RADIATION HEAT TRANSFER Heat TransferRADIANT HEAT TRANSFERRadiant heat transfer is thermal energy transferred by means of electromagneticwaves or particles.EO 1.10 DESCRIBE how the following terms relate to radiantheat transfer:a. Black body radiationb. Emissivityc. Radiation configuration factorThermalRadiationRadiant heat transfer involves the transfer of heat by electromagnetic radiation that arises due tothe temperature of a body. Most energy of this type is in the infra-red region of theelectromagnetic spectrum although some of it is in the visible region. The term thermal radiationis frequently used to distinguish this form of electromagnetic radiation from other forms, suchas radio waves, x-rays, or gamma rays. The transfer of heat from a fireplace across a room inthe line of sight is an example of radiant heat transfer.Radiant heat transfer does not need a medium, such as air or metal, to take place. Any materialthat has a temperature above absolute zero gives off some radiant energy. When a cloud coversthe sun, both its heat and light diminish. This is one of the most familiar examples of heattransfer by thermal radiation.BlackBodyRadiationA body that emits the maximum amount of heat for its absolute temperature is called a blackbody. Radiant heat transfer rate from a black body to its surroundings can be expressed by thefollowing equation.(2-12)QsAT4where:= heat transfer rate (Btu/hr)Qs= Stefan-Boltzman constant (0.174 Btu/hr-ft2-°R4)A = surface area (ft2)T = temperature (°R)HT-02 Page 26 Rev. 0
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