As the speed of a fluid increases through a restriction, what happens to the fluid pressure downstream?

When a fluid flows through a restriction, such as a narrowed section of pipe, its velocity must increase due to the principle of conservation of mass (continuity equation). According to Bernoulli’s principle, as the speed of a fluid increases, the pressure within that fluid decreases.

This phenomenon can be understood through Bernoulli’s equation, which states that an increase in the fluid's velocity (kinetic energy) at the restriction results in a corresponding decrease in the fluid's pressure energy. Thus, as the fluid travels downstream from the restriction and continues at a higher velocity, the pressure downstream will be lower than that immediately before the restriction.

The decrease in pressure is a critical concept in fluid dynamics and is fundamental to the operation of various control systems, pumps, and valves in process industries. Understanding this relationship helps in predicting how changes in velocity and area within a system can influence the overall pressure distribution, aiding effective system design and troubleshooting.