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

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

### Where:

 Units English Metric $$\large{ Q_r }$$ = heat radiation $$\large{\frac{Btu}{hr}}$$ $$\large{ W }$$ $$\large{ A }$$ = area of radiating $$\large{ in^3 }$$ $$\large{ mm^3 }$$ $$\large{ \sigma }$$  (Greek symbol sigma) = Stefan-Boltzmann constant $$\large{\frac{Btu}{hr-ft^2-R^4}}$$ $$\large{\frac{W}{m^2-K^4}}$$ $$\large{ T }$$ = temperature of object emitting $$\large{ F }$$ $$\large{ K }$$ $$\large{ T_e }$$ = temperature of environment $$\large{ F }$$ $$\large{ K }$$