TURBULENCE CHARACTERISTICS OF A TWIN-FLUID ATOMIZER

The role of turbulence on the disintegration of two-phase jets ejected from a twin-fluid atomizer of internal mixing type with orifice, TFA- IM-O, was studied experimentally. The relationship between mixing and flow patterns in the mixing chamber, and atomization patterns of the e jected two-phase jets, were observed, and it was found that fine spray teas generated by the complete mixing of air and liquid and filled wi th bubble flow in the mixing chamber. The geometry of the atomizer to obtain fine spray with lower pressure is discussed and a model of mixi ng and primary disintegration through bubbles related with turbulence within the mixing chamber is proposed. The structure of spray from the TFA-IM-O was studied using a phase Doppler particle analyzer (PDPA), and novel characteristics of this spray were measured. The central zon e was filled with finer droplets of dense flux and the outer zone was coarse and sparse. Change of the drop mean diameters, numbers from nea r the nozzle port toward downstream, and radial direction were analyze d, and it was found that the most intense disintegration of liquid, by primary disintegration within two-phase jets, occurred near the nozzl e port around the axial zone. The droplet number increased after the p rimary disintegration and was considered as the secondary disintegrati on. Turbulent flow characteristics of air within air jets, and spray j ets issued from TFA-IM-O, were measured by LDV and compared with that from a circular tube (CT). It was found that the turbulent intensity o f the TFA-IM-O immediately after ejection was greater by about six tim es than that from the CT. From the experimental results, it was consid ered that the turbulence of liquid and air within two-phase fluid in t he mixing chamber would promote disintegration into filler bubbles, by Reynolds stress, and immediately after ejection from the orifice port , the bubbles separate from the two-phase jet core surface and hurst i nto the fine droplets (primary disintegration). The primary disintegra tion continues from the nozzle port until about 40D(2) (D-2 = orifice diameter). Though the disintegration by relative velocity may continue at the outer zone of the spray jet, the secondary disintegration of d roplets may proceed after 40D(2) to about 100D(2) downstream, by the i ntense Reynolds stress of turbulence of air.