Ligament breakup

Further differences from hydraulic nozzles (controlled by sheet and ligament breakup) are the stronger increase in drop size with increasing surface tension and decreasing gas density. 

Droplet Formation in Gas Atomization. Experimental and modeling studiesl160 161 169] 318] 319] 321]- 325] have shown that gas atomization of liquid metals in spray forming and powder metallurgy processes may take place in two primary modes, i.e., liquid jet-ligament breakup and liquid film-sheet breakup. 

Figure 3.12. Schematic showing Liquid Jet-Ligament Breakup mode (left) and Liquid Film Sheet Breakup mode (right) in two-fluid atomization of melts.

The temperature of a liquid metal stream discharged from the delivery tube prior to primary breakup can be calculated by integrating the energy equation in time. The cooling rate can be estimated from a cylinder cooling relation for the liquid jet-ligament breakup mechanism (with free-fall atomizers), or from a laminar flat plate boundary layer relation for the liquid film-sheet breakup mechanism (with close-coupled atomizers). 

Ligament Breakup. Columns of liquid break up in air owing to the development of oscillations which increase in amplitude until this exceeds... 

The ligament breakup model predicts drop diameter given a set of initial conditions. A distribution of drop sizes results because the initial cmiditions fluctuate, due to vibration of the atomizer, variations in liquid delivery rate, unsteady exit velocity, inhomogeneous liquid physical properties, cavitation-induced pulsations, turbulent flow fields, etc. PDFs are required for all fluctuating quantities. 

Increasing the viscosity of the fluid used in an electrospray dramatically increases the droplet sizes produced and therefore increases the hgament breakup. A dimensionless number has been proposed [22] to determine the importance of viscosity on the electrospray ligament breakup ... 

A more elaborated theoretical model based on interfacial Taylor instability triggering the surface wave was developed by Peskin and Raco [39]. A thin layer of a liquid, wetting the surface of a solid resonator wbch vibrates to its plane, forms a chessboard-like pattern of stationary capillary waves. This phenomenon occurs when the vibration amplibde exceeds a threshold value. Further on, ligament breakup of the liquid occurs and droplets are hurled from the crests of the capillary waves. Together with the wavelength, they introduced wave amplibde and the sheet thickness as parameters to determine the droplet size [39]. 

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