An automobile radiator, where coolant is pumped through tubes, is an example of which convection type?

• A. Natural Convection
• B. Forced Convection
• C. Radiant Heat Transfer
• D. Mixed Convection

Answer: (B)

Convection type is defined by what drives the fluid motion. In this radiator, the coolant is actively moved through the tubes by a pump, so its flow is produced by an external mechanical force. That makes the coolant-side heat transfer a case of forced convection. The air flowing across the fins can be natural or forced depending on whether a fan or high speed is moving it, but the key point is that the coolant itself is propelled by a pump, not by buoyancy. Radiative heat transfer is a separate mechanism, and mixed convection would require both strong buoyancy and forcing to drive the flow in the same region. Thus, forced convection is the best description for the coolant movement in the radiator.