In an adiabatic flow with friction through a constant area duct, the following phenomenons are predicted:
1. The flow downstream tends to be sonic irrespective of the Mach-number upstream.
2. In the case of initially supersonic flow, any increase in duct length beyond chocked flow would make the exit flow subsonic
3. In the case of initially subsonic flow, increase in duct length will not change sonic flow at the exit.
4. The optimum pipe length for sonic outlet in supersonic flow is considerably longer than that of subsonic flow for the same flow rate.
Which of these are correct?
(A) 1, 2 3 and 4 (B) 1, 2 and 3 only
(C) 1, 3 and 4 only (D) 2, 3 and 4 only