Microwave absorption
Microwave absorption
(OP)
Incropera and DeWitt's book has an example problem involving a terrestrial solar collector panel. In the problem they consider microwave absorption. Does anyone have any data on this phenomenon? Why is it seemingly ignored in all other thermal radiation problems?
Tunalover





RE: Microwave absorption
m777182
RE: Microwave absorption
RE: Microwave absorption
Tunalover
RE: Microwave absorption
What edition do you have? I couldn't find a solar collection example with microwaves in my second ed.
The delineation between thermal radiation and microwave radiation at at 10^2 micrometers seems rather arbitrary to me. I find it hard to believe that radiation at 10^1.999 micrometers transfers heat, but at 10^2.00001 doesn't.
RE: Microwave absorption
RE: Microwave absorption
RE: Microwave absorption
Almost all of the heat transfer texts I own include microwave energy implicitly in the use of the Stefan-Boltzman sigma*T4 relationship, which includes microwave radiation. For the simple body to body radiative transfer, microwaves are included.
However, we should note that most of the heliostats were developed using mirror arrays with limited apertures. These limited apertures will not properly reflect nor focus wavelengths comparable to the aperture dimension efficiently. Thus, it might well be that the issue is an optical and not thermal radiation problem.
TTFN
RE: Microwave absorption
RE: Microwave absorption
microwave(rf) is generally considered a coherent source and not black body radiation
that said thermally emitting objects contain all way bands if they are black body radiators....
RE: Microwave absorption
Passively generated microwave is incoherent, since it's from the same quantum process that generates the infrared.
TTFN
RE: Microwave absorption
the problem statement in Incropera and DeWitt is unfortunate, they should have indicated that longer wavelength IR or "black body" radiation was to be considered. to me a matter of semantics...
RE: Microwave absorption
It's obvious that stellar microwave radiation CAN be collected, but NOT with a solar collector. Collection of stellar microwave emissions is done every day with radio telescopes. Their receiving aperture range from the small one at over 40 ft across to VLBI arrays that are hundreds of km across.
TTFN
RE: Microwave absorption
FYI, this radiation term is proportional to the sky temperature (in absolute units) to the fourth. Does that help any?
I'm just trying to understand WHY this term is not shown in every other terrestrial thermal radiation problems.
Tunalover