Parallel-flow heat exchanger concept check In a parallel-flow (co-current) heat exchanger, both fluids enter from the same end. Considering the temperature driving force along the length, is it correct to say that the instantaneous heat-transfer rate and the rate of temperature fall are maximum at the inlet?

Introduction / Context:
Heat exchangers transfer energy between two streams. In a parallel-flow (co-current) arrangement, both hot and cold fluids enter at the same end and move in the same direction. A frequent conceptual question is where the temperature driving force and cooling/heating rates are largest along the exchanger.

Given Data / Assumptions:

• Two-stream, steady-state, parallel-flow heat exchanger.
• Negligible heat loss to surroundings.
• Conventional definition: local heat-transfer rate q' = U * ΔT_local per unit area, where U is an overall coefficient.

Concept / Approach:
In parallel flow, the temperature difference ΔT between hot and cold streams is largest at the inlet because the hot fluid is at its hottest while the cold fluid is at its coldest. Since local q' is proportional to ΔT_local, the instantaneous rate of heat transfer per area and the rate at which each stream's temperature changes with distance are maximum at the inlet and decrease downstream as the two temperatures approach each other.

Step-by-Step Solution:

Verification / Alternative check:
For the same terminal temperatures, the LMTD for parallel flow is lower than for counter flow; however, this does not contradict the fact that within a parallel exchanger the maximum local ΔT occurs right at the inlet.

Why Other Options Are Wrong:

No: ignores the inlet driving-force peak inherent to co-current entry.Only for gases / equal heat capacity rates / low Reynolds number: the inlet ΔT peak is geometric, not limited to specific fluids or flow regimes.

Common Pitfalls:
Confusing local inlet behavior with overall effectiveness; counter flow is generally more effective overall, yet parallel flow still has its maximum local driving force at the inlet.

Final Answer:

Yes