scholarly journals R13 moment equations applied to supersonic flow with solid wall interaction

2019 ◽  
Author(s):  
Maksim Timokhin ◽  
Henning Struchtrup ◽  
Alexey Kokhanchik ◽  
Yevgeniy Bondar
Keyword(s):  
Supersonic Flow ◽  
Solid Wall ◽  
Moment Equations ◽  
Wall Interaction

Application of a High-Order Macroscopic Approach to Force-Driven Poiseuille Flow in the Slip and Transition Regimes

2008 ◽  
Author(s):  
Simon Mizzi ◽  
Xiao-Jun Gu ◽  
David R. Emerson ◽  
Robert W. Barber ◽  
Jason M. Reese
Keyword(s):  
Boundary Conditions ◽  
Poiseuille Flow ◽  
Solid Wall ◽  
Moment Equation ◽  
Moment Equations ◽  
Molecular Collision ◽  
Macroscopic Models ◽  
Gaseous Flows ◽  
Wall Interaction ◽  
The Moment

In this paper various extended macroscopic models are described and applied to force-driven Poiseuille flow. In particular, details are given for the regularized Grad 13- and 20-moment equations. Extended macroscopic models have, until recently, been limited by the uncertainity surrounding the prescription of boundary conditions on solid-walls. The gas-solid wall interaction plays an important role in describing the dynamics of confined gaseous flows. This problem is tackled in the context of the moment equations whereby the simplified Maxwell microscopic formalism is used to derive boundary conditions for a given moment equation set. The proposed governing equations and boundary conditions are applied to force-driven Poiseuille flow where anomalous thermal behavior is observed as the Knudsen number increases. Results are compared to DSMC data and it is established that the proposed extended macroscopic models can capture this non-intuitive behavior. However, the models show some quantitative disparity in representing this behavior. It is proposed that this is addressed by development of a consistent theory of molecular collision geometries in the extended hydro-dynamic model or by the utilization of more extended moment sets.

scholarly journals Forward Flux Sampling of Polymer Desorption Paths from a Solid Surface into Dilute Solution

Polymers ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2275
Author(s):  
Kyle J. Huston ◽  
Christina E. Rice ◽  
Ronald G. Larson
Keyword(s):  
Interaction Energy ◽  
Solid Wall ◽  
Scaling Law ◽  
Rare Event ◽  
Degree Of Polymerization ◽  
Radius Of Gyration ◽  
Exponential Dependence ◽  
Excluded Volume Effects ◽  
Desorption Time ◽  
Wall Interaction

We compute desorption rates for isolated polymers adsorbed to a solid wall with a rare event sampling technique called multilevel splitting, also known as forward flux sampling. We interpret computed rates with theories based on the conjecture that the product tdesDRg2 of the desorption time tdes and diffusivity D divided by squared radius of gyration Rg scales with exp(h/Rg) where h is the equilibrium ratio of adsorbed surface concentration of polymer Γ to bulk concentration of polymer c. As the polymer–wall interaction energy is increased, the slope of lntdesDRg2 vs. NVMFkBT nearly approaches unity, as expected for strongly-adsorbing chains, where N is the degree of polymerization and VMF is the height-averaged monomer–wall interaction energy for a strongly adsorbed chain. However, we also find that this scaling law is only accurate when adsorption strength per monomer exceeds a threshold value on the order of 0.3–0.5 kBT for a freely jointed chain without or with excluded volume effects. Below the critical value, we observe that tdesDRg2 becomes nearly constant with N, so that tdes∝Nα, with α≈2. This suggests a crossover from “strong” detachment-controlled to a “weak” diffusion-controlled desorption rate as VMF/kBT drops below some threshold. These results may partially explain experimental data, that in some cases show “strong” exponential dependence of desorption time on chain length, while in others a “weak” power-law dependence is found. However, in the “strong” adsorption case, our results suggest much longer desorption times than those measured, while the reverse is true in the weak adsorption limit. We discuss possible reasons for these discrepancies.

scholarly journals Computational Study of Gas-Solid Flow in a Horizontal Stepped Pipeline

2019 ◽  
Vol 2019 ◽  
pp. 1-15
Author(s):  
Zhengquan Li ◽  
Kaiwei Chu ◽  
Renhu Pan ◽  
Aibing Yu ◽  
Jiaqi Yang
Keyword(s):  
Pressure Drop ◽  
Pipe Wall ◽  
Computational Study ◽  
Solid Wall ◽  
Fluid Model ◽  
Gas Velocity ◽  
Interaction Forces ◽  
Solid Flow ◽  
Two Fluid Model ◽  
Wall Interaction

In this paper, the mechanism governing the particle-fluid flow characters in the stepped pipeline is studied by the combined discrete element method (DEM) and computational fluid dynamics (CFD) model (CFD-DEM) and the two fluid model (TFM). The mechanisms governing the gas-solid flow in the horizontal stepped pipeline are investigated in terms of solid and gas velocity distributions, pressure drop, process performance, the gas-solid interaction forces, solid-solid interaction forces, and the solid-wall interaction forces. The two models successfully capture the key flow features in the stepped pipeline, such as the decrease of gas velocity, solid velocity, and pressure drop, during and after the passage of gas-solid flow through the stepped section. What is more important, the reason of the appearance of large size solid dune and pressure surge phenomena suffered in the stepped pipeline is investigated macroscopically and microscopically. The section in which the blockage problem most likely occurs in the stepped pipeline is confirmed. The pipe wall wearing problem, which is one of the most common and critical problems in pneumatic conveying system, is analysed and investigated in terms of interaction forces. It is shown that the most serious pipe wall wearing problem happened in the section which is just behind the stepped part.

Evidence for an Increased Generation of Prostacyclin in the Microvasculature and an Impairment of the Platelet α-Granule Release in Chronic Renal Failure

1988 ◽  
Vol 60 (02) ◽  
pp. 205-208 ◽  
Author(s):  
Paul A Kyrle ◽  
Felix Stockenhuber ◽  
Brigitte Brenner ◽  
Heinz Gössinger ◽  
Christian Korninger ◽  
...  
Keyword(s):  
Renal Failure ◽  
Chronic Renal Failure ◽  
Blood Clotting ◽  
Normal Subjects ◽  
Chronic Uraemia ◽  
Wall Interaction ◽  
End Stage ◽  
Granule Release

SummaryThe formation of prostacyclin (PGI2) and thromboxane A2 and the release of beta-thromboglobulin (beta-TG) at the site of platelet-vessel wall interaction, i.e. in blood emerging from a standardized injury of the micro vasculature made to determine bleeding time, was studied in patients with end-stage chronic renal failure undergoing regular haemodialysis and in normal subjects. In the uraemic patients, levels of 6-keto-prostaglandin F1α (6-keto-PGF1α) were 1.3-fold to 6.3-fold higher than the corresponding values in the control subjects indicating an increased PGI2 formation in chronic uraemia. Formation of thromboxane B2 (TxB2) at the site of plug formation in vivo and during whole blood clotting in vitro was similar in the uraemic subjects and in the normals excluding a major defect in platelet prostaglandin metabolism in chronic renal failure. Significantly smaller amounts of beta-TG were found in blood obtained from the site of vascular injury as well as after in vitro blood clotting in patients with chronic renal failure indicating an impairment of the a-granule release in chronic uraemia. We therefore conclude that the haemorrhagic diathesis commonly seen in patients with chronic renal failure is - at least partially - due to an acquired defect of the platelet a-granule release and an increased generation of PGI2 in the micro vasculature.

Further Evidence that Glycoprotein IIb-IIIa Mediates Platelet Spreading on Subendothelium

1991 ◽  
Vol 65 (02) ◽  
pp. 202-205 ◽  
Author(s):  
Harvey J Weiss ◽  
Vincet T Turitto ◽  
Hans R Baumgartner
Keyword(s):  
Platelet Adhesion ◽  
Surface Coverage ◽  
Rabbit Aorta ◽  
Conclusive Evidence ◽  
Initial Contact ◽  
Single Exposure ◽  
Vessel Segment ◽  
Multiple Exposures ◽  
Wall Interaction ◽  
Platelet Spreading

SummaryIn order to explore further the mechanism by which glycoprotein GPIIb-IIIa promotes platelet vessel wall interaction, platelet adhesion to subendothelium was studied in an annular chamber in which subendothelium from rabbit aorta was exposed at a shear rate of 2,600 s−1 to blood from patients with thrombasthenia. Perfusions were conducted for each of 5 exposure times (1 ,2,3, 5 and 10 min), and the percent surface coverage of the vessel segment with platelets in the contact (C) and spread (S) stage was determined. Increased values of platelet contact (C) were obtained in thrombasthenia at all exposure times; this finding is consistent with a defect in platelet spreadirg, based on a previously described kinetic model of platelet attachment to subendothelium. According to this model of attachment, increased values of platelet contact (C) at a single exposure time may be indicative of either a defect in spreading (S) or initial contact (C), but multiple exposures will result in increased contact only for defects which are related to defectiye platelet spreading (s).The results obtained over a broad range of exposure times provide more conclusive evidence that GPIIb-IIIa mediates platelet spreading than those previously obtained at single exposure times.

Thrombin Inhibition and Thrombin Generation by Cultured Aortic Endothelial and Smooth Muscle Cells from Minipig

1982 ◽  
Vol 48 (01) ◽  
pp. 101-103 ◽  
Author(s):  
B Kirchhof ◽  
J Grünwald
Keyword(s):  
Endothelial Cells ◽  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Vessel Wall ◽  
Thrombin Generation ◽  
Muscle Cells ◽  
Thrombin Inhibition ◽  
Generating Capacity ◽  
Wall Interaction ◽  
Cells Cultured

SummaryEndothelial and smooth muscle cells cultured from minipig aorta were examined for their inhibitory activity on thrombin and for their thrombin generating capacity.Endothelial cells showed both a thrombin inhibition and an activation of prothrombin in the presence of Ca++, which was enhanced in the presence of phospholipids. Smooth muscle cells showed an activation of prothrombin but at a lower rate. Both coagulation and amidolytic micro-assays were suitable for studying the thrombin-vessel wall interaction.

Sign in / Sign up

Export Citation Format

Share Document