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Q3. (a) Explain the term choked flow with reference to a convergent nozzle. (4)

(b) Air leaks into an evacuated vessel from the surroundings which are at a pressure of 1.00 bar. The passage through which the air leaks may be considered as a convergent nozzle with exit area 0.8 mm², and the flow within the passage may be assumed isentropic. The temperature of the surroundings is 25°C. Determine the mass flow rate when the pressure in the vessel is:

(i) 0.5 bar; (6)

(ii) 0.8 bar. (6)

Note: For air, g = 1.4 and R = 0.287 kJ/kg K

p_c = p_o × [2/(γ + 1)]^γ/γ-1; a = √γRT