ENGR217 2019 Q A1 (ENGR5003)

ENGR217 2019 Q A1Past paperOld spec ENGR2172:225 marks30 min

Answer ALL parts (a) and (c)

Formulas you may need

Wet steam: $x = m_g/m_{total}$ ; $u, v = (1-x)f + x\,g$ (on the formula sheet)
First law, closed system: $dU = dQ - dW$ (heat in +ve, work out +ve); rigid tank $dW = 0$ so $Q = \Delta U$ (on the formula sheet)
Boundary work at constant pressure: $W = \int p\,dV = p\,(V_2 - V_1)$ (on the formula sheet as $dW = p\,dV$ , sign as printed)
Linear interpolation in the steam tables (learn this)
Steam property values (saturated temperature and pressure tables, superheated table) (learn this: read from the tables provided)

(a)
On a graph of temperature against volume sketch lines of constant pressure for water. Draw and label the saturated liquid line and the saturated vapour line. Draw and label constant temperature lines through the critical point and the triple point. Label a region where water and vapour co-exist and a region ice and vapour can co-exist.
[7]Third
(b(i))
A rigid tank of volume $3\ \mathrm{m^3}$ contains 4 kg of wet steam at $85^\circ\mathrm{C}$ . (i) Determine the dryness fraction
x_1 =-
[4]
(b(ii))
(ii) If the water is heated slowly until it is completely vaporised (i.e. becomes dry steam), using steam tables determine the temperature and pressure at this instant.
T_2 =C
p_2 =kPa
[4]
(b(iii))
(iii) Using steam tables determine how much heat was required for the heating process?
Q =kJ
[4]
(c)
A mass of 2 kg of saturated water vapour at 400 kPa is heated at constant pressure until the temperature reaches $350^\circ\mathrm{C}$ . Calculate the work done by the steam during this process.
W =kJ
[6]