# Fog Chillers and thermal mass



## Evil Andrew (Nov 6, 2009)

A few years ago , I built the typical fog chiller with a cooler and an aluminum dryer hose, and it works OK.

Lately, I've been thinking about thermal mass. Thermal mass is the ability of an object or material to store heat ( or cold). Stone buildings like castles always feel cold, and require huge amounts of energy to heat because of the thermal mass of thick stone walls. Tile floors always feel cool because of thermal mass. Brick walls radiate heat after the sun has gone down because of thermal mass.

So - 

Would get more actual cooling power in my chiller by using a length of thick walled 4" cast iron pipe (because of the thermal mass and thermal conductivity of the metal) over the very thin walled (low thermal mass) making several loops through the chiller ? I've seen a few chiller designs that just use wire mesh, giving the fog direct contact with the ice. 

Any engineers out there that can help me think this through ?


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## HalloweenRick (Nov 25, 2005)

I can only give you what I myself have experienced, which is that using hardware cloth as the "tube" works great! I built myself 2 fog chillers using $4 Target 18 gallon containers, with 4" corrugated pipe leading into the chiller and 1/2 hardware clothfor the inside tubing. Fill that puppy up with ice, and even using the cheap Target fog fluid, I got a nice, dense, low lying fog, which worked even better as the night went on as the temperature dropped. Devious Concotions uses copper tubing in their fog chillers, but have you seen the price of copper lately. Doing it with hardware cloth or chicken wire works just fine.


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## spinman1949 (Jun 29, 2009)

*Thermal transfer.*

I believe the goal is thermal transfer. This likely relates to surface area as well as thermal conductance. Consider the radiator on your car. Likely made from aluminum or in older cars when copper or brass was not as expensive, one of these metals. Thin fins connected to thin walled pipes circulating the coolant. The thin fins help to radiate the heat contained in the coolant and transfer it to the cooler air passing over them. If not for the negative effect of condensation. ( Something we want to avoid with fog machines) , a radiator would probably be a good choice for a fog cooler.

If you made a fog cooler using iron pipe, I doubt you would get very good results. PVC pipe is another bad choice. Wire mesh works because the fog is making direct contact with the ice. One reason aluminum vent hose may not work as well as expected is again the condensation factor. The fog as it travels through the hose is buffeted by the accordian structure. This can cause the fog molecules to fall out of suspension and condense on the side of the hose, thus reducing the overall fog volume.

So the goal in fog chillers is to subject the fog to the largest surface area of a thermal efficient material without impeding the flow of the fog as much as possible.

Oh and re Brick, Stone, Concrete, Etc. These materials do not conduct heat well. In fact they retain heat once heated. The best example of this are the ceramic tiles on the Space Shuttle. Thin tiles less than 1" thick are heated to thousands of degrees, yet you can hold one in the palm of your hand while the opposite surface is heated by a blow torch.


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## Aquayne (Sep 1, 2008)

I believe the fog condenses on the ice as well.


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## Aquayne (Sep 1, 2008)

My chiller worked better when I pushed some of the ice aside allowing the fog to pass through the grid easier without having to as much obstruction.
I wonder about freezing pop bottles. We do it in the summer to put in coolers.
I read alot of stuff about thermal storage. Water is the best because of the convection currents. As the water at the contact surface warms it rises causing current that makes the fluid mix and evenly distribute the warming effect, or cooling. I wonder if we could make a strong salt solution for the bottles. They would not freeze but would allow for better convection current and better heat transfer. I have been looking for a radiator fluid that is environmentally safe. I used to see it at Wal*Mart but not any more.


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## Aquayne (Sep 1, 2008)

The use of the bottles would do away with the need for a drain hole and the problems of water on the floor.


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## Aquayne (Sep 1, 2008)

I think that the smaller the bottle the better to increase surface area for contact. The little water bottles should work.


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## Aquayne (Sep 1, 2008)

The bottles would stack leaving gaps for the fog to pass. There should be fantastic heat transfer. 
No neef for tubes, only a small internal table for the fog to gather beneath the bottles before exiting.
I have a 1000 watt fogger that pointed directly at my PVC fittings with no ill effect on them. I don't think the heat would hurt the bottles.


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## spinman1949 (Jun 29, 2009)

*Plastic bottles ?*

Hmmm !!!

It is a good idea, but again we need to consider thermal conductance. While a cold pop bottle might seem like a good idea, one must consider this aspect of conducting heat. Just because the bottle feels cold to the touch, does not mean it will conduct heat well. Generally speaking, materials that conduit electricity well, also conduct heat well. IE Aluminum, Silver, Brass, and Copper. Plastics and Glass are insulators. Now aluminum cans is an idea. In fact it leads me to think about what could be the ultimate fog chiller. If a means to attach water tight fittings to aluminum cans could be devised, then circulating chilled water through them would provide a constant thermal turbulence inside the can and keep the cans exterior skin at a constant chilling temperature. The cans could be stacked in a cooler with gaps between them horizontally and vertically to allow the fog to meander through. It would certainly be cheaper than the expensive units we see with copper pipe.


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## Aquayne (Sep 1, 2008)

The Dollar tree often has aluminum drink bottles. I believe the convection inside the bottle would be sufficient so there is no need for a circulation pump. In the book "the Solar Greenhouse" they use milk jugs to collect and radiate heat with good results. I believe the aluminum would work better. The anti-freeze version would likely be better than salt due to corrosion.


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## The-Haunter (Sep 24, 2009)

VeI've used frozen water bottles in my chiller for years they work great also worked well for my fog wall


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## heresjohnny (Feb 15, 2006)

<heresjohnny scratching his head> It's been a while since thermodynamics, but I think spinman1949 has touched on a lot of the answers. Some things to think about:

1. When you are talking about thermal mass, I think you are thinking about a thermal sink or source, which is basically a body that can be in contact with a substance at a different temperture, but still maintain it's own constant temprature.
2. I'm not up on what will cause heated fog juice to condense, but I think the goal is to provide a cold thermal source with the largest surface area possible, with the best conductor between the thermal source and the fog. I belive at some point you chill the fog to much, but I don't know were that point is.
3. If memory serves you need a somewhat large difference in temperture in a liguid to cause enough convection to give you any advantage over simple conduction in a closed container. In other words, if the cold water in a can is swirly around will it really keep the outside of the can colder than if the water were still?

Some things I have tried or seen. 
1. First there is a huge thread on a vortex chiller you should read if you haven't. A vortex style chiller full of ice has given me the best results, and I have tried several approaches. If you think about it, you have a lot of surface area, no worries about thermal conductance, and the surface of the ice will basically maintain a temperture of 32 degrees.
2. My most cost efficient chiller I ever made was a 12' long, 4" diameter vinyl carpet tube (free) full of frozen water bottles (free), works pretty good but not as good as a vortex or fog on ice style cooler.
3. I tried frozen water bottles in a cooler, didn't work very well. I think there was to much volume not in contact with a cold surface for the fog to pass through.
4. I have seen somewhere someone that submerged an A/C coil in a salt/ice bath and pushed the fog through.

All that being said, I am always interested in new ways to do things, so please keep exploring


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## Aquayne (Sep 1, 2008)

I am assuming use of a vortex chiller.
If we use brine, convection will be greater. I understand swirling water would be maximum but enough is enough.


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## spinman1949 (Jun 29, 2009)

*Good idea !*



Aquayne said:


> The Dollar tree often has aluminum drink bottles. I believe the convection inside the bottle would be sufficient so there is no need for a circulation pump. In the book "the Solar Greenhouse" they use milk jugs to collect and radiate heat with good results. I believe the aluminum would work better. The anti-freeze version would likely be better than salt due to corrosion.


Now that is a good approach. I will take note with one aspect. The reason you need to circulate your coolant is to maintain the lowest temp possible. An aluminum bottle filled will a solution will loose it's effectiveness if the coolant is not replenished with new cold coolant. In a standard fog chiller the ice melts and is replaced by ice behind or above it. If the ice is contained inside a container, then as it melts it will slowly lose its cooling effect. Never forget that thermal transfer efficiency is based on conductance and temperature difference.


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## Aquayne (Sep 1, 2008)

I think we need to avoid ice. We only need this for a few hours per night.


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## Night Watchman (Aug 15, 2009)

I will pose these questions for thought. 1. What if you froze water in aluminum cans (pop cans/beer cans) and laid them on the ice tray of a vortex chiller or fog on the rocks style chiller, would that work as well as ice? 2. Put a thin layer of ice on the tray and then layer the aluminum cans on top of the ice? 3. Layer the cans and pour ice on top of them? In all cases make the cans cover the entire area of the ice tray, and lay them on their side.


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## Lunatic (Oct 3, 2006)

Interesting methods to cooling the fog. I use the 60 qt cube reverse vortex method and I'm wondering if it's necessary to have the fog in direct contact with the ice. Is it advantageous or not? Does the added moisture that the glycol absorbs add more weight and thermal mass to create a heavier denser fog? I would think so but I'm not absolutely sure.


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## Aquayne (Sep 1, 2008)

It seems to me that the Glycol condenses when it comes in contact with the ice. I have a slimy film inside my vortex chiller from the fog.


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## Aquayne (Sep 1, 2008)

I think the cans could be stacked upright to creat a matric of channels for the fog to travel and be cooled.


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## Lunatic (Oct 3, 2006)

Yeah, I get the slimy film inside my coolers, too. I think the glycol would condense no matter how the fog is cooled. But with the added moisture I'm sure it's worse. A quick rinse of the garden hose cleans it up. I like the idea of the aluminum water bottles. But the question still remains, does the moisture from the ice add something to the quality of the fog or is it detrimental? A drier fog would be cleaner. It would be an interesting side by side evaluation to see what kind of fog the various methods produce. 

I agree with Here's Johnny, lots of ice exposure appears to work best. You gotta admit, adding ice is the easiest and quickest method. However, we're all interested in new approaches to chilling fog. That is why this forum is so important. Good luck!


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## Aquayne (Sep 1, 2008)

I wonder if we put salt on some of the ice to see if the ambiant temp drop would help.


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## niblique71 (Dec 2, 2009)

I wanted to read back on some of the chiller designs and theorys since I made my homebuilt chiller. Some of the concepts discussed seem to be accurate. But one thing just hit me. Although I don't know the exact math, which material has the most surface area??? a cubic yard of sand?? or a C/Y of 6" river stones??

The answer is sand. It also weighs more per cubic yard. 
Thats why Ice cubes probably give better results in a chiller than cans or bottles that are frozen.

So, with that said, If we could get crushed ice we could get the best thermal transfer. The only problem is that Ice melts, So it seems that cubed ice has the best ratio of thermo-transfer vs longevity. Crushed ice would start to form natural cavaties that would form tubes that the fog could more easily escape without being chilled

The other issue that wasn't fully addressed in this thread seems to be contact duration(time) VS surface area.

The longer the fog can be in contact with the ice, the cooler it will become. That seems to be a huge factor in the vortex design, Essentially the chamber of a vortex chiller is a HUGE pipe with a LOT of volume. So... the fog enters through a smaller tube at high velocity drawing in outside air, it enters the expansion chamber and expands, then it is slowed as it passes through the ice since the chamber section (garbage can) is a very large diameter, and is then forced out at close to it's original speed at the exit.
Of course there is also turbulance inside the chamber too, which probably works in the vortex's favor as well.


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