Fill Your Hot Tub With Sand. For Science!

Here at Hackaday, we can understand if you don’t like sand. It’s coarse, rough and irritating, and it gets everywhere. With that said, [Mark Rober] discovered a great way to have fun with sand right in your own back garden.

We’ll preface this by stating that this isn’t the easiest hack to pull off on a lazy Saturday afternoon. You need a spare hot tub, plenty of pipe, and a seriously big air supply. But if you can pull it all together, the payoff is fantastic.

What [Mark] has achieved is turning a regular hot tub into a fluidized bed. In simple terms, this is where a solid particulate material (like sand) is made to act more like a fluid by passing pressurized fluid through the material. Through a carefully built series of drilled copper pipes, [Mark] manages to turn the hot tub into a fluidized bed, much to the enjoyment of his young nephews.

While it’s not the easiest hack to copy at home, [Mark] drives home the science of both the fluidized bed and why certain objects float or sink in the sand. It’s something that can also be easily tackled at a smaller scale, if you’re looking for something more achievable for the average maker.

For more sand science, how about using it to hold up your car?

[Thanks to Keith for the tip!]

62 thoughts on “Fill Your Hot Tub With Sand. For Science!

    1. From the shots of the test bed he built, and the lack of compressor noise anywhere, I think he was using a compressed gas bottle. Just got to keep an eye on the guage I guess!

    2. That would have been an extremely large air compressor to be able to keep up with that SCFM requirement. Even if you only needed a moderate duty cycle. As others have noted, he was using compressed air bottles as he has done in several other videos.

        1. Curious what the math would be in terms of required pressure though. It is after all only needing to go through about two to three feet of sand so it probably wouldn’t actually need that much PSI to do so but would need a fairly large flow rate. A few HP ring blower might actually supply enough CFM and pressure but somebody else would have to do the calculations on that one.

          1. It needs enough pressure to lift the weight of the fluid, in this case, the sand and air mixture. We do this for industrial coaters (think spray a solution on fertilizer pellets or grass seed). The last one I did operated at something like 90 inches water gage.

  1. Seen this around, but wondering if anyone else thinks this is a little dangerous. There are fine particles of sand in the air (thats why there are rainbows) and they breathe them with no hesitation. Silicosis was a major killer to miners

    1. Oh, they all breathed in an absolutely amazing amount of various sizes of mostly silicon dioxide sand particles. This was not a particularly good idea for any of them to do. That’s part of the reason why you no longer see sandboxes in playgrounds anymore. This machine, while novel and interesting, basically amounts to being a silicon dioxide dust generator.

      What they did wasn’t like going to the beach and the bags of sand most likely even had numerous specific warnings about not doing what they did.

      The alternative would have been to use a similar product to sand that had less fine dust and no silicon dioxide but that would have most likely cost more given the volume being used.

      Still didn’t make it a good idea though. Plus, he invited kids to use it as well.

      1. You don’t see sandboxes on playgrounds because of cat and dog excrement (giving your kids nasty things like toxoplasmosis, fecal coliform bacteria, Giardiasis and so on), not silicon dust. Silicon dust of a sandbox is mostly harmless for almost everybody. There are exceptions, of course, but they are exact this: exceptions. Live close to a beach or desert, or large construction, and you will inhale way more sand in one day than those kids their entire lives. The canned air does not last long after all.

        Your nose, throat and lungs can protect themselves from dust. That’s why we have mucus covering all our airways. Don’t worry about sand, our body is made to withstand sand dust. Worry about plastic micro-particles, internal combustion engine smog, industrial smoke, acid rain… We were not build to withstand those…

        This “everything is dangerous” kind of mentality is partially to blame for a lot of people being allergic to pollen, dust, gluten, whatever – the hygiene hypothesis. Our immune system have to work here and there, otherwise anything strange is seen as the ebola, and puts the whole system on full alert. Stay away from dirt, grass, dust, sand, dead leaves, and your immune system does not know what is dangerous and what is harmless. In case of doubt, it will bring in the nukes…

        Let kids have fun with the sand. It’s more dangerous to have a bomb strapped to their faces all day and at the bedside all night (aka smartphone with a very large lithium battery)…

        1. The hygiene hypothesis has nothing to do with silicon dioxide inhalation or plastic microparticles, internal combustion engine smog, industrial smoke or acid rain. Your nose, throat and lungs can at least somewhat protect themselves from small amounts of dust but it still takes a toll and like most things, a small amount is not likely to be something your body cannot repair at all (though probably not 100% every time) but medium to large amounts will very non linearly be a big problem. It’s just like how radiation works. What these people did was not a small amount of exposure. Not even close. That’s the issue with this example.

          Live close to a beach or desert, or large construction, and you will inhale way more sand in one day than those kids their entire lives is not true either.

          I agree that part of the reason why sandboxes have been phased out is due to animal excrement. But the silicone dust also plays a role. Even indoor facilities that have sandboxes no longer use sand anymore and they are not exposed to animals at all. It’s because of the silicon dioxide inhalation issues. They have mostly been replaced with (usually) recycled rubber instead. Which is actually more expensive than sand, which is nearly dirt cheap.

          Nobody is strapping a phone to one’s face here either although the batteries do rarely have major combustive problems.

    2. just put in this way, i would not go anywhere near to that sand machine, even when i see that someone is swiping on the street while i pass by, i use to hold my breath, you only have one health, if you damage it, then you are a goner…

    3. Can’t say I know much about this, but my understanding is that that’s why glass beads (like they used in the video) are used for sandblasting nowadays instead of just sand – that glass beads are silicosis-safe. Again, not something I’m very knowledgeable about, but that’s what I’ve heard.

    4. of course it is only the very finest pieces of dust that get percolated up to get in the kids’ lungs. i mean for gawd sakes, they are Snorkling in the dust… yummy micron sized dust. healthy excited lungs surging with careless deep breaths of (fresh) air. shame that others will monkey see monkey do this one.

      1. ‘Fill your container with fine sand’ – minute 2:36 from the source video.

        ‘Throw your kids into a fluidized bed that is more than capable of killing them’ – the video thumbnail, apparently.

        I gritblast/beadblast on a weekly basis, I know more than enough to know that breathing even the glass dust that comes as a manufacturing byproduct in the bags is a fucking awful idea for your heath.

        Listen much?

        1. Glass is not crystal. Glass beads are listed as a viable substitute for sand to prevent silicosis by OSHA. As for sand, do not throw your kids in it for more than 5 or 10 years. Do not let them play in dust or go outside during wind and dust storms in arid regions. Best is to move off Earth, which is nearly half silicon.

    1. I love how every damn video on Youtube has to do this. It’s thoughtful, as though I haven’t figured out what the “like” or “subscribe” buttons do. I’ve actually quit clicking either since I’ve gotten so tired of everyone begging.

    1. I was wondering if this could be used for some kind of fluid distillation column instead of sieving sand by particle size? I suspect it would be less efficient energy wise though…

  2. I watched this show once that did the same thing. But there’s was an idea for trapping bank robbers, or checkpoint runners, etc. You can lay bricks on the sand, so normally you could just drive over the trap, but a switch of the air and it’s quicksand.

  3. Does it bother anyone else that it takes a DudeBro using Click Bait strategies, overt sensationalism, and Memes, just so people will watch his (pop)science videos? Do we really need more Vsauce style garbage?

    The guy has a masters in engineering and worked for JPL, and he wastes his life churning out 10 minute mattress ads disguised as science videos. Why would HaD bother to feature this?

    I’m not even going to go into the safety issue, or the lack of disclaimers in the video.

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