h a l f b a k e r yClearly this is a metaphor for something.
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I'm going to work up to this in stages, so consider yourself warned. For a synopsis, just read the title and subtitle.
While many clothes washing machines are top-loaders, a number of recent models are front-loaders. These are claimed to use less water, which is good. Unfortunately, they also are
more expensive, probably partly because the door must seal water-tight. One thing to note is that washers have two drums. There is an outer drum you don't see which is water-tight, and the inner drum is what does the spinning, to centrifugally squeeze most of the water out of the clothes, in preparation for drying.
Meanwhile, just about all clothes dryers are front-loaders, for their tumble-dry thing to work. I don't see any great problem with designing the inner drum of a front-loading washer to also work as a dryer tumbler. And, just as in-between the two drums of a washer are various valves and fittings to do things like detect water level and pump water out when done, other valves and fittings can be added to allow hot air to enter the inner tumbling drum (assuming ordinary clothes-dryer technology). Two machines in one would obviously be a worthwhile space-saver, especially since clothes washers and dryers are normally both on the bulky side.
However, a hot-air tumble-dryer has two big problems. First, that tumbling action causes clothes to rub up against each other, and to shake fibers loose. The very substance of your clothes gradually degrades to become lint in the filter. Eventually the clothes must be replaced, and usually sooner than if you had taken them from the washer and hung them on a clothesline to dry. Second, a hot-air dryer is very energy-intensive. We are essentially talking about putting enough heat into those damp clothes to boil all the remaining water out of them -- and that indeed is quite a bit of heat energy. There IS a more efficient way to extract water from something, and that method is known as "freeze drying".
In case you already know all about freeze drying, skip this paragraph. Otherwise, I'm going to be telling you that when you evacuate the air from an enclosed space, any water in that space will automatically start boiling and freezing at the same time. See, water is a mixture of molecules all moving at different speeds, and the temperature of the water actually is equal to an average speed. But when the air is removed, all the fast-enough molecules can now escape directly as water vapor (equivalent to having been boiled), and all the slow molecules clump together to make ice crystals. They really are "cold" water molecules that are doing that thing.
Well, if you vacuum-freeze just-washed clothing, a significant portion of the water will be directly extracted as vapor. And if you knock the remaining ice crystals out of the clothing, then the water is essentially now separated from the clothing, which therefore must be dry.
Now to put the pieces together. Remember that the front-loading washer has a water-tight door and a pump already. We just need to make sure the door is air-tight as well as water tight, and that the pump is able to pull a decent vacuum. So, after the washing and rinsing cycles are finished, the machine now enters vacuum-freezing mode, by tumbling the drum slowly, and sucking all the air out.
Water vapor will be pulled directly, as mentioned. And the tumbling clothes will knock ice crystals out, which fall through the holes in tumbling inner drum, to land inside the waterproof outer drum. I expect this freeze-drying process to be finished in about five minutes. Much less lint fibers will have been lost from your clothes. And MUCH less energy will have been spent, only what is needed just to pump the air out of the drum.
When the freeze-dry cycle is finished, the machine allows air to once again enter the drum, and the door may now be opened, for the clothes to be removed. The ice crystals that had fallen in-between the drums will not immediately melt; they really are conglomerations of cold water molecules. But they will melt as they stay in contact with the ordinary air that has entered this combo unit. The small puddle that forms probably will be of no consequence. Certainly it will mean slightly less water need be added, when the next load of clothes is to be washed.
Regular heat based W/D combo
http://www.lgwasherdryer.com/
[Worldgineer, Sep 11 2006]
How Freeze Drying Works
http://home.howstuf...m/freeze-drying.htm
I'm not sure all of the comments take into account how the process works. [Zimmy, Sep 11 2006]
More about water exposed to vacuum
http://www.madsci.o...984359705.Ph.r.html
I do know what I'm talking about, here.... [Vernon, Sep 15 2006]
Vacuum Freeze Drying of documents.
http://www.unesco.o...uum%20freeze-drying
Apparently this is a standard procedure for water damaged books. [Galbinus_Caeli, Sep 15 2006]
Thor Appliances
http://www.thorappliances.com
Thor washer dryer combos and condensing dryers [ThorAppl, Jul 26 2010]
[link]
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//if you knock the remaining ice crystals out of the clothing// You'll be effectively be sand-drumming your clothes. I doubt they'll survive more than a washing or two. |
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I do like the general concept, but don't have a good feel for how much energy will be required to create this strong of a vacuum. |
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The combo washer-dryer does exist, though with regular heat-based drying. See link. |
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Sandpapering-equivalent, eh? Maybe. Experimentation is in order! Anyway, there are still possibilities here. For example, I had thought about adding a microwave unit, to heat up the water crystals just enough to sublime in the vacuum. This would take somewhat more energy than simply knocking the crystals out of the clothes (and I had wondered about how "simple" that actually was to do), but it should still take less energy than heating the water to well above room temperature, as happens in most dryers. |
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The vacuum, by the way, does not need to be exceptional. Perhaps equivalent to 25,000 meters (82,000 feet). |
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Microwaving in general might be a good idea, since it acts directly on the water molecules. But I'm not convinced that sucking air/vapor out is more energy efficient than blowing it out using air. Maybe if you dry ambient air first, using a dessicant or refrigeration cycle, then blow it past clothes being microwaved? |
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Guys, isn't this baked in the form of regular washer/dryer combinations? I think they are sometimes referred to as condenser dryers. |
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[edit] Nope sorry, I stand corrected. Whether or not such a system were able to create a pure vacuum is unimportant, any reduction in the internal air pressure is liable to have a drying effect on your clothes. Perhaps this technique could be employed in tandem with existing washer dryers in order to make them more efficient? |
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Yes (see link), but they don't freeze-dry your clothes. |
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Is actual freeze-drying absolutely necessary? Even a paltry 10% reduction in pressure should pay dividends on the overall efficiency of using traditional drying techniques. Or are we saying they do that already? |
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I've had a washer/drier for nearly fifteen
years - a common item here. Perhaps I'm
missing something. Should I run a hose
from the fridge into it and try this instead? |
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If you combine the heat and the vaccuum, you could probably dry the clothes in minutes. Just vaccuum might be really slow. |
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Also, I would take issue with the idea that all of the frozen water will just fall off. To test the theory, freeze a wet shirt on a clothesline in December. Put it in a mesh barrel, and shake as long as you want. Now bring the shirt inside. Is it dry when it melts? Probably not. |
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Although a major selling point would be the opportunity to freeze dry foods through a suitable attachment. |
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I think that ice crystals forming in your clothes would be doing some serious internal damage. Hmm. <Goes off to put a wet rag in the freezer.> And, as said above, tumbling them with ice crystals would be bad (I seem to recall "ice-washed" jeans). |
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Regarding energy: A heated dryer isn't putting forth as much energy as required to boil all the water, is it? I think it's heating to a temp that increases evaporation, yes, but the air moving through is doing a lot of work. I mean, I can dry some clothes with just the Air Fluff setting, and the dryer doesn't just sit still and heat up like a dishwasher, it pushes air through. (There's something about vapor pressure, moisture capacity and relative humidity that I cannot put into words.) |
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You'd lose that air-moving advantage if you sealed up the tub and pulled all the air out. Then you would have to do the work required to boil off all the water, and calling it "air pumping" isn't going to reduce the amount of work needed. If you pull a vacuum, which is not easy, even for a partial vacuum, the tub will fill with water vapor, which you then have to pump out. The tub will cool, yes, but then you are pumping harder to get vapor out of colder water. When you are pumping vapor off ice crystals, you are going to be working through two phase changes. |
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Granted, the act of crystallizing will give off some heat. Plus, you could put the pump under the tub so its waste heat will contribute, and maybe keep the warm graywater around for its heat. |
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Or would you rather wrap the tub in freezer coils and start off cold? I don't think so. I think you are going to want heat from somewhere, even if you operate at a very low temp. It has to come from somewhere, and you have to work for it. |
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As I recall, at least five times more energy is required to boil water that to raise it from room temperature to boiling. This is just saving one-fifth of the energy of putting the wet clothes in an dry teakettle on a hotplate. You lose the air-moving advantage, whatever that is, but gain by centrifuging some of the ice crystals instead of boiling them. |
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But if all you get is a "small puddle" worth, your freeze-dryer has only saved the energy needed to boil that puddle away. But a heat-and-air dryer would get rid of that puddle, and all the other water, by evaporating it away with a warm breeze from the built-in fan and heater, or even with the breeze only. |
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Sorry, Vernon, I think this is a very clever bit of thinking and creativity. But I've got a hat and a pair of running shoes drying on my windowsill right now, and there isn't any heater involved, just a lovely breeze courtesy of the attic fan. |
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You should build this anyhow, and sell it to dry cleaners for drying delicate items . . . Wait a minute, how do drycleaning establishments get the drycleaning fluid out of clothing without dumping it into the environment? Something like this? |
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I have several concerns with this idea. |
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A conventional dryer moves by taking ambient air, reducing its relative humidity (through heating) then moving that dry air through the wet clothing, then expelling the now moist air. |
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Your system decreases the pressure, but I don't think you are going to get much temperature reduction. |
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Even if you do achieve a freezing temperature, I don't think you are going to be able to remove the ice crystals from clothing very easily. I recall winters where I have had wet clothing freeze but when it is removed hours or days later, it is again moist. |
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I expect that if this works, it is going to take a rather large amount of energy, and a very large amount of time. |
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From the article that [Zimmy] linked: {{Sublimation}} "continues for many hours (even days) while the material gradually dries out." |
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OK, I admit I knew it takes time for ice to sublime; that's why I suggested using tumbling to break ice crystals loose. Since that didn't go over well, I also suggested using microwaves. This has the advantage that it would basically WARM the ice, making it sublime faster, instead of melting it outright. Some tumbling may still be necessary, though, to ensure even exposure of the ice to the microwaves. |
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/If you combine the heat and the vaccuum/ |
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I like the microwave vacuum combination. One need not have a perfect vacuum. The microwave would heat the water, and the bioling point would be lower from the low air pressure. Vapor would be removed via the vacuum pump. The clothes might tumble a few times during the process, just to make sure there were no pockets of dampness. |
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Just let them cool a while before you grab that metal zipper. |
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Clotheslines work very well in subzero
temperatures ... if you live somewhere
exceedingly dry. I have dried several
clothes items on a porch in a Utah
winter, for example. Being 1390m
above sea level didn't hurt either -- low
pressure and all. The water freezes, the
ice sublimes away, the clothes are left
undamaged. All in a couple hours. |
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The heat in and of itself does little, but it does reduce the relative humidity of the air, improving the moisture transfer. |
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I like the space saving idea of making the washer and dryer into the same cylinder (Most washer-dryers, as I understand them, have the dryer attached above a separate washer.) |
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Evacuating the air will indeed help dry the things faster, but as you've hopefully recognized, the sharp nature of ice crystals, and their propensity to expand when frozen makes freezing clothing while tumbling it a pretty bad idea as far as wear and tear goes. |
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Of course, you can pump out air, and water vapor, and heat, and tumble all at the same time. Whether pumping out the air is a more efficient way of removing the moisture than pumping air through a heated dryer remains to be seen. perhaps it's time to break out some mad calculations, and argue about who can't do math right. |
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All of the above aside, a [+] for the short, concise presentation. Can you modify mine so that I can both make ice cream and heat food as well? |
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Lets not forget the obvious problem towards microwave.. these clothes have zippers.. buttons.. metal parts. |
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I just want to point out one disadvantage of combined washer/dryer units. It can take a lot longer to clean and dry multiple loads of clothes. |
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If the wash cycle takes 30 minutes and the dry cycle takes 60 minutes, you can do one load in 90 minutes. If you have five loads, it is going to take 7.5 hours to complete. |
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With separate washer and dryer units the first load still takes 90 minutes, but because you can have both units operating simultaneously five loads only takes 5.5 hours total. |
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My eldest daughter complained about this fact when she lived in England, where these units are relatively common. |
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Very clever idea but who wants to snuggle up to a fresh fluffy, frozen towel? |
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Intrigued by the microwave option though... well, I'm off to modify the microwave with a vacuum hook-up and then stick it all in the dryer to see how it'll work. |
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[Galbinus_Caeli], with the dry cycle being microwave-assisted vacuum evaporation, I think that less than an hour will be needed for that. Consider how hot a cup of water gets in a regular microwave oven after only a minute or two. And the clothes start out damp, not soaked, because of the spin cycle of the washer. I'm fairly confident that the speed of the dry cycle will be very acceptable for overall performance. |
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You don't want to go much faster than an hour. Otherwise you are going to overheat and shrink the clothes. |
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[Galbinus_Caeli], I hate to have to say this, but apparently you haven't noticed that the main drying method under discussion here is FREEZE drying (with a microwave assist for "sublimation", the direct evaporation of a solid (ice) to a gas). No excess heat at all! |
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[Vernon] It looks to me like there are two key elements here: |
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1) Combining washer and dryer functions into a single unit. |
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2) Drying under a partial vacuum. |
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In addition there has been discussion of adding or removing heat from the system to improve vaporization. |
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Cooling a wet article is not going to dry it faster than heating it. Those pesky laws of physics will get you every time. You have to add energy to a substance to get it to change to a gaseous state from solid or liquid. |
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I am not saying the idea won't work, just that it is unlikely to be faster or more energy efficient than the traditional method. |
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[Galbinus_Caeli], those pesky laws of physics include "Gaussian distributions", otherwise known as "bell curves". And water at any temperature is not a collection of molecules all having that temperature; the molecules have temperatures that are distributed across the curve. |
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Next, there is "vapor pressure", the natural tendency for molecules to escape from the solid or liquid state, into the gaseous state. Despite being heavier than gold atoms, mercury atoms are infamous for their ability to evaporate easily. And water tends to evaorate easily, also, when the humidity is low --as is true when exposed to a vacuum. The vacuum allows all individual water molecules having a temperature greater than the freezing point to escape as vapor. You don't have to add energy to the water for this to happen; those molecules have that energy already, thanks to the bell curve of distribution. And that's why I wrote in the main text that the molecules left behind, that form ice on the clothes in the freeze-drying process, are actually cold. And that's also why I wrote that we only need to add enough energy to help those cold molecules sublime in the vacuum... |
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[Vernon] I disagree with none of that. I only disagree with your assertation that water saturated cloth will lose that moisture rapidly in vacuum. |
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As counterexamples I offer: |
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Comets, Europa, The icecaps of Mars (in winter), and Rhea. All of these consist primarally of water ice exposed to vacuum (well, near-vacuum in the case of Mars' ice caps, but more of a vacuum than you are going to be able to pull in a dryer) |
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Interestingly enough I have found some instances where vacuum freeze drying, is used for water damaged paper. |
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"In freeze-dry operations, the Lockheed Missiles and Space Company (14) places the frozen books on shelves and the chamber is quickly evacuated to less than 4 torr; any free water in the books is frozen. For the first 56 hours the chamber is at 10 3 torr (the condenser is at less than -101 °C or -149°F); the shelf temperature not over 54.4 °C (130 °F), book temperature not over 37.8 °C (100 °F). When the weight of ice on the condenser is stabilized, the chamber is brought to ambient pressure, about 760 torr, it is opened, the ice removed, and if any of the books are dampish, or nearly dried, they are placed on non-heated shelves. The chamber is re-evacuated and held at 10 torr for 26 hours; shelf temperature is not aver 54.4°C (130°F). When book temperatures read above 12.8 °C (55 °F) the cycle is completed, the chamber is brought down to ambient pressure." |
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I expect that tumbled clothes would be quite a bit faster than that, but probably still on the order of hours. |
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[Galbinus_Caeli], you still are not paying attention. In high school I saw a video of a beaker of water in a bell jar as it was evacuated; about half the original volume boiled off as vapor; the rest became ice. And since I've known that all these years since, I don't think I wrote anything here to say that all the water would immediately vaporize. I HAVE written that there wouldn't be a huge amount of water to start with, since the spin cycle of the washer would wring out the clothes, leaving only damp material to be dried. I've also written that the use of microwaves would speed the sublimation of the ice in the vacuum, and THAT is why I say the overall drying time will be reasonably fast. |
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Meanwhile, your "counterexamples" all exist far from the Sun, where ambient temperatures WELL BELOW water's freezing point handily keeps ice from subliming quickly. Not to mention any accumulation of space dust on that ice, acts as an insulation layer, to slow sublimation. |
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I think this idea has legs. I thought of something similar independently and researched whether a patent existed. It turned out someone had got in a month before me and sold the patent to Dyson. It didn't involve knocking ice crystals off, but applying heat instead. Still a lot more efficient than traditional tumble drying. One contributor mentioned the lack of air flow being a disadvantage. But it needn't be if the evacuation level left the remaining particles in viscous-flow rather than molecular-flow, then the vacuum pump would do the work and recreate that advantage. |
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freeze drying usually requires drawing air out of the container into a remote chamber where the water freezes, then is actively thawed by heating. |
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"Honey, I'm sorry I accidentally washed and freeze-dried your ipod." |
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There's a basic error in the asumption of how regular driers work that makes this idea not as effective as believed. A regular, heated, dryer is not trying to "boil" the water out of the clothes. The heating lowers the relative humidity of the air, causing more water to evaporate into it. Pre-drying room-temperature air would have exactly the same effect. A vaccum has a similar effect, but does so by reducing the boiling point so the water does boil. |
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Freeze drying essentially combines these two, with the water never entering a liquid state. This has the advantage of minimizing damage due to moisture. It also has the advantage (from a preservation perspective) of being achievable after deep flash freezing, which minimizes cell damage due to expanding ice crystals. These two things act in combination to reduce the water damage, decay, and mold growth on wet objects. |
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What they aren't is particullarly efficient, since you need to keep drawing a high grade vacuum during the process to achieve any speed. |
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