Begell House Inc.
Atomization and Sprays
AAS
1044-5110
17
2
2007
A NUMERICAL STUDY ON THE EFFECTS OF ANISOTROPIC TURBULENCE ON THE BEHAVIORS OF IMPINGING SPRAYS
99-122
10.1615/AtomizSpr.v17.i2.10
Gwon Hyun
Ko
School of Mechanical Engineering, Chung-Ang University, Chung-Ang University 221, HeukSuk Dong, DongJak Ku, Seoul, 156-756, Korea
Hong Sun
Ryou
School of Mechanical Engineering, Chung-Ang University, Chung-Ang University 221, HeukSuk Dong, DongJak Ku, Seoul, 156-756, Korea
The present study performs an extensive numerical study for analyzing the anisotropic turbulence effects on spatial and temporal behaviors of diesel sprays after wall impingement. The Durbin (P. A. Durbin, Int. J. Heat Fluid Flow, vol. 14, no. 4, pp. 316−323, 1993) k−ε−ν2 model is used to simulate the anisotropic turbulence effects and its results are compared with the predictions by the k−ε model based on the isotropic assumption. In the present study, the Lee and Ryou (S. H. Lee and H. S. Ryou, Atomization and Sprays, vol. 11, pp. 85−105, 2001) model is used for the calculation of the spray-wall interactions. The predicted results by two turbulence models are compared with several experimental data for both the overall structure of impinging sprays and the internal structure, for which the main parameters are the radius and height of impinging sprays, the local velocities and the Sauter mean diameter of droplets, the local velocities of gas-phases, and so on. The k−ε−ν2 model considering the anisotropy of turbulence predicts both gas and droplet tangential velocities better than the k−ε model does. It is concluded that the anisotropy of turbulence should be considered in simulating impinging diesel sprays.
SINGLE-FLUID AND DUAL-FLUID ATOMIZATION METHODS: LOCAL AND GLOBAL SPRAY QUANTITIES
123-151
10.1615/AtomizSpr.v17.i2.20
Julian T.
Kashdan
I.F.P., Rueil-Malmaison, France
Holger
Lienemann
Department of Mechanical Engineering, Imperial College London, London, UK
John S.
Shrimpton
Energy Technology Research Group, School of Engineering Sciences, University of Southampton,
Atomization and Sprays Research Group Dept. Mechanical Engineering, UMIST, Manchester, United Kingdom, SO171BJ
This article describes a one-to-one comparison of spray performance for a single-fluid high-pressure swirl injection system (PSA) and a dual-fluid, air-assisted injection system (AAA) based on high-resolution CCD images and phase Doppler anemometer measurements. Both atomizer concepts are used in direct-injection spark-ignition (DISI) engine applications, and the present experiments were carried out using original engine hardware. Spray characterization was obtained in constant-volume chambers at ambient conditions corresponding to typical injection windows in DISI engines. The temporal and spatial evolution of spray pattern, mean droplet size, and droplet velocity were considered as important parameters. At atmospheric gas conditions, the rate of axial penetration was similar for both sprays, but a fourfold increase in gas density resulted in a reduction of ∼50% and ∼25% for the AAA and PSA, respectively. A higher level of droplet arithmetic mean diameter (D10) was generally observed for both sprays at elevated gas densities, and a correlation factor was introduced to link the space-averaged D10 and the ambient gas density.
EFFECTS OF IMPINGEMENT CONDITIONS ON THE CHARACTERISTICS OF MUTUAL IMPINGING SPRAY
153-170
10.1615/AtomizSpr.v17.i2.30
Gwon Hyun
Ko
School of Mechanical Engineering, Chung-Ang University, Chung-Ang University 221, HeukSuk Dong, DongJak Ku, Seoul, 156-756, Korea
Hong Sun
Ryou
School of Mechanical Engineering, Chung-Ang University, Chung-Ang University 221, HeukSuk Dong, DongJak Ku, Seoul, 156-756, Korea
The present study aims to investigate the influence of the impinging angle, impingement distance, and injection pressure on the characteristics of a mutual impinging spray that is formed by the direct impact between two solid-cone sprays. In the present study, the droplet sizes and velocities are measured by the phase Doppler particle anemometer system and the overall shape of spray is recorded by a photographic technique. The distribution of liquid volume fraction is also measured by the self-manufactured patternator. The results for the mutual impinging sprays are also compared with those for single nozzle-injected sprays. The Sauter mean diameters measured in the interspray impingement system become 35 and 45% smaller for impingement distances of 20 and 50 mm, respectively, compared to those of a single nozzle-injected spray. For different impinging angles, i.e., 60° and 90°, the decreasing rate in droplet velocity is found to be about 60 and 70%, respectively, of that measured in the single nozzle-injected spray. It is confirmed that mutual impinging sprays may be an alternative way to enhance atomization, provided that such optimized conditions are found in engineering applications.
STEADY-STATE HIGH-PRESSURE SPRAY COOLING OF HIGH-TEMPERATURE STEEL SURFACES
171-191
10.1615/AtomizSpr.v17.i2.40
R. A.
Sharief
Department of Mechanical & Aerospace Engineering, Thermo Fluid Division, UMIST, George Begg Building, Manchester, UK
Water-spray cooling of heated surfaces is common in many industrial applications, notably steelmaking, because of its high heat dissipating ability. Quantitative information regarding the parameters affecting spray cooling is relatively scarce. The objective of this research is to obtain such information by using a specially developed experimental technique that provides steady-state cooling of a steel surface using a gas-fired burner to introduce heat. The method provides fundamental information on the spray parameters controlling heat transfer from horizontal heated surfaces for a wide range of mass flux and droplet size and velocity in the film-boiling regime. Measurements are made of the drop sizes and velocities and of the liquid mass flux in the sprays produced by full-cone pressure atomizers. Heat transfer characteristics in the range of surface temperature between 380 K and 1200 K are investigated. Comparisons are made with published data and correlations are developed for heat flux and Nusselt number in the surface temperature range from 800 to 1200 K. It is found that drop size has only a weak effect on heat transfer in these relatively dense sprays. However, droplet velocity is almost as important as mass flux, so that the product of mass flux and velocity, the impinging momentum flux of water, is the dominant parameter.