Radiation Heat Transfer - School of Engineering and...
Transcript of Radiation Heat Transfer - School of Engineering and...
![Page 1: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/1.jpg)
Radiation Heat Transfer
EGR 4345 Heat Transfer
![Page 2: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/2.jpg)
Blackbody Radiation
Blackbody – a perfect emitter & absorber of radiation Emits radiation uniformly in all directions – no
directional distribution – it’s diffuse Joseph Stefan (1879)– total radiation emission per
unit time & area over all wavelengths and in all directions:
=Stefan-Boltzmann constant =5.67 x10-8 W/m2K4
24 mW TEb
![Page 3: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/3.jpg)
Planck’s Distribution Law
Sometimes we’re interested in radiation at a certain wavelength
Spectral blackbody emissive power (Eb) = “amount of radiation energy emitted by a blackbody at an absolute temperature T per unit time, per unit surface area, and per unit wavelength about the wavelength .”
![Page 4: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/4.jpg)
Planck’s Distribution Law
For a surface in a vacuum or gas
Other media: replace C1 with C1/n2
Integrating this function over all gives us the equation for Eb.
constant sBoltzmann'J/K 1038051
Kμm 104391
mμmW 1074232
where
μmmW 1
23
42
24821
2
25
1
-o
o
b
x.k
x.khcC
x.hcC
TCexpCTE
![Page 5: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/5.jpg)
Radiation Distribution
Radiation is a continuous function of wavelength
Radiation increases with temp.
At higher temps, more radiation is at shorter wavelengths.
Solar radiation peak is in the visible range.
![Page 6: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/6.jpg)
Wien’s Displacement Law
Peak can be found for different temps using Wien’s Displacement Law:
Note that color is a function of absorption & reflection, not emission
Km 52897 .T powermax
![Page 7: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/7.jpg)
Blackbody Radiation Function
We often are interested in radiation energy emitted over a certain wavelength.
This is a tough integral to do!
![Page 8: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/8.jpg)
Blackbody Radiation Function
Use blackbody radiation function, F
If we want radiation between 1 & 2,
40
T
dTE
TFb
TFTFTF1221
![Page 9: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/9.jpg)
Surface Emission
![Page 10: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/10.jpg)
Surface Emission
Spectral, directional emissivity
Total, directional emissivity
Spectral, hemispherical emissivity
![Page 11: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/11.jpg)
Surface Emission
Spectral, hemispherical emissivity
Substituting spectral emissive power
![Page 12: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/12.jpg)
Surface Emission
Total, hemispherical emissivity
Total, directional emissivityNormal emissivity predictable
![Page 13: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/13.jpg)
Spectral, normal emissivity
![Page 14: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/14.jpg)
Total, normal emissivity
![Page 15: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/15.jpg)
Total, normal emissivity
![Page 16: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/16.jpg)
Absorption, Reflection, and Transmission
![Page 17: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/17.jpg)
Absorptivity
Spectral, directional absorptivity
Spectral, hemispherical absorptivity
Total, hemispherical absorptivity
![Page 18: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/18.jpg)
Reflectivity
Spectral, directional reflectivity
Spectral, hemispherical reflectivity
Total, hemispherical reflectivity
![Page 19: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/19.jpg)
Reflectivity
![Page 20: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/20.jpg)
Transmissivity
Spectral, hemispherical transmissivity
Total, hemispherical reflectivity
![Page 21: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/21.jpg)
Special Considerations
Semitransparent medium
+ + = 1
Opaque
+ = 1
![Page 22: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/22.jpg)
![Page 23: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/23.jpg)
![Page 24: Radiation Heat Transfer - School of Engineering and …web.ecs.baylor.edu/faculty/vantreuren/EG… · PPT file · Web view · 1998-01-01Radiation Heat Transfer EGR 4345 Heat Transfer](https://reader031.fdocuments.net/reader031/viewer/2022021821/5afecb597f8b9aa34d8f6a94/html5/thumbnails/24.jpg)
Kirchhoff’s Law
=
No real surface can have an emissive power exceeding that of a black surface at the same temperature.
sbs TETE
1
1