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Thread: convection & 'bubbles'

  1. #1 convection & 'bubbles' 
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    i'm making a convection cooled PC.

    A radiator is under 'head' from a reservoir. They system isn't well designed to 'self bleed' - once i bleed the system I think that any air that gets into it will be trapped in the radiator.

    When convection occurs i see little bubbles rising. Not too sure what this is - i speculate it is the result of Nucleate boiling - but definately a result of lower bouyancy created by the heat.

    My question: what will happen to these bubbles when they reach the radiator? When the water gets cool will they diffuse back into the water in a similar process to CO2 in a coke can or is there a chance they will stay in the radiator. It is a closed system by the way.

    Much obliged!


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  3. #2  
    Forum Isotope Bunbury's Avatar
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    Is the hot surface hot enough to boil the coolant? Seems unlikely. I'm guessing the little bubbles are dissolved air coming out of solution. Try using water (assuming it's water you're using) that you've previously boiled to get rid of dissolved air.


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  4. #3  
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    Quote Originally Posted by Bunbury
    Is the hot surface hot enough to boil the coolant? Seems unlikely. I'm guessing the little bubbles are dissolved air coming out of solution. Try using water (assuming it's water you're using) that you've previously boiled to get rid of dissolved air.
    thanks - i will try that.

    any ideas on if the dissolved air will be reabsorbed by the water when it cools?
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  5. #4  
    Forum Radioactive Isotope MagiMaster's Avatar
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    No, it won't, or at least not anytime soon. It all went up with the bubbles, so it can only absorb new gasses from the surface contact, which will be very slow. Just don't shake it up a whole lot.
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  6. #5  
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    Quote Originally Posted by MagiMaster
    No, it won't, or at least not anytime soon. It all went up with the bubbles, so it can only absorb new gasses from the surface contact, which will be very slow. Just don't shake it up a whole lot.
    damn!

    any particular reason for this?

    i presume it doesn't work (eg. like a coke can would) as it is not pressured to the same extent and the chemistry is such to not promote it..............am i on the right track or not?
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  7. #6  
    Forum Radioactive Isotope MagiMaster's Avatar
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    Well, think about what's happening at the surface. Imagine the molecules moving around in the air and the water and you can see that 1) reabsorbtion is going to be slow and 2) it'll be proportional to the surface area of the air-water interface which goes up a whole lot when the water is agitated.

    Also, I've heard to get all the air out, you'd boil it, cool it and boil it again. I think that was from an episode of Good Eats, but I forget which one.
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  8. #7  
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    thanks - i'm gonna try and make an air trap too so the air bypasses the radiator. I had always planed to have air at the top of my reservoir so i'm gonna plump it into there..........
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