Which statement best distinguishes radiative from convective heat transfer in fire modeling?

• A. Radiative heat transfer is energy transfer by radiation from flames; convective heat transfer is heat carried by hot gases.
• B. Radiative heat transfer is heat carried by hot gases; convective heat transfer is energy transfer by radiation.
• C. Radiative heat transfer involves conduction through solids; convective heat transfer involves radiation.
• D. Radiative heat transfer is cooling by evaporation; convective heat transfer is ventilation.

Answer: (B)

Radiative heat transfer is energy transfer by electromagnetic waves emitted by hot objects, such as flames, and it can travel across gaps to heat surfaces without any movement of the gas. Its strength depends on temperature, emissivity of the surfaces, absorptivity, and the geometry between surfaces (view factors). Convection, on the other hand, is energy transfer carried by the bulk motion of a fluid; in a fire this means the hot gases rising and circulating, which transports heat by fluid flow to surfaces and boundaries. So in fire modeling, radiation heats surfaces directly through line-of-sight radiation from flames and hot walls, while convection moves and distributes heat via the movement of the gas. The idea that radiative transfer is heat carried by hot gases mixes up the two mechanisms, since radiation does not require gas motion, whereas convection does.