Project ForgeIn a parallel flow heat exchanger operating under steady state, hot liquid enters at Th,in and leaves at Th,out. Cold liquid enters at Tc,in and leaves at Tc,out. Neglect any heat loss to the surroundings. If Th,in≫Tc,in, then for a given time interval, which ONE of the following statements is true?
- Entropy gained by the cold stream is GREATER than entropy lost by the hot stream
- BEntropy gained by the cold stream is EQUAL to the entropy lost by the hot stream
- CEntropy gained by the cold stream is LESS than the entropy lost by the hot stream
- DEntropy gained by the cold stream is ZERO
Explanation
ΔS=Q/T for each stream. Since the hot stream is at a much higher temperature than the cold stream throughout, dividing the same heat transfer Q by a smaller T (cold stream) gives a larger entropy change than dividing by a larger T (hot stream) — entropy gained by the cold stream exceeds entropy lost by the hot stream, consistent with entropy generation being positive in this irreversible heat transfer.
Source: GATE CH 2012 (2012)
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