Aluminum In water? - The Planted Tank Forum
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post #1 of 21 (permalink) Old 09-05-2010, 04:47 AM Thread Starter
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Aluminum In water?

Howdy. I was just curious as to how fast Aluminum corrodes. I was thinking of making a Passive heat sink for my Goldfish tank. I can always go with Stainless steel but Aluminum has better heat conductivity. But it doe snot like water as i recall so what and how fast could it hurt a .32" sheet of aluminum.
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post #2 of 21 (permalink) Old 09-05-2010, 04:53 AM
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Aluminum should be fine in water; the oxide layer forms almost immediately and passivates the rest of the aluminum.

However, in slightly acidic water, the passivating layer will slowly corrode, freeing aluminum cations into the water column, which may be problematic.

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post #3 of 21 (permalink) Old 09-05-2010, 05:03 AM
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If you want to go with aluminum, you could look into anodized aluminum. Anodizing is a way of putting an artificial oxide coating on the aluminum. This coating is then often dyed and sealed to protect it. Protected aluminum is pretty good stuff and doesn't corrode if given a little bit of care. Natural aluminum also develops the same sort of coating (which is clear so it is hard to see), but it is more porous and fragile compared to anodized coatings.

I don't know whether anodizing would effect the aluminum's conductivity, but I would doubt it.
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post #4 of 21 (permalink) Old 09-05-2010, 05:05 AM
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You're better off just having a fan blowing across the surface.
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post #5 of 21 (permalink) Old 09-05-2010, 07:06 AM Thread Starter
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You're better off just having a fan blowing across the surface.
well see I realize this but I don't feel like having to fill it back up every three days. I have it pretty sealed off to avoid this. if it wasn't the Basments dehumidifier unit would eat it up in a few days. Trust me I have seen it at work when I forgot to put the lid back on the sump.

Thus I will make heat sink and run a fan over that.

Also, I am sure this will work well. The small iceprode fish tank heat sinks are like 4" ^ 2 and they make 20 gallons room temp. This think would be using cheap pre cut sizes that make it quite a bit bigger than Ice Probs lol.
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post #6 of 21 (permalink) Old 09-05-2010, 07:15 AM
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It's going to corrode no matter what pH it's at... trust me on this one...
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post #7 of 21 (permalink) Old 09-05-2010, 07:48 AM
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well see I realize this but I don't feel like having to fill it back up every three days. I have it pretty sealed off to avoid this. if it wasn't the Basments dehumidifier unit would eat it up in a few days. Trust me I have seen it at work when I forgot to put the lid back on the sump.

Thus I will make heat sink and run a fan over that.

Also, I am sure this will work well. The small iceprode fish tank heat sinks are like 4" ^ 2 and they make 20 gallons room temp. This think would be using cheap pre cut sizes that make it quite a bit bigger than Ice Probs lol.
Without a peltier cooler a heat sink won't do anything. and to build your own version of the iceprobe wouldn't be much cheaper and probably work less effectively..

Also peltier aren't very efficient and tend to break alot and suck power like crazy.
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post #8 of 21 (permalink) Old 09-05-2010, 01:57 PM Thread Starter
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wasn't going to get a peltier. I see no peltier Effect things on a Computer heat sink so why would it not work. Or Is it hidden really well? @[email protected] I am a noob to heat movement.
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post #9 of 21 (permalink) Old 09-05-2010, 05:13 PM
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If you isolate aluminum from any other more noble metal, like stainless steel or nickel or chromium, it is pretty free from corrosion. But, let a more noble metal just touch the aluminum, or be connected with an electrolyte, like our aquarium water, and it corrodes badly. Also, few aluminum things are really aluminum, they are made of aluminum alloys, which trade corrosion resistance for improvements in other properties. For example most of the aluminum shapes I see in stores are made of 6061T6 aluminum, which doesn't have good corrosion resistance at all.

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post #10 of 21 (permalink) Old 09-05-2010, 06:47 PM
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wasn't going to get a peltier. I see no peltier Effect things on a Computer heat sink so why would it not work. Or Is it hidden really well? @[email protected] I am a noob to heat movement.
Computer heatsinks work due to the large thermal difference between ambient air and the cpu temperature. A fish tank on the other hand is going to be at the same temp as the ambient air.

A heatsink with fan will never drop the temp below the ambient temperature so thats why I was saying its not going to make any difference.
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post #11 of 21 (permalink) Old 09-05-2010, 07:26 PM Thread Starter
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Computer heatsinks work due to the large thermal difference between ambient air and the cpu temperature. A fish tank on the other hand is going to be at the same temp as the ambient air.

A heatsink with fan will never drop the temp below the ambient temperature so thats why I was saying its not going to make any difference.
well i realize this but my tank is not at room temperature. the tank is at 80 and the room is at 70. (goldfish tank in the basement). So it seems like it could work.

and thank you for explaining hoppy. SO I should go with stainless steel if I decide to proceed with this? Do you think it would work? and advice or tips on design?

also, as far as Al I have these available but some our out o the question price wise. SO I suppose I will go with Stainless. any type to recommend? is it bad for fish?

2024
3003
5052
6061
7075

also, would anodized work? Since they basically just rust it through. would it not corrode faster?

I suppose I could take 2 of these and out them back to back. One in the water and one out. http://www.newegg.com/Product/ImageG...20CPU%20Cooler
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post #12 of 21 (permalink) Old 09-05-2010, 09:39 PM
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I don't think the idea will work. Heat transfer requires optimizing several parameters, including the speed of the water or air across the surface, the temperature difference, the density of the air or water (water good, air bad), the surface area in contact with the air or water, whether the flow is turbulent or not (turbulent much better), etc. To make the air side of the heat exchanger work at all would take a good fan blowing air across/through the heat exchanger. But, just blowing that air across the water works much better because evaporating water removes lots of heat from the water compared to the heat transfer to a heat exchanger.

I suggest looking at where the heat in the water is coming from and trying to reduce that at the source. If it is from a powerhead, for example, don't use one, use an external mounted pump. If it is from the lights, move them farther from the water, so the air blocks some of the heat. And, let the water temperature drop a bit more at night, by lowering the heater setting a couple of degrees or so.

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post #13 of 21 (permalink) Old 09-05-2010, 10:26 PM Thread Starter
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I see no way to move the pump outside. it is a 55 long that I recycled into a sump and did not want to crack it by dilling.

Also, The sump runs at about a gallon every 3 seconds. And I was planning to remove my single Down lines Air and water separator and make it go down and pass upwards though the heat exchanger. Thus it is longer exposer and the air rising through the water would make it quite turbulent.

And as stated before I cannot have evaporating water like that. and I planned to make run AC-ed water over it one day. Sucha method is cheaper than a chiller.
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post #14 of 21 (permalink) Old 09-05-2010, 11:08 PM Thread Starter
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Also, will ANODIZED Corrode all the same? it's heat conductivity is so much better than Stainless. Al is 400 (for get the units) to Stianless's 17
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post #15 of 21 (permalink) Old 09-06-2010, 01:37 AM
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Pure aluminum is pretty resistant to corrosion, once an oxide layer forms, but aluminum alloys aren't nearly that resistant. As I recall, from the list you provided above, the 2024 would be the most corrosion resistant, followed by either the 5052 or 6061, but I'm not familiar with 3003. Anodizing just puts a good thick oxide layer on the aluminum. If almost any other metal contacts bare aluminum alloy any place where there is any moisture or water, corrosion is pretty certain and not very slow.

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