[FRIAM] A new heat engine with no moving parts is as efficient as a steam turbine
Steve Smith
sasmyth at swcp.com
Sat Apr 16 14:19:16 EDT 2022
Cody -
> That would be good for a concentrated solar array. Do you have any
> idea how it works?
https://ui.adsabs.harvard.edu/abs/2019JPhD...52A5501O/abstract
I always wondered if (when) someone would achieve this... as the article
alludes, the effect is similar to the visible-spectrum PV we are
familiar with, but in a much different spectrum (related to a 1900-2400C
black-body). TPVs in the near-infrared are not new but the energy
density isn't as nearly as high and I think primarily used in very niche
applications. https://en.wikipedia.org/wiki/Thermophotovoltaic
You are probably already familiar with Thermocouples, Thermo Electric
Generators (TEG) and heat/cool solid state devices based on the Seebeck
or Peltier (respectively) effects. The TEG effect is less sensitive to
temperature *range* and depends only on a temperature *gradient* and is
related to differential movement of charge-carriers in different
metals. These have very low efficiencies as well as most sources being
intrinsically low-energy density. Common examples are 12V coolers and
woodstove fans where convenience outweighs low efficiency.
https://en.wikipedia.org/wiki/Thermoelectric_effect
There is also a technology known as Thermo Photonic Generation (TPX)
which has an extra level of indirection... with a *biased* LED exposed
to thermal radiation re-emitting the energy at a frequency that can be
used by a more conventional PV cell.
https://en.wikipedia.org/wiki/Thermophotonics
There is a (roughly) 6 meter diameter solar collector near my house (on
Pojoaque Pueblo land) that was part of a proof-of-concept project
spinoff from LANL for concentrated solar *hydrogen* conversion... I
don't remember what temperatures they were achieving at the focal point,
but the "generator" on an articulating boom is probabl .5x1.5 M across
with a quartz? window and well-insulated tubes coming in/out. As I
understand it, the hydrogen-generation was effected with/through
high-temperature steam. I don't know if the working fluid is steam or
something less corrosive. 15 years abandoned, it is now quite defunct
with individual mirror segments (.5mx.5m) dangling from their bases.
An obvious problem with these very high temperature systems is that
common materials tend to be mechanically (melting) and/or chemically
(oxidizing, etc).
I don't know the practical limits on *linear* solar concentrators, but
with the sun offering up approximately 1000W/m^2 one can likely reach
the temperatures for this new device without the complications of 2D
parabolics.
As a neo-retro (mostly) low-tech DIY guy, I am a fan of low-grade energy
sources.
It won't surprise you that I have 2 huge front-surface mirrors just
waiting for someone to put them to a good use. they are roughly
1.5mx2.1m (5'x7') and are optical grade (not that this matters)
aluminized mylar stretched over a frame which happens to be closed on
the back. There are pressure-equalization holes (valves) in the frame
but in principle one could close them up and draw a vacuum and get a
very shallow concave (catenary?) shape. They only weigh about 10-15kg
and I could even deliver! I could probably throw in a 3x5 fresnel lens
if you want to make a sand-fusing 3D printer or solar forge in your
backyard? They would also be useful in a dance studio or
(narcissistic) gym environment. Free for the taking (including delivery).
FWIW I tried to contritely use only CGS/SI units here... but I
continue to reserve the right, no matter the units, to take advantage of
the intuitively (and mechanically) convenient fractional arithmetic that
comes with folding or separating things into halves, thirds, etc as well
as working with 3/4/5 triangles. I grew up *just* before calculators
and computers were common and did learn a slide-rule and acknowledge
that slide rules do not have fractional inch measures on them. I once
had a roughly 1.5 meter one (from a classroom) and one probably no
longer than 10-15cm in length (yes, I have to calculate those from my
intuitive feet and inch estimates). Neither was particularly practical.
>
> Cody Smith
>
>
> On Wed, Apr 13, 2022 at 10:43 AM Roger Critchlow <rec at elf.org> wrote:
>
> https://news.mit.edu/2022/thermal-heat-engine-0413
>
> Thermophotovoltaic, converts 1900-2400C source photons to
> electricity at >40% efficiency.
>
> -- rec --
>
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