The Effect of Red Cell Dynamics on Platelet Spatial Distribution in Sudden Expansion

2007 ◽  
Author(s):  
Rui Zhao ◽  
Joie Marhefka ◽  
Marina Kameneva ◽  
James Antaki
Keyword(s):  
Spatial Distribution ◽  
Sudden Expansion ◽  
Red Cell ◽  
Common Complication ◽  
Complex Flow ◽  
Cell Dynamics ◽  
Stagnation Points ◽  
Recirculation Zones

Thrombosis is a common complication associated with blood contacting devices [1]. Platelets often (or preferably) deposit in specific regions which contain complex flow featuring separations, recirculation zones and stagnation points [2, 3].

Characteristics of a Power Station Boiler

1994 ◽  
Vol 208 (2) ◽  
pp. 89-101 ◽  
Author(s):  
T O'Doherty ◽  
D Froud ◽  
C J Bates ◽  
N Syred
Keyword(s):  
Reverse Flow ◽  
Fluid Dynamic ◽  
Two Dimensions ◽  
Secondary Flows ◽  
Three Dimensions ◽  
Complex Flow ◽  
Power Station ◽  
Stagnation Points ◽  
Recirculation Zones ◽  
Power Station Boiler

An experimental investigation of the flow patterns in a model of a power station boiler has been carried out under isothermal conditions, to produce data for computational fluid dynamic code validation. Measurements were made in three dimensions on a single swirl burner in isolation, in two dimensions on a bank of 12 burners in a 4 × 3 grid and in the model boiler with this bank installed. The single burner exhibited a central reverse flow zone with high levels of turbulence at its boundaries. The general flow pattern found in the single burner was greatly distorted when interaction with surrounding burners in the bank occurred. Several unexpected secondary flows occurred. The model boiler displayed a complex flow arrangement with recirculation zones and two stagnation points.

Roxadustat Improves Erythropoietin Antibody-Mediated Pure Red Cell Aplasia in a Patient with Hemodialysis

2021 ◽  
pp. 1-4
Author(s):  
Sijia Li ◽  
Xueqin Chen ◽  
Penghua Hu ◽  
Suijing Wu ◽  
Jianchao Ma ◽  
...  
Keyword(s):  
Chronic Kidney Disease ◽  
Kidney Disease ◽  
Immunosuppressive Therapy ◽  
Recombinant Human Erythropoietin ◽  
Pure Red Cell Aplasia ◽  
Red Cell ◽  
Common Complication ◽  
Normal Range ◽  
Red Cell Aplasia ◽  
Human Erythropoietin

Anemia is a common complication of chronic kidney disease (CKD). Recombinant human erythropoietin (rHu-EPO) is used extensively in patients with CKD. However, anti-erythropoietin (anti-EPO) antibody has been reported during rHu-EPO treatment, which causes pure red cell aplasia (PRCA). We presented a case of 75-year-old man, who underwent hemodialysis for 2 years. He developed PRCA during rHu-EPO treatment. The rHu-EPO was immediately discontinued, and the patient was given roxadustat treatment. After 6 months of roxadustat treatment, the anti-EPO antibody was disappeared, and hemoglobin recovered normal range. The results suggest that roxadustat can be used to treat patients with anti-EPO antibody-mediated PRCA without immunosuppressive therapy.

The Modeling and Analysis of a Package-Scale Circulating Fluidized Combustor

2001 ◽  
Author(s):  
Matthew J. Kremer ◽  
Savas Yavuzkurt
Keyword(s):  
Fluidized Bed ◽  
Circulating Fluidized Bed ◽  
Gas Temperature ◽  
Complex Flow ◽  
Modeling And Analysis ◽  
Commercial Code ◽  
Carbon Burnout ◽  
Recirculation Zones ◽  
Primary Velocity ◽  
Bubbling Beds

The preliminary analysis of a package-scale circulating fluidized bed (CFB) combustor through modeling and experimentation was performed to help determine particle trajectories and carbon burnout efficiency. The CFB consisted of a primary fast fluidizing bed and two bubbling beds. The fluidized bed models found in literature and a freeboard model utilizing a commercial code, FLUENT, were used in simulations. Primary gas velocity of the fast fluidizing bed was varied between 4.9 and 12.2 m/s and gas temperatures were varied between 800 and 1200 K. For comparison with computations of hydrodynamics, a scaled down version of the combustor was run using granulated plastic particles at 300 K. The results of computations showed that the freeboard has a very complex flow with many recirculation zones that usually become larger and move away from the walls with increasing primary velocity. There was less particle movement in the experiments than in the simulations due to the differences in particle diameters, the type of particles, the gas temperature, and the scaling geometry.

Experimental Flow Studies in Exact-Replica Phantoms of Atherosclerotic Carotid Bifurcations Under Steady Input Conditions

2003 ◽  
Vol 125 (1) ◽  
pp. 38-48 ◽  
Author(s):  
J. Bale-Glickman ◽  
K. Selby ◽  
D. Saloner ◽  
O¨. Savas¸
Keyword(s):  
Three Dimensional ◽  
Carotid Bifurcation ◽  
Reynolds Numbers ◽  
Flow Fields ◽  
Shear Stresses ◽  
Treatment Technique ◽  
Input Flow ◽  
Stagnation Points ◽  
Topological Features ◽  
Recirculation Zones

Extensive flow studies are conducted in two carotid bifurcation flow phantoms. These phantoms exactly replicate the lumen of the plaque excised intact from two patients with severe carotid atherosclerosis. The input flow into the phantom’s common carotid artery is steady. Novel scanning techniques for flow visualization and particle image velocimetry are used. In addition, a novel boundary treatment technique is employed in velocimetry to extract first order accurate velocity gradients at walls. The data show that the flow fields are highly three-dimensional. Numerous separation and recirculation zones dominate the flow domain, except at the lowest Reynolds numbers. The separation regions are often so severe that highly directed internal jets form. At high Reynolds numbers, the flows become unsteady and chaotic, even though the input flow is steady. Flow fields have large regions of energetic flow and almost stagnant recirculation zones. These recirculation zones range in size from the full size of the arteries to zones within crevasses smaller than 1 mm. Velocity field and streamline patterns conform well to the lumen geometry. The streamlines are highly tortuous. Stagnation points correlate well with the topological features of the stenosis. Vorticity maps confirm the highly complex and three dimensional nature of the flow. Wall shear stresses at the stenoses are estimated to be on the order of 10 Pa. These studies conclusively show that the nature of the flow in the diseased bifurcation is primarily dictated by the lumen geometry.

Physiological Flow Studies in Exact-Replica Atherosclerotic Carotid Bifurcations

2003 ◽  
Author(s):  
J. Bale-Glickman ◽  
K. Selby ◽  
D. Saloner ◽  
O¨. Savas¸
Keyword(s):  
Chaotic Behavior ◽  
Three Dimensional ◽  
Carotid Bifurcation ◽  
Flow Patterns ◽  
Shear Stresses ◽  
Multiple Sources ◽  
Complex Flow ◽  
Physiological Flow ◽  
Image Velocimetry ◽  
Recirculation Zones

Some results from a series of physiological flow experiments in a model of an atherosclerotic carotid bifurcation are presented. The flow model exactly replicates the lumen of the plaque excised intact from a patient with severe carotid atherosclerosis. Flow visualization (FV) and particle image velocimetry (PIV) are employed as the tools for this study. The complex internal geometry of the diseased artery combined with the pulsatile input flows gives rise to complex flow patterns. The flow fields are highly three-dimensional and chaotic with details varying from cycle to cycle. These flow patterns also include internal jets, three-dimensional shear layers, numerous separation/recirculation zones and stagnation lines. The vorticity and streamline maps confirm this complex and three-dimensional nature of the flow. Planar streamline maps show the three-dimensional flow by the multiple sources/sinks throughout the model. Wall shear stresses (WSS) are estimated to range form about −7 Pa to 34 Pa at the stenotic neck over time with the peak at peak systolic. These WSS also exhibit chaotic behavior during pulsatile flow cycles.

Diffuser Influence on the Mixing of Coaxial Swirling Jets

2014 ◽  
Author(s):  
Teresa Parra-Santos ◽  
Ruben Perez-Dominguez ◽  
Gonzalo Lorenzo Esteban ◽  
Robert Z. Szasz ◽  
Artur N. Gutkowski ◽  
...  
Keyword(s):  
Mechanical Energy ◽  
Flow Characteristics ◽  
Area Ratio ◽  
Sudden Expansion ◽  
Swirl Number ◽  
Swirling Jets ◽  
Annular Jet ◽  
Turbulence Regime ◽  
Recirculation Zones ◽  
Minimum Residence Time

Numerical results depicting the effects of diffusers on confined isothermal high-swirl jets are presented. The aim is analyze the mixing between a non-swirling inner jet (natural gas) and a swirling annular jet (primary air). This simple setup is widely used in burners to promote stabilized flames of lean mixtures. Flow patterns for sudden-expansion and diffusers are contrasted for swirl number of 1 and expansion area ratio of 4 in a transitional turbulence regime. Diffusers have important influence on size and location of recirculation zones. Hence knowledge of flow characteristics is a prerequisite in the design process. The criteria to establish the optimum diffuser would be better mixing as well as minimum residence time in the recirculation zones to prevent the formation of NOx in the future burner. The dissipated mechanical energy is not important in burner applications.

Red Cell Motion and Deformation in the Microcirculation

1978 ◽  
Vol 100 (3) ◽  
pp. 139-148 ◽  
Author(s):  
S. P. Sutera
Keyword(s):  
Large Scale ◽  
Plug Flow ◽  
Red Cells ◽  
Internal Diameter ◽  
Red Cell ◽  
Cell Dynamics ◽  
Small Vessels ◽  
Dimensionless Correlations ◽  
Cell Motion ◽  
The Relationship

The human microcirculation is taken to include all vessels with internal diameter less than 500 μm. In these small vessels the heterogeneous nature of the blood suspension becomes apparent in the external characteristics of the flow, which signifies that a continuum model of blood flow in this regime is inadequate. The motion and deformation of red cells in the capillaries is discussed in detail with emphasis on the relationship between red cell dynamics and apparent viscosity. Large scale hydraulic models of red cell motion in capillaries have yielded dimensionless correlations applicable to the microscopic prototypes. In the larger vessels the distribution of red cells across the vessel lumen is generally nonuniform and axial velocity profiles reveal the occurrence of partial plug flow. Red cells traveling near the vessel wall where the shear rate is highest may exhibit a transition to liquid droplike behavior.

LES of Hydrogen Enriched Methane/Air Combustion in the SGT-800 Burner at Real Engine Conditions

2018 ◽  
Author(s):  
Daniel Moëll ◽  
Daniel Lörstad ◽  
Xue-Song Bai
Keyword(s):  
High Pressure ◽  
Mixture Fraction ◽  
Flame Structure ◽  
Flame Temperature ◽  
Flow Simulation ◽  
Sudden Expansion ◽  
Inlet Temperature ◽  
Complex Flow ◽  
Control Variables ◽  
Hydrogen Enrichment

DLE (Dry Low Emission) techniques are widely used today to reduce the harmful NOx emissions associated with high combustion temperatures. In many DLE systems the fuel and air are pre-mixed which effectively keep the flame temperature as low as possible, ideally equal to the turbine inlet temperature. By using pre-mixing stability issues such as flash back and combustion driven dynamics may occur. Operating the engine with hydrogen diluted natural gas will decrease the flash back limits of the system due to the high diffusivity and highly reactive nature of hydrogen. In this study the stability effects of hydrogen diluted into methane in the Siemens SGT-800 combustor is studied. The SGT-800 combustor is an annular combustor where the flame is stabilized using a swirl burner combined with a sudden expansion combustor. The expansion gives rise to a vortex break down where the flame stabilizes in the local low speed zones. Here a single burner sector is studied using the flow solver Siemens PLM software STAR-CCM+. The turbulence is simulated through the use of LES (Large Eddy Simulation) where the largest energy carrying flow scales are resolved and only the smaller scales are modelled. The chemistry is coupled to the turbulent flow simulation by the use of FGM (Flamelet Generated Manifolds) which are integrated using presumed probability density functions. The FGM approach assumes that the local flame structure is laminar and that all species across a flame can be related to a set of control variables. The control variables in this case are the heat loss, the mixture fraction and its variance and a reaction progress variable. In this paper two effects are studied, first the transition from an atmospheric flame to a pressurized flame and second the effect of hydrogen enrichment. The flame shape and position are mainly affected by the transition from atmospheric to high pressure, where the power density increases by almost a factor of 20. The flame is moving further upstream closer to the burner in all pressurized cases. The hydrogen enrichment plays a strong role in how the combustion driven dynamics is coupling with the acoustics of the rig. The high pressure pure methane case show a strong pressure peak whereas the hydrogen enriched case dampens that peak and distributes the energy to other frequencies. This work shows that high fidelity CFD is capable of capturing complex flow and flame interactions such as thermoacoustic instabilities in industrial scale systems.

scholarly journals Flow Field and Performance Characteristics of Combustor Diffusers: A Basic Study

1994 ◽  
Author(s):  
R. Hestermann ◽  
S. Kim ◽  
A. Ben Khaled ◽  
S. Wittig
Keyword(s):  
Flow Field ◽  
Performance Characteristics ◽  
Sudden Expansion ◽  
Opening Angle ◽  
Complex Flow ◽  
Basic Study ◽  
Flame Tube ◽  
Ink Jet ◽  
Large Opening ◽  
And Performance

Results of a detailed study concerning the influence of geometrical as well as of fluid mechanic parameters on the performance of a plane model combustor diffuser in cold flow are presented. For a qualitative insight into the complex flow field inside the pre-diffuser, the sudden expansion region and into the flow field around the flame tube dome, results of a flow visualization study with the hydrogen bubble method as well as with the ink jet method are presented for different opening angles of the pre-diffuser and for different flame tube distances. Also, quantitative data from detailed measurements with LDV and conventional pressure probes in a geometrically similar air driven setup are presented. These data clearly demonstrate the effect of boundary layer thickness as well as the influence of different turbulence levels at the entry of the pre-diffuser on the performance characteristics of combustor diffusers. The possibility of getting an unseparated flow field inside the pre-diffuser even at large opening angles by appropriately matching the diffuser’s opening angle and the flame tube distance is demonstrated. Also, for flows with an increased turbulence level at the entrance — all other conditions held constant — an increased opening angle can be realised without experiencing flow separation. The comparison of the experimental data with predictions utilizing a finite-volume-code based on a body-fitted coordinate system for diffusers with an included total opening angle less than 18° demonstrates the capability of describing the flow field in combustor diffusers with reasonable accuracy.

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