An oscillating fan blows currents of cool air across the surface of a warm body. Which heat transfer mechanism is responsible?

An oscillating fan blows currents of cool air across the surface of a warm body. Which heat transfer mechanism is responsible?

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

Answer: (B)

Heat transfer via convection happens when a moving fluid carries heat from one place to another. Here, the fan creates a steady flow of air across the warm surface. The surface warms the adjacent air, and the moving air carries that heat away, continually bringing in cooler air to replace it. This forced airflow increases the rate of heat transfer compared with still air. Conduction would require direct contact without bulk fluid motion, which is slow in air. Radiation transfers energy as infrared waves and doesn’t rely on air movement. Evaporation involves a phase change, not simply cooling by air flow.

Heat transfer via convection happens when a moving fluid carries heat from one place to another. Here, the fan creates a steady flow of air across the warm surface. The surface warms the adjacent air, and the moving air carries that heat away, continually bringing in cooler air to replace it. This forced airflow increases the rate of heat transfer compared with still air.

Conduction would require direct contact without bulk fluid motion, which is slow in air. Radiation transfers energy as infrared waves and doesn’t rely on air movement. Evaporation involves a phase change, not simply cooling by air flow.