Which heat exchanger flow path maintains a higher average temperature difference between the two fluids when they flow in opposite directions?

Which heat exchanger flow path maintains a higher average temperature difference between the two fluids when they flow in opposite directions?

• A. Counterflow
• B. Parallel Flow
• C. Crossflow
• D. Co-current

Answer: (A)

Counterflow keeps a larger average temperature difference between the fluids because they move in opposite directions. As heat transfers, the hot fluid cools while the cold fluid heats, and the opposite-flow arrangement keeps a sizable temperature gap along most of the length. This preserves a stronger driving force for heat transfer, described by a larger log mean temperature difference, for the entire exchanger. In parallel flow, the two streams tend to approach each other in temperature along the path, so the temperature difference—and thus the driving force—drops more quickly. Crossflow can produce good heat transfer, but it generally doesn’t sustain as large an average temperature difference as counterflow.

Counterflow keeps a larger average temperature difference between the fluids because they move in opposite directions. As heat transfers, the hot fluid cools while the cold fluid heats, and the opposite-flow arrangement keeps a sizable temperature gap along most of the length. This preserves a stronger driving force for heat transfer, described by a larger log mean temperature difference, for the entire exchanger. In parallel flow, the two streams tend to approach each other in temperature along the path, so the temperature difference—and thus the driving force—drops more quickly. Crossflow can produce good heat transfer, but it generally doesn’t sustain as large an average temperature difference as counterflow.