Air-Core-Liquid-Ring (ACLR) Atomization: Influences of Gas Pressure and Atomizer Scale Up on Atomization Efficiency

Abstract

Air-core-liquid-ring (ACLR) atomizers present a specific type of internal mixing pneumatic atomizers, which can be used for efficient atomization of high viscous liquids. Generally, atomization efficiency is considered as a correlation between energy input and resulting droplet size. In pneumatic atomization, air-to-liquid ratio by mass (ALR) is commonly used as reference parameter of energy input. However, the pressure energy of the atomization gas is not considered in the calculation of ALR. In internal mixing ACLR atomizers, it can be assumed that this energy contributes to liquid disintegration by expansion of the gas core after exiting the atomizer. This leads to the hypothesis that droplet sizes decrease with increasing gas pressure at constant ALR. Therefore, the use of volumetric energy density (EV) as a reference parameter of energy input was investigated at different gas pressures between 0.4 and 0.8 MPa. Furthermore, scale up-related influences on the atomization efficiency of ACLR atomization were investigated by use of an atomizer with enlarged exit orifice diameter. We can conclude that EV can be applied as a reference parameter of ACLR atomization processes with different gas pressures. However, within the range investigated no clear influence of gas pressure on atomization efficiency was found. Up-scaling of ACLR atomizers allows production of similar droplet sizes, but atomization efficiency decreases with increasing exit orifice diameter.

Air-Core–Liquid-Ring (ACLR) Atomization Part II: Influence of Process Parameters on the Stability of Internal Liquid Film Thickness and Resulting Spray Droplet Sizes

“…As a consequence, the mass flow rate of gas increases leading to an increase in ALR. However, in one of our previous studies on ACLR atomization we found no significant influence of different gas pressure levels at constant ALR on resulting spray droplet sizes [24]. Hence, it can be assumed that the compressed gas core expands completely over the length of the exit orifice to atmospheric conditions at the tip of the nozzle, leading to an increase in gas velocity and therefore in kinetic energy.…”

“…Although relatively high input gas pressures of up to 0.8 MPa were applied, simulations were performed under the assumption of an incompressible gas phase. This simplification was used as complete expansion of the gas phase to atmospheric conditions can be assumed over the length of the atomizer's exit orifice [24]. The potential decrease in accuracy was accepted with regards to significant reduction of computational time and costs in this first study.…”

“…Like in former studies, a modular test rig was used for spray experiments [22][23][24]. Liquid flow rates of 30 and 40 L•h −1 were supplied by an eccentric screw pump (NM011BY, Erich Netzsch GmbH and Co. Holding KG, Waldkraiburg, Germany) and measured by a flow meter (VSI 044/16, VSE GmbH, Neuenrade, Germany).…”

Special Issue on Performance Measurement and Optimization for Sustainable Production Processes Improvement

“…Wittner et al [19,20] focused on the air-core-liquid-ring atomization and Chan and Kuo [21] investigated the wheat germ drying performance. Holgado [22] used system engineering approach to performance-based maintenance services design.…”

Experimental Study on Spray Breakup in Turbulent Atomization Using a Spiral Nozzle

“…It is; therefore, necessary to conduct further research in this area as the description of conical sheets breakup mechanisms is rather scarce in the literature [89]. The measured droplet diameters are mostly much larger compared to different types of atomizers, which produce droplets in the range up to 100-150 µm in diameter, refer to, for example, [58,[90][91][92][93], but in a similar order as compared to fire sprinklers [64,79,94]. Comparing the Sauter mean diameter empirical formulas developed for different atomizers we can also see rather significant differences.…”