
The exergy destruction associated with each process of the Brayton cycle and the exergy of the exhaust gases at the exit of the regenerator.

Answer to Problem 146P
The exergy destruction associated with process 1-2 of the given Brayton cycle is
The exergy destruction associated with process 3-4 of the given Brayton cycle is
The exergy destruction associated with regeneration process of the given Brayton cycle is
The exergy destruction associated with process 5-3 of the given Brayton cycle is
The exergy destruction associated with process 6-1 of the given Brayton cycle is
The exergy of the exhaust gases at the exit of the regenerator is
Explanation of Solution
Show the regenerative Brayton cycle with air as the working fluid, on
For the given regenerative Brayton cycle with air as the working fluid, let
Write the expression of pressure ratio for the regenerative Brayton cycle
Write the pressure ratio and pressure relation for the process 3-4.
Write the expression of efficiency of the turbine
Write the expression of heat added due to regeneration
Here, the effectiveness of the regenerator is
Write the expression of net work output of the regenerative Brayton cycle
Here, the work output by the turbine is
Write the expression of heat input to the regenerative Brayton cycle
Write the expression of heat rejected by the regenerative Brayton cycle
Write the expression of specific enthalpy at state 6
Write the specific enthalpy relation for the regenerator.
Write the expression of exergy destruction associated with the process 1-2 of the given Brayton cycle
Here, the temperature of the surroundings is
Write the expression of exergy destruction associated with the process 3-4 of the given Brayton cycle
Here, entropy of air at state 3 as a function of temperature is
Write the expression of exergy destruction associated with the regeneration process of the given Brayton cycle
Here, entropy of air at state 5 as a function of temperature alone is
Write the expression of exergy destruction associated with the process 5-3 of the given Brayton cycle
Here, the temperature of the heat source is
Write the expression of exergy destruction associated with the process 6-1 of the given Brayton cycle
Here, the temperature of the sink is
Write the expression of stream exergy at the exit of the regenerator (state 6)
Here, the specific enthalpy of the surroundings is
Write the expression of change entropy for the exit of the regenerator
Here, entropy of air at the surroundings as a function of temperature alone is
Conclusion:
Refer Table A-17, “Ideal gas properties of air”, obtain the properties of air at 310 K
Substitute 900 kPa for
Substitute
Refer Table A-17, “Ideal gas properties of air”, obtain the properties of air at 50.06
Rearrange Equation (III) and substitute
Substitute 0.80 for
Substitute
Substitute
Substitute
Substitute 310.24
Rearrange Equation (IX), and substitute 659.84
Refer Table A-17, “Ideal gas properties of air”, obtain the properties of air at 310 K
Substitute 300 K for
Thus, the exergy destruction associated with process 1-2 of the given Brayton cycle is
Substitute 300 K for
Thus, the exergy destruction associated with process 3-4 of the given Brayton cycle is
Substitute 300 K for
Thus, the exergy destruction associated with regeneration process of the given Brayton cycle is
Substitute 300 K for
Thus, the exergy destruction associated with process 5-3 of the given Brayton cycle is
Substitute 300 K for
Thus, the exergy destruction associated with process 6-1 of the given Brayton cycle is
Refer Table A-17, “Ideal gas properties of air”, obtain the properties of air at 300 K
Substitute
Substitute
Thus, the exergy of the exhaust gases at the exit of the regenerator is
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Chapter 9 Solutions
Thermodynamics: An Engineering Approach
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