Fluid Throttles

Throttles induce a sudden drop in pressure by passing fluid through an obstruction.

These are typically:

• Adiabatic ($\dot{Q}\approx 0$). There is neither sufficient time nor large enough area for any effective heat transfer to take place.
• No work ($\dot{W}=0$).
• Potential $\Delta \text{PE}=0$.
• $\Delta \text{KE}=0$. Exit velocity is often considerable higher than the inlet velocity, but the increase in kinetic energy is insignificant
• $h_1\approx h_2$ (Isenthalpic). This is necessary as if we look at the steady-flow process balance equation and see that all of the above terms are all zero.

These are often used for flow control (regulator/valve) or to induce a phase change.