Enhancing the fermentation efficiency of waste in waste warehouses is pivotal for accelerating the pyrolysis process and minimizing harmful gas emissions.This study proposes an integrated approach,combining hot air in...Enhancing the fermentation efficiency of waste in waste warehouses is pivotal for accelerating the pyrolysis process and minimizing harmful gas emissions.This study proposes an integrated approach,combining hot air injection with dual atomizing nozzles,for the thermal treatment of waste piles.Numerical simulations are employed to investigate the influence of various parameters,namely,nozzle height,nozzle tilt angle,inlet air velocity and air temperature,on the droplet diffusion process,spread area,droplet temperature,and droplet size distribution.The results show that reducing the nozzle height increases the temperature of droplets upon their deposition on the waste pile.Specifically,when the nozzle height is lowered to 1.5 m,the temperature of the droplets reaching the waste pile is 1℃higher than when the nozzle height is set at 2 m.Furthermore,an increase in the nozzle tilt angle expands the overlapping heating area.For instance,when the nozzle angle is increased from 15°to 30°,the overlapping spread area expands by 3.21 m2.Additionally,increasing the inlet air velocity enhances the droplet diffusion range.At an air velocity of 2 m/s,the droplet diffusion range grows to 14.4 m,representing a 6.7%increase compared to the nowind condition.While the average droplet diameter decreases to 1.53 mm,the droplet temperature decreases by 1℃.Moreover,the droplet temperature is found to become smaller as the ambient temperature inside the waste warehouse declines.Specifically,a 5℃reduction in the ambient temperature results in a 1℃decrease in the average temperature of the atomized droplets.The study concludes that a nozzle height of 1.5 m and a nozzle tilt angle of 30°effectively meet practical heating requirements.展开更多
Aiming at the problem of air-cooled condenser output limit, a spray humidification system was presented to reduce the inlet air temperature. The pressure atomizing nozzle TF8 was chosen for inlet air spray cooling, an...Aiming at the problem of air-cooled condenser output limit, a spray humidification system was presented to reduce the inlet air temperature. The pressure atomizing nozzle TF8 was chosen for inlet air spray cooling, and the spray cooling experiment with different layouts of nozzles were conducted. Through heat and mass transfer analysis, the cooling effect fitting correlation was acquired with evaporative cooling being the major cooling mechanism. The experimental results under different nozzle layouts show that when the product of dry ball and wet ball temperature difference and spray rate is smaller than 75 ~C-m3/h, opening the TF8 nozzles in row 1 and row 2 （row distance is 500 mm） has better cooling effect than those in row 1 and row 3 （row distance is 1 000 mm）, while when the product is larger than 75 ~C＇m3/h, opening the TF8 nozzles in row 1 and row 3 is superior in cooling effect to those in row 1 and row 2.展开更多
Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimi...Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimizing the geometric parameters of delivery tube outlet and gas outlet to obtain applicable atomization scale parameters. A computational fluid flow model is adopted to investigate the effect of atomization gas pressure ( P0 ) on the gas flow field in gas atomization progress. The numerical results show that the outlet gas velocity of the nozzle is not affected by P0 and the maximum gas velocity reaches 452 m / s. The alternation of aspiration pressure ( ΔP) is caused by the variations of stagnation pressure and location of Mach shock disk, and hardly by the location of stagnation point. The aspiration pressure is found to decrease as P0 increases when P0 < 1. 3 MPa. However,at a higher atomization gas pressure increasing P0 causes an opposite: the aspiration pressure atomization increases with the gas pressure,and keeps a plateau when P0 > 2. 0 MPa. The minimum aspiration pressure ΔP = - 70 kPa is obtained at P0 = 1. 3 MPa. The results indicate that the designed Laval- style annual slot nozzle has well atomization characteristic at lower atomization pressure.展开更多
To simulate the transonic atomization jet process in Laval nozzles,to test the law of droplet atomization and distribution,to find a method of supersonic atomization for dust-removing nozzles,and to improve nozzle eff...To simulate the transonic atomization jet process in Laval nozzles,to test the law of droplet atomization and distribution,to find a method of supersonic atomization for dust-removing nozzles,and to improve nozzle efficiency,the finite element method has been used in this study based on the COMSOL computational fluid dynamics module.The study results showed that the process cannot be realized alone under the two-dimensional axisymmetric,three-dimensional and three-dimensional symmetric models,but it can be calculated with the transformation dimension method,which uses the parameter equations generated from the two-dimensional axisymmetric flow field data of the three-dimensional model.The visualization of this complex process,which is difficult to measure and analyze experimentally,was realized in this study.The physical process,macro phenomena and particle distribution of supersonic atomization are analyzed in combination with this simulation.The rationality of the simulation was verified by experiments.A new method for the study of the atomization process and the exploration of its mechanism in a compressible transonic speed flow field based on the Laval nozzle has been provided,and a numerical platform for the study of supersonic atomization dust removal has been established.展开更多
Based on volume of fluid(VoF)interface capturing method and shear-stress transport(SST)k-ω turbulence model,numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle(MDN)d...Based on volume of fluid(VoF)interface capturing method and shear-stress transport(SST)k-ω turbulence model,numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle(MDN)during gas atomization(GA)process.The experimental validation indicated that the numerical models could give a reasonable prediction on the melt flow process in the MDN.With the decrease of the MDN inner-diameter,the melt flow resistance increased for both molten aluminum and iron,especially achieving an order of 10^(2) kPa in the case of the MDN inner-diameter≤1 mm.Based on the conventional GA process,the positive pressure was imposed on the viscous aluminum alloy melt to overcome its flow resistance in the MDN,thus producing powders under different MDN inner-diameters.When the MDN inner-diameter was reduced from 4 to 2 mm,the yield of fine powder(<150μm)soared from 54.7%to 94.2%.The surface quality of powders has also been improved when using a smaller inner-diameter MDN.展开更多
Pressure nozzle is commonly used in the dust-reduction techniques by spraying of underground coal mines.Based on the internal structure,the pressure nozzle can be divided into the following types:spiral channel nozzle...Pressure nozzle is commonly used in the dust-reduction techniques by spraying of underground coal mines.Based on the internal structure,the pressure nozzle can be divided into the following types:spiral channel nozzle,tangential flow-guided nozzle and X-swirl nozzle.In order to provide better guidance on the selection of nozzles for the coal mine dust-reduction systems by spraying,we designed comparing experiments to study the atomization characteristics and dust-reduction performance of four commonly used nozzles in the coal mine underground with different internal structures.From the experimental results on the atomization characteristics,both the tangential flow-guided nozzle and the X-swirl nozzle have high flow coefficients.The atomization angle is the largest in the spiral non-porous nozzle,and smallest in both the X-swirl nozzle and the spiral porous nozzle.The spraying range and the droplet velocity are inversely proportional to the atomization angle.When the water pressure is low,the atomization performance of the spiral non-porous nozzle is the best among the four types of nozzles.The atomization performance of the X-swirl nozzle is superior to other types when the water pressure is high.Under the high water pressure,the particle size of the atomized droplets is smallest in the X-swirl nozzle.Through the experiments on the dust-reduction performance of the four types of nozzles and the comprehensive analysis,the X-swirl nozzle is recommended for the coal mine application site with low water pressure in the dust-reduction system,while at the sites with high water pressure,the spiral non-porous nozzle is recommended,which has the lowest water consumption and obvious economic advantages.展开更多
The resonant behaviors of an ultra-sonic gas atomization nozzle with a zero mass-flux jet actuator were numerically investigated with FLUENT software by using a double precision unsteady two-dimensional pressure-based...The resonant behaviors of an ultra-sonic gas atomization nozzle with a zero mass-flux jet actuator were numerically investigated with FLUENT software by using a double precision unsteady two-dimensional pressure-based solver. The Spalart-Allmaras turbulence model was adopted in the simulations. Numerical results indicated that the oscillation properties of the gas efflux were effectively improved. Several resonatory frequencies corresponding to different vibration modes of gas were distinguished in the nozzle. With the changing of nozzle geometric parameters, different characters among those modes were elucidated by analyzing the propagations of pressure waves.展开更多
The paper aims at modeling and simulating the atomization process of the close-coupled ring-hole nozzle in vacuum induction gas atomization(VIGA)for metallic powder production.First of all,the primary atomization of t...The paper aims at modeling and simulating the atomization process of the close-coupled ring-hole nozzle in vacuum induction gas atomization(VIGA)for metallic powder production.First of all,the primary atomization of the ring-hole nozzle is simulated by the volume of fluid(VOF)coupled large eddy simulation(LES)model.To simulate the secondary atomization process,we use the method of selecting the droplet sub-model and the VOF model.The results show that the ring-hole nozzle forms a gas recirculation zone at the bottom of the delivery tube,which is the main reason for the formation of an annular liquid film during the primary atomization.In addition,the primary atomization process of the ring-hole nozzle consists of three stages:the formation of the serrated liquid film tip,the appearance and shedding of the ligaments,and the fragmentation of ligaments.At the same time,the primary atomization mainly forms spherical droplets and long droplets,but only the long droplets can be reserved and proceed to the secondary atomization.Moreover,increasing the number of ring holes from 18 to 30,the mass median diameter(MMD,d_(50))of the primary atomized droplets decreases first and then increases,which is mainly due to the change of the thickness of the melt film.Moreover,the secondary atomization of the ring-hole nozzles is mainly in bag breakup mode and multimode breakup model,and bag breakup will result in the formation of hollow powder,which can be avoided by increasing the gas velocity.展开更多
In this paper, the flow fields of three types of nozzles （ Hartmann, Laval and Laminar nozzles ） under the same conditions are simulated, and the corresponding to pressure, temperature, velocity and turbulence inten...In this paper, the flow fields of three types of nozzles （ Hartmann, Laval and Laminar nozzles ） under the same conditions are simulated, and the corresponding to pressure, temperature, velocity and turbulence intensity are obtained. The results suggest that two crushing presents in the atomization process using Hartmann nozzle, but only one crushing presents in the atomization process using the other nozzles, through the comparative research on the flow field features of three types of nozzle. Furthermore, the shockwave plays a more important role in crushing of liquid metal than velocity.展开更多
Single-fuid nozzles and dual-fuid nozzles are the two typical jet crushing methods used in spray dust reduction. To distinguish the atomization mechanism of single-fuid and dual-fuid nozzles and improve dust control e...Single-fuid nozzles and dual-fuid nozzles are the two typical jet crushing methods used in spray dust reduction. To distinguish the atomization mechanism of single-fuid and dual-fuid nozzles and improve dust control efciency at the coal mining faces, the atomization characteristics and dust reduction performance of the two nozzles were quantitatively compared. Results of experiments show that, as water supply pressure increased, the atomization angle of the swirl pressure nozzle reaches a maximum of 62° at 6 MPa and then decreases, but its droplet size shows an opposite trend with a minimum of 41.7 μm. The water supply pressure helps to improve the droplet size and the atomization angle of the internal mixing air–liquid nozzle, while the air supply pressure has a suppressive efect for them. When the water supply pressure is 0.2 MPa and the air supply pressure reaches 0.4 MPa, the nozzle obtains the smallest droplet size which is 10% smaller than the swirl pressure nozzle. Combined with the dust reduction experimental results, when the water consumption at the working surface is not limited, using the swirl pressure nozzle will achieve a better dust reduction efect. However, the internal mixing air–liquid nozzle can achieve better and more economical dust reduction performance in working environments where water consumption is limited.展开更多
This paper reports a laboratory investigation of the fuel injection process in a diesel engine.The atomization process of the considered fuel(a hydrocarbon liquid)and the ensuing mixing with air is studied experimenta...This paper reports a laboratory investigation of the fuel injection process in a diesel engine.The atomization process of the considered fuel(a hydrocarbon liquid)and the ensuing mixing with air is studied experimentally under high-pressure conditions.Different types of injector nozzles are examined,including(two)new configurations,which are compared in terms of performances to a standard injector manufactured by the Bosch company.For the two alternate configurations,the intake edges of one atomizing hole(hole No.1)are located in the sack volume while for the other(hole No.2)they are located on the locking cone of the needle valve.The injection process,the fuel atomization fineness and fuel supply speed characteristics are studied as functions of high-pressure fuel pump camshaft speed and rotation angle.The results obtained show that a decrease in the high-pressure fuel pump camshaft speed can produce fuel redistribution depending on the injector operation.In general,however,the hole No.1 can ensure fuel flow with higher speed with respect to the hole No.2 for all the operation modes of the injector.Based on such an analysis,we conclude that the use of certain injectors can enable a fine tuning of the propagation process of fuel sprays into various areas of the diesel engine combustion chamber.展开更多
In order to obtain appropriate spray pressure and enhance the spraying and dust removal efficiency, various factors including the dust characteristics, nozzle spraying angle, effective spraying range, water consumptio...In order to obtain appropriate spray pressure and enhance the spraying and dust removal efficiency, various factors including the dust characteristics, nozzle spraying angle, effective spraying range, water consumption and droplet size are taken into account. The dust characteristics from different mines and atomization parameters of different pressure nozzles were measured. It was found that the internal pressure of coal cutters and roadheaders should be kept at 2 MPa, which could ensure large droplet size, large spraying angle and low water consumption and hence realizing a large-area covering and capture for large particle dusts. However, the external spray pressure should be kept at 4 MPa for smaller droplet size and longer effective spraying range, leading to effective dust removal in the operator zone. The spray pressure of support moving, drawing opening, and stage loader on a fully mechanized caving face and stage loader on a fully mechanized driving face should be kept at 8 MPa, under which the nozzles have long effective spraying range, high water flow and small droplet size for the rapid capture of instantaneous, high-concentration and small size dust groups. From the applications on the caving and driving faces in the coal mines, it is indicated that the optimization of spray pressure in different spraying positions could effectively enhance dust removal efficiency. Selecting appropriate nozzles according to the dust characteristics at different positions is also favorable for dust removal efficiency. With the selected nozzles under optimal pressures, the removal rates of both total dust and respirable dust could reach over70%, showing a significant de-dusting effect.展开更多
We study here effects of nozzle layout on the droplet ejection of a micro atomizer, which was fabricated with the arrayed nozzles by the MEMS technology and actuated by a piezoelectric disc. A theoretical model was fi...We study here effects of nozzle layout on the droplet ejection of a micro atomizer, which was fabricated with the arrayed nozzles by the MEMS technology and actuated by a piezoelectric disc. A theoretical model was first built for this piezoelectric-liquid-structure coupling system to characterize the acoustic wave propagation in the liquid chamber, which determined the droplet formation out of nozzles. The modal analysis was carried out numerically to predict resonant frequencies and simulate the corresponding pressure wave field. By comparing the amplitude contours of pressure wave on the liquid-solid interface at nozzle inlets with the designed nozzle layout, behaviors of the device under different vibration modes can be predicted. Experimentally, an impedance analyzer was used to measure the resonant frequencies of the system. Three types of atomizers with different nozzle layouts were fabricated for measuring the effect of nozzle distribution on the ejection performance. The visualization experiment of droplet generation was carried out and volume flow rates of these devices were measured. The good agreement between the experiment and the prediction proved that only the increase of nozzles may not enhance the droplet generation and a design of nozzle distribution from a view-point of frequency is necessary for a resonant related atomizer.展开更多
Based on computational fluid dynamics method,the effect of atomization gas pressure on the atomization efficiency of Laval nozzle was studied,and then a discrete phase model was established and combined with industria...Based on computational fluid dynamics method,the effect of atomization gas pressure on the atomization efficiency of Laval nozzle was studied,and then a discrete phase model was established and combined with industrial trials to study the effect of a new type of assisted gas nozzles(AGNs)on powder size distribution and amorphous powder yield.The results show that increasing the atomization pressure can effectively improve the gas velocity for the Laval nozzle;however,it will decrease the aspiration pressure,and the optimal atomization pressure is 2.0 MPa.Compared with this,after the application of AGNs with the inlet velocity of 200 m s^(-1),assisted gas jet can increase the velocity of overall droplets in the break-up and solidification area by 40 m s^(-1) and the maximum cooling rate is increased from 1.9×10^(4) to 2.3×10^(4) K s^(-1).The predicted particle behavior is demonstrated by the industrial trails,that is,after the application of AGNs,the median diameter of powders d50 is decreased from 28.42 to 25.56 lm,the sphericity is increased from 0.874 to 0.927,the fraction of amorphous powders is increased from 90.4% to 99.4%,and only the coercivity is increased slightly due to the accumulation of internal stress.It is illustrated that the AGNs can improve the yield of fine amorphous powders,which is beneficial to providing high-performance raw powders for additive manufacturing technology.展开更多
Air-atomized fog cooling is particularly suitable for the after-pot cooling of galvanized steel strips.With air and water serving as working media,an experimental study was conducted on the atomization characteristics...Air-atomized fog cooling is particularly suitable for the after-pot cooling of galvanized steel strips.With air and water serving as working media,an experimental study was conducted on the atomization characteristics of a newly-developed cross-flow type of fog nozzles.The water flux distribution,spray angle and pressure of water and air were measured.The results show that the water droplet size was small and insensitive to the water flow rate.The spray angle was small and the water flow rate slightly affected the air pressure in the chamber.An empirical correlation between the pressure in the chamber and the gas flow rate was obtained for the purpose of equipment design.展开更多
Gas flow field in nozzles and out of nozzles was calculated for Laval orifice and straight orifice nozzles. The results showed that the flow generated by the Laval nozzle had a higher exit velocity in the vicinity of ...Gas flow field in nozzles and out of nozzles was calculated for Laval orifice and straight orifice nozzles. The results showed that the flow generated by the Laval nozzle had a higher exit velocity in the vicinity of the nozzle, in comparison with that of the straight nozzle, that is to say, a Laval nozzle was more efficient than a straight one in disintegrating the melt stream and was apt to produce finer powders. The flow generated by the Laval nozzle was less convergent and the velocity gradient along the radial direction was more moderate than that of a straight nozzle, which could contribute to a broad distribution of melt particles. According to their flow characteristics, the Laval nozzle was reckoned as a better choice of producing larger spray-formed billets.展开更多
It is a great challenge to find effective atomizing technology for reducing industrial pollution; the twin-fluid atomizing nozzle has drawn great attention in this field recently. Current studies on twin-fluid nozzles...It is a great challenge to find effective atomizing technology for reducing industrial pollution; the twin-fluid atomizing nozzle has drawn great attention in this field recently. Current studies on twin-fluid nozzles mainly focus on droplet breakup and single droplet characteristics. Research relating to the influences of structural parameters on the droplet diameter characteristics in the flow field is scarcely available. In this paper, the influence of a self-excited vibrating cavity structure on droplet diameter characteristics was investigated. Twin-fluid atomizing tests were performed by a self-built open atomizing test bench, which was based on a phase Doppler particle analyzer(PDPA). The atomizing flow field of the twin-fluid nozzle with a self-excited vibrating cavity and its absence were tested and analyzed. Then the atomizing flow field of the twin-fluid nozzle with different self-excited vibrating cavity structures was investigated.The experimental results show that the structural parameters of the self-excited vibrating cavity had a great effect on the breakup of large droplets. The Sauter mean diameter(SMD) increased with the increase of orifice diameter or orifice depth. Moreover, a smaller orifice diameter or orifice depth was beneficial to enhancing the turbulence around the outlet of nozzle and decreasing the SMD. The atomizing performance was better when the orifice diameter was2.0 mm or the orifice depth was 1.5 mm. Furthermore, the SMD increased first and then decreased with the increase of the distance between the nozzle outlet and self-excited vibrating cavity, and the SMD of more than half the atomizing flow field was under 35 μm when the distance was 5.0 mm. In addition, with the increase of axial and radial distance from the nozzle outlet, the SMD and arithmetic mean diameter(AMD) tend to increase. The research results provide some design parameters for the twin-fluid nozzle, and the experimental results could serve as a beneficial supplement to the twin-fluid nozzle study.展开更多
This paper discusses the flowing process inside a nozzle, especially the formation mechanism of cavitations within the nozzle and puts forward a nozzle flow model, which takes account of the injection conditions and n...This paper discusses the flowing process inside a nozzle, especially the formation mechanism of cavitations within the nozzle and puts forward a nozzle flow model, which takes account of the injection conditions and nozzle geometry. By the model being implemented to the KIVA codes, the spray characteristics (e. g., spray penetration and cone angle) of diesel and dimethyl ether (DME) are simulated. The comparisons between the computational and experimental results are performed, which show that the liquid spray characteristics could be more truly demonstrated by considering the existence of the cavitations. Key words nozzle model - spray characteristics - cavitation - atomization CLC number O 35 - TK 402 Foundation item: Supported by the National Natural Science Foundation of China (50376018) and the National 973 Basic Research Program of China (2001CB209207)Biography: WEI Ming-rui (1967-), male, Associate professor, Ph. D, research direction: computational combustion, computational fluid dynamics.展开更多
The ultra-sonic gas atomization （USGA） nozzle is an important apparatus in the metal liquid air-blast atomization process. It can generate oscillating supersonic gas effiux, which is proved to be effective to enforc...The ultra-sonic gas atomization （USGA） nozzle is an important apparatus in the metal liquid air-blast atomization process. It can generate oscillating supersonic gas effiux, which is proved to be effective to enforce the atomization and produce narrow-band particle distributions. A double-actuator ultra-sonic gas nozzle is proposed in the present paper by joining up two active signals at the ends of the resonance tubes. Numerical sim- ulations axe adopted to study the effects of the flow development on the acoustic resonant properties inside the Haxtmann resonance cavity with/without actuators. Comparisons show that the strength and the onset process of oscillation are enhanced remarkably with the actuators. The multiple oscillating amplitude peaks are found on the response curves, and two kinds of typical behaviors, i.e., the Hartmann mode and the global mode, are discussed for the corresponding frequencies. The results for two driving actuators are also investigated. When the amplitudes, the frequencies, or the phase difference of the input signals of the actuators are changed, the oscillating amplitudes of gas effiux can be altered effectively.展开更多
A compressible three-phase solver is presented that takes into account the effects of cavitation and condensation dynamics on sprayatomization,near-nozzle flows,and internal flows,particularly in the context of fuel-i...A compressible three-phase solver is presented that takes into account the effects of cavitation and condensation dynamics on sprayatomization,near-nozzle flows,and internal flows,particularly in the context of fuel-injection systems.The computational fluid dynamics solver tracks three phases-the liquid phase of the fuel,the vapor phase of the fuel,and the noncondensable gas into which the fuel is injected-allowing for complete miscibility between the gaseous phases.It uses the volume of fluid method,within a finite-volume framework,to track the interfaces between the fluid components.The solver is then validated for its ability to track interfaces,for mass conservation,and against experimental data of an expected use case,namely,cavitation in an injector.The solver is shown to perform well in all three validation tests.The solver can also be reduced to just a multiphase solver to study cavitation when the third gaseous component may be absent,such as in hydro-turbines.展开更多
文摘Enhancing the fermentation efficiency of waste in waste warehouses is pivotal for accelerating the pyrolysis process and minimizing harmful gas emissions.This study proposes an integrated approach,combining hot air injection with dual atomizing nozzles,for the thermal treatment of waste piles.Numerical simulations are employed to investigate the influence of various parameters,namely,nozzle height,nozzle tilt angle,inlet air velocity and air temperature,on the droplet diffusion process,spread area,droplet temperature,and droplet size distribution.The results show that reducing the nozzle height increases the temperature of droplets upon their deposition on the waste pile.Specifically,when the nozzle height is lowered to 1.5 m,the temperature of the droplets reaching the waste pile is 1℃higher than when the nozzle height is set at 2 m.Furthermore,an increase in the nozzle tilt angle expands the overlapping heating area.For instance,when the nozzle angle is increased from 15°to 30°,the overlapping spread area expands by 3.21 m2.Additionally,increasing the inlet air velocity enhances the droplet diffusion range.At an air velocity of 2 m/s,the droplet diffusion range grows to 14.4 m,representing a 6.7%increase compared to the nowind condition.While the average droplet diameter decreases to 1.53 mm,the droplet temperature decreases by 1℃.Moreover,the droplet temperature is found to become smaller as the ambient temperature inside the waste warehouse declines.Specifically,a 5℃reduction in the ambient temperature results in a 1℃decrease in the average temperature of the atomized droplets.The study concludes that a nozzle height of 1.5 m and a nozzle tilt angle of 30°effectively meet practical heating requirements.
基金National Key Technologies R&D Program in the 12th Five-Year Plan of China(No. 2011BAJ08B09)
文摘Aiming at the problem of air-cooled condenser output limit, a spray humidification system was presented to reduce the inlet air temperature. The pressure atomizing nozzle TF8 was chosen for inlet air spray cooling, and the spray cooling experiment with different layouts of nozzles were conducted. Through heat and mass transfer analysis, the cooling effect fitting correlation was acquired with evaporative cooling being the major cooling mechanism. The experimental results under different nozzle layouts show that when the product of dry ball and wet ball temperature difference and spray rate is smaller than 75 ~C-m3/h, opening the TF8 nozzles in row 1 and row 2 （row distance is 500 mm） has better cooling effect than those in row 1 and row 3 （row distance is 1 000 mm）, while when the product is larger than 75 ~C＇m3/h, opening the TF8 nozzles in row 1 and row 3 is superior in cooling effect to those in row 1 and row 2.
文摘Gas mass flux rate,metal mass flux rate and outlet gas velocity are three atomization scale parameters which greatly affect the atomization efficiency. A Laval-style annual slot supersonic nozzle is designed by optimizing the geometric parameters of delivery tube outlet and gas outlet to obtain applicable atomization scale parameters. A computational fluid flow model is adopted to investigate the effect of atomization gas pressure ( P0 ) on the gas flow field in gas atomization progress. The numerical results show that the outlet gas velocity of the nozzle is not affected by P0 and the maximum gas velocity reaches 452 m / s. The alternation of aspiration pressure ( ΔP) is caused by the variations of stagnation pressure and location of Mach shock disk, and hardly by the location of stagnation point. The aspiration pressure is found to decrease as P0 increases when P0 < 1. 3 MPa. However,at a higher atomization gas pressure increasing P0 causes an opposite: the aspiration pressure atomization increases with the gas pressure,and keeps a plateau when P0 > 2. 0 MPa. The minimum aspiration pressure ΔP = - 70 kPa is obtained at P0 = 1. 3 MPa. The results indicate that the designed Laval- style annual slot nozzle has well atomization characteristic at lower atomization pressure.
基金Supported by the National Natural Science Foundation of China (NO: 51704146, 51274116, 51704145).
文摘To simulate the transonic atomization jet process in Laval nozzles,to test the law of droplet atomization and distribution,to find a method of supersonic atomization for dust-removing nozzles,and to improve nozzle efficiency,the finite element method has been used in this study based on the COMSOL computational fluid dynamics module.The study results showed that the process cannot be realized alone under the two-dimensional axisymmetric,three-dimensional and three-dimensional symmetric models,but it can be calculated with the transformation dimension method,which uses the parameter equations generated from the two-dimensional axisymmetric flow field data of the three-dimensional model.The visualization of this complex process,which is difficult to measure and analyze experimentally,was realized in this study.The physical process,macro phenomena and particle distribution of supersonic atomization are analyzed in combination with this simulation.The rationality of the simulation was verified by experiments.A new method for the study of the atomization process and the exploration of its mechanism in a compressible transonic speed flow field based on the Laval nozzle has been provided,and a numerical platform for the study of supersonic atomization dust removal has been established.
基金the National Natural Science Foundation of China(No.52074157)Shenzhen Science and Technology Innovation Com-mission,China(Nos.JSGG20180508152608855,KQTD20170328154443162)Shenzhen Key Laboratory for Additive Manufacturing of High-performance Materials,China(No.ZDSYS201703031748354).
文摘Based on volume of fluid(VoF)interface capturing method and shear-stress transport(SST)k-ω turbulence model,numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle(MDN)during gas atomization(GA)process.The experimental validation indicated that the numerical models could give a reasonable prediction on the melt flow process in the MDN.With the decrease of the MDN inner-diameter,the melt flow resistance increased for both molten aluminum and iron,especially achieving an order of 10^(2) kPa in the case of the MDN inner-diameter≤1 mm.Based on the conventional GA process,the positive pressure was imposed on the viscous aluminum alloy melt to overcome its flow resistance in the MDN,thus producing powders under different MDN inner-diameters.When the MDN inner-diameter was reduced from 4 to 2 mm,the yield of fine powder(<150μm)soared from 54.7%to 94.2%.The surface quality of powders has also been improved when using a smaller inner-diameter MDN.
基金Financial support for this work,provided by the National Natural Science Foundation of China(No.51574123)the Hunan Provincial Natural Science Foundation of China(No.2017JJ3076)Hunan Graduate Research and Innovation Project(No.CX2018B661),are gratefully acknowledged.
文摘Pressure nozzle is commonly used in the dust-reduction techniques by spraying of underground coal mines.Based on the internal structure,the pressure nozzle can be divided into the following types:spiral channel nozzle,tangential flow-guided nozzle and X-swirl nozzle.In order to provide better guidance on the selection of nozzles for the coal mine dust-reduction systems by spraying,we designed comparing experiments to study the atomization characteristics and dust-reduction performance of four commonly used nozzles in the coal mine underground with different internal structures.From the experimental results on the atomization characteristics,both the tangential flow-guided nozzle and the X-swirl nozzle have high flow coefficients.The atomization angle is the largest in the spiral non-porous nozzle,and smallest in both the X-swirl nozzle and the spiral porous nozzle.The spraying range and the droplet velocity are inversely proportional to the atomization angle.When the water pressure is low,the atomization performance of the spiral non-porous nozzle is the best among the four types of nozzles.The atomization performance of the X-swirl nozzle is superior to other types when the water pressure is high.Under the high water pressure,the particle size of the atomized droplets is smallest in the X-swirl nozzle.Through the experiments on the dust-reduction performance of the four types of nozzles and the comprehensive analysis,the X-swirl nozzle is recommended for the coal mine application site with low water pressure in the dust-reduction system,while at the sites with high water pressure,the spiral non-porous nozzle is recommended,which has the lowest water consumption and obvious economic advantages.
基金supported by the National Natural Science Foundation of China (Grant Nos.10772107, 10702038)the Shanghai Municipal Key Projects on Basic Research (Grant No.08JC1409800)+1 种基金the Innovation Project of Shanghai Municipal Education Commission (Grant No.08YZ10)the Shanghai Municipal Science and Technology Commission (Grant No.09DZ1141502)
文摘The resonant behaviors of an ultra-sonic gas atomization nozzle with a zero mass-flux jet actuator were numerically investigated with FLUENT software by using a double precision unsteady two-dimensional pressure-based solver. The Spalart-Allmaras turbulence model was adopted in the simulations. Numerical results indicated that the oscillation properties of the gas efflux were effectively improved. Several resonatory frequencies corresponding to different vibration modes of gas were distinguished in the nozzle. With the changing of nozzle geometric parameters, different characters among those modes were elucidated by analyzing the propagations of pressure waves.
基金the National Natural Science Foundation of China(Grant No.51975240)the Open Fund of State Key Laboratory of Advanced Forming Technology and Equipment(Grant No.SKL2019006).
文摘The paper aims at modeling and simulating the atomization process of the close-coupled ring-hole nozzle in vacuum induction gas atomization(VIGA)for metallic powder production.First of all,the primary atomization of the ring-hole nozzle is simulated by the volume of fluid(VOF)coupled large eddy simulation(LES)model.To simulate the secondary atomization process,we use the method of selecting the droplet sub-model and the VOF model.The results show that the ring-hole nozzle forms a gas recirculation zone at the bottom of the delivery tube,which is the main reason for the formation of an annular liquid film during the primary atomization.In addition,the primary atomization process of the ring-hole nozzle consists of three stages:the formation of the serrated liquid film tip,the appearance and shedding of the ligaments,and the fragmentation of ligaments.At the same time,the primary atomization mainly forms spherical droplets and long droplets,but only the long droplets can be reserved and proceed to the secondary atomization.Moreover,increasing the number of ring holes from 18 to 30,the mass median diameter(MMD,d_(50))of the primary atomized droplets decreases first and then increases,which is mainly due to the change of the thickness of the melt film.Moreover,the secondary atomization of the ring-hole nozzles is mainly in bag breakup mode and multimode breakup model,and bag breakup will result in the formation of hollow powder,which can be avoided by increasing the gas velocity.
文摘In this paper, the flow fields of three types of nozzles （ Hartmann, Laval and Laminar nozzles ） under the same conditions are simulated, and the corresponding to pressure, temperature, velocity and turbulence intensity are obtained. The results suggest that two crushing presents in the atomization process using Hartmann nozzle, but only one crushing presents in the atomization process using the other nozzles, through the comparative research on the flow field features of three types of nozzle. Furthermore, the shockwave plays a more important role in crushing of liquid metal than velocity.
基金funded by the National Natural Science Foundation of China(52274237)the Fundamental Research Funds for the Central Universities(2021ZDPYYQ007)+1 种基金the Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX22_2656)the Graduate Innovation Program of China University of Mining and Technology(2022WLKXJ026).
文摘Single-fuid nozzles and dual-fuid nozzles are the two typical jet crushing methods used in spray dust reduction. To distinguish the atomization mechanism of single-fuid and dual-fuid nozzles and improve dust control efciency at the coal mining faces, the atomization characteristics and dust reduction performance of the two nozzles were quantitatively compared. Results of experiments show that, as water supply pressure increased, the atomization angle of the swirl pressure nozzle reaches a maximum of 62° at 6 MPa and then decreases, but its droplet size shows an opposite trend with a minimum of 41.7 μm. The water supply pressure helps to improve the droplet size and the atomization angle of the internal mixing air–liquid nozzle, while the air supply pressure has a suppressive efect for them. When the water supply pressure is 0.2 MPa and the air supply pressure reaches 0.4 MPa, the nozzle obtains the smallest droplet size which is 10% smaller than the swirl pressure nozzle. Combined with the dust reduction experimental results, when the water consumption at the working surface is not limited, using the swirl pressure nozzle will achieve a better dust reduction efect. However, the internal mixing air–liquid nozzle can achieve better and more economical dust reduction performance in working environments where water consumption is limited.
基金supported by the Russian Science Foundation[grant number 19-19-00598].
文摘This paper reports a laboratory investigation of the fuel injection process in a diesel engine.The atomization process of the considered fuel(a hydrocarbon liquid)and the ensuing mixing with air is studied experimentally under high-pressure conditions.Different types of injector nozzles are examined,including(two)new configurations,which are compared in terms of performances to a standard injector manufactured by the Bosch company.For the two alternate configurations,the intake edges of one atomizing hole(hole No.1)are located in the sack volume while for the other(hole No.2)they are located on the locking cone of the needle valve.The injection process,the fuel atomization fineness and fuel supply speed characteristics are studied as functions of high-pressure fuel pump camshaft speed and rotation angle.The results obtained show that a decrease in the high-pressure fuel pump camshaft speed can produce fuel redistribution depending on the injector operation.In general,however,the hole No.1 can ensure fuel flow with higher speed with respect to the hole No.2 for all the operation modes of the injector.Based on such an analysis,we conclude that the use of certain injectors can enable a fine tuning of the propagation process of fuel sprays into various areas of the diesel engine combustion chamber.
基金support from the National Natural Science Foundation of China (Nos.U1261205, 51474139 and 51204103)the Science and Technology Development Plan of Shandong Province (No.2013GSF12004)the Excellent Young Scientific Talents Project of Shandong University of Science and Technology (No.2014JQJH106)
文摘In order to obtain appropriate spray pressure and enhance the spraying and dust removal efficiency, various factors including the dust characteristics, nozzle spraying angle, effective spraying range, water consumption and droplet size are taken into account. The dust characteristics from different mines and atomization parameters of different pressure nozzles were measured. It was found that the internal pressure of coal cutters and roadheaders should be kept at 2 MPa, which could ensure large droplet size, large spraying angle and low water consumption and hence realizing a large-area covering and capture for large particle dusts. However, the external spray pressure should be kept at 4 MPa for smaller droplet size and longer effective spraying range, leading to effective dust removal in the operator zone. The spray pressure of support moving, drawing opening, and stage loader on a fully mechanized caving face and stage loader on a fully mechanized driving face should be kept at 8 MPa, under which the nozzles have long effective spraying range, high water flow and small droplet size for the rapid capture of instantaneous, high-concentration and small size dust groups. From the applications on the caving and driving faces in the coal mines, it is indicated that the optimization of spray pressure in different spraying positions could effectively enhance dust removal efficiency. Selecting appropriate nozzles according to the dust characteristics at different positions is also favorable for dust removal efficiency. With the selected nozzles under optimal pressures, the removal rates of both total dust and respirable dust could reach over70%, showing a significant de-dusting effect.
基金the National Natural Science Foundation of China(50405001).
文摘We study here effects of nozzle layout on the droplet ejection of a micro atomizer, which was fabricated with the arrayed nozzles by the MEMS technology and actuated by a piezoelectric disc. A theoretical model was first built for this piezoelectric-liquid-structure coupling system to characterize the acoustic wave propagation in the liquid chamber, which determined the droplet formation out of nozzles. The modal analysis was carried out numerically to predict resonant frequencies and simulate the corresponding pressure wave field. By comparing the amplitude contours of pressure wave on the liquid-solid interface at nozzle inlets with the designed nozzle layout, behaviors of the device under different vibration modes can be predicted. Experimentally, an impedance analyzer was used to measure the resonant frequencies of the system. Three types of atomizers with different nozzle layouts were fabricated for measuring the effect of nozzle distribution on the ejection performance. The visualization experiment of droplet generation was carried out and volume flow rates of these devices were measured. The good agreement between the experiment and the prediction proved that only the increase of nozzles may not enhance the droplet generation and a design of nozzle distribution from a view-point of frequency is necessary for a resonant related atomizer.
基金funded by Key research and development project of Shandong province in China(Grant Number 2018TSCYCX-10).
文摘Based on computational fluid dynamics method,the effect of atomization gas pressure on the atomization efficiency of Laval nozzle was studied,and then a discrete phase model was established and combined with industrial trials to study the effect of a new type of assisted gas nozzles(AGNs)on powder size distribution and amorphous powder yield.The results show that increasing the atomization pressure can effectively improve the gas velocity for the Laval nozzle;however,it will decrease the aspiration pressure,and the optimal atomization pressure is 2.0 MPa.Compared with this,after the application of AGNs with the inlet velocity of 200 m s^(-1),assisted gas jet can increase the velocity of overall droplets in the break-up and solidification area by 40 m s^(-1) and the maximum cooling rate is increased from 1.9×10^(4) to 2.3×10^(4) K s^(-1).The predicted particle behavior is demonstrated by the industrial trails,that is,after the application of AGNs,the median diameter of powders d50 is decreased from 28.42 to 25.56 lm,the sphericity is increased from 0.874 to 0.927,the fraction of amorphous powders is increased from 90.4% to 99.4%,and only the coercivity is increased slightly due to the accumulation of internal stress.It is illustrated that the AGNs can improve the yield of fine amorphous powders,which is beneficial to providing high-performance raw powders for additive manufacturing technology.
文摘Air-atomized fog cooling is particularly suitable for the after-pot cooling of galvanized steel strips.With air and water serving as working media,an experimental study was conducted on the atomization characteristics of a newly-developed cross-flow type of fog nozzles.The water flux distribution,spray angle and pressure of water and air were measured.The results show that the water droplet size was small and insensitive to the water flow rate.The spray angle was small and the water flow rate slightly affected the air pressure in the chamber.An empirical correlation between the pressure in the chamber and the gas flow rate was obtained for the purpose of equipment design.
基金Item Sponsored by Hi-Tech Research and Development Programof China(2006AA03Z114)National Basic Research Program of China(2006CB605204-2)
文摘Gas flow field in nozzles and out of nozzles was calculated for Laval orifice and straight orifice nozzles. The results showed that the flow generated by the Laval nozzle had a higher exit velocity in the vicinity of the nozzle, in comparison with that of the straight nozzle, that is to say, a Laval nozzle was more efficient than a straight one in disintegrating the melt stream and was apt to produce finer powders. The flow generated by the Laval nozzle was less convergent and the velocity gradient along the radial direction was more moderate than that of a straight nozzle, which could contribute to a broad distribution of melt particles. According to their flow characteristics, the Laval nozzle was reckoned as a better choice of producing larger spray-formed billets.
基金Supported by National Natural Science Foundation of China(Grant No.51705445)Hebei Provincial Natural Science Foundation of China,(Grant No.E2016203324)Open Foundation of the State Key Laboratory of Fluid Power and Mechatronic Systems of China(Grant No.GZKF-201714)
文摘It is a great challenge to find effective atomizing technology for reducing industrial pollution; the twin-fluid atomizing nozzle has drawn great attention in this field recently. Current studies on twin-fluid nozzles mainly focus on droplet breakup and single droplet characteristics. Research relating to the influences of structural parameters on the droplet diameter characteristics in the flow field is scarcely available. In this paper, the influence of a self-excited vibrating cavity structure on droplet diameter characteristics was investigated. Twin-fluid atomizing tests were performed by a self-built open atomizing test bench, which was based on a phase Doppler particle analyzer(PDPA). The atomizing flow field of the twin-fluid nozzle with a self-excited vibrating cavity and its absence were tested and analyzed. Then the atomizing flow field of the twin-fluid nozzle with different self-excited vibrating cavity structures was investigated.The experimental results show that the structural parameters of the self-excited vibrating cavity had a great effect on the breakup of large droplets. The Sauter mean diameter(SMD) increased with the increase of orifice diameter or orifice depth. Moreover, a smaller orifice diameter or orifice depth was beneficial to enhancing the turbulence around the outlet of nozzle and decreasing the SMD. The atomizing performance was better when the orifice diameter was2.0 mm or the orifice depth was 1.5 mm. Furthermore, the SMD increased first and then decreased with the increase of the distance between the nozzle outlet and self-excited vibrating cavity, and the SMD of more than half the atomizing flow field was under 35 μm when the distance was 5.0 mm. In addition, with the increase of axial and radial distance from the nozzle outlet, the SMD and arithmetic mean diameter(AMD) tend to increase. The research results provide some design parameters for the twin-fluid nozzle, and the experimental results could serve as a beneficial supplement to the twin-fluid nozzle study.
文摘This paper discusses the flowing process inside a nozzle, especially the formation mechanism of cavitations within the nozzle and puts forward a nozzle flow model, which takes account of the injection conditions and nozzle geometry. By the model being implemented to the KIVA codes, the spray characteristics (e. g., spray penetration and cone angle) of diesel and dimethyl ether (DME) are simulated. The comparisons between the computational and experimental results are performed, which show that the liquid spray characteristics could be more truly demonstrated by considering the existence of the cavitations. Key words nozzle model - spray characteristics - cavitation - atomization CLC number O 35 - TK 402 Foundation item: Supported by the National Natural Science Foundation of China (50376018) and the National 973 Basic Research Program of China (2001CB209207)Biography: WEI Ming-rui (1967-), male, Associate professor, Ph. D, research direction: computational combustion, computational fluid dynamics.
基金Project supported by the National Natural Science Foundation of China (Nos. 10772107,10702038,and 11172163)the E-Institutes of Shanghai Municipal Education Commission,and the Shanghai Program for Innovative Research Team in Universities
文摘The ultra-sonic gas atomization （USGA） nozzle is an important apparatus in the metal liquid air-blast atomization process. It can generate oscillating supersonic gas effiux, which is proved to be effective to enforce the atomization and produce narrow-band particle distributions. A double-actuator ultra-sonic gas nozzle is proposed in the present paper by joining up two active signals at the ends of the resonance tubes. Numerical sim- ulations axe adopted to study the effects of the flow development on the acoustic resonant properties inside the Haxtmann resonance cavity with/without actuators. Comparisons show that the strength and the onset process of oscillation are enhanced remarkably with the actuators. The multiple oscillating amplitude peaks are found on the response curves, and two kinds of typical behaviors, i.e., the Hartmann mode and the global mode, are discussed for the corresponding frequencies. The results for two driving actuators are also investigated. When the amplitudes, the frequencies, or the phase difference of the input signals of the actuators are changed, the oscillating amplitudes of gas effiux can be altered effectively.
文摘A compressible three-phase solver is presented that takes into account the effects of cavitation and condensation dynamics on sprayatomization,near-nozzle flows,and internal flows,particularly in the context of fuel-injection systems.The computational fluid dynamics solver tracks three phases-the liquid phase of the fuel,the vapor phase of the fuel,and the noncondensable gas into which the fuel is injected-allowing for complete miscibility between the gaseous phases.It uses the volume of fluid method,within a finite-volume framework,to track the interfaces between the fluid components.The solver is then validated for its ability to track interfaces,for mass conservation,and against experimental data of an expected use case,namely,cavitation in an injector.The solver is shown to perform well in all three validation tests.The solver can also be reduced to just a multiphase solver to study cavitation when the third gaseous component may be absent,such as in hydro-turbines.
