Nozzle: Reduction in pressure and increase in velocity of fluid
Diffuser: Reduction in velocity and Increase in pressure of fluid
A nozzle accelerates the flow of a gas or fluid with a resulting decrease in the pressure while a diffuser does pretty much the opposite; it slows down the flow of the gas or fluid and has a resulting increase in the pressure. The mass flow, for a system that has both nozzle and diffuser, remains the same but there is a decrease (nozzle) or increase (diffuser) in the cross sectional area of the boundary of the system.
In Incomprehensible Flow.
In Nozzle Static Pressure is decrease and Velocity is increased.
In Diffuser Static Pressure is increased and velocity is decreased.
Nozzle in compressible supersonic Nozzle
Nozzle has generally three sections.
1. Convergent..2. Divergent. 3. Throat.
In subsonic flow Mach No<1 : Static Pressure is decreased velocity increase
In throat Mach No=1 Flow is Sonic.
In divergent section Velocity is further increased to supersonic Mach No>1 unlike in incomprehensible flow.
Nozzle speed up or increase the flow of substance (gas or liquid); while diffuser reduces the flow of material.