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Year 1996, Volume 6 / Issue 5

Pages: 124

Article price - $35.00

TURBULENCE CHARACTERISTICS OF A TWIN-FLUID ATOMIZER

Takashi Sakai
Department of Bio-Chemical Engineering, Gunma University, Kiryu, Gunma, Japan

D. Q. Zhao
Department of Chemical Engineering, Nanjing Institute of Chemical Technology, Nanjing, P. R. China

M. Iijima
Department of Bio-Chemical Engineering, Gunma University, Gunma, Japan

Masahiro Saito
Department of Mechanical System Engineering, Gunma University, Kiryu, Gunma, Japan

Masayuki Sato
Department of Bio-Chemical Engineering, Gunma University, Kiryu, Gunma, Japan

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 ejected two-phase jets, were observed, and it was found that fine spray was generated by the complete mixing of air and liquid and filled with bubble flow in the mixing chamber. The geometry of the atomizer to obtain fine spray with lower pressure is discussed, and a model of mixing 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 zone was filled with finer droplets of dense flux and the outer zone was coarse and sparse. Change of the drop mean diameters, numbers from near the nozzle port toward downstream, and radial direction were analyzed, and it was found that the most intense disintegration of liquid, by primary disintegration within two-phase jets, occurred near the nozzle port around the axial zone. The droplet number increased after the primary disintegration and was considered as the secondary disintegration.
Turbulent flow characteristics of air within air jets, and spray jets 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 of the TFA-IM-O immediately after ejection was greater by about six times than that from the CT. From the experimental results, it was considered that the turbulence of liquid and air within two-phase fluid in the mixing chamber would promote disintegration into finer bubbles, by Reynolds stress, and immediately after ejection from the orifice port, the bubbles separate from the two-phase jet core surface and burst into the fine droplets (primary disintegration). The primary disintegration continues from the nozzle port until about 40D₂ (D₂ = orifice diameter). Though the disintegration by relative velocity may continue at the outer zone of the spray jet, the secondary disintegration of droplets may proceed after 40D₂ to about 100D₂ downstream, by the intense Reynolds stress of turbulence of air.

pages 577-600

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