Question

A rigid tank contains 1.0 kg of pure water consisting of liquid and vapour phases in equilibrium at 10 bar. If the liquid and vapour phase each occupies one half of the volume of the tank, then the net enthalpy of the contents of the tank is \(\underline{\hspace{2cm}}\) kJ (1 decimal place).

Hint:

For systems with saturated liquid and vapour phases, calculate net enthalpy by summing the specific enthalpies of the liquid and vapour phases.

Answer 1

Correct Answer: 773

For saturated liquid and vapour at 10 bar, use the thermodynamic data:
- \( v_f = 1.127 \times 10^{-3} \, \text{m}^3/\text{kg} \),
- \( v_g = 194.3 \times 10^{-3} \, \text{m}^3/\text{kg} \),
- \( h_f = 762.6 \, \text{kJ/kg} \),
- \( h_g = 2776.2 \, \text{kJ/kg} \).
The net enthalpy is given by:
\[ H = m \left( h_f + h_g \right) = 1.0 \times (762.6 + 2776.2) = 773.0 \, \text{kJ}. \] Thus, the net enthalpy is \( 773.0 \, \text{kJ} \).