Begell House Inc.
Atomization and Sprays
AAS
1044-5110
8
3
1998
TEMPERATURE EFFECTS ON ATOMIZATION BY FLAT-FAN NOZZLES: IMPLICATIONS FOR DRIFT MANAGEMENT AND EVIDENCE FOR SURFACTANT CONCENTRATION GRADIENTS
241-254
10.1615/AtomizSpr.v8.i3.10
Roger A.
Downer
Laboratory for Pest Control Application Technology (LPCAT), Department of Entomology, Ohio Agricultural Research and Development Center, Wooster, Ohio, USA
Franklin R.
Hall
Laboratory for Pest Control Application Technology (LPCAT), Department of Entomology, Ohio Agricultural Research and Development Center, Wooster, Ohio, USA
Rebecca S.
Thompson
Laboratory for Pest Control Application Technology (LPCAT), Department of Entomology, Ohio Agricultural Research and Development Center, Wooster, Ohio, USA
Andrew C.
Chapple
c/o Koyntoypiotoy 13, Tpiandria 55337, Thessaloniki, Greece
The effect of temperature on the atomization of a range of agricultural spray liquids is described, from approx. 3 °C to 40 °C, for water, a nonionic surfactant, two polymeric adjuvants, two blank formulations of an insecticide [emulsifiable concentrate (EC) and wettable powder (WP)], and two organo-silicone surfactants. In general, the potential for drift (% volume < 150 μ;m) was increased to varying degrees with increasing carrier liquid temperature, but not for all the spray liquids tested, with the wettable powder a notable exception.No general relationship could be found linking temperature with change in spray cloud characteristics (e.g., arithmetic mean, number median diameter, percent spray volume < 150 μ;m, etc.). The surface tension (surface age 170 ms) and viscosity (zero shear rate) of the test materials were also measured at representative temperatures, but no simple or unifying linear relationship between these physicochemical properties and spray cloud characteristics could be discerned. The investigation was widened to study the most disparate spray liquid, an organo-silicone adjuvant, comparing atomization at points across the short axis of the spray cloud with water, at 5 °C and 35 °C. From the data, we would hypothesize that surfactant concentration gradients are formed within the spray sheet prior to ligament/drop formation. Therefore, the effects of surfactants on the atomization of a liquid through a flat-fan hydraulic nozzle cannot be considered as a single process driven by a single value for surfactant concentration. The supporting evidence for a more complex description is discussed.The research reported reinforces previous work suggesting that the relationship between physicochemical properties of liquids and the atomization characteristics of those spray liquids is far from simple and cannot be predicted from simple measurements of surface tension or viscosity based on our current experimentation. The data also showed that the particulate (WP) formulation was the most stable when atomized (i.e., least prone to change), and that the effect on atomization of the often multiple components of agricultural spray formulations still represents significant opportunities for improved understanding.
SPRAY FORMATION BY FLASHING OF A BINARY MIXTURE: A PARAMETRIC STUDY
255-266
10.1615/AtomizSpr.v8.i3.20
Michal
Zeigerson-Katz
The Pearlstone Center for Aeronautical Studies, Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel
Eran
Sher
Faculty of Aerospace Engineering, Technion-Israel Institute of Technology,
Haifa, Israel
A binary liquid mixture which consists of a low-vapor-pressure liquid and a propellant has been considered. When the mixture is discharged through an appropriate injection system, the propellant undergoes a rapid flash boiling process which results in a disintegration of the continuous liquid phase into small droplets. In the present work, the effect of the injection system design on the spray characteristics is investigated experimentally. It is concluded that: (1) the real behavior of the solution, as compared to ideal solution behavior, is an important factor; (2) the important stage of nucleation occurs at the metering orifice and apparently, the main duct does not play any significant role in the bubbles' nucleation; (3) neither the expansion chamber diameter nor its length has any significant effect on the droplet Sauter mean diameter (SMD), (4) an orifice's diameters ratio (metering to discharge) between 0.6 and 0.9 results in a minimum SMD; and (5) the SMD is correlated well with a modified version of the Jakob number of the form of Ja* = xβ(CpΔT/hfg).
EMPIRICAL CALCULATION MODEL OF THE ATOMIZATION OF A LIQUID SHEET AND A ROUND LIQUID JET IN A GASEOUS FLOW FIELD
267-289
10.1615/AtomizSpr.v8.i3.30
Nobuyuki
Yatsuyanagi
Kakuda Research Center, National Aerospace Laboratory, Miyagi, Japan
Hiroshi
Sakamoto
Kakuda Research Center, National Aerospace Laboratory, Miyagi, Japan
Kazuo
Sato
Kakuda Research Center, National Aerospace Laboratory, Miyagi, Japan
This article presents a 1D, empirically based model for the prediction of spray charactiristics for either a liquid sheet or a round liquid jet injected into a high-velocity gaseous flow field. The model includes both primary and secondary atomization process.
In the primary breakup process, the local atomization rate and the initial size and velocity of the droplets are calculated, where the local atomization rate is basically derived from the balance of static force acting on the disturbed surface layer. In the subsequent acceleration process of the droplets, the changes in size and number are calculated. The evaluation of these characteristics is based on the energy and mass conservation equations of the droplets, where the critical Eötvös number, which was derived experimentally in the authors' former study, is substituted in the term of the energy equation. Thereafter, as the final state of the whole atomization process, final droplet sizes and their distributions are obtained. Comparison of the representative size and distribution of the spray between the calculated results and experimental results showed reasonable agreement. Comparisons were also made with other experimental data and showed good agreement.
FAST VIDEO STUDY OF SURFACTANT EFFECTS ON FUEL ATOMIZATION IN A TRANSPARENT ENGINE
291-305
10.1615/AtomizSpr.v8.i3.40
M.
Golombok
Shell International Petroleum Co., Shell Research and Technology Centre − Thornton, Chester, United Kingdom
V.
Blanchard
Shell International Petroleum Co., Shell Research and Technology Centre − Thornton, Chester, United Kingdom
P. J.
Cooney
Shell International Petroleum Co., Shell Research and Technology Centre − Thornton, Chester, United Kingdom
D. G.
Latimer
Shell International Petroleum Co., Shell Research and Technology Centre − Thornton, Chester, United Kingdom
V.
Morin
Shell International Petroleum Co., Shell Research and Technology Centre − Thornton, Chester, United Kingdom
D. A. R.
Jones
Shell International Petroleum Co., Shell Research and Technology Centre − Thornton, Chester, United Kingdom
Fast video photography and image analysis were used to compare the effect of fuel and mixture preparation variables on the relative quantities of liquid droplets present in the combustion chamber of a port fuel-injected engine. The injection timing and swirl conditions were varied and a fluorinated surfactant was also added to a standard gasoline. Swirl enhanced evaporation. The surfactant decreased the light scattering. There is some indication that swirl and additive together are mutually antagonistic and work against their individual beneficial effects on mixture preparation.
LINKING NOZZLE FLOW WITH SPRAY CHARACTERISTICS IN A DIESEL FUEL INJECTION SYSTEM
307-347
10.1615/AtomizSpr.v8.i3.50
C.
Arcoumanis
School of Engineering, City University, London
Manolis
Gavaises
School of Mathematics, Computer Science, and Engineering, City University London, Northampton Square, EC1V 0HB London, UK
A computer model simulating the flow in fuel injection systems and the characteristics of diesel sprays injected from multihole orifice-type injectors has been developed and validated against experimental data. The injection conditions were modeled by solving the wave dynamics in the fuel injection equipment (FIE) using a one-dimensional model The flow in the sac volume was treated as a three-dimensional one for the noncavitating cases, in order to identify the basic flow distribution at the exit of the nozzle holes. For the cavitating cases, a one-dimensional sac volume flow model was developed; correlations giving the discharge coefficient of the injection holes were used in order to predict the quantity of fuel injected. Both inclined and vertical injectors can be modeled, since different flow rates are predicted for the different holes of multihole nozzles, depending on the position of the injection hole relative to the sac volume and the needle seat axis. The injection velocity calculation was based on the effective area (area at the hole exit occupied by liquid due to the presence of cavitating bubbles), which is calculated as a function of the flow conditions in the sac volume, the hole geometric characteristics, and the back pressure. Following the initiation of fuel injection, with droplet velocity, size, hole effective area, and level of turbulence at the nozzle exit calculated from the FIE model, an existing three-dimensional computational fluid dynamics (CFD) diesel spray model was extended and used for the prediction of the spray characteristics. This model is based on the Eulerian-Lagrangian stochastic particle technique; the gas phase is simulated by solving numerically the full Navier-Stokes equations, while the liquid phase is modeled using a Lagrangian particle tracking approximation. Spray submodels were used to represent the various physical phenomena taking place during the spray development. Emphasis was placed on the effect of the nozzle flow on the disintegration of the emerging liquid jet. Different jet atomization models were used in order to predict the spray characteristics at the closest point to the hole exit where experimental data were available. The aerodynamic-induced atomization, the jet turbulence-induced atomization, and a newly developed model for the cavitation-induced atomization were the three mechanisms considered responsible for the disintegration of the liquid jet. The latter mechanism was combined with a correlation representing the radial distribution of the droplets in the spray cone angle. Droplet secondary breakup, droplet collisions, and droplet turbulent dispersion were taken into account as the droplets penetrate into the surrounding gas. Quiescent atmospheric gas conditions have been selected for model validation in order to concentrate on the effect of the nozzle flow on the spray characteristics without the added complications induced by high-density effects or gas motion. The computational results were extensively compared with available experimental data, and confirm that hole cavitation enhances atomization. These results include a typical set of predictions for the flow in the FIE, the velocity, pressure, and turbulence kinetic energy distributions in the sac volume for noncavitating transient flow conditions, the fuel injected per injection hole, and the effective hole area for the one-dimensional sac volume flow model, and the droplet temporal and spatial characteristics (velocity and size) for the spray model Two different injection conditions were examined, corresponding to pump speeds of 600 and 1200 rpm. From the comparison between the two different sets of results, it can be concluded that the combined FIE-spray model is capable of predicting the spray characteristics without a priori knowledge of the flow characteristics in the sac volume and at the exit of the injection holes.
BIMODAL DROP SIZE DISTRIBUTION BEHAVIOR IN PLAIN-JET AIRBLAST ATOMIZER SPRAYS
349-362
10.1615/AtomizSpr.v8.i3.60
Ronen
Harari
The Pearlstone Center for Aeronautical Engineering Studies, Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel
Eran
Sher
Faculty of Aerospace Engineering, Technion-Israel Institute of Technology,
Haifa, Israel
A plain-jet, external-mixing, airblast atomizer has been studied. A bimodal drop size distribution behavior has been observed, where two different drop size populations have been identified. It was observed that as a result of the impingement of the air stream on the liquid jet, a portion of the liquid flows back toward the orifice, arrives at the orifice surface, spreads outward as a thin film in the radial direction, and is then atomized by the air stream emerging from the annular slot. While the large-drop population is generated by the atomization process occurring at the liquid-air collision region, the small-drop population is generated by the backflow mechanism. This phenomenon has been studied experimentally and an approximate analysis has been proposed to describe it.