In a choked nozzle, velocity increases, and which of the following also changes according to the data?

• A. Density decreases
• B. Pressure decreases
• C. Pressure increases
• D. Temperature increases

Answer: (C)

In a choked nozzle the flow at the throat reaches Mach 1, and further acceleration is achieved by converting pressure energy into kinetic energy. As the velocity rises, the static pressure falls because the expanding gas is doing work to speed up rather than to maintain high pressure. In an ideal, adiabatic (isentropic) nozzle, total pressure stays essentially constant (neglecting losses) while static pressure, density, and temperature all decrease as velocity increases. So the change that accompanies the velocity increase is a decrease in pressure (not an increase). If the data you’re looking at shows pressure rising, that would indicate non-ideal effects or a different measurement location beyond the choking point.