PLANAR LIQUID SHEET BREAKUP OF PREFILMING AND NONPREFILMING ATOMIZERS AT ELEVATED PRESSURES

Liquid sheet breakup of a prefilming and nonprefilming airblast atomizer is investigated experimentally at ambient temperatures and elevated pressures of air. The breakup is studied by High-Speed flow visualization. The visualizations show the differences between both types of atomizers.. For lower liquid loadings the atomizer edge is always wetted in the prefilming case whereas dry zones are observed for the nonprefilming injector. Different atomization regimes are observed for rising Weber numbers on the prefilmer: Wavy sheet breakup below We = 100, surface stripping above 380 and a transition zone in between. The nonprefilming case always exhibits wavy sheet breakup, provided there is a sheet at the outlet, with the breakup length reducing to 0,5 mm above We 100. Liquid sheet thickness is characterized with side view images. Films which are thin compared to the edge thickness and are not composed of ligaments at the edge wrap around the edge and therefore exhibit a storage mechanism. In the far field dropsizes are characterized with a global SMD measured by PDA. The measured dropsizes, influencd by primary and secondary atomization show only small differences between the two types of atomizers. Correlations for the final drop size are obtained for both atomizers types for the conditions investigated.