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2022 ◽
Vol 12 (1) ◽
Author(s):
Chuntao Jiang ◽
Yongbin Zhang
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AbstractMathematically formulating nanochannel flows is challenging. Here, the values of the characteristic parameters were extracted from molecular dynamics simulation (MDS), and directly input to the closed-form explicit flow factor approach model (FFAM) for nanochannel flows. By this way, the physical nature of the simulated system in FFAM is the same with that in MDS. Two nano slit channel heights respectively with two different liquid-channel wall interactions were addressed. The flow velocity profiles across the channel height respectively calculated from MDS and FFAM were compared. By introducing the equivalent value $${{\Delta_{im} } \mathord{\left/ {\vphantom {{\Delta_{im} } D}} \right. \kern-\nulldelimiterspace} D}$$ Δ im / D , FFAM fairly agrees with MDS for all the cases. The study values FFAM in simulating nanochannel flows.

Author(s):
Chiu-Fan Hsieh ◽
Tehseen Johar ◽
Yi-Hao Lin
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Abstract The geometric design of a gerotor motor has a significant impact on its function, performance, quality, reliability and cost. When designing a gerotor motor all these features must be considered. A gerotor motor can be classified into two types based on the geometric design; gerolor (pin design) and gerotor (nonpin design). In this article geometric parameters of the two design types are discussed briefly and the operation of the gerotor motor is described as well. A numerical analysis is carried out by using computational fluid dynamics (CFD) tool (PumpLinx) to analyze the fluid flow and predict the performance of both types of gerotor designs. Various characteristics of the two designs of the gerotor motor are investigated and compared which include the gerotor design, fluid flow rate, velocity, pressure and output torque. Comparison of the results found out that using pin design gerotor motor, the flow rate, flow velocity, pressure and torque will vary greatly. Nonpin design can significantly reduce variations in all the flow characteristics thereby enhancing the stability and reduction in the leakage risk.

2021 ◽
Author(s):
Jiaze Wang ◽
Lin Li
Keyword(s):

2021 ◽
Author(s):
Juri Romazanov ◽
Andreas Kirschner ◽
Sebastijan Brezinsek ◽
Richard A Pitts ◽
Dmitriy V. Borodin ◽
...
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Abstract The Monte-Carlo code ERO2.0 was used to simulate steady-state erosion and transport of beryllium (Be) in the ITER main chamber. Various plasma scenarios were tested, including a variation of the main species (hydrogen, deuterium, helium), plasma conditions (density, temperature, flow velocity) and magnetic configurations. The study provides valuable predictions for the Be transport to the divertor, where it is expected to be an important contributor to dust formation and fuel retention due to build-up of co-deposited layers. The Be gross and net erosion rates provided by this study can help identifying first wall regions with potentially critical armour lifetime.

2021 ◽
Vol 50 (3) ◽
pp. 66-69
Author(s):
D. A. Niauri ◽
A. F. Harutyunyan
Keyword(s):

The state of regional blood flow in 65 patients before and after endoscopic myomectomy was studied using modem methods such as Doppler examination and color Doppler sonography. It was determined that blood flow velocity indeces obtained during the Doppler examination of myoma vessels and uterine arteries allow to estimate the morphological structure of myomas uninvasively and can be used to define the indications for conservative endoscopic surgical procedures in patients with myoma uteri. Doppler monitoring of regional blood flow during postoperative period makes it possible to evaluate the effectiveness of surgical treatment previously performed.

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Nowadays, synthetic jets have various applications such as cooling enhancement and active flow control. In the present paper, the capability of two turbulence modelling approaches in predicting thermal performance of an impinging synthetic jet is investigated. These two approaches are scale adaptive simulation (SAS) and detached eddy simulation (DES). Comparisons between numerical data and experimental studies reveal that the ability of DES in predicting the asymmetrical trend of heat transfer profiles is better than SAS in almost all the study cases. Although, near the stagnation zone, the performance of SAS is superior. Results show that the effects of parameters such as frequency, cross-flow velocity and suction duty cycle factor are well predicted by both approaches. An increase of cross-flow velocity from 1.81 m/s to 2.26 m/s results in an improvement of [Formula: see text] near the stagnation point by almost 16.3% and 9.2% using DES and SAS, respectively.

2021 ◽
Vol 11 (1) ◽
pp. 204
Author(s):
Srdjan B. Aleksandric ◽
Ana D. Djordjevic-Dikic ◽
Vojislav L. Giga ◽
Ivan A. Soldatovic ◽
...

Background: It has been shown that coronary flow velocity reserve (CFVR) measurement by transthoracic Doppler echocardiography (TTDE) during dobutamine (DOB) provocation provides a more accurate functional evaluation of myocardial bridging (MB) compared to adenosine. However; the cut-off value of CFVR during DOB for identification of MB associated with myocardial ischemia has not been fully clarified. Purpose: This prospective study aimed to determine the cut-off value of TTDE-CFVR during DOB in patients with isolated-MB, as compared with stress-induced wall motion abnormalities (VMA) during exercise stress-echocardiography (SE) as reference. Methods: Eighty-one symptomatic patients (55 males [68%], mean age 56 ± 10 years; range: 27–74 years) with the existence of isolated-MB on the left anterior descending artery (LAD) and systolic MB-compression ≥50% diameter stenosis (DS) were eligible to participate in the study. Each patient underwent treadmill exercise-SE, invasive coronary angiography, and TTDE-CFVR measurements in the distal segment of LAD during DOB infusion (DOB: 10–40 μg/kg/min). Using quantitative coronary angiography, both minimal luminal diameter (MLD) and percent DS at MB-site at end-systole and end-diastole were determined. Results: Stress-induced myocardial ischemia with the occurrence of WMA was found in 23 patients (28%). CFVR during peak DOB was significantly lower in the SE-positive group compared with the SE-negative group (1.94 ± 0.16 vs. 2.78 ± 0.53; p < 0.001). ROC analyses identified the optimal CFVR cut-off value ≤ 2.1 obtained during high-dose dobutamine (>20 µg/kg/min) for the identification of MB associated with stress-induced WMA, with a sensitivity, specificity, positive and negative predictive value of 96%, 95%, 88%, and 98%, respectively (AUC 0.986; 95% CI: 0.967–1.000; p < 0.001). Multivariate logistic regression analysis revealed that MLD and percent DS, both at end-diastole, were the only independent predictors of ischemic CFVR values ≤2.1 (OR: 0.023; 95% CI: 0.001–0.534; p = 0.019; OR: 1.147; 95% CI: 1.042–1.263; p = 0.005; respectively). Conclusions: Noninvasive CFVR during dobutamine provocation appears to be an additional and important noninvasive tool to determine the functional severity of isolated-MB. A transthoracic CFVR cut-off ≤2.1 measured at a high-dobutamine dose may be adequate for detecting myocardial ischemia in patients with isolated-MB.

2021 ◽
Vol 14 (1) ◽
pp. 392
Author(s):
Md. Amir Khan ◽
Nayan Sharma ◽
Jaan Pu ◽
Faisal M. Alfaisal ◽
...
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Researchers have recognized that the successive growth of mid-channel bar deposits can be entertained as the raison d’être for the initiation of the braiding process, which is closely interlinked with the growth, decay, and vertical distribution of fluvial turbulent kinetic energy (TKE). Thus, focused analysis on the underlying mechanics of turbulent flow structures in the proximity of a bar deposit occurring in the middle of the channel can afford crucial scientific clues for insight into the initiating fluvial processes that give rise to braiding. In the study reported herein, a physical model of a mid-channel bar is constructed in an experimental flume to analyze the turbulence parameters in a region close to the bar. Notably, the flow velocity plays an important role in understanding the flow behavior in the scour-hole location in the upstream flow divergence zone as well as near the downstream zone of flow convergence in a mid-channel bar. Therefore, the fluctuating components of turbulent flow velocity are herein discussed and analyzed for the regions located close to the bar. In the present study, the impact of the mid-channel bar, as well as its growth in turbulent flow, on higher-order velocity fluctuation moments are investigated. For near-bed locations, the results show the dominance of ejection events in upstream zones and the dominance of sweep events at locations downstream of the mid-channel bar. In scour-hole sections, the negative value of the stream-wise flux of turbulent kinetic energy and the positive value of the vertical flux of turbulent kinetic energy indicate energy transport in downward and forward directions, respectively. The downward and forward energy transport processes lead to scouring at these locations. The maximum turbulent production rate occurs in the wake region of the bar. The high rate of turbulence production has occurred in that region, which can be ascribed to the process of shedding turbulent vortices. The results show that the impact of the presence of the bar is mainly restricted to the lower layers of flow. The turbulent dissipation rate monotonically decreases with an increase in the vertical distance from the bed. The turbulent production rate first increases and then decreases with successive increases in the vertical distance from the bed. The paper concludes with suggestions for the future potential use of the present research for the practical purpose of examining braid bar occurrences in alluvial rivers to develop an appropriate response through training measures.

2021 ◽
Vol 9 (3) ◽
pp. 114-121
Author(s):
Tamás Tolnai
Keyword(s):

Differences in flow rates of this nature have a significant effect on the unevenness of the moisture content of the dried material, since the material which remains in the drying chamber for an unnecessarily long time is over-dried and the under-drying is a problem for the material remaining in the dryer for too short a time. In this article, I analyzed the effect of increasing particle-wall friction on the unevenness of the particle flow velocity field. The research has shown that dead zones are formed in the vicinity of the rough walls, which reduce the uniformity of the flow. The results show that the tribological properties of the inner wall surfaces of the dryers can have a very significant effect on the efficient operation of the dryers.

Author(s):
Geeta Behera ◽
Gururaj Alur Nagaraj ◽
Suresh Chidambaram Thirunavukarasu ◽
Ramesh Jayaraman ◽
Rajeswari Murugesan ◽
...
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