Studies have shown that the nozzle atomization process […]
Studies have shown that the nozzle atomization process is mainly controlled by four kinds of forces, namely aerodynamic drag, viscous force, surface tension of liquid and inertial force. The interaction between these four forces causes the continuous liquid injection to split and break. It is generally believed that the nozzle atomization process is divided into a jet atomization process and a liquid film atomization process.
Rayleigh analyzed the jet breaking mechanism in 1876. He used the small perturbation method to analyze the conditions required for low-speed jet crushing. It is believed that the jet can be broken only when the wavelength of the symmetric disturbing wave is comparable to the diameter of the jet. By measuring the frequency of jet fracture, Tyler studied the relationship between jet fracture and the wavelength of the disturbance wave, and verified the theoretical analysis of Rayleigh.
Weber developed a more general low-speed viscous jet breaking theory, and proposed that the optimal disruption wave wavelength exists in jet rupture, and its expression is given. By analyzing the interaction of various forces during liquid atomization, he believes that the frictional action of aerodynamic force on liquid and the high-speed flow inertia of the liquid itself are important causes of droplet breakage. When the effect of aerodynamic drag is greater than the surface tension, the liquid will atomize and droplets will peel off on the surface of the liquid. According to this, he proposed a dimensionless constant-Weber number, and gave important index parameters such as critical Weber number and critical liquid velocity.
Haenlein verified Weber's conclusions through experiments and divided liquid jet atomization into four types of processes: droplet formation without air impact, droplet formation with air influence, droplet generation due to jet fluctuations, and jet flow. Completely broken or atomized. Ohnesorge organizes the data according to the importance of the jet force, and introduces the dimensionless number Ohnesorge number to divide the jet crushing process into three phases:
(1) Low Reynolds number segment, at which point the Rayleigh mechanism controls the crushing process:
(2) In the middle Reynolds number segment, the jet crushing is controlled by the jet disturbance;
(3) The high Reynolds number segment, the atomization process is completed within a short distance of the nozzle outlet.