At jet pressures ranging from 80 to 120 MPa, submerged water jets are investigated by numerical simulation and experiment. Numerical simulation enables a systematic analysis of major flow parameters such as jet veloci...At jet pressures ranging from 80 to 120 MPa, submerged water jets are investigated by numerical simulation and experiment. Numerical simulation enables a systematic analysis of major flow parameters such as jet velocity, turbulent kinetic energy as well as void fraction of cavitation. Experiments facilitate an objective assessment of surface morphology, micro hardness and surface roughness of the impinged samples. A comparison is implemented between submerged and non-submerged water jets. The results show that submerged water jet is characterized by low velocity magnitudes relative to non-submerged water jet at the same jet pressure. Shear effect serves as a key factor underlying the inception of cavitation in submerged water jet stream. Predicted annular shape of cavity zone is substantiated by local height distributions associated with experimentally obtained footprints. As jet pressure increases, joint contribution of jet kinetic energy and cavitation is demonstrated. While for non-submerged water jet, impingement force stems exclusively from flow velocity.展开更多
The aim of this study is to examine the effects of local curvature and elastic wall effects of an isothermal hot wall for the purpose of jet impingement cooling performance.Finite element method was used with ALE.Diff...The aim of this study is to examine the effects of local curvature and elastic wall effects of an isothermal hot wall for the purpose of jet impingement cooling performance.Finite element method was used with ALE.Different important parametric effects such as Re number(between 100 and 700),Ha number(between 0 and 20),elasticity(between 104 and 109),curvature of the surface(elliptic,radius ratio between 1 and 0.25) and nanoparticle volume fraction(between 0 and 0.05) on the cooling performance were investigated numerically.The results showed that the average Nu number enhances for higher Hartmann number,higher values of elastic modulus of partly flexible wall and higher nanoparticle volume fraction.When the magnetic field is imposed at the highest strength,there is an increase of3.85% in the average Nu for the curved elastic wall whereas it is 89.22% for the hot part above it,which is due to the vortex suppression effects.Nanoparticle inclusion in the base fluid improves the heat transfer rate by about 27.6% in the absence of magnetic field whereas it is 20.5% under the effects of magnetic field at Ha=20.Curvature effects become important for higher Re numbers and at Re=700,there is 14.11% variation in the average Nu between the cases with the lowest and highest radius ratio.The elastic wall effects on the heat transfer are reduced with the increased curvature of the bottom wall.展开更多
Numerical studies on transient heat transfer characteristics of air-array-jet impingement with a small jet-to-plate distance and a large temperature difference between nozzles and plate were presented.The dimensionles...Numerical studies on transient heat transfer characteristics of air-array-jet impingement with a small jet-to-plate distance and a large temperature difference between nozzles and plate were presented.The dimensionless jet-to-plate distance(H/D)was 0.2,and non-dimensional nozzle-to-nozzle spacing(S/D)was 3,4,5 and 6,respectively.It is found that the quenching time is shortened at a constant total mass flow at air jet inlet m·(m·=218.21 kg/h),and the heat transfer uniformity is deterio-rated as S/D increases.However,the adding reversed-flow nozzles can shorten the quenching time of the glass plate considerably with a modest change in the heat transfer uniformity.The results at variable m·are the same as those at a fixed m·.Furthermore,the parity and arrangement of nozzles are also discussed,It is found that an odd number of nozzles is more beneficial for transient heat transfer.Based on these results,an appropriate proposal for ultra-thin glass tempering process is presented.展开更多
This paper studies the four-engine liquid rocket flow field during the launching phase.Using threedimensional compressible Navier-Stokes equations and two-equation realizable k-epsilon turbulence model,an impact model...This paper studies the four-engine liquid rocket flow field during the launching phase.Using threedimensional compressible Navier-Stokes equations and two-equation realizable k-epsilon turbulence model,an impact model is established and flow fields of plume impinging on the two different shapes of flame deflectors,including wedge-shaped flame deflector and cone-shaped flame deflector,are calculated.The finite-rate chemical kinetics is used to track chemical reactions.The simulation results show that afterburning mainly occurs in the mixed layer.And the region of peak pressure occurs directly under the rocket nozzle,which is the result of the direct impact of exhaust plume.Compared with the wedgeshaped flame deflector,the cone-shaped flame deflector has great performance on guiding exhaust gas.The wedge-shaped and cone-shaped flame deflectors guide the supersonic exhaust plume away from the impingement point with two directions and circumferential direction,respectively.The maximum pressure and temperature on the wedge-shaped flame deflector surface are 37.2%and 9.9%higher than those for the cone-shaped flame deflector.The results provide engineering guidance and theoretical significance for design in flame deflector of the launch platforms.展开更多
The mixing time of impact zone in liquid-continuous impinging streams reactor(LISR) is theoretically calculated by empirical model and modern micromixing model of the fluid mixing process, and the variation laws of ma...The mixing time of impact zone in liquid-continuous impinging streams reactor(LISR) is theoretically calculated by empirical model and modern micromixing model of the fluid mixing process, and the variation laws of macromixing time and micromixing time are quantitatively discussed. The results show that under a continuous and stable operating condition, as the paddle speed increases, the macromixing time and micromixing time calculated by the two models both decrease, even in a linkage equilibrium state. Simultaneously, as the paddle speed increases, the results figured by the two models tend to be consistent. It indicates that two models both are more suitable for calculation of mixing time in high paddle speed. Compared with the existing experimental results of this type of reactor, the mixing time computed in the speed of 1500 r/min is closer to it. These conclusions can provide an important reference for systematically studying the strengthening mechanism of LISR under continuous mixing conditions.展开更多
To further extend knowledge about the detailed knowledge on the crossflow characteristics in a multi-jets system under a confined space,particle image velocimetry (PIV) was employed to investigate the flow structures ...To further extend knowledge about the detailed knowledge on the crossflow characteristics in a multi-jets system under a confined space,particle image velocimetry (PIV) was employed to investigate the flow structures together with the distributions of the mean velocity components for Reynolds numbers (Re) ranging from 6 213 to 13 418,nozzle-to-plate spacing (H/D) varying from 0. 20 to1. 25,respectively. Results show that the crossflow configuration is significantly different from those of large nozzle-to-plate spacing. In addition,a turning point H/D=0.50 is revealed in the profile of the normalized maximum radial velocity which is associated with the heat transfer distribution on the impingement plate.展开更多
Phosphor yttrium aluminum garnet Y3A15O12 （YAG）, activated with trivalent cerium （Ce^3＋）, was synthesized by T-tube impinging streams, T-type vortex impinging streams co-precipitation method （IS-CP） and direct ...Phosphor yttrium aluminum garnet Y3A15O12 （YAG）, activated with trivalent cerium （Ce^3＋）, was synthesized by T-tube impinging streams, T-type vortex impinging streams co-precipitation method （IS-CP） and direct co-precipitation method （D-CP）, respectively. The crystallization, morphologies, particle size and particle size distribution of the phosphors obtained under different experimental conditions were studied. The influence of various factors on the luminescence intensity of the phosphor was also investigated, such as feeding methods, volume flow rate, contents of Ce and initial reactant concentration. The results show that the precursors synthesized by T-tube impinging streams co-precipitation reaction transform to Y3A15O12 （YAG） phosphor at about 1 000 ℃. The particles are far smaller and narrower than those prepared by D-CP. In the impinging streams co-precipitation system, the luminescent intensity of YAG：Ce phosphor increases with the increase of liquid flow rate. The intensity firstly increases then decreases with the increasing Ce^3＋ doping content, and the maximum intensity is shown at 1.67% （molar fraction） Ce. Luminescent intensity gradually decreases with the increase of initial concentration of reactants. At the same operational condition, the luminescent intensity of the phosphors prepared by T-tube impinging streams reactor is higher than that by D-CP, and the luminescent intensity of the phosphors prepared by T-type vortex impinging streams is higher than that by T-tube impinging streams reactor.展开更多
A numerical study was conducted to seek an optimized dimension of jet chamber in the pulsating impinging flow.The flow and heat transfer effect of the pulsation flow through a jet chamber was investigated.The numerica...A numerical study was conducted to seek an optimized dimension of jet chamber in the pulsating impinging flow.The flow and heat transfer effect of the pulsation flow through a jet chamber was investigated.The numerical results indicate that heat transfer effective enhances near the stagnation region for the intermittent pulsed flow with jet chamber compared to that without jet chamber.Simulations of the flow through a jet chamber show that the heat transfer rate on the impingement surface is highly dependent on the velocity at the position which is really close to target surface.Examination of the velocity field suggests that the velocity exists a maximum value as the axis distance increases.In addition,the velocity at the jet hole is enlarged by the jet chamber due to the entrainment effect,and the velocity is amplified even greater as the size of the jet chamber becomes bigger.Nevertheless,the velocity declines quickly while the flow axis distance is more than a certain range,leading to poor heat transfer.Thus,intermittent pulsed flow with jet chamber is suggested as a method of improving heat transfer by employing larger dimensions of jet chamber for appropriate jet-to-surface spacing.展开更多
The method of numerical simulation was applied to investigate the effects of jet impinging plate thickness and its thermal conductivity on the local heat flux distribution along the impinging plate. The results show t...The method of numerical simulation was applied to investigate the effects of jet impinging plate thickness and its thermal conductivity on the local heat flux distribution along the impinging plate. The results show that the two factors have great effects on the heat flux distribution. The non-uniformity of the local heat-flux on the impinging plate surface gets more profound as the plate becomes thicker and thermal conductivity gets larger. When Reynolds number is 5000, the ratio of nozzle-to-plate spacing to nozzle diameter is 5 and thermal conductivity is 16W/(m·K), and even for the plate with only 25μm in thickness, the non-uniformity of the heat flux cannot be neglected. When the plate thickness is 50 μm, only when thermal conductivity is as small as 1W/(m·K), the heat flux curve can be approximately treated as an iso-heat-flux boundary. In the experimental research, a real non-iso-heat-flux boundary is treated as an iso-heat-flux boundary, which would result in under-estimated Nusselt number value in the stagnation zone and an over-estimated value outside. Such an experimental Nusselt number distribution is taken to evaluate turbulent model, and the conclusion would be drawn that the turbulent model over-predicts the stagnation heat transfer. This is one of the important reasons why many literatures reported that k-ε turbulent model dramatically over-predicts the impinging jet heat transfer in the stagnation region.展开更多
基金Projects(51205171,51376081)supported by the National Natural Science Foundation of ChinaProject(1201026B)supported by the Postdoctoral Science Foundation of Jiangsu Province,China
文摘At jet pressures ranging from 80 to 120 MPa, submerged water jets are investigated by numerical simulation and experiment. Numerical simulation enables a systematic analysis of major flow parameters such as jet velocity, turbulent kinetic energy as well as void fraction of cavitation. Experiments facilitate an objective assessment of surface morphology, micro hardness and surface roughness of the impinged samples. A comparison is implemented between submerged and non-submerged water jets. The results show that submerged water jet is characterized by low velocity magnitudes relative to non-submerged water jet at the same jet pressure. Shear effect serves as a key factor underlying the inception of cavitation in submerged water jet stream. Predicted annular shape of cavity zone is substantiated by local height distributions associated with experimentally obtained footprints. As jet pressure increases, joint contribution of jet kinetic energy and cavitation is demonstrated. While for non-submerged water jet, impingement force stems exclusively from flow velocity.
文摘The aim of this study is to examine the effects of local curvature and elastic wall effects of an isothermal hot wall for the purpose of jet impingement cooling performance.Finite element method was used with ALE.Different important parametric effects such as Re number(between 100 and 700),Ha number(between 0 and 20),elasticity(between 104 and 109),curvature of the surface(elliptic,radius ratio between 1 and 0.25) and nanoparticle volume fraction(between 0 and 0.05) on the cooling performance were investigated numerically.The results showed that the average Nu number enhances for higher Hartmann number,higher values of elastic modulus of partly flexible wall and higher nanoparticle volume fraction.When the magnetic field is imposed at the highest strength,there is an increase of3.85% in the average Nu for the curved elastic wall whereas it is 89.22% for the hot part above it,which is due to the vortex suppression effects.Nanoparticle inclusion in the base fluid improves the heat transfer rate by about 27.6% in the absence of magnetic field whereas it is 20.5% under the effects of magnetic field at Ha=20.Curvature effects become important for higher Re numbers and at Re=700,there is 14.11% variation in the average Nu between the cases with the lowest and highest radius ratio.The elastic wall effects on the heat transfer are reduced with the increased curvature of the bottom wall.
基金Natural Science Foundation of China(51335002,51905049)。
文摘Numerical studies on transient heat transfer characteristics of air-array-jet impingement with a small jet-to-plate distance and a large temperature difference between nozzles and plate were presented.The dimensionless jet-to-plate distance(H/D)was 0.2,and non-dimensional nozzle-to-nozzle spacing(S/D)was 3,4,5 and 6,respectively.It is found that the quenching time is shortened at a constant total mass flow at air jet inlet m·(m·=218.21 kg/h),and the heat transfer uniformity is deterio-rated as S/D increases.However,the adding reversed-flow nozzles can shorten the quenching time of the glass plate considerably with a modest change in the heat transfer uniformity.The results at variable m·are the same as those at a fixed m·.Furthermore,the parity and arrangement of nozzles are also discussed,It is found that an odd number of nozzles is more beneficial for transient heat transfer.Based on these results,an appropriate proposal for ultra-thin glass tempering process is presented.
文摘This paper studies the four-engine liquid rocket flow field during the launching phase.Using threedimensional compressible Navier-Stokes equations and two-equation realizable k-epsilon turbulence model,an impact model is established and flow fields of plume impinging on the two different shapes of flame deflectors,including wedge-shaped flame deflector and cone-shaped flame deflector,are calculated.The finite-rate chemical kinetics is used to track chemical reactions.The simulation results show that afterburning mainly occurs in the mixed layer.And the region of peak pressure occurs directly under the rocket nozzle,which is the result of the direct impact of exhaust plume.Compared with the wedgeshaped flame deflector,the cone-shaped flame deflector has great performance on guiding exhaust gas.The wedge-shaped and cone-shaped flame deflectors guide the supersonic exhaust plume away from the impingement point with two directions and circumferential direction,respectively.The maximum pressure and temperature on the wedge-shaped flame deflector surface are 37.2%and 9.9%higher than those for the cone-shaped flame deflector.The results provide engineering guidance and theoretical significance for design in flame deflector of the launch platforms.
基金Project(51276131)supported by the National Natural Science Foundation of ChinaProject(ZRZ0316)supported by the Natural Science Foundation of Hubei Province,ChinaProject(2013070104010025)supported by the Morning Glory Project of Wuhan Science and Technology Bureau,China
文摘The mixing time of impact zone in liquid-continuous impinging streams reactor(LISR) is theoretically calculated by empirical model and modern micromixing model of the fluid mixing process, and the variation laws of macromixing time and micromixing time are quantitatively discussed. The results show that under a continuous and stable operating condition, as the paddle speed increases, the macromixing time and micromixing time calculated by the two models both decrease, even in a linkage equilibrium state. Simultaneously, as the paddle speed increases, the results figured by the two models tend to be consistent. It indicates that two models both are more suitable for calculation of mixing time in high paddle speed. Compared with the existing experimental results of this type of reactor, the mixing time computed in the speed of 1500 r/min is closer to it. These conclusions can provide an important reference for systematically studying the strengthening mechanism of LISR under continuous mixing conditions.
基金National Natural Science Foundation of China(51335002)
文摘To further extend knowledge about the detailed knowledge on the crossflow characteristics in a multi-jets system under a confined space,particle image velocimetry (PIV) was employed to investigate the flow structures together with the distributions of the mean velocity components for Reynolds numbers (Re) ranging from 6 213 to 13 418,nozzle-to-plate spacing (H/D) varying from 0. 20 to1. 25,respectively. Results show that the crossflow configuration is significantly different from those of large nozzle-to-plate spacing. In addition,a turning point H/D=0.50 is revealed in the profile of the normalized maximum radial velocity which is associated with the heat transfer distribution on the impingement plate.
基金Project(200805330032)supported by the Natural Educative Doctoral Foundation of ChinaProjects(20080440987,200902475)supported by the China Postdoctoral Science Foundation
文摘Phosphor yttrium aluminum garnet Y3A15O12 （YAG）, activated with trivalent cerium （Ce^3＋）, was synthesized by T-tube impinging streams, T-type vortex impinging streams co-precipitation method （IS-CP） and direct co-precipitation method （D-CP）, respectively. The crystallization, morphologies, particle size and particle size distribution of the phosphors obtained under different experimental conditions were studied. The influence of various factors on the luminescence intensity of the phosphor was also investigated, such as feeding methods, volume flow rate, contents of Ce and initial reactant concentration. The results show that the precursors synthesized by T-tube impinging streams co-precipitation reaction transform to Y3A15O12 （YAG） phosphor at about 1 000 ℃. The particles are far smaller and narrower than those prepared by D-CP. In the impinging streams co-precipitation system, the luminescent intensity of YAG：Ce phosphor increases with the increase of liquid flow rate. The intensity firstly increases then decreases with the increasing Ce^3＋ doping content, and the maximum intensity is shown at 1.67% （molar fraction） Ce. Luminescent intensity gradually decreases with the increase of initial concentration of reactants. At the same operational condition, the luminescent intensity of the phosphors prepared by T-tube impinging streams reactor is higher than that by D-CP, and the luminescent intensity of the phosphors prepared by T-type vortex impinging streams is higher than that by T-tube impinging streams reactor.
基金Project(51306088)supported by the National Natural Science Foundation of ChinaProject(NJ20160039)supported by the Fundamental Research Funds for the Central Universities,China
文摘A numerical study was conducted to seek an optimized dimension of jet chamber in the pulsating impinging flow.The flow and heat transfer effect of the pulsation flow through a jet chamber was investigated.The numerical results indicate that heat transfer effective enhances near the stagnation region for the intermittent pulsed flow with jet chamber compared to that without jet chamber.Simulations of the flow through a jet chamber show that the heat transfer rate on the impingement surface is highly dependent on the velocity at the position which is really close to target surface.Examination of the velocity field suggests that the velocity exists a maximum value as the axis distance increases.In addition,the velocity at the jet hole is enlarged by the jet chamber due to the entrainment effect,and the velocity is amplified even greater as the size of the jet chamber becomes bigger.Nevertheless,the velocity declines quickly while the flow axis distance is more than a certain range,leading to poor heat transfer.Thus,intermittent pulsed flow with jet chamber is suggested as a method of improving heat transfer by employing larger dimensions of jet chamber for appropriate jet-to-surface spacing.
基金Project(50376076) supported by the National Natural Science Foundation of China
文摘The method of numerical simulation was applied to investigate the effects of jet impinging plate thickness and its thermal conductivity on the local heat flux distribution along the impinging plate. The results show that the two factors have great effects on the heat flux distribution. The non-uniformity of the local heat-flux on the impinging plate surface gets more profound as the plate becomes thicker and thermal conductivity gets larger. When Reynolds number is 5000, the ratio of nozzle-to-plate spacing to nozzle diameter is 5 and thermal conductivity is 16W/(m·K), and even for the plate with only 25μm in thickness, the non-uniformity of the heat flux cannot be neglected. When the plate thickness is 50 μm, only when thermal conductivity is as small as 1W/(m·K), the heat flux curve can be approximately treated as an iso-heat-flux boundary. In the experimental research, a real non-iso-heat-flux boundary is treated as an iso-heat-flux boundary, which would result in under-estimated Nusselt number value in the stagnation zone and an over-estimated value outside. Such an experimental Nusselt number distribution is taken to evaluate turbulent model, and the conclusion would be drawn that the turbulent model over-predicts the stagnation heat transfer. This is one of the important reasons why many literatures reported that k-ε turbulent model dramatically over-predicts the impinging jet heat transfer in the stagnation region.
