1. ACADs (08-006) Covered Keywords Heat tracing, thermal radiation, black body, gray body. Description Supporting Material 1.3.6.25.3.2.8

2. Lesson 14 Radiant 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 f a and f e 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