What does radiation refer to in heat transfer?

Radiation in heat transfer specifically refers to the process by which heat is transferred through electromagnetic waves. Unlike conduction, which requires direct contact between materials, and convection, which involves fluid movement, radiation allows heat energy to travel through a vacuum or air without the need for a medium. This method of heat transfer occurs through infrared radiation emitted by a heat source and can affect objects at a distance. For example, the warmth felt from the sun is a result of radiant heat transfer. It is important in fire behavior as it can cause ignition or increase temperatures even when materials are not in direct contact with a flame or fire. Understanding radiation helps in assessing how heat spreads and affects various materials and environments during a fire event.