ENGR217 2018 Q A1 (ENGR5003)

ENGR217 2018 Q A1Past paperOld spec ENGR2172:225 marks30 min

Answer ALL parts (a) and (b)

Property tables including the steam tables are provided in the Appendix

Formulas you may need

Wet steam: $x = m_g/m_{total}$ ; $u, h, s, v = (1-x)f + x\,g$ , i.e. $s = s_f + x s_{fg}$ (on the formula sheet)
First law, closed system: $dU = dQ - dW$ (heat in +ve, work out +ve) (on the formula sheet)
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)
Isentropic process: $s_2 = s_1$ (learn this)
Steam property values at 20 bar and 1 bar (learn this: read from the steam tables provided)

(a)
Draw a property diagram for the phase-change process of water at a constant pressure of 1 atm. Show change in the specific volume with temperature. (4 marks) Give a phase description, and label the processes or states such as ice, melting, subcooled water, saturated water, evaporation, saturated steam and superheated steam. (3 marks) How will increase in pressure to 1 MPa affect the boiling temperature of water, the specific volume of the saturated water and the specific volume of the saturated steam? (2 marks)
[9]Third
(b)
Dry saturated steam at a pressure of 20 bar is expanded isentropically to a final pressure of 1 bar. Determine the dryness fraction at 1 bar.
x_2 =-
[10]
(b(i))
Find the specific work done by the steam if the expansion is (i) in a cylinder (consider as closed system),
w_closed =kJ/kg
[3]
(b(ii))
(ii) through a turbine (consider as open system).
w_open =kJ/kg
[3]