Nozzles

A nozzle is a device designed to control the direction of fluid flow, the speed of the fluid, and the pressure at which it exits a system. By constricting or shaping the flow, nozzles convert pressure energy into kinetic energy and influence jet shape and dispersion.

Basic principles: The flow rate through a nozzle follows the continuity equation m_dot = rho A v, with Q = A v for incompressible fluids. As the cross-sectional area decreases, velocity increases and static pressure falls (Bernoulli). In compressible flows, the concept of choking can occur when the upstream pressure relative to ambient is sufficient to reach Mach 1 at the nozzle throat; further pressure drop cannot increase mass flow.

Types: Converging nozzles produce subsonic exit velocities; diverging sections are used in combination for supersonic exit flows (convergent-divergent or de Laval nozzles). Atomizing and spray nozzles inject fluids as droplets or vapors, often using air or hydraulic assist. Fuel injection and rocket nozzles are designed for efficient atomization and expansion, with attention to combustion chamber pressure and ambient pressure.

Applications and considerations: Nozzles are central to rocket engines, jet engines, turbines, industrial spraying, irrigation, coating, and water-jet cutting. Design must consider erosion, cavitation, clogging, material compatibility, and maintenance needs. The choice of nozzle geometry, materials, and operating conditions determines performance and efficiency.