B How can we get clothes out of a vacuum chamber without condensing water on them?

[stevendaryl]

I've had the thought for years that it should be possible to dry damp clothes instantly (or almost instantly): You place them into an airtight container, then pump all the air out. In the vacuum, the boiling point of water drops to room temperature, so the water would all boil away, leaving perfectly dry clothes.

The only problem is that now the vacuum chamber is full of water vapor. If you open the door to the chamber to get your clothes out, the vapor would condense again, getting your clothes wet all over.

It's a kooky idea, but I'm just wondering if anybody has a bright idea for getting the clothes out of the vacuum chamber without water condensing on them? If the idea makes a million dollars, I'll split the royalties with you.

 

[Tom MS]

It's a kooky idea, but I'm just wondering if anybody has a bright idea for getting the clothes out of the vacuum chamber without water condensing on them? If the idea makes a million dollars, I'll split the royalties with you.

I suppose if you dropped the clothes into a separate airtight chamber below the original chamber and then separated the two before pushing the clothes out, it could remove most of the water.

Of course, if any pockets of water vapor were in the clothes, that would pose a problem, so knocking the clothes around inside the first chamber might help.

 

[sophiecentaur]

Doesn't sound daft to me. You would have been pumping out the water vapour into the atmosphere during the evacuation process so most of it would have gone. Condensation of the remainder would take time and the clothes could be blown by a fan when they're taken out.
It's an added complication but nowadays you can get tumble dryers with a heat exchanger / refrigeration drying system, which also has a pump. Though with that system the chamber doesn't need to be so strong.
See you later, outside the bank!

 

[Andy Resnick]

I've had the thought for years that it should be possible to dry damp clothes instantly (or almost instantly): You place them into an airtight container, then pump all the air out. In the vacuum, the boiling point of water drops to room temperature, so the water would all boil away, leaving perfectly dry clothes.

Perhaps you've heard of freeze-drying?
https://en.wikipedia.org/wiki/Freeze-drying

 

[stevendaryl]

Perhaps you've heard of freeze-drying?
https://en.wikipedia.org/wiki/Freeze-drying

Hmm. Why is it necessary to freeze food first? As opposed to just evacuating it to get rid of the moisture?

 

[jbriggs444]

Hmm. Why is it necessary to freeze food first? As opposed to just evacuating it to get rid of the moisture?

The Wiki article gives some reasons.

"
Freeze-drying also causes less damage to the substance than other dehydration methods using higher temperatures. Freeze-drying does not usually cause shrinkage or toughening of the material being dried. In addition, flavours, smells and nutritional content generally remain unchanged, making the process popular for preserving food. However, water is not the only chemical capable of sublimation, and the loss of other volatile compounds such as acetic acid (vinegar) and alcohols can yield undesirable results.

Freeze-dried products can be rehydrated (reconstituted) much more quickly and easily because the process leaves microscopic pores. The pores are created by the ice crystals that sublimate, leaving gaps or pores in their place. This is especially important when it comes to pharmaceutical uses. Freeze-drying can also be used to increase the shelf life of some pharmaceuticals for many years.

 

[russ_watters]

Note that the vacuum doesn't eliminate the problem of needing to apply heat to evaporate/boil the water. Perhaps you could blast the clothes with microwaves while running the vacuum pump?

 

[Greg Bernhardt]

It's a kooky idea, but I'm just wondering if anybody has a bright idea for getting the clothes out of the vacuum chamber without water condensing on them? If the idea makes a million dollars, I'll split the royalties with you.

Better patent it fast.

 

[jbriggs444]

How about prepping the clothes by rinsing in ethanol? That would displace a good portion of the water and evaporate more readily. Crystal formation is the enemy of quick drying. Ethanol would resist crystalization under the temperature loss that would tend to accompany evaporation.

 

[TeethWhitener]

The only problem is that now the vacuum chamber is full of water vapor. If you open the door to the chamber to get your clothes out, the vapor would condense again, getting your clothes wet all over.

This isn't the only problem. As @sophiecentaur pointed out, this isn't even a problem. Your main problem will be constructing a vacuum chamber that 1) is large enough to accommodate a standard dryer load, 2) strong enough to stand up to the forces on the walls of the chamber, and 3) light enough that you don't need a crane and floor reinforcements to install it in an upstairs laundry room. The three of these conditions together might be tricky.

Aside from that, it's not a bad idea. You won't need to pull a very high vacuum, but it probably won't be as fast as you envision (as anyone who has tried to boil off solvent under vacuum can tell you). There's still quite a bit of water even in clothes that have been wrung out, but it's spread out over a large surface area, so that helps. The water will cool as it evaporates, meaning the evaporation rate will slow as the clothes get drier. The other issue is that water hydrates many types of fiber (cotton in particular), and dehydrating them completely might give you really bad wrinkles (this is why most clothes irons have a built-in steamer function).

The most expeditious way to do this might be to combine a tumbler and optional heating with a low vacuum (say 0.5 atm). But then the question becomes: how much better is this than what we have now, and would people be willing to pay for the difference. Dryers are pretty cheap, and adding a pump might increase their cost by $100 USD or more, especially if you want to use an oil-free pump (probably a necessity since I doubt anyone wants to take their dryer to Jiffy Lube for an oil change).

 

[Andy Resnick]

How about prepping the clothes by rinsing in ethanol? That would displace a good portion of the water and evaporate more readily. Crystal formation is the enemy of quick drying. Ethanol would resist crystalization under the temperature loss that would tend to accompany evaporation.

Ethanol is for drinking!

 

[Khashishi]

Cool but impractical. If you look at the vapor pressure of water, it rises quite quickly with temperature.
If you drop the pressure to <~2 kPA, you can boil water at room temperature, but the temperature of the clothes will drop quickly so you need to drop the pressure further. You'll probably drop below freezing and have to sublimate the water out of the clothes. But this is pretty slow.

If you heat the clothes, you could make it a LOT faster, but it's hard to heat things evenly without flowing air. You'll probably end up burning the side you heat while the other side remains frozen.

 

[OmCheeto]

I've had the thought for years that it should be possible to dry damp clothes instantly (or almost instantly): You place them into an airtight container, then pump all the air out. In the vacuum, the boiling point of water drops to room temperature, so the water would all boil away, leaving perfectly dry clothes.

The only problem is that now the vacuum chamber is full of water vapor. If you open the door to the chamber to get your clothes out, the vapor would condense again, getting your clothes wet all over.

It's a kooky idea, but I'm just wondering if anybody has a bright idea for getting the clothes out of the vacuum chamber without water condensing on them? If the idea makes a million dollars, I'll split the royalties with you.

I had the same idea also.
I just made one a few minutes ago.
It didn't work.

I will work on this some more.

Here are some numbers I came up with, to think about.

vacuum dryer
                         value     units
water vapor density      0.804     grams/liter
dirty dry dish towel     0.08      kg
dirty wet dish towel     0.21      kg
moisture                 0.13      kg
moisture                 130       grams
evacuated water vapor    162       liters

 

[Vanadium 50]

A dryer has two possible outputs (apart from dry clothes) - water vapor or liquid water. If it's water vapor, somewhere you need to provide the latent heat of vaporization. If it's liquid water, you don't, but you are also going to a much lower entropy state, and that means you need a heat engine, especially if you want to do it quickly. These constrain what can be done by pumping only on the surrounding air.

 

[jim hardy]

Post #12 states the problem.
Water under vacuum cools down to its saturation temperature, aka "dewpoint" .
Some Navy submarines use that phenomenon to chill water for their airconditioning system, relieving the need for a pressurized Freon system that you don't want leaking into a sealed submarine hull full of people.
I've been told by ex -sailors it can freeze the chilled water tank solid.

So you might wind up with clothes frozen in ice.

I've daydreamed for years about using that principle for a "solar air conditioning booster".
Solar collectors on the roof make steam to run a vacuum pump.
Evaporating a 55 gallon drum of water over the course of a day makes about a ton of refrigeration. Circulate that chilled water through a heat exchanger in the central unit's return air plenum.
Should be good for a few bucks a day on the electric bill.
Water is the working fluid so it's only practical in the sunbelt.

Ahhh, 'tis a fine madness !

 

[gjonesy]

Could you install a condenser coil in the vacuum chamber, perhaps separated by a thick perforated metal baffle with the condenser at the opposite end. Keeping the coolant circulating through the camber totally isolated from the vacuum process, perhaps pulling the moisture away from the clothing?

 

[OmCheeto]

This isn't looking good.
Though I haven't looked at all the options, yet.

Anyways, I looked at an oil free vacuum pump of reasonable price($480), and saw that it had a capacity of 23 liters/min. [ref]

From that, I deduced that at 23 liter/min, it could evacuate the water vapor from a dirty wet dish towel in about 7 minutes.
Interpolating from some disgustingly filthy things I have lying around the house, 2.82 kg, which looks to be about 1/2 of a dryer load, I came up with an evacuation time of 4.1 hours.

Could you install a condenser coil in the vacuum chamber, perhaps separated by a thick perforated metal baffle with the condenser at the opposite end. Keeping the coolant circulating through the camber totally isolated from the vacuum process, perhaps pulling the moisture away from the clothing?

I guess it's too late to say; "Don't even get me started..."

ps. Fun thought experiment.

pps. More engineering/practical problems to consider:
1. My blue jeans all have metal zippers. Can you microwave a pair of blue jeans without sparks flying everywhere? (not willing to do this experiment)
2. My ex-roommate from hell used to turn up the dryer setting from low to high, when he decided that my clothes drying operation was going to impede his clothes drying operation. He ruined all of the elastic in my underwear, in a matter of months. ie, there are practical upper thermal limits to this problem.
3. It's been my experience, that when transferring a thought experiment into an actual experiment, 10 other problems pop up.

 

[Salvador]

I think some of you already touched on this issue and let me just repeat it once more.Something so common and consumer intended as a dryer must be affordable and also small enough and light enough for people to actually want to use it , it just doesn't seem a vacuum chamber for this purpose could fulfill all of those critical points needed for civilian mass production to be beneficial to make a business out of it.

sometimes in the summer I throw my t shirts on the rope and their done in like 30 mins with just sunlight and I assume a decent dryer does the job faster at any time of years indoors so wheres the problem that we are trying to solve? the time it takes to do it I assume.

 

[sophiecentaur]

I've daydreamed for years about using that principle for a "solar air conditioning booster".

In lieu of an air conditioner, my firm bought us a 'swamp cooler' It was basically a straw bale, standing in water, with a fan blowing over it and into the room. It was totally hopeless on a hot, humid day in the UK. I do believe that they work very well in very dry climates where the increase in humidity can actually be welcomed by room occupants and the temperature is 'significantly' lower than without it.

 

[TeethWhitener]

I think some of you already touched on this issue and let me just repeat it once more.Something so common and consumer intended as a dryer must be affordable and also small enough and light enough for people to actually want to use it , it just doesn't seem a vacuum chamber for this purpose could fulfill all of those critical points needed for civilian mass production to be beneficial to make a business out of it.

sometimes in the summer I throw my t shirts on the rope and their done in like 30 mins with just sunlight and I assume a decent dryer does the job faster at any time of years indoors so wheres the problem that we are trying to solve? the time it takes to do it I assume.

The idea (broadly: a faster dryer, agnostic to how exactly that's accomplished) isn't necessarily completely without merit. A faster dryer could certainly have niche applications where high throughput is desired: hotels/hospitals, where they have to wash enormous amounts of linens, come to mind. Laundromats might also be good candidates, where the proprietor has a monetary incentive (shorter dryer cycles means more customers per hour) and where patrons might pay a little more for the convenience of getting in and out faster. But I doubt it'll stick in residential applications, where getting a lot of laundry done quickly simply isn't a big priority.

 

[mfb]

Temperature is a huge problem. Let's take @OmCheeto's dirty towel (I found a towel the same mass, and could reproduce the numbers):

dirty dry dish towel     0.08      kg
dirty wet dish towel     0.21      kg

We have 130 grams of water. It will start to freeze as soon as we lower the temperature by 20 K. That is sufficient to evaporate ~1/25 of the total mass, or about 10 grams. We get roughly 20-30 grams more to evaporate before all the water is frozen. Doesn't work.

We can start by heating the towel, but not enough to get rid of the whole water by evaporation without freezing some. Multiple vacuum cycles with hot air in between could work, but that doesn't sound efficient.
A pressure below atmospheric pressure, but sufficient to still deliver heat all the time?

I'm not even sure if evaporation at room temperature and vacuum can beat evaporation at dryer temperatures and atmospheric pressure.

 

[CynicusRex]

The problem is solved when you don't wash your clothes.

 

[TeethWhitener]

I'm not even sure if evaporation at room temperature and vacuum can beat evaporation at dryer temperatures and atmospheric pressure.

For the delicate cycle, dryer temperature is room temperature (or is only slightly above RT). It's just that, in that case, the partial pressure of water is presumably lower in the air being blown through the system than the vapor pressure of water at room temperature. So functionally, it's the same as pulling a vacuum on the system. In either case, it's the (partial) pressure difference that drives evaporation. The big difference is that in the non-vacuum case, you continually replenish the system with room temperature air, so the whole thing is roughly isothermal. In the vacuum case, we have the problem of evaporative cooling as many commenters have pointed out.

 

[Keith_McClary]

What do they do on the Space Station?

 

[Buckleymanor]

I think some of you already touched on this issue and let me just repeat it once more.Something so common and consumer intended as a dryer must be affordable and also small enough and light enough for people to actually want to use it , it just doesn't seem a vacuum chamber for this purpose could fulfill all of those critical points needed for civilian mass production to be beneficial to make a business out of it.

sometimes in the summer I throw my t shirts on the rope and their done in like 30 mins with just sunlight and I assume a decent dryer does the job faster at any time of years indoors so wheres the problem that we are trying to solve? the time it takes to do it I assume.

You need to think outside the box or in this case the inside.The standard vacuum chamber is of a sturdy strong construction using dense heavy materials.
For the consumer intended market it could be flexible lightweight material like heavy gauge PVC.
Pop your wet clothes in the PVC bag seal it and suck out all the air and water the flexible properties has the added advantage of compressing the clothes to enable most of the water to be squeezed out.

 

[OmCheeto]

The problem is solved when you don't wash your clothes.

ummm... Not everyone walks around with cotton wads and chopsticks stuck up their nose...

 

[Jeff Rosenbury]

I like the idea of lowering the pressure to lower the boiling point. There is a lot of low quality "waste" heat in the world which could be used for drying if the boiling temperature were reduced. It would also reduce wear on the clothes.

1/10^th atmosphere seems to be about 45ºC. Using a tumbling, warmed metal cage with a cooler outside wall to precipitate the water might help.

Microwaves are certainly an option as well. I don't think enough is known about microwave absorption in ice to naively pick a frequency, but there's a good chance the waves could be tuned to go after forming ice crystals rather than liquid water. (The data I've seen vary enough that I wouldn't be confident at odd temperatures and pressures without doing further research.)

I've not worked enough with low pressures to know how expensive such a setup would be. Seals would be a problem area, but the main chamber doesn't seem like it would be that much more expensive than a traditional, metal clothes dryer.

But a high air volume, low pressure dryer could theoretically outperform traditional methods. Industrial scale machines for large hotels etc. could use a continuous rather than batch run. This would save on capital costs of linen, actual linen costs, energy costs, and labor costs.

 

[OmCheeto]

What do they do on the Space Station?

They, um, apparently, don't do laundry.

There's No Laundry in Space, So NASA is Trying to Make Clothes That Don't Get Smelly
There is no washer or dryer on board the International Space Station; no cosmic laundromat waiting to take astronauts' quarters each Saturday morning. So when astronauts are done wearing their clothes, they throw them out. They pack their soiled undies into an old spaceship and shoot it into the Earth's atmosphere where it burns up into dust.

Peculiar. But given that they are all rocket scientists, there's probably a good reason for that.

 

[Jeff Rosenbury]

They, um, apparently, don't do laundry.
Peculiar. But given that they are all rocket scientists, there's probably a good reason for that.

No, you can't change your underwear until the next spaceship goes offline in 2019. No requests for reconsideration will be accepted.

 

[Vanadium 50]

"This is Mission Control. We have some good news and some bad news. The good news is we get to change underwear today. The bad news is Smith will change with Jones, Lee will change with Johnson..."

 

[houlahound]

Keep refining your ideas and you will eventually have a standard off the shelf clothes dryer.

 

[Keith_McClary]

They, um, apparently, don't do laundry.

But:
"Even though there's no laundry facility on the Station, Bowersox even figured out a way to wash his shorts using a plastic bag."
Then he could hang them out on the Canadarm while he's spacewalking.

 

[vortextor]

I've had the thought for years that it should be possible to dry damp clothes instantly (or almost instantly): You place them into an airtight container, then pump all the air out. In the vacuum, the boiling point of water drops to room temperature, so the water would all boil away, leaving perfectly dry clothes.

The only problem is that now the vacuum chamber is full of water vapor. If you open the door to the chamber to get your clothes out, the vapor would condense again, getting your clothes wet all over.

It's a kooky idea, but I'm just wondering if anybody has a bright idea for getting the clothes out of the vacuum chamber without water condensing on them? If the idea makes a million dollars, I'll split the royalties with you.

You may put a chilled wall inside of chamber, at -50C. At 10 Pa, this value of temperature is below of the triple point of water,
so you can stop the vacuum pump and the water vapors will be collected by the chilled wall.

 

[Nidum]

Curved non contact black body radiant heating panels .

Moderately powerful suck down which reduces chamber pressure to about 90% atmospheric but not to full vacuum .

Constant small inflow of atmospheric air .

Tumbling action .

Energy recovery system .

 

[sophiecentaur]

Keep refining your ideas and you will eventually have a standard off the shelf clothes dryer.

I just had to bump that post!

The condensing design with a heat exchanger system has been available for some while and, refrigeration units being what they are, you can expect it to work for just as long as one with heating elements in it. It is on our shopping list. But my wife is a real enthusiast for the outdoor washing line. It has the great advantage that UV from the Sun acts as a pretty good bleach and keeps 'whites' good. However, towels can feel a bit rough when dried outside and not tumbled.

 

[Johnny Reb]

Note that the vacuum doesn't eliminate the problem of needing to apply heat to evaporate/boil the water. Perhaps you could blast the clothes with microwaves while running the vacuum pump?

Could you explain why the vacuum wouldn't eliminate the need to apply heat to evaporate or boil water? From my limited understanding of water, boiling point is just when the gas molecules reach the temperature required to overcome atmospheric pressure and escape the liquid.

 

[sophiecentaur]

Could you explain why the vacuum wouldn't eliminate the need to apply heat

There's a simple argument: Why would standard atmospheric pressure be the only pressure where latent heat is needed for evaporation? Work is still done to break the bonds which hold the surface molecules in place so energy still needs to be put into the process (or the temperature will drop and the vapour pressure will reduce)

 

[Jeff Rosenbury]

Curved non contact black body radiant heating panels .

Moderately powerful suck down which reduces chamber pressure to about 90% atmospheric but not to full vacuum .

Constant small inflow of atmospheric air .

Tumbling action .

Energy recovery system .

Why non contact?

 

[Vanadium 50]

Could you explain why the vacuum wouldn't eliminate the need to apply heat to evaporate or boil water?

See Post #14.

 

[Jeff Rosenbury]

I just had to bump that post!

The condensing design with a heat exchanger system has been available for some while and, refrigeration units being what they are, you can expect it to work for just as long as one with heating elements in it. It is on our shopping list. But my wife is a real enthusiast for the outdoor washing line. It has the great advantage that UV from the Sun acts as a pretty good bleach and keeps 'whites' good. However, towels can feel a bit rough when dried outside and not tumbled.

You forgot that clothes last three times as long as when tumble dried. Clothes lines are great where you can get away with them. Zoning laws sometimes interfere, and industrial cleaners can forget clotheslines.

 

[Jeff Rosenbury]

There's a simple argument: Why would standard atmospheric pressure be the only pressure where latent heat is needed for evaporation? Work is still done to break the bonds which hold the surface molecules in place so energy still needs to be put into the process (or the temperature will drop and the vapour pressure will reduce)

This is true, but with lower pressure, the heat can be supplied by lower temperature sources. (Added savings because clothes aren't damaged by overheating as sometimes happens in traditional dryers.)

Most commercial water distillation is done in stages of lower pressure with the re-condensation of one stage providing the boiling heat for the next.

The same ideas could be applied to clothes, saving energy and time.

 

[sophiecentaur]

The same ideas could be applied to clothes, saving energy and time.

That's true if the latent heat is supplied via a heat pump but not if an electric heater is used.
I was re-thinking the original proposal and it strikes me that faster spin speeds are very good value for water extraction. High spin speeds are very stressful on bearings and there will be design issues with water seals and bearing sizes for a conventional front loader washing machine. I wonder if the fast spinning could be done in the dryer unit instead. I realize that the traditional 'bent tin' construction of all the tumble dryers I have seen, would not be adequate but the lifetime of a beefed up spin / tumbler could be very long.

 

[jbriggs444]

That's true if the latent heat is supplied via a heat pump but not if an electric heater is used.
I was re-thinking the original proposal and it strikes me that faster spin speeds are very good value for water extraction. High spin speeds are very stressful on bearings and there will be design issues with water seals and bearing sizes for a conventional front loader washing machine. I wonder if the fast spinning could be done in the dryer unit instead.

Interesting concept. If you have a nice high spin speed you may not even need a fan motor. The whole dryer assembly begins to resemble a squirrel cage fan with hot air being forced through the clothing by centrifugal force.

 

[PAllen]

Note that the vacuum doesn't eliminate the problem of needing to apply heat to evaporate/boil the water. Perhaps you could blast the clothes with microwaves while running the vacuum pump?

Right, and it is also not instant. The speed is proportional to the rate energy is supplied. While the clothes start at a temperature above boiling for vacuum, they will cool and the process will slow down unless energy is added. In vacuum, you won't have conduction or convection from the outside, only radiant transfer which is really slow.

 

[CrunchBerries]

Probably already mentioned, but what about a very fast spin along with the vacuum? The tumbler could be riddled with holes similar to a washing machine, but the centrifugal force would propel the vapor outwards. The vacuum creating mechanism would be hooked up to the outside of the outer tube and collect the vapors at a high speed. At the exit of the vacuum would be liquid water which would be nearing the amount of water extracted from fabrics.. It would be a high powered and loud system, but for a very short period of time.. like maybe 30 seconds at most.

 

[sophiecentaur]

Probably already mentioned, but what about a very fast spin along with the vacuum? The tumbler could be riddled with holes similar to a washing machine, but the centrifugal force would propel the vapor outwards. The vacuum creating mechanism would be hooked up to the outside of the outer tube and collect the vapors at a high speed. At the exit of the vacuum would be liquid water which would be nearing the amount of water extracted from fabrics.. It would be a high powered and loud system, but for a very short period of time.. like maybe 30 seconds at most.

Two problems there. Firstly, the best evaporation would be with the clothes being separate and tumbling. Secondly, high speed spinning can introduce creases. So the two operations, spinning and tumbling, would need to be done consecutively, I think.
We could perhaps take a lesson from the Dyson Airblade, which uses a very fast air blast and ' blows the water off the hands'. I can't think you to apply the principle to clothes - but possibly a drum with a very fine mesh would allow air to be forced through the fabric as it is spinning. (You would need a gentle cycle for some weak fabrics).
It gets more and more complicated, though. Any of the systems we are discussing involve small loads so we'd also need a way of automatically feeding a few items at a time into the system without getting some of them torn up by the violent ride.

 

[jim hardy]

but the centrifugal force would propel the vapor outwards.

Think about that one.

Vapor ? Water ?

Suspended droplets will be slung outward
but water in its vapor phase being less dense than air (18 vs 29 g/mol) will be displaced toward center.

You see this when your kids have a helium balloon in the car - watch and you'll see it lean into a curve not out as you'd expect.

 

[sophiecentaur]

Oh yes, of course. What a smartypants!
So the rotation would keep the clothes against the sides of the drum and a small amount of air, drawn in from the outer case would keep them from sticking to the sides. Sounds like a good idea (with a bit of regulation involved). You could start the vapour removal once the liquid stopped being thrown out.

 

[sophiecentaur]

You see this when your kids have a helium balloon in the car - watch and you'll see it lean into a curve not out as you'd expect.

You can also get warm and cold air sloshing about in that way as you go round a bend, when the heater has just started to operate on a very cold morning (turn off the jet to the feet). Steering into an 'offside' bend will make your head warmer (as the driver).

 

[jbriggs444]

T
Suspended droplets will be slung outward
but water in its vapor phase being less dense than air (18 vs 29 g/mol) will be displaced toward center.

Not when it is dissolved in air. Otherwise we'd be suffocating in argon and CO2 or burning our lungs out in oxygen.