Written by Jerry Ratzlaff on . Posted in Thermodynamics

Heat transfer by radiation, abbreviated as $$Q_r$$ or $$\phi$$ (Greek symbol phi), also called heat radiation or radiation heat transfer, is one of four types of heat transfer: conduction, convection, mixing and radiation.  Radiation is the flow of energy through electromagnetic waves such as infrared, light, microwaves, etc.

### Heat Transfer by Radiation formula

$$\large{ Q_r = \epsilon \; \sigma \; A \left( T^4 - T_e^4 \right) }$$

Where:

$$\large{ Q_r }$$ = heat radiation

$$\large{ \epsilon }$$  (Greek symbol epsilon) = the emissivity of the particular body and is a number between 0 and 1

$$\large{ \sigma }$$  (Greek symbol sigma) = Stefan-Boltzmann constant

$$\large{ A }$$ = radiating area

$$\large{ T }$$ = temperature of the object emitting

$$\large{ T_e }$$ = temperature of the environment