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B Instantaneous Clothes Dryer

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  1. Apr 14, 2016 #1

    stevendaryl

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    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.:wink:
     
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  3. Apr 14, 2016 #2
    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.
     
  4. Apr 14, 2016 #3

    sophiecentaur

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    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!!!
     
  5. Apr 14, 2016 #4

    Andy Resnick

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    Perhaps you've heard of freeze-drying?
    https://en.wikipedia.org/wiki/Freeze-drying
     
  6. Apr 14, 2016 #5

    stevendaryl

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    Hmm. Why is it necessary to freeze food first? As opposed to just evacuating it to get rid of the moisture?
     
  7. Apr 14, 2016 #6

    jbriggs444

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    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.
     
  8. Apr 14, 2016 #7

    russ_watters

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    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?
     
  9. Apr 14, 2016 #8
    Better patent it fast. :biggrin:
     
  10. Apr 14, 2016 #9

    jbriggs444

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    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.
     
  11. Apr 14, 2016 #10

    TeethWhitener

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    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).
     
  12. Apr 14, 2016 #11

    Andy Resnick

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    Ethanol is for drinking!
     
  13. Apr 14, 2016 #12
    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.
     
  14. Apr 14, 2016 #13

    OmCheeto

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    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.
    Code (Text):
    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
     
  15. Apr 15, 2016 #14

    Vanadium 50

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    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.
     
  16. Apr 15, 2016 #15

    jim hardy

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    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 !
     
  17. Apr 15, 2016 #16
    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?
     
  18. Apr 15, 2016 #17

    OmCheeto

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    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.

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

    2016.04.14.techno.washer.dryer.png

    ps. Fun thought experiment. :smile:

    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.
     
    Last edited: Apr 15, 2016
  19. Apr 15, 2016 #18
    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.
     
  20. Apr 15, 2016 #19

    sophiecentaur

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    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.
     
  21. Apr 15, 2016 #20

    TeethWhitener

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    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.
     
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