Internal Flow Effects in Prefilming Airblast Atomizers: Mechanisms of Atomization and Droplet Spectra

1986 ◽  
Vol 108 (3) ◽  
pp. 465-472 ◽  
Author(s):  
T. Sattelmayer ◽  
S. Wittig
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Mass Flow ◽  
High Speed ◽  
Internal Flow ◽  
Droplet Size Distribution ◽  
Drop Formation ◽  
Air Velocity ◽  
Liquid Separation ◽  
Liquid Mass

Fuel atomization with prefilming airblast nozzles has been investigated. The present analysis is directed toward a detailed investigation of the atomization processes and the clarification of the fundamental phenomena. Two-dimensional models were utilized. High-speed films, showing the deterioration of the liquid film close to the atomizing edge, reveal the dynamics of the liquid’s deterioration and show the motion of the film during the drop formation. The liquid separation is shown to be a periodic process with the drop formation caused by momentum transfer. The frequency spectrum of the liquid separation is determined by means of an optical technique. It is seen that the main frequencies depend only on the air velocity. They are always lower than the corresponding wave frequencies. The droplet size measurements obtained by a light scattering technique emphasize the dominant role of the air velocity at the atomizing edge. A decrease in the surface tension provides an improvement in atomization quality. Other parameters such as liquid flow rate, liquid viscosity, gap height, and length of the prefilming surface within the nozzle were found not to affect directly the droplet size distribution produced, if the air velocity in each of the two ducts of the nozzle is kept constant. The pressure drop of the air, however, rises. It is shown that the droplet size distribution can be easily determined, if the arithmetic mean value of the air velocity in both ducts is known, e.g., from a calculation of the internal flow. Due to the high liquid mass flow rates of airblast nozzles, the wavy film is partly atomized within the nozzle before the liquid separates at the atomizing edge. The measurements show that the portion of the liquid mass flow atomized remains relatively small and that the droplet sizes are equivalent to those produced at the atomizing edge.

Study on atomization particle size characteristics of two-phase flow nozzle

2021 ◽  
pp. 1-12
Author(s):  
Haoqi Lilan ◽  
Junbin Qian ◽  
Nan Pan
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Droplet Size ◽  
High Speed ◽  
Droplet Size Distribution ◽  
Average Diameter ◽  
Spray Atomization ◽  
Two Phase ◽  
Nozzle Pressure ◽  
Local Observation

Nozzle spray atomization is widely used in industrial and agricultural production processes and is a very complicated physical change. The spray atomization of the nozzle is a process in which the droplets are continuously broken into finer particles under the action of force, in order to study the effect of nozzle atomization, that is, droplet size distribution characteristics. The experimental average mathematical model of droplet size distribution was established by introducing the average diameter of Sutter (SMD). The droplet size distribution in the atomization field of the nozzle is studied by simulation. In the experimental study, the high-speed camera, external mixing air atomizing nozzle platform experimental device and image processing were used, and the atomization field was divided into multiple observation areas. Through the measurement of several local observation areas, the droplet size distribution of the whole atomization field is constructed. It provides a reference for the study of the atomization field of the nozzle and a basis for the intuitive understanding of the droplet size distribution in the atomization field of the nozzle. The effective atomization area of the nozzle atomization was selected to study the influence of the liquid flow rate, the liquid temperature and the nozzle pressure on the atomized particle size distribution of the externally mixed atomizing nozzle. The internal law is obtained, which provides a basis and reference for effectively controlling the atomization effect in the atomization field.

Influence of Airspeed and Adjuvants on Droplet Size Distribution in Aerial Applications of Glyphosate

2018 ◽  
Vol 34 (3) ◽  
pp. 507-513 ◽  
Author(s):  
Bruno C Vieira ◽  
Guilherme S Alves ◽  
Fernando K Carvalho ◽  
João Paulo AR Da Cunha ◽  
Ulisses R Antuniassi ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Size Distribution ◽  
Droplet Size ◽  
High Speed ◽  
Droplet Size Distribution ◽  
Laser Diffraction ◽  
Flight Speed ◽  
Central Research ◽  
Operating Pressure ◽  
Size Spectra

Abstract. Drift is one of the most hazardous consequences of an improper aerial application of glyphosate. Wind, droplet size, application height, and distance to sensitive areas are the most important factors for drift. Droplet size is affected by nozzle, operating pressure, flight speed, deflection angle, and physicochemical properties of the spray solution. The objective of this study was to evaluate the effect of flight speed and the use of adjuvants on droplet size spectra in aerial applications of glyphosate. The study was conducted in a high-speed wind tunnel at the Pesticide Application Technology Laboratory (University of Nebraska-Lincoln, West Central Research and Extension Center, North Platte, Neb.). Aerial applications were simulated with four different airspeeds (44.4, 52.8, 61.1, and 69.4 m/s) and glyphosate combined with adjuvants (high surfactant oil concentrate, microemulsion drift reduction agent, nonionic and acidifier surfactant, polyvinyl polymer, and glyphosate alone). Droplet size spectra were evaluated using a Sympatec Helos laser diffraction instrument measuring 90 cm from the nozzle tip (CP11-4015). The volumetric droplet size distribution parameters (VMD, DV0.1, and DV0.9) and the percentage of droplets smaller than 100 µm were reported. The relative span was calculated to indicate the droplet size homogeneity [(DV0.9 - DV0.1) / DV0.5]. Glyphosate solutions with adjuvants had a larger VMD than the glyphosate alone solution at 44.4 m/s wind speed. At 69.4 m/s only the glyphosate solution with polymer had a larger VMD. Conversely, the glyphosate with polymer had the smallest DV0.1, and the greatest relative span and percentage of droplets smaller than 100 µm. Generally, adjuvants influence on droplet size was diminished or muted as the airspeed was increased. The polymer tested in this study failed as a drift agent reduction agent, especially at higher airspeeds. While not all polymers were tested, cautions should be taken if using these types of adjuvants in aerial applications. The interaction of airspeed and adjuvants influencing droplet size distribution in aerial applications of glyphosate should be considered by applicators in order to mitigate glyphosate drift to the surrounding environment. Further studies are necessary to better understand the interaction between solution viscosity and air shear effect on the atomization process and droplet size distribution, as well as confirm that trends hold true for other adjuvants in the polymer class. Although applicators tend to operate aircrafts with increased flight speeds in order to optimize the application time efficiency, this practice can reduce or mute adjuvants effects, decrease the droplet size distribution, and increase drift potential in aerial applications of glyphosate. Keywords: Drift reduction technologies, Flight speed, High-speed wind tunnel, Laser diffraction.

Measurement of droplet size distribution in core region of high-speed spray by micro-probe L2F

2008 ◽  
Vol 17 (1) ◽  
pp. 90-96 ◽  
Author(s):  
Daisaku Sakaguchi ◽  
Oluwo le Amida ◽  
Hironobu Ueki ◽  
Masahiro Ishida
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
High Speed ◽  
Droplet Size Distribution ◽  
Core Region

scholarly journals Numerical Simulation of the Oil Droplet Size Distribution Considering Coalescence and Breakup in Aero-Engine Bearing Chamber

2020 ◽  
Vol 10 (16) ◽  
pp. 5648
Author(s):  
Fei Wang ◽  
Lin Wang ◽  
Guoding Chen ◽  
Donglei Zhu
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Mass Flow ◽  
Droplet Diameter ◽  
Droplet Size Distribution ◽  
Oil Droplets ◽  
Oil Droplet ◽  
Aero Engine ◽  
Oil Droplet Size ◽  
Engine Bearing

In order to improve the inadequacy of the current research on oil droplet size distribution in aero-engine bearing chamber, the influence of oil droplet size distribution with the oil droplets coalescence and breakup is analyzed by using the computational fluid dynamics-population balance model (CFD-PBM). The Euler–Euler equation and population balance equation are solved in Fluent software. The distribution of the gas phase velocity field and the volume fraction of different oil droplet diameter at different time are obtained in the bearing chamber. Then, the influence of different initial oil droplet diameter, air, and oil mass flow on oil droplet size distribution is discussed. The result of numerical analysis is compared with the experiment in the literature to verify the feasibility and validity. The main results provide the following conclusions. At the initial stage, the coalescence of oil droplets plays a dominant role. Then, the breakup of larger diameter oil droplet appears. Finally, the oil droplet size distribution tends to be stable. The coalescence and breakup of oil droplet increases with the initial diameter of oil droplet and the air mass flow increasing, and the oil droplet size distribution changes significantly. With the oil mass flow increasing, the coalescence and breakup of oil droplet has little change and the variation of oil droplet size distribution is not obvious.

Calculation of Droplet Size Distribution in Condensing Flow

2006 ◽  
Author(s):  
Rutger H. A. IJzermans ◽  
Rob Hagmeijer ◽  
Ryan S. R. Sidin
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Method Of Moments ◽  
Dynamic Equation ◽  
Mass Density ◽  
Droplet Size Distribution ◽  
Moment Equations ◽  
Liquid Mass ◽  
Condensing Flows ◽  
General Dynamic

Condensing flows can be found in a large variety of industrial machinery such as steam turbines and supersonic gas conditioners. In many of these applications, it is very important to predict the droplet size distributions accurately. In the present research, the droplet size distribution in condensing flows is investigated numerically. We consider condensing flows with droplets that nucleate and grow, but do not slip with respect to the surrounding gas phase. To compute the coupling between the condensed phase and the carrier flow, one could solve the general dynamic equation and the fluid dynamics equations simultaneously. In order to reduce the overall computational effort of this procedure by roughly an order of magnitude, we use an alternative procedure, in which the general dynamic equation is initially replaced by moment equations complemented with a closure assumption. This closure assumption is based on Hill’s approximation of the droplet growth law. The method thus obtained, the so-called Method of Moments, is assumed to approximately accommodate the thermodynamic effects of condensation, such as the temperature, pressure and velocity field of the carrier flow. We use the Method of Moments as a basis for the calculation of the droplet size distribution function. We propose to solve the general dynamic equation a posteriori along a number of selected fluid trajectories, keeping the flow field fixed. This procedure, called Phase Path Analysis [1], leads to accurate size distribution estimates, at a far lower computational cost than solving the general dynamic equation and the fluid dynamics equations simultaneously. In the present paper, we investigate the effect of a variation in the liquid mass density on the droplet size distribution, using the proposed method. In case of a varying liquid mass density, both the equation for the dropltet growth rate and the moment equations are modified. This modified form coincides with the usual form of the moment equations in the event that the variation in liquid density is negligible. This research is relevant for condensation in flows where large temperature differences may occur which lead to significant variations in the liquid mass density. We show that the implementation of a variable liquid mass density in the Method of Moments and the Phase Path Analysis results in a higher extremum in the droplet size distribution, whereas the skewed shape of the distribution function is nearly similar to that obtained in the constant liquid density case.

MODELING DROPLET SIZE DISTRIBUTION NEAR A NOZZLE OUTLET IN AN ICING WIND TUNNEL

2006 ◽  
Vol 16 (6) ◽  
pp. 673-686 ◽  
Author(s):  
Laszlo E. Kollar ◽  
Masoud Farzaneh ◽  
Anatolij R. Karev
Keyword(s):  
Wind Tunnel ◽  
Size Distribution ◽  
Droplet Size ◽  
Droplet Size Distribution ◽  
Nozzle Outlet
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