Answer
$\dot{Q}=Q/\Delta t=1.163\ kW$
Work Step by Step
From tables A-4 to A-6:
Initial ($P_1=175\ kPa, x_1=?$): $v_{1,L}=0.001057\ m³/kg,\ v_{1,G}=v_2,\ u_{1,L}=486.82\ kJ/kg,\ u_{1,G}=u_2$
Final ($P_2=175\ kPa, x_2=1$): $v_2=1.0036\ m³/kg,\ u_2=2524.5\ kJ/kg$
Exiting ($P_2=175\ kPa, x_2=1$): $h_e=2700.2\ kJ/kg$
Initial state (half of the 4L volume of liquid):
$m=V_L/v_L+V_G/v_G$
$mu=u_LV_L/v_L+u_GV_G/v_G$
Hence $m_1=1.895\ kg,\ m_1u_1=926.6\ kJ$
Final state $m_2=V/v_2=0.004\ kg$
From the material balance:
$m_e=m_1-m_2=1.891\ kg$
From the energy balance:
$Q_i-m_eh_e=m_2u_2-m_1u_1$
$Q_i=4188\ kJ$
For a time span of 1h:
$\dot{Q}=Q/\Delta t=1.163\ kW$
