Begell House Inc.
Atomization and Sprays
AAS
1044-5110
5
3
1995
CONTROL OF MEAN DROPLET DIAMETER ISSUED FROM Y-JET-TYPE AIRBLAST ATOMIZER BY USING FLUID AMPLIFIER
243-260
10.1615/AtomizSpr.v5.i3.10
Takao
Inamura
Graduate School of Science and Technology, Hirosaki University, Japan
Nobuki
Nagai
Department of Aeronautics and Space Engineering, Tohoku University, Aramaki Aza Aoba, Aoba-ku, Sendai, Japan
A new type of atomizer has been developed to control mean droplet diameter over a wide range of liquid flow rates; this newly developed atomizer of Y-jet type employs a fluid amplifier to control the liquid flow rate. The liquid flowing into the atomizer is distributed by a fluid amplifier into two ports with different inner diameters. During the present experiments, the liquid flow rate was varied over a turndown ratio of 7, while the air flow rate was kept constant. Generally, the mean droplet diameter is greatly influenced by the atomizing air velocity, and the mean diameter decreases steadily as the atomizing air velocity increases. In the proposed method, to keep the mean diameter constant, the liquid flowing into smaller ports where high-speed air passes is greatly increased with total liquid flow rate. On the other hand, liquid flowing into larger ports, where low-speed air passes through, is gradually increased. Consequently, the mean droplet diameter changes only 10 μm for the optimum design over the turndown ration of 7, whereas the mean diameter changes 30 μ;m without the fluid amplifier.
VISCOSITY AND SURFACE TENSION EFFECTS IN PRESSURE SWIRL ATOMIZATION
261-285
10.1615/AtomizSpr.v5.i3.20
V.
Dorfner
Lehrstuhl für Strömungsmechanik, Universität Erlangen-Nürnberg, Erlangen, Germany
Joachim
Domnick
Hochschule Esslingen, University of Applied Sciences, Fraunhofer-Institut fur Produktionstechnik und Automatisierung, Germany
Franz
Durst
FMP TECHNOLOGY GMBH, Am Weichselgarten 34, 91058 Erlangen, Germany
R.
Kohler
Lehrstuhl für Strömungsmechanik, Universität Erlangen-Nürnberg, Erlangen, Germany
The development of phase-Doppler anemometry has provided a reliable measuring technique for studying local particle size and particle velocity distributions in sprays. Using this technique, the present article summarizes viscosity and surface tension effects on the properties of liquid sprays produced by pressure swirl atomizers. Mean droplet sizes and mean velocities were computed from the measured joint size/velocity distributions to discuss the spray properties in the terminology largely employed in the field of liquid sprays.
The results indicate an increase of the mean diameter with increasing surface tension and increasing viscosity. Concerning the shape of the size distributions, the results suggest that narrow size distributions can be generated by low-viscosity and low-surface-tension fluids. Also, it is shown that surfactants do not lead to an effective surface tension reduction in atomization. Moreover, they introduce a non-Newtonian behavior, which results in a decrease of the number of droplets in the small size range.
TURBULENT SPRAYS IN STAGNATION FLOWS
287-304
10.1615/AtomizSpr.v5.i3.30
S. C.
Li
Center for Energy and Combustion Research, Department of Applied Mechanics and Engineering Sciences, University of California, San Diego, La Jolla, CA 92093, USA
P. A.
Libby
Center for Energy and Combustion Research, Department of Applied Mechanics and Engineering Sciences, University of California, San Diego, La Jolla, CA 92093, USA
Forman A.
Williams
Mechanical and Aerospace Engineering, University of California-San Diego, San Diego, CA, USA
An experimental study of turbulent sprays of methanol impinging on a wall is reported. The turbulence is generated by a grid in the duct carrying the droplets in an air stream. Measurements of droplet diameter and of two components of droplet velocity are made with a phase Doppler particle analyzer (PDPA). Small and large droplets are observed to behave differently. By associating the velocity of the smallest droplets with that of the gas, some aspects of the statistics of the relative velocity between the gas and droplets of various sizes are obtained. Comparison with theoretical estimates of mean and fluctuating droplet velocities helps reveal how different-sized droplets respond differently to turbulence.
MEASUREMENTS OF u′gi u′pi IN MIXING-LAYER FLOW WITH DROPLET LOADING
305-328
10.1615/AtomizSpr.v5.i3.40
Muh-Rong
Wang
Institute of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan, Republic of China
D.Y.
Huang
Institute of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan, Republic of China
Measurements of the turbulence modulation term, u′gi u′pi, between the carrier and dispersed phases from experimental data were performed by a phase Doppler particle analyzer (PDPA) system. The cross-correlation function between phases, u′gi(t) u′pi(t + τ), was first determined from the measured raw data, which involved real-time information about velocities and associated drop sizes. The time delay, τ, was selected based on the flow characteristic time. The velocity of 2-μ;m drops was taken as that of the carrier phase. The cross-correlation functions for 10-μ;m, 20-μ;m, and 30-μ;m drops were then calculated from the raw data for each size range. The value of the cross-correlation function at τ = 0, that is, the turbulence modulation term, was obtained based on the symmetric property of this function and interpolation of the data. Results show that the turbulence modulation term can be expressed as functions of drop relaxation time, τp, turbulence kinetic energies of both phases, κ and κp, Reynolds stress u′g v′g, and velocity correlation of the drop phase, u′p v′p, instead of the formulation suggested by Pourahmadi and Humphrey [5] as well as by Chen and Wood [3, 4], which considered τp and κ only. It is suggested that the modeling of spray flow requires a more complete formulation based on the experimental data shown in this article.
EFFECTS OF DROP LOADING ON TURBULENT DIFFUSIVITY IN A TWO-PHASE MIXING-LAYER FLOW
329-342
10.1615/AtomizSpr.v5.i3.50
Muh-Rong
Wang
Institute of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan, Republic of China
D.Y.
Huang
Institute of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan, Republic of China
Measurements of turbulent diffusivity in a plane mixing-layer flow with and without drop loading were conducted by a phase Doppler particle analyzer (PDPA). The mean free-stream velocity is 10 m/s, corresponding to a flow Reynolds number based on hydraulic diameter (0.15 m) of 95,600.
Analysis of the data on mean velocity, Reynolds stresses, and turbulent velocity fluctuation reveals that the flow can be divided into two regions, the developing region and the fully developed region. In the developing region, the turbulent diffusivity is significantly reduced under two-phase condition except in the initial region (i.e., X < 20 mm), where the turbulent diffusivity is higher under drop loading because the flow has been disturbed due to the existence of drops. This result is also consistent with that of Reynolds stresses and turbulent velocity fluctuation. However, the slope of the variation of turbulent diffusivity under drop loading is lower than that of the single-phase flow condition in this region because of the development of the large-scale structure in the flow. On the other hand, in the fully developed region, the decay of the turbulent diffusivity under the two-phase condition is lower than that of single-phase flow. Hence the energy dissipation due to viscous effects in the fully developed region has been partially compensated by the energy production due to turbulence modulation under the two-phase flow condition. This indicates that the modeling of turbulent diffusivity under the two-phase condition should take into account the turbulence modulation due to drop loading.
FLUID VELOCITY AND SHEAR IN ELLIPTIC-ORIFICE SPRAY NOZZLES
343-356
10.1615/AtomizSpr.v5.i3.60
H.
Zhu
Department of Agricultural Engineering, Ohio State University, OARDC, Wooster, OH 44691, USA
R. D.
Brazee
Application Technology Research Unit, U.S. Department of Agriculture, Agricultural Research Service, Wooster, OH, 44691, USA
D. L.
Reichard
Deceased, formerly, U.S. Department of Agriculture, Agricultural Research Service, Wooster, Ohio, USA
R. D.
Fox
U.S. Department of Agriculture, Agricultural Research Service, Wooster, Ohio, USA
C. R.
Krause
Application Technology Research Unit, U.S. Department of Agriculture, Agricultural Research Service, Wooster, OH, 44691, USA
Andrew C.
Chapple
c/o Koyntoypiotoy 13, Tpiandria 55337, Thessaloniki, Greece
With new pest control and bioregulating formulations under development and coming into use to improve spray retention and coverage, concerns have arisen about possible adverse effects on spray solutions due to fluid shear occurring in nozzles. Mathematical models were developed for velocity and shear-rate distributions for incompressible liquid flow through fan-pattern spray nozzles having approximately elliptic outlet orifices. The velocity distribution model was verified with phase/Doppler particle analyzer measurements and computational fluid dynamic simulations. A mean fluid velocity section of the model predicted the axial flow velocity to be 29.03 m/s for an 8002 brass fan-pattern nozzle with 276 kPa operating pressure, compared with a mean measured value of 29.85 m/s. With the shear rate model, it was found that use of an older equivalent-circle model resulted in significant underestimates of shear rates for fan-pattern nozzles. Liquid shear rates at the orifice wall varied with position, and were estimated to fall in the range 1.2 × 105 to 7 × 105 s−1 for the spray nozzles studied, depending on nozzle characteristics and operating pressure over a range of 138 to 414 kPa.