Answer
$\dot{Q}=455\ kW$
Work Step by Step
From tables A-4 to A-6:
Inlet ($P_1=6\ MPa, T_1=600°C$): $h_1=3658.8\ kJ/kg$
Outlet ($P_2=0.5\ MPa, T_2=200°C$): $h_2=2855.8\ kJ/kg$
From the energy balance:
$\dot{m}(h_1+\mathcal{V}_1^2/2)=\dot{m}(h_2+\mathcal{V}_2^2/2)+\dot{Q}+\dot{W}_s$
Given $\dot{m}=26\ kg/s,\ \dot{W}_s=20\ MW,\ \mathcal{V}_1\approx0,\ \mathcal{V}_2=180\ m/s$:
solving for the heat loss rate:
$\dot{Q}=455\ kW$
