scholarly journals Research on Performance of H2Rich Blowout Limit in Bluff-Body Burner

2012 ◽  
Vol 2012 ◽  
pp. 1-28
Author(s):  
Hongtao Zheng ◽  
Yajun Li ◽  
Lin Cai
Keyword(s):  
Flow Velocity ◽  
Bluff Body ◽  
Negative Temperature ◽  
Main Stream ◽  
Blockage Ratio ◽  
Complete Extinction ◽  
Parabolic Function ◽  
Critical Ignition ◽  
Pdf Model ◽  
The Relationship

In order to investigate H2rich blowout limit at different blockage ratios and flow velocities, a CFD software FLUENT was used to simulate H2burning flow field in bluff-body burner, and the software CHEMKIN was adopted to analyze the sensitivity of each elementary reaction. Composition Probability Density Function (C-PDF) model was adopted to simulate H2combustion field in turbulence flame. The numerical results show that reactions R2 and R9 possess the largest positive and negative temperature sensitivity. Temperature has a very important influence on these two reactions. When equivalence ratio is 1, the mixture is most ignitable, and the critical ignition temperature is 1550 K. There should be an optimal blockage ratio which can stabilize the flame best. When the blockage ratio remains unchanged, the relationship between H2RBL and flow velocity is a logarithmic function. When the flow velocity remains unchanged, the relationship between H2RBL and blockage ratio is a parabolic function. A complete extinction requires three phases: the temperature sudden decline in the main stream, the energy dissipation from the recirculation zone to the main stream, and the complete extinction of the flame.

The relationship between an aortic isthmus blood flow velocity index and the postnatal neurodevelopmental status of fetuses with placental circulatory insufficiency

2005 ◽  
Vol 192 (2) ◽  
pp. 497-503 ◽  
Author(s):  
Jean-Claude Fouron ◽  
Julie Gosselin ◽  
Marie-Josée Raboisson ◽  
Julie Lamoureux ◽  
Claudine-Amiel Tison ◽  
...  
Keyword(s):  
Blood Flow ◽  
Flow Velocity ◽  
Blood Flow Velocity ◽  
Aortic Isthmus ◽  
Circulatory Insufficiency ◽  
The Relationship

scholarly journals Left atrial appendage orifice area and morphology is closely associated with flow velocity in patients with nonvalvular atrial fibrillation

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Lei Chen ◽  
Changjiang Xu ◽  
Wensu Chen ◽  
Chaoqun Zhang
Keyword(s):  
Atrial Fibrillation ◽  
Flow Velocity ◽  
Left Atrial ◽  
Left Atrial Appendage ◽  
Linear Regression Analysis ◽  
Left Ventricular ◽  
Atrial Appendage ◽  
Mechanical Function ◽  
Orifice Area ◽  
The Relationship

Abstract Background Thromboembolic events are the most serious complication of atrial fibrillation (AF), and the left atrial appendage (LAA) is the most important site of thrombosis in patients with AF. During the period of COVID-19, a non-invasive left atrial appendage detection method is particularly important in order to reduce the exposure of the virus. This study used CT three-dimensional reconstruction methods to explore the relationship between LAA morphology, LAA orifice area and its mechanical function in patients with non-valvular atrial fibrillation (NVAF). Methods A total of 81 consecutive patients with NVAF (36 cases of paroxysmal atrial fibrillation and 45 cases of persistent atrial fibrillation) who were planned to undergo catheter radiofrequency ablation were enrolled. All patients were examined by transthoracic echocardiography (TTE), TEE, and computed tomography angiography (CTA) before surgery. The LAA orifice area was obtained according to the images of CTA. According to the left atrial appendage morphology, it was divided into chicken wing type and non-chicken wing type. At the same time, TEE was performed to determine left atrial appendage flow velocity (LAAFV), and the relationship between the left atrial appendage orifice area and LAAFV was analyzed. Results The LAAFV in Non-chicken wing group was lower than that in Chicken wing group (36.2 ± 15.0 cm/s vs. 49.1 ± 22.0 cm/s, p-value < 0.05). In the subgroup analysis, the LAAFV in Non-chicken wing group was lower than that in Chicken wing group in the paroxysmal AF (44.0 ± 14.3 cm/s vs. 60.2 ± 22.8 cm/s, p-value < 0.05). In the persistent AF, similar results were observed (29.7 ± 12.4 cm/s vs. 40.8 ± 17.7 cm/s, p-value < 0.05). The LAAFV in persistent AF group was lower than that in paroxysmal AF group (34.6 ± 15.8 cm/s vs. 49.9 ± 20.0 cm/s, p-value < 0.001). The LAAFV was negatively correlated with left atrial dimension (R = − 0.451, p-value < 0.001), LAA orifice area (R= − 0.438, p-value < 0.001) and left ventricular mass index (LVMI) (R= − 0.624, p-value < 0.001), while it was positively correlated with LVEF (R = 0.271, p-value = 0.014). Multiple linear regression analysis showed that LAA morphology (β = − 0.335, p-value < 0.001), LAA orifice area (β = −  0.185, p-value = 0.033), AF type (β = − 0.167, p-value = 0.043) and LVMI (β = − 0.465, p-value < 0.001) were independent factors of LAAFV. Conclusions The LAA orifice area is closely related to the mechanical function of the LAA in patients with NVAF. The larger LAA orifice area and LVMI, Non-chicken wing LAA and persistent AF are independent predictors of decreased mechanical function of LAA, and these parameters might be helpful for better management of LA thrombosis.

scholarly journals Crown structure of Picea omorika trees in the plantation

2012 ◽  
Vol 64 (2) ◽  
pp. 605-611 ◽  
Author(s):  
M. Krstic ◽  
N. Stavretovic ◽  
V. Isajev ◽  
I. Bjelanovic
Keyword(s):  
Tree Height ◽  
Tree Crown ◽  
Crown Length ◽  
Crown Structure ◽  
Parabolic Function ◽  
Picea Omorika ◽  
Serbian Spruce ◽  
The Relationship ◽  
Total Tree ◽  
Stand Conditions

The study was carried out in Serbian spruce (Picea omorika Panc/Purkyn?) plantations in the western Serbia. The paper presents results of the analysis of crown development. The following elements were analyzed: total tree height, height of the crown base, absolute and relative crown length, maximal crown diameter, coefficient of crown spreading and degree of crown girth. We discuss approaches to the modeling of tree crown growth and development, growing under favorable environmental and stand conditions, without anomalies in development. In order to establish the relationship between analyzed factors, regression analyses were applied. Data fitting was by the analytic method, by the implementation of Prodan?s functions of growth, linear and parabolic function. Received models can be used for the simulation of various growth and developing processes in forest.

Research on Traffic Flow Velocity Characteristic at Temporary Reversible Lane

2014 ◽  
Vol 505-506 ◽  
pp. 1189-1193
Author(s):  
Yi Cao ◽  
Zhong Yi Zuo ◽  
Hui Zhi Xu
Keyword(s):  
Flow Velocity ◽  
Traffic Flow ◽  
Existing Problems ◽  
Before And After ◽  
Relationship Model ◽  
Velocity Characteristic ◽  
Utilization Ratio ◽  
The Individual ◽  
Lane Utilization ◽  
The Relationship

In order to analyze the existing problems of temporary reversible lane, traffic flow velocity characteristic at the period of direction changing was analyzed. Taking Huangpu road as the investigation object, the traffic flow velocity parameters before and after direction changing were investigated respectively. By the method of mathematical statistics, the individual vehicles velocities and the traffic flow velocity before and after direction changing were compared and analyzed. Using the method of regression analysis, the relationship model between velocity and density of reversible lane was constructed. This paper also discussed the problems of this kind of lane. The research showed that, in terms of traffic flow operation velocity of temporary reversible lane, there is obvious and regular difference between before and after direction changing. There is a certain relationship between the velocity and density. The problem of lower lane utilization ratio of temporary reversible lane usually exists.

scholarly journals Dimensionless Assessment Method of Landslide Dam Formation Caused by Tributary Debris Flow Events

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Kun-Ting Chen ◽  
Xiao-Qing Chen ◽  
Gui-Sheng Hu ◽  
Yu-Shu Kuo ◽  
Yan-Rong Huang ◽  
...  
Keyword(s):  
Debris Flow ◽  
Water Depth ◽  
Debris Flows ◽  
Landslide Dam ◽  
Assessment Method ◽  
Main Stream ◽  
Deposition Thickness ◽  
The Relationship ◽  
Prepared Response

In this study, we develop a dimensionless assessment method to evaluate landslide dam formation by considering the relationship between the run-out distance of a tributary debris flow and the width of the main stream, deposition thickness of the tributary debris flow, and the water depth of the main stream. Based on the theory of debris flow run-out distance and fan formation, landslide dam formation may result from a tributary debris flow as a result of two concurrent formation processes: (1) the run-out distance of the tributary debris flow must be greater than the width of the main stream, and (2) the minimum deposition thickness of the tributary debris flow must be higher than the in situ water depth of the main stream. At the confluence, one of four types of depositional scenarios may result: (1) the tributary debris flow enters into the main stream and forms a landslide dam; (2) the tributary debris flow enters into the main stream but overflow occurs, thus preventing complete blockage of the main stream; (3) the tributary debris flow enters into the main stream, does not reach the far bank, and sediment remains partially above the water elevation of the main stream; or (4) the tributary debris flow enters into the main stream, does not reach the far bank, and sediment is fully submerged in the main stream. This method was applied to the analysis of 11 tributary debris flow events during Typhoon Morakot, and the results indicate that the dimensionless assessment method can be used to estimate potential areas of landslide dam formation caused by tributary debris flows. Based on this method, government authorities can determine potential areas of landslide dam formation caused by debris flows and mitigate possible disasters accordingly through a properly prepared response plan, especially for early identification.

The effect of the blockage ratio on the blow-off limit of a hydrogen/air flame in a planar micro-combustor with a bluff body

2013 ◽  
Vol 38 (26) ◽  
pp. 11438-11445 ◽  
Author(s):  
Aiwu Fan ◽  
Jianlong Wan ◽  
Yi Liu ◽  
Boming Pi ◽  
Hong Yao ◽  
...  
Keyword(s):  
Bluff Body ◽  
Blockage Ratio ◽  
Micro Combustor

Flow Characteristics of a Bluff Body Cut From a Circular Cylinder

1997 ◽  
Vol 119 (2) ◽  
pp. 453-454 ◽  
Author(s):  
S. Aiba ◽  
H. Watanabe
Keyword(s):  
Circular Cylinder ◽  
Drag Coefficient ◽  
Flow Velocity ◽  
Bluff Body ◽  
Pressure Coefficient ◽  
Angular Position ◽  
Flow Characteristics ◽  
Uniform Flow ◽  
Base Pressure ◽  
Singular Flow

This is a report on an investigation of the flow characteristics of a bluff body cut from a circular cylinder. The volume removed from the cylinder is equal to d/2(1 − cos θs), where d and θs are the diameter and the angular position (in the case of a circular cylinder, θs, = 0 deg), respectively. θs, ranged from 0 deg to 72.5 deg and Re (based on d and the upstream uniform flow velocity U∞) from 2.0 × 104 to 3.5 × 104. It is found that a singular flow around the cylinder occurs at around θs = 53 deg when Re > 2.5 × 104, and the base pressure coefficient (−Cpb,) and the drag coefficient CD take small values compared with those for otherθs.

Analyzing the relationship between institutional framework and financial inclusion in rural Uganda

2018 ◽  
Vol 13 (4) ◽  
pp. 606-630 ◽  
Author(s):  
George Okello Candiya Bongomin ◽  
John C. Munene ◽  
Joseph Mpeera Ntayi ◽  
Charles Akol Malinga
Keyword(s):  
Social Network ◽  
Direct Effect ◽  
Critical Role ◽  
Financial Inclusion ◽  
Mediating Effect ◽  
Institutional Framework ◽  
Main Stream ◽  
Cross Sectional ◽  
Content Type ◽  
The Relationship

Purpose The purpose of this paper is to report the findings on the mediating effect of social network in the relationship between institutional framework and financial inclusion in rural Uganda. Design/methodology/approach The study employs a cross-sectional research design to collect data used to test for mediation under this study. Structural equation model (SEM) through use of bootstrap in the Analysis of Moment Structures (AMOS) was adopted to establish the existence and type of mediation by social network in the relationship between institutional framework and financial inclusion. Findings Social network had a partial mediating effect in the relationship between institutional framework and financial inclusion. In addition, institutional framework through its regulative, normative and cultural-cognitive pillars also exhibited a significant direct effect on financial inclusion. Besides, social network had a positive and significant effect on financial inclusion. This suggest that there exist both a direct effect of institutional framework on financial inclusion and an indirect effect of institutional framework through social network on financial inclusion. Research limitations/implications While the sample for this study was big enough, it limited itself to only poor households in rural Uganda. Besides, the current study adopted cross-sectional design, thus, leaving out longitudinal design to investigate the characteristics in the sample over time. Practical implications The study makes significant empirical contribution and implications to financial inclusion policy makers on evidence of the critical role played by social network in indirectly enhancing the relationship between institutional framework and financial inclusion of the poor who are vulnerable to exclusion by main stream financial services’ providers. Originality/value The study recommends that social network, which acts as a conduit through which useful information flow and can be shared, plays a critical role in mediating the relationship between institutional framework and financial inclusion in rural Uganda. Therefore, the study contributes to existing body of literature by highlighting the mediating influence of social network in the relationship between institutional framework and financial inclusion, especially in rural Uganda.

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