Consider a recuperative cross flow heat exchanger (both fluids unmixed) used in a gas turbine system that carries the exhaust gases at a flow rate of 7.5 kg/s and a temperature of 5008C. The air initially at 308C and flowing at a rate of 15 kg/s is to be heated in the recuperator. The convective heat transfer coefficients on the exhaust gas and air side are 750 W/m2 ·K and 300 W/m2 ·K, respectively. Due to long term use of the gas turbine the recuperative heat exchanger is subject to fouling on both gas and air side that offers a resistance of 0.0004 m2 ·K/W each. Take the properties of exhaust gas to be the same as that of air (cp 5 1069 J/kg·K). If the exit temperature of the exhaust gas is 3208C determine (a) if the air could be heated to a temperature of 1508C (b) the area of heat exchanger (c) if the answer to part (a) is no, then determine what should be the air mass flow rate in order to attain the desired exit temperature of 1508C and (d ) plot variation of the exit air temperature over a temperature range of 758C to 3008C with air mass flow rate assuming all the other conditions remain the same.
Heat Exchangers
Heat exchangers are the types of equipment that are primarily employed to transfer the thermal energy from one fluid to another, provided that one of the fluids should be at a higher thermal energy content than the other fluid.
Heat Exchanger
The heat exchanger is a combination of two words ''Heat'' and ''Exchanger''. It is a mechanical device that is used to exchange heat energy between two fluids.
Consider a recuperative cross flow heat exchanger
(both fluids unmixed) used in a gas turbine system that carries
the exhaust gases at a flow rate of 7.5 kg/s and a temperature of
5008C. The air initially at 308C and flowing at a rate of 15 kg/s
is to be heated in the recuperator. The convective heat transfer
coefficients on the exhaust gas and air side are 750 W/m2
·K
and 300 W/m2
·K, respectively. Due to long term use of the gas
turbine the recuperative heat exchanger is subject to fouling on
both gas and air side that offers a resistance of 0.0004 m2
·K/W
each. Take the properties of exhaust gas to be the same as that
of air (cp 5 1069 J/kg·K). If the exit temperature of the exhaust gas is 3208C determine (a) if the air could be heated to a
temperature of 1508C (b) the area of heat exchanger (c) if the
answer to part (a) is no, then determine what should be the air
mass flow rate in order to attain the desired exit temperature
of 1508C and (d ) plot variation of the exit air temperature over
a temperature range of 758C to 3008C with air mass flow rate
assuming all the other conditions remain the same.
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