"Paul Ciszek" <nospam@[EMAIL PROTECTED]
> wrote in message
news:fnf01j$jsg$1@[EMAIL PROTECTED]
>
> In article <Itmmj.458$5K1.59@[EMAIL PROTECTED]
>,
> Fred Klingener <gigabitbucket@[EMAIL PROTECTED]
> wrote:
>>"Frank Scrooby" <X@[EMAIL PROTECTED]
> wrote in message
news:fnchp1$1j1$1@[EMAIL PROTECTED]
>>> Greets
>>>
>>> Spotted these links:
>>> http://www.popularmechanics.com/science/earth/4243793.html
>>>
>>> http://www.johnsonems.com/jhtec.html
>>>
>>> Wonder what the residents here would think?
>>
>>Sign me up. The fundamentals are there. I hate and end up not paying any
>>attention to SF (or listen to political campaign promises) that
violate(s)
>>the first or second laws of thermodynamics. JTEC doesn't, so that
>>attribute
>>alone sets it apart.
>
> I quote from the article:
>
> "says he can achieve a conversion efficiency rate that tops 60 percent
> with a new solid-state heat engine."
That's the author of the PM article talking, and I'm inclined to attribute
this to sloppy, maybe sensationalist, re****ting.
A careful reading of the quotes attributed to the engineers shows that
they
base their claims on an assumption that the JTEC cycle could be made to
fit
the Ericsson cycle (1.) isothermal compression, 2.) isobaric expansion,
3.)
isothermal expansion, and 4.) isobaric compression.
The ideal Carnot cycle operating between high temperature Th and cold Tc
has
the thermal efficiency (and the highest thermal efficiency attainable by
any
cycle) you calculate below:
> Using the aforementioned 2nd law of thermo, the maximum possible
> efficiency
> of a heat engine is:
>
> Th -Tc
> Eff = ------
> Th
>
> If Tc is "room temperature", or 293K, then Th has to be at least 732K or
> 459C (or 859F). In order for his "solid state heat engine" to work over
> that temperature difference, whatever magic material it is made of has
to
> retain its magic properties at the high-end temperatures. Color me
very,
> very skeptical.
and to achieve the "claimed" 60% efficiency, the temperature of the hot
junction would have to be ~460C as you calculate.
The thermal efficiences of the ideal raw Stirling and the Ericsson cycles
are less than that of the Carnot cycle. By adding perfect regeneration
sections, the Stirling and Ericsson cycle efficiencies can be made equal
to
the Carnot efficiency.
A couple of points here.
1. "says he can achieve a conversion efficiency rate that tops 60
percent..." is bogus, and I doubt that Johnson would confirm that.
2. Claiming a fundamental thermodynamic advantage for an Ericsson JTEC
over
Stirling engines is bogus.
3. Fitting the ideal Ericsson cycle to JTEC masks an assembly of
assumptions
like material conductivities infinite in places where we want to transfer
heat and zero where we don't, and perfect, lossless performance of the
stacks and regenerator. Heat exchange, especially gas-to-gas has gotten in
the way of development of otherwise nifty engine designs for a couple
hunderd years.
So is the whole thing busted? I don't think so. I think the PM article
unfortunately packages the JTEC in the same wrapper used for truly bogus
ideas.
Might it take JTEC a decade or two to work out design and materials issues
and line up applications? Maybe.
Would I invest money in the idea? If I were younger.
Cheers,
Fred
-----------
In theory, there's no difference between theory and practice. In practice,
there is.
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