Ion transport in a charged conical nanopore filled with viscoelastic fluids: ion current rectification

The ionic current rectification (ICR) is a non-linear current-voltage response upon switching the polarity of the potential across nanopore, similar to the I-V response in the semiconductor diode. The ICR phenomenon finds several potential applications in micro/nano-fluidics (e.g., Bio-sensors and Lab-on-Chip applications). From a biological application viewpoint, most biological fluids (e.g., blood, saliva, mucus, etc.) exhibit non-Newtonian visco-elastic behavior; their rheological properties differ from Newtonian fluids. Therefore, the resultant flow-field should show an additional dependence on the rheological material properties of viscoelastic fluids such as fluid relaxation time (λ) and fluid extensibility (ε). Despite numerous potential applications, the comprehensive investigation of the viscoelastic behavior of the fluid on ionic concentration profile and ICR phenomena has not been attempted. ICR phenomena occur when the length scale and Debye layer thickness approaches of the same order. Therefore, this work extensively investigates the effect of viscoelasticity on the flow and ionic mass transfer along with the ICR phenomena in a single conical nanopore. The Poisson-Nernst-Planck (P-N-P) model coupled with momentum equations have been solved, for a wide range of conditions Deborah number, 1 ≤ De ≤ 100, Debye length parameter, 1 ≤ κRt ≤ 50, fluid extensibility parameter, 0.05 ≤ ε ≤ 0.25, applied electric potential, −40 ≤V ≤ 40, and surface charge density σ = −10 and −50. Four distinct novel characteristics of electro-osmotic flow (EOF) in a conical nanopore have been investigated here, namely (1) detailed structure of flow field and velocity distribution in viscoelastic fluids (2) influence of Deborah number and fluid extensibility parameter on ionic current rectification (ICR) (3) volumetric flow rate calculation as a function of Deborah number and fluid extensibility parameter (4) effect of viscoelastic parameters on concentration distribution of ions in the nanopore. At high applied voltage, both the extensibility parameter and Deborah number facilitate the ICR phenomena. In addition, the ICR phenomena are observed to be more pronounced at low values of κRt than the high values of κRt . This effect is due to the overlapping of the electric double layer at low values of κRt.

Two-Dimensional Structure of Flow Channels and Associated Upward Field-Aligned Currents: Model and Observations

Flow bursts are a major component of transport within the plasma sheet and auroral oval (where they are referred to as flow channels), and lead to a variety of geomagnetic disturbances as they approach the inner plasma sheet (equatorward portion of the auroral oval). However, their two-dimensional structure as they approach the inner plasma sheet has received only limited attention. We have examined this structure using both the Rice Convection Model (RCM) and ground-based radar and all sky imager observations. As a result of the energy dependent magnetic drift, the low entropy plasma of a flow burst spreads azimuthally within the inner plasma sheet yielding specific predictions of subauroral polarization stream (SAPS) and dawnside auroral polarization stream (DAPS) enhancements that are related to the field-aligned currents associated with the flow channel. Flow channels approximately centered between the dawn and dusk large-scale convection cells are predicted to give significant enhancements of both SAPS and DAPS, whereas flow channel further toward the dusk (dawn) convection cell show a far more significant enhancement of SAPS (DAPS) than for DAPS (SAPS). We present observations for cases having good coverage of flow channels as they approach the equatorward portion of the auroral oval and find very good qualitative agreement with the above RCM predictions, including the predicted differences with respect to flow burst location. Despite there being an infinite variety of flow channels’ plasma parameters and of background plasma sheet and auroral oval conditions, the observations show the general trends predicted by the RCM simulations with the idealized parameters. This supports that RCM predictions of the azimuthal spread of a low-entropy plasma sheet plasma and its associated FAC and flow responses give a realistic physical description of the structure of plasma sheet flow bursts (auroral oval flow channels) as they reach the inner plasma sheet (near the equatorward edge of the auroral oval).

Effect of pore pressure on the permeability evolution in low porous Indian sandstone

<p>Permeability evolution of low permeable rocks is of critical importance during the flow of gases in processes like, enhanced reservoir recovery and CO<sub>2</sub> sequestration. Permeability measurement depends on the geometric structure of flow path (hydraulic radius, connectivity, tortuosity), the stress regimes surrounding the rock (isotropic, deviatoric) and the characteristic of the fluid (viscosity, compressibility, pore pressure).  For the case of gas permeability within Knudsen diffusion regime (0.001 < Kn< 0.1), the effect of slippage is prominently observed.</p><p>Laboratory scale permeability experiments on an Indian sandstone having connected porosity ~10%, are performed under hydrostatic condition. Nitrogen gas is selected as pore fluid, to avoid adsorption phenomenon. Transient technique of pore-pressure-pulse decay is used for permeability measurement as it is faster and accurate to measure pressure, than the steady state method. Pore pressures and confining pressures are varied in the study to understand the relative effect of matrix compressibility and fluid compressibility on the permeability. Micro-CT analysis of sample is also performed to quantify the geometric attributes of sample.</p><p>Apparent gas permeability ranging from 0.1 to 1 micro-Darcy is obtained from the experiments. The permeability is found to be decreasing with simple effective stress (σ<sub>ii</sub>-p) for constant pore pressures. But a counter intuitive decrease in permeability with increasing pore-pressure at constant confining pressure is also evident and can be attributed to stress dependent Biot’s coefficient (λ).  Slippage corrected permeability is further analysed theoretically and numerically to formulate nonlinear permeability evolution equation in the functional form, f(σ<sub>ii</sub>-λp)  to support experimental outcomes.</p>

Comprehensive hydrothermal analysis of an inclined mini-channel with fin array: by dual/multi-relaxation-time LBM and experimental process on SiO2-glycol rheological/thermal characteristics

Purpose The purpose of this study is to present a comprehensive hydrothermal analysis on an inclined mini-channel using numerical and experimental techniques. The fin array acts as heat source within the channel, and a wavy wall located at the top of the channel is heat sink. The side walls are insulated with curved profiles. Also, the channel is inclined with four known inclination angles. To solve the governing equations, the dual-multi-relaxation-time lattice Boltzmann method with D2Q9 and D2Q5 lattice models for flow and temperature fields is used, respectively. Also, the channel is filled with SiO2-glycol nanofluid. Design/methodology/approach Identifying the behavior of a thermal component during natural convective flow is a challenging topic due to its complexities. This paper focuses on analyzing the thermal and hydrodynamic aspects of a narrow channel equipping with fin array. Findings Two correlations are proposed considering temperature and volume fraction ranges for thermal conductivity and dynamic viscosity according to measured experimental data which are used in the numerical phase. Finally, the structure of flow, temperature distribution of fluid, local thermal and viscous dissipations, volume-averaged entropy production, Bejan number and heat transfer rate are extracted by numerical simulations. The results show that the average Nusselt number enhances about 57% (maximum enhancement percentage) when volume fraction increases from 1% to 3% at Ra = 106 and θ = 90°. In addition, the value of entropy generation is maximum at φ = 1%, Ra = 106 and φ = 90°. Also, the maximum enhancement of entropy generation in range of Ra = 103 to 106 is about 4 times at φ = 1% and θ = 90°. Originality/value The originality of the present study is combining a modern numerical method (i.e. dual/multi-relaxation-time LBM) with experimental observation on characteristics of SiO2-glycol nanofluid to study the thermal and hydrodynamic properties of the studied mini-channel.

Formation of a cargo frame for a cargo express

Subject of research — the study of the structure of flow forecasting potential volume of traffic and in view of the potential senders of the cargo according to schedule to ensure train traffic market category. The relevance of the work is related to the globalization of world business and the rapid development of international relations, in particular, JSC “Russian Railways” is already implementing a service for accelerated cargo delivery — “Cargo express”. This service has successfully proven itself in many areas. It is necessary to consider the possibility of forming this service on the route “Moscow–Vladivostok”. Used analytical studies of the size of the presentation of cargo by potential senders, the method of exponential smoothing is used for forecasting. The definition of the “Cargo Express”, given the options for the formation of freight trains, examines the key points when travelling of the train in the direction “Moscow–Vladivostok”, the characteristic structure of the intended traffic at key points, made a forecast of estimated volumes of the production of goods for the years to 2030. Analysis of the structure and size of freight traffic will continue to assess the frequency of trains plying market category set the order of its formation, determine the number and type of wagons required for each paragraph of the passage, make an accurate transportation planning and hard route schedule, and provide an additional attraction as key customers and small and medium-sized customers on the rail. The development of terminal and logistics complexes should become the basis of the cargo frame in the studied direction.

Experimental Investigation and CFD Modeling of Supercritical Adsorption Process

The kinetics of the supercritical adsorption process was experimentally studied by the example of ”ibuprofen-silica aerogel” composition obtainment at various parameters: Pressure 120–200 bar and temperature 40–60 °C. Computational Fluid Dynamics (CFD) model of the supercritical adsorption process in a high-pressure apparatus based on the provisions of continuum mechanics is proposed. Using supercritical adsorption process kinetics experimental data, the dependences of the effective diffusion coefficient of active substance in the aerogel, and the maximum amount of the adsorbed active substance into the aerogel on temperature and pressure are revealed. Adequacy of the proposed model is confirmed. The proposed mathematical model allows predicting the behavior of system (fields of velocity, temperature, pressure, composition, density, etc.) at each point of the studied medium. It makes possible to predict mass transport rate of the active substance inside the porous body depending on the geometry of the apparatus, structure of flow, temperature, and pressure.

A Review on Hydrodynamics of Free Surface Flows in Emergent Vegetated Channels

This review paper addresses the structure of the mean flow and key turbulence quantities in free-surface flows with emergent vegetation. Emergent vegetation in open channel flow affects turbulence, flow patterns, flow resistance, sediment transport, and morphological changes. The last 15 years have witnessed significant advances in field, laboratory, and numerical investigations of turbulent flows within reaches of different types of emergent vegetation, such as rigid stems, flexible stems, with foliage or without foliage, and combinations of these. The influence of stem diameter, volume fraction, frontal area of stems, staggered and non-staggered arrangements of stems, and arrangement of stems in patches on mean flow and turbulence has been quantified in different research contexts using different instrumentation and numerical strategies. In this paper, a summary of key findings on emergent vegetation flows is offered, with particular emphasis on: (1) vertical structure of flow field, (2) velocity distribution, 2nd order moments, and distribution of turbulent kinetic energy (TKE) in horizontal plane, (3) horizontal structures which includes wake and shear flows and, (4) drag effect of emergent vegetation on the flow. It can be concluded that the drag coefficient of an emergent vegetation patch is proportional to the solid volume fraction and average drag of an individual vegetation stem is a linear function of the stem Reynolds number. The distribution of TKE in a horizontal plane demonstrates that the production of TKE is mostly associated with vortex shedding from individual stems. Production and dissipation of TKE are not in equilibrium, resulting in strong fluxes of TKE directed outward the near wake of each stem. In addition to Kelvin–Helmholtz and von Kármán vortices, the ejections and sweeps have profound influence on sediment dynamics in the emergent vegetated flows.