Question

What happens to the mass flow rate if the reservoir pressure is doubled?

(a) Doubled

(b) Remains same

(c) Becomes half

(d) Becomes one – fourth

I got this question in a national level competition.

This intriguing question comes from Nozzles in section Quasi-One-Dimensional Flow of Aerodynamics

Answer 1

Right choice is (a) Doubled

The explanation: The mass flow rate depends on the inlet stagnation pressure, temperature and throat area by the relation:

\(\dot {m} ∝ \frac {p_0 A^*}{\sqrt {T_0}} \)

Thus, when the resrvoic pressure is doubled, the mass flow rate through the nozzle also doubles as it is directly proportional to it.