Abstract
Air-core–liquid-ring (ACLR) atomization presents a specific type of internal mixing pneumatic atomization. It can be used for disintegration of high viscous feed liquids into small droplets at relatively low gas consumptions. However, the specific principle of ACLR atomization is still under research and no guidelines for process and atomizer design are available. Regarding literature on pre-filming atomizers, it can be hypothesized for ACLR atomization that the liquid film thickness inside the exit orifice of the atomizer, as well as the resulting spray droplet sizes decrease with increasing air-to-liquid ratio (ALR) and decreasing feed viscosity. In this study, the time dependent liquid film thickness inside the exit orifice of the atomizer was predicted by means of computational fluid dynamics (CFD) analysis. Results were compared to high speed video images and correlated to measured spray droplet sizes. In conclusion, the hypothesis could be validated by simulation and experimental data, however, at high viscosity and low ALR, periodic gas core breakups were detected in optical measurements. These breakups could not be predicted in CFD simulations, as the simplification of an incompressible gas phase was applied in order to reduce computational costs and time. Nevertheless, the presented methods show good potential for improvement of atomizer geometry and process design as well as for further investigation of the ACLR atomization principle.
Highlights
Disintegration of liquids into small and uniform droplets is an important task in many industrial processes, such as combustion, coating or spray drying [1,2]
The focus was on the relations between processing conditions, internal liquid film thickness and resulting spray droplet sizes at different viscosities
It was hypothesized that increasing air-to-liquid ratio (ALR) or decreasing viscosities lead to decreasing liquid film thicknesses inside the exit orifice and to smaller resulting spray droplets
Summary
Disintegration of liquids into small and uniform droplets is an important task in many industrial processes, such as combustion, coating or spray drying [1,2]. For this purpose, different atomization principles can be applied. The kinetic energy of a compressed gas stream is used as source of atomization energy [3,4]. It can be distinguished between internal and external mixing pneumatic atomizers.
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