Abstract
Plain-jet airblast atomizers are widely used in industrial applications. The literature contains numerous papers on Sauter mean diameter, however, there is no estimation method available for spray cone angle, SCA, which derivation is the primary goal of this study. Four distinct, practical model liquids were analyzed: distilled water, diesel oil, light heating oil, and crude rapeseed oil. The atomizing pressure and liquid preheating temperature were varied in the range of 0.3–2.4 bar and 25–85 °C, respectively. This latter parameter enabled a wide and continuous liquid kinematic viscosity investigation range of 0.33–44.2 mm2/s. The resulting sprays were imaged at various shutter speeds for proper edge detection. An adaptive thresholding algorithm was developed in Matlab software environment to calculate SCA. The methodology is discussed in detail to facilitate the re-implementation of this technique since there is no generally accepted method for SCA measurement. SCA inversely varied with liquid density and followed a power law with the air-to-liquid mass flow ratio; however, the derived expression also performed well by replacing air-to-liquid mass flow ratio by either Mach number or momentum flux ratio. A simple empirical equation was derived, which allows the estimation of SCA of airblast atomization in a wide parameter range within a 3.5% deviation. The measured results were evaluated in the light of high-speed camera images in the vicinity of the nozzle; it was found that increased liquid jet breakup length decreases SCA while intense ligament formation increases it.
Highlights
The most important parameter of a liquid spray is its mean droplet size, which determines the average evaporation/solidification time, impingement, and the general interaction with the surrounding gas flow
SCA determination for swirl atomizers shows a high sensitivity on the atomizer constant [6], and analytical approximations are available for inviscid flow [7]
Since the parameter fitting results in high R2 values, the fitted coefficients were perturbed by 1% to see their effect on the sum of the squared estimate of errors, SSE, to find the results with low sensitivity and potentially applicable for SCA estimation
Summary
The most important parameter of a liquid spray is its mean droplet size, which determines the average evaporation/solidification time, impingement, and the general interaction with the surrounding gas flow. The second highlighted parameter is the Spray Cone Angle, SCA, which characterizes spray spreading. It bears an emphasized role in numerous applications, including cooling [1], metallurgy [2], and combustion systems [3]. Practical atomizers work in a turbulent flow field that couples with the droplet movement [5]. The literature is significantly thinner for other atomizer types in which SCA is determined by the resulting spray instead of a well-localized liquid sheet. The droplet-turbulence interaction makes spray edge detection a nontrivial task [8].
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