ANS:B - flows outside the tubes.

In an extended surface heat exchanger, the fluid with the lower coefficient of heat transfer typically: b) flows outside the tubes. Extended surface heat exchangers, commonly known as finned tube heat exchangers, have additional surface area provided by fins attached to the tubes. These fins increase the heat transfer area and thus enhance heat transfer efficiency. In such heat exchangers, the fluid with the lower coefficient of heat transfer is often directed to flow outside the tubes where the extended surface (fins) is located. This arrangement maximizes the heat transfer effectiveness by ensuring that the fluid with the lower coefficient is exposed to the extended surface area for more efficient heat exchange.