Hot exhaust gases of an internal combustion engine are to be used to produce saturated water vapor at 2 MPa pressure. The exhaust gases enter the heat exchanger at 400oC at a rate of 32 kg/min while water enters at 15oC. The heat exchanger is not well insulated, and it is estimated that 10% of heat given by the exhaust gases is lost to the surroundings. The mass flow rate of the exhaust gases is 15 times that of the water and constant specific heat properties of the exhaust gases can be approximated using the properties of air at 600K. Determine the temperature of the exhaust gases leaving the heat exchanger and the rate of heat transfer to the water.

Respuesta :

Answer:

The flowrate of water is 0.03556kg/s

Explanation:

Exhaust gases inlet temperature T1=4000C

Water inlet temperature T3=150C Exit Pressure of water as saturated vapor P4=2MPa

Mass flow rate of exhaust gases Heat lost to the surroundings Qgases=32kg/min

Mass flow rate of exhaust gases is 15 times that of the water

Heat exchangers typically involve no work interactions (w = 0) and negligible...

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Answer:

a) 5,000K

b) 1740J/s/K

Explanation:

Flow rate of gas,Qg = 32Kg/min; Temperature of gas entering the heat exchanger, Tg1 = 400°C = (273 + 400)K = 673K; acceleration due to gravity = 9.8m/s²

The fiow rate of gas is 15 times that of water, Qw = 32Kg/min/15 = 2.13Kg/min; Temperature of water, Tw = 15°C = (273 + 15)K = 288K

a) Qg/Qw = Tg/Tw, where Tg = Tg2 - Tg1 ( Tg2 = Temperature of gas leaving the heat exchanger

32/2.13 = Tg2 - 673/288

2.13(Tg2 - 673) = 32 X 288

2.13Tg2 - 1435.73 = 9216

∴ Tg2 = 10651.73/2.13 = 5,000K

b) Heat transfer by the water = 2.13Kg/min X 5,000K X 9.8m/s² = 10,651.73 X 9.8m/s² = 104386/60 = 1,740J/s/K