Which mechanism describes heat transfer via circulating air or fluids around the body?

• A. Conduction
• B. Convection
• C. Radiation
• D. Evaporation

Answer: (B)

Convection is the mechanism of heat transfer that occurs when circulating air or a liquid carries heat to or away from the body. When air moves across the skin, or when bodily fluids like blood circulate, heat is transported by the moving medium. This can be natural convection, where warmer air rises and cooler air replaces it, or forced convection, such as from a fan moving air. This differs from conduction, which needs direct contact for heat to pass through a solid or still liquid; radiation, which transfers heat through electromagnetic waves without needing a medium; and evaporation, which cools mainly through the phase change of sweat. Convection explains how heat is gained or lost when air around the body is in motion or when circulating fluids carry heat to the surface.