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Dry Ice Question #4.2 Million

Discussion in 'Special Effects' started by gabei, Dec 20, 2008.

  1. gabei

    gabei Member

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    I know, I know...there are a ton of threads already out there on dry ice and how to use it, but after searching for over and hour I haven't found the answer to my question.

    I am using dry ice for a newer play version of "Les Miserable". My dad and I built our own fogger, consisting of a 31 gallon Rubbermaid container, a 4 inch duct fan which we grounded and wired to a on and off switch, and a dryer hose to carry the fog from the wing. We plan on building one more and placing one on each side of the stage.

    After playing around, I have figured out the more water you have, the better the fog, but what I haven't figured out is "How much do I need?".

    The beginning of our show starts with the scrim down and a timeline being projected on it, building up to the French revolution. We are wanting to dry ice our stage enough that we can raise the scrim, some will roll out and stand on the stage for about one minute. Our stage area we are wanting covered for this is 22'X40'. How much dry ice do I need for each one of these foggers for this effect?

    Also, we are wanting to use a small amount of dry ice for a graveyard scene and also a river scene. The dry ice is not suppose to be the river, but instead just an added effect and something for the lighting designer to play off of. How much would we need?

    Thanks! :)
     
  2. Footer

    Footer Senior Team Senior Team Premium Member

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    First things first, to get a good dry ice fog effect you must heat your water and keep it hot. The show I am currently working on (and watching for that matter), we have two aqua foggers and burn through 50# of dry ice a night for a 6 min effect. Also keep in mind these are very effeciant machines. Have you tried your machines onstage yet? Dry ice fog is less about the fan, its more about the heat. Infact, a fan can make things worse.
    Posted via Mobile Device
     
  3. icewolf08

    icewolf08 CBMod CB Mods

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    As with most fog effects, you really need to test it in the space. You also need to realize that every day it will behave differently. Heat, humidity, air pressure, what doors are open, and how full the house is all play a huge part in how any fog effect works. So, in order to best figure how much dry ice you need you will need to run a test in the space with the scrim and such in place. You will probably need a significant amount of ice to test with, and you will probably find that with a space the size you describe you will need a lot of ice for each performance.

    As [user]Footer[/user] said, in order to get the most from your effect you need to heat the water and keep it hot. You want to start with the water as hot as you can SAFELY get it because when you put in the dry ice you cool the water amazingly fast and the effect peters out as the water cools. This is one of the reasons people use 55 gallon drums as foggers, the more water you have at temperature compared to the amount of dry ice, the slower the water cools.
     
  4. David Ashton

    David Ashton Active Member

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    What no-one has said explicitly is that you need to feed the dry ice in at the slowest rate you can get away with, as all the extra dry ice you put in is cooling down that water rapidly, so a slow continuous feed is much better than dropping one big load in.As soon as the water cools to a point the effect ceases and there's no point in adding more dry ice.
     
  5. gabei

    gabei Member

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    Thanks for all the information! :)


    From previous roadshows and such, I already knew the problem with keeping the water hot. But since for this show it is a very brief time that we want to have it (one minute or less), do I need to really invest in some form of a water heater? My idea was to heat around ten gallons of water, place it in the container, and then add the dry ice slowly to that over a course of a minute. After the scene I have a good amount of time before we would use the effect again.

    And Footer stated that a fan isn't important. Maybe it doesn't play a big role in your machines set-up, but without one in mine, the fog does not get down the 8' of hose without it. The fan is extremly small, about silent, and easy to control so I love having it as a part of my set up.
     
  6. gabei

    gabei Member

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    This is what the beginning of our show is wanting to look like. This is the world class Jacob School of Music doing "The Nutcracker" this year. The ballet isn't world class, but it is a school of MUSIC. The effect is I believe about minute 52. It is the beginning of Act II. They use four foggers, we are using two because we don't want ours to be that big! :)

    http://music.indiana.edu/iumusiclive/streaming/
     
    Last edited: Dec 21, 2008
  7. 1kfresnel

    1kfresnel Member

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    I found the heater an important element in our dry ice foggers, especially when running an effect for more than a short burst, to keep the water up at its most efficient temperature level.

    We recently used 4 small units, each with a 2000w/120v water heater that was picked up from the hardware store for about 10$. I then used a 1" copper pipe flange to thread it into the bucket. It came with its own sealing rings. I also soldered a ground conductor to the body of the element (on the outside of the bucket), as this ground is normally provided by the metal body of the tank. I used another (1.5" I believe) PVC cap to cover all the electrical connections for safety.

    The heaters come in 1500/2000w @ 120v for about $10 or 3500/3800w @ 240v for about $9 at your local big box hardware store. There is also a monstrous 5500w version. The copper screw flange and PVC cap couldn't have cost more than 2 bucks extra.

    It significantly helped improve the reliability and effective feed rate of our foggers, and saved us from carting around water, which really helped because part of the effect was in the house!

    Another thing that helped was adding insulation to the outside of the bucket, to reduce heat loss. We use a commercial insulation product called Armaflex(?), since we had connections to an insulation contractor.

    Warning: working with electricity and water is a dangerous mix. Consult a licensed professional for assistance.

    Best of luck with your effect!
     
  8. gabei

    gabei Member

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    I have figured out a way to heat a bucket of water and keep it hot for dry ice fog effects for CHEAP! The best thing is it is grounded and you don't have to do any wiring yourself, like you do with traditional water heater elements and such.

    Here is the link for it on the company's website:

    Bucket Heater

    I found it at Tractor Supply Co. for $33 bucks.
     
  9. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Just a little example on a small scale for you to experiment with in order to get the big picture. Let's say you want to do your classic smoking drink cup. So you take a cup, you put moderately warm water in it, and you drop in a hunk of dry ice. The ice can easily freeze all the water in the cup before it finishes melting and you will find you have a hunk of dry ice encased in frozen water. The same thing can also happen on a fog machine. That's why you need the water as hot as possible, and you need to carefully experiment with how much dry ice and how fast it get's added. Just using tap water and heating some of it will not do nearly as good of a job as water that is very nicely heated.
     
  10. 1kfresnel

    1kfresnel Member

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    Very true. This is also why another variable is the size of the pieces you are putting in. The more surface area, the better. In some instances, you can get the dry ice in pellet form from the supplier -- though not all suppliers will do this. When they do, it's very convenient :)
     
  11. gabei

    gabei Member

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    I understand the idea of keeping the water warm, but what I was struggling with the "how" factor. I talked to the company who builds the bucket warmer (NOT a bucket DEFROSTER), and according to them, it can reach up to 200*F, which I think would be fine. For example: If the water is 200*F, and I add the dry ice is which is 109.3*F (=110*F) to it, it would drop the water to around 90*F. 90*F is more than enough to keep the water from freezing and the dry ice effect to keep working.
     
  12. jwl868

    jwl868 Active Member

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    [I think the temperature should read -110 degrees F for the dry ice.]

    In any case, the heat of sublimation of dry ice is 246 BTU/lb dry ice. [That is, it takes 246 BTU for 1 lb dry ice to vaporize.] The quantity of dry ice wasn't stated, but I don't think 10 gallons of water is enough, in light of the posts by several others.

    I took some time do some basic calculations (attached) (Maybe I have too much time on my hands, but the mathematics of it appear to be ignored.)

    [I also attached it rather than posted it becasue it would take too much space.]

    Joe
     

    Attached Files:

  13. tomed101

    tomed101 Active Member

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    Another thing to think about is to have your water container with the largest possible surface area. If you have tall narrow containers, an ice cap can form over the top. When this happens, pressure builds up under the cap. I suppose it would be possible for it to explode but what happened once to me is the cap broke and I ended up with about 20L of water on the stage and very nearly got into the floor pockets.

    Just my 2c
     
  14. gabei

    gabei Member

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    So I tested it last night. I used our garage, which is about 1/2 the size of the stage that we are using it on. Using a five gallon horse watering bucket, and the bucket heater which I let sit for about ten minutes before using. I added five roughly 3" cubes of dry ice into it and closed the lid. Flipped the fan switch and the best dry ice fog I have ever seen came out.

    It was extremly thick, moved quickly, and it tended to haze out instead of just fading. The bucket heater keep the water warm the whole time, and I even added more dry ice as I went along, ending up putting about ten pounds of dry ice through out the cycle in it. It works great. This one by itself was covered the garage in a pretty dense fog, and we plan on using four of these foggers for the production, so I think it will be just fine!

    Thanks for all the help! :)
     
  15. 1kfresnel

    1kfresnel Member

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    That's great to hear. Glad it's working out so well for you. Best of luck with your production!
     
  16. Footer

    Footer Senior Team Senior Team Premium Member

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    You might also want to look at some type of basket to pull the dry ice if you want to stop the effect.
     
  17. gabei

    gabei Member

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    No bucket is needed since the fan can be turned on and off. Once the fan is turned off, the fog stops moving down the tube, and instead just stays in the container., turning into a small amount of water.
     
  18. BillESC

    BillESC Well-Known Member Premium Member

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    Another trick is to salt the water. It will retard the formation of ice around the dry ice.

    Won't stop it but will slow it.
     
  19. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    The purchased fog machines all have the basket. Yes the fog will stop flowing when you turn the fan off, but without the basket you are still burning through you Dry Ice. The basket removes the ice from the water stopping the process and allowing your water to reheat. Depending on the show and affect you can stop the effect, wait a while, and then do it again by raising and lowering the ice basket. The basket also allows you a little control of how fast you drop the ice into the hot water which means a little control on how much fog comes out.

    Please post some pictures of your machine for the benefit of others considering building their own machine.
     
  20. gabei

    gabei Member

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    Here are some of the pictures of the fogger I built. I will try to give you a idea of how to build it and what everything is.

    Picture 1: The "Machine". This is what that fogger looks like when it is all but together. What you can see from the outside is a 31 gallon Rubbermaid container and a dry hose vent.

    [​IMG]

    Picture 2: The "Fan". It is just simple air-duct fan that I bought from Home Depot. The fan is already incased in a a four-inch tube. I just had to wire the fan to the light switch and ground it. I also attached the electric box to the outside of the metal tube the fan is in. It helps to have more than one person to do that because it is a small space to work in.

    [​IMG]

    Picture 3: The "Connection". This picture shows the connection between the fan and the Rubbermaid container. It is attached with the help of a dry exit vent. I cut a hole in the Rubbermaid container that was a 4inch circle, cut the tube on the end of the dry vent exit in half, and put it through the hole. Then I simple bolted this to the Rubbermaid container. Also, the vent faces down, and since the dry ice fog falls the vent pulls more fog than air.

    [​IMG]

    Picture 4: The Water Heater. This is a bucket heater, not a bucket defroster. It found it at a Tractor Supply Company. It is really simple to use: put it it in a bucket of water and plug it in. It is grounded, has a safety guard, and shuts off when the water gets below 6". Here is a link for the company who makes it:

    Bucket Heater

    And a picture so you can see how big it is:

    [​IMG]

    Picture 5: Inside the Fogger. This is what everything looks like inside when set up. I know some people like the idea of using a bucket with holes to hold the dry ice, so I made sure there was room for it to sit in there too. The green bucket holds about five gallons of water and the heater. The yellow would hold the dry ice. (I know the hose isn't connected in this picture, but would need to be. Also, the hose is painted black now to help hide it.)

    [​IMG]


    Hope this helps you anyone who wants to build their own. This one cost about $100 to build, but you could do it for alot cheaper. I just bought the stuff when I found it. For example: I bought the Rubbermaid that cost $15. You can find an off-brand for less than half of that. Plus, if you have the stuff laying around, then you save there too.
     

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