The Atomization Characteristics of Fully Automatic Fog Cannon Nozzles

These fully automatic fog cannons are now a common sight on our roads. During operation, they spray large volumes of fine water mist to suppress and reduce dust. What are the atomization features of these nozzles? Read on to find out. A typical nozzle for fully automatic fog cannon machines is the flat-orifice nozzle, widely used in combustion chambers for automotive, aircraft, and rocket engines. A circular jet formed by flat-orifice nozzles is ejected at high velocity under high discharge pressure and fragmented by the turbulent effects of the gas flow. As long as the surface wave wavelength of the liquid circular jet approaches twice the diameter of the circular jet, the turbulent effects of the gas flow will cause the circular jet to break up. However, turbulent circular jets can only fragment through their own turbulent pulsations without any external force. When the liquid forms small patches, lines, or droplets, it reaches a new equilibrium. Once the liquid overcomes surface tension again due to its own or gas turbulence, it further fragments into finer particles. The viscosity of the liquid suppresses the growth of circular jet instability, delaying the fragmentation process. This allows atomization to occur in the downstream region where gas-liquid relative velocities are lower. In most cases, liquid turbulence, nozzle cavitation, increased ambient gas density, and aerodynamic effects all favor atomization. Fully automatic fog cannon nozzles capable of producing liquid film jets atomize the liquid and achieve thorough liquid-gas mixing. Planar liquid film jets are typically generated by high-pressure liquid passing through a slit, such as fan-shaped nozzles used in the apparel industry. These fully automatic fog cannon nozzles require specific discharge pressures or rotational centrifugal forces to achieve adequate discharge velocities. Once formed, the initial hydrodynamic stability of the liquid film jet is disrupted by aerodynamic disturbances. As the jet expands away from the nozzle, its thickness gradually increases, leading to fragmentation into liquid threads and droplets. If discharge pressure is sufficiently high, the liquid atomizes into fine particles at the nozzle outlet without a linear transition zone.