Magnitude Of Pressure Gradient Research Articles

Magnetohydrodynamic (MHD) peristaltic flow of blood containing cylindrical shaped gold nanoparticles in a non-uniform tube in the presence of Joule dissipation

This research scrutinizes the peristaltic transport of blood-based nanofluid comprising cylindrical-shaped Gold (Au) nanoparticles in a non-uniform tube under the influence of magnetic field. Effects of Joule heating and viscous dissipation are also explored. Governing equations are firstly modelled and then simplified by utilizing long wavelength and small Reynold number assumptions. Exact solutions are computed in terms of modified Bessel’s functions. The effects of concerned physical parameters on the dimensionless velocity, trapping, temperature, magnitude of pressure gradient, heat transfer rate is discussed through graphs and tables. Velocity of the fluid decreases by increasing the magnitude of non-uniform parameter. Heat transfer rate is high in the uniform channel as compared to the tapered channel. Moreover, reduction in temperature and axial pressure gradient is also observed in non-uniform channel in comparison to uniform channel. The computation of exact solutions that can be used to test the accuracy of various numerical schemes applicable to these types of complex flow problems is also a novel aspect of this study. Hopefully, this analysis will be helpful in a variety of biomedical therapies, such as in drug delivery, magnetic resonance imaging and magnetic hyperthermia.

Scalable Simulation of Pressure Gradient-Driven Transport of Rarefied Gases in Complex Permeable Media Using Lattice Boltzmann Method

Accurate representations of slip and transitional flow regimes present a challenge in the simulation of rarefied gas flow in confined systems with complex geometries. In these regimes, continuum-based formulations may not capture the physics correctly. This work considers a regularized multi-relaxation time lattice Boltzmann (LB) method with mixed Maxwellian diffusive and halfway bounce-back wall boundary treatments to capture flow at high Kn. The simulation results are validated against atomistic simulation results from the literature. We examine the convergence behavior of LB for confined systems as a function of inlet and outlet treatments, complexity of the geometry, and magnitude of pressure gradient and show that convergence is sensitive to all three. The inlet and outlet boundary treatments considered in this work include periodic, pressure, and a generalized periodic boundary condition. Compared to periodic and pressure treatments, simulations of complex domains using a generalized boundary treatment conserve mass but require more iterations to converge. Convergence behavior in complex domains improves at higher magnitudes of pressure gradient across the computational domain, and lowering the porosity deteriorates the convergence behavior for complex domains.

Periodic Unsteady Natural Convection on CNT Nano-powder Liquid in a Triangular Shaped Mechanical Chamber

Nanoparticle is highly used in enhancing thermal performance, especially in lid-driven cavity flow in powder-related applications. Many researchers considered different conditions, such as MHD, radiation, and mixed convection incorporating nano liquid in such flow. However, no study was carried out with CNT-water nano liquid in a triangular cavity, heated sinusoidally under natural convection to determine the Rayleigh number (Ra) and nano-powder liquid concentration effect on heat transfer. As a result, this study attempts to find the Rayleigh number and particle concentration effects in such transient cavity flow. The governing equations were employed with the Galerkin residual method. While calculating the thermal conductivity and dynamic viscosity of the nano liquid, Brownian motion was taken into consideration. The four solid volume fractions (0.01, 0.05, 0.1, 0.15) and the Ra (104 ≤ Ra ≤ 106) were chosen to evaluate the impact within dimensionless time (0.1 ≤ τ ≤ 1). The findings have been shown by plotting the streamlines, isotherms, heat transfer variation, and pressure gradient. It is found that when the Rayleigh number goes up, the velocity, vorticity, and pressure gradient magnitude become high. But, the fluid flow vortices decrease with dimensionless time. Due to the sinusoidal heat flux conditions, the variation of the result was found to be sinusoidal as well. When the nanoparticle concentration rises, the heat transfer rate and average fluid temperature also increase. Therefore, the highest heat transfer rate is found using the nano liquid with a15% concentration.

Excitation and Linear Instability of Stationary Modes in Falkner-Skan-Cooke Boundary Layer

Past studies showed that a micron-sized surface roughness may cause the generation of a significant ‎unstable, stationary wave in a crossflow boundary layer, and consequently promote or delay the laminar-‎turbulent transition. The crossflow boundary layer is usually driven by the favorable pressure gradient ‎which is produced by accelerated inviscid velocity. Hence, for a fixed sweep angle, the magnitude of ‎pressure gradient is the key parameter for the excitation and evolution of the stationary crossflow mode. ‎In order to study the effect of pressure gradient on the excitation and subsequent linear development of ‎stationary mode, a classical Falkner-Skan-Cooke boundary layer is introduced so that the magnitude of ‎pressure gradient can be easily parameterized by an acceleration coefficient. Numerical simulation is ‎performed to induce the stationary perturbation by chordwise-isolated, spanwise-periodic roughness at ‎the lower branch of neutral curve. Then the excited waves develop into Rayleigh modes in the ‎downstream region. The stationary modes with different spanwise wavenumbers in various favorable-‎pressure-gradient boundary layers are simulated and analysed to determine the effect of pressure ‎gradient. And the corresponding coupling coefficients are calculated to connect the initial amplitude and ‎the eigenmode of linear stability theory for implementing the existing prediction method of laminar-‎turbulent transition‎‎.

The steady motion of microbubbles in bifurcating airways: Role of shear-thinning and surface tension

Mucous fluid is non-Newtonian secretions in the lower lung airways that accumulates when the alveolar-capillary membrane ruptures during acute respiratory distress syndrome. The mucus fluid has, therefore, different types of non-Newtonian properties like shear-thinning, viscoelasticity, and non-zero yield stress. In this paper, we numerically solved the steady Stokes equations along with arbitrary Eulerian-Lagrangian moving mesh techniques to study the microbubble propagation in a two-dimensional asymmetric bifurcating airway filled with non-Newtonian fluid where the fluid has shear-thinning behavior described by the power-law model. Numerical results show that both shear-thinning and surface tension characterized by the behavior index (n) and Capillary number (Ca), respectively, had a significant impact on microbubble flow patterns and the magnitude of the pressure gradient. At low values of both n and Ca, the microbubble leaves a thin film-thickness with the airway wall while a large and sharp peak of the pressure gradient near the thin bubble tip. Interestingly, increasing both n and Ca, leads to an increase in film thickness and a decrease in the pressure gradient magnitude in both the daughter airway walls. It is observed the magnitude of the pressure gradient is more sensitive to Ca compared to n. We concluded that shear-thinning and surface tension not only significantly impact the patterns of microbubble propagation but also the hydrodynamic stress magnitudes at the airway wall.

Fracture propagation in an initially stressed anisotropic reservoir under shear: Reorientation and fluid lag

We study the propagation of a fracture in an initially stressed anisotropic reservoir under shear. The focus is made on the deviation of the fracture from the principal direction due to the shearing conditions. An asymptotic model is developed, which yields the solution in terms of the effective K2c and the deviation angle. Then, we analyse formation of the fluid lag during propagation of a hydraulic fracture in the cases of plane and radial fracture. It is shown that there is lag between the fluid and the fract ure tip, which may be as large as half of the fracture at early stages of fracture propagation and its actual length is highly dependent on the compressibility of the reservoir rock, tectonic strength and leak-off conditions at the fracture face. In this case the speed of the fracture tip exceeds that of the fluid and is related to the length of the lag. The influence of the fluid front structure on the law of fracture propagation is studied. It is revealed that the magnitude of pressure gradient and its distribution along the fracture have a significant impact on the lag size.

Decomposition of the mean friction drag in adverse-pressure-gradient turbulent boundary layers

From an energy budget perspective, the decomposition of mean friction drag in adverse-pressure-gradient turbulent boundary layers is conducted, obtaining contributions associated with dissipation, production, and convection across the boundary layer. In the wall-normal distributions of the decomposed constituents, positions of inner peaks are well scaled in viscous units, whereas outer peaks scale in outer units, regardless of Reynolds number and pressure-gradient magnitude.

Effects of gravity and surface tension on steady microbubble propagation in asymmetric bifurcating airways.

Mechanical ventilation is nowadays a well-developed, safe, and necessary strategy for acute respiratory distress syndrome patients to survive. However, the propagation of microbubbles in airway bifurcations during mechanical ventilation makes the existing lung injury more severe. In this paper, finite element and direct interface tracking techniques were utilized to simulate steady microbubble propagation in a two-dimensional asymmetric bifurcating airway filled with a viscous fluid. Inertial effects were neglected, and the numerical solution of Stokes’s equations was used to investigate how gravity and surface tension defined by a Bond (Bo) number and capillary (Ca) number influence the magnitudes of pressure gradients, shear stresses, and shear stress gradients on the bifurcating daughter airway wall. It is found that increasing Bo significantly influenced both the bubble shape and hydrodynamic stresses, where Bo ≥ 0.25 results in a significant increase in bubble elevation and pressure gradient in the upper daughter wall. Although for both Bo and Ca, the magnitude of the pressure gradient is always much larger in the upper daughter airway wall, Ca has a great role in amplifying the magnitude of the pressure gradient. In conclusion, both gravity and surface tension play a key role in the steady microbubble propagation and hydrodynamic stresses in the bifurcating airways.

Hemodynamic effects of aortic valve and heart rate on coronary perfusion

BackgroundReduced coronary flow reserve in aortic stenosis and after transcatheter aortic valve implantation is usually attributed to physiological factors taking place during systole, such as an increase in coronary resistance, and backward waves intensity. In this paper, we suggest an additional factor related to the diastolic hemodynamics in the aortic root. MethodsWe measured left ventricle, aortic and coronary pressure and coronary perfusion in in-vitro models of healthy, aortic stenosis and an artificial valve at different heart rates and cardiac output conditions, to isolate the effect of hemodynamic factors in the aortic root during diastole. FindingsOur results show that during diastole, coronary perfusion depends on the pressure gradient between the aorta and the coronary inlet. This aorta-coronary pressure gradient is influenced by the hemodynamic flow field in the aortic root. The ratio between the aorta-coronary pressure gradient magnitude in stress to that under rest conditions of a healthy model is ten times higher than the same ratio in the aortic stenosis model and twice higher as compared to the artificial valve model result. The coronary flow reserve of the healthy model is correspondingly higher compared to the artificial valve and the aortic stenosis models. These results are in agreement with the clinical evidence. InterpretationThis study supports the hypothesis of a hemodynamic mechanism in the aortic root that increases coronary flow during rest but reduces the coronary flow reserve in aortic stenosis and artificial valve cases. The results may provide valuable insights regarding valve design.

Identification of the pore size distribution of a porous medium by yield stress fluids using Herschel-Bulkley model

In this paper, we present a new method to determine the pore-size distribution (PSD) in a porous medium. This innovative technique uses the rheological properties of non-Newtonian yield stress fluids flowing through the porous sample. In a first approach, the capillary bundle model will be used. The PSD is obtained from the measurement of the total flow rate of fluid as a function of the imposed pressure gradient magnitude. The mathematical processing of the experimental data, which depends on the type of yield stress fluid, provides an overview of the pore size distribution of the porous material. The technique proposed here was successfully tested analytically and numerically for usual pore size distributions such as the Gaussian mono and multimodal distributions. The study was conducted for yield stress fluids obeying the classical Bingham model and extended to the more realistic Herschel-Bulkley model. Unlike other complex methods, expensive and sometimes toxic, this technique presents a lower cost, requires simple measurements and is easy to interpret. This new method could become in the future an alternative, non-toxic and cheap method for the characterization of porous materials.

Experimental realisation of near-equilibrium adverse-pressure-gradient turbulent boundary layers

A new experimental database of adverse-pressure-gradient (APG) turbulent boundary layers (TBLs) obtained through hot-wire anemometry and oil-film interferometry covering a momentum–loss Reynolds number 450<Reθ<23450 and Clauser pressure-gradient-parameter range up to β≈2.4 is presented. Both increasing and approximately constant β distributions with the same upstream history are characterised. Turbulence statistics are compared among the different pressure-gradient distributions with additional numerical and experimental zero-pressure-gradient (ZPG) TBL data. Cases at approximately constant β, which can be considered as canonical representations of the boundary layer under a certain pressure-gradient magnitude, exhibit skin-friction and shape-factor curves consistent with the ones proposed by Vinuesa et al. (2017). These curves show a similar scaling behaviour as those proposed by Nagib et al. (2007) for ZPG TBLs. The pre-multiplied power-spectral density is employed to study the differences in the large-scale energy content throughout the boundary layer. Two different large-scale phenomena are identified, the first one related to the pressure gradient and the second one (also present in high-Re ZPG TBLs) due to the Reynolds number. Recently proposed scaling laws by Kitsios et al. (2016) and Maciel et al. (2018) are tested over a wider Reynolds-number range and for different β cases. The mean velocity and streamwise velocity fluctuation profiles are found to be dependent on the upstream development. The mean velocity profile is found to be self-similar only in the outer region, in agreement with classical theory. The mean and higher-order statistics of the new APG TBL database are made available under www.flow.kth.se.

DC/AC magnetohydrodynamic-micropump of a generalized Burger's fluid in an annulus

The article describes a new model for investigating the effect of a uniform magnetic field and an imposed electric field through two coaxial tubes on a flow of DC and AC-operated micropumps. Assumptions are made in order to reach to closed-form solutions. Expressions for the velocity, flow rate, magnitude of pressure gradient, and shear stress are derived by means of Laplace transforms along with numerical inversion algorithms. Graphical results are presented for the physical variables with different parameters involved in the flow field. Comparisons are made with the other non-Newtonian fluids and discussed graphically. Critical values for the magnetic and material parameters are found around which the flow velocity is reversed for the DC magnetohydrodynamic-micropump. The present study might provide a reference for controlling and manipulating small non-Newtonian fluid volumes.

Correlation between angiographic stenosis and physiologic venous sinus outflow obstruction in idiopathic intracranial hypertension

IntroductionThe relationship between degree of angiographic venous sinus stenosis and the trans-stenosis pressure gradient magnitude in idiopathic intracranial hypertension (IIH) is poorly understood. The present study aimed to assess the...

A simple method for estimating transition locations on blade surface of model propellers to be used for calculating viscous force

Effects of inflow Reynolds number (Re), turbulence intensity (I) and pressure gradient on the transition flow over a blade section were studied using the γ-Reθ transition model (STAR-CCM+). Results show that the ReT (transition Re) at the transition location (PT) varies strongly with Re, I and the magnitude of pressure gradient. The ReT increases significantly with the increase of the magnitude of favorable pressure gradient. It demonstrates that the ReT on different blade sections of a rotating propeller are different. More importantly, when there is strong adverse pressure gradient, the PT is always close to the minimum pressure point. Based on these conclusions, the PT on model propeller blade surface can be estimated. Numerical investigations of pressure distribution and transition flow on a propeller blade section prove these findings. Last, a simple method was proposed to estimate the PT only based on the propeller geometry and the advance coefficient.

Atmospheric structure favoring high sea surface temperatures in the western equatorial Pacific

AbstractWe investigated the atmospheric processes over high sea surface temperature called Hot Event (HE) in the western equatorial Pacific from climatological analysis and a case study of the HE which began on 28 May 2003 (hereafter, HE030528). Climatological analysis shows that during the development stage of HE, solar radiation inside the HE area is higher than its climatology and wind speed is lower than the decay stage. During the decay stage, strong westerly wind often occurs inside HE area. The case study of HE030528 shows that the suppressed convection above high SST area resulted from the deep convection from the northern and southern areas outside HE. The suppressed convection created a band‐shaped structure of low cloud cover along HE area increasing solar radiation during the development stage. Thus, the theory of “remote convection” was supported for the HE030528 formation mechanisms. The large sea level pressure gradient magnitude between the southern side of the terrain gap and the northern coast of the Solomon Islands, through which strong wind blew, indicated the role of land topography for the increase of wind speed during the decay of HE030528. Moreover, surface wind had an important role to influence the variability of solar radiation during the occurrence of HE030528 by controlling the water vapor supply in the upper troposphere through surface evaporation and surface convergence variation. Thus, surface wind was the key factor for HE030528 occurrence. The representativeness of HE030528 and the possible relation between HE and Madden‐Julian Oscillation are also discussed.

Computational analysis of microbubble flows in bifurcating airways: role of gravity, inertia, and surface tension.

Although mechanical ventilation is a life-saving therapy for patients with severe lung disorders, the microbubble flows generated during ventilation generate hydrodynamic stresses, including pressure and shear stress gradients, which damage the pulmonary epithelium. In this study, we used computational fluid dynamics to investigate how gravity, inertia, and surface tension influence both microbubble flow patterns in bifurcating airways and the magnitude/distribution of hydrodynamic stresses on the airway wall. Direct interface tracking and finite element techniques were used to simulate bubble propagation in a two-dimensional (2D) liquid-filled bifurcating airway. Computational solutions of the full incompressible Navier-Stokes equation were used to investigate how inertia, gravity, and surface tension forces as characterized by the Reynolds (Re), Bond (Bo), and Capillary (Ca) numbers influence pressure and shear stress gradients at the airway wall. Gravity had a significant impact on flow patterns and hydrodynamic stress magnitudes where Bo &gt; 1 led to dramatic changes in bubble shape and increased pressure and shear stress gradients in the upper daughter airway. Interestingly, increased pressure gradients near the bifurcation point (i.e., carina) were only elevated during asymmetric bubble splitting. Although changes in pressure gradient magnitudes were generally more sensitive to Ca, under large Re conditions, both Re and Ca significantly altered the pressure gradient magnitude. We conclude that inertia, gravity, and surface tension can all have a significant impact on microbubble flow patterns and hydrodynamic stresses in bifurcating airways.

Alongshore momentum balance analysis on a cuspate foreland

[1] Nearshore measurements of waves and currents off Cape Hatteras, North Carolina, U.S.A, are used to investigate depth-averaged subtidal circulation and alongshore momentum balances in the surf and inner shelf region around a cuspate foreland. Data were collected on both sides of the cape representing shorefaces with contrasting shoreline orientation (north-south vs. northwest-southeast) subjected to the same wind forcing. In the nearshore, the subtidal flow is aligned with the local coastline orientation while at the cape point the flow is along the existing submerged shoal, suggesting that cape associated shoals may act as an extension of the coastline. Alongshore momentum balance analysis incorporating wave-current interaction by including vortex and Stokes-Coriolis forces reveals that in deep waters surface and bottom stress are almost in balance. In shallower waters, the balance is complex as nonlinear advection and vortex force become important. Furthermore, linearized momentum balance analysis suggests that the vortex force can be of the same order as wind and wave forcing. Farther southwest of Cape Hatteras point, wind and wave forcing alone fail to fully explain subtidal flow variability and it is shown that alongshore pressure gradient as a response to the wind forcing can close the momentum balance. Adjacent tide gauge data suggest that the magnitude of pressure gradient depends on the relative orientation of local coastline to the wind vector, and in a depth-averaged sense the pressure gradient generation due to change in coastline orientation even at km length scale is analogous to the effect of alongshore variable winds on a straight coastline.

Does Don Fisher's high-pressure manifold model account for phloem transport and resource partitioning?

The pressure flow model of phloem transport envisaged by Münch (1930) has gained wide acceptance. Recently, however, the model has been questioned on structural and physiological grounds. For instance, sub-structures of sieve elements may reduce their hydraulic conductances to levels that impede flow rates of phloem sap and observed magnitudes of pressure gradients to drive flow along sieve tubes could be inadequate in tall trees. A variant of the Münch pressure flow model, the high-pressure manifold model of phloem transport introduced by Donald Fisher may serve to reconcile at least some of these questions. To this end, key predicted features of the high-pressure manifold model of phloem transport are evaluated against current knowledge of the physiology of phloem transport. These features include: (1) An absence of significant gradients in axial hydrostatic pressure in sieve elements from collection to release phloem accompanied by transport properties of sieve elements that underpin this outcome; (2) Symplasmic pathways of phloem unloading into sink organs impose a major constraint over bulk flow rates of resources translocated through the source-path-sink system; (3) Hydraulic conductances of plasmodesmata, linking sieve elements with surrounding phloem parenchyma cells, are sufficient to support and also regulate bulk flow rates exiting from sieve elements of release phloem. The review identifies strong circumstantial evidence that resource transport through the source-path-sink system is consistent with the high-pressure manifold model of phloem transport. The analysis then moves to exploring mechanisms that may link demand for resources, by cells of meristematic and expansion/storage sinks, with plasmodesmal conductances of release phloem. The review concludes with a brief discussion of how these mechanisms may offer novel opportunities to enhance crop biomass yields.

A Possible Mechanism for Protrusions Formation at the Metal/Oxide Interface During Short Time Oxidation of Ferritic Stainless Steel

High temperature oxidation of ferritic stainless steel for short durations leads to the formation of an original morphology at the metal/oxide interface. This interface is composed of metallic protrusions localized in a chromium-rich oxide layer through a discontinuous silica film. In this paper we propose a mechanism based on preferential diffusion paths for the oxygen through the oxide that are governed by the distribution of the hydrostatic pressure in this layer. We point out that the mechanical contrast between the oxide and the metal subjected to creep can be critical for the hydrostatic pressure gradient magnitude inside the oxide layer. This observation is likely to promote the formation of protrusions for specific conditions of temperature and time of exposure to oxidation.

Abstract 235: Ischemia-Reperfusion Injury Decreases Myocardial Hydration Potential Without Changing Flow Resistance in the Interstitial Matrix

Interstitial edema is an early response to myocardial ischemia, leading to fibrosis and remodeling in several heart failure conditions. We aimed to clarify whether osmotic, frictional, or mechanical forces drive fluid accumulation. Equilibrium and dynamic interstitial hydration parameters were determined, compared, and analyzed using osmotic stress approaches in explants from ischemic and nonischemic myocardial regions of pig heart. They were isolated after injury induced by ligating 3-4 branches of the left anterior descending coronary artery, for 85 min followed by 3 hours’ reperfusion. Their volume changed (Δ V max ) linearly with colloidosmotic pressure in both ischemic and nonischemic areas, yielding interstitial compliance values of 1.04 ± 0.09 and 1.08 ± 0.05 µl/g/ mmHg , which do not differ significantly, and hydration potentials from the abscissa intercepts at Δ V max = 0, of -121.4 ± 28 and -14.7 ± 7.6 mmHg, which do (mean ± SE, n = 5 , P-value = 0.001). These hydration potential differences manifest ex-vivo influx rates 8.5 ± 2.7- fold slower in ischemic than nonischemic myocardium. Surprisingly, interstitial flow resistance values derived from net-flow rates at an imposed pressure difference of 216 mmHg were 0.23 ± 0.08 and 0.19 ± 0.01 µl -1 . g. min and did not differ significantly between the areas. The similarity in interstitial compliance and fluid resistance indicates that the more negative hydration potential and faster efflux rates in at-risk regions after reperfusion are due to increased hydrostatic pressure rather than decreased osmotic or frictional forces. Tissue distends due to interstitial fluid accumulation against matrix mechanical forces, including elastic recoil of the collagen elastin mesh and fibroblast action, consistent with impaired drainage and persistent diastolic-like conditions during reperfusion of at-risk areas in vivo . These results indicate changes in pressure gradient magnitude and may have clinical and therapeutic implications; for example, reversal of paracrine interstitial flows during early remodeling