7.3 clothing, insulation and climate new ideas for today: thermal radiation emissivity insulation...
TRANSCRIPT
![Page 1: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/1.jpg)
7.3 Clothing, Insulation 7.3 Clothing, Insulation and Climate and Climate
New ideas for New ideas for today:today:
• Thermal radiation• Emissivity• Insulation and Climate
![Page 2: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/2.jpg)
The Electromagnetic The Electromagnetic SpectrumSpectrum
RainbowRainbow
![Page 3: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/3.jpg)
0 degree Kelvin
surface of sun 6,000 K Visible light
lava1,200 K
Red light
Body temperature309 K
infrared light
Universe2.7 K
microwavesabsolute zero
Objects at different Objects at different temperatures emit temperatures emit electromagnetic electromagnetic radiation.radiation.
Black Body:Black Body:
Object that emits Object that emits radiation but does not radiation but does not reflect radiation. It reflect radiation. It absorbs all incoming absorbs all incoming radiation!radiation!
IR radiationIR radiation
![Page 4: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/4.jpg)
The Blackbody SpectrumThe Blackbody Spectrum
The wavelength and intensity of electromagnetic waves from a black body depend only on its temperature
Blackbody radiationBlackbody radiation
![Page 5: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/5.jpg)
The Stefan-Boltzmann LawThe Stefan-Boltzmann Law
This amount of power that a surface, which has an emissivity of e, a temperature of T and a surface area of A, radiates.
P = e T4 APower = emissivity × Stefan-Boltzmann constant × temperature4 × surface area
is the Stephan Boltzmann constantwith value 5.67 x 10–18 J / (s m2 K4)
![Page 6: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/6.jpg)
Courtesy of PHET
![Page 7: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/7.jpg)
Emissivity, eEmissivity, eThe efficiency with which an object
emits or absorbs energyRanges from e=0 to e=1
e is low (near 0)For white, shiny, or clear surfaces(poor emitter / absorber)
e is high (near 1) For black surfaces(good emitter / absorber)
Leslie cubeLeslie cube
![Page 8: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/8.jpg)
Clicker questionClicker questionWhich fleece should you wear to stay warmest at night?
(A) Black (B) White
![Page 9: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/9.jpg)
InsulationInsulation
• Well insulated windows
• Poorly insulated windows
What makes the
difference ?
![Page 10: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/10.jpg)
Ways to lose thermal energyWays to lose thermal energy
• Conduction (glass to air on surface)
• Convection (remove air layer on surface!)
• RadiationT
window
Convectioncurrents
Heat flowTw=
200C
atmosp
here &
surface
TA&S=
-10oC
radiation
![Page 11: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/11.jpg)
(I) Reducing Conductive (I) Reducing Conductive LossesLosses
• Heat flow by conduction is given by thermal conductivity, k:
• Thermal conductivity is a material property:
Argon 0.016 W/m K∙ Air 0.025 W/m K∙ Glass 0.8 W/m K∙ Copper 380.0 W/m K∙
separation of distancearea difference etemperaturk flowheat
![Page 12: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/12.jpg)
(I) Reducing Conductive (I) Reducing Conductive LossesLosses• Glass window thermal conductivity 0.8 W/m K∙ conductive losses: ~ 3200 W
• Double glass window with air gap thermal conductivity 0.025 W/m K∙ conductive losses ~ 100 W
• Double glass window with argon gap thermal conductivity 0.016 W/m K∙ conductive losses ~ 65 W 4 x wider argon gap ~ 16 W
argon
Reduces losses
by factor 200 !
![Page 13: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/13.jpg)
Window design with argon Window design with argon gapgap
Wide argon gap can reduce
heat loss from conduction
by factor ~ 200 !
Challenge: heat expansion
between glass and frame
tends to break argon seal
Bimetallic stripBimetallic strip
![Page 14: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/14.jpg)
(II) Reducing Convection (II) Reducing Convection LossesLosses
The gap design already does the trick:
The Argon in the gap remains stationary and the heat absorbed in the argon cannot be carried away through convection currents!
argon
Convectioncurrents
![Page 15: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/15.jpg)
(III) Reducing Radiation (III) Reducing Radiation LossesLosses
Room temperature ~ 290 K infrared radiation
glass is black for infrared
light, e ~ 0.92
Glass absorbs radiation
and can re-emit radiation
to the outside !
![Page 16: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/16.jpg)
(III) Reducing Radiation (III) Reducing Radiation LossesLosses
Solution:
cover inside surface of glasswith indium-tin-oxide (ITO)
ITO is transparent to visible lightbut a mirror for infrared light!
visible light
Infrared light
Thermos bottlesThermos bottles
![Page 17: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/17.jpg)
Insulation w trapped air or Insulation w trapped air or argon:argon:
![Page 18: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/18.jpg)
Earth as a GreenhouseEarth as a Greenhouseradiation from the sun enters the atmospherethe emissivity for visible light is small
the energy from theSolar radiation heats atmosphere + surface The emissivity for infrared
is larger than for visible light some infrared reflected back some escapes to space
atmosphere
Taverage ~ 15oC
surface
Taverage ~ -18oC
space
![Page 19: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/19.jpg)
Changing the emissivityChanging the emissivityradiation from the sun enters the atmospherethe emissivity for visible light is small
the energy from theSolar radiation heats atmosphere + surface increasing the emissivity (eg. by
adding CO2 or methane to the
atmosphere) would change thesurface (greenhouse) temperature
atmosphere
Taverage ~ 17oC
surface
Taverage ~ -18oC
space
![Page 20: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/20.jpg)
IPCC 2007
![Page 21: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/21.jpg)
Muir Glacier, August 1941
![Page 22: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/22.jpg)
Muir Glacier, August 2004
![Page 23: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/23.jpg)
North Pole
![Page 24: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/24.jpg)
Computer models
Predicting the futureIPCC 2007
![Page 25: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/25.jpg)
See you next class!
For next class: Read Section 8.1
![Page 26: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/26.jpg)
1 m = 109 nm1 m = 1,000,000,000 nm
1 nm = 10–9 m1 nm = 0.000000001 m
700 nm 550 nm 400 nm
A nanometer is very smallA nanometer is very small
Visible Light (approx):Visible Light (approx):
![Page 27: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/27.jpg)
Blackbody spectrum: universeBlackbody spectrum: universe
Bob Wilson and Arno Penzias: Nobel Prize, 1978
Cosmic Microwave Background Radiation
(Universe 13.7 billion years old now)
![Page 28: 7.3 Clothing, Insulation and Climate New ideas for today: Thermal radiation Emissivity Insulation and Climate](https://reader035.vdocuments.site/reader035/viewer/2022062221/56649db65503460f94aa7b53/html5/thumbnails/28.jpg)
Volume expands w/ increasing Temperature: Makes sealing windows challenging!
Higher temperature: Increasing thermal motion Increasing separation
between atomsExpansion of volume and
outer dimension of object
heat expansion depends on
material …