During the isothermal heat addition process of a Carnot cycle, 900 kJ of heat is added to the working fluid from a source at 400oC. What is the entropy change of the working fluid? What is the entropy change of the source? What is the total entropy change for the process? [

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Answer:

the entropy change of the fluid during the process process is is 1.337 kJ/K, the change for the source is -1.337 kJ/K and the total entropy change is 0

Explanation:

since the Carnot cycle is a reversible cycle, the entropy change is related with the heat exchanged through:

ΔS =∫dQ/T

since the temperature remains constant

ΔS =∫dQ/T=(1/T)*∫dQ = Q/T

Q= heat added to the system

T= absolute temperature = 400°C= 673 K

therefore

ΔS = Q/T = 900 kJ/ 673 K = 1.337 kJ/K

ΔS working fluid = 1.337 kJ/K

since the process is reversible, the entropy change of the universe (total entropy change)  is 0 (there is no entropy generation). thus

ΔS universe = ΔS working fluid + ΔS source = 0

ΔS source= -ΔS working fluid = -1.337 kJ/K

The entropy change of the fluid is -1.337kJ/K, the entropy change of the source is -1.337kJ/K and the entropy change of the system is 0J/K

Data;

  • Q = 900kJ
  • T = 400°C

Entropy of a System

This is a rate of disorderliness of a system.

The entropy of the fluid is calculated as

[tex]\delta S_f = \frac{Q}{T}\\ \delta S_f = \frac{900}{673} \\\delta S_f = 1.337 kJ/K[/tex]

The entropy change of the fluid is -1.337kJ/K

b)

The entropy change of the source

This is calculated as

[tex]\delta S_s = -\frac{Q}{T} \\\delta S_s = -\frac{900}{673} = -1.337kJ/K[/tex]

The entropy change of the source is -1.337kJ/K

c)

Total entropy change of the process is the sum of the entropy change of the fluid and entropy change of the source

[tex]\delta S = \delta S_f + \delta S_s\\\delta S = -1.337 + 1.337 = 0[/tex]

The entropy change of the system is 0J/K

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