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Wednesday, August 6, 2008

A question about heat...

I just sent the following to will post response as soon as it arrives.

Conversion of chemical to radiative heat...

What determines the rate at which chemical heat (convection) becomes electromagnetic heat (radiation)?  I am trying to get a handle on the Earth's energy budget.  Obviously, heat is being transfered in-system through convection... but what is the process that converts this chemical heat (brownian motion that needs a material medium) to photonic heat (that can leave the planet and travel through space)?  What factors limit this phase transition?  In terms of total energy transfer, how can one determine the delta between the rate of transfer (comparing convection and radiation) when a system has both.  What are the limits of efficiency when comparing both chemical and radiative energy transfer?  I know that convection is restricted by the sound limit, so I assume that radiative heat is likewise restricted by the speed of light.  However, because light doesn't seem to interact with other light, how dense does light have to be before we see dramatic self limiting effects?  I am guessing that E=mC^2 will answer my question as dense light becomes matter which provides the upper limit to the speed of light?  All of my questions are motivated by a desire to understand the base physics that underlies and predicts the Earth's energy budget and how these natural systems are effected by green house gasses and human energy conversion (releasing heat), especially with regard to the ratio of rate of change vs. dissipative capacity of the natural systems.

Thank you,

Randall Reetz


Randall Lee Reetz said...

First Reply from

Emission of radiation from a hot body is governed by the Stefan-Boltzmann Law:

Pay particular attention to the emissivity coefficient, that's what you're after. E=mc^2 has no bearing in this case, you'd be talking about ridiculous amounts of energy for light to create appreciable (near black hole levels) of gravitation and affect itself, nothing applicable to the Earth at all. The Stefan-Bolzmann Law for radiative heat loss can give you the power (amount of heat per unit time) radiated from the Earth. If you balance the absorption of sunlight by the Earth with the power it radiates you can calculate the Earth's temperature. It's a common problem in undergraduate physics textbooks.

Randall Lee Reetz said...

I have re-posted the question with a postscript requesting the causal mechanics that give rise to the conversion of convective to radiative heat (and not the formulas).

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