low tech, only -5C temp drop, ... but maybe for something?

[Canoe]

Not sure what to think of this.

From: eco-cooler design

Cites a 5C temperature drop:

• re-purposed plastic bottles installed on sheet using their own caps,
• sheet installed in a window opening (or purpose made hole) with the small openings towards the inside,
• wind blowing into the large opening compresses the airflow,
• air coming out the small opening expands, resulting in a temperature drop.

header-element-img.png

re-purpose-plastic-bottles.jpg

plastic bottle compresses air, expands for cooling.jpg

Perhaps someone can leverage what it does, using it with something else, to make something more effective?

• Providing 5C cooler air to cooling coils?
• Providing 5C cooler air to a generator's baffle box? (without messing with cooling or combustion air flow)
• Feed to a centrifugal filter so it passively filters the sand/dust before passing into the structure?
• Can they string in series for a larger temperature drop?
• ...

(An encasing structure to precool the air into a swamp-cooler? Except you're introducing all sorts of fan-pressure issues for only a 5C improvement - and then only if you get it right.)

[Popeye]

When you compress air you add energy to it and increase the temperature (Heat of Compression). https://en.wikipedia.org/wiki/Gas_compr ... emperature
This article suggests tha the air coming out of the bottle necks is cooler than the air going in. Where does heat removed in the bottle necks go?
Could it be that the perception of cooling from the increase in air velocity is caused by the chill factor? If so the total heat content of the air moving through all the bottlenecks is greater than the heat content of the air moving through an opening the same size as the wide part of the the bottle neck.
When you open your mouth wide and "puff" the slow moving air will have more moisture than the fast moving air when you blow. The 98.6 degree moisture hitting your hand will will keep your hand from radiating heat. When you stop "puffing" the moisture on your hand will vaporize and cool your hand.
You can't get something for nothing.

[Canoe]

...Where does heat removed in the bottle necks go?
If so the total heat content of the air moving through all the bottlenecks is greater than the heat content of the air moving through an opening the same size as the wide part of the the bottle neck.

ya, laws of thermal dynamics will not be violated

Their demo by blowing on hand could easily be very flawed, in that it doesn't accurately demo what's happening with the bottles. So it's not worth getting into the temp of the exhaled air vs. the hand's boundary layer vs. induced ambient flow, etc., that may be happening with their hand demo. But that doesn't mean that they're not actually observing something real with the device constructed.

As to what that is: given if it is true that when the air expands upon outlet it cools (cooler than immediately before in the neck and just before that as it's compressing), then there's the potential for some of the heat energy in the compressed air to be removed before it's released on the other side. To me it appears that potential is small if not tiny (possibly simply the transfer from the heat differential between the air compressing in the bottle vs. that of the temperature outside surrounding the bottle, hence a tiny energy transfer), that could explain why the "cooling" is minimal. Radiated? Conducted?

Be fun to run a heat pipe vertically through the compressed path to see how much heat it could remove... Might improve the device, or make a device that doesn't work, work.
Depending on where you were, you could "turbo" that and put the upper/condenser end of the heatpipe into a water bath that was cooling from evaporation.

I believe that they don't report -5C at the outlet, but that's the temperature drop inside the shelter over time.

Very suspect, but feels like it's somewhere between possible and plausible. I don't know the math enough to estimate temperatures and heat energy to see if it is plausible, or even possible.

Damn. Now I want to test it with heat-pipes.

[Skuzzy61]

Hmmm,...the only way I see this as being possible is if the plastic bottles were absorbing some of the thermal energy, in the airflow, and dissipating it over the flat sheet they are attached to and to the frame it was attached to. Some of that energy could dissipate on both sides of the sheet.

But a -5C drop? I am skeptical.

[AntiM]

Screw cooling, let's fill the bottlenecks with reeds, whistles, and kazoos.

[FIGJAM]

Just a guess, but that looks like a humid climate.

Could the compression of the humid air be causing the cooling?

[Canoe]

Hmmm,...the only way I see this as being possible is if the plastic bottles were absorbing some of the thermal energy, in the airflow, and dissipating it over the flat sheet they are attached to and to the frame it was attached to. Some of that energy could dissipate on both sides of the sheet.

• Bottle-to-sheet is where the compression is the most, so temperature diff will be the most: small area, but fastest transfer rate, at least when it starts. And the blowing wind would dissipate collected heat from the outside surface of the sheet.
• The heat can be conducting/radiating from compressed-air to plastic bottle to the air surrounding the bottle, and with the wind blowing the air around the bottle away, that air would be getting renewed to ambient, keeping a temperature differential for continued heat transfer - but how much...

I can see it, but I can't see 5C worth.
But if it does remove some heat from the air entering the interior, then over time, does a -5C interior become plausible...

As the air is compressed and raises in temperature, it should be able to hold more water molecules (before it is saturated). As the bottle starts constricting: the volume decreases, the compression increases, the temperature increases and the capacity to hold water increases.
Is there time for the more-compressed air to absorb more moisture from the air behind it in the airflow? If so, if saturated by the time it goes through the neck, then when the air expands and cools, it could be precipitating moisture.

This is starting to hurt my head, and now it's accompanied by an imaginary kazoo chorus.

[Molotov]

I think a project like this would have real art value if all the bottle necks were connected to the business ends of whoopie cushions, slide whistles, duck calls, kazoos as previously mentioned, etc. With a little tuning to harmonize the sound output, and putting the bottle board on a free swinging pivot to face the wind, you could create hours of entertainment or at least untold annoyance of the P&P camp neighborhoods.

[Skuzzy61]

The more I think about it, the more I am convinced it cannot work. The mere act of moving air over a surface creates friction and thermal energy which must be dissipated. Compress the air, and more thermal energy is created.

The cones would have to act like heat sinks without imparting any of the heat back into the stream.

[maladroit]

Here's how it works. Ingeniously engineered by the employees of a Bangladesh social media firm, the wide rims of the bottles funnel and compress Facebook likes into the necks of the bottles (and guaranteed to be crammed down our own necks from time to time as friends and relatives occasionally re-post it for years to come).

[Token]

Dem pesky laws of thermodynamics make the claims pure horseshit.

However, the whole glory-hole / pee-funnel aspect of the illustration opens up a new dimension of possibilities for effective cooling.

[GreyCoyote]

Dem pesky laws of thermodynamics make the claims pure horseshit.

SO much this.

Why are educated people even having this discussion? Res ipsa loquitor, baby!

[Canoe]

The more I think about it, the more I am convinced it cannot work. The mere act of moving air over a surface creates friction and thermal energy which must be dissipated. Compress the air, and more thermal energy is created. The cones would have to act like heat sinks without imparting any of the heat back into the stream.

At these velocities, thermal energy from friction will be minimal, and that's without considering a friction reducing boundary layer.
Minimal compression, minimal thermal increase.

And then the thing is, there are two paths to take that heat away.

• ...the blowing wind would dissipate collected heat from the outside surface of the sheet.
• The heat can be conducting/radiating from compressed-air to plastic bottle to the air surrounding the bottle, and with the wind blowing the air around the bottle away, that air would be getting renewed to ambient, keeping a temperature differential for continued heat transfer - but how much...

Is it enough to do what they claim... not likely, but... without numbers to show what is really going on, it's still in the possible/plausible camp.

And it's not a lot of compression, so not a lot of thermal energy into the air flow. If only part of that airflow has part of its thermal energy dropped through the side of the bottle, then upon expansion...

People are having this discussion because there are thermal paths and design that don't inherently violate the laws, such that without numbers to prove the final claim of -5C is impossible, the damn thing has to count as possible (possibly plausible). Which is what makes it such a very crafty device or a very very crafty "story".

Even if you look at a boundary layer on the inside of the bottle, there's how thick, how much turbulent flow, how thermally conductive - or convective within the boundary layer - as a thermal path from the compressed airflow through to the side of the bottle to the cooling refreshed ambient air on the outside of the bottle.
Arrrrrrrrrgh

Tricky b!@%!$#s.

Hats off to them, one way or the other.

[Jackass]

Build one, test it day and night, see what the results are. Seems easy enough, be your very own mythbuster. Go viral on the interwebs...
Or make one for the playa with all sorts of pneumatic and wind driven gismos added on, that would be interesting.

[GreyCoyote]

Lets make this easy.

Assume a perfect venturi with a 5:1 intake to throat ratio
Assume a perfectly oriented aperture.
Assume standard temp and pressure
Assume an air velocity of 40 mph.
Assume adiabatic compression (yeah, I know. I'm trying to throw you a bone here)
Assume normal and instantaneous non-adiabtic expansion back to STP.

My math says 0.2 F in a perfect, lossless world

Its easy to grab a coke bottle, thermocouples, and some duct tape. Hang it out your truck window and publish your results.

Insert hippie Woo Factor alert here...

[Canoe]

Damn. I want to know.
I have a thermocouple that came with a multi-meter. Not calibrated.
Can I trust that setup to "calibrate" candy thermometers to know how far each is off of the ambient temperature, then place them in appropriate parts of the airflow and rely upon the results?
Wouldn't give an accurate temperature reading, but it should give a repeatable reading, and we're after an indication of a temperature differential that is: near or far to -5C, or no-delta. Yes/no?

And I have a pair of Ranco ETC-111000-000 new in boxes, not even a power cord yet. But they only display to the nearest degree F.

Suggestions? (other than don't waste my time...)

[maladroit]

I wouldn't bother. Remember a few years ago all the blogs were fawning over some kid in Nepal who made a solar cell from human hairs.

[Popeye]

I think in fahrenheit, 5 d C is about 9 d F. On a 70 degree day put 5 of these in series and see if you can make ice.
Bet you a scotch at the most expensive bar on the Playa that you can't.

[Canoe]

sigh
in their video,

• they show the 'before' thermometer as 45C
• they show the 'after' thermometer as 35C
• they call that a reduction of 5 degrees...

temps.jpg

Note the 'before' image light: appears to be taken indoors.
Note the 'after' image light: appears to be taken outdoors.

Damn.
Intuition says this can't work (conservation of energy). GreyCoyote's numbers says it can't work. But as there's a plausible path for the removal of heat, I have to see this for myself.

[Token]

You guys are spending way too much time stuck in the weeds, fun details and whatnot.

You only need to look at the whole system; no energy is put into the system, hence there is no possibility of energy being moved from one area to another.

It is smoke and mirrors with enough pseudo-science sprinkled in to fool the casual observer.

Unless you remove heat after the gas is compressed, the gizmo cannot work as described.

Entropy Enthalpy and the end if the universe and all that.

[Canoe]

... You only need to look at the whole system; no energy is put into the system, hence there is no possibility of energy being moved from one area to another...
Unless you remove heat after the gas is compressed, the gizmo cannot work as described.
Entropy Enthalpy and the end if the universe and all that.

Exactly.
Which is why it pisses me off as there IS a path for energy removal: conducting/radiating through the side of the bottle, and it's passive (requiring no external energy to drive it), AND, the energy used to enhance that energy removal is the wind, flushing the air surrounding the outside of the bottle thereby maintaining the maximum temperature differential for the maximum possible thermal transfer rate. So there is an explainable path, and it doesn't require that we input an external main-controlled/generated/concentrated/burnt energy to drive it.

Which brings me back to:

Tricky b!@%!$#s.
Hats off to them, one way or the other.

GreyCoyote's math kills their amount of cooling claimed, unless there's something really weird taking place that we're missing (not likely). But I have a mind that is too inquiring. I know myself too well: I know I'm going to waste my time testing this, and I'm 99 44/100 % sure that I'm wasting my time, but I have to do it anyway.

[Token]

With PET bottles there is no effective energy transfer during the gas compression. Plastic insulates real nice. The heat of compression will travel down the patch of least resistance, which is the air stream and out the "cooling" end. Forced air convection will take any transitory heat event and zero it out on the other side.

Extruded aluminum with heat sink fins, lots and lots of fins ... Maybe I'll get mildly curious if there are two thermal systems, one with the Venturi cooling effect and the other independent system that uses the wind to cool the Venturi Tube.

Otherwise 100% bust.

[Canoe]

...Extruded aluminum with heat sink fins, lots and lots of fins ... Maybe I'll get mildly curious if there are two thermal systems, one with the Venturi cooling effect and the other independent system that uses the wind to cool the Venturi Tube...

Now, assuming that the outcome is the dud we expect, consider this hack to make it work:

• Heat pipe running vertically through the compressed air stream, angled to the outside where the ambient wind will cool it.
• Vertical orientation as you can use cheap heat pipes - even diy from copper - without any ribs or sintering as their orientation makes them thermal diodes.

Depending on the range of temperatures, range of wind & compressed stream velocities, there will be optimum sizes and fins to maximize the heat removed from the compressed flow.

(sigh. another rabbit-hole)

[Token]

Exactly, a second thermal loop in a heat pipe could provide the evaporative/capillary transport to isolate the energy of the wind to do work.

Figjams bucket and some ice melt is allot simpler.

[mudpuppy000]

Figjams bucket and some ice melt is allot simpler.

Yeah, plus you don't really need any extra cooling when the wind is blowing unless you're trying to keep the dust out. This doesn't really help at all with that unless you try and stick a filter on each nozzle.

[ZigZag]

I gotta say, never have I seen so much energy and analysis go into an idea that nearly everyone agrees cannot work.

Its really impressive.

I can't wait for someone to actually build this damn thing and prove once and for all that everyone is right!!!

[Jackass]

It's about as plausible as the solar cell built from human hair...

The interwebs are magical like that.

[Bless]

[maladroit]

video

Bless, that is the video from the link that was in the first post of this thread, unless I'm missing something?

Edit: Ah, I see their site is down (with a hilarious message)