Steam enters the condenser (heat exchaner) of a steam power plant at 20kPa and a
ID: 2998279 • Letter: S
Question
Steam enters the condenser (heat exchaner) of a steam power plant at 20kPa and a quality of 95% with a mass flow rate of 20,000kg/h. A nearby river is used as a source of cooling water where the water will circulate through the tubes within the condenser. To prevent thermal pollution of the river, the cooling water is not to have more than a 10 degree C increase in temperature. If the steam is to leave the condenser as a saturated liquid at 20kPa, what is the mass flow rate of the cooling water required?
Explanation / Answer
Enthalpy of steam at 20 kPa, Hg=2608.9 kJ/kg
Enthalpy of water at 20 kPa, Hf=251.4 kJ/kg
Quality of steam, x=95%=0.95
Enthalpy of steam entering, H=Hf +x(Hf - Hg)
=251.4+0.95(2608.9-251.4)
=2491.025 kJ/kg
Energy to be removed= Enthalpy*Mass flow rate of steam
=2491.025*20000
=4.982*106 kJ/h
Let m be mass flow rate of cooling water required.
mCdT=Energy to be removed
m*4.18*10=4.982*106
m=1.1919*106 kg/h