Thermal radiation

Thermal radiation

Thermal radiation refers to heat transfer through the absorption and emission of electromagnetic waves, without utilizing a carrier medium. The magnitude of radiative heat transfer has a very strong dependency on the emissivity and temperature of the surface material. Generally, non-metallic and non-transparent materials exhibit a high emissivity which typically exceeds 0.80. The emissivity of metals can vary between 0.02 (e.g. aluminum foil) and 0.90 (e.g. anodized aluminum) depending on the geometrical arrangement and surface treatment of the metal surface. A polished, shiny metal surfaces radiate very little heat. A painted or anodized surface radiates significantly more heat than a bright, unpainted one. The electromagnetic radiation rate of a material is proportional to its rate of absorption. Therefore, black colored surfaces that absorb more radiation than lighter colors such as white or metallic surfaces are more efficient in thermal heat transfer. The thermal energy transmitted through radiation increases steeply as the temperature rises. However, radiative heat dissipation at normal temperatures (0 - 100 °C) is generally negligible as compared to heat transfer by convection.