plates

Two-time level finite-difference method for solving the downstream diffusion for flow between Parallel plates

Investigation of the impact of nitrogen and water vapor dilution in oxidizer stream on flame structure, soot production and extinction of a laminar ethylene-fueled co-flow diffusion flame

This paper discusses the effect of nitrogen (N2) and water vapor (H2O) dilution in oxidizer stream on the flame structure, and soot production and extinction of laminar ethylene (C2H4)-fueled co-flow diffusion flame (CFDF). The total oxidizer stream flow rate is kept constant while varying the flow rates of air, N2, and H2O to achieve the desired oxygen concentration called oxygen index (OI). As OI reduces, the flame starts to lift off from the burner surface and shows upward and downward oscillations before extinction through blow-off. The OI at which the flame blows off is called the limited oxygen index (LOI), and it depends on burner configuration, fuel, and oxidizer flow conditions. LOI value for C2H4-fueled laminar CFDF were found to be 12.4% and 14% when the diluent was N2 and H2O, respectively. The experiment and simulation results are presented from 21% O2 concentration in oxidizer to very low oxygen concentration in oxidizer close to extinction. Through quantitative measurements of soot volume fraction (SVF), the result shows a notable reduction in the peak concentrations of SVF as the OI decreases. This decrease is more pronounced with H2O than N2 dilution. One-dimensional (1D) opposed flow diffusion flame simulations are performed to understand various effects of the addition of diluents like H2O and N2. It is observed that in addition to inert, thermal and diffusion effect of H2O in reduction of flame temperature and temperature-dependent production rate of key species, H2O also affects flame chemistry through OH + H2 = H + H2O, 2OH = O + H2O. As a result there is a further drop in the concentration of active radicals (like H, O) which leads to quicker soot inhibition and flame extinction.

Influence of a hydrophobic membrane on evaporation rate of water placed in a top-cooled circular cavity

The present study investigates changes in the evaporation rate of an initially warm body of water covered by a hydrophobic membrane in a top-cooled circular cavity. Evaporation from pure water and saline solution of NaCl have been considered. The interfacial heat fluxes are measured in a Mach-Zehnder interferometer. Membrane-controlled evaporation is numerically modeled for coupled heat and moisture transport on air and water sides of their interface. The model predictions are in reasonably good agreement with measured heat fluxes. The two are also found to be in good agreement for evaporation without the membrane cover. Transport mechanisms in the membrane pores, namely, Knudsen diffusion, ordinary diffusion, and Poiseuille flow are compared. Interfacial heat fluxes in an open-surface evaporation arrangement are about twice the value realized in membrane-controlled evaporation but decrease with increasing salinity. A circular cavity shows higher heat and mass transfer rates compared to the rectangular, bringing in the effect of the confining walls. Instantaneous Nusselt and Sherwood numbers show good correlation, owing to the coupling between the heat and mass transfer processes. The presence of salt reduces the evaporation mass fluxes below that of pure water for both open-surface and membrane evaporation.

Investigating the impact of adsorbent particle size on column adsorption kinetics through a mathematical model

Experimental data demonstrates that the breakthrough curves of column adsorption exhibit qualitative differences related to the size of the adsorbent particles. Standard models do not account for particle size, consequently, in this paper we develop a new formulation that incorporates the diffusion of the adsorbate into the adsorbent particles. Two kinetic models are considered, Langmuir adsorption and a linear driving force. Approximate analytical solutions are developed for these two models coupled to mass flow and intra-particle diffusion equations. The accuracy of the analytical solutions is verified through comparison with numerical solutions of the full mathematical model. Comparison with experimental data confirms that the new analytical solutions show better agreement than previous models. However, in certain cases, neither form of model predicts the behaviour suggesting a combination of different effects contribute to the breakthrough form.

Evidence of a distal axis inactive high-temperature hydrothermal field on the ultraslow spreading Southwest Indian Ridge: Insights from mineralogy and geochemistry studies

The development of hydrothermal activities on mid-ocean ridges is primarily influenced by magmatic and tectonic activities close to the ridge axis. On slow and ultraslow spreading ridges featured by limited magma supply, prolonged hydrothermal activity can also occur in non-transform offsets (NTO), where sustained ultramafic-related hydrothermal circulation happens due to prolonged hydrothermal processes associated with the expose of ultramafic rocks. In contrast, basalt-hosted hydrothermal fields are barely developed in NTOs, especially in off-axis area, due to insufficient magma supply. In this study, we reported the occurrence of a distal axis (∼9.5 km) basalt-hosted hydrothermal field (50.63°E) on the NTO of segment 27 of the ultraslow spreading Southwest Indian ridge. The hydrothermal products are characterized by layered crusts mainly composed of oxides, such as limonite and goethite, rich in Fe and depleted in Si. These crusts contain high contents of trace elements derived from seawater, such as P, As, Mo, U, and Sb and show REE pattens with negative Eu and mostly positive Ce anomalies. However, the high Cu content (1.82 ± 0.89 wt%, N = 27), low absorption ratio of Cu (18.39 ± 12.71%, N = 9), and residual chalcopyrite altered by goethite suggest prior high-temperature hydrothermal activity. Lead isotopic composition with basaltic rocks signatures that distinct from those of low-temperature crusts of seawater origin also support this conclusion. The Fe-rich crusts appears to be the result of high-temperature sulfides altered by late-stage low-temperature diffuse flow. This field is currently the furthest known distal axis basalt-hosted hydrothermal field located in NTOs of ultraslow spreading ridges. The hydrothermal circulation is likely due to a combination of off-axis normal fault and gabbro diking. Our results emphasize the occurrence of distal axis basalt-hosted high-temperature hydrothermal activities on NTOs of ultraslow spreading ridges, and may lead to an increased estimation of hydrothermal heat and chemical influx to the ocean.

The physical basis of osmosis.

Osmosis is an important force in all living organisms, yet the molecular basis of osmosis is widely misunderstood as arising from diffusion of water across a membrane separating solutions of differing osmolarities, and hence different water concentrations. In 1923, Peter Debye proposed a physical model for a semipermeable membrane emphasizing the repulsive forces between solute molecules and membrane that prevent the solute from entering the membrane. His work was hardly noticed at the time and slipped out of view. We show that Debye's analysis of van 't Hoff's law for osmotic equilibrium also provides a consistent and plausible mechanism for osmotic flow. A difference in osmolyte concentrations in solutions separated by a semipermeable membrane leads to different pressures at the two water-membrane interfaces because the total repulsive force between solute molecules and the membrane is different at the two interfaces. Water is therefore driven through the membrane for exactly the same reason that pure water flows in response to an imposed hydrostatic pressure difference. In this paper, we present the Debye model in both equilibrium and flow conditions. We point out its applicability regardless of the nature of the membrane with examples ranging from the predominantly convective flow of water through synthetic membranes and capillary walls to the purely diffusive flow of independent water molecules through a lipid bilayer and the flow of a single-file column of water molecules in narrow protein channels.

Analysis of flow diffusion of secondary lubricant in water-lubricated bearings

To reduce the lubrication failure of water-lubricated bearings under short-term harsh conditions, preliminary experiments have shown that temporarily supplying a small amount of lubricating oil into a bearing as a secondary lubricant can improve the load capacity of the water film therein. However, the physical flow and diffusion state of this secondary lubricant (oil) in water are unclear. Therefore, a mixed lubrication model and a volume-of-fluid model are incorporated to study the diffusion behavior of a small amount of lubricating oil in a water-lubricated bearing. The results show that there is a backflow effect in the local area inside the bearing, where the fluid velocity is in the opposite direction to the linear velocity of the shaft. This backflow effect intensifies with increasing eccentricity ratio, which enlarges the oil-free zone in the middle part of the bearing. In the convergence area at the water inlet end of the bearing, the water supply pressure and backflow effect prevent the lubricating oil from escaping. Increasing the shaft speed has a positive effect on the diffusion of the oil and the load capacity of the fluid. To enhance the assisted lubrication effect of the oil, the oil injection port should be set in the loading zone to avoid the backflow zone. This research provides some fundamental data for reducing the friction and wear of water-lubricated bearings under harsh conditions.

Joint effect of air flow and substrate wettability on evaporation of a sessile droplet on a solid surface

We study the evaporation of microliter droplets of water on hydrophilic, hydrophobic, and superhydrophobic substrates subjected to airflow around them. While there is a large body of literature on diffusion-limited evaporation, evaporation in the presence of external convection is not fully-explored. We use side-view imaging and a custom-built flow channel to record the evaporating droplets from the side and develop an analytical model for evaporation in the presence of convection. Based on the droplet’s inlet flow velocity and wetted diameter, the maximum Reynolds number is 203. We quantify the time-variation of droplet volume, wetted diameter, and dynamic contact angle as a function of substrate wettability and airflow velocity. We found that the droplet lifetime decreases with the airflow, which is explained by the larger contribution of the convective mass loss rate compared to the diffusive mass flow rate computed by the model. Interestingly, the droplet lifetime is longer on a hydrophobic substrate due to the smallest area of liquid-gas interface among the three substrates for a given airflow. In general, evaporation occurs at constant contact radius (CCR) mode for hydrophilic surface in case of without flow and for all cases of airflow velocity. The CCR followed by constant contact angle (CCA) mode is observed for hydrophobic surface, and CCA followed by mixed mode is reported for superhydrophobic surface. The theoretical model reasonably predicts the measurements of different cases of airflow velocity and substrate wettability.

A computational study on entropy optimized nonlinear convective dual diffusive slip flow of rate type liquid under modern diffusion concepts

Flows configured by moving surface holds considerable importance in fluid mechanics. The moving surface finds widespread usages in distinct real-world scenarios, for illustration rubber sheets, hot rolling, plastic drawing, paper manufacturing, glass blowing and wire fabrication. The rate of stretching/cooling during these processes play a vital role in ensuring the production of high-excellence end-products. This attempt features entropy optimized slip flow featuring rate type (Jeffrey) liquid subjected to Cattaneo–Christov (CC) dual diffusion and nonlinear convection aspects. Variable fluid aspects (i.e., thermal conductivity and mass diffusivity) along with thermal source and first order chemical reaction are scrutinized. The problem is formulated by employing fundamental laws of fluid dynamics. The non-linear partial differential equations are transformed into the ordinary ones using suitable transformations. Subsequently, optimal homotopic methodology (OHAM) is employed to achieve computational results. Developed nonlinear problems are determined for velocity, temperature and concentration fields. Bejan number, skin friction and the graphs of entropy generation parameters have been plotted and argued. To validate the problem, the comparison for different parameters has been addressed through Shooting and OHAM techniques. Total residual error is calculated. Main outcomes are presented in conclusions.

Thermo-solutal dual diffusive flow of chemically reactive magneto couple-stress nanomaterial capturing robin conditions, transpiration and thermal generation/sink

Nanomaterials have attracted extensive relevance from researchers and scientists around the globe because of their unique thermo-physical features and ample potential advantages and utilizations in crucial areas, for illustration, biomedicine, electronics, energy, vehicles and aerospace. This attempt accounts magnetohydrodynamics and chemical reaction consideration in couple-stress nanomaterial confined by convectively heated vertical surface. Flow is mixed convective and thermally radiative. Brownian motion, heat generation, thermophoresis, Robin conditions and transpiration are considered for formulation. Boundary-layer expressions representing couple-stress liquid are implied utilizing transformation procedure. The obtained nonlinear expressions are tackled analytically by implementing series solution methodology (known as homotopy analysis method (HAM)). Convergence of analytical solutions is authenticated arithmetically (i.e., via table) and by drawing ℏ− curves. In addition, the significant parameters occurring in dimensionless expressions are addressed graphically. Our findings indicate retardation in flow when suction variable is augmented. Transfer of heat is higher for radiation and heat source parameters. Nanoparticles concentration decays for larger estimations of destructive reaction factor while it upsurges for generative reaction factor.