Begell House
Atomization and Sprays
Atomization and Sprays
1044-5110
24
11
2014
EXPERIMENTAL STUDY OF THE LAWS OF INTERACTION BETWEEN SMALL PARTICLES AND LARGE DROPS
We present some results of our experimental investigation of the dynamic interaction of small solid particles with large drops as applied to the process of wet cleaning of dusty gases. We show that the picture of interaction is far from complete coalescence and obtain a generalizing relation for the coalescence parameter as a function of Reynolds and Laplace numbers and a geometric simplex. For correct determination of the efficiency of gas cleaning, it is necessary to take into account this relation.
A. A.
Shraiber
Energy Institute, Ukrainian National Academy of Sciences, Kiev, Ukraine
V. V.
Dubrovsky
Energy Institute, Ukrainian National Academy of Sciences, Kiev, Ukraine
A. M.
Podvysotsky
Energy Institute, Ukrainian National Academy of Sciences, Kiev, Ukraine
937-947
THE EFFECT OF VISCOSITY AND CONVECTION ON THE STABILITY OF ANNULAR LIQUID SHEETS
A nonlinear stability model for the breakup of annular liquid sheets subject to inner and outer gases of negligible inertia was developed. Using this model, we demonstrate the effect of viscosity and advection velocity on the breakup process. The formulation used is similar to that of Eggers and Dupont (1994) and involves expanding the flow field variables as asymptotic expansions of a "thin" variable
and then solving the one-dimensional equations using the Galerkin finite element framework. One-dimensional
(paravaricose) disturbances were assumed and the long wave ansatz was employed. We show that a nonzero mean axial velocity allows convection of disturbances downstream and can cause disturbance waves that are linearly stable to grow in time and eventually lead to sheet breakup (if the
initial disturbance amplitude is greater than a critical value). We also show that the annular sheet could form satellite rings (analogous to the satellite drops that have been observed when cylindrical jets break up) under certain conditions. Model predictions show that increasing the Ohnesorge number yields the expected stabilization of the sheet. Finally, we show that the effect of the annular sheet
thickness is counterintuitive, in that thicker sheets tend to break up faster.
Mahesh V.
Panchagnula
Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai 600036,
India
Paul E.
Sojka
Maurice J. Zucrow Laboratories (formerly Thermal Sciences and Propulsion Center), School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, 47907-2014, USA
Anil K.
Bajaj
School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907-1003, USA
949-976
A MODEL OF AN ATOMIZING DROP
This paper presents a two-level mathematical model that describes the aerodynamics of an evaporating mist around an atomizing spherical drop in a uniform air stream at large Weber numbers. The lower-level model describes the mechanics of daughter droplet formation at the parent drop surface. The model utilizes the concept of quasi-continuous, high-frequency periodic dispersion from the unstable part of the drop surface caused by the hydrodynamic instability of the gradient flow in conjugated boundary layers. The upper-level model reflects spatial aerodynamics of the evaporating spray being generated by atomizing drop. In this model, daughter droplets are assumed to behave as a multivelocity continuum and the ballistics of an axisymmetric evaporating mist are rendered as equations in dynamic four-dimensional space. The model rests on the following assumptions: the air-velocity field around a spherical drop is potential; the daughter droplets and their associated vapor do not influence the air flowfield; the initial velocity of newborn droplet is equal to that of the fastest unstable wave on the parent drop surface that produces it; the Ranz-Marshall model is appropriate for describing droplet evaporation. The variance in time of the spatial distributions of the breakaway
droplets' mass, number density, and of the vapor density is processed and analyzed in video format. The detailed fields of the droplets' mean diameters are also obtained. Large vapor concentrations and a decreasing local gas-phase temperature are revealed.
Oleksandr G.
Girin
Odessa National Maritime University, Odessa, Ukraine
977-997
APPROXIMATE RELATIONS OF THE EVAPORATING DROPLET BALLISTICS
The problem of evaporating droplet ballistics in a uniform gas stream is solved analytically. The main regularities of the process are obtained as the approximate solution of the governing differential equations of the droplet motion and evaporation in a practically important range of the determinant parameters. The equations reflect convective evaporation enhancement and transiency of droplet diameter and relative velocity, which have an influence on both droplet motion and evaporation. Formulas for droplet lifetime and path length, the moving droplet evaporation law, and the law of evaporating droplet motion are obtained in an implicit form. Found dependences provide the
possibility to analyze theoretically the droplet behavior in a stream. The found relationships show that the convective enhancement of the evaporation reduces the droplet path length up to 3 times, and life-time up to 9 times. Two main regimes of the droplet evaporation ballistics are revealed: the dynamic evaporation and dynamic acceleration, which occur depending on the ballistic criterion value. The
power-mode evaporation law is realized only within the dynamic evaporation regime. Calculations testify to the strong influence of the evaporation on a droplet motion. An approximate expression for the vapor mass production history along droplet trajectory is obtained. The obtained relationships have an acceptable error in a wide range of the found criteria. They allow significant simplification
of the quantitative description of evaporation ballistics in sprays and are applicable to various engineering
problems. The results are limited to the cases when the evaporation rate may be expressed by some effective evaporation constant value.
Oleksandr G.
Girin
Odessa National Maritime University, Odessa, Ukraine
999-1016
A NUMERICAL METHOD FOR ANALYSIS OF SPRAY BEHAVIOR WITH DESIGN OF EXPERIMENT
The purpose of the present study is to optimize the diesel engine injector. Discharge of many cavitation bubbles and high injection velocity were set up for the design purpose. Injector optimization was progressed through computational fluid dynamics (CFD) and the design of the experiment was used to study the interior of the injector. ANSYS CFX 13.0 was used as the CFD tool to perform the CFD analysis of 16 experimental cases; these include four cases of each design variable; the hole diameter, the hole length, the hole angle, and the K factor. The results of the analysis show that the largest impact on the cavitation comes from the K factor, and the injection velocity dominantly depends on the hole diameter. The optimum injector derived based on these results has the size of 2, 4, 4, and 4 levels,
respectively, for the hole diameter, the hole length, the hole angle, and the K factor. For the injection
velocity of 460 m/s, it gives the best performance when 36% volume fraction of cavitation bubbles are injected.
Jeongkuk
Yeom
Department of Mechanical Engineering, Dong-A Univ., 37 Nakdong-Daero 550 beon-gil saha-gu, Busan 604-714, Korea
Hyungsoo
Ha
Graduate School, Department of Mechanical Engineering, Dong-A Univ., 37 Nakdong-Daero 550 beon-gil saha-gu, Busan 604-714, Korea
1017-1033