Begell House Inc.
Atomization and Sprays
AAS
1044-5110
15
2
2005
ON SAMPLING FROM PRESCRIBED DROPLET PDFS USING COMPUTATIONAL PARCELS
119-131
10.1615/AtomizSpr.v15.i2.10
John C.
Hewson
Sandia National Laboratories, Fire Science & Technologies, P. O. Box, 5800, Albuquerque, NM, 87185-1135
Sam S.
Yoon
Mechanical Engineering Department, Korea University, Anamdong, 5-Ga, Sungbukgu, Seoul, 136-713, Korea
The relationship between the distribution of collections of particles (referred to as parcels or clouds) and the distribution of the individual particles is presented. While the parcel size distribution for the given χ2 distribution is available in the literature, the distribution for the Rosin-Rammler, log-normal, and Gaussian distributions are not available in the literature. Analytical expressions of the particles and parcels for the Rosin-Rammler, log-normal, and Gaussian distributions are developed. Monte Carlo results are presented to show that the original droplet distributions are recovered.
EFFECT OF FAN SPEED AND ELECTROSTATIC CHARGE ON DEPOSITION OF ORCHARD CANOPY SPRAYS
133-144
10.1615/AtomizSpr.v15.i2.20
G. N.
Laryea
Department of Agricultural Machinery Engineering, Chungbuk National University, Cheongju, Korea
Soo-Young
No
Dept. of Biosystems Engineering, Dept of Agricultural Machinery Engineering, Chungbuk National University, South Korea
This work is a continuation of an ongoing project, performed in an orchard, to determine the effect of air flow velocity on electrostatic forces in plant canopy. Field applications were made using the fluorescent tracer manganese(II) sulfate (MnSO4), applied through seven electrostatic pressure-swirl nozzles with and without charge when fitted to an axial-fan orchard airblast sprayer with selected fan speeds of 1000, 1500, and 2000 rpm. Spray deposition was analyzed for two varieties of semidwarf apple trees referred to as M9 and M26 East Malling Roots. The field experiment was performed with single and twin passes of the sprayer at a constant ground velocity of 0.82 km/h. Statistical methods were used to analyze and to compare the effect of the selected fan speeds on electrostatic forces at sampling locations between the uncharged and charged sprays. The charged spray showed an increase of 2.47−2.51-fold at a fan speed of 2000 rpm for one pass and two passes, respectively, for M9 trees. The charged spray deposition was superior to the uncharged spray by 1.65−1.89-fold at 2000 rpm for both passes. There was no significant difference between the charged and uncharged spray deposition for the fan speed of 1500 rpm for two passes. It therefore emerged that the charged spray was superior to the uncharged spray at a fan speed of 2000 rpm.
EFFERVESCENT ATOMIZATION OF LIQUIDS
145-168
10.1615/AtomizSpr.v15.i2.30
Marc
Lorcher
Bayer AG, BTS-ENG-CP-ACSC, Rheinufer 7-9, R85, 47829 Krefeld, Germany
Florian
Schmidt
University of Hannover, Institut fur Verfahrenstechnik (Process Engineering), Callinstr. 36, 30167 Hannover, Germany
Dieter
Mewes
University of Hannover, Institut fur Verfahrenstechnik (Process Engineering), Callinstr. 36, 30167 Hannover, Germany
Liquids or suspensions are dispersed into sprays of small droplets by atomization of two-phase gas-liquid mixtures. Thus narrow droplet diameter distributions and a high interface area density of the liquid phase are generated in order to increase heat and mass transfer. The mean droplet diameter of the spray is time dependent. It also depends on the total pressure upstream from the nozzle, the volumetric flow rates of the liquid and the gas phase, as well as on the flow regime inside the nozzle. The radial and axial profiles of the void fraction inside the nozzle are measured with an electrical measurement technique. In addition, the flow in the nozzle is visualized by a high-speed camera. Three flow regimes are identified. A model is established to predict the flow regime inside the atomizer. It turns out that the flow regime changes by accelerating the flow to critical conditions. The visualized flow fields are compared to calculated ones. A model to predict the breakup regime is established considering the phase distribution and the critical flow conditions at the exit cross section.
ATOMIZATION OF VISCOUS MELTS
169-180
10.1615/AtomizSpr.v15.i2.40
H.
Lohner
Department of Chemical Engineering, University of Bremen, Bremen, Germany
C.
Czisch
University Bremen, Chemical Engineering Departmen, Badgasteiner Str. 3 D-28359 Bremen, Germany
P.
Schreckenberg
Department of Chemical Engineering, University of Bremen, Bremen, Germany
Udo
Fritsching
Particles and Process Engineering Department, Faculty of Production
Engineering, University Bremen, Bibliothekstr. 1, 28359 Bremen, Germany; Leibniz Institute for Materials Engineering IWT, Badgasteiner Str. 3, 28359
Bremen, Germany
Klaus
Bauckhage
Chemical Engineering Department, University of Bremen, Institut for Werkstofftechnik, Bremen, Germany
Specific melt types have high viscosity and comparably low surface tension. Therefore, conventional twin-fluid atomization of these viscous melts for powder production often results not in spherical particles but in a great amount of fiber material. In this investigation, viscous mineral melts are atomized in a pilot plant by means of hot gases for spherical particle granulation. Experimental results show that an almost fiber-free product (97% spherical powder) can be obtained. Usually, the atomization process is controlled by the gas pressure only (here before the expansion in the atomizer nozzle). For constant atomization pressure the mass median diameter of the powder yield decreases with increasing atomization gas temperature.
Numerical simulations of the gas flow field in the atomizer vicinity support the analysis of the melt fragmentation process by obtaining the gas temperature distribution and the gas flow conditions within the atomization process. Simulations for different atomizer nozzle designs and several operating conditions have been realized. From the discussion of the experimental results together with the results of the simulations, the relevant shear process between the melt jet and the atomization gas, characterized by the Reynolds number, can be determined as the main driving mechanism of the atomization and spheroidization process.
GROWTH OF LONGITUDINAL WAVES IN PLANE LIQUID SHEETS HAVING LATERAL WAVE MODES WHEN EXPOSED TO TWO GAS STREAMS OF UNEQUAL VELOCITIES
181-200
10.1615/AtomizSpr.v15.i2.50
T. John
Tharakan
Liquid Propulsions Systems Centre, Indian Space Research Organization,Valiamala, Thiruvananthapuram 695547, India
K.
Ramamurthi
Thermodynamics and Combustion Laboratory, Indian Institute of Technology, Madras, Chennai 600036, India
The growth of waves along the direction of motion of thin viscous liquid sheets is investigated when lateral waves are additionally present. Gas streams are considered to move at different relative velocities over the gas—liquid interfaces. A dispersion relation is derived using spatial growth of the longitudinal waves. Para-antisymmetric waves are shown to have significant growth rates in the presence of lateral wave motion at larger values of Weber number, gas-to-liquid density ratio, and relative velocity ratio. The presence of lateral wave motion does not affect the growth rates when gas Weber number exceeds 10.
The droplet sizes, formed from the disintegration of the liquid sheets, are also determined from the longitudinal and lateral wave numbers. The distribution of droplet sizes is modeled and it is shown that the droplet sizes, formed in the presence of lateral wave motion, are restricted over a smaller range of diameters as compared to the wider distribution obtained in the absence of the lateral wave modes.
EXPERIMENTAL CHARACTERIZATION OF AN INTERMITTENT GASOLINE SPRAY IMPINGING UNDER CROSS-FLOW CONDITIONS
201-222
10.1615/AtomizSpr.v15.i2.60
Miguel R. Oliveira
Panão
ADAI, LAETA, Associacao para o Desenvolvimento da Aerodinamica Industrial, University of Coimbra, 3030-788 Coimbra, Portugal
Antonio L. N.
Moreira
IN+ Center for Innovation, Technology and Policy Research, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisbon 1049-001, Portugal
This article reports an experimental study on an intermittent gasoline spray impinging onto a flat surface in the presence of a cross flow. The experiments include detailed phase Doppler anemometry (PDA) measurements of droplet size, velocity, and volume flux to quantify the time-dependent fluid dynamic interactions between the spray and the cross flow. The analysis is performed in terms of the expected influence on the outcome of impact.
Interposition of the wall decreases the penetration rate of the spray, and therefore the energy available at impact is smaller than would be expected from the analysis of the free spray. However, the main effect of the wall is due to the formation of a three-dimensional time-varying vortical structure in the vicinity of the wall, which entrains reatomized droplets to reimpinge with smaller Reynolds numbers, thus contributing to the formation of the wall liquid film. Although spray/wall interaction is altered due to deviation of the impinging spray by the cross flow, the main effect is due to drag of small droplets from the vortical structure, thus reducing the number of droplets predicted to stick at the wall. However, it is suggested that the cross flow enhances the interaction between crowns at the target surface and impinging droplets, in such a way that the volume flux of small droplets flying way from the surface may overcome the volume flux of impinging droplets.
LIQUID JET BREAKUP AND ATOMIZATION BY ANNULAR SWIRLING GAS JET
223-247
10.1615/AtomizSpr.v15.i2.70
Arnaud
Dunand
Laboratoire de Combustion et Detonique, CNRS UPR 9028, University of Poitiers, ENSMA, 1 Avenue Celement Ader, BP 40109, 86961 Futuroscope, Chasseneuil Cedex, France
Jean-Louis
Carreau
Institut PPRIME, Département Fluides, Thermique, Combustion, CNRS ENSMA Université de Poitiers UPR 3346, ENSMA BP 109, 86960 FUTUROSCOPE Cedex, France
Francis
Roger
Institut PPRIME, Département Fluides, Thermique, Combustion, CNRS ENSMA Université de Poitiers UPR 3346, ENSMA BP 109, 86960 FUTUROSCOPE Cedex, France
In spray systems, swirl motion is generally imparted to the liquid jet in order to favor its fragmentation. In coaxial atomization applications, however, due to its higher momentum, the dynamics of the flow is controlled mainly by the annular gas jet. As a consequence, we examine the effect of a swirling coaxial gas jet on breakup and atomization of a liquid jet as a function of the rotation intensity, given by the swirl number S, gas-to-liquid momentum flux ratio J, and surrounding pressure. The main results were: low enhancement of the atomization with no major changes of the jet development for low swirl, but, when a critical amount of rotational flow is imparted to the gas stream according to experimental conditions, topology of the flow is significantly modified. This transition leads to a significant decrease in liquid jet breakup length and an inversion of droplet distribution. The second kind of flow is linked with the appearance of a stagnation point on the jet centerline, whose occurrence and characteristics depend on operating conditions.