Jet breakup

It has been postulated that jet breakup is the result of aerodynamic interaction between the Hquid and the ambient gas. Such theory considers a column of Hquid emerging from a circular orifice into a surrounding gas. The instabiHty on the Hquid surface is examined by using first-order linear theory. A small perturbation is imposed on the initially steady Hquid motion to simulate the growth of waves. The displacement of the surface waves can be obtained by the real component of a Fourier expression ... 

FIG. 14-85 a) Idealized jet breakup suggesting uniform drop diameter and... 

A link between laminar and turbulent lifted flames has been demonstrated based on the observation of a continuous transition from laminar to turbulent lifted flames, as shown in Figure 4.3.13 [56]. The flame attached to the nozzle lifted off in the laminar regime, experienced the transition by the jet breakup characteristics, and became turbulent lifted flames as the nozzle flow became turbulent. Subsequently, the liftoff height increased linearly and finally blowout (BO) occurred. This continuous transition suggested that tribrachial flames observed in laminar lifted flames could play an important role in the stabilization of turbulent lifted flames. Recent measurements supported the existence of tribrachial structure at turbulent lifted edges [57], with the OH zone indicating that the diffusion reaction zone is surrounded by the rich and lean reaction zones. 

Liquid Column/Jet Breakup. When a liquid jet issues from a nozzle, oscillations and perturbations form on the jet surface as a... 

The phenomenon of liquid j et breakup has been the subj ect of theoretical and experimental investigations for more than one century. [37H41][115][21°][219H230] Reviews of liquid jet breakup mechanisms have been made by Tanasawa and Toyoda, 411 McCarthy and Molloy,[230] and Reitz and Bracco,12291 among others. 

In the idealized mode, liquid jet breakup and droplet formation are fairly regular. The liquid jet running downwards collapses, forming droplets of uniform size at uniform spacing. After breakup, the liquid jet of length 4.51 d0 converts into a spherical droplet so that ... 

To account for the effect of liquid viscosity on liquid jet breakup, Weber extended Rayleigh s theory to a more general theory for low-velocity j et breakup. In Weber s theory it is assumed that... 

Weber s theory has been further extended by many investi-gators[391 [4ill204 [22°][22-7] t0 account for high-velocity jet breakup and droplet formation under the influence of ambient air. Various mechanisms of jet breakupl40H41Pio][220][227][232] have been pro posed and divided into breakup regimes to reflect the differences in the appearance of jets and to identify the dominant forces leading to jet breakup as operation conditions are changed. 

For steady injection of a liquid through a single nozzle with circular orifice into a quiescent gas (air), the mechanisms of jet breakup are typically classified into four primary regimes (Fig. 3 2)[4°][41][22°][227] according to the relative importance of inertial, surface tension, viscous, and aerodynamic forces. The most commonly quoted criteria for the classification are perhaps those proposed by Ohnesorge)40] Each regime is characterized by the magnitudes of the Reynolds number ReL and a dimensionless number Z ... 

Rayleigh Jet Breakup (Varicose Breakup) Surface Tension Force We <0.4 or We <1.2 + 3.41Oh0... 

Figure 3.2. Breakup regimes of round liquid jets in quiescent air. I Rayleigh Jet Breakup (Varicose Breakup) II First Wind-Induced Breakup (Sinuous Wave Breakup) III Second Wind-Induced Breakup (Wave-like Breakup with Air Friction) IV Atomization.

Based on their experiments, Tanasawa and Toyoda1411 proposed a new dimensionless number for the classification of jet breakup regimes. This number, called Jet number, is defined as ... 

Although the Jet number is used for the classification, it should be noted that the intrinsic characters of a liquid flow depend on the Reynolds number. By combining the Jet number with the Reynolds number and introducing a correction factor for viscosity, the modes and configurations of liquid jet breakup can be clearly defined and described.[41]... 

Factors influencing jet breakup may include (a) flow rates, velocities and turbulence of liquid jet and co-flowing gas, (b) nozzle design features, (c) physical properties and thermodynamic states of both liquid and gas, (d) transverse gas flow,[239] (e) dynamic change of surface tension, 1151[2401 (f) swirlj241 242 (g) vaporization and gas compressibility,[243] (h) shock waves,[244] etc. 

Quantitative correlations for jet breakup length have been proposed by many investigators based on experiments. I381141 ] 122°]l247 I248]... 

They also proposed an empirical correlation for laminar jet breakup length ... 

The mechanical breakup mode occurs around the rims of the sheet where the air-liquid relative velocity is low, forming relatively large droplets. At low relative velocities, aerodynamic forces are much smaller than surface tension and inertia forces. Thus, the breakup of the liquid rims is purely mechanical and follows the Rayleigh mechanism for liquid column/jet breakup. For the same air pressure, the droplets detached from the rims become smaller as the liquid flow rate is increased. 

Table 4.15. Empirical Correlations for Droplet Sizes of Liquid Metals in Gas Atomization Jet Breakup...

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