SPRAY EVOLUTION IN A TWIN-FLUID SWIRL ATOMIZER

Abstract

The paper describes an experimental study of the evolution of spray structure in an internally mixed, twin- fluid swirl atomizer. A laser sheet visualization technique was used to study the primary spray formation process. The order of magnitude of the ALR (Air-liquid ratio) for which the study was made ranged from 10-3 to 10-1. It was observed that at low ALR a fully developed air core inside the hollow conical spray is present suggesting the assistance provided by the atomizing air to the atomization process by de-stabilizing the liquid internally. At high ALR conditions of around 0.1, a solid cone spray shape is observed. At moderate ALR`s, a mixed cone is formed, having an outer hollow structure and a solid core, with a gap between the inner and outer cone. This can be attributed to the combined effect of swirl (producing the hollow cone) and the increase in the axial momentum of the liquid inside the atomizer due to squeezing by the surrounding atomizing air (forming the inner core). Also, the phenomenon of liquid break up in terms of breaking distance at various ALR conditions was analyzed in this study. It was observed that the structure of the spray, e.g., cone angle, solidity and breaking distance, do not change much with the increase in ALR beyond a critical value of 0.08. The variation from hollow to solid cones demonstrated by the atomizer in this study makes it flexible and efficient enough to be used for commercial applications, as the atomizer is capable of providing a wide range of spray patterns depending upon the application requirement.