HT Radiation Heat Transfer Radiation Notes

Question Answer
____; is heat transferred by electromagnetic waves. Thermal Radiation
Radiation always occurs from one ____ to another and always flows from high temperature body to a lower temperature body. Mass
The difference between emitted and absorbed radiation for any object is the _______ heat transfer from the object. Net Radiation
Radiation is emitted at many different wavelengths, but all electromagnetic waves travel at the same _____ known as the _____. Speed, Speed of light
____: is defined as the portion of the electromagnetic spectrum from 0.1 micrometers to 100 micrometers. This includes all of the visible and infrared portion, as well as a portion of the UV spectrum Thermal Radiation
Electromagnetic waves can also be viewed as collections of discrete particles of energy called ____. Photons
____: occurs from a surface to the surroundings due to oscillations of electrons near the surface and occurs from all surfaces at a finite temp. Emission
____: occurs as radiation incident to the surface (incident to the surface=striking the surface) is transformed to internal energy. Absorption
___: occurs as radiation incident to the surface is redirected away without being absorbed. Reflection
___: occurs when radiation passes through an object without being absorbed. This only occurs with transparent or semi-transparent objects. Transmission
___: is the incident radiation striking a surface which is what is reflected, absorbed, and transmitted. Surface Irradiation (G)
___: is the total radiation leaving a surface which is what is emitted and reflected. Radiosity (J)
Two major difficulties associated with radiation are its ___ and ____ nature Spectral, Directional
Surfaces will respond differently to irradiation depending on the distribution of _____, absorbing some and reflecting others. This is how color can be perceived. Wavelengths
____: emission and reflection are constant for all directions. Directionally Diffuse
Surfaces also emit and absorb radiation to/from different directions and the magnitude depends on the ____, Direction
___: rate at which radiation is emitted at a particular wavelength and in a particular direction (per unit solid angle, per unit wavelength, per unit surface area). Radiation Intensity (Ie)
Black bodies are ideal surfaces with properties (3): 1. perfect absorber 2. perfect emitter 3. Diffuse
____: black body spectral emissive power depends on wavelength and temperature. This equation shows that as the temp. increases the wavelength where the maximum black body spectral emissive power decreases. Wien's Displacement Law
___: a fraction of the total emission from a black body that occurs only in a certain wavelength. Band-Emission
Even for real (non-blackbody) surfaces, radiation heat transfer depends on delta T4. We can make the following qualitative statements (2): 1. radiation becomes more important as the temps of the participating surfaces increase. 2. radiation becomes more important as temp difference increases. It is often negligible for small delta T and dominant for large delta T.
Gray surfaces have no preferred _____ reflection. Color
Kirchoffs Law for gray surfaces states _____. And for real surfaces states ____. emissivity and absorptivity are equal. emissivity and absorptivity are equal at each particular wavelength and direction.
Kirchoffs Law ensures that for any surface radiation exchange, net heat transfer always occurs from _____. high to low
____: is defined as the fraction of the radiation leaving surface i that is intercepted (incident) to surface j. View Factor
Shape factor, angle factor, and configuration factors are all different names for the ___. View Factor
____: two (or more) surfaces that possess symmetry about a third surface will have identical view factors from that surface. Symmetry Rule

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