Mass of water mw = 0.25Kg/sec
Initial temperature of water TW1 = 30°C
Final temperature of water TW2 = 60°C
Entry Temperature of hot gas = Tg1 = 180°C
Exit Temperature of hot gas = Tg2 = 80°C
Mass flow rate mf =?
Specific heat of gas CPg = 1.08KJ/kg-K
Specific heat of water CW = 4.186KJ/kg-K
Heat gives by the gas = Heat taken by water
ms CPs.dTs = mWCPW.dTW
ms × 1.08 × (180 – 100) = 0.25 × 4.186 × (60 – 30)
Mass flow rate of gases = ms = 0.291 Kg/sec
Change of Entropy of water = dsW = mW.CPW. ln (T2/T1)
= 4.186 × 0.25 × ln [(60 + 273)/ (30 + 273)]
Change of Entropy of water = 0.099 KJ/°K
Change of Entropy of Hot gases = dsg = m g.CPg. ln (T2/T1)
= 0.291 × 1.08 × ln [(80 + 273)/ (180 + 273)]
Change of Entropy of Hot gas = -0.0783 KJ/°K