Increase In Wall Shear Stress Research Articles

CFD study and experimental validation of low liquid-loading flow assurance in oil and gas transport: studying the effect of fluid properties and operating conditions on flow variables

Low liquid-loading flow frequently occurs during the transport of gas products in various industries, such as in the Oil & Gas, the Food, and the Pharmaceutical Industries. Even small amounts of liquid can have a significant effect on the flow conditions inside the pipeline, such as increased pressure loss, pipe wall stresses and corrosion, and liquid holdup along the pipeline. However, most studies that analyze this type of flow only use atmospheric pressures and horizontal 1-in or 2-in pipes, which do not accurately represent the range of operating conditions present in industrial applications. Therefore, this study focused on modeling low liquid-loading flow in medium-sized (6–10 in) pipes, using CFD simulations and experimental data from the University of Tulsa, and then applying it to real operating conditions from a Colombian gas pipeline. An acceptable difference was observed between experimental and CFD data, both for the liquid holdup (18%) and for the pressure drop (12%). Variables like pressure drop and wall shear stress increase with phase velocity, operating pressure, and pipe inclination. Liquid holdup increases with liquid velocity but decreases with all other factors. The relation of flow variables with phase velocities is of particular interest: Doubling the gas velocity decreased holdup 70% and increased pressure drop tenfold. On the other hand, the presence of the liquid phase seems to be more influential on process variables than its exact flowrate; the introduction of the liquid phase to a single-phase gas causes an increase in pressure loss by a factor of three, but doubling the liquid velocity only increases the pressure loss by a further 30%.

Effective use of the streamwise waviness in the control of turbulent separation

It is commonly known that for a sufficiently high Reynolds number, for flow over a rough surface and other previously examined wall topologies, turbulent boundary layer separation generally occurs earlier, and the separation bubble is noticeably larger due to a greater momentum deficit caused by wall irregularities. The recently discovered amplitude modulation effect has provided an improved understanding of the momentum transport that occurs from the outer to the inner part of the boundary layer and its subsequent effect on skin friction. At sufficiently large Reynolds numbers, large-scale motion first causes an increase and then decrease in the flow velocity near the wall. This results in an increased net convection velocity of small structures in the streamwise direction, and consequently an increase in wall shear stress. In this work, we demonstrate that a wavy wall, with a streamwise waviness with carefully selected amplitude and period, can effectively enhance the amplitude modulation effect and ensure an increase in the wall shear stress, thereby postponing turbulent separation. The experimental results are presented in normalized general form using suitable flow scaling. The research goal is to find values of the amplitude, period, and length (always with the total number of periods) of the wavy wall for which the highest rise in skin friction is gained at a fixed point downstream of the wavy wall. The most effective wavy wall geometry investigated ensured a 13% increase in skin friction (relative to the value at zero-pressure-gradient inlet flow) at the location where flow separation occurred on an unmodified surface (i.e. on a flat plate).

In-vivo blood flow parameters can predict at-risk aortic aneurysms and dissection: a comprehensive biomechanics model

Abstract Background Abnormal blood flow patterns can alter the material properties of the thoracic aorta via altered vascular biology and tissue biomechanics. In-vivo haemodynamic assessment of the aorta is yet to penetrate clinical practice due to our limited understanding of its effect on aortic wall properties. The decision for surgical treatment is based on size thresholds, limited to a single measurement of aortic diameter from routine imaging, although many aortic dissections (40–60%) occur below these size thresholds. This multi-centre study aims to assess the clinical utility of biomechanics principles in thoracic aortic aneurysm (TAA) risk rupture prediction using a substantial sample size. Methods Fifty-five patients undergoing surgery for root or ascending TAA were recruited from five cardiac centres. Bicuspid aortic valves and connective tissue disease were excluded from this study.Haemodynamic assessment Pre-operative 4-dimensional flow magnetic resonance imaging (4D-MRI) were conducted. Direct 4D-flow analysis and computational fluid dynamics (CFD) were performed creating detailed wall shear stress (WSS) maps across the whole aneurysms. Aortic wall assessment The aneurysmal aortic sample was obtained from surgery and subjected to region specific uniaxial failure tests in the circumferential and longitudinal directions, as well as delamination testing within the aortic media. Whole aneurysm histological characterisation was also conducted using computational pathology techniques. Blood flow, tissue mechanics and microstructural properties were used to develop a risk prediction model with assessment of elastin, collagen and smooth muscle cell composition, as well as failure strain assessment and dissection energy function. Results Outcomes of mechanical properties were: Young's Elastic Modulus as a measure of aortic stiffness (0.85 MPa ±0.69), as well as maximal tensile strength (0.49 MPa ± 0.36), which demonstrated reduced aortic wall strength in the outer curvature. This correlated with increased wall shear stress (WSS) (up to 10 Pa) and flow velocity (up to 43 l/min). Regions of abnormal flow and tissue mechanics correlated significantly with degraded medial microstructure (elastin abundance: 34 vs 66%; collagen abundance 26 vs 57%, p<0.05). Conclusions CFD modelling has the potential to provide a risk prediction of acute events in TAA beyond the current size classification, as validated by altered aortic tissue properties. Future longitudinal studies are warranted to validate this methods in moderately enlarging thoracic aortas. Flow, mechanical, histology properties Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): NIHR Imperial College BRC

On the severity of aortic stenosis in ascending aortic aneurysm: A computational tool to examine ventricular-arterial interaction and aortic wall stress

An ascending thoracic aortic aneurysm (ATAA) is a life-threatening cardiovascular consequence of vessel dilatation that portends adverse events and death. From a clinical perspective, ATAA should not be treated as an isolated disease, and surgery is often carried out in the presence of AS, aortic insufficiency or a calcified valve leaflet. Aortic stenosis (AS) is common in ATAAs and leads to both vessel rigidity and left ventricular (LV) impairment. In this study, lumped-parameter modeling and computational analysis were used to assess the change in the wall shear stress (WSS) and intramural wall stress of patient-specific ATAA models with different degrees of AS (i.e., mild to severe). The ATAAs of four patients were reconstructed from imaging data and AS was simulated virtually using the lumped-based CircAdapt tool using clinical and echocardiographic data. Results show that LV work derived from pressure-volume loops increased with the severity of AS. Post-stenotic hemodynamic and structural variables markedly increased with AS severity, with WSS showing a 10-fold increase for the most severe AS model as compared to the baseline model with a well-functioning aortic valve. Most importantly, the increase in WSS and aortic wall stress was associated with pronounced values of valvulo-arterial impedance as an indicator of LV dysfunction. This study provides novel insights into progression of AS in patients with ATAAs at high risk of adverse events, and the potential value of valvulo-arterial impedance to predict changes in hemodynamic and structural parameters with the severity of AS.

Fractional order model for thermochemical flow of blood with Dufour and Soret effects under magnetic and vibration environment

We examine the effect of the Caputo-Fabrizio derivative of fractional-order model on the flow of blood in a porous tube having thermochemical properties under the magnetic and vibration mode. Blood is considered as the biviscosity non-Newtonian fluid having thermal radiation and chemical reaction properties to observe its impact on energy flux and mass flux gradients. We provided analytical solution via the Laplace, finite Hankel transform, and the corresponding inverse techniques. The study shows that blood velocity and temperature both decrease in ascending values of the fractional-order parameter as memory effect. The permeability of blood flow medium resists to drive the fluid fast. The chemical reaction causes an increase in wall shear stress. Dufour effect influences to rise in the Nusselt number. Thus the study may help to explore further information about the fractional-order model, adsorption of nutrients and their strong correlation with the surface chemistry and applied them in pathology.

Effects of viscous dissipation and chemical reaction on MHD squeezing flow of Casson nanofluid between parallel plates in a porous medium with slip boundary condition

The present numerical study investigates magnetohydrodynamic squeezing flow of Casson nanofluid embedded in a porous medium with velocity slip under the influence of viscous dissipation and chemical reaction. Buongiorno’s nanofluid model is considered in this study. Suitable similarity transformations are used to convert the governing nonlinear partial differential equations into the system of nonlinear ordinary differential equations. Then, the equations are solved using an implicit finite difference scheme known as Keller-box method. The present method is validated by comparing the numerical results of skin friction coefficient, Nusselt and Sherwood numbers with previous published results and found to be in good agreement. Graphical results for velocity, temperature and nanoparticles concentration as well as wall shear stress, heat and mass transfer rate are examined with pertinent parameters. Findings reveal that fluid velocity and wall shear stress increase when the plates move closer. Also, increment of Casson and Hartmann number reduce the fluid velocity, temperature and nanoparticles concentration. The presence of viscous dissipation and thermophoresis enhance the fluid temperature and the convective heat transfer rate. Moreover, the rate of convective mass transfer decrease when Brownian motions of nanoparticles occurs, while it rises with increase in chemical reaction and thermophoresis.

INCREASED APOPTOSIS ASSOCIATED WITH ELEVATED WALL SHEAR STRESS AND INCREASED LEVELS OF AORTA-SPECIFIC CELL-FREE DNA IN BICUSPID VALVE AORTOPATHY

Bicuspid aortic valve (BAV) is commonly associated with aortopathy and potential catastrophic rupture. Identifying those patients at greatest risk for dissection and who would benefit from surgical intervention is challenging. Given that BAV creates abnormal hemodynamics in the ascending aorta which have been associated with regions of increased wall shear stress (WSS), we hypothesized that elevated levels of WSS are associated with increased cell death in the aorta. Since dying cells release fragmented DNA into the blood, we also hypothesized that levels of aorta-specific cell-free DNA (cfDNA), identified by the presence of tissue-specific differentially methylated regions (DMRs), could be leveraged as a biomarker. Our research objective was to identify the relationship between elevated WSS and programmed cell death (apoptosis) in the ascending aorta of human patients and identify aorta-specific DMRs in the plasma cfDNA of BAV patients

Evidence for wall shear stress-dependent t-PA release in human conduit arteries: role of endothelial factors and impact of high blood pressure.

Tissue plasminogen activator (t-PA) converts plasminogen into the serine protease plasmin, which in turn degrades fibrin clots. This study assessed whether an increase in shear stress is associated in humans in vivo with the release of t-PA in peripheral conduit arteries, the impact of high blood pressure and the role of NO and CYP450-derived epoxyeicosatrienoic acids (EETs). Local t-PA levels were quantified at baseline and during a sustained increase in radial artery wall shear stress induced by hand skin heating (from 34 to 44 °C) in a total of 25 subjects, among whom 8 were newly diagnosed essential hypertensive patients. The impact of the brachial infusion of NO synthase (L-NMMA) and CYP450 inhibitors (fluconazole) on t-PA release was assessed. The increase in shear stress induced by heating was associated with an increase in local t-PA release (from 3.0 ± 0.5 to 19.2 ± 5.5 ng/min, n = 25, P < 0.01). The magnitude of t-PA release was positively correlated with the increase in shear stress (r = 0.64, P < 0.001) and negatively correlated with mean blood pressure (r = -0.443, P = 0.027). These associations persisted after multiple adjustments for confounding factors. Finally, t-PA release was reduced by L-NMMA and to a larger extent by the combination of L-NMMA and fluconazole without a change in shear stress. The increase in wall shear stress in the peripheral conduit arteries induces a release of t-PA by a mechanism involving NO and EETs. The alteration of this response by high blood pressure may contribute to reducing the fibrinolytic potential and enhancing the risk of arterial thrombosis during exercise.

Investigation of convective heat transfer enhancement for nanofluid flow over flat plate

In this paper, the laminar flow over flat plate of three different nanofluids is investigated. The fluid is considered as water with three different kind of solid particles Al2O3, TiO2, and Fe3O4 of different volume fractions (1, 2, 3, and 4%). The values of viscosity, heat capacity, density, and thermal conductivity depending on volume fraction for the three nanofluids are evaluated. Numerical simulation has been conducted for analysis the impact of the nanoparticles on the heat transfer properties, on the temperature and velocity profiles, on the wall shear stress and on the skin friction coefficient. The results show that as the value of volume fraction increases the values of the wall shear stress, skin friction, and heat transfer increase, but the velocity decreases. A comparison between the three nanofluids presents the difference in the thermal enhancement, velocity profiles, and thermal boundary layer. With the volume fraction for all three nanofluids polynomial connections has been obtained to describe for the relation of the wall shear stress, skin friction coefficient and average heat transfer coefficient.

EndOxy: Mid-term stability and shear stress resistance of endothelial cells on PDMS gas exchange membranes.

Endothelialized oxygenator devices (EndOxy) with a physiological, nonthrombogenic, and anti-inflammatory surface offer the potential to overcome current shortcomings of conventional extracorporeal membrane oxygenation such as complications like thromboembolism and bleeding that deteriorate adequate long-term hemocompatibility. The approach of endothelialization of gas exchange membranes, and thus the formation of a nonthrombogenic and anti-inflammatory surface, is promising. In this study, we investigated the mid-term shear stress resistance as well as gas transfer rates and cell densities of endothelial cells seeded on RGD-conjugated polydimethylsiloxane (RGD-PDMS) gas exchange membranes under dynamic conditions. Human umbilical vein endothelial cells were seeded on RGD-PDMS and exposed to defined shear stresses in a microfluidic bioreactor. Endothelial cell morphology was assessed by bright field microscopy and immunocytochemistry. Furthermore, gas transfer measurement of blank, RGD-conjugated, and endothelialized PDMS oxygenator membranes was performed. RGD-PDMS gas exchange membranes proved suitable for the dynamic culture of endothelial cells for up to 21days at a wall shear stress of 2.9 dyn/cm2 . Furthermore, the cells resisted increased wall shear stresses up to 8.6 dyn/cm2 after a previous dynamic preculture of each one hour at 2.9 dyn/cm2 and 5.7 dyn/cm2 . Also, after a longer dynamic preculture of three days at 2.9 dyn/cm2 and one hour at 5.7 dyn/cm2 , increased wall shear stresses of 8.6 dyn/cm2 were tolerated by the cells and cell integrity could be remained. Gas transfer (GT) tests revealed that neither RGD conjugation nor endothelialization of RGD-PDMS significantly decrease the gas transfer rates of the membranes during short-term trials. Gas transfer rates are stable for at least 72hours of dynamic cultivation of endothelial cells. Immunocytochemistry showed that the cell layer stained positive for typical endothelial cell markers CD31 and von Willebrand factor (VWF) after all trials. Cell density of EC on RGD-PDMS increased between 3 and 21days of dynamic culture. In this study, we show the suitability of RGD-PDMS membranes for flow resistant endothelialization of gas-permeable membranes, demonstrating the feasibility of this approach for a biohybrid lung.

Biomechanical properties and histomorphometric features of aortic tissue in patients with or without bicuspid aortic valve.

BackgroundWe sought to investigate and compare biomechanical properties and histomorphometric findings of thoracic ascending aorta aneurysm (TAA) tissue from patients with bicuspid aortic valve (BAV) and tricuspid aortic valve (TAV) in order to clarify mechanisms underlying differences in the clinical course.MethodsCircumferential sections of TAA tissue in patients with BAV (BAV-TAA) and TAV (TAV-TAA) were obtained during surgery and used for biomechanical tests and histomorphometrical analysis.ResultsIn BAV-TAA, we observed biomechanical higher peak stress and lower Young modulus values compared with TAV-TAA wall. The right lateral longitudinal region seemed to be the most fragile zone of the TAA wall. Mechanical stress-induced rupture of BAV-TAA tissue was sudden and uniform in all aortic wall layers, whereas a gradual and progressive aortic wall breakage was described in TAV-TAA. Histomorphometric analysis revealed higher amount of collagen but not elastin in BAV-TAA tunica media.ConclusionsThe higher deformability of BAV-TAA tissue supports the hypothesis that increased wall shear stress doesn’t explain the increased risk of sudden onset of rupture and dissection; other mechanisms, likely related to alteration of specific genetic pathways and epigenetic signals, could be investigated to explain differences in aortic dissection and rupture in BAV patients.

On the reversibility of deposit formation in low temperature milk microfiltration with ceramic membranes depending on mode of adjustment of transmembrane pressure and wall shear stress

During the microfiltration of skim milk, flux and protein permeation decrease due to the formation of a deposit layer. For a better understanding of the deposit formation during the microfiltration of skim milk at 10 °C, flux and protein permeation were studied with a ceramic multichannel membrane (nominal pore size (nps) = 0.1 µm) at wall shear stress (τw) values from 45 to 341 Pa. When the limiting transmembrane pressure was applied, the flux showed a nearly linear increase with increasing wall shear stress and peaked at a critical τw. A further increase of τw resulted in a reduction of the flux until it levelled off. Thus, we could define a limiting τw additionally to the critical τw, at which no further changes in flux were observable. The limiting flux indicates that no structural changes in the deposit layer occur beyond the limiting τw. This conclusion is reassured by the development of the protein permeation. Beyond the limiting τw, no changes in the protein permeation could be observed. The critical and limiting τw are useful values for the design of fractionation processes by means of ceramic microfiltration.

A smaller heart-aorta-angle associates with ascending aortic dilatation and increases wall shear stress

ObjectivesThe aim of this study was to evaluate whether the orientation of the heart, measured as an angle between the long axis of the heart and ascending aorta midline (heart-aorta-angle, HAA), associates with ascending aortic (AA) dilatation. Furthermore, the association between HAA and wall shear stress (WSS) was studied.MethodsHAA was retrospectively measured in 1000 consecutive coronary artery computed tomographic angiography (CCTA) images in patients with low-to-moderate pretest probability for coronary artery disease (CAD). To evaluate the effects of HAA on AA flow, 4D flow MRI was performed for 28 patients with AA dilatation (> 40 mm) and WSS was analyzed.ResultsThe mean age of patients undergoing CCTA was 52.9 ± 9.8 years; 66.5% were women. Their median HAA was 128.7° and interquartile range 123.3–134.1°. HAA was significantly smaller in patients with dilated AA (median 126.7° [121.3–130.8°]) compared with the patients with normal AA (median 129.5° [124.3–135.3°], p < 0.001). HAA was smaller in males (p < 0.001) and in patients with diabetes (p = 0.016), hypertension (p = 0.001), CAD (p = 0.003), hypercholesterolemia (p < 0.001), and bicuspid aortic valve (p = 0.025) than without these factors. In a subpopulation without any of these underlying diseases (n = 233), HAA was still significantly smaller in the patients with dilated AA (median 127.9° [124.3–134.3°]) compared with patients with normal AA (median 131.9° [127.6–136.9°], p = 0.013). In 4D flow MRI, a smaller HAA correlated with increased total WSS in the outer curvature of the proximal AA (r = − 0.510, p = 0.006).ConclusionA smaller HAA associates with AA dilatation and affects the blood flow in the proximal AA.Key Points• A smaller angle between the long axis of the heart and ascending aorta midline associated with ascending aortic dilatation.• A smaller heart-aorta-angle correlated with increased total wall shear stress in the outer curvature of the proximal ascending aorta.

A Microfluidic-Based Investigation of Bacterial Attachment in Ureteral Stents.

Obstructions of the ureter lumen can originate from intrinsic or extrinsic factors, such as kidney stones, tumours, or strictures. These can affect the physiological flow of urine from the kidneys to the bladder, potentially causing infection, pain, and kidney failure. To overcome these complications, ureteral stents are often deployed clinically in order to temporarily re-establish urinary flow. Despite their clinical benefits, stents are prone to encrustation and biofilm formation that lead to reduced quality of life for patients; however, the mechanisms underlying the formation of crystalline biofilms in stents are not yet fully understood. In this study, we developed microfluidic-based devices replicating the urodynamic field within different configurations of an occluded and stented ureter. We employed computational fluid dynamic simulations to characterise the flow dynamic field within these models and investigated bacterial attachment (Pseudomonas fluorescens) by means of crystal violet staining and fluorescence microscopy. We identified the presence of hydrodynamic cavities in the vicinity of a ureteric occlusion, which were characterised by low levels of wall shear stress (WSS < 40 mPa), and observed that initiation of bacterial attachment occurred in these specific regions of the stented ureter. Notably, the bacterial coverage area was directly proportional to the number of cavities present in the model. Fluorescence microscopy confirmed that the number density of bacteria was greater within cavities (3 bacteria·mm−2) when compared to side-holes of the stent (1 bacterium·mm−2) or its luminal surface (0.12 bacteria·mm−2). These findings informed the design of a novel technological solution against bacterial attachment, which reduces the extent of cavity flow and increases wall shear stress over the stent’s surface.

Microstructure of early embryonic aortic arch and its reversibility following mechanically altered hemodynamic load release.

In the embryonic heart, blood flow is distributed through a bilaterally paired artery system composed of the aortic arches (AAs). The purpose of this study is to establish an understanding of the governing mechanism of microstructural maturation of the AA matrix and its reversibility, toward the desired macroscopic vessel lumen diameter and thickness for healthy, abnormal, and in ovo repaired abnormal mechanical loading. While matrix-remodeling mechanisms were significantly different for normal versus conotruncal banding (CTB), both led to an increase in vessel lumen. Correlated with right-sided flow increase at Hamburger & Hamilton stages 21, intermittent load switching between collagen I and III with elastin and collagen-IV defines the normal process. However, decreases in collagen I, elastin, vascular endothelial growth factor-A, and fibrillin-1 in CTB were recovered almost fully following the CTB-release model, primarily because of the pressure load changes. The complex temporal changes in matrix proteins are illustrated through a predictive finite-element model based on elastin and collagen load-sharing mechanism to achieve lumen area increase and thickness increase resulting from wall shear stress and tissue strain, respectively. The effect of embryonic timing in cardiac interventions on AA microstructure was established where abnormal mechanical loading was selectively restored at the key stage of development. Recovery of the normal mechanical loading via early fetal intervention resulted in delayed microstructural maturation. Temporal elastin increase, correlated with wall shear stress, is required for continuous lumen area growth.NEW & NOTEWORTHY The present study undertakes comparative analyses of the mechanistic differences of the arterial matrix microstructure and dynamics in the three fundamental processes of control, conotruncal banded, and released conotruncal band in avian embryo. Among other findings, this study provides specific evidence on the restorative role of elastin during the early lumen growth process. During vascular development, a novel intermittent load-switching mechanism between elastin and collagen, triggered by a step increase in wall shear stress, governs the chronic vessel lumen cross-sectional area increase. Mimicking the fetal cardiovascular interventions currently performed in humans, the early release of the abnormal mechanical load rescues the arterial microstructure with time lag.

Increase of wall shear stress caused by arteriovenous fistula reduces neointimal hyperplasia after stent implantation in healthy arteries.

Wall shear stress plays a critical role in neointimal hyperplasia after stent implantation. It has been found that there is an inverse relation between wall shear stress and neointimal hyperplasia. This study hypothesized that the increase of arterial wall shear stress caused by arteriovenous fistula could reduce neointimal hyperplasia after stents implantation. Thirty-six male rabbits were randomly divided into three groups: STENT, rabbits received stent implantation into right common carotid artery; STENT/arteriovenous fistula, rabbits received stent implantation into right common carotid artery and carotid-jugular arteriovenous fistula; Control, rabbits received no treatment. After 21 days, stented common carotid artery specimens were harvested for histological staining and protein expression analysis. In STENT group, wall shear stress maintained at a low level from 43.2 to 48.9% of baseline. In STENT/arteriovenous fistula group, wall shear stress gradually increased to 86% over baseline. There was a more significant neointimal hyperplasia in group STENT compared with the STENT/arteriovenous fistula group (neointima area: 0.87mm2 versus 0.19mm2; neointima-to-media area ratio: 1.13 versus 0.18). Western blot analysis demonstrated that the protein level of endothelial nitric oxide synthase in STENT group was significantly lower than that in STENT/arteriovenous fistula group, but the protein levels of proliferating cell nuclear antigen, vascular cell adhesion molecule 1, phospho-p38 mitogen-activated protein kinase (Pp38), and phospho-c-Jun N-terminal kinase in STENT group were significantly higher than that in the STENT group. High wall shear stress caused by arteriovenous fistula as associated with the induction in neointimal hyperplasia after stent implantation. The underlying mechanisms may be related to modulating the expression and activation of endothelial nitric oxide synthase, vascular cell adhesion molecule 1, p38, and c-Jun N-terminal kinase.

Left Ventricular Assist Device Shear Stress Quantification Utilizing Computational Fluid Dynamics: Using Physics and Physiology to Optimize Programmable Flow Algorithms

Our current understanding of left ventricular assist device (LVAD) flow algorithms and their impact on shear stress and platelet activation remains incompletely understood. Computational fluid dynamics (CFD) allows for analysis of flow in the cardiovascular system. CFD simulations were carried out on a patient with a HeartMate II. Simulations were also done substituting for HVAD with or without Lavare cycle, HeartMate 3 in continuous mode or with Artificial Pulse as well as novel flow algorithms including copulsation and counterpulsation modes. LVAD flow was calculated using a lumped-parameter-model (LPM) of the systemic circulation, which was calibrated with patient-specific ventricular volume changes from 4 dimensional CT and hemodynamic tracings. The LVADs were implemented in the LPM via published H-Q curves. Shear stress and platelet activation were quantified for each flow algorithm and pump type. Wall shear stress was greater with the HVAD when compared to the HMII or HM3 (Figure Top). In the aortic arch and carotid arteries, a 42% increase in shear stress was noted with the HVAD compared to the HM3 in continuous mode (1.86 vs. 1.31 Pa) with little impact from the addition of the Lavare Cycle (Figure Bottom). Platelet activation was similarly greatest with the HVAD in the carotid arteries. The addition of the artificial pulse to the HM3 flow algorithm led to a 168% increase in shear stress (0.363 vs 0.139 Pa) throughout the ascending aorta (Figure Bottom). CFD analysis reveals that the artificial pulse increases wall shear stress in the ascending aorta and may represent a plausible mechanism to explain the high observed rates of aortic insufficiency seen with the HM3. Similarly, the higher shear stress rates in the carotid arteries seen with the HVAD might partly explain the higher residual rates of stroke with this pump. These hypothesis generating questions need to be prospective explored.

Numerical Analysis on Velocity and Temperature of the Fluid in a Blast Furnace Main Trough

The main trough is a part of the blast furnace process for hot metal and molten slag transportation from the tap hole to the torpedo, and mechanical erosion of the trough is an important reason for a short life of a campaign. This article employed OpenFoam code to numerically study and analyze velocity, temperature and wall shear stress of the fluids in the main trough during a full tapping process. In the code, a three-dimensional transient mass, momentum and energy conservation equations, including the standard k-ε turbulence model, were developed for the fluid in the trough. Temperature distribution in refractory is solved by the Fourier equation through conjugate heat transfer with the fluid in the trough. Change velocities of the fluid during the full tapping process are exactly described by a parabolic equation. The investigation results show that there are strong turbulences at the area of hot metal’s falling position and the turbulences have influence on velocity, temperature and wall shear stress of the fluid. With the increase of the angle of the tap hole, the wall shear stress increases. Mechanical erosion of the trough has the smallest value and the campaign of the main trough is estimated to expand over 5 days at the tap hole angle of 7°.

Analysis and manegement of laminar blood flow inside a cerebral blood vessel using a finite volume software program for biomedical engineering

Background and objectiveHemodynamic blood flow analysis in the cerebrovascular is has become one of the important research topics in the bio-mechanic in recent decades. The primary duty of the cerebral blood vessel is supplying Glucose and oxygen for the brain. MethodsIn this investigation, the non-Newtonian blood flow in the cerebral blood vessels studied. For modeling the geometry of this problem, we used Magnetic Resonance Image (MRI) approach to take Digital Imaging and Communications in Medicine (DICOM) images and using an open-source software package to construct the geometry, which is a complicated one. The power-law indexes, heat flux, and Reynolds number range in the investigation are 0.6 ≤ n ≤ 0.8, 5 ≤ q ≤ 15Wm−2 and 160≤Re≤310. Effects of Reynolds number, power-law indexes and heat fluxes are investigated. ResultsWe found that the pressure drop increase with increasing the Reynolds number and power-law index. The maximum Nusselt number in the cerebral blood vessels accrued in the running position of the body in n = 0.8. Also, the highest average wall shear stress occurs in maximum power-law indexes and Reynolds number. ConclusionBy increasing the power-law index and Reynolds number, the wall shear stress increases.

Numerical investigation of unsteady pulsatile Newtonian/non-Newtonian blood flow through curved stenosed arteries.

A numerical investigation of Newtonian/non-Newtonian unsteady pulsatile entry blood flow inside a 3D curved stenosed artery is presented. For considering the non-Newtonian effect (shear thinning or shear thickening behavior), the blood viscosity is characterized by the power-law model (Ostwald de Waele Equation). At the inlet of the artery, a realistic pulsatile waveform is utilized according to the experimental data reported by other researchers. This study belongs to the analysis of the curvature ratios, percentage and length ratio of stenosis, and blood thickening on hemodynamic characteristics of the flow. The results emphasize that the maximum wall shear stress happens near the stenosis neck and as expected, by decreasing the stenosis length, the maximum value of wall shear stress increases. In addition, the results indicate that the shear thickening fluid shows a more stable velocity profile rather than the shear thinning fluid flow.