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Thermoacoustic Cooler Means Green-Friendly Icecream
MuddyRiverDoc writes "National Public Radio aired a story describing ice cream
manufacturer Ben & Jerry's sponsored
development of a thermoacoustic refrigeration technology, which uses helium gas
subjected to ultra-loud 173 db sound to chill an ice cream cooler. The NPR interview and
pictures of the Penn State researchers who did the development is
available. There is also a brief description of the technique at the Penn State Live site and at the BBC, and an
over-cute Ben & Jerry's broadband presentation, Sounds Cool!, that
does however provide a useful diagram. Thermoacoustic refrigeration has been a focus of research
for more than a decade at Purdue
and elsewhere,
and has reportedly flown on the Space Shuttle, but this prototype is reportedly
the first that demonstrates the size, efficiency, and quiet operation that
promises successful commercial introduction. Cool Sound Industries,
Inc. is reportedly exclusively licensed for this thermoacoustic technology."
I heard this interview on the radio. Apparently the process doesn't save any energy. It doesn't use ozone depleting chemicals though. Unless it ends up being much less expensive to manufacture I doubt it will go anywhere.
"God fights on the side with the best artillery." - Napoleon, Marshal of France - speaking truth to power
Well, here's yet another link that says..
But from the outside, it's no noisier than your typical icebox. The noise generated by the Penn State fridge can only be reached when the gas is under tremendous amounts of pressure -- 10 atmospheres worth. If the gas escapes, the pressure dissipates and the sound dies down.
Inside the canister there's 198 Decibels going on... That would shatter your ear drums and make your eyes bleed (possibly) pretty quick I understand...
Outside the container all your hear is a regular humming noise at one frequency...
If you ignore the other uses of a tool, does that make the tool less useful, or you less useful?
Peltier coolers are very inefficient in terms of heat shift. Right now, the best known materials aren't much more than ~10% of Carnot (thermodynamically limited) efficiency. This means that they produce a lot of heat to move just a little. This is why your Peltier block will get pretty chilly on one side but scalding hot on the other and why CPU Peltier rigs virtually require a water block to operate. Standard phase-change coolers are much better, and these new devices (haven't read the article yet) may be even better.
They opperate at 5% efficiency, while top end refrigeration is at 45%. Instead, these guy should be looking at cool chips, which opperate at 55% efficiency.
I prefer the "u" in honour as it seems to be missing these days.
OTOH, one can't convert thermal energy back into microwaves, so the heat must get out of the food by thermal conduction, which isn't very quick in the usual food substances.
Besides the low efficiency mentioned above, there are two other problems with Peltier chips. One is cost. The second problem is that, being made of lead telluride, they aren't very environment-friendly. Lead compounds are rather toxic and do not degrade in nature.
Unfortunately, there's absolutely no way to move heat from anywhere to a warmer place. When one wants to cool something to a temperature that's lower than the ambient we are in, one must first raise the temperature of the medium we want to cool. In both "classical" refirgerators, where a compressor is used, and in these new thermoacoustic chillers, the means used to raise the temperature is by compressing a gas. The compressed gas becomes warmer than the ambient and radiates heat away, through a heat exchanger. When the gas is expanded its temperature drops. Since we let it radiate heat when it was compressed, this expansion will make it drop its temperature to a point that's lower than the ambient temperature.
Reported maximums (research-only included) in terms of Carnot efficiency:
Stirling-cycle (phase-change): ~50%
Peltier junction (solid state): ~10%
Thermoacoustics (standing wave in gas): ~40%
Using a 'speaker fridge' now would be quite wasteful in terms of efficiency, although researchers believe that they can surpass the old CFC-type compressors soon.
The question that comes to my mind, though, is why the focus on the cooling itself. For a non-emissive object like ice cream, better energy conservation may be more easily achieved through better insulation. How about investing in cheaper silica aerogel, hippies? This stuff is virtually as light as air, essentially made of sand, almost as insulative as pure vacuum, and fairly strong. Having a cooling engine without any ozone-depleting chemicals is great, but it's kind of silly if your freezers still have interior styrofoam lining.
First off, the 190db figure is the sound level INSIDE the unit. Acording to the reporter, the sound level outside the unit was no louder then a standard cooling unit.
From the description of given, the tech sounds interesting. They use a powerfull speaker to create areas of high and low preassure in the chamber. In the areas of low preassure they place tubes which run to the cold case. In the areas of high pressure they place tubes which run to an external heat exchanger to vent the waste heat.
I can definately see this technology comeing into widespread use in the future, as stricter enviromental controls continue to restrict conventional refirgerants. I also wonder how well it would work in an automotive setting, where the high level of vibration makes coolant loss more of an issue.
I always liked these - not too hard to make, but also not as effecient as other methodes. Apply compressed air, tube gets hot on one end and cold on the other.
try { do() || do_not(); } catch (JediException err) { yoda(err); }
The key difference between helium and argon is density. Helium is (obviously) lighter than air, and when released, floats to the top of the atmosphere. Presumably some evaporates into interplanetary space, given the energetic environment, there. Argon is denser than air, so it will tend to stay in the lower atmosphere.
Both are fossils of creation, but helium is also generated by alpha decay of radioactives inside the Earth. (Alpha decay particle steals two electrons from an unsuspecting nearby atom and presto, helium.)
If there were enough desire for helium, it might be possible to scoop it from the upper atmosphere. There has been talk of space planes running an oxygen liqufaction cycle for an 'air-breathing rocket'. If we can actually do that, we're halfway to mining helium. Helium would be part of the stuff that *didn't* liquify on the first part of the cycle.
The living have better things to do than to continue hating the dead.