Answer
$\dot{m}=0.4005\ kg/s$
$\dot{Q}=45.1\ kW$
Work Step by Step
From table A-6:
Inlet ($P_1=2\ MPa, T_1=300°C$): $v_1=0.12551\ m³/kg,\ h_1=3024.2\ kJ/kg$
Outlet ($P_2=1.8\ MPa, T_2=250°C$): $h_2=2911.7\ kJ/kg$
The mass flowrate is given by:
$\dot{m}=\frac{A_1\mathcal{V}_1}{v_1}$
Given $A_1=\frac{\pi}{4}D_1^2,\ D_1=0.08\ m,\ \mathcal{V}_1=2.5\ m/s$:
$\dot{m}=0.4005\ kg/s$
From the energy balance:
$\dot{m}h_1=\dot{Q}+\dot{m}h_2$
Hence $\dot{Q}=45.1\ kW$
