Heat transfer by circulation of a fluid in direct contact is known as?

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

Answer: (A)

Convection is heat transfer by the circulation of a fluid. When a fluid moves and stays in direct contact with a surface, it carries thermal energy with it, transferring heat as it flows. This is different from conduction, which happens through stationary matter by molecular interactions without bulk motion, and from radiation, which transmits energy through electromagnetic waves without needing a medium. Evaporation involves a phase change and can influence temperature, but it isn’t the mechanism described by circulating fluid in direct contact. In refrigeration systems, convection happens when a liquid or gas is moved by a pump or buoyancy-driven flow, improving heat transfer by the moving fluid.