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ACADs (08-006) Covered Keywords Heat tracing, thermal radiation, black body, gray body.

Radiant Heat Transfer. ACADs (08-006) Covered Keywords Heat tracing, thermal radiation, black body, gray body. Description Supporting Material. Lesson 14 Radiant Heat Transfer. DESCRIBE how the following terms relate to radiant heat transfer: a. Black body radiation b. Emissivity

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ACADs (08-006) Covered Keywords Heat tracing, thermal radiation, black body, gray body.

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  1. Radiant Heat Transfer ACADs (08-006) Covered Keywords Heat tracing, thermal radiation, black body, gray body. Description Supporting Material

  2. Lesson 14Radiant Heat Transfer DESCRIBE how the following terms relate to radiant heat transfer: a. Black body radiation b. Emissivity c. Radiation configuration factor

  3. Thermal Radiation • The transfer of heat by electromagnetic radiation that arises due to the temperature of a body. • Most in the infra-red region of the electromagnetic spectrum • Distinguished from other forms of radiation, such as radio waves, x-rays, or gamma rays. • Does not need a medium, such as air or metal, to take place. • Any material that has a temperature above absolute zero gives off some radiant energy. • Examples: • When a cloud covers the sun, both its heat and light diminish. • The transfer of heat from a fireplace across a room in the line of sight.

  4. Black Body Radiation • A body that emits the maximum amount of heat for its absolute temperature • Can be expressed by the following equation:

  5. Net flow rate of heat between two black bodies

  6. Emissivity • A factor by which we multiply the black body heat transfer to take into account that the black body is the ideal case • Emissivity is a dimensionless number and has a maximum value of 1.0. • Modified formula for emissivity:

  7. Radiation Configuration Factor Radiative heat transfer rate between two gray bodies can be calculated by the equation stated below.

  8. Radiation Configuration Factor (cont.) A simplified version is obtained by combining fa and fe giving the Radiation Configuration Factor (f):

  9. Resistive Electrical Heating • Electrical Heaters • Heat Tracing

  10. Electric Heaters

  11. Heat Tracing • Used on mechanical piping systems that carry borated water, caustic soda, and other solutions • Performs critical process temperature control • Also applied on water piping systems to prevent them from freezing in cold weather • Application must include • Identification of requirements • Heater design considerations • Power systems design considerations • Temperature control considerations • Alarm considerations • Finished drawings and documents • Installation of materials • Startup testing • Temperature tests • Maintenance of electric pipe heating systems

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