Liquid water at 293 K and 1.8 kg/s is mixed with steam at 573K in a heating chamber. The water leaves the chamber at 300 kPa and 333K. Determine the mass flow rate of the steam. Where it exists in such a state, you may assume compressed liquid to have the same properties as saturated liquid at that temperature.
Properties of liquid water entering,
T1=293K=20oC , m1=1.8kg/s , P1=300kPa
Properties of steam,
T2=573K=300oC , m2= ? ,P2=300kPa
Properties of water leaving the chamber,
T3=333K=60oC , m3= ? , P3 = 300kPa
Tsat@300kPa=133.5oC(From steam tables)
Enthalpies,
h1=hf@20oC=83.9kJ/kg
h2=2995.1kJ/kg
h3=hf@60oC=251.1kJ/kg
Take the heating chamber as the system,
Mass balance,
min-mout=msystem=0 i.e. m1+m2=m3
Energy balance,
Ein-Eout=Esystem=0
Ein=Eout
m1h1+m2h2=m3h3
Mass flow rate of steam,
m2=m1(h1-h3)/(h3-h2)=(1.8)(83.9-251.1)/(251.1-2995.1)=0.1096kg/s
m3=m1+m2=1.8+0.1096=1.9096kg/s
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