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Monthly Science: Dehumidification by Rice

As part of a discussion on the M2 forums about using rice to dehumidify 3D printer filament, I replaced the 500 g bag of silica gel in the basement safe with a bowl containing 200 g of long-grain brown rice from our rice supply and let it sit for a while:

Basement Safe Humidity - Rice vs. Silica Gel - 2015-10-31

Basement Safe Humidity – Rice vs. Silica Gel – 2015-10-31

The abrupt drop in humidity from 52% to the logger’s minimum 15% marks the point where I replaced the rice with a fresh bag of silica gel, with a door opening shortly thereafter. The basement air outside the safe varied between 52% and 54% during that time, so the air inside the safe trended upward toward that goal.

The rice still weighed exactly 200 g after its stay in the safe, so we can conclude it hadn’t absorbed or released any water.

Conclusion: nope, rice doesn’t work as a dehumidifier…

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  1. #1 by madbodger on 2015-11-01 - 08:03

    I would guess that white rice would work better, but that’s mostly for quickly removing the first chunk of water quickly (for example, a cellphone dropped in a puddle). For more stay-really-dry tasks (such as plastic filament), silica gel or other techniques seem like a much better idea.

    • #2 by Ed on 2015-11-01 - 09:04

      As nearly as I can tell, there’s a whole lot of wishful thinking going on out there in Wet Phone Land… [grin]

      • #3 by madbodger on 2015-11-01 - 09:51

        That may well be. Common knowledge isn’t always correct. I’ve seen rice in salt shakers as a dessicant for years, I don’t really know if that works either.

        • #4 by Ed on 2015-11-01 - 10:12

          I was raised to put rice in the shakers “to dry the salt”, too, but I’m pretty sure it just rattles around and breaks up the salt clumps. Dunno how you’d test that, though…

  2. #5 by Red County Pete on 2015-11-01 - 19:02

    Mumblty many years ago, I interned at a Moto hybrid circuit R&D lab. One of the vacuum systems used zeolites to do the roughing pumpdown before the ion pump would be started. If I really needed God’s Own Desiccant, it’d involve zeolites. IIRC, it was recharged by heating the cannisters to a couple hundred degrees C for a while. On the gripping hand, not sure just how well an LCD screen would do in a really good vacuum.

    • #6 by Ed on 2015-11-01 - 19:51

      I’m sure the warranty would pop right off: “You did what with the LCD?”

    • #7 by madbodger on 2015-11-01 - 22:11

      Our lab used those too. The zeolite container had a bunch of internal baffles that worked like heatsinks. We’d put a styrofoam container around it, close all the valves, and surround the zeolite container with liquid nitrogen. We’d let it steep for 20 minutes or so until the zeolite was good and cold and would adsorb gases readily. Then we’d open that valve and WHOOSH it would gobble up a truly amazing amount of gas. We’d close that valve after a few seconds in the hope that we’d get a little extra vacuum by intertia and lower boiling point gases (like helium) would get swept along by the others. Then we’d fire up the ion pumps to go the rest of the way down. We’d monitor the first part of the process with nice durable Pirani gauges, and when it was down far enough, we’d light up the fancy Bayard-Alpert ones that worked like inside out vacuum tubes. We’d usually run around 10E-8 torr. Good times.

      • #8 by Red County Pete on 2015-11-02 - 00:18

        I didn’t work directly with that system, but as I recall, it could do 10E-9 torr or a bit better on a very good day. I did a helmholtz coil on the bell jar on another machine, diffusion pump and Welch super-sucker as I recall. We were trying to do magnetic bubble devices, and were 6 months to a year behind what IBM published. The coil was an attempt to lay down a film in a uniform magnetic field. Sort of uniform; bell jars and coils aren’t a good mix…

        (A friend worked for the Intel Magnetics subsidiary when they were trying to build bubble memories. I don’t recall them getting to market…)

        • #9 by madbodger on 2015-11-02 - 08:40

          We were working on periodic focusing. The ultimate goal was inertial confinement fusion, but instead of squashing the fuel with laser beams, we were going to use mercury ions. The idea was that we could have the ion beam equipment separated by a fair distance, and could use regularly spaced magnetic lenses to keep the beams from diverging. Our lab was testing this with a scale model that fit in a room, and we were using electrons as scale model mercury ions. We’d squirt the beam in one end, let it expand and refocus it forty times, then measure the beam quality at the other end. One thing we were testing was electron gun design, so we had to keep opening the vacuum system to switch electron guns. The main pump was a big 1200 liter per second turbomolecular pump, but with this long thin tube (gas is effectively very viscous at very low pressures), we had a bunch of small ion pumps. Sounds like you and I worked on some similarly arcane projects.

  3. #10 by Daniel B Martin on 2015-11-02 - 15:12

    Where is the punch line in this blog post? Readers need resolution, closure. What did you serve with the rice? Shish kabob? Stir fry? Possum peters?

    • #11 by Ed on 2015-11-02 - 20:13

      Shish kabobbed possum peters FTW! [ouch]

      Actually, I poured it back in the rice container: stir fry comin’ on strong later this week.

  4. #12 by Len on 2015-11-04 - 13:00

    You mean this wouldn’t actually work? http://xkcd.com/1598/