Investigations of the effects of two typical jet crushing methods on the atomization and dust reduction performance of nozzles

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.

Continuing Results for Effervescent Aerosol Salt Water Spray Nozzles Intended for Marine Cloud Brightening

Marine Cloud Brightening (MCB) by effervescent spray atomization of mixed sea water brine with air is a candidate for solar radiation management to compensate for global warming. We discovered that the flow from mixing tee nozzle described earlier had occasional unstable slug flow. A new design that adding rotational swirl to the salt brine as it is mixed into the air stabilized the nozzle flow and no longer showed slug flow in spray pictures. Flow equations were developed for the relatively low speed of sound of a choked flow mixed brine and air nozzle. Experimental mixed flow measurements with 300b pressure and a 200 μm diameter nozzle and calculations using perfect gas, and isotropic processes equations compared well with the chocked flow equations. Analysis in EXCEL of particle sizers measurements from both a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS) showed production of many nanometer sized particles estimated as usable for MCB. A small number of micron sized particles were also always present but with about 90% of the sprayed mass. This is a first report with good data over the complete size range. The micron sized particles measured were similar to the measurements of earlier reports which reported no nanometer sized particles. We hypothesize that many nano-particles are always produced by liquid-air effervescent sprays, but earlier, were not observed because SMPS instruments were not available. The presence of the large mass percentage of large particles in the spray may cause problems by evaporative cooling preventing the rise of the MCB particles. We suggest future systems design with an impactor filter to remove the large particles. Calculations combining increased brine concentration, lower pressure, and larger nozzle area showed that significant reductions in required power and number of nozzles could be realized. An EXCEL model is developed to calculate flow from experimental analysis equations and compare with mixed choked flow equations. Solving with the model predicted the power required and the number of nozzles required to produce 1015 particles/s. The model showed that increasing brine concentration strongly lowered total power. Lowering pressure decreased power and increased number of nozzles. Increasing nozzle area lowered the number of nozzles. This model predicted that, at 300b pressure and 200μm diameter nozzle as the experiment but using an increased brine concentration of 0.1 instead of 0.032 would require only 115 nozzles instead of 358 and power of 146 kw instead of 493 kw. Combining increased brine concentration, lower pressure, and larger nozzle area, the model predicted that with a 1 mm diameter nozzle at 30b pressure and salt concentration of 0.2, the nozzle count and power required would drop to only 24 nozzles and power of 28 kw. Whether extending the model to these conditions is valid is not known but suggests further development should be investigated. Filtering out and reusing the 90% or greater large particles mass sprayed combined with the lower power advantage of higher brine concentration is suggested for future systems.

Multi-Schlieren CT Measurements of Supersonic Microjets from Circular and Square Micro Nozzles

Instantaneous three-dimensional (3D) density distributions of a shock-cell structure of perfectly and imperfectly expanded supersonic microjets escaping into an ambient space are measured. For the 3D observation of supersonic microjets, non-scanning 3D computerized tomography (CT) technique using a 20-directional quantitative schlieren optical system with flashlight source is employed for simultaneous schlieren photography. The 3D density distributions data of the microjets are obtained by 3D-CT reconstruction of the projection’s images using maximum likelihood-expectation maximization. Axisymmetric convergent-divergent (Laval) circular and square micro nozzles with operating nozzle pressure ratio 5.0, 4.5, 4.0, 3.67, and 3.5 have been studied. This study examines perfectly expanded, overexpanded, and underexpanded supersonic microjets issued from micro nozzles with fully expanded jet Mach numbers Mj ranging from 1.47 - 1.71, where the design Mach number is Md = 1.5. A complex phenomenon for free square microjets called axis switching is clearly observed with two types “upright” and “diagonal” of “cross-shaped”. The initial axis-switching is 45° within the first shock-cell range. In addition, from the symmetry and diagonal views of square microjets for the first shock-cells, two different patterns of shock waves are viewed. The shock-cell spacing and supersonic core length for all nozzle pressure ratios are investigated and reported.

Experimental study on atomization characteristics and dust-reduction performance of four common types of pressure nozzles in underground coal mines

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.

A Laboratory Investigation into the Fuel Atomization Process in a Diesel Engine for Different Configurations of the Injector Nozzles and Flow Conditions

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.

Structure Optimization of SENs and Upper Nozzles

The structure of SEN and upper nozzles was optimized and simulated. Relevant trials were conducted on site during thecasting of Al-killed steel. These optimizations effectively solve the nozzle clogging and reduce the defects of the casting slab.

TRANSONIC SHOCK SOLUTIONS TO THE EULER SYSTEM IN DIVERGENT-CONVERGENT NOZZLES

In this paper,we study the transonic shock solutions to the steady Euler system in a quasi-one-dimensional divergent-convergent nozzle.For a given physical supersonic inflow at the entrance,we obtain exactly two non-isentropic transonic shock solutions for the exit pressure lying in a suitable range.In addition,we establish the monotonicity between the location of the transonic shock and the pressure downstream.

Feasibility study of symmetric solution of molecular argon flow inside microscale nozzles

The computational cost of numerical methods in microscopic-scales such as molecular dynamics(MD) is a deterrent factor that limits simulations with a large number of particles. Hence, it is desirable to decrease the computational cost and run time of simulations, especially for problems with a symmetrical domain. However, in microscopic-scales, implementation of symmetric boundary conditions is not straightforward. Previously, the present authors have successfully used a symmetry boundary condition to solve molecular flows in constant-area channels. The results obtained with this approach agree well with the benchmark cases. Therefore, it has provided us with a sound ground to further explore feasibility of applying symmetric solutions of micro-fluid flows in other geometries such as variable-area ducts. Molecular flows are solved for the whole domain with and without the symmetric boundary condition. Good agreement has been reached between the results of the symmetric solution and the whole domain solution. To investigate robustness of the proposed method, simulations are conducted for different values of affecting parameters including an external force, a flow density, and a domain length. The results indicate that the symmetric solution is also applicable to variable-area ducts such as micro-nozzles.

The Acoustic Performance of 3D Printed Multiple Jet Nozzles with DifferentConfigurations

This work investigated multiple jet nozzles with various geometrical shape,number of exits,and material on reducing noise radiated from jet flows.Nozzles are categorized in two groups with few and many exit numbers,each with various exit shapes,slot and circular,and geometry.Firstly,nozzles are designed and then fabricated by a 3D printer,Form Labs,Form2USA,with polymeric resin.Also,the nozzle with the most noise reduction made of stainless steel.Noise and air thrust were measured at three air pressure gauges,3,5,7 BAR and directions from nozzle apex,30°,90°,135°.Nozzles with slot exit shape made of both plastic and stainless steel revealed the most noise reduction among all nozzles with few exit numbers,nearly 11–14 dB(A)and 11.5–15 dB(A),respectively.On average,slotted nozzle noise reduction was nearly 5–6 dB(A)more than finned nozzle.However,nozzles with more exit numbers,finned and finned-central exit,illustrated much more noise reduction than nozzles with few exit numbers,by almost 16–18 dB(A),they represented similar sound.All tested nozzles and open pipe demonstrated equal air thrust at each pressure gauges.The nozzles with slotted exit shape,either plastic or stainless steel,can provide reasonable noise reduction in comparison to other configuration with few exit numbers.In contrast,nozzles with more exit numbers demonstrated the most noise reduction.

Effect of the structure of backward orifices on thejet performance of self-propelled nozzles

Self-propelled nozzle is a critical component of the radial jet drilling technology.Its backward orifice structure has a crucial influence on the propulsive force and the drilling performance.To improve the working performance of the nozzle,the numerical simulation model is built and verified by the experimental results of propulsive force.Then the theoretical model of the energy efficiency and energy coefficient of the nozzle is built to reveal the influence of the structural parameters on the jet performance of the nozzle.The results show that the energy efficiency and energy coefficient of the backward orifice increase first and then decrease with the angle increases.The energy coefficient of forward orifice is almost constant with the angle increases.With the increase in the number and diameter,energy efficiency and energy coefficient of the forward orifice gradually decrease,but the backward orifice energy coefficient first increases and then decreases.Finally,it is obtained that the nozzle has better jet performance when the angle of backward orifice is 30°,the number of backward orifice is 6,and the value range of diameter is 2-2.2 mm.This study provides a reference for the design of efficiently self-propelled nozzle for radial jet drilling technology.

A Combined Experimental and Numerical Study of Shotcrete Jets and Related Wet Spray Nozzles

In this research,the dynamics of wet spray nozzles with different geometries,used to accelerate shotcrete,are investigated on the basis of a suitable three-dimensional mathematical model and related numerical method.Simulations have been conducted in the frame of the SIMPLEC algorithm.The k-εturbulence model has been used to account for turbulent effects.The study shows that when the angle of the convergent section is less than 3°,it has a scarce effect on the dynamics of the jet of shotcrete;with the increase of the convergence angle,the shotcrete jet velocity decreases and the nozzle wear increases;when this angle is greater than 6°,the concrete outlet jet velocity is very small and the nozzle can easily be blocked.Experimental results are in good agreement with the outcomes of the numerical simulations,which indicates that the used approach is reliable.

Research Progress on Anti-clogging Technology of Submerged Entry Nozzles for Continuous Casting

The causes, the formation process, and the prevention of submerged entry nozzle(SEN) clogging were introduced. The influence of electric field on the SEN clogging was focused on, including the basic theory and measurement of SEN charging,the preliminary research on SEN charging, the influence of molten steel on the wetting behavior of refractory materials in electric field, and the influence of electric field on the oxide inclusions in molten steel. Based on the influence of the hydrodynamics, chemistry and other factors on refractory materials, structure, inclusion particle transfer and adhesion, many anti-clogging researches have been carried out, such as optimizing process conditions, compositing anti-clogging inner lining materials, innovating SEN structure and applying physical fields, which solve the problem of SEN clogging to a certain extent.However, the problems of weak adaptability and superficial study on clogging mechanism are still prominent. The electric field control is a new technology to prevent clogging. Although it has achieved certain results in on-site continuous casting trials,some problems such as the method of applying electric field, the electric field parameters and the equipment still need to be gradually improved, and the surface characteristics of inclusions and SEN materials at high temperatures need to be further studied. It was pointed out that the combination of materials and applied electric field will become an important direction for SEN anti-clogging technology.

Structure and Flow Characteristics of Flat Fan Nozzles with a Single Orifice Formed by a Rectangular Cut

The flat fan nozzle with a single orifice formed by a rectangular cut at the nozzle exit through a semi-ellipsoid blind end was developed. The flow rate characteristic of the nozzle was analyzed. Theoretical analysis shows that the discharge coefficient of the nozzle is a function of the ratio of the projected exit flow area to the cross sectional area of the nozzle input section. Water spraying experiment results show that the discharge coefficient increases with the increase of the ratio of the projected exit flow area to the cross sectional area of the nozzle input section when the rectangular cut depth doesn't exceed the distance from the center of the hemisphere to the nozzle end; conversely,the discharge coefficient decreases with the increase of the ratio; for a given nozzle,the discharge coefficient varies with Reynolds number.

Optical Measurements of Shock Waves in Critical Nozzles at Low Reynolds Numbers

Two-dimensional critical nozzle flows at low Reynolds numbers are visualized by the rainbow schlieren deflectometry. Experiments have been performed in a region of overexpanded nozzle flow. The variation of the shock structure against the back pressure ratio can be clearly visible with color gradation. Static pressure rises due to the shock-induced flow separation are compared with the previous theories. The unsteady characteristics of overexpanded critical nozzle flows at low Reynolds numbers are quantitatively and qualitatively visualized using laser schlieren and Mach-Zehnder interferometer systems combined with a high-speed digital camera. It was found that an oscillating normal shock wave appears inside the nozzle, and that the shock wave has a specified dominant frequency. Also the time-history of the oscillating shock wave is obtained from both the systems and compared with each other.

Simulation and experiment investigations on fabrication of Fe-based amorphous powders by a novel atomization process equipped with assisted gas nozzles

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.

Propulsion tests on ultra-high-temperature ceramic matrix composites for reusable rocket nozzles

Ultra-high-temperature ceramic matrix composites(UHTCMCs)based on a ZrB_(2)/SiC matrix have been investigated for the fabrication of reusable nozzles for propulsion.Three de Laval nozzle prototypes,obtained by sintering with either hot pressing(HP)or spark plasma sintering(SPS),were tested 2-3 times in a hybrid rocket motor for proving reusability.Sections were extracted after oxidation tests to study the microstructural changes and oxidative and thermomechanical stresses induced by the repeated tests.Compared to a reference graphite nozzle,no measurable erosion was observed for the UHTCMC-based nozzles.The oxidation mechanism consisted in the formation of a ZrO_(2)intermediate layer,with a liquid silicon oxide(SiO_(2))layer on the surface that was displaced by the action of the gas flux towards the divergent part of the nozzle,protecting it from further oxidation.Both specimens obtained by HP and SPS displayed similar performance,with very slight differences,which were attributed to small changes in porosity.These tests demonstrated the capability of complex-shaped prototypes made of the developed UHTCMCs to survive repeated exposure to environments representative of a realistic space propulsion application,for overall operating time up to 30 s,without any failure nor measurable erosion,making a promising step towards the development of reusable rocket components.

Optimization for aerodynamic performance of double serpentine nozzles with spanwise offsets using Taguchi-based CFD analysis

Serpentine nozzles are widely used in combat aircraft to realize strong stealth characteristics.Based on the layout characteristics within a confined space,a series of double serpentine nozzles with spanwise offsets are established.Using computational fluid dynamics and Taguchi method,the influence mechanisms of the Distribution of Area(DA),Distributions of Centerline for the first and second‘S’sections in the Vertical direction(DCV1 and DCV2),and Distribution of Centerline in the Spanwise direction(DCS)are analyzed.The impact of these factors on the total pressure recovery coefficient can be ranked as DA>DCV2>DCS>DCV1,whereas their impacts on the discharge coefficient and axial thrust coefficient can be ranked as DCV2>DCS>DA>DCV1.Considering the statistical significance of these factors,a nozzle in which DA changes rapidly at the exit and DCV1,DCV2,and DCS change rapidly at the entrance gives the best aerodynamic performance.Compared to the worst configuration,the total pressure recovery coefficient,discharge coefficient,and axial thrust coefficient are improved by 1.6%,3.5%and 3.6%,respectively.DA influences the gas flow acceleration in the entire serpentine channel,resulting in different wall shear stress and friction losses.The various centerline distributions influence the gas flow acceleration effects and form complex wave structures in the constantarea extension section,resulting in different local and friction losses.

A numerical simulation on the infrared radiation of hot exhausting nozzles with a coupled flow and heat transfer model

A coupled model among flow field,solid temperature,species concentration and gas radiation,which was based on statistical narrow-band correlated-k model,was employed to predict the infrared radiations from hot exhausting nozzles. The parameters of narrow-band model were deduced from HITEMP line-by-line database. Several methods to increase computational efficiency and to save computational resources were employed,thus all the complicated computations could be operated on a personal computer. The predictions for three cases have been conducted to validate the accuracy of the methods mentioned above,including the temperature distribution of a water-cooling nozzle in rocket engines,the carbon dioxide absorptivity at the wavelength of 4.3 micron and the infrared radiation of a cylindrical furnace. Finally,the aerothermodynamic and infrared characteristics of two nozzles were predicted. It was shown that the infrared radiation intensity of chevron ejecting nozzle were obviously smaller than that of common axisymmetric convergent-divergent nozzle.

The Optimization Design of the Nozzle Section for theWater Jet Propulsion System Applied in Jet Skis

The performance of a water jet propulsion system is related to the inlet duct,rotor,stator,and nozzle.Generally,the flow inlet design must fit the bottom line of the hull,and the design of the inlet duct is often limited by stern space.The entire section,from the rotor to the nozzle through the stator,must be designed based on system integration in that the individual performance of these three components will influence each other.Particularly,the section from the rotor to the nozzle significantly impacts the performance of a water jet propulsion system.This study focused on nozzle design and established referable analysis results to facilitate subsequent integrated studies on the design parameters regarding nozzle contour.Most existing studies concentrate on discussions on rotor design and the tip leakage flow of rotors or have replaced the existing complex computational domain with a simple flow field.However,research has yet to implement an integrated,optimal design of the section from the rotor to the nozzle.Given the above,our program conducted preliminary research on this system integration design issue,discussed the optimal nozzle for this section in-depth,and proposed design suggestions based on the findings.This program used an existing model as the design case.This study referred to the actual trial data as the design conditions for the proposed model.Unlike prior references’simple flow field form,this study added a jet ski geometry and free surface to the computational domain.After the linear hull shape was considered,the inflow in the inlet duct would be closer to the actual condition.Based on the numerical calculation result,this study recommends that the optimal nozzle outlet area should be 37%of the inlet area and that the nozzle contour should be linear.Furthermore,for the pump head,static pressure had a more significant impact than dynamic pressure.

Jet Characteristics and Optimization of a Cavitation Nozzle for Hydraulic Fracturing Applications

Hydraulic jetting is a form of fracturing that involves using a high-pressure jet of water to create fractures in the reservoir rock with a nozzle serving as the central component of the hydraulic sandblasting perforation tool.In this study,the flow behavior of the nozzle is simulated numerically in the framework of a SST k-ωturbulence model.The results show that the nozzle structure can significantly influence the jet performance and related cavitation effect.Through orthogonal experiments,the nozzle geometric parameters are optimized,and the following configuration is found accordingly:contraction angle 20°,contraction segment length 6 mm,cylindrical segment diameter 6 mm,cylindrical segment length 12 mm,spread segment length 10 mm,and spread angle 55°.