Begell House Inc.
Atomization and Sprays
AAS
1044-5110
3
2
1993
SPARK-IGNITED SPHERICAL FLAMES PROPAGATING IN A SUSPENDED DROPLET CLOUD
125-135
10.1615/AtomizSpr.v3.i2.10
Yukio
Mizutani
Department of Mechanical Engineering, School of Science and Engineering, Kinki University, Osaka, Japan
Kazuyoshi
Nakabe
Department of Mechanical Engineering and Science, Kyoto University; Advanced Research Institute of Fluid Science and Engineering, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan
Manabu
Fuchihata
Mazda Motor Corporation, Hiroshima, Japan
Fumiteru
Akamatsu
Department of Mechanical Engineering, Osaka University, Japan
Masataka
Zaizen
Department of Mechanical Engineering, Faculty of Engineering, Osaka, University, Suita, Osaka 565, Japan
Salah Hassan
El-Emam
Mansoura University, El-Mansoura, Egypt
A droplet suspension of liquid fuel produced by an ultrasonic atomizer was ignited using an electric spark. The Sauter mean diameter (SMD) of the droplet suspension was 57μ;m to 66 μ;m for fuel injection rates of 2.13 cm3/min to 4.44 cm3/min, respectively. The droplet distribution for any fuel injection rate included a negligible amount of droplets smaller than 20 μ;m or larger than 100 μ;m in diameter. The flame ball propagating outward was monitored by observing light emission from OH- and C2-radical bands using photomultipliers, a highly sensitive CCD camera, and a high-speed camera. Thereby, the mechanism of flame propagation and the complicated structure of spray flames were observed. It was found that a nonluminous flame was propagating continuously through a gas-phase mixture, followed by luminous flamelets, such that a number of small-scale droplet clusters with luminous emissions appeared randomly and discontinuously behind the flame front propagating in a premixed combustion mode. This result shows that the group structure of spray flames is not simple.
EFFERVESCENT ATOMIZER OPERATION AND SPRAY CHARACTERISTICS
137-155
10.1615/AtomizSpr.v3.i2.20
J. D.
Whitlow
Thermal Science and Propulsion Center, School of Mechanical Engineering, Purdue University, West Lafayette, Indiana
Arthur H.
Lefebvre
Emeritus Professor, Cranfield University, Stratford, U.K., and Purdue University, W. Lafayette, IN, USA
An experimental study was conducted to examine the performance of a plain-orifice, twin-fluid atomizer that urns designed to produce effervescent atomization at low air/liquid ratios. The liquid employed was water and the atomizing gas was air. The parameters varied were the air/liquid mass ratio (ALR) and the atomizer operating pressure. Studies of spray characteristics included measurements of Sauter mean diameter (SMD), drop size distribution, and radial liquid distribution of the liquid mass within the spray.
It was found that SMD decreases with an increase in either ALR or operating pressure. The effect of ALR on SMD diminishes as the value of ALR increases. Changes in operating pressure and ALR have little effect on the Rosin-Rammler drop size distribution parameter. Measurements of radial liquid distribution showed a significantly larger spray cone angle than those produced by conventional plain-orifice pressure atomizers.
EFFERVESCENT ATOMIZATION OF HIGH-VISCOSITY FLUIDS: PART II. NON-NEWTONIAN LIQUIDS
157-170
10.1615/AtomizSpr.v3.i2.30
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
Harry N.
Buckner
Thermal Sciences and Propulsion Center, School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907
Previous Newtonian effervescent atomization work is extended to non-Newtonian fluids, with the influence of non-Newtonian fluid rheology being of particular interest. Mean drop size data obtained during this study show no dependence on either non-Newtonian flow behavior index or consistency index, as they varied from 0.85 to 0.95 and 400 to 968 cP sn−1, respectively. An increase in mean drop size relative to a Newtonian fluid with equal apparent viscosity was observed, however, upon addition of polymer. This phenomena is attributed to the yield stress associated with polymeric fluids. These observations suggest that primary atomization is unimportant during effervescent spray formation and that secondary atomization is the controlling factor.
PRESOLIDIFICATION LIQUID METAL DROPLET COOLING UNDER CONVECTIVE CONDITIONS
171-191
10.1615/AtomizSpr.v3.i2.40
Constantine M.
Megaridis
Department of Mechanical Engineering, The University of Illinois at Chicago, Chicago, Illinois 60607, USA
A model investigating the heat and fluid flow fundamentals of liquid metal droplet cooling during spray deposition processes is presented. The droplet configuration studied involves a laminar, axisymmetric gaseous flow around a spherical, superheated, all-liquid, pure metal droplet, which initially has no internal motion and a uniform temperature before it is injected with zero velocity into a cool, uniform gas stream. This flow configuration is identical to one where the droplet is injected into a quiescent gas with a specified velocity. A detailed solution approach is adopted in both gas and liquid phases, even though the temperatures within typical liquid metal droplets are expected to be almost uniform. However, the establishment of temperature differences of even a few degrees in the droplet interior would create very high temperature gradients, given the small sizes of the droplets. High temperature gradients, in turn, have a strong influence on solidification, with a decisive effect on the material properties of the solidified substance. The model, which accounts for variable thermophysical properties in the gas phase, transient droplet cooling with internal liquid circulation, and droplet deceleration with respect to the free flow due to drag, produces time-varying spatially resolved data for the entire flow field in the vicinity of the droplet. These results provide information on the fundamental processes governing the energy and momentum exchange between the droplet and the gaseous stream. The laminar flow simulations for a liquid aluminum droplet at atmospheric pressure show that temperature gradients of the order of 25,000 K/m are maintained in the droplet interior throughout the droplet flight. These gradients are very significant for the subsequent onset of solidification, which has not been modeled in this study. In addition, the relatively high convective cooling rates achieved (> 105 K/s) are enhanced by reduced ambient pressures. The model predictions for the droplet drag coefficient and Nusselt numbers are compared with the values obtained through widely used correlations for the evaluation of these quantities in more populous metal sprays.
HOLOGRAPHIC INVESTIGATION OF MICROEXPLOSION IN AN EMULSIFIED DIESEL OIL SPRAY
193-202
10.1615/AtomizSpr.v3.i2.50
H.
Xu
I. C. Engine Research Institute, Department of Energy Engineering, Zhejiang University, Hangzhou 310027, People's Republic of China
C. G.
Zhu
I. C. Engine Research Institute, Department of Energy Engineering, Zhejiang University, Hangzhou 310027, People's Republic of China
Y. B.
Shen
Department of Mechanical Engineering, University of Illinois at Chicago, Chicago, Illinois
Dimos
Poulikakos
Department of Mechanical and Process Engineering,
Eidgenössische Technische Hochschule Zürich,
Zürich, Switzerland
In this article an experimental study is reported on the atomization and vaporization characteristics of pure and emulsified diesel oil sprays in a high-temperature bomb. Fraunhofer holography was utilized to collect the necessary experimental data. The emulsified oil spray exhibited better atomization characteristics than the pure ой spray. Droplet fragmentation was observed in the emulsified oil spray, and this is attributed in part to the distinct phase boundaries present in the emulsion and in part to the puffing of vaporizing water in a high-temperature environment. For a spray created with a pintle diesel nozzle, it was found that the droplets of the outer spray region art larger than the droplets of the inner spray region, more so in a low-temperature environment.
SPRAY GROUP COMBUSTION IN A CYLINDRICAL NONPREMIXED COMBUSTOR
203-221
10.1615/AtomizSpr.v3.i2.60
Tsung-Leo
Jiang
Institute of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan 70101 ROC
Huei-Huang
Chiu
Institute of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan,70101, ROC
The present spray combustion computation studies numerically the effects of spray angles and injected droplet sites on the combustion efficiency and combustion modes of a cylindrical, nonpremixed combustor through implementation of a realistic droplet combustion model. Combustion efficiency increases with increasing spray cone angle, achieving a maximum value at an optimal injected mean droplet size. The predicted combustion modes indicate that fuel is consumed by the complementary processes of droplet and gas-phase combustion, and are significantly influenced by both spray cone angle and injected mean droplet size. Two flame patterns are identified based on injected droplet size. Small droplet spray is characterized by a diffusion flame separating the fuel and air streams, while large droplet spray exhibits intense mixed droplet and gas-phase combustion near the combustor watt. The results show that combustion efficiency for the former and latter increases and decreases, respectively, with increasing injected droplet sizes. The optimal injected droplet size is therefore suggested to occur at the transition between these two flame patterns.
NEW CLOSED-FORM ANALYTICAL SOLUTIONS OF THE DISCRETE COAGULATION EQUATION WITH SIMULTANEOUS EVAPORATION AND THEIR USE FOR VALIDATION OF SECTIONAL SOLUTIONS
223-248
10.1615/AtomizSpr.v3.i2.70
Yoram
Tambour
Faculty of Aerospace Engineering, Technion—Israel Institute of Technology, Haifa 32000, Israel
Savely
Khosid
RAFAEL
Smoluckowski's classical analytic solution of the discrete coagulation equation is extended here to include simultaneous evaporation. Since the present analytical solutions an accurate, they have the advantage of serving as a reference for the validation of sectional solutions. Thus, a comparison between these two types of solutions is presented here and recommendations are made as to the number of sections that should be used in the representation of polydisperse sprays to retain a given required accuracy in the calculated results. New results are presented for the effects of simultaneous evaporation and coalescence on the evolution of polydisperse droplet size distributions.