Experimental Investigation of Spray Characteristics of Pre-Filming Air-Blast Atomizers II – Influence of Liquid Properties

One of the most important advantages of twin-fluid atomizers over other atomizers is the opportunity of atomizing liquids in a wide range of liquid properties efficiently. Thus, the fundamentals of spray dynamics, such as spray pattern, liquid breakup length, and spatial droplet size evolution using different liquid properties need to be investigated in some detail. The purpose of this study is therefore to examine and describe the influence of the liquid viscosity and surface tension on the spray performance of prefilming air-blast atomizers. A high-speed background shadowgraphy technique associated with particle tracking and Phase Doppler Anemometry (PDA) as a non-intrusive high-resolution local measurement technique were utilized to study the atomization process regarding the influence of the liquid properties on the spray quality. Generally, the break up mechanism is considerably influenced by the liquid viscosity. The breakup length ( ) is dependent on liquid viscosity with for Pa = 0.25 and 0.6 bar air pressure, respectively. Droplet size distribution profiles of different liquids in axial and radial directions are studied. No significant influences of the surface tension and viscosity were observed on the mean droplet velocity downstream of the spray. A minor increase of the droplet mean diameter was observed with liquid viscosity variations from 22 to 111 mPas, however, the liquid surface tension was verified to play an important role in the atomization process at prefilming airblast atomizers as well. According to the available experimental data, it has subsequently been possible to develop an original and descriptive model based on a dimensional approach at different air pressure ranges.