Radial Flows Research Articles

Figuring Out Gas & Galaxies in Enzo (FOGGIE). VI. The Circumgalactic Medium of L ∗ Galaxies Is Supported in an Emergent, Nonhydrostatic Equilibrium

The circumgalactic medium (CGM) is often assumed to exist in or near hydrostatic equilibrium, with the regulation of accretion and the effects of feedback treated as perturbations to a stable balance between gravity and thermal pressure. We investigate global hydrostatic equilibrium in the CGM using four highly resolved L * galaxies from the Figuring Out Gas & Galaxies in Enzo (FOGGIE) project. The FOGGIE simulations were specifically targeted at fine spatial and mass resolution in the CGM (Δx ≲ 1 kpc h −1 and M ≃ 200M ⊙). We develop a new analysis framework that calculates the forces provided by thermal pressure gradients, turbulent pressure gradients, ram pressure gradients of large-scale radial bulk flows, centrifugal rotation, and gravity acting on the gas in the CGM. Thermal and turbulent pressure gradients vary strongly on scales of ≲5 kpc throughout the CGM. Thermal pressure gradients provide the main supporting force only beyond ∼0.25R 200, or ∼50 kpc at z = 0. Within ∼0.25R 200, turbulent pressure gradients and rotational support provide stronger forces than thermal pressure. More generally, we find that global equilibrium models are neither appropriate nor predictive for the small scales probed by absorption line observations of the CGM. Local conditions generally cannot be derived by assuming a global equilibrium, but an emergent global equilibrium balancing radially inward and outward forces is obtained when averaging over the nonequilibrium local conditions on large scales in space and time. Approximate hydrostatic equilibrium holds only at large distances from galaxies, even when averaging out small-scale variations.

A note on special solutions for magnetohydrodynamics system in the van der Waals fluid

The present article deals with the study of special flows such as circulatory, radial, and spiral flows, respectively, for the magnetohydrodynamics system with the van der Waals fluid. Employing the method of hodograph transformation, the solutions have been obtained in the (u,v)-plane. An inversion of the spiral solution back to the (x,y)-plane is possible under a specific requirement, i.e.,bˆ2>2aρ, where bˆ represents Alfven speed and a is the van der Waals parameter.

Wind-Forced Seasonal Exchange between Marginal Seas and the Open Ocean

Abstract The circulation within marginal seas subject to periodic winds, and their exchange with the open ocean, are explored using idealized numerical models and theory. This is motivated by the strong seasonal cycle in winds over the Nordic Seas and the exchange with the subpolar North Atlantic Ocean through the Denmark Strait and Faroe Bank Channel. Two distinct regimes are identified: an interior with closed f/h contours and a shallow shelf region that connects to the open ocean. The interior develops a strong oscillating along-topography circulation with weaker ageostrophic radial flows. The relative importance of the bottom Ekman layer and interior ageostrophic flows depends only on ωh/Cd, where ω is the forcing frequency, h is the bottom depth, and Cd is a linear bottom drag coefficient. The dynamics on the shelf are controlled by the frictional decay of coastal waves over an along-shelf scale Ly = f0LsHs/Cd, where f0 is the Coriolis parameter, and Ls and Hs are the shelf width and depth. For Ly much less than the perimeter of the basin, the surface Ekman transport is provided primarily by overturning within the marginal sea and there is little exchange with the open ocean. For Ly on the order of the basin perimeter or larger, most of the Ekman transport is provided from outside the marginal sea with an opposite exchange through the deep part of the strait. This demonstrates a direct connection between the dynamics of coastal waves on the shelf and the exchange of deep waters through the strait, some of which is derived from below sill depth. Significance Statement The purpose of this study is to understand how winds over marginal seas, which are semienclosed bodies of water around the perimeter of ocean basins, can force an exchange of water, heat, salt, and other tracers through narrow straits between the marginal sea and the open ocean. Understanding this exchange is important because marginal seas are often regions of net heat, freshwater, and carbon exchange with the atmosphere. The present results identify a direct connection between processes along the coast of the marginal sea and the flow of waters through deep straits into the open ocean.

Searching for Coleman–de Luccia bubbles in AdS compactifications

Coleman-de Luccia transitions are spontaneous processes of nucleation of bubbles within metastable gravitational vacua including in their interior a true stable vacuum. From the perspective of lower-dimensional gauged supergravities obtained by truncating Type II and M-theory, these instantonic processes are represented by smooth domain walls featured by de Sitter foliations. These geometries must connect two different AdS vacua in such a way that the wall is defined by an interior and an exterior. We propose a first-order formulation for such radial flows and present two fully backreacted examples of gravitational instantons obtained through this technique, beyond the thin-wall approximation. In the first we consider minimal 7d supergravity describing the truncation of M-theory over a squashed 4-sphere and admitting two AdS$_7$ vacua, one supersymmetric and the other not. Secondly we apply the same strategy to 6d Romans supergravity obtained with consistent truncation of massive IIA supergravity. Also in this case we derive a dS domain wall interpolating between the Brandhuber-Oz vacuum and the non-supersymmetric AdS$_6$ vacuum of the theory.

Numerical analysis of a flywheel energy storage system for low carbon powertrain applications

Flywheel energy storage has emerged as a viable energy storage technology in recent years due to its large instantaneous power and high energy density. Flywheel offers an onboard energy recovery and storage system which is durable, efficient, and environmentally friendly. The flywheel and the housing surface temperatures can be considerably influenced by the friction induced windage losses associated with non-vented airflows in the air-gap of a high-speed rotating flywheel. Many engineering applications have been interested in the features of radial and axial air-gap flows. The flow within the annulus of a flywheel is extremely complicated. This study has developed a numerical technique using ANSYS Fluent solver to model turbulent Taylor vortices formation and oscillation for thermal performance evaluation, and windage loss prediction of high-speed flywheel storage systems, operating under atmospheric and partial vacuum conditions. The numerical model has been experimentally validated with good accuracy. Several rotational speeds and pressures were investigated experimentally and numerically. The results demonstrated that a 40 % reduction in the operating pressure can reduce the flywheel surface temperature and windage loss by 20 % and 30 %, respectively. Consequently, a partial vacuum environment can achieve better energy conversion efficiencies provided an appropriate bearing seal is achieved to maintain the pressure inside the housing. The investigated flywheel energy storage system can reduce the fuel consumption of an average light-duty vehicle in the UK by 22 % and decrease CO2 emission by 390 kg annually.

Cretaceous opposite rotations of North China Block and southern Sikhote Alin, northeast China/Russia: Relation to rifting in the petroliferous Songliao Basin

Paleomagnetic data from northeast Asia confirm that the Korea/North China and southern Sikhote Alin blocks rotated in opposite directions from the Berriasian to the Campanian (145–72 Ma). The Songliao Basin evolved between these rotated blocks with synrift sequences dating from the Tithonian or the Berriasian/Hauterivian. Geologic maps and tomographic images demonstrate a curvilinear subduction zone with associated accretionary wedge/magmatic arc stretched from Sikhote Alin, to Japan and southeast Korea near the Cretaceous Tertiary boundary. Arc-related volcanism migrated over 1000 km southeastwards across northeast Asia to the Japan Sea and Sikhote Alin coast from ∼ 140 – 70 Ma. This suggests that opposite microplate rotations resulted from Pacificward retreat of a curved subduction zone from Early to Late Cretaceous. Toroidal or radial flows in the mantle wedge exerting basal drag on the over-riding microplates is a likely driving mechanism. Anisotropic tomography suggesting fossil curved mantle flows which match the forces required to produce opposite rotations and the distribution of crustal thickness and Vp/vs ratios under the Songliao Basin support this mechanism. A major petroliferous basin in China may therefore be the result of double saloon door tectonics occurring during the Cretaceous behind a contemporaneous continental arc.

Gas kinematics around filamentary structures in the Orion B cloud

Context. Understanding the initial properties of star-forming material and how they affect the star formation process is key. From an observational point of view, the feedback from young high-mass stars on future star formation properties is still poorly constrained. Aims. In the framework of the IRAM 30m ORION-B large program, we obtained observations of the translucent (2 ≤ AV < 6 mag) and moderately dense gas (6 ≤ AV < 15 mag), which we used to analyze the kinematics over a field of 5 deg2 around the filamentary structures. Methods. We used the Regularized Optimization for Hyper-Spectral Analysis (ROHSA) algorithm to decompose and de-noise the C18O(1–0) and 13CO(1–0) signals by taking the spatial coherence of the emission into account. We produced gas column density and mean velocity maps to estimate the relative orientation of their spatial gradients. Results. We identified three cloud velocity layers at different systemic velocities and extracted the filaments in each velocity layer. The filaments are preferentially located in regions of low centroid velocity gradients. By comparing the relative orientation between the column density and velocity gradients of each layer from the ORION-B observations and synthetic observations from 3D kinematic toy models, we distinguish two types of behavior in the dynamics around filaments: (i) radial flows perpendicular to the filament axis that can be either inflows (increasing the filament mass) or outflows and (ii) longitudinal flows along the filament axis. The former case is seen in the Orion B data, while the latter is not identified. We have also identified asymmetrical flow patterns, usually associated with filaments located at the edge of an H II region. Conclusions. This is the first observational study to highlight feedback from H II regions on filament formation and, thus, on star formation in the Orion B cloud. This simple statistical method can be used for any molecular cloud to obtain coherent information on the kinematics.

Analysis of Combined Vertical and Radial Consolidation of Soil under Time-Dependent Loading

Fine-grained compressible soils are usually associated with strength challenges in the course of carrying structures, roadways, embankments, and other civil engineering facilities. In addition, due to their low permeabilities, compressible soils take an awfully long duration to achieve optimal consolidation, with its attendant negative effects on the facilities supported by the soils. Engineering practitioners and researchers have established the efficacy of vertical drains for accelerating the consolidation process of such soils through the shortening of horizontal flow distances, thereby stabilizing them and improving their load-bearing capacities. Application of the pre-loading surcharge provides additional drive for rapid consolidation. The case of soils carrying time-dependent loading is quite topical because it reflects reality most appropriately. However, a rigorous analysis of soils undergoing vertical and radial consolidation with a constant or time-varying surcharge is conspicuously lacking in the literature because most authors of publications in this subject area have largely based their solution procedure on the assumed decoupling of the vertical and radial flows by treating their associated pore pressures as separate. This assumption, notwithstanding the simplification it introduces into the mathematics of the problem, is not supported by physics. Therefore, the theory presented herein aims at addressing that gap in the literature. Throughout this analysis, the coupled (vertical and radial) flow, driven by a common pore water pressure, is handled as a single process. Successive applications of the integral transformations of Laplace and finite Hankel have been used to obtain an explicit expression for the image of the pore water pressure as a function of the transformation parameters. This is followed by successive inversions of the integral transforms, leading to a closed-form solution in the sense of a generalized Fourier series. The classical definition of the average degree of consolidation is easily applied in this case, unlike other methods in the literature that rely on the principle of superposition, whose applicability in this circumstance remains questionable. The validity of the present analysis has been established through logical checks and comparison with previous results in the literature. This theory has been proven to be applicable to cases of constant as well as time-varying surcharges. Doi: 10.28991/CEJ-2023-09-01-014 Full Text: PDF

Radially symmetric non-isentropic Euler flows: Continuous blowup with positive pressure

We establish the existence of radial self-similar Euler flows in which a continuous incoming wave generates a blowup of primary (undifferentiated) flow variables. A key point is that the solutions have a strictly positive pressure field, in contrast to Guderley's classic construction of converging shock waves. In Guderley's solutions, a converging shock invades a quiescent region at zero pressure (due to vanishing temperature), and the velocity and pressure in its immediate wake become unbounded at the time of collapse. It is reasonable that the lack of upstream counter-pressure is conducive to large speeds, with concomitant large amplitudes. Based on Guderley's original solutions, it is therefore unclear if it is the zero-pressure region that is responsible for blowup. The same applies to self-similar Euler flows describing radial cavity flow. Our results demonstrate that the geometric mechanism of wave focusing is sufficiently strong on its own to drive unbounded growth. We propagate the solution beyond blowup and observe numerically that there are two distinct possibilities depending on the incoming flow: either an expanding spherical shock wave is generated, or the flow propagates in a continuous manner. Focusing on the former case, we show that the resulting flows define global admissible weak solutions to the full, multi-d compressible Euler system. These solutions have the unusual property that the flow is isentropic in each of the two regions separated by the shock.

Selecting a model fluid with properties similar to crude oil to test the formation of W/O emulsions

This study selected a model fluid with the potential to produce stable emulsions with physical-chemical properties and chemical profile similar to a reference crude oil following the physical-chemical evaluation and medium infrared absorption spectrometry of five fluids. A water-in-oil emulsion of the selected model fluid was prepared with 10% v/v of saline solution 35 g L−1 and evaluated for the following factors: surfactant concentration, rotation, flow, time of the kinectic stability, and drop size distribution. According to the results, the medium lubricating oil (ρ = 0.8885 g cm3) presented a compositional profile, in terms of physical-chemical properties, compatible with the reference oil and formation of stable emulsions in a time greater than 48 h. The surfactant Triton X-100 (HLB = 13.4, cC = −0.3 and HLD >1) favored the formation of a W/O emulsion. The results indicate that the increase in TX100 concentration increased the kinetic stability in the time up to 48 h. The emulsions prepared at the concentration of 0.1% v/v of TX100 formed the largest droplet sizes with an average of 19.97 μm and 23.92 μm in the axial and radial flows, respectively. Stable emulsions were produced either by homogenization with an inclined paddle rod (30–100 rpm) or by Ultra-turrax above 3000 rpm, this result indicates that the homogenization depends on the rod as much as it depends on the flow generated in the sample domain.

A root functional-structural model allows assessment of the effects of water deficit on water and solute transport parameters.

Root water uptake is driven by a combination of hydrostatic and osmotic forces. Water transport was characterized in primary roots of maize seedlings grown hydroponically under standard and water deficit (WD) conditions, as induced by addition of 150 g l-1 polyethylene glycol 8000 (water potential= -0.336 MPa). Flow measurements were performed using the pressure chamber technique in intact roots or on progressively cut root system architectures. To account for the concomitant transport of water and solutes in roots under WD, we developed within realistic root system architectures a hydraulic tree model integrating both solute pumping and leak. This model explains the high spontaneous sap exudation of roots grown in standard conditions, the non-linearity of pressure-flow relationships, and negative fluxes observed under WD conditions at low external hydrostatic pressure. The model also reveals the heterogeneity of driving forces and elementary radial flows throughout the root system architecture, and how this heterogeneity depends on both plant treatment and water transport mode. The full set of flow measurement data obtained from individual roots grown under standard or WD conditions was used in an inverse modeling approach to determine their respective radial and axial hydraulic conductivities. This approach allows resolution of the dramatic effects of WD on these two components.

Fingering Convection in the Stably Stratified Layers of Planetary Cores

AbstractStably stratified layers may be present at the top of the electrically conducting fluid layers of many planets either because the temperature gradient is locally subadiabatic or because a stable composition gradient is maintained by the segregation of chemical elements. Here we study the double‐diffusive processes taking place in such a stable layer, considering the case of Mercury's core where the temperature gradient is stable but the composition gradient is unstable over a 800 km‐thick layer. The large difference in the molecular diffusivities leads to the development of buoyancy‐driven instabilities that drive radial flows known as fingering convection. We model fingering convection using hydrodynamical simulations in a rotating spherical shell and varying the rotation rate and the stratification strength. For small Rayleigh numbers (i.e., weak background temperature and composition gradients), fingering convection takes the form of columnar flows aligned with the rotation axis and with an azimuthal size comparable with the layer thickness. For larger Rayleigh numbers, the flows retain a columnar structure but the azimuthal size is drastically reduced leading to thin sheet‐like structures that are elongated in the meridional direction. The azimuthal size decreases when the thermal stratification increases, following closely the scaling law expected from the linear planar theory (Stern, 1960, https://doi.org/10.1111/j.2153-3490.1960.tb01295.x). We find that the radial flows always remain laminar with local Reynolds number of order 1–10. Equatorially symmetric zonal flows form due to latitudinal variations of the axisymmetric composition. The zonal velocity exceeds the non‐axisymmetric velocities at the largest Rayleigh numbers. We discuss plausible implications for planetary magnetic fields.

Effect of radial flows in fuel channels on thermal performance of counterflow tubular solid oxide fuel cells

Increasing the volumetric power density of solid oxide fuel cell (SOFC) stacks could enable their wider adoption in powering vehicles. The radial flows generated by inserts in gas channels of the tubular SOFC could enhance electrochemical reactions in porous electrodes and improve the power density. In this study, numerical simulations are performed to examine the influence of the enhanced exothermic electrochemical reactions on the temperature distributions in a counterflow tubular SOFC with inserts. We show that the radial flow in the fuel channel could improve the SOFC power density by 30% but lead to an increase in the maximum cell temperature gradient from 12 ℃/cm to 23 ℃/cm. The effects of radial flows under different inlet mass flow rates of hydrogen and methane are also examined. Compared with the conventional tubular SOFC, the percentage of power density improvements and the maximum cell temperature gradients of the tubular SOFC with inserts both increase with increasing inlet hydrogen mass flow rates. The maximum cell temperature gradient is increased from 12.8 ℃/cm to 47.5 ℃/cm as the percentage of net power density improvement is increased from 20% to 45%. We also demonstrate that increasing the inlet methane flow rate could adversely affect the SOFC performance, since the strong radial flow can remove the steam in porous anode, which impedes the methane steam reforming reaction and consequently reduces the output power density. The present work helps improve our understanding of heat and mass transfer characteristics of the radial flows in the tubular SOFC and helps build a foundation for SOFC channel designs.

Influence of Radial Flows on Power Density and Gas Stream Pressure Drop of Tubular Solid Oxide Fuel Cells

The development of solid oxide fuel cells (SOFCs) for powering vehicles requires high power densities. The radial flows generated by the insert structures in SOFC fuel channels could improve the power density by facilitating the fuel to enter the porous anode for electrochemical reactions. In this paper, we developed a 2D axisymmetric numerical model to examine the influence of a convergent conical ring insert on the flow and mass transfer characteristics in a tubular SOFC. The mass transfer conductance of fuel was analyzed and proposed to quantify the performance of different insert designs. The effects of the radius and offset angle of the convergent conical ring insert were examined and analyzed. We demonstrate that increasing the insert radius could increase the fuel mass transfer conductance and effectively improve the net output power of the tubular SOFC by 12% while the offset angle of the inserts exhibits a negligible impact on the fuel mass transfer conductance. Increasing the offset angle could help reduce the gas-phase pressure drop in fuel channels by 42%. The present study helps improve our understanding of the relationship between fuel mass transfer conductance and electrochemical reactions. It also proposes channel design methods based on mass transfer conductance for high-power-density solid oxide fuel cells.

Surface tension effects on flow dynamics and alveolar mechanics in the acinar region of human lung

BackgroundComputational fluid dynamics (CFD) simulations, in-vitro setups, and experimental ex-vivo approaches have been applied to numerous alveolar geometries over the past years. They aimed to study and examine airflow patterns, particle transport, particle propagation depth, particle residence times, and particle-alveolar wall deposition fractions. These studies are imperative to both pharmaceutical and toxicological studies, especially nowadays with the escalation of the menacing COVID-19 virus. However, most of these studies ignored the surfactant layer that covers the alveoli and the effect of the air-surfactant surface tension on flow dynamics and air-alveolar surface mechanics. MethodsThe present study employs a realistic human breathing profile of 4.75s for one complete breathing cycle to emphasize the importance of the surfactant layer by numerically comparing airflow phenomena between a surfactant-enriched and surfactant-deficient model. The acinar model exhibits physiologically accurate alveolar and duct dimensions extending from lung generations 18 to 23. Airflow patterns in the surfactant-enriched model support previous findings that the recirculation of the flow is affected by its propagation depth. Proximal lung generations experience dominant recirculating flow while farther generations in the distal alveolar region exhibit dominant radial flows. In the surfactant-enriched model, surface tension values alternate during inhalation and exhalation, with values increasing to 25 mN/m at the inhalation and decreasing to 1 mN/m at the end of the exhalation. In the surfactant-deficient model, only water coats the alveolar walls with a high surface tension value of 70 mN/m. ResultsResults showed that surfactant deficiency in the alveoli adversely alters airflow behavior and generates unsteady chaotic breathing through the production of vorticities, accompanied by higher vorticity magnitudes (100% increase at the end of exhalation) and higher velocity magnitudes (8.69% increase during inhalation and 11.9% increase during exhalation). In addition, high air-water surface tension in the surfactant-deficient case was found to induce higher shear stress values (by around a factor of 10) on the alveolar walls than that of the surfactant-enriched case. ConclusionOverall, it was concluded that the presence of the surfactant improves respiratory mechanics and allows for smooth breathing and normal respiration.

Sessile droplet array for sensitive profiling of multiple extracellular vesicle immuno-subtypes

The sensitive detection of the multiple immuno-subtypes of cancer-specific extracellular vesicles (EVs) has emerged as a promising method for multiclass cancer diagnosis; however, its limitations in sensitivity, accessibility, and multiple detection of EV subtypes have hindered its further implementation. Here, we present a platform for sensitive EV detection enabled by sessile droplet array (eSD) that exploits enhanced immuno-capture of EVs via evaporation-driven radial flows in a sessile droplet. Compared to a micro-well without internal flows, this platform demonstrates significantly enhanced EV capture and detection by detecting low levels of EVs with a detection limit of 384.7 EVs per microliter, which is undetectable in the micro-well. In addition, using a small sample consumption of ∼0.2 μL plasma per droplet, the platform detects EV immuno-subtypes against seven different antibodies in patient plasma samples of different cancer types (liver, colon, lung, breast and prostate cancers). Further, using the profiling data, the platform exhibits a sensitivity of 100% (95% confidence interval (CI): 83–100%) and a specificity of 100% (95% CI: 40–100%) for the diagnosis of cancer, and classified cancer types with an overall accuracy of 96% (95% CI: 86–100%) using a two-staged algorithm based on quadratic discriminant analysis technique for machine learning.

Effects of Radial and Circumferential Flows on Power Density Improvements of Tubular Solid Oxide Fuel Cells

Improving the power density of SOFC stacks will accelerate their integration into mobile applications. We developed a 3D Multiphysics model validated by experimental results from early studies to examine the effect of radial and circumferential flows on the power density improvements in a micro-tubular SOFC. The inserts were placed inside the fuel channel to generate flow in different directions. The effects of geometric parameters of these inserts on flow and mass transfer in the fuel channel and porous anode were analyzed. We demonstrate that the radial flow enables the fuel to penetrate directly into the porous anode, increasing the local fuel concentration and enhancing the fuel diffusion to the anode triple-phase boundaries. We found that the circumferential flow has a negligible effect on the diffusion process in the anode and on the increase in power density. The impact of local convective and diffusive mass transfer mechanisms on power density improvement is analyzed using the local Péclet number along the axial direction. Enlarging the radial velocity component perpendicular to the porous anode could effectively increase the power density of the micro-tubular SOFC by 37%. This study helps improve our understanding of mass transfer in fuel channels and helps build a foundation for SOFC channel designs and optimizations.

DESCRIPTION OF THE RADIATION MODULE OF MULTIPHYSICAL CODE FOR ANALYSIS OF THE BAFFLE GEOMETRY DEGRADATION

To date, the possibility of lifetime extension for nuclear power units beyond the project period is extremely important, as well as developing new approaches to expand the previously estimated possible years of lifetime extension of power units, for which this period is almost exhausted. According to the design limit of safe operation for power units with VVER type of reactors - the limiting factor in terms of changes in the geometric state is the contact of baffle and peripheral fuel. Preliminary analysis of the geometric changes of reactor internals, which is mandatory during lifetime extension, showed that more expected is the contact of the baffle metal and barrel, which precedes the contact with nuclear fuel assemblies. An additional factor is that due to the design features of the baffle there are radial flows of coolant from the core to bypass. This situation is not foreseen by the project, so there are discussions in the domestic industry about further safe operation. The main reason for the change in geometry is the combination of accumulated radiation dose and the temperature field unevenness. The "classical" analysis, which is used for lifetime extension, consists of successive stages: the assessment of radiation conditions, temperature field calculation and, finally, the stress-strain state estimation. This approach is acceptable only in the case of a weak link between the physical modules (steps), and requires the conservative evaluation at each step. To date, this approach has almost exhausted itself, as the reserve of "guaranteed safe operation" years, which are estimated by the consistent approach, is almost expired. This paper describes the module for radiation loads estimation, which is a component of the multiphysical code for the analysis of baffle state in terms of its geometry degradation. This approach is developed by specialists of IPP-Centre LLC and PhD students and students of the university.

Mathematical modeling of MHD flow and radiative heat transfer past a moving porous rotating disk with Hall effect

PurposeThe present study aims to investigate the effect of radiation on the unsteady magnetohydrodynamic (MHD) flow of a viscous, electrically conducting Newtonian fluid over rotating disk moving upward/downward immersed in a porous medium, considering the Hall effect. The study is motivated by the various applications in the context of solar power technology, electric power generation, Hall accelerators, MHDs generators and other industrial areas when the fluid flow is subjected to the previously mentioned effects such as MHD, Hall effect and thermal radiation.Design/methodology/approachSuitable similarity transformations are employed to reduce the governing nonlinear partial differential equations into the nonlinear ordinary ones. The solutions of the reduced system are numerically obtained using the boundary value problem (BVP) Midrich scheme in Maple. The results are presented graphically for vertical disk movement, magnetic parameter, Hall current, Darcy parameter, thermal radiation and Schmidt number. Skin frictions, mass and heat transfer rates are numerically tabulated.FindingsIt is revealed that the vertical motion of the disk significantly boosts the radial and annular flows. Moreover, the Hall parameter has contrasting effects on velocity profiles for the range of magnetic field but temperature field is oblivious of this behavior. It is observed that heat and mass transfer considerably enhance along vertical disk movement. Also magnetic field, temperature ratio and radiation parameter significantly enhance the temperature field, while reaction rate parameter and Schmidt number decrease the concentration profile. The current model is calibrated in its reduced form to an already published literature with good correlation to ensure the numerical scheme's validity.Originality/valueThis work is original within the best efforts of the authors.

From radial to unidirectional water pumping in zeta-potential modulated Nafion nanostructures

Chemically propelled micropumps are promising wireless systems to autonomously drive fluid flows for many applications. However, many of these systems are activated by nocuous chemical fuels, cannot operate at high salt concentrations, or have difficulty for controlling flow directionality. In this work we report on a self-driven polymer micropump fueled by salt which can trigger both radial and unidirectional fluid flows. The micropump is based on the cation-exchanger Nafion, which produces chemical gradients and local electric fields capable to trigger interfacial electroosmotic flows. Unidirectional pumping is predicted by simulations and achieved experimentally by nanostructuring Nafion into microarrays with a fine tune modulation of surrounding surface zeta potentials. Nafion micropumps work in a wide range of salt concentrations, are reusable, and can be fueled by different salt cations. We demonstrate that they work with the common water-contaminant cadmium, using the own capture of this ion as fuel to drive fluid pumping. Thus, this system has potential for efficient and fast water purification strategies for environmental remediation. Unidirectional Nafion pumps also hold promise for effective analyte delivery or preconcentration for (bio)sensing assays.