n. The process of transferring energy through two mechanisms: random molecular motion, (in other words, conduction) and the bulk motion of the fluid (in other words, a moving gas or liquid).
Convection is defined at the boundary of either two fluids or a fluid/solid interface. The rate of energy transfer by convection is weakly dependent on the thermal conductivity of the material; however, it is much more dependent on the velocity, turbulence, and density of the fluid. In the context of wildland fire, thermal convection is one of the dominant energy transfer mechanisms for transferring energy from high temperature flames and gases to lower temperature fuel, vegetation, or soil components in and around the fire.
Convection is often defined within two regimes: forced and free. Forced convection refers to energy transfer due to a fluid moving as a result of some force (fans, wind, pumps, and so on). Free convection is that which is driven by buoyancy forces (in other words, density differences most often caused by differences in temperature).