In this paper, we experimentally investigate the near-field flow characteristics of turbulent free jets respectively issued from circular, triangular, diamond, rectangular, and notched-rectangular orifice plates into ...In this paper, we experimentally investigate the near-field flow characteristics of turbulent free jets respectively issued from circular, triangular, diamond, rectangular, and notched-rectangular orifice plates into air surroundings. All the orifice plates have identical opening areas or equivalent diameters（De） and their aspect ratios（AR） range from 1 to 6.5. Planar particle image velocimetry（PIV） is used to measure the velocity field at the same Reynolds number of Re = 5 × 10^4,where Re = Ue De/ν with Ue being the exit bulk velocity and ν the kinematic viscosity of fluid. The mean and turbulent velocity fields of all the five jets are compared in detail. Results show that the noncircular jets can enhance the entrainment rate, reflected by the higher acceleration rates of mean velocity decay and spread, shorten the length of the unmixed core,expedite the increase of turbulent intensity compared with the circular counterpart shortened unmixed core, and increase turbulent intensity comparing to the circular counterpart. Among the five jets, the rectangular jet（AR = 6.5） produces the greatest decay rate of the near-field mean velocity, postpones the position at which the 鈥榓xis-switching鈥檖henomenon occurs. This supports that axis switching phenomenon strongly depends on jet initial conditions. In addition, the hump in the centerline variation of the turbulence intensity is observed in the rectangular and triangular jets, but not in the circular jet, nor in diamond jet nor in notched-rectangular jet.展开更多
A double fluid model for a liquid jet surrounded by a coaxial gas stream was constructed. The interfacial stability of the model was studied by Chebyshev pseudospectral method for different basic velocity profiles. Th...A double fluid model for a liquid jet surrounded by a coaxial gas stream was constructed. The interfacial stability of the model was studied by Chebyshev pseudospectral method for different basic velocity profiles. The physical variables were mapped into computational space using a nonlinear coordinates transformation. The general eigenvalues of the dispersion relation obtained are solved by QZ method, and the basic characteristics and their dependence on the flow parameters are analyzed.展开更多
This paper investigates the possibility of using the free expansion of gaseous CO2 in portable air-cooling systems. The cooling capacity of the gaseous CO2 free jet expansion was calculated using three different appro...This paper investigates the possibility of using the free expansion of gaseous CO2 in portable air-cooling systems. The cooling capacity of the gaseous CO2 free jet expansion was calculated using three different approaches and the results showed that the simplified calculations would give approximated cooling values with an 11.6% maximum error. The mass flow rate, upstream pressure and cooling capacity of the gaseous CO2 decreased with time. A maximum 48.5 watts of cooling was recorded at minute 4 and a minimum value of 10.4 watts at the end of the test. The drop in cooling capacity is due to the evaporation of the liquid CO2 inside the small cylinder which cools the two-phase CO2 mixture and causes a pressure drop (from 6 MPa to 2.97 MPa), which also affects the mass flow rate of gaseous CO2 exiting the orifice (from 0.56 g/s to 0.24 g/s). If this cooling technique is to be considered in portable compact-cooling systems, the mass, pressure and cooling capacity drop with time must be solved. One of the solutions could be to cover the cylinder with a heating coat to compensate for the heat absorbed by the evaporation of the liquid CO2.展开更多
The recent research about cavitation jet mainly focuses on the organ-pipe nozzle and triangular nozzle. The research content mainly includes the optimized design about the structure of nozzles, the observation and flo...The recent research about cavitation jet mainly focuses on the organ-pipe nozzle and triangular nozzle. The research content mainly includes the optimized design about the structure of nozzles, the observation and flow analysis about the cavitation jet in the water, and the theory of rock attacked by the cavitation jet, while the energy characteristic of the free jet is not studied yet. In China, the research about the central-body nozzle is almost empty. For the purpose of studying the energy characteristic and the structure of free water jet discharged from central-body nozzle, an experiment with phase Doppler particle anemometry（PDPA） technology is carried out to measure the free water jet flow, which is produced by a central-body nozzle under the jet pressure of 15 MPa. While five sections with different axial distances from the nozzle outlet are selected for data process and analysis, the axial and radial velocity and the droplets of the particle size are studied. Meanwhile, numerical calculation of corresponding flow field is conducted by using volume of fluid（VOF） multiphase model, and the jet flow feature is discussed. The experimental and calculating results show that the axial velocity of high speed jet flow dissipates slowly in the air, and the core area and diffused area are discovered. The diameter of droplet in the core area is small, and jet energy is concentrated, while in the diffusion area, water is mingled with ambient air and radial velocity is relatively large. Obvious low-pressure area exists behind the central body and potential cavitation may occur in that area. The proposed research reveals the energy characteristic of free jet discharged from central-body nozzle, provides the theoretical basis for preestimating erosion feature of the central-body nozzle and also the theoretical foundation for revealing the mechanism of erosion.展开更多
The simplified modeling for analysis on MHD stability of free surface jet flow in a gradient magnetic fields is based on the theoretical and experimental results on channel liquid metal MHD flow, especially, the resul...The simplified modeling for analysis on MHD stability of free surface jet flow in a gradient magnetic fields is based on the theoretical and experimental results on channel liquid metal MHD flow, especially, the results of MHD flow velocity distribution in cross-section of channels (rectangular duct and circular pipe), and the expected results from the modeling are well agreed with the recent experimental data obtained. It is the first modeling which can efficiently explain the experimental results of liquid-metal free surface jet flow.展开更多
The purpose of this paper is to present a two-phase 3D magnetohydrodynamics （MHD） flow model that combines the volume of fluid （VOF） method with the technique derived from induced-magnetic-field equations for liqu...The purpose of this paper is to present a two-phase 3D magnetohydrodynamics （MHD） flow model that combines the volume of fluid （VOF） method with the technique derived from induced-magnetic-field equations for liquid metal free surface MHD-jet-flow. Analogy between the induced-magnetic-filed equation and the conventional computational fluid dynamics （CFD） equation is made, so that the equation can be conveniently accounted for by CFD. A penalty factor numerical method is introduced in order to force the local divergence-free condition of the magnetic fields and an extension of the void insulating calculation domain is applied to ensure that the induced-magnetic field at its boundaries is null. These simulation results for lithium liquid metal jets under magnetic field configurations of Magnetic Torus （Mtor） and National Spherical Torus Experiment （NSTX） outboard divertor have shown that three dimensional jet can not be annihilated by magnetic braking and its cross-section will deform in such a way that the momentum flux of the jet is conserved. 3D MHD effects from a magnetic field gradient cause return currents to interact with applied magnetic fields and produce unfavorable Lorentz forces. Under 3D applied non-uniform magnetic fields of the divertor, unfavorable Lorentz forces lead to a substantial change in flow pattern and a reduction in flow velocity, with the jet cross-section moving to one side of the jet space. These critical phenomena can not be revealed by 2D models.展开更多
In this paper, the internal fluid motion of a jet system is described by the Navier Stokes mechanics equations. For the simulation of the motion, the penalty function finite element method is used, and the velocity ve...In this paper, the internal fluid motion of a jet system is described by the Navier Stokes mechanics equations. For the simulation of the motion, the penalty function finite element method is used, and the velocity vectors and stream function curves are obtained. Using the Prandtl theory, this paper derives the free jet velocity and the jet bunch width in a half-space, the latter of which is amended by experiment. The results obtained in this paper are applied to micro-type high pressure water jet cleaner and the ejector of rocket engine.展开更多
在30kW级直流电弧等离子体喷射化学气相沉积(DC Arc P lasm a Jet CVD)设备上,采用Ar-H2-CH4混合气体,通过调节甲烷浓度以及控制其他沉积参数,在Mo衬底上沉积出微/纳米复合自支撑金刚石膜。实验表明,当微米金刚石膜层沉积结束后,在随后...在30kW级直流电弧等离子体喷射化学气相沉积(DC Arc P lasm a Jet CVD)设备上,采用Ar-H2-CH4混合气体,通过调节甲烷浓度以及控制其他沉积参数,在Mo衬底上沉积出微/纳米复合自支撑金刚石膜。实验表明,当微米金刚石膜层沉积结束后,在随后的沉积中,随着甲烷浓度的增加,金刚石膜表面的晶粒大小是逐渐减小的。当甲烷浓度达到20%以上时,金刚石膜生长面晶粒呈现菜花状的小晶团,膜体侧面已经没有了粗大的柱状晶,而是呈现出光滑的断口,对该层进行拉曼谱分析显示,位于1145 cm-1附近有一定强度的散射峰出现。这说明所沉积的晶粒全部变为纳米级尺寸。展开更多
Under optimal conditions free-standing high quality diamond films were prepared by DC arc plasma jet CVD method at a growth rate of 7-10 Pm/h. Surface and cross section morphologies of the diamond films were observed ...Under optimal conditions free-standing high quality diamond films were prepared by DC arc plasma jet CVD method at a growth rate of 7-10 Pm/h. Surface and cross section morphologies of the diamond films were observed by SEM. Raman spectrometer wasused to characterize the quality of diamond films. The IR transmittivity measured by IR spectrometer is close to the theoretical value ofabout 71% in the far infrared band. The thermal conductivity measured by photothermal deflection exceeds 18 W/cm' K. <l 10> is thepreferential growth orientation of the films detected by X-ray diffractometer. As s result, the extremely high temperature of DC arc plasma jet can produce supersaturated atomic hydrogen, which played an important role in the process for the deposition of high quality diamond films.展开更多
Electrospinning is a new type of free-end spinning built on the electric field. The electric force of polyacrylonitrile( PAN)polymer solution overcomes the surface tension of the solution,and then it causes wave and f...Electrospinning is a new type of free-end spinning built on the electric field. The electric force of polyacrylonitrile( PAN)polymer solution overcomes the surface tension of the solution,and then it causes wave and forms jet flow. In the process of injection,the solution is evaporated or solidified,eventually forming a fiber on the receiving device. Different from ordinary single needle head,in the study,a new type of 3D free surface spinneret is used to produce multiple jets at the same time, and this will greatly improve production efficiency. In the paper,the model of 3D free surface is analyzed by the theory of fluid mechanics. The relationship among the wave length,surface tension and the electric field is obtained.After the mechanical analysis on the stable period of the jet,the relationship between the jet radius and the distance from the spinneret to jet is carried out. At the same time the relationship between the jet velocity and the tensile force is carried out. After mechanics analyzing on the unstable period of the jet,it can be concluded that the radius of the jet is inversely proportional to one half power of the distance from the jet to the spinneret,and the electrostatic spinning jet's velocity is directly proportional to one half power of the tensile force. After the mechanical analysis of the unstable period of the electrospinning jet,it can be concluded that the radius of the jet is inversely proportional to one fourth power of the jet intercept point distance.展开更多
Based on the mechanical system of free-end fibers and the analysis of pulling free-end fibers out of the spun yarn during spinning,a low-fiber hollow spindle is designed and the air distribution of fluent field is sim...Based on the mechanical system of free-end fibers and the analysis of pulling free-end fibers out of the spun yarn during spinning,a low-fiber hollow spindle is designed and the air distribution of fluent field is simulated numerically. The negative pressure effect is much bigger at the top of low-fiber hollow spindle than that in Murata No.861,which is more conducive for single fiber to get into the channel of hollow spindle. The tangential velocity in 0-3 mm at the top of hollow spindle increases and the fluctuation of radial velocity is much stronger,which enhance the wrapping effect. In the addition,the distribution of axial velocity remains the same.展开更多
Polyethylene （PE） films are treated using an atmospheric pressure plasma jet （APPJ） with He or He/O2 gas for different periods of time. The influence of gas type on the plasma polymer interactions is studied. The ...Polyethylene （PE） films are treated using an atmospheric pressure plasma jet （APPJ） with He or He/O2 gas for different periods of time. The influence of gas type on the plasma polymer interactions is studied. The surface contact angle of the PE film can be effectively lowered to 58° after 20 s of He/O2 plasma treatment and then remains almost unchanged for longer treatment durations, while, for He plasma treatment, the film surface contact angle drops gradually to 47° when the time reaches 120 s. Atomic force microscopy （AFM） results show that the root mean square （RMS） roughness was significantly higher for the He/O2 plasma treated samples than for the He plasma treated counterparts, and the surface topography of the He/O2 plasma treated PE films displays evenly distributed dome-shaped small protuberances. Chemical composition analysis reveals that the He plasma treated samples have a higher oxygen content but a clearly lower percentage of COO than the comparable He/O2 treated samples, suggesting that differences exist in the mode of incorporating oxygen between the two gas condition plasma treatments. Electron spin resonance （ESR） results show that the free radical concentrations of the He plasma treated samples were clearly higher than those of the He/O2 plasma treated ones with other conditions unchanged.展开更多
基金Project supported by the Fundamental Research Funds for the Central Universities,China(Grant No.3132014050)the General Science Research Project of the Education Department of Liaoning Province,China(Grant No.L2013198)+1 种基金the Natural Science Foundation of Liaoning Province,China(Grant No.L2014025012)the National Natural Science Foundation of China(Grant Nos.10921202 and 11072005)
文摘In this paper, we experimentally investigate the near-field flow characteristics of turbulent free jets respectively issued from circular, triangular, diamond, rectangular, and notched-rectangular orifice plates into air surroundings. All the orifice plates have identical opening areas or equivalent diameters（De） and their aspect ratios（AR） range from 1 to 6.5. Planar particle image velocimetry（PIV） is used to measure the velocity field at the same Reynolds number of Re = 5 × 10^4,where Re = Ue De/ν with Ue being the exit bulk velocity and ν the kinematic viscosity of fluid. The mean and turbulent velocity fields of all the five jets are compared in detail. Results show that the noncircular jets can enhance the entrainment rate, reflected by the higher acceleration rates of mean velocity decay and spread, shorten the length of the unmixed core,expedite the increase of turbulent intensity compared with the circular counterpart shortened unmixed core, and increase turbulent intensity comparing to the circular counterpart. Among the five jets, the rectangular jet（AR = 6.5） produces the greatest decay rate of the near-field mean velocity, postpones the position at which the 鈥榓xis-switching鈥檖henomenon occurs. This supports that axis switching phenomenon strongly depends on jet initial conditions. In addition, the hump in the centerline variation of the turbulence intensity is observed in the rectangular and triangular jets, but not in the circular jet, nor in diamond jet nor in notched-rectangular jet.
文摘A double fluid model for a liquid jet surrounded by a coaxial gas stream was constructed. The interfacial stability of the model was studied by Chebyshev pseudospectral method for different basic velocity profiles. The physical variables were mapped into computational space using a nonlinear coordinates transformation. The general eigenvalues of the dispersion relation obtained are solved by QZ method, and the basic characteristics and their dependence on the flow parameters are analyzed.
文摘This paper investigates the possibility of using the free expansion of gaseous CO2 in portable air-cooling systems. The cooling capacity of the gaseous CO2 free jet expansion was calculated using three different approaches and the results showed that the simplified calculations would give approximated cooling values with an 11.6% maximum error. The mass flow rate, upstream pressure and cooling capacity of the gaseous CO2 decreased with time. A maximum 48.5 watts of cooling was recorded at minute 4 and a minimum value of 10.4 watts at the end of the test. The drop in cooling capacity is due to the evaporation of the liquid CO2 inside the small cylinder which cools the two-phase CO2 mixture and causes a pressure drop (from 6 MPa to 2.97 MPa), which also affects the mass flow rate of gaseous CO2 exiting the orifice (from 0.56 g/s to 0.24 g/s). If this cooling technique is to be considered in portable compact-cooling systems, the mass, pressure and cooling capacity drop with time must be solved. One of the solutions could be to cover the cylinder with a heating coat to compensate for the heat absorbed by the evaporation of the liquid CO2.
基金supported by National Natural Science Foundation ofChina (Grant No. 50806031)
文摘The recent research about cavitation jet mainly focuses on the organ-pipe nozzle and triangular nozzle. The research content mainly includes the optimized design about the structure of nozzles, the observation and flow analysis about the cavitation jet in the water, and the theory of rock attacked by the cavitation jet, while the energy characteristic of the free jet is not studied yet. In China, the research about the central-body nozzle is almost empty. For the purpose of studying the energy characteristic and the structure of free water jet discharged from central-body nozzle, an experiment with phase Doppler particle anemometry（PDPA） technology is carried out to measure the free water jet flow, which is produced by a central-body nozzle under the jet pressure of 15 MPa. While five sections with different axial distances from the nozzle outlet are selected for data process and analysis, the axial and radial velocity and the droplets of the particle size are studied. Meanwhile, numerical calculation of corresponding flow field is conducted by using volume of fluid（VOF） multiphase model, and the jet flow feature is discussed. The experimental and calculating results show that the axial velocity of high speed jet flow dissipates slowly in the air, and the core area and diffused area are discovered. The diameter of droplet in the core area is small, and jet energy is concentrated, while in the diffusion area, water is mingled with ambient air and radial velocity is relatively large. Obvious low-pressure area exists behind the central body and potential cavitation may occur in that area. The proposed research reveals the energy characteristic of free jet discharged from central-body nozzle, provides the theoretical basis for preestimating erosion feature of the central-body nozzle and also the theoretical foundation for revealing the mechanism of erosion.
基金The project partly supported by National Nature Science Foundation of China (No. 10275019)
文摘The simplified modeling for analysis on MHD stability of free surface jet flow in a gradient magnetic fields is based on the theoretical and experimental results on channel liquid metal MHD flow, especially, the results of MHD flow velocity distribution in cross-section of channels (rectangular duct and circular pipe), and the expected results from the modeling are well agreed with the recent experimental data obtained. It is the first modeling which can efficiently explain the experimental results of liquid-metal free surface jet flow.
基金National Natural Science Foundation of China (No. 503006006) and by the Scientific Research Foun-dation for the Returned Overseas Chinese Scholars, State Education Ministry
文摘The purpose of this paper is to present a two-phase 3D magnetohydrodynamics （MHD） flow model that combines the volume of fluid （VOF） method with the technique derived from induced-magnetic-field equations for liquid metal free surface MHD-jet-flow. Analogy between the induced-magnetic-filed equation and the conventional computational fluid dynamics （CFD） equation is made, so that the equation can be conveniently accounted for by CFD. A penalty factor numerical method is introduced in order to force the local divergence-free condition of the magnetic fields and an extension of the void insulating calculation domain is applied to ensure that the induced-magnetic field at its boundaries is null. These simulation results for lithium liquid metal jets under magnetic field configurations of Magnetic Torus （Mtor） and National Spherical Torus Experiment （NSTX） outboard divertor have shown that three dimensional jet can not be annihilated by magnetic braking and its cross-section will deform in such a way that the momentum flux of the jet is conserved. 3D MHD effects from a magnetic field gradient cause return currents to interact with applied magnetic fields and produce unfavorable Lorentz forces. Under 3D applied non-uniform magnetic fields of the divertor, unfavorable Lorentz forces lead to a substantial change in flow pattern and a reduction in flow velocity, with the jet cross-section moving to one side of the jet space. These critical phenomena can not be revealed by 2D models.
文摘In this paper, the internal fluid motion of a jet system is described by the Navier Stokes mechanics equations. For the simulation of the motion, the penalty function finite element method is used, and the velocity vectors and stream function curves are obtained. Using the Prandtl theory, this paper derives the free jet velocity and the jet bunch width in a half-space, the latter of which is amended by experiment. The results obtained in this paper are applied to micro-type high pressure water jet cleaner and the ejector of rocket engine.
文摘在30kW级直流电弧等离子体喷射化学气相沉积(DC Arc P lasm a Jet CVD)设备上,采用Ar-H2-CH4混合气体,通过调节甲烷浓度以及控制其他沉积参数,在Mo衬底上沉积出微/纳米复合自支撑金刚石膜。实验表明,当微米金刚石膜层沉积结束后,在随后的沉积中,随着甲烷浓度的增加,金刚石膜表面的晶粒大小是逐渐减小的。当甲烷浓度达到20%以上时,金刚石膜生长面晶粒呈现菜花状的小晶团,膜体侧面已经没有了粗大的柱状晶,而是呈现出光滑的断口,对该层进行拉曼谱分析显示,位于1145 cm-1附近有一定强度的散射峰出现。这说明所沉积的晶粒全部变为纳米级尺寸。
文摘Under optimal conditions free-standing high quality diamond films were prepared by DC arc plasma jet CVD method at a growth rate of 7-10 Pm/h. Surface and cross section morphologies of the diamond films were observed by SEM. Raman spectrometer wasused to characterize the quality of diamond films. The IR transmittivity measured by IR spectrometer is close to the theoretical value ofabout 71% in the far infrared band. The thermal conductivity measured by photothermal deflection exceeds 18 W/cm' K. <l 10> is thepreferential growth orientation of the films detected by X-ray diffractometer. As s result, the extremely high temperature of DC arc plasma jet can produce supersaturated atomic hydrogen, which played an important role in the process for the deposition of high quality diamond films.
基金National Natural Science Foundations of China(Nos.51373033,11172064)the Fundamental Research Funds for the Central Universities,China(No.CUSF-DH-M-EG2016014)
文摘Electrospinning is a new type of free-end spinning built on the electric field. The electric force of polyacrylonitrile( PAN)polymer solution overcomes the surface tension of the solution,and then it causes wave and forms jet flow. In the process of injection,the solution is evaporated or solidified,eventually forming a fiber on the receiving device. Different from ordinary single needle head,in the study,a new type of 3D free surface spinneret is used to produce multiple jets at the same time, and this will greatly improve production efficiency. In the paper,the model of 3D free surface is analyzed by the theory of fluid mechanics. The relationship among the wave length,surface tension and the electric field is obtained.After the mechanical analysis on the stable period of the jet,the relationship between the jet radius and the distance from the spinneret to jet is carried out. At the same time the relationship between the jet velocity and the tensile force is carried out. After mechanics analyzing on the unstable period of the jet,it can be concluded that the radius of the jet is inversely proportional to one half power of the distance from the jet to the spinneret,and the electrostatic spinning jet's velocity is directly proportional to one half power of the tensile force. After the mechanical analysis of the unstable period of the electrospinning jet,it can be concluded that the radius of the jet is inversely proportional to one fourth power of the jet intercept point distance.
基金Program for Changjiang Scholars and Innovative Research Team in University,China(No.IRT1220)Shanghai Natural Science Foundation,China(No.13ZR1400900)Keygrant Project of Chinese Ministry of Education(No.113027A)
文摘Based on the mechanical system of free-end fibers and the analysis of pulling free-end fibers out of the spun yarn during spinning,a low-fiber hollow spindle is designed and the air distribution of fluent field is simulated numerically. The negative pressure effect is much bigger at the top of low-fiber hollow spindle than that in Murata No.861,which is more conducive for single fiber to get into the channel of hollow spindle. The tangential velocity in 0-3 mm at the top of hollow spindle increases and the fluctuation of radial velocity is much stronger,which enhance the wrapping effect. In the addition,the distribution of axial velocity remains the same.
基金supported by the Fundamental Research Funds for the Central Universities of China(Nos.JUSRP1044 and JUSRP1045)National Natural Science Foundation of China(Nos.51203062 and 51302110)the Cooperative Innovation Fund,Project of Jiangsu Province,China(Nos.BY2012064,BY2013015-31 and BY2013015-32)
文摘Polyethylene （PE） films are treated using an atmospheric pressure plasma jet （APPJ） with He or He/O2 gas for different periods of time. The influence of gas type on the plasma polymer interactions is studied. The surface contact angle of the PE film can be effectively lowered to 58° after 20 s of He/O2 plasma treatment and then remains almost unchanged for longer treatment durations, while, for He plasma treatment, the film surface contact angle drops gradually to 47° when the time reaches 120 s. Atomic force microscopy （AFM） results show that the root mean square （RMS） roughness was significantly higher for the He/O2 plasma treated samples than for the He plasma treated counterparts, and the surface topography of the He/O2 plasma treated PE films displays evenly distributed dome-shaped small protuberances. Chemical composition analysis reveals that the He plasma treated samples have a higher oxygen content but a clearly lower percentage of COO than the comparable He/O2 treated samples, suggesting that differences exist in the mode of incorporating oxygen between the two gas condition plasma treatments. Electron spin resonance （ESR） results show that the free radical concentrations of the He plasma treated samples were clearly higher than those of the He/O2 plasma treated ones with other conditions unchanged.
