Nozzles and Diffusers

A nozzle increases the velocity of a fluid at the expense of pressure.

A diffuser increases the pressure of a fluid by slowing it down.

Properties:

• Adiabatic ($\dot{Q}\approx 0$). The fluid has high velocities, and thus it does not spend enough time in the device for any significant heat transfer to take place.
• No work ($\dot{W}=0$).
• Potential energy is negligible, $\Delta \text{PE}\simeq 0$.
• The change in kinetic energy must be accounted for, $\Delta \text{KE}\not\equiv 0$, as the fluid passing through the nozzle/diffuser experiences large changes in velocity.