Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Dr. Kamran Siddiqui

Abstract

Effervescent atomization uses the internal gas-liquid mixture to produce spray. The behavior of two-phase flow inside the atomizer influences the spray characteristics and is dependent on the atomizer internal geometry and operating conditions. The present study is conducted in two parts; study of the bubble formation from a novel submerged nozzle in a liquid cross-flow and investigation of the internal and external two-phase flows in an effervescent atomizer.

The present study investigated the performance of a novel nozzle developed by Gadallah and Siddiqui (2013) in the liquid cross-flow. The impact of the nozzle shape, its configurations and orientations was experimentally investigated. The results showed that the novel nozzle generates smaller bubbles at higher detachment frequency for all cases compared to the standard nozzle. It is found that the elastic rebound of the bubble from a side hole plays a key role in the early bubble detachment.

For the effervescent atomizer study, the impact of atomizer’s internal geometry on the internal flow and spray droplet characteristics were studied. The results demonstrated that a conical base aerator tube and shorter mixing zone length provide more uniform bubbles in smaller size. A new type of bubble breaker was designed and tested in an effervescent atomizer. The results show that both internal and external two-phase flows in the atomizer were strongly influenced by bubble breaker configurations (diameter and number of holes). It was found that the liquid shear stress is the dominant force causing the bubble elongation and its eventual breakup.

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