Questions: Heat Exchanger Basics

Question 1

In a counterflow heat exchanger, the hot and cold fluids flow in:

• A. The same direction
• B. Opposite directions
• C. Perpendicular directions
• D. Random directions

Answer: (B)

Counterflow means the fluids flow in opposite directions. This maintains a temperature difference along the entire length of the exchanger, making it more efficient than parallel flow where the temperatures converge.

Question 2

A car radiator is an example of a heat exchanger.

• T. True
• F. False

Answer: True

A car radiator transfers heat from the hot engine coolant to the ambient air. The coolant flows through thin tubes while air flows over fins attached to the tubes. The two fluids (coolant and air) exchange heat without mixing, which is exactly what a heat exchanger does.

Question 3

Why is a counterflow heat exchanger more effective than a parallel flow one of the same size?

Model answer: In counterflow, the hottest part of the hot fluid meets the warmest part of the cold fluid, and the coolest part of the hot fluid meets the coldest incoming cold fluid. This maintains a temperature difference along the entire length. In parallel flow, both fluids start with a large temperature difference but quickly approach the same temperature, reducing the driving force for heat transfer.

The rate of heat transfer is proportional to the temperature difference. Counterflow maintains this difference uniformly, while parallel flow starts strong but weakens. The result is that a counterflow exchanger of the same size transfers significantly more total heat.