Begell House
Atomization and Sprays
Atomization and Sprays
1044-5110
16
2
2006
EXPERIMENTAL CHARACTERIZATION OF INDUSTRIAL TWIN-FLUID ATOMIZERS
The aim of this work is focused on the characterization of the behavior of large-capacity multihole industrial twin-fluid atomizers. Sauter mean diameter (SMD), discharge coefficient, and air-to-liquid mass flow rate ratio are the parameters that have been selected for the experimental study. Two kinds of nozzles have been tested: a commercial "Y" type and a new-concept twin-fluid nozzle with an internal swirl chamber. This new-concept nozzle, which is specifically designed to atomize crude petroleum in power plants, is made with two different pieces, which eases cleaning and maintenance tasks. The best performance has been obtained for the new-concept nozzle without Y ports in the internal part, yielding smaller droplets with a lower air mass flow rate. A nondimensional relationship between the SMD-to-air core diameter at the exit holes (Dao) versus the air Reynolds number defined with Dao has been found. This nondimensional relation reproduces very well the experimental measurements for the whole range of atomizing conditions, which includes the actual power plant operating conditions.
Felix
Barreras
LITEC/CSIC, Zaragoza; and Centro Politecnico Superior de Ingenieros, Area de Mecanica de Fluidos, Universidad de Zaragoza
Antonio
Lozano
LIFTEC, CSIC - Universidad de Zaragoza
Jorge
Barroso
LITEC/CSIC. Maria de Luna 10, 50018 Zaragoza, Spain
Eduardo
Lincheta
CECYEN, Universidad de Matanzas, Autopista a Varadero, km 3½, 44740 Matanzas, Cuba
127-146
TWO TYPES OF LINEAR THEORIES FOR ATOMIZING LIQUIDS
The onset of breakup of liquid jets or sheets is commonly predicted by determining how infinitesimal disturbances grow with time. This theory is usually called temporal theory. A more recently developed theory predicts how a disturbance evolves in space and time. The latter theory is termed spatiotemporal theory. This article demonstrates how temporal theory may mispredict the nature of the onset of instability. A very important type of instability called absolute instability also totally escaped the prediction of temporal theory. The misprediction and the incompleteness of the temporal theory is demonstrated by use of an example of sheet breakup preceding the atomization.
Sung P.
Lin
Department of Mechanical and Aeronautical Engineering, Clarkson University, Potsdam, New York
147-158
ACCURATE NUMERICAL SOLUTION OF THE SPRAY EQUATION USING PARTICLE METHODS
Particle methods are commonly used to obtain numerical solutions to Williams' spray equation, which describes the evolution of the droplet distribution function (DDF) f(x,v,r,t). Accurate, efficient, and numerically convergent particle methods are needed for predictive computational modeling of sprays. In this work, a simple vaporization test problem is proposed that admits analytic solutions to the spray equation and is useful for testing the accuracy of numerical solutions. This study shows that a simple particle method solution using uniform sampling of the DDF yields an accurate solution to the simple vaporization test problem. However, many spray codes, such as KIVA, use importance sampling of the mass-weighted DDF on the grounds that this is more computationally efficient. The implementation of importance sampling in KIVA results in an inaccurate numerical solution of the spray equation that does not converge to the analytic solution for the simple vaporization test, even for a very large number of computational particles. We show that importance sampling can be accurate and computationally efficient if statistical weights are correctly assigned to match the initial radius distribution. Simulations also reveal that the discontinuous evolution of statistical weights corresponding to vaporization in existing particle methods results in numerical estimates of spray statistics that do not unconditionally converge to a continuous asymptotic limit as the time step is decreased. An algorithm of continuously evolving weights is developed that yields numerically convergent results that also match the analytic solution very well. These improvements to the particle method solution of the spray equation, which result in an excellent match of numerical predictions with the analytical solution in the test problem, can be expected to dramatically improve the accuracy of complex spray calculations at minimum computational expense.
G. M.
Pai
Department of Mechanical Engineering, Iowa State University, Ames, IA 50011
Shankar
Subramaniam
Iowa State University
159-194
NUMERICAL MODEL OF PAINT TRANSFER AND DEPOSITION IN ELECTROSTATIC AIR SPRAYS
Electrostatic air spray paint applicators are widely used to apply paints. In spite of their common use, the basic process by which a bulk volume of paint is transported to the workpiece is poorly understood. The goal of this research is to develop an improved understanding of paint transfer in electrostatic air spray processes for which there is considerable margin to improve appearance and reduce both paint usage and solvent emissions. A paint transport simulation that accounts for the paint momentum, aerodynamic drag, gravitational forces, and electrostatic attraction is developed and used to provide insight into the electrostatic augmentation of paint transfer efficiency. The paint transfer simulation uses a Lagrangian particle tracking, an Eulerian airflow, and an Eulerian electrostatic field solution. The unsteady aerodynamic drag on the paint is incorporated using a stochastic separated flow approach. The simulation results are verified using measurements of paint transfer efficiency and drop transfer efficiency. The results reveal that the amount of charge on the paint directly alters the paint flow structure, deposition characteristics, and paint transfer efficiency.
James E.
McCarthy, Jr.
Thermal Sciences and Propulsion Center, School of Mechanical Engineering, Purdue University, West Lafayette, Indiana; Eaton Corporation, 26201 Northwestern Highway, Southfield, MI 48076
Dwight W.
Senser
Thermal Sciences and Propulsion Center, School of Mechanical Engineering, Purdue University, West Lafayette, Indiana
195-222
NUMERICAL AND EXPERIMENTAL STUDY ON CYLINDRICAL SWIRL ATOMIZERS
The pressure swirl atomizer is widely used in liquid fuel combustion devices in the aerospace and power generation industries. The experimental and numerical predictions of air core diameter da, the coefficient of discharge Cd, and the spray cone angle ψ of a cylindrical swirl-spray pressure atomizer have been made in the present study. The standard k-ε model of turbulence is used for numerical computation of flow within the nozzle. The diameter of the stable central air core inside the nozzle has been predicted at given operating conditions. The values of Cd and ψ have been evaluated from the radial distribution of velocity components of liquid flow at the nozzle exit plane. It has been observed from numerical and experimental investigations that the coefficient of discharge Cd decreases, while the air core diameter da and the spray cone angle ψ increase with the increase in nozzle flow in its lower range. However, all these parameters, Cd, ψ, and da, finally become independent of nozzle flow. Both da/D and ψ increase but Cd decreases with a decrease in Dp/D for the nozzles of constant L/D, where Dp, D, and L are the entry port diameter, swirl chamber diameter, and length of atomizer, respectively. Also, both da/D and ψ decrease, while Cd increases with an increase in L/D for the nozzles of constant Dp/D.
M. R.
Halder
Department of Mechanical Engineering, Khulna University of Engineering & Technology, Bangladesh
S. K.
Som
Department of Mechanical Engineering, I. I. T. Kharagpur, India
223-236