[time-nuts] Thunderbolt stability and ambient temperature

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Jun 10 23:00:37 EDT 2009


Hal Murray wrote:
> phk at phk.freebsd.dk said:
>   
>>> Can I get reflections without some inductance?
>>> Is there any inductance in a system of alternating
>>> layers of insulation/storage?
>>>       
>
>   
>> I think you are overstretching the badly chosen nomenclatures
>> parallels to electricity. 
>>     
>
> It was actually a (somewhat?) serious question on several grounds.
>
> Can I get reflections from a lumped circuit model of a transmission line made 
> out of just Rs and Cs?  If so, I can probably do the same in the thermal 
> world.
>
> Can I get reflections in a thermal context?  Bruce's URLs say yes, but my 
> math is rusty enough that I can't quickly understand what's going on.
>
> If a thermal problem can generate reflections, does that mean it also has 
> something corresponding to inductance?  If so, what is it?
>
> It's possible that the key idea is time-delay.  In the electrical world, a 
> delay is a transmission line which has both C and L.  I'm not sure what the 
> one-dimensional equivalent in the thermal world is.
>
> What's the speed-of-light equivalent in the thermal world?
>
>
>
>
>
>   
Hal

Thermal wave group velocity = 2*SQRT(4*PI*(thermal diffusivity)/(thermal
wave period)).

for a derivation see:
http://books.google.co.nz/books?id=qSyAKzgwedIC&pg=PA153&lpg=PA153&dq=thermal+wave+velocity+diffusivity&source=bl&ots=95aUo2w5Ho&sig=t5seHCNo7H_RacyFUPcn6NFS2q0&hl=en&ei=DG0wSo-zGZ2MtgPX79C-Aw&sa=X&oi=book_result&ct=result&resnum=8#PPA153,M1
<http://books.google.co.nz/books?id=qSyAKzgwedIC&pg=PA153&lpg=PA153&dq=thermal+wave+velocity+diffusivity&source=bl&ots=95aUo2w5Ho&sig=t5seHCNo7H_RacyFUPcn6NFS2q0&hl=en&ei=DG0wSo-zGZ2MtgPX79C-Aw&sa=X&oi=book_result&ct=result&resnum=8#PPA153,M1>
pages 153 -154

Note there is dispersion - the propagation velocity depends on the
period of the thermal wave.


Bruce





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