Studies On Impinging-Jet Atomizers

Abstract

Characteristics of impinging-jet atomizers in the context of application in liquid propulsion systems are studied in this thesis. A review of past studies on impinging jets revealed the necessity of a correlation in terms of injector parameters for predicting Sauter Mean Diameter (SMD) of a spray. So, an experimental study of atomization in doublet and triplet impinging jet injectors is conducted using water as the stimulant? The major injector parameters considered are orifice diameter, impingement angle and jet velocity. Relative influences of these parameters are explained in terms of a single parameter, specific normal momentum. SMD of the spray reduces as specific normal momentum is increased. A universal expression between non-dimensional SMD and specific normal momentum is obtained, which satisfactorily predicts SMD in doublets as well as triplets. Noting that practical impinging injectors are likely to have skewness (partial impingement), the study is extended to understand the behavior of such jets. In perfectly impinging doublet, a high aspect ratio ellipse-like mass distribution pattern is obtained with major axis normal to the plane of two jets whereas in skewed jets the major axis turns from its normal position. A simple correlation is obtained, which shows that this angle of turn is a function of skewness fraction and impingement angle only and is independent of injection velocity. Experimental data from both mass distribution and photographic technique validate this prediction. SMD is found to decrease as skewness is increased. This may be the combined effect of shearing of liquid sheet at the point of impingement and more sheet elongation. Hence, skewness turns out to be an important parameter in controlling drop size.