For given hot and cold fluid inlet and outlet temperatures, the Logarithmic Mean Temperature Difference of a counter-flow heat exchanger compared to a parallel-flow heat exchanger is:
Options:
(A) Always greater than or equal to that of parallel flow ($LMTD_{counter} \ge LMTD_{parallel}$)
(B) Always smaller than that of parallel flow
(C) Identical under all circumstances
(D) Zero
Answer Key:
A
Step-by-Step Solution & Explanation
Counter-flow arrangement maintains a more uniform temperature difference throughout the length of the exchanger, resulting in a higher $LMTD$ than parallel flow for the same terminal temperatures, thereby requiring less heat transfer area.