| Consider two heat transfer processes A and B occurring as shown below. |
 |
| In both cases, 2000 kJ of heat is taken from source and transferred to sink. Source temperature is 800 K and sink temperatures in A and B are 500 K and 750 K, respectively. Which of the processes is easily reversed? |
A) Both A and B
B) A
C) B
D) None of A and B
Correct Answer: C
Solution :
| In process A, |
| \[\Delta {{S}_{\text{source}}}=\frac{Q}{T}=\frac{-\,2000}{800}=-2.5\frac{kJ}{K}\] |
| \[\Delta {{S}_{\text{sink}}}=\frac{Q}{T}=\frac{2000}{500}=4\frac{kJ}{K}\] |
| \[\Delta {{S}_{\text{Total}}}=\Delta {{S}_{\text{source}}}+\Delta {{S}_{\text{sink}}}=1.5\,kJ/K\] |
| In process B, |
| \[\Delta {{S}_{\text{source}}}=\frac{-\,2000}{800}=-\,2.5\frac{kJ}{K}\] |
| \[\Delta {{S}_{\text{sink}}}=\frac{2000}{750}=27\frac{kJ}{K}\] |
| \[\Delta {{S}_{\text{Total}}}=-2.5+2.7=0.2\frac{kJ}{K}\] |
| As, \[\Delta {{S}_{\text{Total}}}\]is less for process B. So, it has less irreversibility or B can be more easily reversed. |
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