Which heat transfer mode occurs when thermal energy is transported away from a system boundary by a moving medium?

Which heat transfer mode occurs when thermal energy is transported away from a system boundary by a moving medium?

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

Answer: (B)

Convection is the heat transfer mode at play when thermal energy is carried away from a system boundary by a moving fluid. When the medium moves, it can pick up heat at the boundary and transport it into the bulk of the fluid, and similarly remove energy from the surface as the fluid that is hotter or cooler flows past. The rate of this transfer depends on how fast the fluid moves and the temperature difference between the surface and the fluid, with forced convection occurring when an external agent (like a fan or pump) drives the flow, and natural convection arising from buoyancy due to density differences. This differs from conduction, which relies on molecular interactions and requires no bulk motion of the medium; radiation, which transfers energy via electromagnetic waves and does not depend on a medium to carry the heat, and evaporation, which involves a phase change at the surface and latent heat rather than bulk transport by moving fluid.

Convection is the heat transfer mode at play when thermal energy is carried away from a system boundary by a moving fluid. When the medium moves, it can pick up heat at the boundary and transport it into the bulk of the fluid, and similarly remove energy from the surface as the fluid that is hotter or cooler flows past. The rate of this transfer depends on how fast the fluid moves and the temperature difference between the surface and the fluid, with forced convection occurring when an external agent (like a fan or pump) drives the flow, and natural convection arising from buoyancy due to density differences.

This differs from conduction, which relies on molecular interactions and requires no bulk motion of the medium; radiation, which transfers energy via electromagnetic waves and does not depend on a medium to carry the heat, and evaporation, which involves a phase change at the surface and latent heat rather than bulk transport by moving fluid.