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  • best cool pack liquid

    Yard sale shopping today, and bought a water container that's about the right size for my cooler. Yes, I could just buy ice, but I want a less messy system. Because water expands when it freezes, it could easily rupture a container. Adding alcohol would appear to lower the freezing temperature and prevent freezing, but the question is- what happens to the latent heat properties?

    From what I know, water will absorb 4 or more times as much cooling during the change from liquid to ice as it does while it remains liquid. In other words, it continues to absorb 'cool' once it's at freezing temperature, without getting colder, until it's fully transformed into ice. At that point, further cooling will make it get colder.

    An ice pack will get colder before it freezes than water, but does that mean its 'heat capacity' is reduced? And what about antifreeze- does it lessen the heat capacity of water while preventing it from freezing?

    I'm nearly at the point of dumping all my cool-packs into this new-to-me container so I can have one larger 'heat sink' that won't freeze and damage its container, but if I'm getting reduced cooling capacity it seems kind of inane.

    Can anybody in the 'know' clear up this issue for me?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    I am solly Darryl I am not in the know. But as a side note I do make ice packs for my knee right now that are 50/50 isopropyl and water.

    Reason being it doesn't freeze solid and forms around my knee better.

    Also. If you have a freezer that gets below the freezing temp of H2O then it makes sense the alcohol mix would be colder than the 100% water pack right? Its still absorbing cold, or removing heat prolly well after the waters ability to change temp. JR
    My old yahoo group. Bridgeport Mill Group

    https://groups.yahoo.com/neo/groups/...port_mill/info

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    • #3
      The phase change is important. That is where you get the most "cold". If you prevent the phase change, you don't get that large amount of cooling.

      Here's an example with 25 grams of water:

      Step 1: Heat required to convert 0 °C ice to 0 °C water

      Use the formula

      q = m·ΔH f

      where
      q = heat energy
      m = mass
      ΔH f = heat of fusion

      q = (25 g)x(334 J/g)
      q = 8350 J

      Heat required to convert 0 °C ice to 0 °C water = 8350 J

      Step 2: Heat required to raise the temperature of 0 °C water to 100 °C water
      q = mcΔT

      q = (25 g)x(4.18 J/g·°C)[(100 °C - 0 °C)]
      q = (25 g)x(4.18 J/g·°C)x(100 °C)
      q = 10450 J

      Heat required to raise the temperature of 0 °C water to 100 °C water = 10450 J

      So from all this calculation, you can see that just turning ice to water will absorb about 8300 joules of energy. That is almost (80%) as much energy as it takes to take water from nearly frozen to boiling.

      Water has more heat capacity than any other substance. So anything you add to water just decreases its thermal performance.



      Sent from my iPad using Tapatalk

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      • #4
        That's kind of what I figured- the heat capacity is mostly in the phase change. From what I've read, taking water from boiling to gone (fully vaporized) takes even more heat.

        Taking that further, it would be true that vaporizing either a liquid ( say nitrogen ) or solid (dry ice) would give even more cooling capacity. But now I'm straying-

        Suppose that a very small amount of alcohol was added to water, just enough to lower the freezing point by say 10 degrees. Could you now have a block of ice at -10 with virtually the same heat capacity? You might be able to keep something frozen for a time with that, as compared to a block of ice which could at best keep something from warming up past 0 for a time.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          I think that will work. Your frozen mixture would keep the temperature below freezing point (of pure water) for a long time


          Sent from my iPhone using Tapatalk

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          • #6
            I finally found some information relating alcohol/water ratios and freezing temperatures. At 10% alcohol, freezing temp went down to -4C, at 20% it is -9, and at 30% it is -15C. I'm going to make an assumption that you will lose roughly that same percentage of heat capacity to get the lower freezing temperatures.

            I didn't expect the alcohol content to be so high for the minimally lower freezing temperature. Also, I didn't find any info on the expansion ratio of a water/alcohol mixture at freezing point.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              I would use food grade glycol.

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              • #8
                Yacht freezers often utilise a eutectic mixture in their hold-over plates, designed to keep the compartment at -15C as long as possible between engine runs. The brew is often just salty water. Too much or too little salt reduces the amount of heat the hold-over plate can absorb without the temperature changing significantly. I forget the optimum ratio of salt to water, but you should be able to Google it.

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                • #9
                  Before glycol was invented or in wide spread use, most cars up to the mid/late-20s used an alcohol/water mix for antifreeze. They also used calcium chloride mixed with water. This is still used today in tractor tires that are liquid filled and subject to freezing temperatures. I have a copy of the mixing chart published in 1924 for "anti-freeze" solutions if that would help.

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                  • #10
                    Originally posted by JRouche View Post
                    I do make ice packs for my knee right now that are 50/50 isopropyl and water.
                    Have you checked out those pump+cooler+wrap re-circulating contraptions? "Cold therapy" they call them. They have cuffs designed to wrap around particular parts of the body. The lines have quick disconnect fittings, so you can unplug to move around. You just toss the ice in the cooler and you can also adjust the pump to regulate the temp. These are a big improvement if you ice regularly. Also, the cuff for hard to ice spots like the shoulder is really nice.

                    These are usually prescribed after knee replacement surgery but can be purchased fairly inexpensively on ebay.

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                    • #11
                      I used a lot of icepacks when I got migraines often.

                      My findings are there are two general types of icepacks: those that freeze solid for food and those that freeze to a gel like state for injures.

                      The ones that freeze to a gel like state do not hold NEARLY as much cold. However, they also last a LOT longer before leaking as the solid ones like to rip through the plastic, especially if you bend them while frozen
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                      • #12
                        So far almost everything I've googled is related to the medical use of cool packs. I suppose that's where the most interest is in the subject, which is fine. The sparse amount of actual scientific info I did manage to scrounge up was enough to give me the answers I wanted.

                        I ended up filling my container about 3/4 with plain water- well, not plain water, it's chlorine-stinky water- and noted the water level before it went in the freezer. Just now I noted that the level is higher, meaning it expanded upwards as it froze. I'm sure it expanded outwards as well, but I have no real way of knowing by how much- it certainly didn't expand upwards by 11% so the expansion was not limited to vertical rise alone. I will see in the coming few days if the container has become ruptured.

                        All I'm trying to do is keep the melting ice from flooding the cooler. Even bagged it's a bit of a sloppy thing to mess with- I just want to be able to pull the 'ice pack' out and throw it back in the freezer for later use again, and not have to drain the cooler as the ice pack thaws.

                        Perhaps what I really need to do is wrap about 8 beer cans with a canvas or felt of some kind, stack them together in a circle or rectangular shape, put in a canvas bottom, then paint the inside of this with a rubbery compound. I would finish this off with a top with a filler hole and a handle. I could then fill it with water and freeze it and not worry about the container leaking. Once frozen you could handle it easily. Doing some homework I could arrive at a suitable thickness for the canvas or felt (or some other material) that would allow the frozen block to keep the beer and cooler contents cold enough without freezing it, and at the same time last for a few days. Sounds like a custom cooler design is coming up-
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                        • #13
                          Have you tried freezing plastic water bottles? The ribs allow them to expand without breaking. It is better to refill them for this purpose - I find new ones taste funny after they have been frozen.

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                          • #14
                            I've been using 1/2 gal milk bottles for some time. Keeps everything dry and lasts quite awhile.using plain water, I have never had a container rupture. Bob.

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                            • #15
                              Originally posted by Bob Fisher View Post
                              I've been using 1/2 gal milk bottles for some time. Keeps everything dry and lasts quite awhile.using plain water, I have never had a container rupture. Bob.
                              I have also successfully frozen 2L pop bottles repeatedly. they work quite well, very strong plastic that can give a little if needed. Only fill them 3/4~ of the way to allow for expansion.

                              Id wager the main problems with containers bursting is in rigid plastics (PVC pipe), glass and metal, Especially with larger volumes that may freeze unevenly and exert all the expansion at one point, and completely full containers (as in, as full as when you buy them)
                              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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