Thread: Peltier Fog Chiller

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Hi, I've been wanting to build a fog chiller for ages. I started one a few years ago but never got around to finishing it. I know there are a lot of threads about fog chillers in general but I can't find any that mention using Peltier modules. I was just wondering if they could possibly do the job.

The plan is to make a thin, long box with a bunch of heatsinks inside. The Peltier modules would be in the sides of the box and more heatsinks on the outside. The idea is that the Peltier modules move the heat outside of the box so the heatsinks on the inside are cold.

A lot of people have said that more contact with ice is better. Hopefully heatsinks should provide a lot of contact. Is there any hope for this idea or is there a reason that I've not heard of anyone else trying it?

Smithy,

What is the BTU for these Peltier modules. Keep in mind that it is not only contact that you need to consider, it is heat transfer. How quickly can these units transfer heat. Keep in mind that even a 400 watt fogger is putting out nearly 8000 CFM. That is nearly steam temperature vapor you are trying to cool. It is like the idea some have regarding using a refrigerator unit. If you turn off a freezer and let it get to room temp, how long does it take until it returns that relatively small CF of air to return to 32 degrees. Now insert 180 degree vapor. If you wish to approach this from a non ice basis, then investigate the coiled copper tubing concept or try using heater cores. Personally I think a few heater cores lined up in a cooler could work quite well. The trick is to be constantly circulating chilled water through the core. The concept is the reverse of the process a car uses to keep it's coolant below boiling under pressure. The key to fog chillers is surface area contact along with thermal transfer rate. A large contact area will do no good unless you can pull the heat from that contact area rapidly. So if you have one of these peltier modules you can do a quick test. Energize one and see how fast it gets cold. The dunk it in hot water and remove. If when you bring it out it is ice cold, then you may have something. But if it takes like 5 seconds to get cold again, I do not see much future in it's use. Now cooling in stages could help, but again. In most coolers the fog comes in contact with ice. The ice melts but still there is more ice to come into contact with. Do you see my point?

Hi Smithy. I haven't tried using Peltier modules in a fog chiller, but I've been experimenting with them quite a bit on a secret prop I'm building. From what I've seen, I don't think they would work all that well. Here's my reasoning but remember: I'm a prop builder, not an engineer so don't trust anything I say.

1. They're not magic. All they do is transfer heat from the cold side to the hot side, which is about 1/8 of an inch away. To do this, they use a lot of power and generate a LOT MORE HEAT. You then have to deal with all of that transferred heat as well as the generated heat.

2. Small surface area. Most common/cheap Peltiers are 40mm to 50mm square. That's all the area you can pull heat from. You can't put a very big heatsink on the cold side before you overload it and it's entire cooling potential is used up just trying to get the cold heatsink cooled below ambient. (If that makes sense...)

3. There's a limit on the temperature difference between the hot and cold side. I think most state a 60 degree Fahrenheit difference, but that's under idea conditions. Under normal room temperatures including insulation between the hot and cold side heatsinks, using thermal grease on polished copper plates on the heat sinks, and pretty large cooling fans, I'm getting 40 degree temperature differences after a sustained 30 minutes. Let the hot side get up to 80, and the cold side will only be around 40... I don't know what the lowest temperature they'll get down to is, but they are useless if the hot side gets above 80-90 F.

4. They take a LOT of power. The 40mm (~1 1/2") modules I'm using are 90 watt. That's 7.5 amps DC at 12 volts. Put 10 of them in a tube and you need 75 AMPS to run them. Anything below the peak amperage, and they don't work well. You then also need to dissipate that 900 watts of heat PLUS the heat you draw out of the tube. That's a lot!

I'm not trying to burst your fog bubble. I really hope you can figure out a way to make them work. It would be great to have a waterless fog chiller! Good luck!


Edit: To add on what Spinman said, it does take a few seconds to get cold again after heating up. Probably 3 seconds to go from room temperature to freezing without a heatsink on the cold side. With a 50mm square piece of 2mm thick copper on a 135 watt Peltier, it takes about 8-10 seconds.

That makes a lot of sense. I have a single Peltier module already. It can cool from room temperature to very cold almost instantly. My main worry was if they would actually be cold enough to cool the fog properly. The chiller will be run outside so I expect quite a low ambient temperature. I live in the UK afterall, even our summers are cold

The ones I would be looking at are 100W and are fairly small. They are designed to help cool CPUs. I know CPUs can kick out a lot of heat so they must be doing something good.

Last year I put smoke through a few meters of drainpipe. The smoke didn't resemble dry ice but it definately reacted differently to normal. The pipe was quite cold due to the ambient temperature.

I was planning to have a box where the inside is a similar dimension to the tube and have Peltiers on either side. That way I can use pretty small heatsinks. I may have to include fans on the outer heatsinks which will be larger anyway. I'm hoping to put something like 16 modules in the box.

I understand the current issues. I need to try stringing a few of them together in series. I don't know if that will actually work but if I ran them in sets of 4 then I would need 48V but only as much current as 4 of them would take.

My aim is to make a chiller that works effectively, is as self contained as possible and doesn't need anything putting in it. Our freezer is very small so we can't make much ice. Peltier modules may not be the way to go. They are just 1 of many ideas.

Good luck.

I have to tell you that I honestly believe this is not going to give you the results you are looking for.

How are you going to get the cold side of the peltier into the fog stream without whatever heatsink you use on the hot side from being exposed to the fog? FYI Most effective coolers have literally square feet of conductive surface in the path of the fog. Be it ICE, Aluminum pipe or copper tubing.

Keep in mind the CFM. 8000 CFM is a lot of air mass moving at a very fast pace. 8000 CFM is the equivalent of filling a room 20X40X10 ft. That is a lot of hot moist vapor.

But if you are willing to make the investment to try this approach, then by all means please do so. We may indeed learn a new and unique way to cool fog.

Oh and re ambient temp. Basic rule. Heat rises. So if you have a very low ambient temp, the best fog chiller in the world will not keep the fog on the ground. If it is 32 degrees out, then unless you can get the fog temp below that, the fog is going to rise. Some of the professional dry ice units can provide dense low lying fog at any ambient temp, but they are using dry ice. No heated fog juice.

Fravak,

OK spill. What secret prop? No secrets allowed. LOL !!! How about a hint? I know. It is going to be the grim reaper with ice cold hands of death. Right ?

Ohhh. Cold hands of death. I like that!

I guess I have to tell you now. Sorry to temporarily hijack your thread, Smithy. I was planning on making a fool out of myself in private before I posted it on the forum and someone says "you know, they have that same thing at www.obscurehalloweenwebsite.com for $0.99 and it's a lot better..."

I'm changing my theme this year to Harry Potter and I've been playing with making lots of little "magic" props. One of them is a Marauder Map that's drawn on paper and has printed footprints that move. I'm using Peltier's behind it to precisely heat and cool thermochromic paint on different parts of the paper to make things appear and disappear. I'm going to use the same trick to make the eyes of a painting look like they move but it's obvious they can't because it's just painted canvas. I want people at our party to get chills up their backs not because something jumped out at them, but because they may or may not have seen something out of the corner of their eye that couldn't possibly have happened.

I love the eye's moving idea. Do you paint a bunch of pupils and iris's in an array?

Heat reactive paint. Oh I am so looking into this.

Very cool ideas !!

That sounds like a really good idea. I can't wait to see the end result.

spinman1949: You gave me an idea with those heater cores. I wonder if pumping water from a tap would work. It does seem a bit wastefull but I could setup a valve to turn it on a set period of time before fog comes out.

I never realilsed before that the fog has to be colder than the ambient temperature. I just thought it had to be cold. It makes perfect sense now you mention it. We would probably be looking at around 5C ambient (41F I believe). In that case I would have to make the fog very cold to stick to the ground. Does anyone know at what temperature the fog would condense?

I will have a think about other ways to do it but aside from building an actual freezer it might not be possible.

Spinman, I haven't figured that out yet but I will let you know when I do.

instead of just pumping water through the heater coils, what about using a fountain pump to recirculate ice water? That would eliminate the wasted water.