The Experts below are selected from a list of 104418 Experts worldwide ranked by ideXlab platform
Lei Tan - One of the best experts on this subject based on the ideXlab platform.
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tip clearance on pressure fluctuation intensity and vortex characteristic of a mixed Flow pump as turbine at pump mode
Renewable Energy, 2018Co-Authors: Yabin Liu, Lei TanAbstract:Abstract The present work investigates the pressure fluctuation intensity and vortex characteristic of a mixed Flow pump as turbine at pump mode with a tip clearance. The tip clearance between the blade tip and shroud can induce tip leakage Flow and interact with main Flow, which causes the unstable Flow structure and complex vortex in the passage. The external characteristics of experimental results and numerical simulations are in agreement. With tip clearance increasing, the head and efficiency of pump decrease by 10.8% and 6.26%, respectively. The distribution of pressure fluctuation intensity is presented as a triangular shape under design Flow Rate. Results show that the tip leakage vortex (TLV) can be divided into four categories, namely, primary TLV, secondary TLV, entangled TLV, and dispersed TLV. The Flow Rate has a significant influence on the TLV structure and trajectory, and the starting point of the primary TLV shifts to approximately 20% of the blade chord at Large Flow Rate. The relative vorticity transport equation is introduced to analyze the vortex derivation by using the relative vortex stretching, Coriolis force and viscous diffusion.
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controllable velocity moment and prediction model for inlet guide vanes of a centrifugal pump
Engineering Computations, 2018Co-Authors: Ming Liu, Lei Tan, Yabin Liu, Shuliang CaoAbstract:This paper aims to investigate the effect of three-dimensional (3D) inlet guide vanes (IGVs) on performance of a centrifugal pump.,A design method for 3D IGVs is proposed based on the controllable velocity moment, which is determined by a fourth-order dimensionless function. Numerical simulation of the centrifugal pump with IGVs is carried out by solving the Reynolds-averaged Navier–Stokes equations. The method of frozen rotor is applied to couple the stationary and rotational domain.,The efficiency of pump with 3D IGVs is higher than that with 2D IGVs for most prewhirl angles, which validate the advancement of 3D IGVs on prewhirl regulation. The effect of prewhirl regulation at small Flow Rate is more significant than that at Large Flow Rate.,A prediction model of velocity moment based on the Oseen vortex is proposed to describe the Flow pattern downstream the IGVs.
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Numerical investigation of clocking effect on a centrifugal pump with inlet guide vanes
Engineering Computations, 2016Co-Authors: Lei Tan, Shuliang Cao, Yuchuan WangAbstract:Purpose – The purpose of this paper is to investigate the clocking effect on a centrifugal pump with inlet guide vanes (IGVs). Design/methodology/approach – The paper uses a computation fluid dynamics framework to solve the unsteady Flows in a centrifugal pump with IGVs. The relative position between the stationary vanes and the stationary volute tongue is defined as the clocking position when IGVs inside the suction pipe rotate along the circumferential direction. Findings – The results show that clocking positions have little effect on the pump head and efficiency, however their influences are obvious for the pressure fluctuation and Flow field in the centrifugal pump. The maximum difference of pressure amplitude at dominant frequency reach up to 28 percent on the monitoring point V8 at different clocking positions under design Flow Rate. For the Large Flow Rate, the clocking effect on Flow field and pressure fluctuation in centrifugal pump is similar to that of design Flow Rate. However, the clocking e...
Yabin Liu - One of the best experts on this subject based on the ideXlab platform.
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tip clearance on pressure fluctuation intensity and vortex characteristic of a mixed Flow pump as turbine at pump mode
Renewable Energy, 2018Co-Authors: Yabin Liu, Lei TanAbstract:Abstract The present work investigates the pressure fluctuation intensity and vortex characteristic of a mixed Flow pump as turbine at pump mode with a tip clearance. The tip clearance between the blade tip and shroud can induce tip leakage Flow and interact with main Flow, which causes the unstable Flow structure and complex vortex in the passage. The external characteristics of experimental results and numerical simulations are in agreement. With tip clearance increasing, the head and efficiency of pump decrease by 10.8% and 6.26%, respectively. The distribution of pressure fluctuation intensity is presented as a triangular shape under design Flow Rate. Results show that the tip leakage vortex (TLV) can be divided into four categories, namely, primary TLV, secondary TLV, entangled TLV, and dispersed TLV. The Flow Rate has a significant influence on the TLV structure and trajectory, and the starting point of the primary TLV shifts to approximately 20% of the blade chord at Large Flow Rate. The relative vorticity transport equation is introduced to analyze the vortex derivation by using the relative vortex stretching, Coriolis force and viscous diffusion.
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controllable velocity moment and prediction model for inlet guide vanes of a centrifugal pump
Engineering Computations, 2018Co-Authors: Ming Liu, Lei Tan, Yabin Liu, Shuliang CaoAbstract:This paper aims to investigate the effect of three-dimensional (3D) inlet guide vanes (IGVs) on performance of a centrifugal pump.,A design method for 3D IGVs is proposed based on the controllable velocity moment, which is determined by a fourth-order dimensionless function. Numerical simulation of the centrifugal pump with IGVs is carried out by solving the Reynolds-averaged Navier–Stokes equations. The method of frozen rotor is applied to couple the stationary and rotational domain.,The efficiency of pump with 3D IGVs is higher than that with 2D IGVs for most prewhirl angles, which validate the advancement of 3D IGVs on prewhirl regulation. The effect of prewhirl regulation at small Flow Rate is more significant than that at Large Flow Rate.,A prediction model of velocity moment based on the Oseen vortex is proposed to describe the Flow pattern downstream the IGVs.
Bo Xiao - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of hydraulic fracture propagation in shale gas reservoir
Journal of Natural Gas Science and Engineering, 2015Co-Authors: Tiankui Guo, Yushi Zou, Shicheng Zhang, Bo XiaoAbstract:Abstract On the basis of damage mechanics, a 2D fracture propagation model for seepage-stress-damage coupling in multi-fracture shales was established. Numerical simulations of hydraulic fracture propagation in the presence of natural fractures were carried out, with the use of mechanical parameters of shale reservoirs. The results showed that when hydraulic fractures encountered natural fractures in a shale reservoir, the morphology of fracture propagation was jointly affected by the properties of natural fractures (permeability and mechanical properties of rocks), approaching angle, horizontal stress difference, and Flow Rate of fracturing fluids. At a small horizontal stress difference, or low approaching angle, or small friction coefficient, natural fractures had increased potential to be damaged due to shear and tension. In such cases, the hydraulic fractures tended to propagate along the natural fractures. As the Flow Rate of fracturing fluid increased and the width of hydraulic fractures expanded, branch fractures formed easily when the net pressure exceeded the sum of horizontal stress difference and tensile strength of the rocks in which natural fractures with approaching angle smaller than 60° existed. It is seen, a high Flow Rate will increase the complexity of fracture network. However, when a Large number of natural fractures with approaching angles greater than 60° existed, a Large Flow Rate generally led to propagation of hydraulic fractures beyond natural fractures, which was not favored. Hence, an appropriate Flow Rate should be selected based on the orientations of natural fractures and hydraulic fractures. At the early stage of hydraulic fracturing, a low Flow Rate was favorable for the initiation of natural fractures and the growth of complexity of regional fractures near the well. Later, a higher Flow Rate facilitated a further propagation of hydraulic fractures into the depth of reservoir, thus forming a network of fractures. The underlying control mechanism of Flow Rate and net pressure on the formation of fracture network still requires clarification. The bending degree of the fracture propagation path depended on the ratio of net pressure to stress difference at a distant point as well as on the spacing between fractures. When the horizontal stress difference (
Pengfei Jiang - One of the best experts on this subject based on the ideXlab platform.
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key technologies and equipment for a fully mechanized top coal caving operation with a Large mining height at ultra thick coal seams
International Journal of Coal Science & Technology, 2015Co-Authors: Jinhua Wang, Guofa Wang, Hongpu Kang, Debing Mao, Yuntao Liang, Pengfei JiangAbstract:Thick and ultra-thick coal seams are main coal seams for high production Rate and high efficiency in Chinese coal mines, which accounts for 44 % of the total minable coal reserve. A fully mechanized top-coal caving mining method is a main underground coal extraction method for ultra-thick coal seams. The coal extraction technologies for coal seams less than 14 m thick were extensively used in China. However, for coal seams with thickness greater than 14 m, there have been no reported cases in the world for underground mechanical extraction with safe performance, high efficiency and high coal recovery ratio. To deal with this case, China Coal Technology & Engineering Group, Datong Coal Mine Group, and other 15 organizations in China launched a fundamental and big project to develop coal mining technologies and equipment for coal seams with thicknesses greater than 14 m. After the completion of the project, a coal extraction method was developed for top-coal caving with a Large mining height, as well as a ground control theory for ultra-thick coal seams. In addition, the mining technology for top-coal caving with a Large mining height, the ground support technology for roadway in coal seams with a Large cross-section, and the prevention and control technology for gas and fire hazards were developed and applied. Furthermore, a hydraulic support with a mining height of 5.2 m, a shearer with high reliability, and auxiliary equipment were developed and manufactured. Practical implication on the technologies and equipment developed was successfully completed at the No. 8105 coal face in the Tashan coal mine, Datong, China. The major achievements of the project are summarized as follows: 1. A top-coal caving method for ultra-thick coal seams is proposed with a cutting height of 5 m and a top-coal caving height of 15 m. A structural mechanical model of overlying strata called cantilever beam-articulated rock beam is established. Based on the model, the load resistance of the hydraulic support with a Large mining height for top-coal caving method is determined. With the analysis, the movement characteristics of the top coal and above strata are evaluated during top-coal caving operation at the coal face with a Large mining height. Furthermore, there is successful development of comprehensive technologies for preventing and controlling spalling of the coal wall, and the top-coal caving technology with high efficiency and high recovery at the top-coal caving face with a Large mining height. This means that the technologies developed have overcome the difficulties in strata control, top-coal caving with high efficiency and high coal recovery, and enabled to achieve a production Rate of more than 10 Mtpa at a single top-coal caving face with a Large mining height in ultra-thick coal seams; 2. A hydraulic support with 5.2 m supporting height and anti-rockburst capacity, a shearer with high reliability, a scraper conveyor with a Large power at the back of face, and a Large load and long distance headgate belt conveyor have been successfully developed for a top-coal caving face with Large mining height. The study has developed the key technologies for improving the reliability of equipment at the coal face and has overcome the challenges in equipping the top-coal caving face with a Large mining height in ultra-thick coal seams; 3. The deformation characteristics of a Large cross-section roadway in ultra-thick coal seams are discovered. Based on the findings above, a series of bolt materials with a high yielding strength of 500–830 MPa and a high extension ratio, and cable bolt material with a 1 × 19 structure, Large tonnage and high extension ratio are developed. In addition, in order to achieve a safe roadway and a fast face advance, installation equipment for high pre-tension bolt is developed to solve the problems with the support of roadway in coal seams for top-coal caving operation with a Large mining height; 4. The characteristics of gas distribution and uneven emission at top-coal caving face with Large mining height in ultra-thick coal seams are evaluated. With the application of the technologies of gas drainage in the roof, the difficulties in gas control for high intensive top-coal caving mining operations, known as “low gas content, high gas emission”, are solved. In addition, Large Flow-Rate underground mobile equipment for making nitrogen are developed to solve the problems with fire prevention and safe mining at a top-coal caving face with Large mining height and production Rate of more than 10 Mtpa. A case study to apply the developed technologies has been conducted at the No. 8105 face, the Tashan coal mine in Datong, China. The case study demonstRates that the three units of equipment, i.e., the support, shearer and scraper conveyor, are rationally equipped. Average equipment usage at the coal face is 92.1 %. The coal recovery ratio at the coal face is up to 88.9 %. In 2011, the coal production at the No. 8105 face reached 10.849 Mtpa, exceeding the target of 10 Mtpa for a top-coal caving operation with Large mining height performed by Chinese-made mining equipment. The technologies and equipment developed provide a way for extracting ultra-thick coal seams. Currently, the technologies and equipment are used in 13 mining areas in China including Datong, Pingshuo, Shendong and Xinjiang. With the exploitation of coal resources in Western China, there is great potential for the application of the technologies and equipment developed.
Tiankui Guo - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of hydraulic fracture propagation in shale gas reservoir
Journal of Natural Gas Science and Engineering, 2015Co-Authors: Tiankui Guo, Yushi Zou, Shicheng Zhang, Bo XiaoAbstract:Abstract On the basis of damage mechanics, a 2D fracture propagation model for seepage-stress-damage coupling in multi-fracture shales was established. Numerical simulations of hydraulic fracture propagation in the presence of natural fractures were carried out, with the use of mechanical parameters of shale reservoirs. The results showed that when hydraulic fractures encountered natural fractures in a shale reservoir, the morphology of fracture propagation was jointly affected by the properties of natural fractures (permeability and mechanical properties of rocks), approaching angle, horizontal stress difference, and Flow Rate of fracturing fluids. At a small horizontal stress difference, or low approaching angle, or small friction coefficient, natural fractures had increased potential to be damaged due to shear and tension. In such cases, the hydraulic fractures tended to propagate along the natural fractures. As the Flow Rate of fracturing fluid increased and the width of hydraulic fractures expanded, branch fractures formed easily when the net pressure exceeded the sum of horizontal stress difference and tensile strength of the rocks in which natural fractures with approaching angle smaller than 60° existed. It is seen, a high Flow Rate will increase the complexity of fracture network. However, when a Large number of natural fractures with approaching angles greater than 60° existed, a Large Flow Rate generally led to propagation of hydraulic fractures beyond natural fractures, which was not favored. Hence, an appropriate Flow Rate should be selected based on the orientations of natural fractures and hydraulic fractures. At the early stage of hydraulic fracturing, a low Flow Rate was favorable for the initiation of natural fractures and the growth of complexity of regional fractures near the well. Later, a higher Flow Rate facilitated a further propagation of hydraulic fractures into the depth of reservoir, thus forming a network of fractures. The underlying control mechanism of Flow Rate and net pressure on the formation of fracture network still requires clarification. The bending degree of the fracture propagation path depended on the ratio of net pressure to stress difference at a distant point as well as on the spacing between fractures. When the horizontal stress difference (
