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.

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.

Studies on Droplet Size Distributions during Coalescence in Immiscible Polymer Blends Filled with Silica Nanoparticles

The effect of silica nanoparticles on the morphology of （10/90 wt%） PDMS/PBD blends during the shear induced coalescence of droplets of the minor phase at low shear rate was investigated systematically in situ by using an optical shear technique. Two blending procedures were used： silica nanoparticles were introduced to the blends by pre-blending silica particles first in PDMS dispersed phase （procedure 1） or in PBD matrix phase （procedure 2）. Bimodal or unimodal droplet size distributions were observed for the filled blends during coalescence, which depend not so much on the surface characteristics of silica but mainly on blending procedure. For pure （10/90 wt%） PDMS/PBD blend, the droplet size distribution exhibits bimodality during the early coalescence. When silica nanoparticles （hydrophobic and hydrophilic） were added to the blends with procedure l, bimodal droplet size distributions disappear and unimodal droplet size distributions can be maintained during coalescence; the shape of the different peaks is invariably Gaussian. Simultaneously, coalescence of the PDMS droplets was suppressed efficiently by the silica nanoparticles. It was proposed that with this blending procedure the nanoparticles should be mainly kinetically trapped at the interface or in the PDMS dispersed phase, which provides an efficient steric barrier against coalescence of the PDMS dispersed phase. However, bimodal droplet size distributions in the early stage of coalescence still occur when incorporating silica nanoparticles into the blends with procedure 2, and then coalescence of the PDMS droplets cannot be suppressed efficiently by the silica nanoparticles. It was proposed that with this blending protocol the nanoparticles should be mainly located in the PBD matrix phase, which leads to an inefficient steric barrier against coalescence of the PDMS dispersed phase; thus the morphology evolution in these filled blends is similar to that in pure blend and bimodal droplet size distributions can be observed during the early coalescence. These results imply that exploiting non-equilibrium processes by varying preparation protocol may provide an elegant route to regulate the temporal morphology of the filled blends during coalescence.

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.

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.

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.

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.

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.