A Cool Mist that Dries Your Clothes

This one is both wild enough to be confused as a conspiracy theory and common sense enough to be the big solution staring us in the face which nobody realized. Until now. Oak Ridge National Laboratory and General Electric (GE), working on a grant from the US Department of Energy (DOE), have been playing around with new clothes dryer technology since 2014 and have come with something new and exciting. Clothes dryers that use ultrasonic traducers to remove moisture from garments instead of using heat.

If you’ve ever seen a cool mist humidifier you’ll know how this works. A piezo element generates ultrasonic waves that atomize water and humidify the air. This is exactly the same except the water is stored in clothing, rather than a reservoir. Once it’s atomized it can be removed with traditional air movement.

This is a totally obvious application of the simple and inexpensive technology — when the garment is laying flat on a bed of transducers. This can be implemented in a press drying system where a garment is laid flat on a bed or transducers and another bed hinges down from above. Poof, your shirt is dry in a few seconds.

But individual households don’t have these kinds of dryers. They have what are called drum dryers that spin the clothes. Reading closely, this piece of the puzzle is still to come:

They play [sic] to scale-up the technoloogy to press drying and eventually a clothes dryer drum in the next five months.

We look at this as having a similar technological hurdle as wireless electricity. There must be an inverse-square law on the effect of the ultrasonic waves to atomize water as the water moves further away from the transducers. It that’s the case, tranducers on the circumference of a drum would be inefficient at drying the clothing toward the center. This slide deck hints that that problem is being addressed. It talks about only running the transducers when the fabric is physically coupled with the elements. It’s an interesting application and we hope that it could work in conjunction with traditional drying methods to boost energy savings, even if this doesn’t pan out as a total replacement.

With a vast population, cost adds up fast. There are roughly 125 M households in the United States and the overwhelming majority of them use clothes dryers (while many other parts of the world have a higher percentage who hang-dry their clothing). The DOE estimates $9 billion a year is spent on drying clothes in the US. Reducing that number by even 1/10th of 1% will pay off more than tenfold the $880,000 research budget that went into this. Of course, you have to outfit those households with new equipment which will take at least 8-12 years through natural attrition, even if ultrasonics hit the market as soon as possible.

There is a lot of room for new ideas on saving energy and resources while washing and drying clothes. Working on this challenge would make a great Hackaday Prize entry. As it so happens, just last year we saw a method that leveraged arid desert air as a heat source for drying.

[via reddit via Yahoo Finance]

76 thoughts on “A Cool Mist that Dries Your Clothes

    1. Just realized how bad that could be. Forget a few coins and you end up with wet clothes covered in piezoelectric crystals.

      Metal zippers and snaps/buttons would likely do damage as well, so no drying jeans with this prototype.

  1. I can’t help but think the ultrasound should be washing without detergents first then self drying. Single unit washer-dryers are common now. Many soils could be blasted out without any water to begin with, just air.

  2. Many modern plastic based fabrics are ultrasonically welded instead of sewn.

    For fun, students used to melt DVDs in those fountain fog machines.
    I have to wonder if the washer is for natural fibers only….
    ;-)

    1. A regular drum dryer is pretty hard on clothes. I wonder whether this ultrasonic dryer would be similar or worse?
      Hang drying shirts last me for 10 to 20 years. Back when I used a clothes dryer, 3 to 5 years was about the limit. Since black tee shirts don’t seem to go out of style, time doesn’t matter.
      BobH

    1. 3.5 cents per kWh here. Build nuclear plants and forget all this BS. How much is saved in materials, costs, and manufacturing infrastructure, with plain motor and heat dryers? You can not do any better with electrical efficiency than turning electric power into heat.

      I don’t see how this can actually dry fabric. I can see it removing more water than a washing machine spin cycle, like a really good squeezer of some sort. There is an equilibrium point with no reason for more water to leave the fabric just because there are sound waves. It will have to finish with heat.

        1. You can already buy dehumidifier clothes dryers and they do use about 1/3 the energy of a conventional dryer. Still comes at quite a price premium even though the technology is quite cheap. See DIY version below for those who want it cheap. :)

          Still can’t beat a drying rack for efficiency. Add a small fan to decrease the drying time considerably with only a tiny use of energy.

          And then there’s that cabinet dryer that is advertised to be gentle on clothes, something that can be replicated by simply putting a dehumidifier in a closet.

          1. A heat pump, as the name implies, moves heat. It does not create heat – except as waste from the pumping process. Being a heat mover, efficiency does not have any meaning without a basket of parameters for any given situation and a goal to compare against.

  3. Hm the slide deck nowhere mentions square-distance law; it reads to me, far more like:

    If we put the clothes directly on the transducer, there’s more kick to it than when we just try to transfer power in via air.

    So, the point here is not the increased distance, but the fact that the energy transfer from air to clothing is far worse than from transducer directly to clothing.

    So, if I was to make an EM wave analogy:

    If you want to shock someone with a high power RF amplifier, have them touch the antenna with both hands, rather than stand in the beam.

    1. With arrays of transducers, effectively acting like a very large transducer, the fabric is in the near-field and there is no inverse square. Inverse square is for point sources.

    2. I guess that then this technology would better work for “cold ironing” of dampened clothes, rather then for bulk drying of a batch of laundered clothes. Which is good actually, energy consumption wise. Electrical irons are often around 2kW of power, have inherent great thermal losses because of low duty cycle when in use. Any cloth dryer is probably more efficient then even the best iron.

    1. When surveyed one witty dog said “A dryer that doesn’t use heat? That’s cool!”
      Another dog responded with a question “Does my collar really need so much equipment?”
      From the bats we had this respondent “It’s all well and good, but will it dry my suits properly?”

      1. +1

        seriously, ultrasonic is a huge frequency range, and those animals only hear the lower parts of it; this is kind of an exaggeration, but that’s like asking

        “X-ray diagnostics? What will the bees say of it, I’ve heard they can see frequencies above our vision’s range”

        The slide deck (from hell/the mid-nineties, crowdedness-wise) doesn’t explicitly state frequency, just amplitude/frequency product. However, the simulation graphics on slide 8 indicate some 100 kHz frequency; that’s far above dog’s hearing range, but might be within a bat’s hearing range. Luckily, building dampening systems at these frequencies is very simple, soooo yeah. Don’t operate your dryer next to the sleeping cave of an especially sensitive bat. The rumbling of the tumbling motor will disturb the poor creatures.

          1. Figure on slide 8. Look at the red line that’s labeled “Piezo Vibration”. Count number of cycles per time axis tick. (I did that manually, because I couldn’t be bothered to whip out my python).

    2. If you lookup cheap ultrasonic fogger transducers, on your favourite Chinese site ( less than 40 cents each in lots of five), some are 25mm 1.7MHz or 16mm 3MHz. But at that kind of frequency they would only be efficient if immersed under water or used in a press. That kind of frequency range under normal operation if well outside of bats (10-115kHz) and dogs (67 Hz to 45 kHz) hearing, or even a porpoises (75Hz to 150kHz). Also there the higher the frequency the more rapidly it is attenuated. And I’m sure that a safety cut-out could be added to all commercial products detecting faults and generate audio which would be harmful to cats (55Hz – 77kHz) and humans (31Hz -19kHz).

      If a transducers is smashed (belt buckle/coins) it would produce even higher frequencies, so the only failure mode I can think of would be a harmonic resonance within the structure of the device generating a lower frequency audio signal. Say an empty clothes basket left sitting on top of the device vibrating and generating a lower frequency.

  4. Its interesting how ones personal world view filters what you read, we have a conventional drier but have used it maybe once in 5 years. Line drying in the part of the world I live in is the norm.

    So I read this and think yeah thats an interesting idea but pointless – somewhere where line drying is not possible most of the year its a necessary device.

  5. This has me really thinking.
    Oh how I wish I had the room.
    This looks like one of those projects I would love to get into and see what else can be done.
    Good luck.
    when this comes out Im sure it will pay for it self in less then a year.

  6. Anytime anyone mentions “Oak Ridge National Laboratory” – All I can think of is that great 90’s movie about the guy that built an atomic bomb in a basement.

  7. What impressed me, is on the very first slide, the graph indicates that this new method is faster. Apparently much, much, much faster. By a factor of several hundred if the graph is to be believed. That’s a huge selling point right there.

  8. Cost per load using a natural gas dryer is much cheaper (less than half the cost) of using electricity. Yet even in homes with a natural gas furnace and water heater, you’ll usually find an electric clothes dryer. I guess capital cost is the deterrent, so for the transducer dryer to catch on, the capital costs will have to be in line with a standard electric dryer.

    1. hm, well, if it’s really that much faster, then there’d be another reason to buy one of these ultrasonic dryers.

      It most certainly will be more expensive in purchase. It has all the same components as a “standard” electric drier, minus the heating, plus all the electronics, and some way to get rid of *condensed* water (as opposed to just blowing it out the window as steam).

      Now, I don’t really know the component cost of a dryer heater unit – but considering it can’t be more than an air-cooled piece of resistor wire…

    2. Gas dryers are more dangerous. Some localities ban them because of the fire risk.
      And some places ban clotheslines because boo-hoo they don’t like the way it looks. :/

  9. Ultrasonic transducers have their dangers. Put your finger in a ultrasonic cleaner and watch it go black in one day. Any if you’re unlucky go have the gangrenous appendage amputated a week later. The black colour comes from the internal bleeding caused by cells broken by the ultrasound.

    1. I have touched one in an ultrasonic mister before, can confirm.
      Only a second or two, hurt like hell! Fingertip went numb for a few hours. Was very worried for a week.

  10. This is both “Not New” and “Misleading”. Any lead-in showing a tumble-type dryer is useless in this application (unless you spin so fast that all the wet target items are essentially flat and in-contact with a large and expensive array of adaptive-impedance matched transducers).

    Ultrasonic water-removal is a time-proven and fully understood method in many industrial/manufacturing processes. Whether it works well or not all depends on efficient acoustic coupling of the transducers to the target product, as well as managing impedance mis-matches between the transducers and the product (i.e., matching an RF transmitter to an antenna, but more difficult with dispersive-variable “wet” targets).

    The mathematics, engineering and design of this ultrasonic drying method is well known. If what these “researchers” claim to do is akin to “magic” – that hasn’t been done before, I’m not seeing it. In-fact if they’re doing something new that significantly competes with a consumer-level thermal home tumble-dryer in total cost of ownership, it would have already been done by now.

    There is a picture of an “Ironing-Board” like mechanism. That’s one approach (vs. rolling process). That’s one way high-volume ultrasonic dryers work – albeit automated. But they are too inefficient to be commercially viable at the consumer level.

    My real question is: Who is paying for this so-called “research”, Me; the Taxpayer?

    1. Yep. “It would take decades of work, by thousands of scientists, in a particle accelerator powered by dump trucks of flaming grant money! Of course there would be no guarantee of success, and in any case, I’d never live to see it ”

      The “never live to see it” is the nirvana-grant of research science.

      Yesterday several youngish “science” enthusiasts told me that man made warming is “established science”. I asked them why anyone needs any more research money, and barely escaped with my life.

  11. My grandmother had a dryer that did not use heat. It was called a wringer. You took the cloths out of the washtub and ran them through the two rotating cylinders. Amazingly enough most of the water was squeezed out. Today’s dryers displaced the wringer I suspect primarily because you could just fill them up and let them go on autopilot. If you are going to have to handle each piece of clothing with an ultrasonic dryer I suspect it will suffer a similar fate.

  12. Ultrasonics do strange things to peoples emotions… (for myself they make me quite hostile). I can see it now; household arguments centered upon laundry days. May we live in interesting times…

  13. How efficient is it once the clothes are already maximally dry from spinning? They contain lots of air then and are not permissive to ultrasound. Second question: how much strain does it put on the fabric? Sounds like it might wear stuff down pretty quickly.

    1. Another issues the transducers would likely be using some sort of slip ring on the tumbler how well will these hold up.
      Of course it might be possible to use an inductive coupling similar to wireless chargers but this would be costly at those power levels.

  14. Seriously? They can’t figure out how to better keep the clothes coupled with the elements? Ever seen a top loading washing machine before? Hell, this sounds like a better setup for a washing machine anyway.

    Just put the transducers on the wall of the drum, a large fan on the with louvers that open and have it all activate during the spin cycle. Hell, this is probably within the realm of a lot of the folks here to try this out.

  15. I recall sitting in the front row of a Grateful Dead concert. Thank God I had ear plugs as the first bass note popped all the dust out of my shirt! True story! Even with the earplugs mybhearing has never been the same.

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