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.
Highlights
Continuous atomization of high viscous concentrates is an important task in different industrial processes, like combustion, spray drying or coating [1,2]
The arithmetic mean value ρL av = 1200 kg·m−3 was used for linear prediction of the correlation between air-to-liquid ratio by mass (ALR) and EV at constant gas pressure, based on Equation (8)
It was assumed that pressure-dependent expansion energy of atomization gas contributes to liquid disintegration in ACLR atomization
Summary
Continuous atomization of high viscous concentrates is an important task in different industrial processes, like combustion, spray drying or coating [1,2]. For atomization of high viscous feeds, external-mixing pneumatic (ExMP) atomizers are commonly used [2]. In ExMP atomizers, gas and liquid are mixed under atmospheric conditions, outside the atomizer. As both media are supplied in separated streams, ExMP atomizers provide easy and independent control of gas and liquid flow rates [8]. Especially in spray-drying processes they do not meet the requirements of industrial applications on atomization efficiency, due to very high gas consumption rates [3,4]. In this case atomization efficiency is defined as a correlation between energy input and resulting spray droplet size. The energy input is typically correlated with the specific gas consumption under applied processing conditions, which is Processes 2019, 7, 139; doi:10.3390/pr7030139 www.mdpi.com/journal/processes
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