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Thread: Who is good with fluid / thermal dynamics - in particular, condensing liquids?

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    Who is good with fluid / thermal dynamics - in particular, condensing liquids?

    OK, I'm willing to admit that this is dull as dishwater, but it's something I need to figure out.

    If a space was prone to condensation, would filling it with lots of tiny (non porous) spheres increase or decrease the amount of condensation that forms?
    Where ever you go, never take an idiot with you. You can be sure you'll find one when you get there.

    Quote Originally Posted by TomK View Post
    The lower front bar was also showing the typical signs of any metal attached to an s13

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    Guest skinz180189's Avatar
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    Increased surface area will mean more settles.

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    Guest dannyboi200sx's Avatar
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    but condensation wont be able to "stick" to a sphere so there will be less...

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    Guest marko14a's Avatar
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    That's the way I understand it. Isn't that the basic principle behind cloud seeding etc?

    Quote Originally Posted by dannyboi200sx View Post
    but condensation wont be able to "stick" to a sphere so there will be less...
    Last edited by marko14a; 16-11-2011 at 19:41.

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    Guest StanTM's Avatar
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    This is either about polystyrene wall insulation or a condenser chamber. Really need a bit more info on size (tiny could be 1cm downward, smaller will tend to condense and drip quicker, but greatly depends on the following), material (ie metal would cool faster increasing condensation, than plastic), tightly packed or 'distributed' [free to move because of flow through them] (exposed surface area), air flow (faster will hold vapour in the air - this speed is much lower than you'd think)
    Hope this gives you a direction

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    OK, well here's the background:

    I need to insulate the corrugated roof in the garage.

    I had done a test area with rockwool and boarded over it, but after deciding that laying rockwool from underneath was a hideous exercise, and learning that it's actually not very good at insulating unless you have about 12" of it, I took it down a few weeks later. It was soaking wet.

    So, I'm now treading carefully with my other options. The favoured option, cost wise, is to fill the areas between the purlins (which are about 2" thick) with PIR or Polystyrene, but this leaves long thin cells of empty space in the corrugations, which I am concerned will suffer from condensation. I've probably not done myself a favour by sealing up the ends of these, at the eaves and ridge, but I wanted to stop anything living in there.

    One option is to insulate OVER the purlins, leaving a 2" gap and on the inside of the roof to put vents along the ridge and eaves, to allow air to circulate, but I don't know if this would be a viable substitute for getting air fresh air in from outside.

    Another other option is to get profiled insulation - it's machined to follow the contours of the corrugated roof, but will cost LOTS!

    So, hence my physics question, it occurred to me that I could panel over, leaving the 2" gap, and then flood the gap with tiny polystyrene balls. But, will they just increase the surface area and promote condensation, or, by displacing any air, will they reduce it?
    Where ever you go, never take an idiot with you. You can be sure you'll find one when you get there.

    Quote Originally Posted by TomK View Post
    The lower front bar was also showing the typical signs of any metal attached to an s13

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    Guest skinz180189's Avatar
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    Quote Originally Posted by dannyboi200sx View Post
    but condensation wont be able to "stick" to a sphere so there will be less...
    Good point, totally missed the fact they're spherical.

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    Quote Originally Posted by skinz180189 View Post
    Good point, totally missed the fact they're spherical.
    But won't it just drip off them?
    Where ever you go, never take an idiot with you. You can be sure you'll find one when you get there.

    Quote Originally Posted by TomK View Post
    The lower front bar was also showing the typical signs of any metal attached to an s13

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    Can't you fill the void with polyurethane foam ?

    Don't put too much at a time though, it will expand and could compress/deform anything around it if the expansion is contained.

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    Guest skinz180189's Avatar
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    Quote Originally Posted by Jesus-Ninja View Post
    But won't it just drip off them?
    Probably.

    Why not get a dehumidifier?

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    Guest marko14a's Avatar
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    Quote Originally Posted by Jesus-Ninja View Post
    But won't it just drip off them?
    If you filled it with spheres, even if the water didnt condense on them, wouldn't it just move through the gaps until it found a flat surface to condense on?

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    Quote Originally Posted by skinz180189 View Post
    Probably.

    Why not get a dehumidifier?
    In a 50mm gap?
    Where ever you go, never take an idiot with you. You can be sure you'll find one when you get there.

    Quote Originally Posted by TomK View Post
    The lower front bar was also showing the typical signs of any metal attached to an s13

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    Quote Originally Posted by folken View Post
    Can't you fill the void with polyurethane foam ?

    Don't put too much at a time though, it will expand and could compress/deform anything around it if the expansion is contained.
    Yeah, I'm looking at kits that you use to spray a layer on with. Looking like a better option too, although I'd have been a lot better off doing it before any of the other work in there. Would have to seal off everything!
    Where ever you go, never take an idiot with you. You can be sure you'll find one when you get there.

    Quote Originally Posted by TomK View Post
    The lower front bar was also showing the typical signs of any metal attached to an s13

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    Guest skinz180189's Avatar
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    Quote Originally Posted by Jesus-Ninja View Post
    In a 50mm gap?
    Surely you can get one with a tube?

    TBH, sealing it all up is probably the reason it's doing it so badly.

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    Quote Originally Posted by skinz180189 View Post
    TBH, sealing it all up is probably the reason it's doing it so badly.
    I know

    I think that might be another avenue to explore - seeing if I can ventilate it externally, whilst still keeping it infestation free.

    EDIT - I wonder if I'd get away with just having ventilation at the eaves, and not at the ridge?
    Where ever you go, never take an idiot with you. You can be sure you'll find one when you get there.

    Quote Originally Posted by TomK View Post
    The lower front bar was also showing the typical signs of any metal attached to an s13

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    Guest marko14a's Avatar
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    If you wanted to cutsome holes, I can get you some extremely fine stainless steel mesh to cover them that wouldnt allow anything to get through.

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    Right, been speaking about this with a few other folk. A mate had a similar roof in a house of his - a narrow cavity between the outside roof and the panelling inside, which followed the line of the roof. This was only ventilated at the eaves and he had no problems with it. It was packed with rockwool too, so not much movement of air.

    So, I think the plan is to ventilate at the eaves - probably using a hole cutter to cut through the expanding foam, and then short pieces of tube with a fine mesh at the end, inserted into these holes. The only decision then is whether to:

    a) Panel between the purlins with 50mm of insulation- this will use zero head room and look neat, but will mean that every rib in the corrugated roof will need it's own ventilation. It will require a bit of buggering around where there are cables running under the roof.
    b) Panel over the purlins with 50mm of insulation - this will bring the roof down a touch, but will leave a 50mm gap, and should remove the need to ventilate every rib in the corrugated roof. I might also be able to pack the gap with rockwool - adding a touch more insulation.
    c) Somewhere between the two - 25mm between the purlins, with a 25mm gap, and then 25mm over the top of the purlins for a really tidy finish.

    I like option c) so far.
    Where ever you go, never take an idiot with you. You can be sure you'll find one when you get there.

    Quote Originally Posted by TomK View Post
    The lower front bar was also showing the typical signs of any metal attached to an s13

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    Well, it seems I have a bit of condensation but, bizarrely enough, not where I was concerned it would be. The roof has 50mm of polystyrene between the purlins and is yet to have a final 25mm which will cover over the purlins with 3mm ply over that. There is no sign of condensation, despite the cold weather and me sweating away with an oil heater on and boiling the kettle every hour or so.

    The condensation is on the floor. Doh!
    Where ever you go, never take an idiot with you. You can be sure you'll find one when you get there.

    Quote Originally Posted by TomK View Post
    The lower front bar was also showing the typical signs of any metal attached to an s13

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