Answer to Question #210897 in Mechanical Engineering for christian

Question

A reheat cycle with two stages of reheating is executed with steam expanding initially from 20 MPa and . The two reheater pressures are 3.8 MPa and 0.97 MPa, and the steam leaves each reheater at . Condensation occurs at . Compute for  for a 1kg/s of steam.

Answer 1

$P_1=20MPa ; T_1=540^OC \implies h_1=3365.26kJ/kg$

$P_2=3.8MPa ; T_3=540^OC \implies h_2=2801.35kJ/kg ; h_3=3538.30kJ/kg$

$P_4=P_5=0.97MPa ; T_1=540^OC \implies h_4=2779.70kJ/kg; h_5=3565.48 kJ/kg$

$T_6=60^0C \implies h_6=2608.85 kJ/kg$

Heat added $=\dot{m}((h_3-h_2)+(h_5-h_4))$

Heat added $=1((3538.3-2801.35)+(3565.48-2779.70))=1522.7 kJ/s$

Work $=\dot{m}((h_1-h_2)+(h_3-h_4)+(h_5-h_6))$

Work =$1((3365.26-2801.35)+(3538.3-2779.70)+(3565.48-2608.85))=2279.1 kJ/s$

Heat rejected = Work - Heat added

Heat rejected = $2279.1-1522.7=756 kJ/s$