Written by Jerry Ratzlaff on . Posted in Thermodynamics

Heat transfer by radiation ( $$Q_r$$ or $$\phi$$ (Greek symbol phi) ) is the flow of energy through electromagnetic waves such as infrared, light, microwaves, etc.

### Heat Transfer by Radiation formula

$$\large{ Q_r = \epsilon \sigma A \Delta T ^4 }$$

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

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

Where:

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

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

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

$$\large{ A }$$ = cross sectional area

$$\large{ \Delta T }$$ = change in absolute temperature  $$\large{ \left( T_o \;-\; T_e \right)^4 }$$

$$\large{ T_o }$$ = absolute temperature of the object emitting

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