Abstract
A simple experiment is described where the IR (infrared) radiation level is kept constant while the temperature of an IR absorbing and a non-absorbing solid object are changed. The two objects, made from black-painted and highly polished Al foil envelopes, respectively, are placed in a chamber where the temperature is controlled. When heated by the surrounding air the black object becomes about 40% colder than the non-IR absorbing object! However, when the two objects are cooled by the surrounding air, the black becomes ca. 40% warmer than the non-IR absorbing object (and the surrounding air). This effect was surprising to us, and it gave us an opportunity to quantify the relationship between IR radiation flow and thermal energy flow. The unexpected large value of the (Fourier) thermal conductivity coefficient was found to be the reason for the reduced warming/cooling of the black object. The interaction between radiative and thermal energy transfer, when an IR absorbing object (like the surface of the Earth) is warmed, should be included in the climate models used by the Intergovernmental Panel on Climate Change (IPCC), since the global land temperature is measured in the air above Earth’s surface. This leads to ca. 15% of the temperature increase predicted by the climate models.
Highlights
When the Sun shines on the Earth’s surface, it heats up
The interaction between radiative and thermal energy transfer, when an IR absorbing object is warmed, should be included in the climate models used by the Intergovernmental Panel on Climate Change (IPCC), since the global land temperature is measured in the air above Earth’s surface
This leads to ca. 15% of the temperature increase predicted by the climate models
Summary
2) Radiative energy: The relationship between the infrared (IR) radiation energy flow EIR in W/m2 from a black body and its temperature T is given by the Stefan-Boltzmann law [2]: EIR = σ T 4. Where T is the temperature in Kelvin and σ = 5.67 × 10−8 W/(m2K4) is the Stefan-Boltzmann constant Based on this law the IR radiation energy transfer ΔEIR between two black body objects, with temperatures TA and TB, can be expressed as:. By derivation of Equation (2) with T equal average of TA and TB : Δ= EIR 4σ T 3∆T (4) Both objects emit IR radiation and absorb it, but the net energy flow always goes from the hot to the cold object. For the object that absorbs (and emits) IR radiation, this will maximize the interaction between radiative and thermal energy transfer. (Note that using a very thin body that absorbs all incident rays was introduced as a definition of a black body by Gustav Kirchhoff in 1860 [3])
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