What type of heat exchangers have no physical contact between the two fluids and are separated by a metallic tube wall boundary?

• A. Indirect Contact
• B. Direct Contact
• C. Crossflow
• D. Parallel Flow

Answer: (A)

Indirect contact heat exchangers keep the two fluids completely separate with a solid wall between them, usually a metal tube. Heat is transferred by conduction through that wall and convection on each side, so there is no mixing of the fluids. This is the defining feature here. Direct contact would involve the fluids touching and possibly exchanging components, which is not the case. Crossflow and parallel flow describe how the streams move relative to each other, not whether there’s a separating barrier. So the best answer is the indirect contact type.