Electromagnetic waves and thermal radiation

From Thermal-FluidsPedia

(Difference between revisions)
Jump to: navigation, search
 
(20 intermediate revisions not shown)
Line 1: Line 1:
-
References
+
[[Image:Electromagnetic_wave_propagating.png|thumb|400 px|alt=Electromagnetic wave propagating in the x-direction with associated electric (E<sub>y</sub>) and magnetic (H<sub>z</sub>) components|'''Figure 1: Electromagnetic wave propagating in the x-direction with associated electric (E<sub>y</sub>) and magnetic (H<sub>z</sub>) components''']]
 +
 
 +
[[Image:The_electromagnetic_spectrum.png|thumb|400 px|alt= The electromagnetic spectrum
 +
|'''Figure 2: The electromagnetic spectrum''']]
 +
 
 +
Energy transfer by thermal radiation differs in fundamental ways from conduction and convection. Radiative energy is carried by electromagnetic waves, which require no medium for their propagation. Thus, unlike the other heat transfer modes, radiative energy can be transferred through a vacuum, for example allowing us to receive solar energy through the vacuum of space.
 +
 
 +
Electromagnetic (EM) waves are described mathematically by ''Maxwell's Equations'' [[#References|(Siegel and Howell, 2002; Modest, 2003; Bohren and Huffman, 1983)]], which formulate the propagation of the perpendicular amplitudes of the electric and magnetic components, <math>E</math> and <math>H</math>, of the waves (Figure 1). The energy carried by the wave is proportional to the square of the amplitude of the electrical component <math>E</math> of the wave. These equations can be used to predict the interaction of the waves with interfaces between differing materials, allowing prediction of the radiative properties of various materials in terms of electrical and magnetic properties.
 +
 
 +
The EM waves can be generated in various ways. Depending on the source of the EM waves, they may have differing wavelengths, extending from very short (nm) to very long (km) (Fig. 2). For radiative heat transfer, we are interested in EM waves originating from microscopic energy transitions that occur because of the internal energy state of a substance, which is in turn dependent on the absolute temperature of a material that is in thermodynamic equilibrium. EM waves originating from such a source are called thermal radiation, and this radiation is emitted by any substance that is above absolute zero temperature. ''This dependence means that all radiative transfer relations must be in terms of absolute temperature''. Thermal radiation is roughly in the range of 0.1 < <math>\lambda</math>< 1000 <math>\mu</math>m. The thermal radiation portion of the logarithmic wavelength scale of Fig. 2 is thus fairly small, and the visible portion of the spectrum is small indeed. Electromagnetic waves travel without attenuation (loss) through a vacuum and through perfectly transparent materials (ideal dielectrics). Some media will absorb wave energy, converting the radiation into internal energy. Air is generally transparent, although some gases such as carbon dioxide and water vapor can absorb radiation in certain ranges of the infrared portion of the spectrum as it travels. Solids, particularly metals, are very strong absorbers, and can completely absorb radiation over very short distances. Other solids (glass, for example) are quite transparent to radiation over wide ranges of wavelength.
 +
 
 +
To provide the basis for computing energy transfer by thermal radiation, we must connect the temperature of a radiating surface to its rate of electromagnetic energy emission by radiation.
 +
 
 +
==References==
 +
 
Bohren, C.F. and Huffman D.R., 1983, ''Absorption and Scattering of Light by Small Particles'', John Wiley & Sons, New York, NY.
Bohren, C.F. and Huffman D.R., 1983, ''Absorption and Scattering of Light by Small Particles'', John Wiley & Sons, New York, NY.
-
Chang, S.L. and Rhee, K.T., 1984, “Blackbody Radiation Functions,” ‘‘Int. Comm. Heat and Mass Transfer’‘, Vol. 11, pp. 451-455.
+
 
-
Catton, I., Ayyaswamy, P.S., and Clever, R.M., 1974, “Natural Convection Flow in a Finite, Rectangular Slot Arbitrarily Oriented with Restpect to the Gravity Vector,” ‘‘Int. J. Heat Mass Transfer’‘, Vol. 17, pp. 173-184.
+
Faghri, A., Zhang, Y., and Howell, J. R., 2010, ''Advanced Heat and Mass Transfer'', Global Digital Press, Columbia, MO.
-
Duffie, John A. and Beckman, William A., 2006, ‘‘Solar Engineering Of Thermal Processes’‘,  3<sup>rd</sup>  ed., John Wiley & Sons, Inc., New York, NY..
+
 
-
Frewin, M.R. and Scott, D.A., 1999, “Finite Element Model of Pulsed Laser Welding,” Welding Research Supplement 1999, 15s-22s.
+
-
Greffet, J.J., Carminati, R., Joulain, K., Mulet, J. P., Mainguy, S. and Chen, Y., 2002, “Coherent Emission of Light by Thermal Sources, ‘‘Nature’‘ (London), Vol. 416, pp. 61-64.
+
-
Han, L., Liou, F.W., and Musti, S., 2005, “Thermal Behavior and Geometry Model of Melt Pool in Laser Material Process,” ‘‘J. Heat Transfer’‘, Vol. 127, pp. 1005-1014.
+
-
Harrison, W.N., Richmond, J.C., Plyler, E.K., Stair, R. and Skramstad, H.K., 1961, Standardization of Thermal Emittance Measurements, WADC-TR-59-510 (Pt.2), 21 pp.
+
-
Harrison, W.N., Richmond, J.C., Shorten, F.J., and Joseph, H.M., 1963, Standardization Of Thermal Emittance Measurements, WADC-TR-59-510 (Pt.4), 90 pp.
+
-
Heltzel, A.J., 2006, ‘‘Laser/Microstructure Interaction and Ultrafast Heat Transfer’‘, PhD Dissertation, Mechanical Engineering Department, The University of Texas at Austin, Austin, TX.
+
-
Heltzel, A. Theppakuttai, S., Howell, J.R. and Chen, S., 2005, “Analytical and Experimental Investigation of Laser-Microsphere Interaction, for Nanoscale Surface Modification, ‘‘J. Heat Transfer’‘, vol. 127, pp. 1231-1235.
+
-
Hollands, K.G.T., Unny, S.E., Raithby, G.D., and Konicek, L., 1976, “Free Convection Heat Transfer. Across Inclined Air Layers,” ‘‘J. Heat Transfer’‘, Vol. 98, 189-193.
+
-
Lide, D.R. (ed.), ‘‘Handbook of Chemistry and Physics’‘, 89<sup>th</sup> ed., CRC Press, Boca Raton, 2008.
+
-
Mie, G., 1908, “Beiträge zur Optik trüber Medien speziell kolloidaller Metallösungen,” ‘‘Ann. Phys’‘., Vol. 25, pp. 377-445.
+
Modest, M.F., 2003, Radiative Heat Transfer, 2<sup>nd</sup> ed., Academic Press, Sand Diego, CA.  
Modest, M.F., 2003, Radiative Heat Transfer, 2<sup>nd</sup> ed., Academic Press, Sand Diego, CA.  
-
Qu, Y., Puttitwong, E., Howell, J. R. and Ezekoye, O. A., 2007a, “Errors Associated with Light-pipe Radiation Thermometer Temperature Measurements,” ‘‘IEEE Trans. Semiconductor Manufacturing’‘, Vol. 20, pp. 26-38. 
+
 
-
Qu, Y., Howell, J. R. and Ezekoye, O. A., 2007b, “Monte Carlo Modeling of a Light-pipe Radiation Thermometer,” ‘‘IEEE Trans. Semiconductor Manufacturing’‘, Vol. 20, pp. 39-50. 
+
Siegel, R. and Howell, J.R., 2002, ''Thermal Radiation Heat Transfer'', 4<sup>th</sup> ed., Taylor and Francis, New York, NY.
-
Randall, K. R., Mitchell, J. W., and El-Wakil,  M. M., 1979, “Natural Convection Heat Transfer Characteristics of Flat Plate Enclosures,” ‘‘J. Heat Transfer’‘, Vol. 101, pp. 120-125.
+
 
-
Rohsenow, W.M., Hartnett, J.P., and Cho, Y.I., 1998, ‘‘Handbook of Heat Transfer’‘, 3<sup>rd</sup> ed., Chap. 18, Heat Transfer in Materials Processing, McGraw-Hill, New York, NY.
+
==Further Reading==
-
Rosenthal, D., 1946, “The Theory of Moving Sources of Heat and its Application to Metal Treatments,” Trans. ASME, Vol. 43, pp. 849–866.
+
 
-
Schmidt, E. and Eckert, E.R.G., 1935, Über die Richtungsverteilung der Wärmestrahlung von Oberflächen, Forschung Geb. D. Ingenieurwes., Vol. 6, pp.175-183.
+
==External Links==
-
Siegel, R. and Howell, J.R., 2002, ‘‘Thermal Radiation Heat Transfer’‘, 4<sup>th</sup> ed., Taylor and Francis, New York, NY.
+
-
Theppakuttai, S., 2006, ‘‘Laser Micro/Nano Scale Processing of Glass and Silicon’‘, PhD Dissertation, Mechanical Engineering Department, The University of Texas at Austin, Austin, TX.
+
-
Torrance, K.E. and Catton, I., 1980, “Natural Convection in Enclosures,” ‘‘Proc Nineteenth National Heat Transfer Conf’‘., HTD-Vol. 8, Orlando, FL, July 27-30, 1980
+
-
Touloukian, Y.S. and DeWitt, D.P., (eds.), ‘‘Thermophysical Properties of Matter’‘, vol. 7, Thermal radiative properties: metallic elements and alloys, and v. 8. Thermal radiative properties: non-metallic solids, IFI/Plenum, New York, 1970-[79].
+
-
Zaworski, J., Welty, J.R., and Drost, M.K., 1996, “Measurement and Use of Bidirectional  Reflectance,” ‘‘Int. J. Heat Mass Transfer’‘, Vol. 39, pp. 1149-1156.
+

Current revision as of 06:54, 13 July 2010

Electromagnetic wave propagating in the x-direction with associated electric (Ey) and magnetic (Hz) components
Figure 1: Electromagnetic wave propagating in the x-direction with associated electric (Ey) and magnetic (Hz) components
 The electromagnetic spectrum
Figure 2: The electromagnetic spectrum

Energy transfer by thermal radiation differs in fundamental ways from conduction and convection. Radiative energy is carried by electromagnetic waves, which require no medium for their propagation. Thus, unlike the other heat transfer modes, radiative energy can be transferred through a vacuum, for example allowing us to receive solar energy through the vacuum of space.

Electromagnetic (EM) waves are described mathematically by Maxwell's Equations (Siegel and Howell, 2002; Modest, 2003; Bohren and Huffman, 1983), which formulate the propagation of the perpendicular amplitudes of the electric and magnetic components, E and H, of the waves (Figure 1). The energy carried by the wave is proportional to the square of the amplitude of the electrical component E of the wave. These equations can be used to predict the interaction of the waves with interfaces between differing materials, allowing prediction of the radiative properties of various materials in terms of electrical and magnetic properties.

The EM waves can be generated in various ways. Depending on the source of the EM waves, they may have differing wavelengths, extending from very short (nm) to very long (km) (Fig. 2). For radiative heat transfer, we are interested in EM waves originating from microscopic energy transitions that occur because of the internal energy state of a substance, which is in turn dependent on the absolute temperature of a material that is in thermodynamic equilibrium. EM waves originating from such a source are called thermal radiation, and this radiation is emitted by any substance that is above absolute zero temperature. This dependence means that all radiative transfer relations must be in terms of absolute temperature. Thermal radiation is roughly in the range of 0.1 < λ< 1000 μm. The thermal radiation portion of the logarithmic wavelength scale of Fig. 2 is thus fairly small, and the visible portion of the spectrum is small indeed. Electromagnetic waves travel without attenuation (loss) through a vacuum and through perfectly transparent materials (ideal dielectrics). Some media will absorb wave energy, converting the radiation into internal energy. Air is generally transparent, although some gases such as carbon dioxide and water vapor can absorb radiation in certain ranges of the infrared portion of the spectrum as it travels. Solids, particularly metals, are very strong absorbers, and can completely absorb radiation over very short distances. Other solids (glass, for example) are quite transparent to radiation over wide ranges of wavelength.

To provide the basis for computing energy transfer by thermal radiation, we must connect the temperature of a radiating surface to its rate of electromagnetic energy emission by radiation.

References

Bohren, C.F. and Huffman D.R., 1983, Absorption and Scattering of Light by Small Particles, John Wiley & Sons, New York, NY.

Faghri, A., Zhang, Y., and Howell, J. R., 2010, Advanced Heat and Mass Transfer, Global Digital Press, Columbia, MO.

Modest, M.F., 2003, Radiative Heat Transfer, 2nd ed., Academic Press, Sand Diego, CA.

Siegel, R. and Howell, J.R., 2002, Thermal Radiation Heat Transfer, 4th ed., Taylor and Francis, New York, NY.

Further Reading

External Links