Answer to Question #150026 in Molecular Physics | Thermodynamics for Muhammad shehzad

Question

0.05 kg of steam at 10 bar dryness fraction 0.84 is heated reversibly in a rigid vessel until the pressure is 20 bar calculate the change of entropy and heat supplied show the area which represents the heat supplied on a T-s diagram

Answer 1

$m_s = 0.05kg$

At 10 bar,

$\begin{aligned} s_1 &= s_{f1} + x_1s_{fg1}\\ &= 2.138 + 0.84(4.448)\\ &= 5.874 kJ/J.kg \end{aligned}$

At 10 bar, $v_{g1}$ = 0.1944m³/kg

$v_1 = x_1(v_{g1})$

$v_1 = 0.84×0.1944$ = 0.163m³/kg

$\dfrac{V_1}{V_2} = (\dfrac{P_1}{P_2})^{\frac{1}{1.1}}$

$V_2 =$ 0.163(10/20)¹.¹ = 0.163 × 0.533 = 0.087m³/kg

$x_2 = v_2/v_{g2}$ = 0.082/3.992 = 0.021

$s_2 = s_{f2} + x_2s_{fg2}$

= 1.026 + 0.021(6.646) = 1.166 kJ/kg.K

Change of entropy = $s_2 - s_1$ = 1.166 - 5.874 = -4.708 kJ/kg.K