This paper presents a frame figure of the recovery system concerning waste heat of steam condensate. When steam phase changes into liquid state in the condenser, the heat equilibium equation, gas state equation, mass ...This paper presents a frame figure of the recovery system concerning waste heat of steam condensate. When steam phase changes into liquid state in the condenser, the heat equilibium equation, gas state equation, mass flow calculating equation of the jet steam and incondensable gas equation are established. The coupling function between condensate unit and recovery pump of the hot condensate with ejector is studied. The paper sets up the fluid continuity equation, heat equilibium equation and efficiency equation of the ejector and points out the technical key how the prevent hot condensate change into steam phase. When fluid passes from circulation loop through pump to export, the energy equations are obtained here. At last, signal figure of the applied examples are given and settle the techanical questions of the jet system are discussed.展开更多
Walled-off pancreatic necrosis and a pancreatic abscess are the most severe complications of acute pancreatitis. Surgery in such critically ill patients is often associated with significant morbidity and mortality wit...Walled-off pancreatic necrosis and a pancreatic abscess are the most severe complications of acute pancreatitis. Surgery in such critically ill patients is often associated with significant morbidity and mortality within the first few weeks after the onset of symptoms. Minimal invasive approaches with high success and low mortality rates are therefore of considerable interest. Endoscopic therapy has the potential to offer safe and effective alternative treatment. We report here on 3 consecutive patients with infected walled-off pancreatic necrosis and 1 patient with a pancreatic abscess who underwent direct endoscopic necrosectomy 19-21 d after the onset of acute pancreatitis. The infected pancreatic necrosis or abscess was punctured transluminally with a cystostome and, after balloon dilatation, a non-covered self-expanding biliary metal stent was placed into the necrotic cavity. Following stent deployment, a nasobiliary pigtail catheter was placed into the cavity to ensure continuous irrigation. After 5-7 d, the metal stent was removed endoscopically and the necrotic cavity was entered with a therapeutic gastroscope. Endoscopic debridement was performed via the simultaneous application of a high-flow water-jet system; using a flush knife, a Dormia basket, and hot biopsy forceps. The transluminal endotherapy was repeated 2-5 times daily during the next 10 d. Supportive care included parenteral antibiotics and jejunal feeding. All patients improved dramatically and with resolution of their septic conditions; 3 patients were completely cured without any further complications or the need for surgery. One patient died from a complication of prolonged ventilation severe bilateral pneumonia, not related to the endoscopic procedure. No procedure related complications were observed. Transluminal endoscopic necrosectomy with temporary application of a self-expanding metal stent and a high-flow water-jet system shows promise for enhancing the potential of this endoscopic approach in patients with walled-off pancreatic necrosis and/or a pancreatic abscess.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
BACKGROUND Several methods,such as finger fracture,Pean crush,cavitron ultrasonic surgical aspirator(CUSA),and water jet(WJ),are used for hepatic parenchymal dissection in liver surgery.CUSA is the conventional method...BACKGROUND Several methods,such as finger fracture,Pean crush,cavitron ultrasonic surgical aspirator(CUSA),and water jet(WJ),are used for hepatic parenchymal dissection in liver surgery.CUSA is the conventional method in Japan.WJ is a relatively novel method for parenchymal dissection.Although it has several advantages,such as lower volume of blood loss and shorter operative time,the effect of the WJ system for hepatic dissection on the remnant liver has not yet been investigated.AIM To investigate and compare the effect of the WJ method vs CUSA on the remnant liver cut surface.METHODS This observational study compared the two types of parenchymal transection methods(WJ vs CUSA)in liver surgery.In total,24 and 40 patients who underwent hepatectomy using the WJ method and CUSA,respectively,were included in the analysis.Accordingly,the clinicopathological characteristics and clinical outcomes of 24 and 40 patients were compared.Furthermore,postoperative contrast-enhanced computed tomography(CT)scan was performed to assess the cut surface length of the remnant liver and the degenerative thickness of the areas with a reduced contrast effect in the dissected plane.Then,the two groups were compared.RESULTS On CT scan,the median areas of denaturation in the liver dissection planes were 522(range:109.5-1242)mm^(2) in the CUSA group and 324(range:93.6-1529)mm^(2) in the WJ group.The area did not significantly differ between the two groups;however,the denaturation thickness of the WJ group was significantly lower than that of the CUSA group[5.8(range:0.7-11.1)mm vs 3.3(range:1.7-10.4)mm,P<0.001].CONCLUSION The WJ group had significantly thinner contrast-enhanced areas in the post hepatectomy detached section than the CUSA group.展开更多
To analyze the errors of processing data, the testing principle for jet elements is introduced and the property of testing system is theoretically and experimentally studied. On the basis of the above, the method of p...To analyze the errors of processing data, the testing principle for jet elements is introduced and the property of testing system is theoretically and experimentally studied. On the basis of the above, the method of processing data is presented and the error formulae, which are the functions of the testing system property, are derived. Finally, the methods of reducing the errors are provided. The measured results are in correspondence with the theoretical conclusion.展开更多
To study the draft sensation distribution of an air jet supply system in a large space building in summer,experiments are conducted in a large laboratory.The temperature,velocity and draft sensation distributions at a...To study the draft sensation distribution of an air jet supply system in a large space building in summer,experiments are conducted in a large laboratory.The temperature,velocity and draft sensation distributions at a nozzle height of 4 m in the occupied zone are obtained.Then,the numerical simulation under the test condition is carried out by the computational fluid dynamics（CFD）method.The calculation results of the indoor vertical temperature and the draft sensation distribution are validated by the test data.Simulations with different nozzle heights are conducted.The satisfactory air supply condition is determined by analyzing the draft sensations and the temperatures in the occupied zone under three conditions.The simulation results show that the optimal draft sensation distribution and the uniform temperature and velocity fields can be obtained at a nozzle height of 5 m.展开更多
Based on the two existing abrasive water-jet（AWJ） systems, the dia-jet （or pre-jet） and the post-jet, a new type of abrasive water-jet system is put forward, which combines the dia-jet＇s advantage, low operating ...Based on the two existing abrasive water-jet（AWJ） systems, the dia-jet （or pre-jet） and the post-jet, a new type of abrasive water-jet system is put forward, which combines the dia-jet＇s advantage, low operating system pressure, slender stream jet, and more concentrative abrasive in the blended stream, with merits of post-jet, the less sophisticate apparatus, successive supply of abrasives. The theoretic analysis is brought out in detail, and the nozzle system structure is concisely illustrated. Its relevant experiment results are demonstrated, proving that this new system is effective in various aspects, enlarging penetrating capability without raising system pressure, saving machining power supply, lessening energy loss, etc.展开更多
This paper focuses on the usage of the forward-facing cavity and opposing jet combinatorial configuration as the thermal protection system （TPS） for hypersonic vehicles. A hemispherecone nose-tip with the combinator...This paper focuses on the usage of the forward-facing cavity and opposing jet combinatorial configuration as the thermal protection system （TPS） for hypersonic vehicles. A hemispherecone nose-tip with the combinatorial configuration is investigated numerically in hypersonic free stream. Some numerical results are validated by experiments. The flow field parameters, aerodynamic force and surface heat flux distribution are obtained. The influence of the opposing jet stagnation pressure on cooling efficiency of the combinatorial TPS is discussed. The detailed numerical results show that the aerodynamic heating is reduced remarkably by the combinatorial system. The recirculation region plays a pivotal role for the reduction of heat flux. The larger the stagnation pressure of opposing jet is, the more the heating reduction is. This kind of combinatorial system is suitable to be the TPS for the high-speed vehicles which need long-range and long time flight.展开更多
The three-dimensional Navier Stokes equation and the k-ε viscous model are used to simulate the attack angle characteristics of a hemisphere nose-tip with an opposing jet thermal protection system in supersonic flow ...The three-dimensional Navier Stokes equation and the k-ε viscous model are used to simulate the attack angle characteristics of a hemisphere nose-tip with an opposing jet thermal protection system in supersonic flow conditions. The numerical method is validated by the relevant experiment. The flow field parameters, aerodynamic forces, and surface heat flux distributions for attack angles of 0°, 2°, 5°, 7°, and 10° are obtained. The detailed numerical results show that the cruise attack angle has a great influence on the flow field parameters, aerodynamic force, and surface heat flux distribution of the supersonic vehicle nose-tip with an opposing jet thermal protection system. When the attack angle reaches 10°, the heat flux on the windward generatrix is close to the maximal heat flux on the wall surface of the nose-tip without thermal protection system, thus the thermal protection has failed.展开更多
In this paper, a Non-Ablative Thermal Protection System(NATPS) with the spiked body and the opposing jet combined configuration is proposed to reduce the aerodynamic heating of the hypersonic vehicle, and the coupled ...In this paper, a Non-Ablative Thermal Protection System(NATPS) with the spiked body and the opposing jet combined configuration is proposed to reduce the aerodynamic heating of the hypersonic vehicle, and the coupled fluid-thermal numerical analysis is performed to study the thermal control performance of the NATPS. The results show that the spiked body pushes the bow shock away from the protected structure and thus reduces the shock intensity and the wall heat flux. In addition, the low temperature gas of the opposing jet separates the high temperature gas behind the shock from the nose cone of the spiked body, ensuring the non-ablative property of the spiked body. Therefore, the NATPS reduces the aerodynamic heating by the reconfiguration of the flow field, and the thermal control efficiency of the system is better than the Thermal Protection System(TPS) with the single spiked body and the single opposing jet. The influencing factors of the NATPS are analyzed. Both increasing the length of the spiked body and reducing the total temperature of the opposing jet can improve the thermal control performance of the NATPS and the nonablative property of the spiked body. However, increasing the heat conductivity coefficient of the spiked body can enhance benefit the non-ablative property of the spiked body, but has little influence on the thermal control performance of the NATPS.展开更多
The multiple jets impingement heat transfer is widely applied in the wing anti-icing system.It is challenging to apply the similarity criterion to carry out the anti-icing experiments due to the complex flow and heat ...The multiple jets impingement heat transfer is widely applied in the wing anti-icing system.It is challenging to apply the similarity criterion to carry out the anti-icing experiments due to the complex flow and heat transfer behavior.In the present study,the full-scale slat model is used to carry out anti-icing experimental researches in a 2 m×3 m icing wind tunnel of China Aerodynamics Research and Development Center.The effects of icing parameters Liquid Water Content(LWC)and Median Volume Diameter(MVD)and hot air parameters(mass flow rate and temperature)on the thermal performance of an inner-liner anti-icing system with jets impingement heat transfer are studied.The effects of the experimental parameters are analyzed in detail by combining impingement and evaporation heat transfer mechanisms.The impingement hot air mass flow rate dramatically affects the heat transfer performance of the impingement stagnation region within the range of the experimental parameters.The temperature of impingement hot air and that of wing skin are approximately linear correlated.The experimental results show the effects of LWC and MVD on water film formation and runback ice accretion.The formation of water film is analyzed by an analytical method based on the wing skin temperature difference of dry and wet air conditions.展开更多
A CFD code has been developed based on the conservation principles describing gas and solid flow in fluidized beds. This code is employed to simulate not only the spatiotemporal gas and solid phase velocities and v...A CFD code has been developed based on the conservation principles describing gas and solid flow in fluidized beds. This code is employed to simulate not only the spatiotemporal gas and solid phase velocities and voidage profiles in a two dimensional bed but also fluid dynamics in the jet region. The computational results show that gas flow direction is upward in the entire bed accompanied with random local circulations, whilst solid flow direction is upward at the center and downward near the wall. The radical reason of strong back mixing of solid particles and good transfer behavior between two phases is that the jet entrains solid particles. Numerical calculation indicates that gas velocity, solid velocity and pressure profile have a significant change when the voidage is 0 8. The simulated time averaged voidage profiles agree with the experimental results and simulated data reported by Gidaspow and Ettehadieh(1983). Therefore, CFD model can be regarded as a useful tool to study the jet characteristics in dense gas solid fluidized beds.展开更多
This paper used optical emission spectroscopy （OES） to study the gas phase in high power DC arc plasma jet chemical vapour deposition （CVD） during diamond films growth processes. The results show that all the depo...This paper used optical emission spectroscopy （OES） to study the gas phase in high power DC arc plasma jet chemical vapour deposition （CVD） during diamond films growth processes. The results show that all the deposition parameters （methane concentration, substrate temperature, gas flow rate and ratio of H2/Ar） could strongly influence the gas phase. C2 is found to be the most sensitive radical to deposition parameters among the radicals in gas phase. Spatially resolved OES implies that a relative high concentration of atomic H exists near the substrate surface, which is beneficial for diamond film growth. The relatively high concentrations of C2 and CH are correlated with high deposition rate of diamond. In our high deposition rate system, C2 is presumed to be the main growth radical, and CH is also believed to contribute the diamond deposition.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
Flow separation is typically an undesirable phenomenon, and boundary layer control is an important technique for the separation problems on airfoils. The synthetic jet actuator is considered as a promising candidate f...Flow separation is typically an undesirable phenomenon, and boundary layer control is an important technique for the separation problems on airfoils. The synthetic jet actuator is considered as a promising candidate for flow control applications because of its compact nature and ability to generate momentum without the need for fluidic plumbing. In the present study, an active separation control system using synthetic jets is proposed and practically applied to the stall control of the NACA0012 airfoil in a wind tunnel test. In our proposed system, the flow conditions (stalled or unstalled) can be judged by calculating from two static pressure holes on the airfoil upper surface alone. The experimental results indicate that the maximum lift coefficient increases by 11% and the stall angle rises by 4°in contrast to the case under no control. It is confirmed that our proposed system can suppress the stall on the NACA0012 airfoil and that the aerodynamic performance of the airfoil can be enhanced. The proposed system can also be operated prior to the onset of stall. Therefore, separation control is always attained with no stall for all flow fields produced by changing the angle of attack that were examined.展开更多
For achieving optimized jet grout parameters and W/C ratio it is concluded to set trial tests in constant local soil as the conclusion depends on local soil and presence of the extensive range of the effective paramet...For achieving optimized jet grout parameters and W/C ratio it is concluded to set trial tests in constant local soil as the conclusion depends on local soil and presence of the extensive range of the effective parameters. Considering the benefits, due to abundance of the involved variables and the intrinsic geological complexity, this system follows a great expense in the trial and implementation phases. Utilizing the soft computing methods, this paper proposes a new approach to reduce or to eliminate the cost of the trial phase. Therefore, the Adaptive Neuro Fuzzy Inference System (ANFIS) was utilized to study the possibility of anticipating the diameter of the jet grout (Soilcrete) columns on the trial phase based on the Trial and Error procedure. Data were collected from several projects and formed three sets of data. Consequently, parameters were held constant (as input) and the diameters of the Soilcrete columns were recorded (as output). To increase the precision, aforementioned data sets were combined and ten different data sets were created and studied, with all the results being assessed in two different approaches. Accordingly, Gaussian Function results in a huge number of precise and acceptable outcomes among available functions. Based on the measurements, Gaussian Function achieves the values of the R which are frequently more than 0.8 and lower values of the RMSE. Therefore, utilizing Gaussian Function, mainly a congruent relation between the R and RMSE is experienced and it leads to close proximity of the actual and predicted values of the Soilcrete diameter.展开更多
An experimental investigation of the jet nanofluids impingement heat transfer characteristics of mini-channel heat sink for cooling computer processing unit of personal computer is performed. The experiments are teste...An experimental investigation of the jet nanofluids impingement heat transfer characteristics of mini-channel heat sink for cooling computer processing unit of personal computer is performed. The experiments are tested under the real personal computer operating conditions: no load and full load conditions. The experiments are performed for the following ranges of the parameters: coolant flow rate varies from 0.008 to 0.020 kg/s, the nozzle diameter is set to 1.00, 1.40, 1.80 mm, the distance nozzle-to-fins tip is 2.00 mm, the channel width of the mini-channel heat sink is 1.00 mm. The nanofluids with suspending of TiO2 particles in base fluid are used as a working fluids. It was observed that the average CPU temperatures obtained from the jet nanofluids impingement cooling system are 3.0%, 6.25% lower than those from the jet liquid impingement and from the conventional liquid cooling systems, respectively. However, this cooling system requires higher energy consumption.展开更多
A jet noise reduction technique by using the external chevron nozzle with lobed mixer in the double-mixing exhaust system is investigated under cold conditions.The computations of jet field and the experiments of nois...A jet noise reduction technique by using the external chevron nozzle with lobed mixer in the double-mixing exhaust system is investigated under cold conditions.The computations of jet field and the experiments of noise field are conducted with scaled model of high-bypass-ratio turbofan engine mixing exhaust system composed of external chevron nozzle with lobed mixer.The computational results indicate that comparing with the baseline nozzle with lobed mixer,the external chevron nozzle with lobed mixer increases mixing of jet and ambient air near the nozzle exit.The experimental results show that the external chevron nozzle with lobed mixer has better jet noise reduction at low frequencies,and this reduction rises with the increase of chevron bend angle.The experimental results also show that the external chevron nozzle with lobed mixer has sound pressure level(SPL)increase which is not obvious at high frequencies.With chevron bend angle increasing,SPL has relatively marked increase at 60°(directivity angle measured from upstream jet axis)and little fluctuations at 90°and 150°.The external chevron nozzle with lobed mixer has overall sound pressure level(OASPL)reduction in varying degrees at 60°and 150°,but it has little OASPL increase at 90°.展开更多
Recently,there has been an investigation of polishing processes that has considered new ultra-precision polishing technology for micro parts and optical parts such as those with aspheric and complex shapes.One suitabl...Recently,there has been an investigation of polishing processes that has considered new ultra-precision polishing technology for micro parts and optical parts such as those with aspheric and complex shapes.One suitable means of polishing complex shapes is to use a jet of abrasive fluid.However,aerodynamic disturbances and radial spreading are generated by the unstable polishing process of the jet on the surface of the workpiece when it is being polished.A method of jet stabilization has been proposed in which the original nozzle form of a jet of magnetorheological(MR)fluid contains abrasive particles that are magnetized using a magnetic.This paper details the design of an MR jet polishing system that uses an electromagnet,a nozzle,and a hydraulic unit to stabilize a slurry jet based on MR fluid, Second,for silica glass,the polishing spot and section profile are analyzed and the effect of the MR fluid jet polishing process is evaluated.The results of the experiment show that the removal profile is W-shaped and that,in this case,a stable can be proof of a distance of several tens of millimeters from the nozzle.Such results show the possibility of applying the proposed polishing method using MR fluids in ultra-precision micro and optical parts production processes. MR jet polishing shows great potential for use as a new type of precision surface polishing technology.In particular,this is a highly valuable process for the polishing of complex shapes such as micro parts,concaves parts,and cavities.展开更多
文摘This paper presents a frame figure of the recovery system concerning waste heat of steam condensate. When steam phase changes into liquid state in the condenser, the heat equilibium equation, gas state equation, mass flow calculating equation of the jet steam and incondensable gas equation are established. The coupling function between condensate unit and recovery pump of the hot condensate with ejector is studied. The paper sets up the fluid continuity equation, heat equilibium equation and efficiency equation of the ejector and points out the technical key how the prevent hot condensate change into steam phase. When fluid passes from circulation loop through pump to export, the energy equations are obtained here. At last, signal figure of the applied examples are given and settle the techanical questions of the jet system are discussed.
文摘Walled-off pancreatic necrosis and a pancreatic abscess are the most severe complications of acute pancreatitis. Surgery in such critically ill patients is often associated with significant morbidity and mortality within the first few weeks after the onset of symptoms. Minimal invasive approaches with high success and low mortality rates are therefore of considerable interest. Endoscopic therapy has the potential to offer safe and effective alternative treatment. We report here on 3 consecutive patients with infected walled-off pancreatic necrosis and 1 patient with a pancreatic abscess who underwent direct endoscopic necrosectomy 19-21 d after the onset of acute pancreatitis. The infected pancreatic necrosis or abscess was punctured transluminally with a cystostome and, after balloon dilatation, a non-covered self-expanding biliary metal stent was placed into the necrotic cavity. Following stent deployment, a nasobiliary pigtail catheter was placed into the cavity to ensure continuous irrigation. After 5-7 d, the metal stent was removed endoscopically and the necrotic cavity was entered with a therapeutic gastroscope. Endoscopic debridement was performed via the simultaneous application of a high-flow water-jet system; using a flush knife, a Dormia basket, and hot biopsy forceps. The transluminal endotherapy was repeated 2-5 times daily during the next 10 d. Supportive care included parenteral antibiotics and jejunal feeding. All patients improved dramatically and with resolution of their septic conditions; 3 patients were completely cured without any further complications or the need for surgery. One patient died from a complication of prolonged ventilation severe bilateral pneumonia, not related to the endoscopic procedure. No procedure related complications were observed. Transluminal endoscopic necrosectomy with temporary application of a self-expanding metal stent and a high-flow water-jet system shows promise for enhancing the potential of this endoscopic approach in patients with walled-off pancreatic necrosis and/or a pancreatic abscess.
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BACKGROUND Several methods,such as finger fracture,Pean crush,cavitron ultrasonic surgical aspirator(CUSA),and water jet(WJ),are used for hepatic parenchymal dissection in liver surgery.CUSA is the conventional method in Japan.WJ is a relatively novel method for parenchymal dissection.Although it has several advantages,such as lower volume of blood loss and shorter operative time,the effect of the WJ system for hepatic dissection on the remnant liver has not yet been investigated.AIM To investigate and compare the effect of the WJ method vs CUSA on the remnant liver cut surface.METHODS This observational study compared the two types of parenchymal transection methods(WJ vs CUSA)in liver surgery.In total,24 and 40 patients who underwent hepatectomy using the WJ method and CUSA,respectively,were included in the analysis.Accordingly,the clinicopathological characteristics and clinical outcomes of 24 and 40 patients were compared.Furthermore,postoperative contrast-enhanced computed tomography(CT)scan was performed to assess the cut surface length of the remnant liver and the degenerative thickness of the areas with a reduced contrast effect in the dissected plane.Then,the two groups were compared.RESULTS On CT scan,the median areas of denaturation in the liver dissection planes were 522(range:109.5-1242)mm^(2) in the CUSA group and 324(range:93.6-1529)mm^(2) in the WJ group.The area did not significantly differ between the two groups;however,the denaturation thickness of the WJ group was significantly lower than that of the CUSA group[5.8(range:0.7-11.1)mm vs 3.3(range:1.7-10.4)mm,P<0.001].CONCLUSION The WJ group had significantly thinner contrast-enhanced areas in the post hepatectomy detached section than the CUSA group.
文摘To analyze the errors of processing data, the testing principle for jet elements is introduced and the property of testing system is theoretically and experimentally studied. On the basis of the above, the method of processing data is presented and the error formulae, which are the functions of the testing system property, are derived. Finally, the methods of reducing the errors are provided. The measured results are in correspondence with the theoretical conclusion.
基金The National Natural Science Foundation of China(No.50478113)the Leading Academic Discipline Project of Shanghai Municipal Education Commission(No.J50502)
文摘To study the draft sensation distribution of an air jet supply system in a large space building in summer,experiments are conducted in a large laboratory.The temperature,velocity and draft sensation distributions at a nozzle height of 4 m in the occupied zone are obtained.Then,the numerical simulation under the test condition is carried out by the computational fluid dynamics（CFD）method.The calculation results of the indoor vertical temperature and the draft sensation distribution are validated by the test data.Simulations with different nozzle heights are conducted.The satisfactory air supply condition is determined by analyzing the draft sensations and the temperatures in the occupied zone under three conditions.The simulation results show that the optimal draft sensation distribution and the uniform temperature and velocity fields can be obtained at a nozzle height of 5 m.
文摘Based on the two existing abrasive water-jet（AWJ） systems, the dia-jet （or pre-jet） and the post-jet, a new type of abrasive water-jet system is put forward, which combines the dia-jet＇s advantage, low operating system pressure, slender stream jet, and more concentrative abrasive in the blended stream, with merits of post-jet, the less sophisticate apparatus, successive supply of abrasives. The theoretic analysis is brought out in detail, and the nozzle system structure is concisely illustrated. Its relevant experiment results are demonstrated, proving that this new system is effective in various aspects, enlarging penetrating capability without raising system pressure, saving machining power supply, lessening energy loss, etc.
基金co-supported by National Natural Science Foundation of China (No. 90916018)Research Fund for the Doctoral Program of Higher Education of China (No.200899980006)
文摘This paper focuses on the usage of the forward-facing cavity and opposing jet combinatorial configuration as the thermal protection system （TPS） for hypersonic vehicles. A hemispherecone nose-tip with the combinatorial configuration is investigated numerically in hypersonic free stream. Some numerical results are validated by experiments. The flow field parameters, aerodynamic force and surface heat flux distribution are obtained. The influence of the opposing jet stagnation pressure on cooling efficiency of the combinatorial TPS is discussed. The detailed numerical results show that the aerodynamic heating is reduced remarkably by the combinatorial system. The recirculation region plays a pivotal role for the reduction of heat flux. The larger the stagnation pressure of opposing jet is, the more the heating reduction is. This kind of combinatorial system is suitable to be the TPS for the high-speed vehicles which need long-range and long time flight.
基金Project supported by the National Natural Science Foundation of China (Grant No. 90916018)the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 200899980006)the Natural Science Foundation of Hunan Province,China(Grant No. 09JJ3109)
文摘The three-dimensional Navier Stokes equation and the k-ε viscous model are used to simulate the attack angle characteristics of a hemisphere nose-tip with an opposing jet thermal protection system in supersonic flow conditions. The numerical method is validated by the relevant experiment. The flow field parameters, aerodynamic forces, and surface heat flux distributions for attack angles of 0°, 2°, 5°, 7°, and 10° are obtained. The detailed numerical results show that the cruise attack angle has a great influence on the flow field parameters, aerodynamic force, and surface heat flux distribution of the supersonic vehicle nose-tip with an opposing jet thermal protection system. When the attack angle reaches 10°, the heat flux on the windward generatrix is close to the maximal heat flux on the wall surface of the nose-tip without thermal protection system, thus the thermal protection has failed.
基金supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘In this paper, a Non-Ablative Thermal Protection System(NATPS) with the spiked body and the opposing jet combined configuration is proposed to reduce the aerodynamic heating of the hypersonic vehicle, and the coupled fluid-thermal numerical analysis is performed to study the thermal control performance of the NATPS. The results show that the spiked body pushes the bow shock away from the protected structure and thus reduces the shock intensity and the wall heat flux. In addition, the low temperature gas of the opposing jet separates the high temperature gas behind the shock from the nose cone of the spiked body, ensuring the non-ablative property of the spiked body. Therefore, the NATPS reduces the aerodynamic heating by the reconfiguration of the flow field, and the thermal control efficiency of the system is better than the Thermal Protection System(TPS) with the single spiked body and the single opposing jet. The influencing factors of the NATPS are analyzed. Both increasing the length of the spiked body and reducing the total temperature of the opposing jet can improve the thermal control performance of the NATPS and the nonablative property of the spiked body. However, increasing the heat conductivity coefficient of the spiked body can enhance benefit the non-ablative property of the spiked body, but has little influence on the thermal control performance of the NATPS.
基金co-supported by the National Numerical Wind Tunnel Project(No.NNW2018-ZT2B04)the “973”Program of China(No.2015CB755800)。
文摘The multiple jets impingement heat transfer is widely applied in the wing anti-icing system.It is challenging to apply the similarity criterion to carry out the anti-icing experiments due to the complex flow and heat transfer behavior.In the present study,the full-scale slat model is used to carry out anti-icing experimental researches in a 2 m×3 m icing wind tunnel of China Aerodynamics Research and Development Center.The effects of icing parameters Liquid Water Content(LWC)and Median Volume Diameter(MVD)and hot air parameters(mass flow rate and temperature)on the thermal performance of an inner-liner anti-icing system with jets impingement heat transfer are studied.The effects of the experimental parameters are analyzed in detail by combining impingement and evaporation heat transfer mechanisms.The impingement hot air mass flow rate dramatically affects the heat transfer performance of the impingement stagnation region within the range of the experimental parameters.The temperature of impingement hot air and that of wing skin are approximately linear correlated.The experimental results show the effects of LWC and MVD on water film formation and runback ice accretion.The formation of water film is analyzed by an analytical method based on the wing skin temperature difference of dry and wet air conditions.
文摘A CFD code has been developed based on the conservation principles describing gas and solid flow in fluidized beds. This code is employed to simulate not only the spatiotemporal gas and solid phase velocities and voidage profiles in a two dimensional bed but also fluid dynamics in the jet region. The computational results show that gas flow direction is upward in the entire bed accompanied with random local circulations, whilst solid flow direction is upward at the center and downward near the wall. The radical reason of strong back mixing of solid particles and good transfer behavior between two phases is that the jet entrains solid particles. Numerical calculation indicates that gas velocity, solid velocity and pressure profile have a significant change when the voidage is 0 8. The simulated time averaged voidage profiles agree with the experimental results and simulated data reported by Gidaspow and Ettehadieh(1983). Therefore, CFD model can be regarded as a useful tool to study the jet characteristics in dense gas solid fluidized beds.
文摘This paper used optical emission spectroscopy （OES） to study the gas phase in high power DC arc plasma jet chemical vapour deposition （CVD） during diamond films growth processes. The results show that all the deposition parameters （methane concentration, substrate temperature, gas flow rate and ratio of H2/Ar） could strongly influence the gas phase. C2 is found to be the most sensitive radical to deposition parameters among the radicals in gas phase. Spatially resolved OES implies that a relative high concentration of atomic H exists near the substrate surface, which is beneficial for diamond film growth. The relatively high concentrations of C2 and CH are correlated with high deposition rate of diamond. In our high deposition rate system, C2 is presumed to be the main growth radical, and CH is also believed to contribute the diamond deposition.
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.
文摘Flow separation is typically an undesirable phenomenon, and boundary layer control is an important technique for the separation problems on airfoils. The synthetic jet actuator is considered as a promising candidate for flow control applications because of its compact nature and ability to generate momentum without the need for fluidic plumbing. In the present study, an active separation control system using synthetic jets is proposed and practically applied to the stall control of the NACA0012 airfoil in a wind tunnel test. In our proposed system, the flow conditions (stalled or unstalled) can be judged by calculating from two static pressure holes on the airfoil upper surface alone. The experimental results indicate that the maximum lift coefficient increases by 11% and the stall angle rises by 4°in contrast to the case under no control. It is confirmed that our proposed system can suppress the stall on the NACA0012 airfoil and that the aerodynamic performance of the airfoil can be enhanced. The proposed system can also be operated prior to the onset of stall. Therefore, separation control is always attained with no stall for all flow fields produced by changing the angle of attack that were examined.
文摘For achieving optimized jet grout parameters and W/C ratio it is concluded to set trial tests in constant local soil as the conclusion depends on local soil and presence of the extensive range of the effective parameters. Considering the benefits, due to abundance of the involved variables and the intrinsic geological complexity, this system follows a great expense in the trial and implementation phases. Utilizing the soft computing methods, this paper proposes a new approach to reduce or to eliminate the cost of the trial phase. Therefore, the Adaptive Neuro Fuzzy Inference System (ANFIS) was utilized to study the possibility of anticipating the diameter of the jet grout (Soilcrete) columns on the trial phase based on the Trial and Error procedure. Data were collected from several projects and formed three sets of data. Consequently, parameters were held constant (as input) and the diameters of the Soilcrete columns were recorded (as output). To increase the precision, aforementioned data sets were combined and ten different data sets were created and studied, with all the results being assessed in two different approaches. Accordingly, Gaussian Function results in a huge number of precise and acceptable outcomes among available functions. Based on the measurements, Gaussian Function achieves the values of the R which are frequently more than 0.8 and lower values of the RMSE. Therefore, utilizing Gaussian Function, mainly a congruent relation between the R and RMSE is experienced and it leads to close proximity of the actual and predicted values of the Soilcrete diameter.
文摘An experimental investigation of the jet nanofluids impingement heat transfer characteristics of mini-channel heat sink for cooling computer processing unit of personal computer is performed. The experiments are tested under the real personal computer operating conditions: no load and full load conditions. The experiments are performed for the following ranges of the parameters: coolant flow rate varies from 0.008 to 0.020 kg/s, the nozzle diameter is set to 1.00, 1.40, 1.80 mm, the distance nozzle-to-fins tip is 2.00 mm, the channel width of the mini-channel heat sink is 1.00 mm. The nanofluids with suspending of TiO2 particles in base fluid are used as a working fluids. It was observed that the average CPU temperatures obtained from the jet nanofluids impingement cooling system are 3.0%, 6.25% lower than those from the jet liquid impingement and from the conventional liquid cooling systems, respectively. However, this cooling system requires higher energy consumption.
文摘A jet noise reduction technique by using the external chevron nozzle with lobed mixer in the double-mixing exhaust system is investigated under cold conditions.The computations of jet field and the experiments of noise field are conducted with scaled model of high-bypass-ratio turbofan engine mixing exhaust system composed of external chevron nozzle with lobed mixer.The computational results indicate that comparing with the baseline nozzle with lobed mixer,the external chevron nozzle with lobed mixer increases mixing of jet and ambient air near the nozzle exit.The experimental results show that the external chevron nozzle with lobed mixer has better jet noise reduction at low frequencies,and this reduction rises with the increase of chevron bend angle.The experimental results also show that the external chevron nozzle with lobed mixer has sound pressure level(SPL)increase which is not obvious at high frequencies.With chevron bend angle increasing,SPL has relatively marked increase at 60°(directivity angle measured from upstream jet axis)and little fluctuations at 90°and 150°.The external chevron nozzle with lobed mixer has overall sound pressure level(OASPL)reduction in varying degrees at 60°and 150°,but it has little OASPL increase at 90°.
基金Item Sponsored by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of EducationScience and Technology[No.2009-0074199+1 种基金2012R1A1A2008399]the Ministry of Knowledge Economy (MKE) and Korea Institute for Advancement of Technology (KIAT) through the Workforce Development Program in Strategic Technology
文摘Recently,there has been an investigation of polishing processes that has considered new ultra-precision polishing technology for micro parts and optical parts such as those with aspheric and complex shapes.One suitable means of polishing complex shapes is to use a jet of abrasive fluid.However,aerodynamic disturbances and radial spreading are generated by the unstable polishing process of the jet on the surface of the workpiece when it is being polished.A method of jet stabilization has been proposed in which the original nozzle form of a jet of magnetorheological(MR)fluid contains abrasive particles that are magnetized using a magnetic.This paper details the design of an MR jet polishing system that uses an electromagnet,a nozzle,and a hydraulic unit to stabilize a slurry jet based on MR fluid, Second,for silica glass,the polishing spot and section profile are analyzed and the effect of the MR fluid jet polishing process is evaluated.The results of the experiment show that the removal profile is W-shaped and that,in this case,a stable can be proof of a distance of several tens of millimeters from the nozzle.Such results show the possibility of applying the proposed polishing method using MR fluids in ultra-precision micro and optical parts production processes. MR jet polishing shows great potential for use as a new type of precision surface polishing technology.In particular,this is a highly valuable process for the polishing of complex shapes such as micro parts,concaves parts,and cavities.
