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rotate
04-21-2011, 11:27 AM
Sometime back, I posted a question about building vacuum chamber out of plastic. (http://bbs.homeshopmachinist.net/showthread.php?t=46007). It was for a science fair project for my nephew and now that it's complete, I thought I shared the results.

The final project was built using 4" ABS drain pipe, and lots of trap cleaning fittings. The window into the chamber was made using 1/2" clear acrylic, which in retrospect was an overkill (at least for the size of the window). I was amazed how well it held vacuum. There was very little leak, even with all the holes for passing wires. I'd say that once pumped down, it would take over an hour before it lost 0.5 atm.

For those who are interested, the project was about "boiling" the water from wet laundry at low temperature (~50*C) by reducing the pressure to near vacuum. Lots of experiments were done and I was amazed to discovered that it used only 1/3 the energy of a real clothes dryer. This was a "SCIENCE FAIR PROJECT" so it was not an attempt to build a commercial solution but rather to explore through experiments the science of vaporization under varying conditions.

http://i7.photobucket.com/albums/y287/rotate85/DSC00394.jpg

http://i7.photobucket.com/albums/y287/rotate85/DSC00400.jpg

http://i7.photobucket.com/albums/y287/rotate85/DSC00396.jpg

http://i7.photobucket.com/albums/y287/rotate85/DSC00425.jpg

rotate
04-21-2011, 11:28 AM
http://i7.photobucket.com/albums/y287/rotate85/DSC00407.jpg

http://i7.photobucket.com/albums/y287/rotate85/DSC00404.jpg

Harvey Melvin Richards
04-21-2011, 11:50 AM
Nice job. Vacuum has some very interesting properties.

flathead4
04-21-2011, 12:38 PM
Cool. I'd always wanted a vacuum chamber after seeing one in a high school physics class. How are you lowering the pressure? Is there a vauum pump involved? I don't recognize the equipment on your bench.


Vacuum has some very interesting properties.

I would argue that a vacuum has no properties. The effects you see are caused by pressure. I find it funny that we have a name for something that does not exist.

Tom

lynnl
04-21-2011, 01:15 PM
Actually we have lots of names for something that doesn't exist:
none, no, null, nothing (h'mmm, they all seem to start with n), wait there's zero, void. That's all I can think of at the moment.

Tho I guess those are all concepts, rather than an entity.

Toolguy
04-21-2011, 01:38 PM
Don't forget intangibles tax. They can tax you for something that doesn't exist.

RWO
04-21-2011, 02:01 PM
FWIW, an ordinary pint glass Mason jar works pretty well. I keep one around about half full of 30 Wt oil to reimpregnate Oilite bearings after a teardown and clean of yard machinery. It is amazing to see how much air bubbles out of a bearing in the first minute or so after the pump starts.

RWO

rotate
04-21-2011, 02:15 PM
Cool. I'd always wanted a vacuum chamber after seeing one in a high school physics class. How are you lowering the pressure? Is there a vauum pump involved? I don't recognize the equipment on your bench.


There is a proper rotary vacuum pump under the table. It's good for about 10-3 torr.

BTW, I first tried using regular plumbing valves. They all leak badly. The valves in the picture are all vacuum valves.

rotate
04-21-2011, 02:18 PM
Actually we have lots of names for something that doesn't exist:
none, no, null, nothing (h'mmm, they all seem to start with n), wait there's zero, void. That's all I can think of at the moment.

Tho I guess those are all concepts, rather than an entity.

Of course they exist. They exists as a unique neuronal pattern in our brains.

I had fun bantering with my kids about what comes out of a broken tap when you turn it on. Nothing of course. When you close it, nothing keeps coming out. :D

flathead4
04-21-2011, 02:41 PM
They can tax you for something that doesn't exist.


And they can even tax you after you don't exist.

beanbag
04-21-2011, 04:14 PM
So how well does the clothes dryer work and how fast to boil all the water out? Not sure if your pump is designed to pump water vapor, though.

aboard_epsilon
04-21-2011, 04:59 PM
Nice job. Vacuum has some very interesting properties.

Yup, sure has,

I was at a car boot sale today ..

An old farmer, that i see there regularly, was carrying with him, a different sort of vacuum pump that he had found...and bought, he thought it was for an aquarium...

Then everyone breaks down into laughter around him ..when i told him what it really was ..a pxnis enlarger . :D

all the best.markj

alanganes
04-21-2011, 05:11 PM
Most all of the work the company I work for is done in vacuum chambers. My boss, who is in charge of building and maintaining all of our vacuum systems, whan asked what he does answers: "I'm an expert in nothing..."

rotate
04-21-2011, 05:39 PM
So how well does the clothes dryer work and how fast to boil all the water out? Not sure if your pump is designed to pump water vapor, though.

No the vacuum pump is shut off and the valve closed once the pressure has reached near vacuum. From that point on the only gas in the chamber will be water vapor, which is condensed by the condenser (coiled copper tube) and trapped at the bottom.

As for how well it works, if the experimental results can be scaled, the clothes should dry in 1/3 the time as conventional dryer using the same power. Another way of looking at this is that it will use 1/3 the total energy.

I think there's a real potential for this concept to be commercialized, however considering how cheap electricity is (it's 0.08/kWh here), the payback will be very long (not unlike Hybrid cars).

macona
04-21-2011, 06:17 PM
1/2" acrylic is a good size. Anything thinner might have cracked. There is a lot of pressure on that plastic and with those to through lines you have stress risers that cracks can propagate from.

When running the pump you need to watch out for water in the oil. Make sure you are using the gas ballast if you have it. It will keep the water from condensing between stages in the pump.

If I recall there is a company that makes a dryer that lowers the pressure to help drying. Of course this makes something as dead simple and near maintenance free become something that is not.

2ManyHobbies
04-21-2011, 06:21 PM
No the vacuum pump is shut off and the valve closed once the pressure has reached near vacuum. From that point on the only gas in the chamber will be water vapor, which is condensed by the condenser (coiled copper tube) and trapped at the bottom.

As for how well it works, if the experimental results can be scaled, the clothes should dry in 1/3 the time as conventional dryer using the same power. Another way of looking at this is that it will use 1/3 the total energy.
So it runs sorta like a vacuum-assisted condenser dryer? That is a neat setup.

Thought about magnetic gearing to let it tumble? It could save you the trouble of sealing a driveshaft or having a motor in there.

Yow Ling
04-21-2011, 06:34 PM
So which bit did your nephew make?

Evan
04-21-2011, 06:35 PM
Very cool project considering it depends entirely on something that sucks. :D

As for the properties of a vacuum, that depends on whether we are discussing the true vacuum or the false vacuum... Nah, I'll leave that alone. ;)

flathead4
04-21-2011, 10:52 PM
..real potential for this concept to be commercialized

I could see this being used in an industrial setting or by a laundry service but I think there would be issues in a home setting. The time to equalize the pressure so you could open the door and throw that sock you found in the washer would take some getting used to. Also, since there is no heat involved I doubt it would remove wrinkles like a convential dryer will. Any wrinkle data?

Still a pretty neat idea. I was wondering what the copper coil was for but I see you answered that question.

Tom

Evan
04-21-2011, 11:46 PM
Have you tried freeze drying any food items? Ice cream comes to mind. It actually works really well. You can also use it to freeze dry small animals like birds. It helps if they are (recently) dead first.

rotate
04-22-2011, 12:03 AM
So which bit did your nephew make?

Ah, good question. About 80% of the work was done by my nephew. I was mostly involved with design and theory. I made sure that he had his hands dirty every step of the way and understood the theory behind everything.

rotate
04-22-2011, 12:06 AM
Also, since there is no heat involved I doubt it would remove wrinkles like a convential dryer will. Any wrinkle data?


There is heat involved. The heat is provided to the sample cloth using two large power resistors (not shown). If there wasn't external heat source, the sample would become cooler and stop the boiling and the evaporation process.

As for the wrinkle, my guess is that tumbling with heated air is much better than the vacuum method.

ckelloug
04-22-2011, 04:09 AM
I left some water with some nanomaterial glop in my vacuum chamber overnight hoping to get some of the water out. With no external heat, the top surface of the water in the beaker actually froze into ice. External heat is definitely necessary as the vacuum pump removes the gas molecules with high kinetic energies causing a net outflow of heat from inside the chamber.

Black_Moons
04-22-2011, 04:43 AM
Intresting.

How about two pressurised (water?) radiators, one inside, one outside, to transfer ambiant heat into the chamber?

"New dual perpose cloths dryer and room AC!"

ckelloug
04-22-2011, 05:31 AM
In response to black moons, go one better and circulate the vacuum pump oil which is hot through the radiator in the chamber. The vacuum pump could even be designed to accomplish this without another circulating pump. Since the pump ends up hot due to friction etc as well as absorbing the heat in the oil from transferring the highest kinetic energy molecules from inside the chamber, you can use the same energy twice for a more efficient setup.

Lew Hartswick
04-22-2011, 10:57 AM
In response to black moons, go one better and circulate the vacuum pump oil which is hot through the radiator in the chamber. The vacuum pump could even be designed to accomplish this without another circulating pump. Since the pump ends up hot due to friction etc as well as absorbing the heat in the oil from transferring the highest kinetic energy molecules from inside the chamber, you can use the same energy twice for a more efficient setup.
Be careful there. It sounds like you're treading on "perpetual motion"
grounds. :-)
...lew...

flathead4
04-22-2011, 11:03 AM
How about two pressurised (water?) radiators, one inside, one outside, to transfer ambiant heat into the chamber?


That brings up another issue using this to dry clothes. A conventional dryer works mostly by convection. In a vacuum, there are little to no air molecules so you would be left with only radiation. Maybe some conduction if you hung the clothes on the radiator.

Tom

rotate
04-22-2011, 11:10 AM
That brings up another issue using this to dry clothes. A conventional dryer works mostly by convection. In a vacuum, there are little to no air molecules so you would be left with only radiation. Maybe some conduction if you hung the clothes on the radiator.


The initial attempt was to use heat lamp to heat the clothes. We were amazed to find out inefficient this process is. It's ironic that this is how the earth gets all its energy from the sun.

The power resistors which were used to heat the wet clothes had to be direct contact. Since there was little or no air, it meant that no heat was being robbed by the air which in part explains the efficiency.

macona
04-22-2011, 12:11 PM
At that point you can use an infrared lamp to supply heat. Problem with this, of course, different materials will heat better than others. Best would be a heated tumbling drum.

ckelloug
04-22-2011, 12:50 PM
Be careful there. It sounds like you're treading on "perpetual motion"
grounds. :-)
...lew...

Err. No perpetual motion. Just using energy that would be radiated to space by sending most of the energy used in removing the water vapor back into the system to keep the temperature constant. If you don't, you have a system that is constantly decreasing in temperature and needs heat lamps etc.

An ordinary dryer just creates a lot of hot air which minimally raises the vapor pressure of the water in the clothes and eventually is able to drive the clothes towards equilibrium with the humidity of the air. The vacuum dryer adjusts the pressure around the clothes which has a much greater direct effect on removing water but without effort does not provide energy to replace the heat lost by continuously removing the fastest moving water molecules in the system.

Circulating hot vacuum pump oil is just an easy way of replenishing the heat lost by the clothes as the water in them evaporates. Heat stops being lost when the clothes are dry so no perpetual motion: just physics.

Evan
04-22-2011, 01:53 PM
This idea actually does have commercial applications. It needn't be a vacuum. Lowering the pressure even a little reduces the boiling point of water considerably. If a regular dryer were constructed to pull a partial vacuum while still allowing airflow the reduced volume of air might well be made up by the ease of evaporating the water.

MichaelP
04-25-2011, 12:00 PM
Most all of the work the company I work for is done in vacuum chambers. My boss, who is in charge of building and maintaining all of our vacuum systems...
You work for Bernard Madoff or Wall Street, in general, don't you? ;)

Dawai
04-25-2011, 06:19 PM
We had a discussion on distillation of alcohol, by vacuum.. cool process... no heat required. Higher yield... Also, molasses thickening.

boslab
04-25-2011, 07:43 PM
reading the posts you may [or not!] be interested in the following, i just serviced a fisons XRF spectrometer, she was having trouble holding a good vaccuum in the secondary chamber, the modus operandi for diagnosing leaks is to use a wash bottle filles with isopropyl alcohol [propan II ol if you like]
watch the vac gauge and squirt joints with the wash bottle, when you hit the leak the vac develops nicely, for a short while, its fairly safe to plastic and such too
thought you may find that useful [it turned out to be a hard o ring BTW]
Now i get to calibrate the thing,,again
regards
mark