Venturi Effect

Its Role in Maritime Ops.

What is it?

Reduction in fluid pressure that results when fluid flows through a constricted section of pipe.

Velocity of fluid increases as cross-sectional area decreases as static pressure correspondingly decreasing; Jet effect.

Named after Giovanni Battista Venturi (1746–1822 ) Italian physicist.

Workings

“Fluid velocity must increase as it passes through a constriction to satisfy

principles of continuity while its pressure must decrease to

satisfy the principle of conservation of mechanical

energy; Gain in kinetic energy in a fluid may accrue due to its increased velocity

though constriction is regated by a drop in

pressure.” Laws of Fluid Dynamics.

When a fluid such as water flows through a tube that narrows to a smaller diameter and partial restrictions cause a higher pressure at the inlet than the narrow end. Pressure difference causes the fluid to accelerate towards the low pressure narrow section in which it maintains a higher speed.

Choked Flow

Limiting case of Venturi effect: When fluid reaches state of choked flow where

the fluid velocity approaches the local speed of sound. In choked flow, the mass flow rate will not increase with a

further decrease in the downstream pressure

environment. Mass flow rate for a compressible fluid can

increase with increased upstream pressure which will

increase density of fluid through constriction; velocity

remains constant.

Uses and Presence

Cargo eductor/ejector on oil product and chemical tankers.

Flue gas scrubbers. Ventilators Emptying bilge water from

moving boats via hull waste gate; air pressure inside being greater than water.

Dredging

Summary

Reduction in fluid pressure that results when a fluid flows through constricted section of a pipe.