Proposal, compressed air to make ice

[spinningmagnets]

There have been recent interesting discussions about root cellars for food storage, which naturally stay below 60F even in the summer.

I have worked a great deal with compressed air in the Navy. Though compressed air (CA) does not use a liquid/gas phase-change like Freon, I observed significant heat/cold cycles resulting in freezing temps.

As air is compressed, heat energy that was spread out becomes concentrated, and the compressor and storage tank became very hot. As the stored CA cooled over time, trapped humidity would condense and pool at the bottom of the storage tank. It was part of my job to regularly open a small drain valve to spray out the moisture.

If this moisture was allowed to accumulate, then the air was used in a sudden high outflow, iceplugs would form at 90-deg piping elbows. Ice could also be observed forming on the outsides of the dump valves as ambient humidity was suddenly cooled. The CA in question was for emergency surfacing of a submarine.

It is also useful to know that saltwater will freeze at a much lower temp than freshwater. I propose to exhaust CA through stainless steel 1/2" hydraulic tubing (easily bent) in a saltwater bath, into which aluminum trays of freshwater have been set.

A recent study uncovered that some off-grid homes have used large out-of-date  propane storage tanks (300-PSI capable) as storage for air that had been compressed by a multi-bladed high-solidity wind turbine similar to those found for water-pumping on farms, cattle ranches, and for antique steam railroads.

If the CA cylindrical storage tank were mounted vertically, you could bond aluminum angle to its sides to form vertical fins and wrap the fins to form a shroud for vertical thermosiphon flow to speed ambient air cooling.

Of course the wind compressor turbine and storage tank are mounted above ground. If the cooling coils and ice trays are underground in a heavily insulated root cellar, I believe ice blocks could be made with no electricity and low wind speeds.

If extra cooling of the stored CA was needed to achieve the desired result, pressure-dumping could be scheduled for the coolest part of the summer nights. In addition, water-dripping onto the tank, and perhaps a VAWT-driven fan (blowing ambient air through the shroud) could further cool the tank if needed.

I believe it would be possible to chill the saltwater bath to 20F and for the exhausting air to further cool the airspace by purging air that was warmed by adding ambient-temp foods to the space.

Just an idea, probably very inefficient, but could be easily home-made. I would appreciate any suggestions for improvements or pointing out significant flaws.

   

[Phssthpok]

I had a similar brain-fart a few years back for general cooling (not ice making) by keeping the CA under pressure until it reached a (new) automotive radiator (or turbo intercooler) where it would expand thereby absorbing heat. The 'dumped' air would then circulate through the exhaust side of an automotive 'turbocharger' unit (and then outside) with the compressor side replaced by a bladed fan to circulate ambient air in the root cellar through the radiator.

My scheme relied upon a water wheel connected to a small a small mechanical compressor, and a pressure relief valve system to build and maintain a steady flow of compressed air through the system. A side benefit of this would be the ability to pre-chill the CA by running the line through the creek for a distance before it reached the root cellar.

[spinningmagnets]

Yes, the colder the stored CA tank when you start, the colder it would be after pressure is released.

I hadn't thought of a waterwheel to compress the air. To generate electricity, many have posted it is best to have high head, and a high-velocity jet operating a Pelton/Turgo/ or flowing through an enclosed turbine (similar in shape to a turbocharger). but people with a flat creek often don't use it for anything.

Enthusiasts with nearly flat land and steady waterflow could use a water-wheel to compress air, and a small auxiliary pump attached to the waterwheel could flow water to cool the CA tank. Great idea, thanks!

[willib]

Hot & Cold

One side gets cold the other gets hot, as compressed air goes through it.

It was around 1980 that i heard of a device that produced hot air out one side , and cold air out the other , with compressed air going in the center.I think it had to do with the shape of the cavity .

I just searched , and found it is called a vortex tube.

http://www.airtxinternational.com/how_vortex_tubes_work.php

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[spinningmagnets]

Thanks willib! I have never heard of this before. Great to have that reference in this thread. Its so simple (and I assume cheap, reliable, and long-lasting) I will be looking at this some more.

I'm sure there will be several situations where it will be useful. In fact, the more I think about it, this is probably exactly what a device that makes ice from compressed air probably needs to get the best performance from the smallest amount of compressed air...

[Phssthpok]

To KISS (Keep It Stupidly Simple), you wouldn't even need an aux. pump to circulate water to chill the tank. Just make sure the tank is shaded (no solar gain) and the input and output lines run for some distance (say 10 feet or so) in the flowing creek before making their way to either the tank or the 'cool room' (or both). In reality, since the idea is to have a pressure relief valve set at the end of the output line (as close to the expansion unit as possible), once the system is up to operating pressure, you wouldn't even need a tank since it's designed to work constantly, not in a 'build pressure and dump' mode. The whole thing would pump cold air into the room 24/7 so long as the creek flowed at an adequate rate.

Also, to clarify the design somewhat; the reason for utilizing the turbo unit is to drive the circulating fan without using any electrical power, or adding ANY heat from an  electrically driven motor (however minor it might be).

[scottsAI]

Spinningmagnets,

Such a system can be made to work, better with a few improvements.

ICE can store the energy better than the compressed air in a tank.

144BTU/lb of energy absorbed when melting, make the ICE as you can then store it.

Get rid of the tank.

Is there an outbuilding by this storage facility?

Compressed air produces lots of heat, the heat can be used for hot water and heat the building. Excess heat then goes in the river if one handy. Or Air to Air heat exchanger outside.

As stated cooler the air is after compressed the better.

Next improvement Exhaust Decompresser (ED)(turbine / piston) to extract the energy from compressed air, provides two benefits, the energy produced by the ED, and reducing the energy in the compressed air. The ED can be on the same shaft as the main compressor reducing the energy needed to run the main compressor. The energy recovery will be in the 30 to 50% range.

Air Pressure is potential energy, releasing the pressurized air through an orifice it becomes kinetic energy, which is heat!

Cryogenic systems work the same way. They use an exhaust turbine to extract as much energy as possible to get to 4K temperatures. Very high pressures... 4500psi.

Have fun,

Scott Beversdorf.

[stop4stuff]

I remember a TV programme several years ago on UK TV where they used a (Hilsch) vortex tube to simultainiously cool a fridge and heat living space. The air was supplied by an adapted 2 cylinder motorcycle engine (600cc iirc), the engine (as a compressor) was run from a hydro source. I made a vortex tube with simple copper plumbing fittings, with air supplied from a high speed fan... it worked, albeit it very inefficiently.

[spinningmagnets]

stop4stuff, I must confess I still haven't figured out how a vortex tube works, but I believe it does! I now think this would add a major improvement to the concept.

Most enthusiasts can use a solar-PV system, some are allowed to have a 60' tower for a wind-turbine, a lucky few have a useful hydro resource. This concept has a very limited user profile, but I hope worth discussing.

Low winds that are usually wasted because they are too low for serious electrical generation. Plus the desire to avoid running generator to cool down a conventional freezer in an off-grid home...

A machine could be made to cycle automatically and keep salt-water bath very cold. I'm now thinking ice molds should be shape of a large picture book, but only as thick as a finger.

Vortex tube...there is only so much heat energy in a chunk of air. Initial concept is based on compress air, cool the CA storage down to ambient air or creek temps, then release air. Expanded air is guaranteed to be significantly colder.

If cool CA released through a vortex tube makes hot air out one side (exhausted outside of root-cellar), then The cool end MUST be cooler than it would have been by just expanding through a regular tube run (coiled in salt-water bath)

3,000 PSI guaranteed to make ice (submarine) but can it be done with 200 PSI? (generated without electricity by wind or water) Ultimate success would be making ice in the summer, but even if this would only work 8 months a year, it could be very useful to some.

[stop4stuff]

the vortex tube works by the very nature of hot gas moving faster than cold gas... take a look at the diagram in willib's link... within the tube, the hot air on the outside (moving faster) exits the tube, the cold air in the center (moving slower) is bounced back to the other end. The votex tube i made had a vacuum cleaner fan to provide the air pressure... the cold end was noticably cold, the hot end had hot air coming out.

Liquid propane is stored in cylinders at under 200psi, & normal useage (low pressure decompression) can cause ice to form on the outside of the gas bottle.

I found this paper earlier on the feasability study of using vortex tube refridgeration systems in developing countries... it includes some useful calculations & information about the requirements for using votex tubes.

http://www.dissigno.com/downloads/Vortex%20Tube%20White%20Paper.pdf (~554 kB)

[willib]

Did ya'll see the wikipedia report on the vortex tube? they say it can produce cryogenic temps when cascaded , how cool is that?

so if the cold output of one goes the input of another and the cold output of the second goes to the input of the third, then the cold output of the third should be really really cold.

This cold be something if you are getting all your compressed air from a windmill .

a while back we were talking about using a windmill to compress air , i wonder if anyone has tried it yet ?

[stop4stuff]

Yep, the cascade was an interesting concept, the efficiency would be horribly low unless the hot air coming off could be utilised.

I found a patent for an evaporative cooling system that includes a vortex tube... linky

something to consider...

air is a gas...

gases can be considered to have similar properties to fluids...

water is a fluid...

Could a vortex tube using water flow create a 'cold end' & 'hot end'?

[Kwazai]

interesting subject.
Vortex tube looks like a pulse jet and both rijke and sondhauss tubes come to mind.

The meteorological theory( one of em) for hail stones is water droplets caught in a dry 150mph updraft. convective cooling. probably be huge (over 32ft long(tall?)-terminal velocity for quantum zero level energy particles-(one molecule drop size)) to work well or cascaded. ---extreme evaporative cooling with Re turbulent.

sondhauss tube cooling and heating is thermoacoustic (turbulent Re -resonant (rijke sound ?)). pulsejets flows are similar except mach speeds(resonance). The vortex tube on youtube has the inlet at about 1/4 to 1/3 (rijke best resonance). other designs have cool and hot on one end (closer to sondhauss resonant cooling). The tangential velocity flow pattern(tesla) puts lower density warm to outside and higher density cooler to the center thermally, while resonance causes pressure fluctuations. does water form inside the vortex tube?
 
an ordinary air hose with open end smaller fitting will condense water drops (no filter/drier) and cool the air marginally by removing some heat with the water condensation associated with the dew point pressure drop at the nozzle(same for 90 elbows..).

-an evaporative cooler fed cool 'dry' air might come close.

-maybe making ice by taking the cool dry vortex tube exhaust and a print head from an inkjet printer to 'blast' tiny droplets onto an insulated 'ice collector'.
 
-maybe use the compressed 'dry' air evaporative cooler to cool the 'blast' even further before 'dripping'(blasting?) ice chips onto the 'ice collector'.

Random thoughts- food for thought.
L8r
Mike

[GreatBallofFire]

I have worked a great deal with compressed air in the Navy. Though compressed air (CA) does not use a liquid/gas phase-change like Freon, I observed significant heat/cold cycles resulting in freezing temps.


Just an idea, probably very inefficient, but could be easily home-made. I would appreciate any suggestions for improvements or pointing out significant flaws.
   

Expanding compressed air can definitely be used for cooling or to generate ice, however to keep the efficiency high it should be a byproduct of the expansion and not the direct motive otherwise there are better ways.

Vortex tubes absolutely work but have really really low effective efficiencies so they are normally used with low pressure "waste" compressed air rather than a purpose built design, but the concept does work.

-Mark

[bob g]

back in i believe '75 or early '76, popular mechanic's or popular science magazine had a shop project illustrating the vortex tube made from common components.

i built one and tested it, it was made from a piece of 5/16" brake tubing, a 1" cube of mild steel, a small machine  screw #10 iirc and a bit of brass rod.

the thing would freeze your fingers on the one end, and sure as snot blister your fingers on the other end! it would blow bits of ice condensed from water vapor in the air supply, and you could easily see smoke coming off the oils that were on the hot end from my greasy fingers and manufacture. 

i think given a source of free air, i could have easily chilled a six pack of beer quite easily with a small styrofoam cooler.

on the subject of compressed air, yes you will make a lot of heat in compression, and the losses mount when the tank cools, however

compress at night when the temperature is lowest, paint the tank flat black and leave it in the sun, harvest it when hot... let the sun provide for some of what is lost.

the sun will certainly heat a flat black tank to a quite high temperature, maybe not recovering all of the pumping loss heat from the compressor but my bet is it would recover have of the lost heat and therefore improve efficiency.

bob g

[GreatBallofFire]

on the subject of compressed air, yes you will make a lot of heat in compression, and the losses mount when the tank cools, however

compress at night when the temperature is lowest, paint the tank flat black and leave it in the sun, harvest it when hot... let the sun provide for some of what is lost.

the sun will certainly heat a flat black tank to a quite high temperature, maybe not recovering all of the pumping loss heat from the compressor but my bet is it would recover have of the lost heat and therefore improve efficiency.

bob g

Bob, there are ways to compress air closer to the isothermal line than what is common today. Compressed air is often viewed as a necessary evil for manufacturing or production and reliability drives the market as it should for those particular applications. There have been great improvements made with large rotary screw compressors but there are some major limitations to those designs including cost, size and most importantly, they demand close to 100% duty cycle.

I don't want to be spamming links into a post especially since I just joined this forum, but if you click on the website listed under my username there is a page that talks about compressing air efficiently.

I agree completely that using thermal energy from the sun can help offset some compression losses.

-Mark

[dnix71]

For a vortex tube to make ice properly it needs to be at least 2 stage. The first stage dries the air almost to the point of freezing.

Otherwise in a humid climate like south Florida, you will ice up the cold side in a hurry.

The energy problem with a vortex tube is that you need compressed air to begin with. Compressing air is very energy intensive and makes lots of waste heat. It you lived in a cold climate and could use the low grade heat for something, or had a parallel industrial process that required low grade heat, then co-gen might pay.

http://chemistry.proteincrystallography.org/article9.html You also need to be careful at cryogenic temps since O2 and N can be separated by their different boiling points. If your rig concentrated O2 in places the fire factor and corrosion factors would need to be considered. I think the people who fraction air for a living simply brute force compress dry filtered air to a liquid, then fraction it.

[GreatBallofFire]

The energy problem with a vortex tube is that you need compressed air to begin with. Compressing air is very energy intensive and makes lots of waste heat. It you lived in a cold climate and could use the low grade heat for something, or had a parallel industrial process that required low grade heat, then co-gen might pay.

I don't wont to sound like a bad broken record. Yes, most of compressed air is generated using very energy intensive methods that also generates a lot of waste heat. However, there are other ways to compress air closer to the isothermal level, it's just not very common now days. Reliability still reigns king for compressed air designs and it should, but there are other methods of compressing air without so much waste heat.

-Mark

[Bruce S]

 Reliability still reigns king for compressed air designs and it should, but there are other methods of compressing air without so much waste heat.

-Mark

Care to expound on those a little deeper :-)?
 

[GreatBallofFire]

 Reliability still reigns king for compressed air designs and it should, but there are other methods of compressing air without so much waste heat.

-Mark

Care to expound on those a little deeper :-)?

Bruce, most air compressors are expected to be plugged in and then run for years with only modest maintenance required. Because of this most compressor are reciprocating designs that happen to have some of the worst total efficiencies of any compressor. The newer large rotary screw designs are definitely an improvement, but they usually have to be run close to full duty cycle to be considered "efficient." The rotary screws are also expensive and are usually only available for larger outputs.

However, there is an old isothermal air compressor design that was used with great success in the mining industry. I don't wont to spam this thread with links, but if you were to venture over to http://mac1enterprises.com/efficient-air-compressor/ there is some background information. Now, the older design is not very practical, but it shows some amazing results including: 50-80% total efficiency, compressed air exited very close to ambient temperature (isothermal), and compressed air also was dryer than the ambient air (no external dryer required). Reciprocating compressor designs could only dream of those results.

A modern version of the older isothermal compressor is under development right now with the goal to bring those same amazing results to a current design that is a little more practical.

-Mark 

[Frank S]

I knew a guy once who had conducted  experimentation with cooling air  by first compressing it then using a vortex or venturi the air was exhausted via a nozzle in the center of the venturi drawing ambiant air through it it had good cooling effects however the compressor could only supply a limited amount of air making it impractical he even tried hooking the exhaust from an old Kirby vacuum cleaner to the intake of the compressor . this effectively doubled or more the output of the compressor but still used far more energy than the Smokiy Unick thing that was not much more than a rotary vane  compressor some ducts and a heat ex-changer  I remember reading something about it along about the time the change over to Freon 134a was taking effect but I don't recall much more

[Bruce S]

Mark;
Yep, easy stuff to understand. I thought you were implying something newer.

One individual who was both highly intelligent and became a close personal family friend Pepa (RIP) who used to post here; had actually built an 8 foot tall Savonius type mill that had a piston type compressor he got from an old Semi. I'll try to find an old pic i took of him standing next to it.
His was mounted so the mill being a good drag type would turn the pulley compressing the air into air tanks he had in both series and parallel , so he could run these types of experiments.
His idea was to pump the air slowly, continuously, with a one-way check valve and pressure regulator at the far end to test Venturi valve cooling so his sons and son-in-laws could quick cool their beer :-).

Here's Pepa with the "helper" wing idea he got from Windstuff Ed.
I have more pics, just not here at work.

Scroll compressors; Are pretty easy to understand IF you have worked around superchargers.

AS a GM, I am supposed to kill links until you are up over 50 posts, and since the link DOES go to your website AND you are pushing your book on there; I really should remove the link.
BUT since it's not an overly spammy link I'll leave it as is for now as an informational link, BUT if I get one complaint I'll remove the link.
Let's keep the external link to a minimum please 
Bruce S

[JW]

Hi Bruce, I noticed guests could not see attachments in this section, from your post here. I corrected it so attached images will now be displayed to guests. I think this was caused by the merge. When I spot this type of thing I go ahead and fix it. Just wanted to let you know.

JW

[Bruce S]

JW;
I think it was OE  .
At work if a call comes in, I have to either post what I have or let it ride hoping I don't need to jump from one server to another.
ZenApps is great but jumping into and out of different ones can be a pain.
Thanks
Bruce S

[GreatBallofFire]

His idea was to pump the air slowly, continuously, with a one-way check valve and pressure regulator at the far end to test Venturi valve cooling so his sons and son-in-laws could quick cool their beer :-).

Let's keep the external link to a minimum please 

Sounds like his priorities were in the proper order.

I didn't want to post a link and I didn't want to write a full page response either, so I took a chance on the link. If you need to remove the link, I understand completely.

Interest in compressed air has had a bit of a resurgence since everyone is desperately trying to make intermittent sources not so intermittent.

-Mark