Fluid Flow Research Articles

The role of adsorbent microstructure and its packing arrangement in optimising the performance of an adsorption column

Physical adsorption takes place inside narrow pores where the attractive interaction between the surface of the adsorbent and the contaminant molecules is strong enough to retain the molecules. Adsorption columns involve a range of mass-transport mechanisms: advection through the free spaces between the adsorbent pellets, diffusion through the macro/mesopores of the adsorbent, and adsorption at the surface, where the micropores exist. The adsorbent specifications along with its assembly within the sorption column are key factors when optimizing the filtration of pollutants. In this work we present a mathematical model based on advection–diffusion equations coupled with Langmuir kinetics that accounts for a geometrical approach to the porosity structure inside the adsorbent, formed by a radial lattice of cylinders, and the channels through which the fluid flows surrounding the cylindrical pellets. The model is tested using typical lab-scale values based on VOC adsorption, and we use it to identify optimal macro/mesopore size and column porosity for energetic considerations.

Structural controls on hydrothermal fluid flow in a carbonate geothermal reservoir: Insights from giant carbonate veins in western Germany

This study examines the impact of polyphase tectonics on the development of structurally controlled hydrothermal fluid pathways in carbonate geothermal reservoirs. Our case study focuses on hydrothermal carbonate veins and vein-filled faults in Devonian carbonates from the North Rhine-Westphalia region in western Germany, currently being explored as a potential low-enthalpy geothermal reservoir at depths of 4–5 km. These veins, which can be up to 20 m thick, are subvertical and strike NNW, N, or ESE. They exhibit pinch-and-swell undulating geometries, faulted vein-wall contacts, and occasional fillings of hydrothermal breccias. Vein-filled normal faults show hybrid shear-dilatant openings, with fault tips characterized by horsetail vein terminations. The textures, orientations, and age of the veins suggest their formation at low confining pressures and at depths < 2 km during the Post-Variscan East-West extension. Orthogonal North- and East-striking strike slip faults, inherited from the Variscan orogeny, were likely reactivated during post-Variscan extension, with a significant dilatant component that formed the observed veins. In the Ruhr Basin, the dilation tendency analysis indicates that NNW-striking veins or joints are optimally oriented for re-opening under the current strike-slip stress regime, characterized by NNW-trending maximum horizontal stress. The intersections of fractures may currently create moderately SSE-plunging linear zones of enhanced fluid flow. The main uncertainty regards the presence of similar structures at geothermal reservoir depths of ∼4–5 km in the Middle Devonian carbonates underneath the Ruhr Basin. As the study veins are likely to have formed at depths <2 km, the existence of analogous dilatant conduits at greater depths remains speculative. Eventually, we propose that zones characterized by open discontinuities and channelized fluid flow in carbonate geothermal reservoir in strike-slip tectonic settings can be: (a) dilational jogs between overlapping strike-slip faults, (b) bends along faults, and (c) strike-slip fault terminations with horsetail extensional structures. These zones can also be prone to enhanced karstification.

Twisting vortex lines regularize Navier-Stokes turbulence.

Fluid flows are intrinsically characterized via the topology and dynamics of underlying vortex lines. Turbulence in common fluids like water and air, mathematically described by the incompressible Navier-Stokes equations (INSE), engenders spontaneous self-stretching and twisting of vortex lines, generating a complex hierarchy of structures. While the INSE are routinely used to describe turbulence, their regularity remains unproven; the implicit assumption being that the self-stretching is ultimately regularized by viscosity, preventing any singularities. Here, we uncover an inviscid regularizing mechanism stemming from self-stretching itself, by analyzing the flow topology as perceived by an observer aligned with the vorticity vector undergoing amplification. While, initially, vorticity amplification occurs via increasing twisting of vortex lines, a regularizing anti-twist spontaneously emerges to prevent unbounded growth. By isolating a vortex, we additionally demonstrate the genericity of this self-regularizing anti-twist. Our work, directly linking dynamics of vortices to turbulence statistics, reveals how the Navier-Stokes dynamics avoids the development of singularities even without the aid of viscosity.

Erosion of surfaces by trapped vortices

Two two-dimensional free boundary problems describing the erosion of solid surfaces by the flow of inviscid fluid in the presence of trapped vortices are considered. The first problem tackles an initially flat, infinite fluid-solid interface with uniform flow at infinity and a vortex in equilibrium above the surface. The second involves flow around a finite body with a trailing Föppl-type vortex pair. The conformal invariance of the complex potential permits both problems to be formulated as a Polubarinova–Galin (PG) type equation in which the time-dependent eroding surface in the physical z-plane is mapped to the fixed boundary of the ζ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\zeta $$\\end{document}-disk. The Hamiltonian governing the equilibrium position of the vortex (or vortex pair in the second problem) is also found from the same map. In each problem, the PG equation giving the conformal map is found numerically and the time-dependent evolution of the interface and vortex location is determined. Different models governing the erosion of the interface are investigated in which the normal velocity of the boundary depends on some given function of the fluid flow velocity at the boundary. Typically, in the infinite surface case, erosion leads to the formation of a symmetric valley beneath the vortex which, in turn, moves downward toward the interface. A finite body undergoes erosion which is asymmetric in the flow direction leading to a flattening of the lee surface of the body so displaying some similarity to the experiments and associated viscous theory of Ristroph et al, Moore et al (Proc Natl Acad Sci 109(48):19606–19609, 2012, Phys Fluids 25(11):116602, 2013).

Mathematical modelling and computational reduction of molten glass fluid flow in a furnace melting basin

Mathematical modelling and computational reduction of molten glass fluid flow in a furnace melting basin

Theory for electrodiffusional wall shear stress measurement by directionally sensitive twin semicircular probe

This study investigates the theoretical aspects of mass transport at the surface of a twin semicircular electrodiffusion probe tailored to measure the magnitude and direction of near-wall fluid flows. A critical aspect of this research is the development of a theoretical framework that facilitates experimental measurements by analytically relating measured electric currents to the wall shear stress vector. Central to the study is the derivation of analytical expressions for the mass transfer coefficients of the front and rear segments of the probe, which are essential for quantifying near-wall hydrodynamics. Validation of these analytical relations is achieved through numerical solutions of the convection–diffusion equation, providing a robust confirmation of the underlying theory. A comprehensive procedure for experimental data processing is proposed, taking into account both frontal and reverse flow conditions across the probe. In addition, a sensitivity analysis of the twin semicircular probe is performed. This analysis focuses on the response of current ratios to changes in the flow direction, an aspect critical to understanding the operational performance of the probe. The results of this analysis are compared to the characteristics of two-segment strip probes, highlighting the distinct sensitivity nuances of the twin semicircular probe. Our findings provide insight into the optimal application of this probe in various fluid dynamics scenarios.

Nonlinear hydrodynamic assessment of a floating solar double-hull substructure using viscous numerical wave tank

This paper assesses a viscous numerical solver for hydrodynamic simulations of floating double-hull substructures supporting solar panels, critical for advancing floating solar technologies. Using the OpenFOAM repository, the study develops a model based on the Finite Volume method and Volume of Fluid approach, focusing on a range of wave frequencies, from weakly to strongly nonlinear, at intermediate depths. A free decay test calibrated the mesh morphology of the control volume, enabling comparative analysis of single and double-cylinder structures exposed to Stokes second-order nonlinear waves, alongside nonlinear potential models and experimental data. Spectral analysis of these solutions quantifies the nonlinearities' influence on structural responses and high-order dynamic prediction accuracy. The key findings demonstrate that the viscous model accurately predicted heave and surge responses, outperforming the potential model under steep waves. The gap distance between the cylinder in the double-cylinder platforms significantly affects fluid flow and stability, especially under shorter waves. Accurate wave-body simulations require appropriate mesh resolution and tailored wavemaker functions for nonlinear waves. These findings highlight the need to incorporate viscous effects in floating solar platform design to enhance stability and performance in real-world environments.

Continuous Focusing of Particles by AC-Electroosmosis and Induced Dipole Interactions.

Continuous particle focusing by using microfluidics is an effective method for separating particles, cells, or droplets for analytical purposes. Previously, it was shown that an alternating current across rectangular microchannels with slightly deformed side walls results in vortex flow patterns caused by alternating current electroosmosis (AC-EOF) and could lead to particle focusing. In this work, we explore this mechanism by experimentally studying the particle focusing behavior for various fluid flow velocities through a microchannel. Since it is unlikely that the particles are kept in their focused position solely by convection, a theoretical force balance between the hydrodynamic and the induced dipole force was determined. In our experiments, it was found that there is no substantial effect of the pressure-driven fluid velocity on the particle focusing velocity within the studied range. From the theoretical force balance calculations, it was determined that while the addition of the induced dipole force can still not completely describe the experimentally observed particle focusing, the induced dipole can be strong enough to overcome the hydrodynamic force. Finally, it is hypothesized that under specific circumstances, including a repulsive electrostatic force between a particle and electrode wall can complete the theoretical particle focusing force balance. Alternative phenomena that could also play a role in particle focusing are proposed.

Comment on: “Fluid flow and heat transfer characteristics of natural convection in square cavities due to discrete source-sink pairs” [International Journal of Heat and Mass Transfer 51 (2008) 5949–5957]

The following observations report incorrect/missing information, inaccurate mathematical expressions, and incorrect findings in the above-mentioned paper.

Numerical study of fluid flow and entropy optimization subject to second order slip condition across a permeable curved surface

The entropy generation analysis has great significance in the industrial sectors with heat transmission and fluid flows, for evaluating the irreversibility aspect of a system in heat transfer operations. The numerical simulation of entropy generation and the nanofluid flow across a permeable curved surface subject to cross-diffusion and irregular heat source/sink is reported in the current investigation. The thermodynamics 2nd law is used to simulate the entropy optimization. The flow phenomena are mathematically described by partial differential equations (PDEs), which are derived in a curvilinear coordinate system. The system of ODEs (ordinary differential equations) is derived by using the similarity conversion, which is further numerically calculated through the parametric continuation method (PCM) using MATLAB software. The results reveal that the velocity slip and curvature parameters improve the velocity profile whereas the inverse effect is observed against the surface permeability parameter. It can also be noticed that the entropy optimization enhances with the variation in Brinkman number and temperature ratio parameter. The impact of Schmidt number and chemical reaction decline the mass transmission ratio.

Exploration of the dynamics of heated non-Newtonian Casson fluid within an annular region of eccentric cylinders subject to peristaltic motion

The flow of non-Newtonian fluids is widely observed in industry and biology, for example, enhanced oil recovery, chemical processes such as in distillation towers and fixed-bed reactors and in the applications of pumping fluids such as synthetic lubricants, colloidal fluids, liquid crystals, and biofluids (e.g., animal and human blood). Therefore, the present study delineates the heat transfer analysis of a Casson fluid within the annular region of eccentric cylinders subjected to peristaltic motion, considering the influence of thermal radiation. The outer cylinder remains rigid and moves at a constant speed, while the inner cylinder, featuring a sinusoidal wave along its wall, exhibits flexibility. The governing two-dimensional equations for the movement of the Casson fluid are reformulated under the assumption of the lubrication hypothesis. The perturbation scheme is used to find approximate results for velocity, temperature, and pressure gradient. A graphical representation is utilized to study the fluctuation of various flow fields with different imperative parameters. The results reveal that the liquid velocity declines as the Casson parameter increases, while the temperature decreases due to the amplified effect of thermal radiation. This study has applications in endoscopy, which is important for diagnosing problems in internal organs. Additionally, the variation of the pressure gradient helps maintain the flow rate, which is essential during the insertion of a catheter into an artery.

Effect of MHD and radiation on biviscous Bingham fluid flow on Marangoni boundary for heat source/sink with chemical reaction

A significance of Marangoni-driven convective magnetohydrodynamics (MHD) was investigated in a planned study. The present study examines the impact of radiation and chemical reactions on the two dimensional boundary layer flow of bi-viscous Bingham fluid on a thermosolutal Marangoni boundary with magnetic field and heat source/sink. The physical flow problem is mathematically modelled into Navier–Stokes equations. These nonlinear partial differential equations are then mapped into a set of nonlinear ordinary differential equations using similarity transformation. The elegant analytical method is used to obtain analytic approximations for the resulting system of nonlinear differential equations. The analytical solution for the temperature and concentration profiles is expressed in terms of Kummer's confluent hypergeometric function. The features of flow characteristics such as velocity, temperature, and concentration profiles in response to the variations of the emerging parameters are simulated and examined with a physical explanation through graphs. Surface tension is considered to be corresponding to heat and mass. The results reveal that the velocity profile decreases with increasing the magnetic field, while the Marangoni number value increases with increasing the velocity profile. Moreover, the temperature profile rises with rising the radiation parameter and whereas the value chemical reaction parameter upsurges with decline concentration profile. The present problem has great interest due to its applications in industrial applications such as drying of silicon wafers, thin layers of paint, glues, in heat exchangers, crystal growth in space, biological fluids, blood, synovial liquids, plasma, lubricants, many pharmaceutical products, proteins, sewage sludge, china clay, and many more.

Generation of entropy for MHD flow of Casson fluid past a vertical cone with Dufour effect

Generation of entropy for MHD flow of Casson fluid past a vertical cone with Dufour effect

Fluid flow control around unequal cylinder spacing behind three side-by-side cylinders

Fluid flow control around unequal cylinder spacing behind three side-by-side cylinders

Artificial Gravity: An Effective Countermeasure for Microgravity-Induced Headward Fluid Shift?

Long-duration spaceflight is associated with pathophysiological changes in the intracranial compartment hypothetically linked to microgravity-induced headward fluid shift. This study aimed to determine if daily artificial gravity (AG) sessions can mitigate these effects, supporting its application as a countermeasure to spaceflight. Twenty-four healthy adult volunteers (16 men) were exposed to 60 days of six-degree head-down tilt bed rest (HDTBR) as a ground-based analog of chronic headward fluid shift. Subjects were divided equally into three groups: No AG (control), daily 30-minute intermittent AG (iAG), and daily 30-minute continuous (cAG). Internal carotid artery (ICA) stroke volume (ICASV), ICA resistive index (ICARI), ICA flow rate (ICAFR), aqueductal cerebral spinal fluid flow velocity (CSFV), and intracranial volumetrics were quantified at 3T. MRI was performed at baseline, 14 and 52 days into HDTBR, and three days after HDTBR(recovery). A mixed model approach was used with intervention and time as the fixed effect factors and the subject as the random effect factor. Compared to baseline, HDTBR was characterized by expansion of lateral ventricular, white matter, gray matter, and brain + total intracranial cerebral spinal fluid volumes, increased CSFv, decreased ICASV, and decreased ICAFR by 52 days into HBTBR (All Ps <0.05). ICARI was only increased 14 days into HDTBR (P <0.05). Neither iAG nor cAG significantly affected measurements compared to HDTBR alone, indicating that thirty minutes of daily exposure was insufficient to mitigate the intracranial effects of headward fluid shift. Greater AG session exposure time, gravitational force or both are suggested for future countermeasure research.

Experimental study on the change of the orientation of high aspect ratio nozzle slit relative to the airflow

An experimental study to investigate the flow of liquid jet issued from a high aspect ratio nozzle slit into an incoming airflow by changing the orientation angle from the incoming free-stream was performed. A two-dimensional liquid sheet emerged from the narrow slit into the subsonic air crossflow. Different orientation angles between 0 and 90 degrees were studied. High-speed photography and shadowgraphy techniques were utilized to visualize the flow physics. The influence of the slit orientation angle on the flow morphology and the flow regimes of liquid sheets was investigated. Some fluid flow parameters were obtained by analyzing the images. The changes in breakup height of different orientations were measured. A model was offered for the breakup height of the liquid sheet based on the liquid-to-gas momentum ratio, gas Weber number, and a new non-dimensional parameter as a representation of the angle of slit orientation. Also, the defined sheet trajectory for each orientation angle was obtained, and the variations were examined. Empirical correlations for the defined trajectory of the sheet in terms of liquid to gas momentum ratio and gas Weber number for each orientation angle were proposed.

Measuring the polarized complex forward-scattering amplitudes of single particles in unbounded fluid flow: CAS-v2 protocol

Measuring the polarized complex forward-scattering amplitudes of single particles in unbounded fluid flow: CAS-v2 protocol

Computation of soret effect in sisko nanofluid flow over a stretching sheet encompassing chemical reaction and viscous dissipation

This article examines the characteristics of mass and heat transfer in Sisko fluid flow. The consideration is given to continuous, two-dimensional movement of Sisko fluid exhibiting incompressible and viscous characteristics. The fluid flows over a stretching sheet encompassing chemical reaction and subjected to the soret effect and viscous dissipation. The arising set of interconnected PDEs is converted to nonlinear ODEs using similarity transformations. This study reveals that an increase in the Soret number induces an upward shift in the concentration profile across the flow region. Also, an increase in the Sisko fluid parameter gives rise in the skin-friction coefficient. Following the calculations, the results for the heat, mass transfer rate and skin-friction coefficient, are compiled and presented in a tabulated form. A systematic discussion of similarity solutions in comparison with established findings not only validates the accuracy of the numerical results but also underlines the reliability and robustness of the methodology applied in this study.

Numerical simulation of pulsatile flow of tangent hyperbolic fluid in a diseased curved artery with electro-osmotic effects

Numerical simulation of pulsatile flow of tangent hyperbolic fluid in a diseased curved artery with electro-osmotic effects

An investigation of the Nernst–Planck model of an electro-viscous fluid flow between squeezing plates with homogeneous–heterogeneous reactions

An investigation of the Nernst–Planck model of an electro-viscous fluid flow between squeezing plates with homogeneous–heterogeneous reactions