Dry Ice Sublimation Rate

For reasons I’m not at liberty to discuss, we had a cooler of dry ice pellets in the freezer for a few days. I used about a pound of it a time to mumble.

I started with “10 pounds” of dry ice in a half-pound Styrofoam container with 1.5-inch thick walls; the total weights include the container. For what it’s worth, dry ice costs $3.50/pound under 10 pounds, then $2.75/pound over that. It used to be plenty cheaper in the old days, evidently, but everything else was, too.

In between withdrawals, the cooler sat in the freezer and and the dry ice quietly sublimated; here’s how the weight varied between uses.

Starting weight: 9.2 lb gross, so I lost quite a bit in transit. Which, as it happened, was about half an hour in a bike trailer during a rather hot afternoon.

A) 7.2 to 6.7 lb -> 0.5 lb / 15 hr = 0.033 lb/hr

B) 3.8 to 3.0 lb -> 0.8 lb / 11 hr = 0.072 lb/hr

C) 2.7 lb to 2.0 lb -> 0.7 lb / 11 hr = 0.064 lb/hr

I’m suspicious of that low number for the first stay, too. Maybe a side effect of having the cooler’s cavity nearly full of dry ice? Or the freezer ran defrost cycles for the other two?

Anyhow, to a back-of-the-envelope resolution the cooler loses a bit over 0.05 lb/hour of dry ice. Call it 15 hr/lb.

The temperature of sublimation is, according to Wikipedia, -109°F. The freezer is around 0°F: a differential of 109°F across 1.5 inches of Styrofoam. Assuming the cooler foam has R=4 with units of (ft^2·hr·°F) / (BTU·in ) and an internal surface area of 304 in^2, the cooler leaks heat at 38 BTU/hr. Call it 11 W.

Cross check: Wikipedia says the enthalpy of sublimation at STP is 571 kJ/kg. Sublimating 0.07 lb = 0.031 kg requires 18 kJ (18 kW·s) and doing that over the course of an hour requires 5 W.

Well, considering the rough-and-ready measurements and the fact that the freezer isn’t at STP and that I’m ignoring gas leakage and a bunch of other stuff, a factor of two error is spot on.

If I were you, though, I’d double-check those calculations before leaping to any particular conclusions. Fair enough?

When all was said and done, I found this thing in the bottom of the cooler. It wasn’t there when we started, soooo

Dry Ice Thing

Dry Ice Thing

  1. #1 by Steve on 2010-08-27 - 13:47

    We use to go through a lot of dry ice where I work (used it to cool PMTs on an aircraft instrument). It always made me cringe when I saw people putting it in their drinks; you’d be surprised the stuff we found. The thing we were trying to cool quite often had a black greasy film on it, and not that uncommon was to find cigarette butts after all the ice was gone…

    I once filled my garbage disposal with dry ice, ran the hot water, then turned it on creating quite a bit of surface area to come in contact with the hot water. Massive volcano billowing up and bouncing off the ceiling…

    – Steven Ciciora

    • #2 by Ed on 2010-08-27 - 14:57

      I once filled my garbage disposal with dry ice

      All I can say is, it must’a made sense at the time. I know that feeling!

      Evidently, you can sandblast with the stuff, too, It works just like any hard particle with the benefit of leaving no residue behind. I can’t imagine an application for that around here, but why should that be a limitation?

      • #3 by david on 2010-08-29 - 05:32

        Sounds like fun to me!

        FYI, keeping CO2(s) in the freezer is not really good for the freezer, or so says all the paperwork anyway.

        • #4 by Ed on 2010-08-29 - 06:59

          keeping CO2(s) in the freezer is not really good for the freezer

          OK, I’ll bite. Why is that?

          Other than filling the refrigerator with inert gas and killing all the fauna, what else happens?

          • #5 by david on 2010-08-29 - 21:47

            Well, honestly I’m not 100% sure — that’s just what They Say. My first theory was that you might freeze the freon and explode the heat exchanger, but that doesn’t seem tremendously likely. I think it’s just that you’re generally taking components below their design temperature range…

            • #6 by Ed on 2010-08-30 - 08:13

              Well, as we all know, They Must Be Right…

              On the other paw, this was inside a foam box with a cooling effect of maybe ten watts. Can’t see as how that makes much difference inside a big box that’s leaking an order of magnitude more heat from the room.

              Didn’t find any dead fauna, either, but we don’t have a lot of refrigerator fauna under normal circumstances.

              Now, laying a slab of dry ice right on the floor of the freezer box, I’ll grant you that seems like a Bad Idea.

  2. #7 by FM on 2011-02-11 - 10:55

    Hi:
    If you never took the dry ice out to test weigh it and using your sublimation rate, I’m to surmise the dry ice in the cooler would last approximately 2 days in the freezer?

    By any chance have you tested the sublimation rate in the same cooler while sitting in ambient air?
    If so, what was your findings?

    Email me this answer when you can. THANKS!
    FM

    • #8 by Ed on 2011-02-11 - 12:05

      IIRC, the freezer kept the ice for about two days, even though we opened the foam box to pour out the granules.

      CO2 chunks in the same foam box, sitting on a table, were good for a day, which is why we decided to try those pitiful yeast reactors.

      None of those numbers have more than one significant figure of accuracy!

      Email me this answer when you can.

      If you’re not interested enough to check back, then I’m not interested enough to bother with an email… let us keep the conversation here, so everyone can benefit. Fair enough?

      • #9 by FM on 2011-02-11 - 12:51

        THANKS Ed for the responce.

        I didn’t see the “Notify me of follow-up comments via email” line until after I hit POST COMMENT.

        • #10 by Ed on 2011-02-11 - 14:16

          It’s not like I’ve never done anything like, oh, say, hit [SEND] before attaching a file…

          Welcome back!

          • #11 by FM on 2011-02-11 - 15:20

            On a further note of Dry Ice.
            I’m looking to extend the storage of it as long as possible, . . . UPDATE !
            I just (I mean just) got this email from a dry ice mfg.

            “10 lbs of dry ice would keep your frozen products deeply frozen for a week. The insulation layer would slow the freezer burn that may affect your product sitting directly above the ice. Layers of cloth rags and cardboard along the edges and bottom will help slow the sublimation process. I would consider putting blue ice packs on the dry ice as your insulation and fill in the spaces with more rags. Once the dry ice is gone, the blue ice will continue to help keep the product cold. Put your product in the cooler pre-frozen, and if there is room, frozen packs of blue ice on top. That way the blue ice packs acts as an indicator to the level of cooling.”

            Passing along info for all to read and learn.
            Thanks again.
            FM

            • #12 by Ed on 2011-02-11 - 18:59

              Layers of cloth rags and cardboard along the edges and bottom

              I assume this is inside a more-or-less sealed container with very thick foam walls. If not, beware of condensation: the exterior drops below the dew point in short order and stays there as long as there’s dry ice inside.

              Good luck…

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