Carnot's shock loss

If the pipe diameter or flow cross-section suddenly widens from A₁ to A₂, the fluid does not enter the wider area as a constant jet with the velocity v₁ but mixes with the surrounding fluid, accompanied by marked turbulence and vortex formation. At the end of a transition zone the fluid once again forms a uniform flow at a lower velocity v₂. See Fig. 1 Carnot's shock loss

The pressure loss (Δp) due to mixing is called Carnot's shock loss and can be derived from the principle of conservation of momentum:

ρ    Density of the fluid handled

See Fig. 1 Fluid mechanics