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 <[email protected]> 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 <[email protected]> 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. > > -- rec -- > -. --- - / ...- .- .-.. .. -.. / -- --- .-. ... . / -.-. --- -.. . > FRIAM Applied Complexity Group listserv > Fridays 9a-12p Friday St. Johns Cafe / Thursdays 9a-12p Zoom > https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fbit.ly%2fvirtualfriam&c=E,1,H_ghMqPU-KLT6f1yS4wIgeiFE6jlYxa6ONQKe9WyfT46vnFatR0xy9cbgB5G1AryFHstk0yAr4W9t5oo5qD9Y9QUoBb34_pYy3qcLKTtK976Zp3hQv1dOA,,&typo=1 > to (un)subscribe > https://linkprotect.cudasvc.com/url?a=http%3a%2f%2fredfish.com%2fmailman%2flistinfo%2ffriam_redfish.com&c=E,1,ovRQH0ag4XKJ5em_qkxCX4zFhQw2BmqhY5TW3Xln9Vu-y4ZUfnFNfDKNEIskf4JQX3BtDYMR4qlBiIcjZP3m_rvKjnqgcpqjbeLSwU1O08ssDH0E&typo=1 > FRIAM-COMIC > https://linkprotect.cudasvc.com/url?a=http%3a%2f%2ffriam-comic.blogspot.com%2f&c=E,1,XwiB_CPfUJC4hd-mdMEjARwF-CYUhwwrbh8CWD11DwU45qurr5e_qqi0VZcmtYEMpJ9_row7X5vYixMOqZYCXJd9p63LkLUywuJN6Ezz_yCxhNg,&typo=1 > archives: 5/2017 thru present > https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fredfish.com%2fpipermail%2ffriam_redfish.com%2f&c=E,1,8GE0j2-9OGzp5XSJt1cxOVoamDv3htNt9ZGr9RRLtlsd3xp_CwQadLLMNnMTQRAHBblMHYHH1r3LgzFUhGCL1XOWgAI6XM-HHn_v9iCizYI,&typo=1 > 1/2003 thru 6/2021 http://friam.383.s1.nabble.com/ > > > -. --- - / ...- .- .-.. .. -.. / -- --- .-. ... . / -.-. --- -.. . > FRIAM Applied Complexity Group listserv > Fridays 9a-12p Friday St. Johns Cafe / Thursdays 9a-12p Zoom > https://bit.ly/virtualfriam > to (un)subscribe http://redfish.com/mailman/listinfo/friam_redfish.com > FRIAM-COMIC http://friam-comic.blogspot.com/ > archives: 5/2017 thru present > https://redfish.com/pipermail/friam_redfish.com/ > 1/2003 thru 6/2021 http://friam.383.s1.nabble.com/ >
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