What is parallel flow in a heat exchanger?

• A. Concurrent; tube side and shell side flow in the same direction
• B. Counter flow
• C. Cross flow
• D. Mixed flow

Answer: (A)

Parallel (or concurrent) flow is when the hot and cold fluids enter the heat exchanger from the same end and flow in the same direction through the unit. In this setup, the temperature difference driving heat transfer is largest at the inlets and steadily decreases along the length as the fluids move together toward similar temperatures. This makes parallel flow straightforward to design and adequate for moderate duty, though it’s typically less effective for large temperature differences than other patterns.

In contrast, counterflow has the streams moving in opposite directions, maximizing the temperature driving force along the entire length; cross flow involves perpendicular flow directions; mixed flow combines characteristics of different patterns.