# Plastic water bottle "air conditioner"- thermodynamics **URL:** \ **Category:** Factual Questions\ **Created:** [July 12, 2016, 2:02pm UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719 "2016-07-12T14:02:46Z")\ **Posts on this page:** 11\ **Page:** 3
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [July 13, 2016, 8:37pm UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719/41 "2016-07-13T20:37:58Z")
> [@BubbaDog](#): > > I agree with you that the results are bogus but I think your statement about change in state being critical for heat transfer is wrong. > > Change in state may represent the limit of the thermal process but it isn’t necessary in order to pump the heat. > > Anyone who has ever filled a scuba tank will tell you that the tank gets very hot as the air is compressed into it yet no air from the supply side nor the delivery side is liquefied. Good point … I’ve been trying to debunk the claim that the air is cooled somehow with the device in the video … and this effort is based on strictly theoretical conditions. As some posters have pointed out … friction would play a roll in all this making the air actually slightly warmer. When filling a SCUBA tank we’re going to see a hell of a lot more friction, instead of just a doubling the pressure in our bogus device, in a tank we’re increasing pressure 200 times (thereabouts). That’s a mess of air being frantically pumped through some narrow hoses. Here friction makes a profound addition of heat energy to the system. My claim of change-of-state was specific to refrigeration circuits. Indeed air makes a piss poor refrigerant, unsuitable for such a purpose and for the exact reason you’ve pointed out. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 13, 2016, 9:00pm UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719/42 "2016-07-13T21:00:50Z")
> [@watchwolf49](#): > > When filling a SCUBA tank we’re going to see a hell of a lot more friction, instead of just a doubling the pressure in our bogus device, in a tank we’re increasing pressure 200 times (thereabouts). That’s a mess of air being frantically pumped through some narrow hoses. Here friction makes a profound addition of heat energy to the system. Friction isn’t the issue. When you compress air, it gets hot because you are doing mechanical work to push against the air pressure and force it into a smaller volume. A frictionless compressor that doesn’t push the air through any hoses (just keeps it in a chamber that gets changed from large volume to small volume) will still generate hot, compressed air. This phenomenon (adiabatic heating) is why [fire pistons](https://en.wikipedia.org/wiki/Fire_piston) work. The reverse (i.e. adiabatic cooling) happens when air expands. Now the parcel of air is doing mechanical work to push away its surroundings, and this is why it cools off. Regulators on high-pressure gas cylinders can sometimes develop frost on their exterior if they are flowing a lot of gas to a low-pressure outlet. Friction doesn’t cause cooling. FWIW, compressed air is [a useful refrigerant in some circumstances.](http://www.nex-flow.com/tool_cooling.htm) ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [July 13, 2016, 9:07pm UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719/43 "2016-07-13T21:07:22Z")
> [@Machine\_Elf](#): > > Friction isn’t the issue. When you compress air, it gets hot because you are doing mechanical work to push against the air pressure and force it into a smaller volume. A frictionless compressor that doesn’t push the air through any hoses (just keeps it in a chamber that gets changed from large volume to small volume) will still generate hot, compressed air. This phenomenon (adiabatic heating) is why [fire pistons](https://en.wikipedia.org/wiki/Fire_piston) work. > > The reverse (i.e. adiabatic cooling) happens when air expands. Now the parcel of air is doing mechanical work to push away its surroundings, and this is why it cools off. Regulators on high-pressure gas cylinders can sometimes develop frost on their exterior if they are flowing a lot of gas to a low-pressure outlet. Friction doesn’t cause cooling. > > FWIW, compressed air is [a useful refrigerant in some circumstances.](http://www.nex-flow.com/tool_cooling.htm) Yeah, when you say it that way I think you’re right … thanx for the correction. ---
**Author:** ![breezman](https://avatars.discourse-cdn.com/v4/letter/b/4491bb/32.png) [@breezman](https://boards.straightdope.com/u/breezman)\ **Post date:** [July 14, 2016, 4:04am UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719/44 "2016-07-14T04:04:52Z")
Is it possible that this device works like an array of (really weak) [vortex tubes](https://en.wikipedia.org/wiki/Vortex_tube)? ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 14, 2016, 11:51am UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719/45 "2016-07-14T11:51:51Z")
> [@breezman](#): > > Is it possible that this device works like an array of (really weak) [vortex tubes](https://en.wikipedia.org/wiki/Vortex_tube)? The Wikipedia article mentions vortex tubes that operate at 100 psi and produce a temperature shift on the order of 100 degrees. The stagnation pressure available in an eco cooler is a tiny fraction of a psi, so even if it _did_ work like a vortex tube, you would only expect a comparably small temperature change. All of which is irrelevant, since the eco cooler definitely does not work like a vortex tube. The latter separates the incoming high-pressure supply air into a hot stream and a cold stream via some interesting thermophysical processes, whereas the former just has one input stream and one out put stream with no vortex involved anywhere in the process. ---
**Author:** ![Blue\_Blistering\_Barnacle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_blistering_barnacle/32/3386_2.png) [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)\ **Post date:** [July 14, 2016, 12:22pm UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719/46 "2016-07-14T12:22:13Z")
Maybe a vortex might arise spontaneously as the air moves down the funnel. If the concept is in play at all, it suggests some interesting modifications. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [July 14, 2016, 1:13pm UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719/47 "2016-07-14T13:13:41Z")
> [@Blue\_Blistering\_Barnacle](#): > > Maybe a vortex might arise spontaneously as the air moves down the funnel. > > If the concept is in play at all, it suggests some interesting modifications. I’m thinking it’s not in play, starting with compressed air, ending with the exhaust … my complaint about the eco-cooler is where does the heat energy go. With the vortex tube we have that answer, there’s both a cool air exhaust side and a hot air exhaust side to the tube. One input, two outputs … that’s not even close to the eco-cooler. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 14, 2016, 2:54pm UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719/48 "2016-07-14T14:54:44Z")
> [@Blue\_Blistering\_Barnacle](#): > > Maybe a vortex might arise spontaneously as the air moves down the funnel. > > If the concept is in play at all, it suggests some interesting modifications. A vortex is not something that arises spontaneously. [Angular momentum](https://en.wikipedia.org/wiki/Angular_momentum) is conserved; if the incoming flow is not rotating, and there are no vanes in the device that impart rotation as the flow passes through, then the exiting flow will not be rotating. Even if there were a vortex present, a flow-separating conical nozzle - one of the defining features of a vortex tube - is not present. Even if there were a flow-separating conical nozzle present - in other words, if you threw away the eco cooler and replaced it with a vortex tube - the maximum operating pressure you would expect on a windy day is a tiny fraction of a PSI, and so the maximum temperature depression you’d expect would be a tiny fraction of a degree. ---
**Author:** ![Blue\_Blistering\_Barnacle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_blistering_barnacle/32/3386_2.png) [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)\ **Post date:** [September 11, 2016, 5:07pm UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719/49 "2016-09-11T17:07:48Z")
I also pitched this to my son for science project. ---
**Author:** ![Blue\_Blistering\_Barnacle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_blistering_barnacle/32/3386_2.png) [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)\ **Post date:** [December 27, 2016, 1:37pm UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719/50 "2016-12-27T13:37:45Z")
My son did do this for his science project. It does appear that claims were probably exaggerated. He’s writing it up over Xmas break. Details at 11. ---
**Author:** ![Blue\_Blistering\_Barnacle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/blue_blistering_barnacle/32/3386_2.png) [@Blue\_Blistering\_Barnacle](https://boards.straightdope.com/u/Blue_Blistering_Barnacle)\ **Post date:** [January 9, 2017, 5:48pm UTC](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719/51 "2017-01-09T17:48:00Z")
My son submits his project today. Basically, he used a single 16 oz bottle to model the Eco-cooler and a small cardboard box to model a hut. He used a fan (crudely estimated wind speed of 3mph) and a shop-vac in blower mode (labeled as 175mph, prob much less, but still at least gale force) for wind. He also tried amplifying the system by using a 2-L bottle. He also did a test with the 16oz bottle duct-taped to the blower. He did not reproduce the hot conditions of natural use, but merely looked for temperature change. He used two electronic terrarium thermometers we had lying around. These read out to 0.1 degree F or C, but are somewhat unstable, with recorded temp varying about 0.5 degrees at constant temp. He handled this with repeated measures. Results: Fan & 16 oz bottle- no change Fan & 2L- 0.4F degree drop Blower & 16oz- 2.2F drop Blower & 2L- 1.6F drop Blower taped to 16oz- 6.8F drop Even the last (very unrealistic) setup does not equal the 9F drop purported by Eco-cooler. I think they have (hopefully unintentionally) not accounted for a ventilation effect. That is, I suspect that the “baseline” temperature shown in the video is with the window closed. [Previous page](https://boards.straightdope.com/t/plastic-water-bottle-air-conditioner-thermodynamics/759719.md?page=2)