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  • #16
    From a physics Handbook:

    A very dramatic illustration of a gas cooling as it expands is the formation of dry ice from a carbon dioxide fire extinguisher. As the CO2 gas leaves the nozzle of the cylinder, it expands into the air and cools enough to solidify, forming dry ice. So why does the expanding gas cool?

    They would have both an extreme temprature and a dense particulate manner. And a fire station (if that is where the video was shot) would have extinguishers laying around.

    Maybe too much freetime during a practice class?
    "They who can give up essential liberty to obtain a little temporary safety, deserve neither liberty nor safety." -- Benjamin Franklin

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    • #17
      Originally posted by MarcusKspn
      From a physics Handbook:

      A very dramatic illustration of a gas cooling as it expands is the formation of dry ice from a carbon dioxide fire extinguisher. As the CO2 gas leaves the nozzle of the cylinder, it expands into the air and cools enough to solidify, forming dry ice. So why does the expanding gas cool?

      They would have both an extreme temprature and a dense particulate manner. And a fire station (if that is where the video was shot) would have extinguishers laying around.

      Maybe too much freetime during a practice class?
      CO2 is a rare animal. The reason that the gas cools is through a process called Joule Thompson cooling or as we in the Industrial gas business call it the J-T Effect. As a gas expands it cools, the reason a can gets cold is because the heat is conducted through the metal warming the gas back up causing the metal to cool. That is why there is a rubber handle on the horn for the CO2 extinguisher. The CO2 in the extinguisher is partially liquid. As the gas is expelled from the extinguisher it decompresses cooling and thats where the dry ice snow comes from.
      firemanjb wasnt completely correct in his interpretation of what happens. The can cools because the gas cools it. Kind of like a heat sink in reverse.
      Shawn M. Cecula
      Firefighter
      IACOJ Division of Fire and EMS

      Comment


      • #18
        Originally posted by doughesson
        Nice going.The library just started allowing drinks in the place again and I sprayed my coke all over the screen watching that.Thanks for getting me bounced again.
        We used to use the TIC during parades for a more mature purpose:seeing whose were real and which ones were silicone.
        There is a discernable heat differential(boy,that's hard to spell)between the implants and the body's normal temperature.Gone are the days of wondering if you're admiring a hopefully legal woman or a couple bags of saline.
        Well...I know where I am going to ask to ride in next years 4th of July parade.
        "If people concentrated on the really important things in life, there'd be a shortage of fishing poles."
        ********

        IACOJ

        ********

        "Criticism is prejudice made plausible."
        - H. L. Mencken (1880-1956)

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        • #19
          Originally posted by Lewiston2Capt
          CO2 is a rare animal. The reason that the gas cools is through a process called Joule Thompson cooling or as we in the Industrial gas business call it the J-T Effect. As a gas expands it cools, the reason a can gets cold is because the heat is conducted through the metal warming the gas back up causing the metal to cool. That is why there is a rubber handle on the horn for the CO2 extinguisher. The CO2 in the extinguisher is partially liquid. As the gas is expelled from the extinguisher it decompresses cooling and thats where the dry ice snow comes from.
          firemanjb wasnt completely correct in his interpretation of what happens. The can cools because the gas cools it. Kind of like a heat sink in reverse.
          I am not a chemist, so I apologize if I have led people astray. However, when you take a container, such as LPG and run it, the container gets cold. I thought this is because the liquid is being heated (or absorbing heat from the cylinder) to boil and turn into a gas.
          My comments are sometimes educated, sometimes informed and sometimes just blowing smoke...but they are always mine and mine alone and do not reflect upon anyone else (especially my employer).

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          • #20
            Originally posted by firemanjb
            I am not a chemist, so I apologize if I have led people astray. However, when you take a container, such as LPG and run it, the container gets cold. I thought this is because the liquid is being heated (or absorbing heat from the cylinder) to boil and turn into a gas.
            That is some of it, but the expansion of the gas is also endothermic. Go here for some technical info on the JT effect.
            Shawn M. Cecula
            Firefighter
            IACOJ Division of Fire and EMS

            Comment


            • #21
              Originally posted by JTFIRE80
              The speed limit in front of the station is 25MPH. It's always fun to park the duty officer's vehicle on the front apron, and stand there with the TIC and pointing it at cars as they go by and watch the break lights come on!!
              Cool...Now I have 2 new things to try with the TIC.
              Fire Marshal/Safety Officer

              IAAI-NFPA-IAFC/VCOS-Retired IAFF

              "No his mind is not for rent, to any god or government"
              RUSH-Tom Sawyer

              Success is when skill meets opportunity
              Failure is when fantasy meets reality

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              • #22
                Originally posted by WaterbryVTfire View Post
                Well...I know where I am going to ask to ride in next years 4th of July parade.
                We used to be able to ride the hosebed and the midships station during the P-rades but that got halted last Memorial day and we now have to either ride in the cab or walk beside the rig.
                Since the hosebed is one of the better vantage points when you pass by a former female boss in her tank top(looks like Brooke Gordon with blue eyes.oobah-doobah),that really takes the fun out of going parading.

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