contraction angle
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Machines ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 60
Author(s):  
Lihuan Chen ◽  
Muzheng Cheng ◽  
Yi Cai ◽  
Liwen Guo ◽  
Dianrong Gao

The technology of increasing coal seam permeability by high-pressure water jet has significant advantages in preventing and controlling gas disasters in low-permeability coal seam. The structural parameters of a nozzle are the key to its jet performance. The majority of the current studies take strike velocity as the evaluation index, and the influence of the interaction between the nozzle’s structural parameters on its jet performance is not fully considered. In practice, strike velocity and strike area will affect gas release in the process of coal breaking and punching. To further optimize the structural parameters of coal breaking and punching nozzle, and improve water jet performance, some crucial parameters such as the contraction angle, outlet divergence angle, and length-to-diameter ratio are selected. Meanwhile, the maximum X-axis velocity and effective Y-axis extension distance are used as evaluation indexes. The effect of each key factor on the water jet performance is analyzed by numerical simulation using the single factor method. The significance and importance effect of each factor and their interaction on the water jet performance are quantitatively analyzed using the orthogonal experiment method. Moreover, three optimal combinations are selected for experimental verification. Results show that with an increase in contraction angle, outlet divergence angle, and length-to-diameter ratio, the maximum X-axis velocity increases initially and decreases thereafter. The Y-direction expansion distance of the jet will be improved significantly with an increase in the outlet divergence angle. Through field experiments, the jet performance of the improved nozzle 3 is the best. After optimization, the coal breaking and punching diameter of the nozzle is increased by 118%, and the punching depth is increased by 17.46%.


2021 ◽  
pp. 117048
Author(s):  
Feng Zhou ◽  
Jianping Li ◽  
Daolong Yang ◽  
Yuze Li ◽  
Jiangnan Luo

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Britt J. M. van Rooij ◽  
Gábor Závodszky ◽  
Alfons G. Hoekstra ◽  
David N. Ku

Abstract Occlusive thrombi formed under high flow shear rates develop very rapidly in arteries and may lead to myocardial infarction or stroke. Rapid platelet accumulation (RPA) and occlusion of platelet-rich thrombi and clot shrinkage have been studied after flow arrest. However, the influence of margination and shear rate on occlusive clot formation is not fully understood yet. In this study, the influence of flow on the growth and shrinkage of a clot is investigated. Whole blood (WB) and platelet-rich plasma (PRP) were perfused at high shear rates (> 3,000 s−1) through two microfluidic systems with a stenotic section under constant pressure. The stenotic section of the two devices are different in stenotic length (1,000 vs 150 μm) and contraction angle of the stenosis (15° vs 80°). In all experiments, the flow chamber occluded in the stenotic section. Besides a significantly increased lag time and decreased RPA rate for PRP compared to WB (p < 0.01), the device with a shorter stenotic section and steeper contraction angle showed a shear-dependent occlusion and lag time for both PRP and WB. This shear-dependent behavior of the platelet aggregate formation might be caused by the stenotic geometry.


Water ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 2194 ◽  
Author(s):  
Pan Tang ◽  
Juan Manzano Juárez ◽  
Hong Li

The venturi tube is a special kind of pipe which has been widely applied in many fields. Cavitation is one of the most important research issues for the Venturi tube. Hence, three key structural parameters (contraction angle, diffusion angle and contraction ratio) were selected to investigate the influence of different factors on cavitation characteristics, using the computational fluid dynamics (CFD) method. A series of experiments for measuring the relationship between differential pressure and flow rate were carried out to verify the accuracy of the simulation method. Results showed that the simulation results had a high accuracy and the numerical method was feasible. The average vapor volume fraction of cross-section from the throat in the axial direction increased with increasing contraction angle. The cavity length increased with increasing contraction angle. The average volume fraction in the diffusion section rapidly decreased with increasing diffusion angle. The diffusion angle had no significant effect on the cavitation characteristics in the throat section and had a significant influence in the diffusion section. The average vapor volume fraction increased with decreasing contraction ratio. The contraction ratio had no significant effect on the cavity length under the same differential pressure. The average vapor volume fraction increased with decreasing contraction ratio. However, the variation in the throat section was less than the diffusion section. Under the same inlet and outlet pressure, the cavity lengths for different contraction ratios were basically the same, which indicated that the contraction ratio had no significant effect on the cavity length.


2019 ◽  
Vol 2019 ◽  
pp. 1-7
Author(s):  
Hetang Wang ◽  
Yan Tang

Mine dust is one of the most serious environmental hazards in the coal mining process. This paper introduces a numerical simulation of a novel foam generator used for dust control in coal mines. The amount of foam generated by this device significantly depends on the amount of air entrainment. Therefore, a computational fluid dynamics (CFD) method was used to study three influencing factors, namely, throat-nozzle distance, mixing throat length, and the contraction angle of the suction chamber. The predicted values by the CFD simulation proved to be in good agreement with the experimental data. The results revealed that the air entrainment reached its maximum when the ratio of throat-nozzle distance to mixing throat length was 2/3. The optimum values of the throat ratio (its length to diameter) and the contraction angle of the suction chamber were obtained at 20 and 5°, respectively. This research provides essential guidance in the geometric parameter design of the self-suction type foam generator, which has the advantage of negating the need for compressed-air pipelines and having high reliability, compared to traditional foam generators.


Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1349
Author(s):  
Zhong Tian ◽  
Wei Wang ◽  
Ruidi Bai ◽  
Nan Li

The use of flaring gate piers (FGPs) along with finite crest-length weirs changes the shape of plunging jets and increases the efficiency of energy dissipation in some projects; however, the FGPs may affect the discharge capacity. In this study, the flow pattern and discharge coefficient were experimentally investigated under different conditions by varying the weir lengths Lw, contraction ratio β, contraction angle θ, and water heads H. A comparative analysis of the weirs with and without FGPs was performed. For the finite crest-length weirs with FGPs, the water-surface profiles in the flow channel were backwater curves. Moreover, the plunging jets leaving the weir became narrower and then subsequently diffused largely in the transverse and longitudinal directions in air. The discharge coefficients of the weirs with FGPs were approximately equal for various weir lengths. Moreover, following the earlier studies on traditional finite crest-length weirs, a discharge-coefficient equation was developed for the weir with an FGP in this study. The results showed that in the weirs with FGPs, the discharge coefficients clearly increased with the increase in the contraction ratio and water head, but the changes in their values along with the contraction angle were neglected.


2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Simindokht Saemi ◽  
Mehrdad Raisee ◽  
Michel J. Cervantes ◽  
Ahmad Nourbakhsh

A common method to calculate the flow rate and consequently hydraulic efficiency in hydropower plants is the pressure-time method. In the present work, the pressure-time method is studied numerically by three-dimensional (3D) simulations and considering the change in the pipe cross section (a contraction). Four different contraction angles are selected for the investigations. The unsteady Reynolds-averaged Navier–Stokes (URANS) equations and the low-Reynolds k–ω shear stress transport (SST) turbulence model are used to simulate the turbulent flow. The flow physics in the presence of the contraction, and during the deceleration period, is studied. The flow rate is calculated considering all the losses: wall shear stress, normal stresses, and also flux of momentum in the flow. The importance of each term is evaluated showing that the flux of momentum plays a most important role in the flow rate estimation while the viscous losses term is the second important factor. To extend the viscous losses calculations applicability to real systems, the quasi-steady friction approach is employed. The results showed that considering all the losses, the increase in the contraction angle does not influence the calculated errors significantly. However, the use of the quasi-steady friction factor introduces a larger error, and the results are reliable approximately up to a contraction angle of ϴ = 10 deg. The reason imparts to the formation of a local recirculation zone upstream and inside the contraction, which appears earlier as the contraction angle increases. This feature cannot be captured by the quasi-steady friction models, which are derived based on the fully developed flow assumption.


2015 ◽  
Vol 21 (4) ◽  
pp. 398-411 ◽  
Author(s):  
Shuhei Miyashita ◽  
Cagdas D. Onal ◽  
Daniela Rus

This study demonstrates a new approach to autonomous folding for the body of a 3D robot from a 2D sheet, using heat. We approach this challenge by folding a 0.27-mm sheetlike material into a structure. We utilize the thermal deformation of a contractive sheet sandwiched by rigid structural layers. During this baking process, the heat applied on the entire sheet induces contraction of the contracting layer and thus forms an instructed bend in the sheet. To attain the targeted folding angles, the V-fold spans method is used. The targeted angle θout can be kinematically encoded into crease geometry. The realization of this angle in the folded structure can be approximately controlled by a contraction angle θin. The process is non-reversible, is reliable, and is relatively fast. Our method can be applied simultaneously to all the folds in multi-crease origami structures. We demonstrate the use of this method to create a lightweight mobile robot.


2013 ◽  
Vol 864-867 ◽  
pp. 2185-2192
Author(s):  
Xiao Xia Hou ◽  
Ju Rui Yang ◽  
Jian Shu Zhen

In order to study the aerated cavity length and negative pressure on stepped spillway which combined with Y-shape asymmetric flaring gate pier body type, this paper applied RNG turbulence model,VOF model of water vapor two-phase, iterative solution of geometry reconstruction format of unsteady flow to generate free surface. Numerically simulated the length of aerated cavity and negative pressure of stepped spillway which combined with asymmetrical Y-shape flaring gate pier that with the contraction ratio respectively of 598, 0.497 and 0.445, the range from the upstream reservoir to downstream stilling basin. And compared the simulation results with experimental results, found that the aerated cavity length on steps basically consistent with the measured cavity length, the maximum error is 9.7%. The simulation results shows that the aeration cavity length on steps increases with asymmetric flaring gate pier contraction ratio decreases, and the aerated cavity length of lateral side with smaller contraction angle is larger 4 to 5 times than lateral side with larger contraction angle.


2013 ◽  
Vol 318 ◽  
pp. 231-234
Author(s):  
Dong Hai Su ◽  
Hao Jing ◽  
Yue Ling Wang

Focus on the technology and requirements of nozzle in fire engine to optimize the ability of blasting of nozzle, this paper built the model of fluid in nozzle, and simulation studied based on Fluent. This paper analysis the stage of nozzle, contraction angle, size of entrance and slenderness ratio as the influencing factors, supplied the reliable theoretical foundation for the design and structural improvement of nozzle in fire engine.


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