The transfer of heat or mass by large-scale fluid movements. When the process occurs, due to density and temperature differences, it is termed natural convection. When the process occurs due to external devices (such as fans), it is termed forced convection.

The transfer of heat by molecular collision. This process is more efficient in metals and other thermal conductors and poorer in fluids and insulators such as refractory.

A dimensionless number used in the study of forced convection which gives a measure of the ratio of the total heat transfer to conductive heat transfer, and is equal to the heat-transfer coefficient times a characteristic length divided by the thermal conductivity. Symbolized NNu.

The part of a furnace between the radiant section and the stack. The area is filled with tubes or pipes which carry process steam and which absorb heat via convection heat transfer from the hot gases passing through the area on their way out of the stack. The convection section forms an obstacle to the combustion gas flow and can greatly affect furnace draft in the radiant section of the furnace.

All warm bodies emit light (electromagnetic radiation, mostly infrared). When this radiation is absorbed or emitted by a body, heat is transferred and termed 'heat transfer by radiation'. Such heat transfer requires a line of sight (view factor) and is proportional to the fourth power of the absolute temperature difference between bodies and the emissivity of the bodies.

For a fluid confined in a vessel, the rate of flow of heat out of the fluid, per unit area of vessel wall divided by the difference between the temperature in the interior of the fluid and the temperature at the surface of the wall. Also known as convection coefficient.