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Thread: convection currents

  1. #1 convection currents 
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    D is capped at the end (horizontal).
    Warm water and gas (air boiled out) travels up A.
    Gas accumilates at top and increases pressure in both C and D.
    I want this pressure to act on the downward flow B but not A.

    B leads to a radiator which goes back to the heat source.

    Will the pressure that might be acting against heat travelling up A increase or decrease rate of the convection currents?

    I did some math on this ages ago but can't be bothered to dig it out so thought I would post to see if anyone has any pennies worth to help my copper pipes [/img]


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  3. #2  
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    Your system will just vapor lock at the top. The condenser (radiator) needs to be at the top of the circuit so you will have condensate instead of a steam/water mixture going down B. Then the density difference will drive the circuit.


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  4. #3  
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    thanks - I see where you are coming from and agree.

    There sholdn't be any very hot steam in this system as the temperatures should be below 90 degrees celcius. there will be room further along the pipe for mass but it will essentially be a sealed system with a layer of water always covering the entrance to B.

    The reason it has evolved this way is that in my previous system I found it VERY difficult to bleed the radiator plus I want the radiator to work its best rather than having any air in it. So this way the system self bleeds as it works. It also has to be simple.

    I am also trying to use some of the heat as an aid (call it a power source) to increase the efficiency of the system. Hence my question in RED in the original post.................
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  5. #4  
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    What do you mean by "very hot steam?" If your system is at atmospheric pressure near sea level, you will either have steam at 100C or you will have water. At 90C it's water. There could be some parts of your system where the pressure is below atmospheric, but I don't think you are dealing with any significant elevation changes.

    How do you think it would self bleed?
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  6. #5  
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    my apologies - I said that as there will always be water particles in the air (steam being a gas phase of water) - a detail point not worth worrying about.

    It will self bleed as when I fill it up all routes lead up with no places that air can be trapped. When in use air will boil out of the water and settle at the top.

    Yes this will be kept at atmospheric level.
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  7. #6  
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    As far as I can see, there will be a bubble of air trapped in the high point which is shown in your first post, so it is not being bled off unless you put some kind of vent valve up there. Having this high point vent will not necessarily prevent bubbles from being trapped in the piping elsewhere, where there is a local high point.

    Heating the water will tend to drive off dissolved air, but that is not the same as boiling.

    The air bubble at the top of your system will actually be the lowest pressure in the system. The pressure at any other point in the system will be equal to that pressure plus the head of water above the given point.

    The pressure in the air bubble will be equal throughout the bubble, so there is no way it is going to press down more on one side or the other.
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  8. #7  
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    thanks harold.

    I am aiming to avoid any local points where air can be trapped. Not gonna have a vent valve (closed airtight system) but as I am not playing with large amounts of heat there shouldn't be a great amount of pressure to deal with.

    the dissolved air is what I am having to account for in terms of keeping the system well bled. The top will act like an expansion tank.

    i am simply trying to get a bit more work out of the heat that there will be but it is proving VERY difficult! I have a few ideas but don't want to commit to one just yet...........
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