Analysis of Volumetric Residence Time of Blood Elements in Stenosed Arteries

2003 ◽  
Author(s):  
M. C. Kim ◽  
C. S. Lee ◽  
C. J. Kim
Keyword(s):  
Residence Time ◽  
Transient Flow ◽  
Fluid Dynamic ◽  
Viscous Drag ◽  
Shear Stresses ◽  
Drag Forces ◽  
Area Reduction ◽  
Dynamic Factors ◽  
Recirculation Zones ◽  
Computational Fluid Dynamics Cfd

Blood flow in arteries is known to be closely related to atherosclerosis. Presence of recirculation zones, and low, high, and oscillatory wall shear stresses have been suggested to be important fluid dynamic factors causing development and progress of atherosclerosis. Our study was motivated to develop fluid mechanical indices between residence time of blood particles in arteries and atherosclerosis. In rigid models of stenosed arteries with 75% area reduction, trajectories of blood particles were numerically computed and used to determine local volumetric residence time (VRT) of platelets. The motion of particles in the model artery was computed by considering viscous drag forces between blood particles and presolved transient flow field from computational fluid dynamics (CFD). Many cardiac cycles were considered in the computation to reflect temporally accumulative characteristics of VRT in the recirculation zones. Our results showed that VRT in the recirculation zone was relatively low in the first cardiac cycle. However it increased in the subsequent cycles as more particles were trapped in the same zone. The results suggested that VRT contour calculated in the present study would be an effective indicator of the presence of atherosclerosis.

scholarly journals Turbulence Enhancement and Mixing Analysis for Multi-Inlet Vortex Photoreactor for CO2 Reduction

Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2237
Author(s):  
Jesús Valdés ◽  
Jorge Luis Domínguez-Juárez ◽  
Rufino Nava ◽  
Ángeles Cuán ◽  
Carlos M. Cortés-Romero
Keyword(s):  
Residence Time ◽  
Turbulence Intensity ◽  
Mass Fraction ◽  
Fluid Dynamic ◽  
Co2 Reduction ◽  
Point Of View ◽  
Molar Ratio ◽  
Cylindrical Shape ◽  
Turbulent Regime ◽  
Computational Fluid Dynamics Cfd

In this article, we describe a prototype photoreactor of which the geometrical configuration was obtained by Genetic Algorithms to maximize the residence time of the reactant gases. A gas reaction mixture of CO2:H2O (1:2 molar ratio) was studied from the fluid dynamic point of view. The two main features of this prototype reactor are the conical shape, which enhances the residence time as compared to a cylindrical shape reference reactor, and the inlet heights and position around the main chamber that enables turbulence and mass transfer control. Turbulence intensity, mixing capability, and residence time attributes for the optimized prototype reactor were calculated with Computational Fluid Dynamics (CFD) software and compared with those from a reference reactor. Turbulence intensity near the envisioned catalytic bed was one percentage point higher in the reference than in the optimized prototype reactor. Finally, the homogeneity of the mixture was guaranteed since both types of reactors had a turbulent regime, but for the prototype the CO2 mass fraction was found to be better distributed.

DIAGNOSTIC AND THERAPEUTIC TREATMENTS OF PLAQUES IN THE CAROTID BIFURCATION — STUDIES IN MODELS WITH STENTS AND FILTERS

2014 ◽  
Vol 14 (03) ◽  
pp. 1450030
Author(s):  
D. LIEPSCH ◽  
A. BALASSO ◽  
C. ZIMMER ◽  
H. BERGER ◽  
R. BURKHART ◽  
...  
Keyword(s):  
Flow Rate ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Carotid Bifurcation ◽  
Flow Rate Ratio ◽  
Shear Stresses ◽  
Dynamic Factors ◽  
Rate Ratios ◽  
Visualization Techniques

Fluid dynamics, especially forces and velocity distribution, influence the development of plaques. Flow parameters: pulsatility, the non-Newtonian flow behavior of blood and wall elasticity are considered. Flow visualization techniques (dyes and birefringent solution with a photo-elasticity apparatus) and LDA measurements demonstrate the importance of the flow. Accurate in vivo velocity measurements are necessary to calculate shear stresses. Different bifurcation angles and flow rate ratios were tested in true to life artery models. The most important fluid dynamic factors at bifurcations are the flow rate ratio and the geometry which create flow separation regions which are responsible for platelet aggregation and intima damage. It is necessary to measure all three velocity components to calculate the velocity vector. The highest shear stresses in a healthy carotid artery are 16 Pa and are found just at the apex. In artery models with 90% stenosis, shear stresses up to 250 Pa were found. Distally, vortices were created where particles remained over several pulse cycles. Measurements show that stents must be selected carefully and placed precisely. Filters must be closed during the systolic phase before removal, so that no trapped particles can escape.

PULSATILE FLOW FIELDS IN A MODEL OF ABDOMINAL AORTA WITH ITS PERIPHERAL BRANCHES

2003 ◽  
Vol 15 (05) ◽  
pp. 170-178 ◽  
Author(s):  
D. LEE ◽  
J. Y. CHEN
Keyword(s):  
Flow Field ◽  
Steady Flow ◽  
Abdominal Aorta ◽  
Pulsatile Flow ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Computer Code ◽  
Flow Fields ◽  
Dynamic Factors ◽  
Recirculation Zones

In a previous study by the authors, steady flow fields in a model of abdominal aorta with its seven peripheral branches were reported. In the present study, the some aorta model was simulated numerically with a pulsatile inlet waves for both the resting and exercise conditions. The baseline pulsatile flow field was presented in terms of velocity vectors and iso-velocity contours as well as the wall shear stress (WSS) distribution and the recirculation zones. The time-averaged behavior of the flow field represented by the fluid dynamic factors was discussed. The results were consistent with those obtained experimentally and numerically by other investigators. It was also found that under the present conditions, the steady flow behavior could adequately describe the time-averaged behavior of its corresponding pulsatile case, particularly in the regions where convective flow dominated. The present computer code may provide a platform for clinical simulations.

Computational fluid dynamic prediction of the residence time of a vortex separator applied to disinfection

2005 ◽  
Vol 52 (3) ◽  
pp. 29-36 ◽  
Author(s):  
D. Egarr ◽  
M.G. Faram ◽  
T. O'Doherty ◽  
D. Phipps ◽  
N. Syred
Keyword(s):  
Fluid Dynamics ◽  
Residence Time ◽  
Air Conditioning ◽  
Fluid Dynamic ◽  
Dynamic Prediction ◽  
Disinfection Process ◽  
Computational Fluid Dynamics Cfd ◽  
Vortex Separator ◽  
The Mean ◽  
Computational Fluid Dynamic Prediction

A Hydrodynamic Vortex Separator (HDVS) has been modelled using Computational Fluid Dynamics (CFD) in order to predict the residence time of the fluid at the overflow and underflow outlets. A technique which was developed for use in Heating, Ventilation and Air Conditioning (HVAC) was used to determine the residence time and the results have been compared with those determined experimentally. It is shown that in using CFD, it is possible to predict the mean residence time of the fluid and to study the response to a pulse injection of tracer. It is also shown that it is possible to apply these techniques to predict the mean survival rate of bacteria in a combined separation and disinfection process.

Particle Volumetric Residence Time Calculations in Arterial Geometries

1996 ◽  
Vol 118 (2) ◽  
pp. 158-164 ◽  
Author(s):  
Mads J. Kunov ◽  
D. A. Steinman ◽  
C. Ross Ethier
Keyword(s):  
Residence Time ◽  
Threshold Value ◽  
Shear Stresses ◽  
Residence Times ◽  
Particle Distributions ◽  
Transient Nature ◽  
High Particle ◽  
Area Reduction ◽  
Tracer Particles ◽  
Percent Area

The quantification of particle (platelet) residence times in arterial geometries is relevant to the pathogenesis of several arterial diseases. In this manuscript, the concept of “volumetric residence time” (VRT) is introduced. The VRT takes into account where particles accumulate and how long they remain there, and is wellsuited to characterizing particle distributions in the complex geometries typical of the cardiovascular system. A technique for the calculation of volumetric residence time is described, which assumes that platelets are neutrally buoyant passive tracer particles, and which tracks small Lagrangian fluid elements containing a uniform concentration of platelets. This approach is used to quantify particle (platelet) residence times in the region of a modeled stenosis with a 45 percent area reduction. Residence time distributions are computed for a representative population of platelets, and for a subpopulation assumed to be “activated” by exposure to shear stresses above a threshold value. For activated platelets, high particle residence times were observed just distal to the apex of the stenosis throat, which can be explained by the presence of high shear stresses and low velocities in the throat immediately adjacent to the vessel wall. Interestingly, the separation zone distal to the stenosis showed only modestly elevated residence times, due to its highly mobile and transient nature. This calculation demonstrates the utility of the VRT concept for cardiovascular studies, particularly if a subpopulation of all particles is to be tracked. We conclude that the volumetric residence time is a useful tool.

Fluid dynamics and the thromboembolic reaction in mesenteric arterioles and venules

1991 ◽  
Vol 260 (6) ◽  
pp. H1826-H1833
Author(s):  
M. G. Oude Egbrink ◽  
G. J. Tangelder ◽  
D. W. Slaaf ◽  
R. S. Reneman
Keyword(s):  
Thrombus Formation ◽  
Fluid Dynamic ◽  
Vessel Diameter ◽  
Area Reduction ◽  
Dynamic Factors ◽  
Cell Velocity ◽  
Red Blood Cell Velocity ◽  
Stenosed Vessel ◽  
The Difference ◽  
Velocity Changes

In the mesentery of the anesthetized rabbit, the thromboembolic reaction after wall puncture lasts six times longer in arterioles than in venules, a difference that cannot be explained by fluid dynamic conditions before puncture. In the present study, it was investigated whether this difference in response between arterioles and venules results from a different degree of stenosis by the thrombus and/or a difference in velocity changes resulting in a different pressure drop over the thrombus. Arteriolar and venular mean red blood cell velocity and vessel diameter were measured before puncture and after this injury in the stenosed vessel segment and upstream. Thrombi with similar heights were formed in arterioles and venules and induced similar degrees of stenosis. A surface area reduction less than 55% induced only a small and similar decrease in volume flow (less than 10%) in arterioles and venules. Reduced velocity, a measure of wall shear rate, increased similarly in both vessel types for similar degrees of stenosis. In conclusion, changes in fluid dynamic factors, as induced by thrombus formation, cannot be held responsible for the difference in thromboembolic reaction between arterioles and venules.

scholarly journals Computational fluid dynamic prediction of the residence time distribution of a prototype hydrodynamic vortex separator operating with a base flow component

2005 ◽  
Vol 219 (1) ◽  
pp. 53-67 ◽  
Author(s):  
D. A. Egarr ◽  
M. G. Faram ◽  
T O'Doherty ◽  
D. A. Phipps ◽  
N Syred
Keyword(s):  
Residence Time ◽  
Air Conditioning ◽  
Fluid Dynamic ◽  
Base Flow ◽  
Hydraulic Systems ◽  
Dynamic Prediction ◽  
Computational Fluid Dynamics Cfd ◽  
Vortex Separator ◽  
The Mean ◽  
Computational Fluid Dynamic Prediction

A hydrodynamic vortex separator (HDVS) has been modelled using computational fluid dynamics (CFD) in order to accurately determine the residence time of the fluid at the two outlets of the HDVS using a technique that was developed for use in heating, ventilation, and air conditioning (HVAC). The results have been compared with experimental data [1]. It is shown that, in using CFD, it is possible to study the response to a variety of inputs, and also to determine the mean residence time of the fluid within the separator. Although the technique used for determining the residence time was developed for use in HVAC, it is shown here to be applicable for the analysis of hydraulic systems, specifically, wastewater treatment systems.

Performance of lamella clarifiers for juice and syrup clarification

2017 ◽  
pp. 144-150
Author(s):  
Peter W. Rein ◽  
M. Getaz ◽  
A. Raghunandan ◽  
N. du Pleissis ◽  
H. Saleh ◽  
...  
Keyword(s):  
Residence Time ◽  
Flow Characteristics ◽  
Preliminary Test ◽  
Practical Experience ◽  
Operating Costs ◽  
Capital Costs ◽  
Computational Fluid Dynamics Cfd ◽  
Improved Performance ◽  
Work Done ◽  
Good Flow

A new design for syrup and juice clarifiers is presented. The design takes advantage of the considerably improved performance of clarifiers incorporating lamella plates, and the reasons for the improvement are outlined. Computational fluid dynamics (CFD) work done to simulate the performance is summarised. This design enables the residence time to be dramatically reduced and the simplified design leads to cheaper and better clarifiers. Practical experience with factory scale units is described, confirming the good flow characteristics. The results of preliminary test work on a factory syrup clarifier are presented, which is also shown to operate efficiently as a phosphatation clarifier. In addition the performance of a full-scale juice clarifier has been evaluated and compared with the performance of a Rapidorr clarifier. This work confirms the considerable advantages which this type of design provides, in realising substantial reductions in residence time, capital costs and operating costs.

scholarly journals Risk Analysis of Road Tunnels: A Computational Fluid Dynamic Model for Assessing the Effects of Natural Ventilation

2020 ◽  
Vol 11 (1) ◽  
pp. 32
Author(s):  
Ciro Caliendo ◽  
Gianluca Genovese ◽  
Isidoro Russo
Keyword(s):  
Natural Ventilation ◽  
Fluid Dynamic ◽  
Movement Time ◽  
Radiant Heat ◽  
Heat Fluxes ◽  
Maximum Heat ◽  
Road Tunnels ◽  
Maximum Heat Release ◽  
Computational Fluid Dynamics Cfd ◽  
Time Required

We have developed an appropriate Computational Fluid Dynamics (CFD) model for assessing the exposure to risk of tunnel users during their evacuation process in the event of fire. The effects on escaping users, which can be caused by fire from different types of vehicles located in various longitudinal positions within a one-way tunnel with natural ventilation only and length less than 1 km are shown. Simulated fires, in terms of maximum Heat Release Rate (HRR) are: 8, 30, 50, and 100 MW for two cars, a bus, and two types of Heavy Goods Vehicles (HGVs), respectively. With reference to environmental conditions (i.e., temperatures, radiant heat fluxes, visibility distances, and CO and CO2 concentrations) along the evacuation path, the results prove that these are always within the limits acceptable for user safety. The exposure to toxic gases and heat also confirms that the tunnel users can safely evacuate. The evacuation time was found to be higher when fire was related to the bus, which is due to a major pre-movement time required for leaving the vehicle. The findings show that mechanical ventilation is not necessary in the case of the tunnel investigated. It is to be emphasized that our modeling might represent a reference in investigating the effects of natural ventilation in tunnels.

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