ENGR217 2018 Q A2 (ENGR5003)

ENGR217 2018 Q A2Past paperOld spec ENGR2172:225 marks30 min

Answer ALL parts (a) - (c).

Formulas you may need

Ideal gas: $pv = R_gT$ , so $\rho = \dfrac{p}{R_gT}$ (on the formula sheet)
Continuity: $\dot m = \rho A C$ (learn this)
SFEE: $\dot Q - \dot W = \dot m\left[\left(h + \tfrac{C^2}{2} + gZ\right)_{out} - \left(h + \tfrac{C^2}{2} + gZ\right)_{in}\right]$ (on the formula sheet)
Ideal gas enthalpy change: $dh = c_p\,dT$ (on the formula sheet)
Brayton cycle: $\eta = 1 - r_p^{-(\gamma-1)/\gamma}$ , work ratio $r_w = 1 - \dfrac{T_1}{T_3} r_p^{(\gamma-1)/\gamma}$ (on the formula sheet)

(a(i))
Air enters a nozzle at a pressure of 5 bar, $200^\circ\mathrm{C}$ and a velocity of $30\ \mathrm{m\,s^{-1}}$ , it exits at 1 bar and $180\ \mathrm{m\,s^{-1}}$ . The nozzle inlet area is $100\ \mathrm{cm^2}$ . The gas constant is $R = 0.287\ \mathrm{kJ\,kg^{-1}\,K^{-1}}$ , and the specific heat is $c_p = 1.005\ \mathrm{kJ\,kg^{-1}\,K^{-1}}$ . Determine for steady adiabatic flow: (i) the mass flow rate of air;
mdot =kg/s
[4]
(a(ii))
(ii) the air exit temperature;
T_2 =K
[4]
(a(iii))
(iii) the nozzle exit area.
A_2 =cm^2
[4]
(b)
A gas turbines operating on the ideal Brayton cycle, draw and label: (i) pressure against volume (P-V) diagram, (2 marks) (ii) temperature against entropy (T-s) diagram. (2 marks) Show on the T-s diagram and explain in terms of the work input and output, how the actual gas-turbine cycle differs from the ideal Brayton cycle. (4 marks)
[8]Third
(c)
List three main components of a gas turbine system operating in an ideal cycle. (3 marks) How can the cycle efficiency and the work output be improved with addition of new components to the system? (2 marks)
[5]Third