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Heat Transfer by Radiation

 

Heat Transfer by Radiation Formula

Qr=σA(T4T4e) 
Symbol English Metric
Qr = Heat Radiation Btu/hr  W
σ  (Greek symbol sigma) = Stefan-Boltzmann Constant Btu/hrft2R4 W/m2K4
A = Radiating Area in3 mm3
T = Emitting Object Temperature F K
Te = Environment Temperature F K

conduction convection radiantHeat transfer by radiation, abbreviated as Qr or ϕ (Greek symbol phi), also called heat radiation or radiation heat transfer, is the transfer of energy from one object to another through electromagnetic waves without the need for any medium or contact between the two objects.  The energy transfer occurs through the emission of electromagnetic waves, such as infrared radiation, by a warmer object and the absorption of these waves by a cooler object.

Heat Transfer by Radiation Formula

Qr=ϵσA(T4sT4) 
Symbol English Metric
Qr = Heat Radiation Btu/hr  W
ϵ  (Greek symbol epsilon) = Surface Emissivity dimensionless dimensionless
σ  (Greek symbol sigma) = Stefan-Boltzmann Constant Btu/hrft2R4 W/m2K4
A = Surface Area in3 mm3
Ts = Surface Temperature F K
T = Environment Temperature F K

Radiation is the primary mode of heat transfer in the vacuum of space, where there is no air or other matter to conduct or convect heat.  Examples of heat transfer by radiation include the warmth of the sun's rays felt on the skin, the heat radiated from a fire, or the warmth felt from a hot object held near the face.  The transfer of thermal energy can occur through three modes of heat transfer: conduction, convection, and radiation.

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