Microscopic and macroscopic atomization characteristics of a pressure-swirl atomizer, injecting a viscous fuel oil

Combustion of heavy fuels is one of the main sources of greenhouse gases, particulate emissions, ashes, NOxand SOx. Gasification is an advanced and environmentally friendly process that generates combustible and clean gas products such as hydrogen. Some entrained flow gasifiers operate with Heavy Fuel Oil(HFO) feedstock. In this application, HFO atomization is very important in determining the performance and efficiency of the gasifiers.The atomization characteristics of HFO(Mazut) discharging from a pressure-swirl atomizer(PSA) are studied for different pressures difference(Δp) and temperatures in the atmospheric ambient. The investigated parameters include atomizer mass flow rate( _m), discharge coefficient(CD), spray cone angle(θ), breakup length(Lb), the unstable wavelength of undulations on the liquid sheet(λs), global and local SMD(sauter mean diameter) and size distribution of droplets. The characteristics of Mazut sheet breakup are deduced from the shadowgraph technique. The experiments on Mazut film breakup were compared with the predictions obtained from the liquid film breakup model. Validity of the theory for predicting maximum unstable wavelength was investigated for HFO(as a highly viscous liquid). A modification on the formulation of maximum unstable wavelength was presented for HFO. SMD decreases by getting far from the atomizer. The measurement for SMD and θ were compared with the available correlations. The comparisons of the available correlations with the measurements of SMD andθ show a good agreement for Ballester and Varde correlations, respectively. The results show that the experimental sizing data could be presented by Rosin-Rammler distributions very well at different pressure difference and temperatures.

MODELING OF A SOLID CONE PRESSURE-SWIRL ATOMIZER

A Ballistic Modeling (BM) / Discrete Droplet Modeling (DDM) method is used to de- termine the characteristics of a solid cone pressure-swirl atomizer (Dyna Coin nozzle) . The charac- teristic of its liquid spray is of considerable importance to the operation and performance of com- bustion systems. A two-dimensional spray model has been developed to simulate a continuous spray under steady-state condition . This model can simulate the resultant drop-sizc of atomization and reveal the effects of the important physical variables such as fuel injection pressure, air pressure(or density), co-axial air flow and fuel properties on the result of atomization process. Dimensional analysis is used to simulate the drop-size immcdiately after jet breakup and further breakup of the droplets is determined by testifying the critical condition of aerodynamics breakup i.e.(Wed)c= 8 / CD.

An improved theoretical formulation for Sauter mean diameter of pressure-swirl atomizers using geometrical parameters of atomization

This study discusses the development of a mathematical model that is capable ofpredicting the drop size mean diameter of the spray generated by a pressure swirl atomizer,considering the effects of the liquid’s viscosity and the geometrical parameters of this typeof injector, as well as the angle of incidence of the inlet channels (j and b) and atomizationparameters (k, 8), obtained from hyperbolic relations. Additionally, this model investigatesthe phenomena of rupture and stability that are observed in the conical liquid film, in whichthe importance of a new geometrical parameter of atomization, “8”, which immediately influences the drop size diameter of the spray, should be highlighted. The results that are obtainedusing this model are compared with analytical results of Couto, Wang and Lefebvre, Jasuja,Radcliffe and Lefebvre, experimental results and numerics (Hollow cone atomization model),using the Ansys Fluent software for the validation and consistency of the model proposed in Rivas (2015). This model yields good approximations as compared to that yielded using otheralternative mathematical models, demonstrating that the new atomization geometric parameter“8” is an “adjustment” factor that exhibits considerable significance while designing pressureswirl atomizers according to the required SMD. Furthermore, this model is easy to use, withreliable results, and has the advantage of saving computational time.

Experiments and modeling of discharge characteristics in water-mist sprays generated by pressure-swirl atomizers

Pressure-swirl atomizers are often employed to generate a water-mist spray,typically employed in fire suppression.In the present study,an experimental characterization of dispersion(velocity and cone angle)and atomization(drop-size axial evolution)was carried out following a previously developed methodology,with specific reference to the initial region of the spray.Laser-based techniques were used to quantitatively evaluate the considered phenomena:velocity field was reconstructed through a Particle Image Velocimetry analysis;drop-size distribution was measured by a Malvern Spraytec device,highlighting secondary atomization and subsequent coalescence along the spray axis.Moreover,a comprehensive set of relations was validated as predictive of the involved parameters,following an inviscid-fluid approach.The proposed model pertains to early studies on pressure-swirl atomizers and primarily yields to determine both initial velocity and cone angle.The spray thickness is also predicted and a classic correlation for Sauter Mean Diameter is shown to provide good agreement with experimental results.The analysis was carried out at the operative pressure of 80 bar;two injectors were employed featuring different orifice diameters and flow numbers,as a sort of parametric approach to this spray typology.

Experimental Studies on Fuel Spray Characteristics of Pressure-Swirl Atomizer and Air-Blast Atomizer

In this work,the effects of fuel temperatures and pressure drops on the flow field and spray characteristics of a pressure-swirl atomizer were discussed using the Particle Imaging Velocimetry(PIV),Planar Laser Induced Fluorescence(PLIF)and Laser Particle Size Analyzer(LPSA)methods.Then the air-blast atomizer was selected to study the interaction of initial atomization and flow field.The effect of fuel-air ratio on the air-blast atomizer were also considered,where the fuel-air ratio was varied by adjusting mass flow rate of the air and fuel respectively.The results show that the spray angle of the pressure-swirl atomizer increases first and changes a little after the pressure drop higher than 0.5 MPa.However,more fuel concentrate on the central region,which is mainly caused by the increase of the proportion of small droplets with lower centrifugal force.The fuel temperature can improve the spray angle only in lower pressure drop,and it has a little effect under higher pressure drops.In addition,the fuel pressure drop has an obvious influence on the fuel distribution and flow field near the nozzle exit compared with the downstream.For the air-blast atomizer,the spray angle increases compared with the pressure-swirl atomizer for the introduction of swirl air.Furthermore,the spray angle decreases with the air mass rate increasing,and it increases with the fuel mass rate increasing.The distribution of velocity and droplet near the nozzle exit is influenced by the air mass rate,and the fuel mass rate mainly affects the distribution in the downstream.The fuel accumulates in the annular area below the nozzle,and the distribution of it changes little with the development along the axial direction.

Research Progress of Atomizers and Drugs Used in Atomization Therapy

At present,the commonly used treatment methods for chronic respiratory diseases are drug,oxygen,interventional and atomization therapy.Atomization therapy is the most widely used because of its characteristics of fast effect,high local drug concentration,less drug dosage,convenient application and few systemic adverse reactions.In this paper,the mechanism,characteristics,commonly used drugs and clinical application of atomization therapy are discussed.

Design and evaluation of a Laval-type supersonic atomizer for low-pressure gas atomization of molten metals

A Laval-type supersonic gas atomizer was designed for low-pressure gas atomization of molten metals. The principal design ob-jectives were to produce small-particle uniform powders at lower operating pressures by improving the gas inlet and outlet structures and op-timizing structural parameters. A computational fluid flow model was developed to study the flow field characteristics of the designed atom-izer. Simulation results show that the maximum gas velocity in the atomization zone can reach 440 m＆#183;s-1;this value is independent of the atomization gas pressure P0 when P0〉0.7 MPa. When P0=1.1 MPa, the aspiration pressure at the tip of the delivery tube reaches a mini-mum, indicating that the atomizer can attain the best atomization efficiency at a relatively low atomization pressure. In addition, atomization experiments with pure tin at P0=1.0 MPa and with 7055Al alloy at P0=0.8 and 0.4 MPa were conducted to evaluate the atomization capa-bility of the designed atomizer. Nearly spherical powders were obtained with the mass median diameters of 28.6, 43.4, and 63.5μm, respec-tively. Compared with commonly used atomizers, the designed Laval-type atomizer has a better low-pressure gas atomization capability.

Experimental study of a heavy fuel oil atomization by pressure-swirl injector in the application of entrained flow gasifier

The available SMD(Sauter mean diameter) correlations on pressure-swirl injectors predict droplet sizing very different from each other, especially for heavy fuels. Also there was a lack in the literature for comparing available correlations. So an experimental study was conducted on a heavy fuel oil(HFO) spray, Mazut 380. A pressure swirl injector was designed and fabricated. The experiments for Mazut at 40℃ and 80℃ were compared with the results for water, including spray half cone angle, breakup length and mean droplet diameter,at different injection pressures. Lower spray angle, higher breakup length and larger droplets were observed for lower injection pressures and higher liquid viscosity. SMD was about 75 μm for water and about 87 μm for Mazut at 80℃. The results for droplet mean diameter were also compared with correlations from previous studies on pressure swirl atomizers. The SMD results show that for water spray, LISA method was in good agreement,also Babu and Ballester correlations were successful when high viscosity fluid was injected.

Numerical simulation of heavy fuel oil atomization using a pulsed pressure-swirl injector

It is known that increasing the injection pressure reduces the breakup length and the droplet size.Adding pulses,on the other hand,helps to atomize the liquid into finer droplets,similar to airassisted injectors but without altering the airtofuel concentration.To further reduce the droplet size and breakup length,a novel injector type,called''Pulsed PressureSwirl"(PPS),is introduced in this work,which is a combination of pressureswirl and ultrasonic pulsed injectors.A pressureswirl atomizer was designed and fabricated specifically for Mazut HFO(Heavy Fuel Oil).The droplet formation process and droplet size distribution have been studied experimentally(by shadowgraphy high speed imaging)and numerically(with the opensource VolumeofFluid code Gerris).Changing liquid injection pressure effect on the spray angle and film thickness has been quantified.These simulations have been used to study the primary breakup process and quantify the droplet size distributions,using different injection pulse frequencies and pressures.The numerical results have revealed that the new injector concept successfully produces finer droplets and results in a decrease in the breakup length,especially when applying high pulse frequencies,with no significant changes in the spray angle.

Simulation and Experimental Study on the Atomization Character of the Pressure-Swirl Nozzle

In this paper the atomization character of the pressure-swirl injector was measured by using the Phase Doppler Particle Analyzer (PDPA) in the section of 150 mm below the outlet of the orifice. The orifice diameter of the pressure-swirl injector is 0.62 mm. The atomization character includes the spray angle, the water flow rate, the Sauter mean diameter (SMD), the velocity of the particles and their distribution in the radial and the axial directions under the pressure from 1 MPa to 4.5 MPa. After that the atomization character of the pressure-swirl injector was simulated in the DPM panel. The same atomization character of the injector was calculated and compared with the experimental data. The simulation was corrected by using the experimental data which can make it accurately and the model can be used to predict and calculate the atomization character of different injectors.

Study on the Atomization Mechanism of Hydrides in Graphite Furnace Atomizers

The influence of the surface state of the graphite furnace atomizer on the atomization of hydrides has been studied by means of surface film coating and quantum chemistry CN-DO/2 calculations. The results of the study prove that the atomization of AsH3, SbH3 and BiH3 in the graphite furnace atomizer is not a simple gas phase pyrolytic process, but a surface catalysis pyrolytic process.

Numerical simulation of flow in Hartmann resonance tube and flow in ultrasonic gas atomizer

The gas flow in the Hartmann resonance tube is numerically investigated by the finite volume method based on the Roe solver. The oscillation of the flow is studied with the presence of a needle actuator set along the nozzle axis. Numerical results agree well with the theoretical and experimental results available. Numerical results indicate that the resonance mode of the resonance tube will switch by means of removing or adding the actuator. The gas flow in the ultrasonic gas atomization （USGA） nozzle is also studied by the same numerical methods. Oscillation caused by the Hartmann resonance tube structure, coupled with a secondary resonator, in the USGA nozzle is investigated. Effects of the variation of parameters on the oscillation are studied. The mechanism of the transition of subsonic flow to supersonic flow in the USGA nozzle is also discussed based on numerical results.

Numerical simulation of droplet-formation in rotary atomizer

Numerical simulations of the liquid flow scattering from rotary atomizers are performed using an incompressible smoothed particle hydrodynamics (SPH) method. The influence of grooves at the edges of the atomizers on the formation of ligaments and droplets is investigated changing the numbers and shapes of the grooves. As a result, it is found that small droplets are likely to be generated when the number of grooves is large and the depth of grooves is deep. It is also found that the grooves work more effectively in bell-cup atomizers than in disk type atomizers.

FLUID KINETICS PRINCIPLE AND DESIGN CRITERIA OF ATOMIZER

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Flow field simulation of double layer atomizer

The influences of parameters,such as delivery tube structure,gas pressure and the distance between the primary atomizer and the secondary atomizer,on gas flow field were investigated by simulation.The effects of primary pressure on gas velocity at the centerline were compared.Water atomizing experiment was carried out to validate gas scatter angle.The results show that the structure of primary atomizer plays an important role in the flow field near the exit of delivery tube.Metal protector with conical surface at the body extends certain length into the gas flow field to generate greater negative pressure near the tip of delivery tube. The application of primary gas can suppress the circulation generated by only using the secondary atomizer.

The effect of nozzle layout on droplet ejection of a piezo-electrically actuated micro-atomizer

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.

Computational Modelling of the Hydride Generation Reaction in a Tubular Reactor and Atomization in a Quartz Cell Atomizer

In this study, we present a model whereby the centre of the atomization channel is shown to be the optimal location for the spectrometric data acquisition in a quartz cell atomizer. The study aims to explore the hydride generation technique which is normally coupled with efficient thermal source to apply determination of heavy metals in water samples via spectrometric analysis. The arsenic hydride generation process and the atomization of the generated hydride in a quartz cell atomizer were studied analytically as model case studies. The hydride generation (HG) process was analyzed by adopting two hypotheses, the nascent hydrogen and formation of intermediate hydroboron species, where the results based on the second hypothesis are found to be more realistic for design purposes. Moreover, the release of the generated hydride from the liquid phase and their transport to the gas phase is simulated in a helical tubular section, in which the actual tubular section length required for separation is deduced. The analytical results have been verified experimentally by measuring the signal intensity for the free arsenic atoms against several reaction tube lengths, in which increasing the tubular section length from 12 cm to 100 cm results in signal amelioration by no more than 6.6%. Furthermore, the atomization of the hydride and the distribution of the generated free atoms are deduced in two configurations of tubular quartz atomizers. The results obtained from both studied cases illustrate that a high concentration of the free analyte atoms is generated in the first part of the atomization channel, saturates to a maximum in a position at the atomizer centre, and dissipates at the inside wall of the tubular atomizer before reaching the atomizer outlet edge, which is found to be in total agreement with the current understanding of atomization mechanism in tubular atomizer and emphasizes the fact that the centre of the quartz cell atomizer is the best location for the spectrometric data acquisition.

Advances in Piezoelectric Atomizers

Piezoelectric atomizers exhibit the advantages of structural simplicity,portability,low energy consumption,low production costs,and good atomization.They have been extensively used in various fields,including inhalation therapy,inkjet printing,and spray cooling.Here,the research of piezoelectric atomizers is first summarized from the perspectives of theoretical investigation and applications.Subsequently,the existing investigation and applications on piezoelectric atomizers are classified in terms of their functionalities.The functions of inkjet printing,spray cooling,and inhalation therapy are described in detail.Finally,the future trends in this field are analyzed.It is indicated that the vibrating-mesh atomizer has a promising prospect in the market,signaling strong demand especially in upgaraded consumption and medical scenarios.

Metal-organic framework-based single-atom electro-/ photocatalysts: Synthesis, energy applications, and opportunities

Single-atom catalysts(SACs)have gained substantial attention because of their exceptional catalytic properties.However,the high surface energy limits their synthesis,thus creating significant challenges for further development.In the last few years,metal–organic frameworks(MOFs)have received significant consideration as ideal candidates for synthesizing SACs due to their tailorable chemistry,tunable morphologies,high porosity,and chemical/thermal stability.From this perspective,this review thoroughly summarizes the previously reported methods and possible future approaches for constructing MOF-based(MOF-derived-supported and MOF-supported)SACs.Then,MOF-based SAC's identification techniques are briefly assessed to understand their coordination environments,local electronic structures,spatial distributions,and catalytic/electrochemical reaction mechanisms.This review systematically highlights several photocatalytic and electrocatalytic applications of MOF-based SACs for energy conversion and storage,including hydrogen evolution reactions,oxygen evolution reactions,O_(2)/CO_(2)/N_(2) reduction reactions,fuel cells,and rechargeable batteries.Some light is also shed on the future development of this highly exciting field by highlighting the advantages and limitations of MOF-based SACs.

Single-atom Pt on carbon nanotubes for selective electrocatalysis

Utilizing supported single atoms as catalysts presents an opportunity to reduce the usage of critical raw materials such as platinum,which are essential for electrochemical reactions such as hydrogen oxidation reaction(HOR).Herein,we describe the synthesis of a Pt single electrocatalyst inside single-walled carbon nanotubes(SWCNTs)via a redox reaction.Characterizations via electron microscopy,X-ray photoelectron microscopy,and X-ray absorption spectroscopy show the single-atom nature of the Pt.The electrochemical behavior of the sample to hydrogen and oxygen was investigated using the advanced floating electrode technique,which minimizes mass transport limitations and gives a thorough insight into the activity of the electrocatalyst.The single-atom samples showed higher HOR activity than state-of-the-art 30%Pt/C while almost no oxygen reduction reaction activity in the proton exchange membrane fuel cell operating range.The selective activity toward HOR arose as the main fingerprint of the catalyst confinement in the SWCNTs.