Radiation Heat Transfer

Thermal Radiation

Radiation = Heat Transfer

• From a surface
• Over long distances
• Even in vacuum

Example: Gray Bodies

• Hot surface emits $Aϵ\sigma T_H^4$
• Cold surface emits $Aϵ\sigma T_C^4$
• Net Heat transfer $Aϵ\sigma (T_H^4-T_C^4)=\alpha (T_H-T_C)$

Recall: Definition of Heat

• Energy transferred across boundaries of system due to temperature difference