Subtopic: Counterflow vs parallel flow thermal comparison
Question Statement:
For identical fluid mass flow rates, inlet temperatures, and overall heat transfer coefficient, a counterflow heat exchanger compared to a parallel flow heat exchanger:
Options:
(A) Has a higher Log Mean Temperature Difference (LMTD) and requires smaller heat transfer surface area
(B) Has a lower LMTD and lower effectiveness
(C) Cannot achieve outlet cold temperature higher than outlet hot temperature
(D) Has zero thermal effectiveness
Answer Key:
A
Step-by-Step Solution & Explanation
Counterflow heat exchangers provide higher temperature driving force along the entire length, resulting in a strictly higher LMTD ($LMTD_{counter} > LMTD_{parallel}$) and smaller required surface area for identical thermal duties.