[FRIAM] new thermal tech

Sun Jan 8 14:10:48 EST 2023

I learned most everything I know about thermoacoustic heat engines while
trying to read those papers, then I went back to the day job hacking code.

-- rec --

On Sun, Jan 8, 2023 at 6:34 AM David Eric Smith <desmith at santafe.edu> wrote:

> The thermoacousktic one is interesting, and surprises me a bit.
>
> I worked on these systems a bit in the mid-1990s, when in a kind of
> purgatory in a navy research lab that mostly did acoustics.
>
> Broadly, there are two limiting cases for a thermoacoutic engine.  One
> uses a standing wave and is simple and robust to design and run.  The other
> uses a traveling wave and is much harder to tune and keep tuned.
>
> A difference is that the SW version, which we might say runs on a
> “thermoacousktic cycle”, makes intrinsic use of the phase lag for diffusion
> of heat through a boundary layer.  As such, it has no nontrivial reversible
> limit, and has severe limits on the efficiency (or coefficient of
> performance, if you are running it as a refrigerator).  So hearing that
> they get COPs comparable to existing mechanical systems would make me
> suspicious of they were using SW.
>
> The TW version runs on, effectively, the Stirling cycle, and in principle
> it does have a reversible, Carnot-efficient limit.  However, it has
> parasitic losses from viscous boundary layers.  The engineering limit you
> need to approach ideal thermal transfer efficiency is one that chokes off
> the flow of the working fluid, and makes the viscous drag explode.  Using
> an ideal gas like He reduces the viscosity, though also the heat capacity
> and diffusion rate through the fluid.
>
> On their website, they have a little advertising graphic of a sound wave,
> which shows a traveling wave (or a mixed wave with large TW component).  It
> would be reasonable, if they are scientists or engineers, for them to make
> their public graphics true representations of at least qualitatively what
> their system does.
>
> In view of the fact that there is very little conceptual to do with a
> thermoacousktic engine, and it is all materials science and tweaking
> engineering details, I really wonder what would have taken 27 years to
> figure out, or to get around to doing.
>
>
> For geeks who like this stuff, there is a fun continuum:
>
> 1. When I was a little kid, I got an ultra-simple Stirling engine from a
> mail advertisement (back when those weren’t all scams), and was delighted
> by it.
>
> 2. In reading more about Stirling cycles etc., I learned about
> “free-piston” Stirling engines, which have the same compartments and
> barriers, but use the compression-bounce of the gas to move the displacer
> piston rather than a mechanical linkage.
>
> 3. The TW thermoacousktic engine is just a free-piston Stirling without
> the piston: the shuttle of gas becomes the displacer.
>
> 4. Some years later, having been thrown out of String Theory for being too
> stupid to understand it, I was interested in the way adiabatic
> transformations look like mere coordinate deformations in state spaces,
> which means that one should be able to make Carnot-efficient reversible
> movement identical to equilibrium by use of a conformal field (the String
> Theorist’s universal symmetry transformation, back in those days).  So we
> can do thermoacousktic engines using String Theory (Horray!):
> https://journals.aps.org/pre/abstract/10.1103/PhysRevE.58.2818
> http://www.santafe.edu/~desmith/PDF_pubs/Carnot_1.pdf
> and then
> https://journals.aps.org/pre/abstract/10.1103/PhysRevE.60.3633
> http://www.santafe.edu/~desmith/PDF_pubs/Carnot_2.pdf
> Papers I know no-one has ever had any interest in, and very possibly
> no-one has ever read.
>
> I thought it was very fun to be able to derive Carnot’s theorem directly
> from a symmetry transformation, so entropy flux behaves like any other
> conserved quantity, rather than having to make arguments about limits to
> thermodynamic efficiency by daisy-chain proofs-by-contradiction (If you
> could do such-and-such, then by running an exemplar Carnot engine in
> reverse, you could make a perpetual-motion machine of type-XYZ).  But I
> never did anything with it that yielded a new calculation, as opposed to
> just a restatement of common knowledge.
>
> Anyway…
>
> Eric
>
>
>
>
>
> On Jan 6, 2023, at 8:27 AM, Roger Critchlow <rec at elf.org> wrote:
>
> I was amused to see an announcement of a thermoacoustic heat pump  the
> other day:
>
>
> https://www.pv-magazine.com/2023/01/02/residential-thermo-acoustic-heat-pump-produces-water-up-to-80-c/
> <https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fwww.pv-magazine.com%2f2023%2f01%2f02%2fresidential-thermo-acoustic-heat-pump-produces-water-up-to-80-c%2f&c=E,1,OiK5I3jqVzs0YmBcsTYEvneGYZ1FEG28fiRx3ORcJqyfO1RYvaNtVheIXHOQn5kEDLKn-6-EP20t-76MRRk3ELbJ6W-Bs3A2-bQupekjrWftCWx_4KE1&typo=1>
>
> then an ionocaloric refrigerator announcement turns up this morning
>
>   https://newscenter.lbl.gov/2023/01/03/cool-new-method-of-refrigeration/
> <https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fnewscenter.lbl.gov%2f2023%2f01%2f03%2fcool-new-method-of-refrigeration%2f&c=E,1,iAUwwTChDuxb9xOXSzMsHYIRxOSXe0tMdebJdWYF2_mAo6ayMqaAT3VacwosXksSM2F4bAvq53cQQusX66IRJmWrzqfU0BdHdbD4hor2Sd1emyC_O8I_CJY,&typo=1>
>
> It seems that you won't recognize your air conditioner in a few years.
>
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