Announcement

Collapse
No announcement yet.

Dry Ice weight calc

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Dry Ice weight calc

    OK smart guys.. How much (in theory) dry ice (assume it's at sublimation temp of -78C) will it take to cool 1 gallon of Ethyl alcohol (97%) from -12C (my freezer) to -70C? I'm making a dry ice cooling bath to cool a cylinder sleeve for shrink fit insertion... tomorrow. I'd rather not buy 20lb to find 5lb worked... or 5lb and need more.
    Last edited by lakeside53; 03-15-2017, 12:05 AM.

  • #2
    Originally posted by lakeside53 View Post
    OK smart guys.. How much (in theory) dry ice (assume it;s at sublimation temp of -78C) will it take to cool 1 gallon of Ethyl alcohol (97%) from -12C (my freezer) to -70C? I'm making a dry ice cooling bath to cool a cylinder sleeve for shrink fit insertion... tomorrow. I'd rather not buy 20lb to find 5lb worked... or 5lb and need more.
    Mass of alcohol x specific heat of alcohol x temperature change desired < mass of dry ice x heat of sublimation

    Therefore mass of alcohol x specific heat of alcohol x temperature change desired / heat of sublimation < mass of dry ice
    Last edited by Lee Cordochorea; 03-14-2017, 10:52 PM. Reason: simplified/solved equation

    Comment


    • #3
      1 gallon Ethyl alcohol is 2.99 kg.
      Specific heat of EA is 0.6cal/gm
      Temp change desired = -70- (-12) = 58C
      Heat of sublimation is 32.3kJ/mol

      The mol part leave me uncertain... CO2 molar mass is 44g/mol.

      Now what?

      Comment


      • #4
        32.3kJ/mol x 1mol/44g = 32.3kJ/44g = 734J/g

        One calorie = 4.184 Joule

        Comment


        • #5
          I'll give you $1.00 if you tell me the answer


          My guess...

          2999 * 0.6 = 1799.4 cal per deg C. X 58 = 104365.2 cal. heat to be removed.

          104365.2 / (734 x 4.184) = 33.93 grams dry ice.

          WRONG... confused...
          Last edited by lakeside53; 03-15-2017, 12:06 AM.

          Comment


          • #6
            I think you misplaced the 4.184
            (104365.2 x 4.184) / 734 = 594.91 grams dry ice.
            Location: Long Island, N.Y.

            Comment


            • #7
              lol.. yes... One beer too many.

              Heck... that's only 1.3lb of dry ice! I can afford at least 2X that Petty cheap considering I'll get back most of my Ethyl Alcohol.


              I want the 8 inch deep cast iron cylinder sleeve to drop into a cast iron block. I bored the block for a 2 thou interference fit. I hope to heat the Block to 100 - 125C... I get one chance to pop it in or i'll have to resort to driving in cold with a big press. Don't want to do that with a thin wall sleeve.
              Last edited by lakeside53; 03-15-2017, 12:29 AM.

              Comment


              • #8
                Does that mean I get the dollar?
                Location: Long Island, N.Y.

                Comment


                • #9
                  yep!

                  Comment


                  • #10
                    Originally posted by lakeside53 View Post
                    OK smart guys.. How much (in theory) dry ice (assume it's at sublimation temp of -78C) will it take to cool 1 gallon of Ethyl alcohol (97%) from -12C (my freezer) to -70C? I'm making a dry ice cooling bath to cool a cylinder sleeve for shrink fit insertion... tomorrow. I'd rather not buy 20lb to find 5lb worked... or 5lb and need more.
                    Ethanol/dry ice baths are good to about -72 C... so you are okay there.

                    https://en.wikipedia.org/wiki/List_of_cooling_baths

                    However, the calculation that shows that about 1.3 lbs will be enough has forgotten several things ...

                    1) cooling the container
                    2) freezing the water
                    3) cooling the cylinder sleeve

                    The container is probably relatively low thermal capacity... but I'd add 10 to 20% just to offset that.

                    It's only 3% water, but the heat capacity of the phase transition of water to ice is high. To make it more complicated the actual freezing temp of the water in a EtOH/H2O mix depends on the composition of the mix so it's possible that only part of the water will freeze out. Looking that data up looks like a lot of bother, so I'd just assume that all of the water freezes out and use that to calc the heat required to freeze 3% of 1 gallon of water. Oh heck, that seems like a lot of work. Just add another 10% of dry ice to compensate.

                    You didn't mention the weight and metal of the cylinder sleeve. If it's a thin sleeve that only weighs a couple dozen grams it's not a big thing... but if it's thick and tall and weighs a few pounds then you better add the heat capacity of that.

                    Don't forget that while you are cooling the sleeve, there will be heat transfer through the container walls. Better add 10% for that.

                    How soon after you buy it are you going to use it? It's going to be be subliming on the way home. Better add a little for that.

                    Oh heck, buy a lot ...

                    Comment


                    • #11
                      yep.. all a consideration! I just wanted to get into the zone.. I'll call it 2lb per gallon and never calc it again. This time a 5lb pack will do it.

                      I'll post pics soon... The bath is thin wall stainless in 3 inches of spray foam. Tiny losses there. Cylinder sleeve - yep - frozen in the freezer so same 58C drop required, but some compensation required. The Ethyl is actually a lab grade mix of 97 parts ethyl, 1 part methanol and 2 parts of other stuff to make it undrinkable. It doesn't list water content but I'm sure it has some by now. I'll add a few more cubes of dry ice!

                      Much of this is a grand experiment. I need to shrink stuff often but never seem to have the time to figure it out or have a bath ready. Now i will have.

                      Might have time to freeze some flowers and smash them with a hammer! Or deal with those rubber coated shafts that need turning, , or...
                      Last edited by lakeside53; 03-15-2017, 01:06 AM.

                      Comment


                      • #12
                        I Dont know how much you pay or how long drive you have, but in some cases getting co2 ice from bottle is easier and cheaper. And you dont need to use more than necessary, rest of it can be used year later, unlike dry ice.

                        Comment


                        • #13
                          3 miles.. our local supermarkets carry it! Last time I bought it year ago it as 99c a lb. I''m sure its more now, but not expensive.

                          Comment


                          • #14
                            Originally posted by lakeside53 View Post
                            3 miles.. our local supermarkets carry it! Last time I bought it year ago it as 99c a lb. I''m sure its more now, but not expensive.
                            Sucks to be you, around here its anything from 20 to 100 mile drive, you have to order it 2 days in advance and smallest amount is something like 20 pounds and 100 usd!

                            Comment


                            • #15
                              Lots of miscellaneous variables (heat radiation, mass of the work, dally time, drafts, spills, ambient temperature, etc) to screw up a precise answer so I suggest you simply roughly it out and add a safety margin. I'd start with a couple pounds of dry ice as being cheap enough and a little waste excess wont break the bank.

                              Besides, dry ice is fun to play with. Smudge under your eyes with soot, develop a hideous cackle, and wander the shop dragging a foot, chanting "Brains! Want brains!" carrying a coffee cup of dry ice in water drooling curdled looking vapor over the top.

                              You can't heat the cylinder? Generally simpler and you don't have to deal with the iron hard bark of condensate ice that instantly forms on parts at cryogenic temperatures. Move fast from bath to insertion. Rehearse every step.
                              Last edited by Forrest Addy; 03-15-2017, 06:28 AM.

                              Comment

                              Working...
                              X