Question

Calculate the internal energy of 0.3 m3 of steam at 4 bar and 0.95 dryness. If this steam is superheated at constant pressure through 30°C, determine the heat added and change in internal energy

Answer 1

$u = 0.3\textsf{ m³}\\ p = 4\textsf{ bar}\\ x = 0.95\\ T = 30 \textsf{°C} = 30 +273 = 303\textsf{ K}$

according to the pressure steam table corresponding to 4 bar

h_f = 604.65 kJ/kg, u_f = 604.22 kJ/kg, u_g = 2553.1 kJ/kg.

Specific internal energy of wet steam,

$\begin{aligned} u &= (1 – x)u_f+ xu_g\\ &= (1 – 0.95) × 604.22+ 0.95 × 2553.1\\ &=2455.656\textsf{ kJ/kg} \end{aligned}\\$