Radiant Heat Transfer

Radiation is the energy transfer across a system boundary due to ΔT, by the method of photon emission or electromagnetic wave emission. The Radiant heat transfer is thermal energy transferred by the means of electromagnetic particles or waves.

In another words thermal radiation is energy emitted by matter as electromagnetic waves due to the pool of thermal energy which all the matter possesses and has a temperature above absolute zero. The thermal radiation transmits without the presence of matter via the vacuum of space.

The thermal radiation is a direct outcome of the random movements of atoms and molecules in matter. As these atoms and molecules are comprised of charged particles (i.e., protons &electrons), their movement outcomes in the release of electromagnetic radiation, that carries energy away from the surface.

Dissimilar conductive and convective kinds of heat transfer, thermal radiation can be focused in a minute spot by using reflecting mirrors that is exploited in concentrating solar power production. For instance, the sunlight reflected from mirrors heats the PS10 solar power tower and throughout the day it can heat water to 285 °C (545 °F).

All the bodies radiate energy in the form of photons moving in a haphazard direction, with random phase and frequency. Whenever radiated photons reach the other surface, they might be absorbed, reflected or transmitted. The manners of a surface with radiation incident upon it can be explained by the quantities shown below:

α = absorptance - fraction of an incident radiation absorbed

ρ = reflectance - fraction of the incident radiation reflected

τ = transmittance - fraction of the incident radiation transmitted.