Production of Artificial Fog in the PAVIN Fog and Rain Platform: In Search of Big Droplets Fog

In fog, visibility is reduced. This reduction in visibility is measured by the meteorological optical range (MOR), which is important for studying human perception and various sensors in foggy conditions. The Cerema PAVIN Fog & Rain platform is capable of producing calibrated fog in order to better analyses it and understand its consequences. The problem is that the droplets produced by the platform are not large enough to resemble real fog. This can have a major impact on measurements since the interaction between electromagnetic waves and fog depends on the wavelength and diameter of the droplets. To remedy this, Cerema is building a new platform with new equipment capable of generating fog. This study analyses different nozzles and associated usage parameters such as the type of water used and the pressure used. The aim is to select the best nozzle with the associated parameters for producing large-diameter droplets and therefore more realistic fog.

Effect of Velocity Ratio,Viscosity Ratio,Contact Angle,and Channel Size Ratio on Droplet Formation

This study uses a T-junction to examine the effects of different parameters(velocity ratio,viscosity,contact angle,and channel size ratio)on the generation of microdroplets,related rate,and size.More specifically,numerical simulations are exploited to investigate situations with a velocity varying from 0.004 to 1.6 m/s for the continuous phase and from 0.004 to 0.8 m/s for the dispersed phase,viscosity ratios(0.668,1,6.689,10,66.899),contact angle 80°<θ<270°and four different canal size ratios(1,1.5,2 and 4).The results show that canal size influences droplet size and the generation rate.The contact angle has an impact on the form and the quality of generated droplets.Moreover,the relationship between velocity and viscosity ratios,droplet size,and generation rate is non-monotonic.

Effects of piperacillin synthesis on the infterfacial tensions and droplet sizes

Piperacillin is a polar organic substance,and can reduce the interfacial tension of oil and water when dissolved in water.In this study,changes in dichloromethane–water interfacial tensions and microdroplet sizes during piperacillin synthesis from an aqueous solution of ampicillin and dichloromethane solution of 4-ethyl-2,3-dioxo-1-piperazine carbonyl chloride(EDPC)were observed using a pendent drop technique and a coaxial ring tube system with embedded high-speed camera,respectively.It was found that the rapid N-acylation reaction caused the piperacillin at the interface to synthesize rapidly and diffuse out slowly,resulting in the interfacial tension decreased from 19.5 m N·m-1 to 7.2 m N·m-1 rapidly and then increased slowly as the concentrations of ampicillin and EDPC were 0.05 mol·L-1 and 0.1 mol·L-1.Meanwhile,the increase in the concentration of EDPC increased the peak concentration of piperacillin at the interface,and the addition of ethyl acetate to the ampicillin solution promoted mass transfer and reduced the aggregation of piperacillin effectively.During synthesis,the interfacial tension decreased,leading to a change in droplet sizes in the micro-reaction system.The two-phase reaction was carried out in a coaxial ring tube,with ampicillin and EDPC solutions as continuous and dispersed phases,respectively.The reaction reduced the dripping flow area,and the addition of ethyl acetate to the ampicillin solution slightly affected the division of the flow pattern.Under the same flow conditions,the droplet sizes of the reaction group were smaller than those of the no reaction group.The experimental results demonstrated that the increase of the continuous phase,decrease in the dispersed phase flow rate,or increase in EDPC concentration making droplet sizes smaller,and the addition of ethyl acetate slightly affected droplet sizes.These findings are important for the design and optimization of piperacillin synthesis reactors.

An experimental study on oil droplet size distribution in subsurface oil releases

Oil droplet size distribution （ODSD） plays a critical role in the rising velocity and transport of oil droplets in subsurface oil releases. In this paper, subsurface oil release experiments were conducted to study ODSD under different experimental conditions in a laboratory water tank observed by two high-speed cameras in March and April 2017. The correlation formulas Oh=lO.2Re-~ and Oh=39.2Re-1 （Re represents Reynolds number and Oh represents Ohnesorge number） were established to distinguish the boundaries of the three instability regimes in dimensionless space based on the experimental results. The oil droplet sizes from the experimental data showed an excellent match to the Rosin-Rammler distribution function with determination coefficients ranging from 0.86 to 1.00 for Lvda 10-1 oil. This paper also explored the influence factors on and change rules ofoil droplet size. The volume median diameter d50 decreased steadily with increasing jet velocity, and a sharp decrease occurred in the laminar-breakup regime. At Weber numbers （We） 〈100, the orifice diameter and oil viscosity appeared to have a large influence on the mean droplet diameter. At 100〈We〈1 000, the oil viscosity appeared to have a larger influence on the relative mean droplet diameter.

Relationships between Cloud Droplet Spectral Relative Dispersion and Entrainment Rate and Their Impacting Factors

Cloud microphysical properties are significantly affected by entrainment and mixing processes.However,it is unclear how the entrainment rate affects the relative dispersion of cloud droplet size distribution.Previously,the relationship between relative dispersion and entrainment rate was found to be positive or negative.To reconcile the contrasting relationships,the Explicit Mixing Parcel Model is used to determine the underlying mechanisms.When evaporation is dominated by small droplets,and the entrained environmental air is further saturated during mixing,the relationship is negative.However,when the evaporation of big droplets is dominant,the relationship is positive.Whether or not the cloud condensation nuclei are considered in the entrained environmental air is a key factor as condensation on the entrained condensation nuclei is the main source of small droplets.However,if cloud condensation nuclei are not entrained,the relationship is positive.If cloud condensation nuclei are entrained,the relationship is dependent on many other factors.High values of vertical velocity,relative humidity of environmental air,and liquid water content,and low values of droplet number concentration,are more likely to cause the negative relationship since new saturation is easier to achieve by evaporation of small droplets.Further,the signs of the relationship are not strongly affected by the turbulence dissipation rate,but the higher dissipation rate causes the positive relationship to be more significant for a larger entrainment rate.A conceptual model is proposed to reconcile the contrasting relationships.This work enhances the understanding of relative dispersion and lays a foundation for the quantification of entrainment-mixing mechanisms.

In-Situ Measurement of Droplet Size Distribution by Light Scattering Method

Inversion of droplet size distribution in two-phase flow from light scattering has been considered involved because it is in general reduced to the solution of Fredholm integral equation of the first kind that was always ill-posed. By using the Rosin-Rammler distributiona priori as the particulate size distribution model in the liquid-gas two-phase flow, a method via the solution of a two-parameter nonlinear programming problem to determine the droplet size distribution has been developed. A measurement system based on the technique is designed and applied in the shock test of blades of steam turbine. 100-hours continuous monitoring of the droplets in the liquid-gas two-phase flow of 8.0 Pa and 120 °C was performed and the details of the experiments are given out. It is shown that the technique is simple and efficient for in-situ real time measuring droplets in the liquid-gas two-phase flow.

Experimental study on the improvement of spray characteristics of aero-engines using gliding arc plasma

A gliding arc plasma fuel atomization actuator suitable for aeroengines was designed,and a gliding arc plasma fuel spray experimental platform was built to address the fuel atomization problem in aeroengine combustion chambers.The spray characteristics for different airflows,fuel flows,and discharge voltages were analyzed using laser particle size analysis.The research shows that the fuel atomization effect is improved from the increased airflow.The decreased fuel flow not only reduces the injection pressure of the fuel but also changes the discharge mode of the gliding arc,which affects reductions in the discharge power and inhibits fuel atomization.Gliding arc discharges accelerate the breaking,atomization,and evaporation of fuel droplets while reducing the particle size,which increases the proportion of small droplets.Compared with the working conditions of plasma-assisted atomization without the gliding arc,the D0.5,D0.9,and average particle size of the fuel droplets are reduced by 4.7%,6.5%,and 4.1%,respectively,when the modulation voltage of the gliding arc power supply is 200 V.

Microphysical Characteristics of Sea Fog over the East Coast of Leizhou Peninsula, China

Microphysical properties of sea fog and correlations of these properties were analyzed based on the measurements from a comprehensive field campaign carried out from 15 March to 18 April 2010 on Donghai Island （21°35″N, 110°32″5′E） in Zhanjiang, Guangdong Province, China. There were four types of circula- tion pattern in favor of sea fog events in this area identified, and the synoptic weather pattern was found to influence the microphysical properties of the sea fogs. Those influenced by a warm sector in front of a cold front or the anterior part of low pressure were found to usually have a much longer duration, lower visibility, greater liquid water content, and bigger fog droplet sizes. A fog droplet number concentration of N≥1 cm-a and liquid water content of L≥0.001 g m-a can be used to define sea fogs in this area. The type of fog droplet size distribution of the sea fog events was mostly monotonically-decreasing, with the spectrum width always being 〉20 μm. The significant temporal variation of N was due in large part to the number concentration variation of fog droplets with radius 〈3 μm. A strong collection process appeared when droplet spectrum width was 〉10 μm, which subsequently led to the sudden increase of droplet spectrmn width. The doln- inant physical process during the sea fog events was activation with subsequent condensational growth or reversible evaporation processes, but turbulent mixing also played an important role. The collection process occurred, but was not vital.

Relationship between Cloud Characteristics and Radar Reflectivity Based on Aircraft and Cloud Radar Co-observations

Cloud properties were investigated based on aircraft and cloud radar co-observation conducted at Yitong, Jilin, Northeast China. The aircraft provided in situ measurements of cloud droplet size distribution, while the millimeter-wavelength cloud radar vertically scanned the same cloud that the aircraft penetrated. The reflectivity factor calculated from aircraft measurements was compared in detail with sinmltaneous radar observations. The results showed that the two reflectivities were comparable in warm clouds, but in ice cloud there were more differences, which were probably associated with the occurrence of liquid water. The acceptable agreement between reflectivities obtained in water cloud confirmed that it is feasible to derive cloud properties by using aircraft data, and hence for cloud radar to remotely sense cloud properties. Based on the dataset collected in warm clouds, the threshold of reflectivity to diagnose drizzle and cloud particles was studied by analyses of the probability distribution function of reflectivity from cloud particles and drizzle drops. The relationship between refiectivity factor （Z） and cloud liquid water content （LWC） was also derived from data on both cloud particles and drizzle. In comparison with cloud droplets, the relationship for drizzle was blurred by many scatter points and thus was less evident. However, these scatters could be partly removed by filtering out the drop size distribution with a large ratio of reflectivity and large extinction coefficient but small effective radius. Empirical relationships of Z-LWC for both cloud particles and drizzle could then be derived.

Spray and mixing characteristics of liquid jet in a tubular gas-liquid atomization mixer

For the design and optimization of a tubular gas-liquid atomization mixer,the atomization and mixing characteristics of liquid jet breakup in the limited tube space is a key problem.In this study,the primary breakup process of liquid jet columnwas analyzed by high-speed camera,then the droplet size and velocity distribution of atomized droplets were measured by Phase-Doppler anemometry(PDA).The hydrodynamic characteristics of gas flow in tubular gas-liquid atomization mixer were analyzed by computational fluid dynamics(CFD)numerical simulation.The results indicate that the liquid flow rate has little effect on the atomization droplet size and atomization pressure drop,and the gas flowrate is themain influence parameter.Under all experimental gas flowconditions,the liquid jet column undergoes a primary breakup process,forming larger liquid blocks and droplets.When the gas flow rate(Qg)is less than 127 m^(3)·h^(−1),the secondary breakup of large liquid blocks and droplets does not occur in venturi throat region.The Sauter mean diameter(SMD)of droplets measured at the outlet is more than 140μm,and the distribution is uneven.When Qg>127 m^(3)·h^(−1),the large liquid blocks and droplets have secondary breakup process at the throat region.The SMD of droplets measured at the outlet is less than 140μm,and the distribution is uniform.When 127<Qg<162m^(3)·h^(−1),the secondary breakup mode of droplets is bag breakup or pouch breakup.When 181<Qg<216m^(3)·h^(−1),the secondary breakup mode of droplets is shear breakup or catastrophic breakup.In order to ensure efficient atomization and mixing,the throat gas velocity of the tubular atomization mixer should be designed to be about 51 m·s^(−1) under the lowest operating flow rate.The pressure drop of the tubular atomization mixer increases linearly with the square of gas velocity,and the resistance coefficient is about 2.55 in single-phase flow condition and 2.73 in gas-liquid atomization condition.

Formulation of self-nanoemulsifying drug delivery systems containing monoacyl phosphatidylcholine and Kolliphor^(■) RH40 using experimental design

The development of self-nanoemulsifying drug delivery systems(SNEDDS) to enhance the oral bioavailability of lipophilic drugs is usually based on traditional one-factor-at-a-time approaches. These approaches may be inadequate to analyse the effect of each excipient and their potential interactions on the emulsion droplet size formed when dispersing the SNEDDS in an aqueous environment. The current study investigates the emulsion droplet sizes formed from SNEDDS containing different levels of the natural surfactant monoacyl phosphatidylcholine to reduce the concentration of the synthetic surfactant polyoxyl 40 hydrogenated castor oil(Kolliphor ~? RH40). Monoacyl phosphatidylcholine was used in the form of Lipoid S LPC 80(LPC, containing approximately 80% monoacyl phosphatidylcholine, 13% phosphatidylcholine and 4% concomitant components). The investigated SNEDDS comprised of long-chain or medium-chain glycerides(40% to 75%), Kolliphor ~? RH40(5% to 55%), LPC(0 to 40%) and ethanol(0 to 10%). D-optimal design, multiple linear regression, and partial least square regression were used to screen different SNEDDS within the investigated excipient ranges and to analyse the effect of each excipient on the resulting droplet size of the dispersed SNEDDS measured by dynamic light scattering. All investigated formulations formed nano-emulsions with droplet sizes from about 20 to 200 nm. The use of mediumchain glycerides was more likely to result in smaller and more monodisperse droplet sizes compared to the use of long-chain glycerides. Kolliphor~? RH40 exhibited the most significant effect on reducing the emulsion droplet sizes. Increasing LPC concentration increased the emulsion droplet sizes, possibly because of the reduction of Kolliphor~? RH40 concentration. A higher concentration of ethanol resulted in an insignificant reduction of the emulsion droplet size. The study provides different ternary diagrams of SNEDDS containing LPC and Kolliphor ~? RH40 as a reference for formulation developers.

How Much Do Adjuvant and Nozzles Models Reduce the Spraying Drift? Drift in Agricultural Spraying

The spraying of herbicides in crops has become the main form of weed control. Although it means unexpected effects on non-target plants resulted by spraying drift. Thus, improvements in application techniques, as the best selection of spray nozzles and adjuvant, are essential to avoid environmental contamination and economic losses. On this work, we evaluate how much adjuvant associated with nozzles can reduce the spray drift. The nozzles used at experiment were air induction flat tip, hollow cone and twinjet and the spray liquids, which were composed of herbicide glyphosate and phosphatidylcholine + propionic acid adjuvant. Measurements were made at wind tunnel and droplet sizer, at laser diffraction method. The models of nozzles influence in droplet size characteristics and in occurrence of spray drift. The use of adjuvants reduces the spray drift only combined with the twinjet nozzle, while for the other models the adjuvant did not reduce the global spray drift at significant levels. The adjuvant reduced the spray drift until 39%, while the nozzles model reduced until 74%. Both techniques when combined were able to reduce until 80%. The model of nozzle has the biggest result on drift mitigation and the use of adjuvants can increase the drift mitigation specially with nozzles that produces smallest droplets.

Destabilising persistent coal froth using silicone oil

Persistent froth is becoming more and more common in coal and mineral flotation plants and presents safety and operational challenges.No effective method has been developed to destabilise persistent froth.As a new initiative,this study examined the structural difference between persistent foam and coal froth,based on which a solution was developed to maximumly destabilise coal froth.Destabilisation test,oscillatory rheology measurement and scanning electron microscopy(SEM) analysis indicated that the coal froth was more stable than the foam due to the formation of thin capillaries and tightly arranged coal particles on bubble surfaces.Although 107 μm silicone oil droplet could completely destabilise the foam at 2 mmol/L concentration,it only destabilised less than 50% coal froth even at 6 mmol/L concentration.To maximumly destabilise the coal froth formed by-38 and-20 μm particles,24 and 18 μm silicone oil droplets were required to pass through the thin capillaries and enter the bubble films,respectively.However,smaller silicone oil droplets could not bridge the bubble films to destabilise coal froth and therefore a critical droplet size occurred depending on the size of particles stabilising the froth.

Influence of Viscosity in Fluid Atomization with Surface Acoustic Waves

In this work, aqueous glycerol solutions are atomized to investigate the influence of the viscosity on the droplet size and the general atomization behavior in a setup using standing surface acoustic waves (sSAW) and a fluid supply at the boundary of the acoustic path. Depending on the fluid viscosity, the produced aerosols have a monomodal or polymodal size distribution. The mean droplet size in the dominant droplet fraction, however, decreases with increasing viscosity. Our results also indicate that the local wavefield conditions are crucial for the atomization process.

Influence of Surface State on Moisture Sensitivity of Carbon Fiber and Its Composite Interfacial Properties

The influence of surface state on the moisture sensitivity of carbon fiber was analyzed by applying a T800 grade carbon fiber with five different surface conditions,namely,with and without surface oxidation,in the presence or absence of sizing agent.The interfacial properties of their composites in the presence of two epoxy matrices（respectively EP07 and EP10） were also characterized by micro-droplet tests.The overall results show that both oxidized and sizing-coated fibers have higher moisture equilibrium content than that of the pristine unsurface-treated fiber,due to higher amount of activated carbon groups.After moisture absorption of the carbon fibers,almost all the fiber/epoxy systems show decrease in the interfacial shear strength and the unsurface-treated fiber system exhibits the largest decline.Moreover,both interfacial shear strength and interlaminar shear strength of carbon fiber/EP10 composite demonstrate better water resistance performance than that of the carbon fiber/EP07 composite,consistent with DSC results of the two resins.

Design of a high-voltage electrostatic ultrasonic atomization nozzle and its droplet adhesion effects on aeroponically cultivated plant roots

In the process of aeroponics cultivation,the atomizer is one of the most important influencing factors on the cultivation process.This study presented the design of an ultrasonic atomization nozzle using contact charging and a root droplet adhesion test rig.The purpose of this study was to reveal the relationship between the main operating parameters of the high-voltage electrostatic ultrasonic atomization nozzle and the atomization effect using droplet adhesion measurements.In this study,the ultrasonic effect of nozzle was achieved by using Laval tube,and the design of the key parameters for the high-voltage electrostatic ultrasonic atomization nozzle were inlet pressure,electrostatic voltage root core electrode material and spray distance;the droplet size variation and root adhesion patterns were obtained through experiments.The best operating parameters were analyzed by using the orthogonal test method,and the droplet deposition distribution of the root system at different scales was investigated in the atomization chamber.The test results revealed that when the root core electrode material was coppe and the nozzle working parameters were at 0.4 MPa of inlet pressure,at 1.75 m the spray distance,at 12 kV of the electrostatic voltage,the root system has the highest droplet adhesion.

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.

In situ characterization of particle formation in spray flame synthesis using wide-angle light scattering

Wide-angle light scattering(WALS)was used for in situ measurements of droplet and nanoparticle size distributions during the synthesis of titania and iron oxide particles from liquid precursor solutions in the standardized SpraySyn burner for spray flame synthesis.Titania was synthesized from titanium tetraisopropoxide(TTIP)and iron oxide from iron(II)nitrate nonahydrate(INN)using ethanol(EtOH)as solvent.Scattering images were taken at heights up to 120 mm above the burner surface and classified into droplet and particle scattering.Droplet size distributions were derived from a sequential analysis of scattering data containing the oscillating Mie pattern,the lognormal size distribution parameters for spherical and fractal particle fractions from a multivariate approach on averaged particle scattering data.The results show that the precursor addition leads to altered evaporation behavior and even droplet disruption probably induced by puffing or micro-explosions compared to pure EtOH.In the case of TTIP(a hygroscopic alkoxide),the synthesis of a large fraction of spheres was observed,while the nitrate INN leads to the formation of mostly fractal aggregates.

Atomization characteristics of pyrolysis oil derived from waste tires

The atomization characteristics play a key role in the highly efficient combustion of pyrolysis oil derived from waste tires.In this study,the fuel properties of tire pyrolysis oil(TPO)were initially studied,and then a high-speed camera and a phase Doppler particle analyzer were employed to characterize the atomization feature of TPO.The influence of pressure and nozzle orifice diameter on atomization characteristics such as spray angle,droplet velocity,and droplet size distribution was investigated.The results showed that TPO had a high calorific value of about 43.6 MJ/kg and a low viscosity of 3.84×10^(–6)m^(2)/s at 40℃,which made it have the potential to be used as an alternative fuel.Higher pressure expanded the spray angle and extended the spray in both the axial and radial directions.With increasing pressure,spray angle and droplet velocity raised,and the increase in crushing effect of air reduced the Sauter mean diameter(SMD)of the droplets.To obtain proper atomization quality for combustion,the pressure is expected to be higher than 1.25 MPa.With increasing nozzle orifice diameter,droplet velocity increased,and the SMD of the droplets increased as well due to weakened crushing effect of the orifice.Therefore,the pressure must be increased to maintain the atomization quality when using a nozzle with a larger orifice.Due to the lower viscosity,the velocity and particle size distribution of TPO droplets after atomization were smaller than those of diesel droplets.The extremely small carbon black contained in TPO also contributed to the breaking of droplets and played a certain role in the size reduction of the oil droplets,but it may cause the risk of nozzle blockage.In summary,TPO showed great atomization characteristics for alternative fuel applications.

Research into Configuration and Flow of Wall Oil Film in Bearing Chamber Based on Droplet Size Distribution

The lubrication design and heat transfer determination of bearing chambers in aeroengine require a sufficient understanding of the oil droplet-film interaction and physical characteristic in an oil/air two-phase flow state. The analyses of oil droplet movement, mass and momentum transfer during the impingement of droplet/wall, as well as wall oil film thickness and flow velocity are very important for the bearing chamber lubrication and heat transfer calculation. An integrated model in combination with droplet movement, droplet/wall impact and film flow analysis is put forward initially based on the consideration of droplet size distribution. The model makes a contribution to provide more practical and feasible technical approach, which is not only for the study of droplet-film interaction and physical behavior in bearing chambers with oil/air two-phase flow phenomena, but also useful for an insight into the essence of physical course through droplet movement and deposition, film formation and flow. The influences of chamber geometries and operating conditions on droplet deposition mass and momentum transfer, and wall film thickness and velocity distribution are discussed. The feasibility of the method by theoretical analysis is also verified by the ex- isting experimental data. The current work is conducive to expose the physical behavior of wall oil film configuration and flow in bearing chamber, and also significant for bearing chamber lubrication and heat transfer study under oil/air two-phase flow conditions.