Rheological Effects of Blood in a Nonplanar Distal End-to-Side Anastomosis

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Qian-Qian Wang ◽  
Bao-Hong Ping ◽  
Qing-Bo Xu ◽  
Wen Wang
Keyword(s):  
Flow Rate ◽  
Stokes Equations ◽  
Bypass Graft ◽  
High Flow ◽  
Secondary Flows ◽  
Newtonian Fluids ◽  
Low Flow ◽  
Flow Rates ◽  
Flow Recirculation ◽  
Low Flow Rate

This study investigates rheological effects of blood on steady flows in a nonplanar distal end-to-side anastomosis. The shear-thinning behavior of blood is depicted by a Carreau–Yasuda model and a modified power-law model. To explore effects of nonplanarity in vessel geometry, a curved bypass graft is considered that connects to the host artery with a 90deg out-of-plane curvature. Navier–Stokes equations are solved using a finite volume method. Velocity and wall shear stress (WSS) are compared between Newtonian and non-Newtonian fluids at different flow rates. At low flow rate, difference in axial velocity profiles between Newtonian and non-Newtonian fluids is significant and secondary flows are weaker for non-Newtonian fluids. At high flow rate, non-Newtonian fluids have bigger peak WSS and WSS gradient. The size of the flow recirculation zone near the toe is smaller for non-Newtonian fluids and the difference is significant at low flow rate. The nonplanar bypass graft introduces helical flow in the host vessel. Results from the study reveal that near the bed, heel, and toe of the anastomotic junction where intimal hyperplasia occurs preferentially, WSS gradients are all very big. At high flow rates, WSS gradients are elevated by the non-Newtonian effect of blood but they are reduced at low flow rates. At these locations, blood rheology not only affects the WSS and its gradient but also secondary flow patterns and the size of flow recirculation near the toe. This study reemphasizes that the rheological property of blood is a key factor in studying hemodynamic effects on vascular diseases.

scholarly journals Spheres in the vicinity of a bifurcation: elucidating the Zweifach–Fung effect

2011 ◽  
Vol 674 ◽  
pp. 359-388 ◽  
Author(s):  
V. DOYEUX ◽  
T. PODGORSKI ◽  
S. PEPONAS ◽  
M. ISMAIL ◽  
G. COUPIER
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Volume Fraction ◽  
Initial Distribution ◽  
High Flow ◽  
High Flow Rate ◽  
Low Flow ◽  
Two Dimensional ◽  
Flow Rates ◽  
Low Flow Rate

The problem of the splitting of a suspension in bifurcating channels divided into two branches of non-equal flow rates is addressed. As has long been observed, in particular in blood flow studies, the volume fraction of particles generally increases in the high-flow-rate branch and decreases in the low-flow-rate branch. In the literature, this phenomenon is sometimes interpreted as the result of some attraction of the particles towards this high-flow-rate branch. In this paper, we focus on the existence of such an attraction through microfluidic experiments and two-dimensional simulations and show clearly that such an attraction does not occur but is, on the contrary, directed towards the low-flow-rate branch. Arguments for this attraction are given and a discussion on the sometimes misleading arguments found in the literature is given. Finally, the enrichment of particles in the high-flow-rate branch is shown to be mainly a consequence of the initial distribution in the inlet branch, which shows necessarily some depletion near the walls.

A Meanline Model for Impeller Flow Recirculation

2008 ◽  
Author(s):  
Xuwen Qiu ◽  
David Japikse ◽  
Mark Anderson
Keyword(s):  
Flow Rate ◽  
Recirculation Zone ◽  
Reverse Flow ◽  
Low Flow ◽  
Suction Surface ◽  
Blade Loading ◽  
Flow Recirculation ◽  
Impeller Outlet ◽  
Active Flow ◽  
Low Flow Rate

Flow recirculation at the impeller inlet and outlet is an important feature that affects impeller performance, especially the power consumption at a very low flow rate. Although the mechanisms for this flow phenomenon have been studied, a practical model is needed for meanline modeling of impeller off-design performance. In this paper, a meanline recirculation model is proposed. At the inlet, the recirculation zone acts as area blockage to relieve the large incidence of the active flow at a low flow rate. The size of the blockage is estimated through a critical area ratio of an artificial “inlet diffuser” from the inlet to throat. The intensity of the reverse flow can then be calculated by assuming a linear velocity profile of meridional velocity in the recirculation zone. At the impeller outlet, a recirculation zone near the suction surface is established to balance the velocity difference on the pressure and suction sides of the blade. The size and the intensity of the outlet recirculation zone is assumed related to blade loading, which can be evaluated based on flow turning and Coriolis force. A few validation cases are presented showing a good comparison between test data and prediction by the model.

Experimental Investigation of Pressure Fluctuations on Inner Wall of a Centrifugal Pump

2019 ◽  
Vol 36 (4) ◽  
pp. 401-410 ◽  
Author(s):  
Xiao-Qi Jia ◽  
Bao-Ling Cui ◽  
Zu-Chao Zhu ◽  
Yu-Liang Zhang
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
High Flow ◽  
Low Flow ◽  
Centrifugal Pumps ◽  
Flow Rates ◽  
Pressure Distributions ◽  
Blade Passing Frequency

Abstract Affected by rotor–stator interaction and unstable inner flow, asymmetric pressure distributions and pressure fluctuations cannot be avoided in centrifugal pumps. To study the pressure distributions on volute and front casing walls, dynamic pressure tests are carried out on a centrifugal pump. Frequency spectrum analysis of pressure fluctuation is presented based on Fast Fourier transform and steady pressure distribution is obtained based on time-average method. The results show that amplitudes of pressure fluctuation and blade-passing frequency are sensitive to the flow rate. At low flow rates, high-pressure region and large pressure gradients near the volute tongue are observed, and the main factors contributing to the pressure fluctuation are fluctuations in blade-passing frequency and high-frequency fluctuations. By contrast, at high flow rates, fluctuations of rotating-frequency and low frequencies are the main contributors to pressure fluctuation. Moreover, at low flow rates, pressure near volute tongue increases rapidly at first and thereafter increases slowly, whereas at high flow rates, pressure decreases sharply. Asymmetries are observed in the pressure distributions on both volute and front casing walls. With increasing of flow rate, both asymmetries in the pressure distributions and magnitude of the pressure decrease.

scholarly journals Inter-Blade Vortex and Vortex Rope Characteristics of a Pump-Turbine in Turbine Mode under Low Flow Rate Conditions

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2554 ◽  
Author(s):  
Seung-Jun Kim ◽  
Jun-Won Suh ◽  
Young-Seok Choi ◽  
Jungwan Park ◽  
No-Hyun Park ◽  
...  
Keyword(s):  
Flow Rate ◽  
Stokes Equations ◽  
Low Flow ◽  
Renewable Energy Resources ◽  
Two Phase ◽  
Constant Frequency ◽  
Pump Turbine ◽  
Vortex Rope ◽  
Turbine Mode ◽  
Low Flow Rate

Pump-turbines are often used to provide a stable power supply with a constant frequency in response to intermittent renewable energy resources. However, existing pumped-storage power stations often operate under off-design conditions because of the increasing amounts of inconsistent renewable resources that have been added to the grid. Under off-design low flow rate conditions, inter-blade vortex and vortex rope phenomena usually develop in the runner and draft tube passages, respectively, in turbine mode. These vortices cause complicated flow patterns and pressure fluctuations that destabilize the operation of the pump-turbine system. Therefore, this study investigates the influence of correlation between the inter-blade vortex and vortex rope phenomena under low flow rate conditions. Three-dimensional steady- and unsteady-state Reynolds-averaged Navier–Stokes equations were calculated with a two-phase flow analysis using a shear stress transport as the turbulence model. The inter-blade vortices in the runner passages were captured well at the low flow rate conditions, and the vortex rope was found to develop within a specific range of low flow rates. These vortex regions showed a blockage effect and complicated flow characteristics with backflow in the passages. Moreover, higher unsteady pressure characteristics occurred at locations where the vortices were especially pronounced.

scholarly journals An In Vitro Evaluation of the Red Cell Damage and Hemocompatibility of Different Central Venous Catheters

2020 ◽  
Vol 2020 ◽  
pp. 1-9
Author(s):  
Alojz Ihan ◽  
Stefan Grosek ◽  
David Stubljar
Keyword(s):  
Blood Cell ◽  
Flow Rate ◽  
Blood Cells ◽  
Cell Damage ◽  
Central Venous Catheters ◽  
High Flow ◽  
High Flow Rate ◽  
Low Flow ◽  
Central Venous ◽  
Flow Rates

Background. The aim of our study was to evaluate the damaging impact of characteristics of the central venous catheters (CVCs) on red blood cells. Methods. CVCs from three different manufacturers were analyzed, including the presence of coating, tunnel geometry, length, lumen diameter, and number of lumens with two respective flow rates (33 mL/min and 500 mL/min). Blood cell damage was defined by analyzing microparticle (MP) and hematologic analysis. MPs were isolated by ultracentrifugation of erythrocyte concentrate and analyzed on a flow cytometer. Results. Characteristics of catheters were not associated with blood cell damage at a low flow rate but showed an effect with a high flow rate. CVCs with a polyhexanide methacrylate coating have caused statistically less blood cell damage than noncoated CVCs. The length of lumens, diameter, and geometry of the tunnel showed no differences in blood cell damage. Meanwhile, the number of lumens was predicted to have a greater effect on the erythrocyte damage, which was revealed with the formation of MPs and hematological parameters. CVCs with five lumens caused significantly less damage to the blood cells than CVCs with a single lumen. Moreover, a high flow rate of 500 mL/min caused less damage to the blood cells than a low rate of 33 mL/min. Conclusion. Properties of CVCs are an important factor for quality patient care, especially when transfusing blood with high flow rates, as we want to provide a patient with high-quality blood with as few damaged cells as possible.

CFD Analysis of Performance of Five-Stage High-Pressure Volute Pump

2016 ◽  
Author(s):  
Takayuki Suzuki ◽  
Takashi Takemura
Keyword(s):  
High Pressure ◽  
Flow Rate ◽  
Measurement Data ◽  
High Flow ◽  
High Flow Rate ◽  
Low Flow ◽  
Model Computation ◽  
Pump Performance ◽  
Computation Efficiency ◽  
Low Flow Rate

It is important in development of turbomachinery to predict their performance precisely. Especially the prediction of multistage pump performance is one of the challenging problems because internal phenomena which relate to the performance are complicated. Therefore, in this research, we verified accuracy of Computational Fluid Dynamics (CFD) in predicting performance of a five-stage high-pressure volute pump by comparing predicted values by CFD with measurement data. We tried two methods to predict the pump performance. One is a computation with a complete pump model which includes all five stages and leakage passages. This method can be expected to represent total internal flow phenomena. The other method is totaling up the performance data from separate computations of 1st–2nd stages and series stages. This method is simpler than the former and involves less computational cost. As a result, it was clarified that all the methods could predict pump head at the best efficiency point to some extent, even by steady computation. However, no prediction can predict positive gradient in Q-H curve which was observed in measurement at low flow rate. Except for the unsteady complete pump model computation, efficiency and shaft power could not be predicted precisely. In addition, at high flow rate, unsteady computation of the complete pump model shows the best agreement in head. In the complete pump model computation at high flow rate, the series stage next to the long crossover has larger head because of the influence of it. Therefore, the separated model has difficulty in representing series stages’ performance. In order to predict performance at high flow rate, unsteady computations also including properly the influence of the long crossover properly are necessary. In addition, to predict performance at low flow rate, unsteady computation is necessary.

scholarly journals 119 PHOTOSYNTHESIS AND RESPIRATION OF APPLE PLANTS AT DIFFERENT CARBON DIOXIDE CONCENTRATIONS

HortScience ◽  
1994 ◽  
Vol 29 (5) ◽  
pp. 445d-445
Author(s):  
Qiyuan Pan ◽  
Bruno Quebedeaux
Keyword(s):  
Flow Rate ◽  
Dark Respiration ◽  
Air Flow ◽  
High Flow ◽  
High Flow Rate ◽  
Low Flow ◽  
Crop Canopy ◽  
Ambient Level ◽  
Photosynthesis And Respiration ◽  
Low Flow Rate

Low CO2 concentrations ([CO2]) frequently occur in dense crop canopy. To determine plant performance under sub-atmospheric [CO2], young `Gala' apple plants were phytotron-grown at 928 mmole m-2s-1 light intensity. Whole-plant photosynthesis and respiration under [CO2] between 0 and the ambient level (382 to 460 ml 1-1) were measured by monitoring [CO2] of the air entering and coming out of a 38-1 clear plexiglass gas exchange chamber at either 3.4 or 6.2 1 min-1. The chamber seals two plants of up to 77 cm height for long-term experiments. There was a linear relationship between [CO2] and net photosynthesis (Pn), with the R2 being as high as 0.99. The increase of Pn with increased [CO2] was 51% greater for the high air flow than for the low air flow. At the ambient CO2 level Pn at the high flow rate was 49% higher than that at the low flow rate. CO2 compensation points were 57.6 and 58.5 ml 1-1 at the high and low flow rates, respectively. The relationship between [CO2] and dark respiration was linear. Dark respiration decreased by 20% on average as the [CO2] increased from 0 to the ambient level, and it was 11% higher at the high flow rate than at the low flow rate. These results suggest that wind may act to reduce Pn depression in dense crop canopy by both reducing leaf resistance and atmospheric [CO2] gradient outside the boundary layer.

Acoustic Measurements From an Automotive Centrifugal Compressor With a Switchable Dual-Port Casing Treatment for Extended Operating Range

2016 ◽  
Author(s):  
Rick Dehner ◽  
Ahmet Selamet ◽  
Michael Steiger ◽  
Harold Sun ◽  
Dave Hanna ◽  
...  
Keyword(s):  
Flow Rate ◽  
Broadband Noise ◽  
High Flow ◽  
Low Flow ◽  
Acoustic Measurements ◽  
Suction Surface ◽  
Flow Rates ◽  
Casing Treatment ◽  
Operating Range ◽  
Operating Region

An effective measure to improve the surge margin of a centrifugal compressor, without sacrificing efficiency, is to implement a recirculating casing treatment inside the compressor cover. However, introduction of an additional sound propagation path directly over the rotating impeller blades exposes the inherently unsteady internal flow-field as an added potential noise source, which is of concern for automotive applications. The present study conducts performance and acoustic measurements of a new compressor which was designed to achieve high isentropic efficiency over a wide flow range, featuring an impeller with splitter blades and a vaneless diffuser. A dual-port active casing treatment (ACT) was also incorporated into the compressor cover to independently extend both the low and high flow rate operating regions of the compressor. The slot of the first (surge) port is positioned between the main and splitter blades of the impeller, similar to passive casing treatments that are already widely adopted. This port extends the low-flow boundary of the compressor operating range by reducing flow separation on the suction surface of the main blades near the shroud. The slot of the second (choke) port is located just behind the splitter blades, and it is studied in both the open and closed positions. This second port allows for increased air flow near choke, due to the slot position just downstream of the aerodynamic throat of the compressor. The current ACT design leaves the surge port open at all times, while the choke port is only opened when the compressor operates near choke conditions. In addition to comparing experimental results from this new compressor in both configurations (choke port open and closed), measurements from a comparable (baseline) compressor without splitter blades and a single-port shroud are utilized to assess the acoustics of the new design. Acoustic measurements were completed over the low to mid-speed operating range, which is a region heavily weighted in customer drive cycles for light and medium duty vehicles. The conscientious design of the impeller and surge slot of the new compressor to minimize flow separation on the suction surface of the inducer blades is shown to not only improve efficiency and extend the low-flow operating range, but (with the choke port closed) broadband noise is significantly reduced in the mid to high flow rate operating region. At low flow rates, the new compressor (with the choke port closed) is slightly louder than the baseline compressor at the inlet duct measurement location, but essentially equal to the baseline compressor at the external microphone location near the compressor inlet duct opening. When the choke port of the new compressor is open, broadband noise increases slightly relative to the closed configuration. More importantly, the peak sound pressure level at (main) blade-pass frequency is reduced by opening the choke port, and the operating region of elevated tonal noise shifts from mid to high flow rates.

Secondary Flows in Centrifugal Pump Impellers: PIV Measurements and CFD Computations

2009 ◽  
Author(s):  
R. W. Westra ◽  
L. Broersma ◽  
K. van Andel ◽  
N. P. Kruyt
Keyword(s):  
Reynolds Number ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Stokes Equations ◽  
Suction Side ◽  
Velocity Profiles ◽  
Secondary Flows ◽  
Design Flow ◽  
Low Velocity ◽  
Flow Rates

Two-dimensional Particle Image Velocimetry measurements and three-dimensional Computational Fluid Dynamics (CFD) analyses have been performed of the flow field inside the impeller of a low specific-speed centrifugal pump operating with a vaneless diffuser. Flow rates ranging from 80% to 120% of the design flow rate are considered in detail. It is observed from the velocity measurements that secondary flows occur. These flows result in the formation of regions of low velocity near the intersection of blade suction side and shroud. The extent of this jet-wake structure decreases with increasing flow rate. Velocity profiles have also been computed from Reynolds-averaged Navier-Stokes equations with the Spalart-Allmaras turbulence model, using a commercial CFD-code. For the considered flow rates the qualitative agreement between measured and computed velocity profiles is very good. Overall, the average relative difference between these velocity profiles is around 7%. Additional CFD computations have been performed to assess the influence of Reynolds number and shape of the inlet velocity profile on the computed velocity profiles. It is found that the influence of Reynolds number is mild. The shape of the inlet profile only has a weak effect at the shroud.

scholarly journals Pumping Schedule Optimization in Acid Fracturing Treatment by Unified Fracture Design

2021 ◽  
Author(s):  
Rahman Lotfi ◽  
Mostafa Hosseini* ◽  
Davood Aftabi ◽  
Alireza Baghbanan ◽  
Guanshui Xu
Keyword(s):  
Sensitivity Analysis ◽  
Flow Rate ◽  
High Flow ◽  
High Flow Rate ◽  
Low Flow ◽  
Fluid Viscosity ◽  
Fracture Geometry ◽  
Acid Fracturing ◽  
Closure Stress ◽  
Low Flow Rate

Acid fracturing simulation is used widely to optimize carbonate reservoirs and improve acid fracturing treatment performance. In this study, a method was used to minimize the risk of the acid fracturing treatment. First, optimal fracture geometry parameters with UFD methods are calculated. After that, design components change as long as fracture geometry parameters reach their optimal values. The results showed a high flow rate needed to achieve optimal fracture geometry parameters with increasing acid volume. Sensitivity analysis was performed on controllable and reservoir parameters. It observed that a high flow rate should be applied for a low fluid viscosity to achieve the optimization goals. Straight acid reaches optimal conditions at a high flow rate and low volume. These conditions for retarded acids appear only at a low flow rate and high volume. The study of the acid concentration for gelled acid showed that as it increased, the flow rate and volume increased. Besides, for low permeability formation, a large fracture half-length and small fracture width are desirable. In this case, a higher flow rate will be required. The sensitivity analysis showed that the optimum flow rate and acid volume increase and decrease for the high Young's modulus. The effect of closure stress was also investigated and observed for a sample with high closure stress, low flow rate, and high acid volume are required.

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