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sansa

Registered: 11/17/09
Posts: 647
Last seen: 10 years, 4 months
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Low RH suggests high CO2?
#11728363 - 12/27/09 08:27 PM (15 years, 23 days ago) |
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I just noticed my tub had slipped off the risers on the bottom so it was sitting directly on the aluminum tray which meant the holes on the bottom were plugged up.
My RH was also barely above 75%. I propped it back up on the risers and checked it a few minutes later and the RH is back in the 90's.
Does CO2 hold less humidity than O2? I'm wondering why increasing the flow of air on the bottom would raise the RH?
Edit: Is it simply that when the air is saturated with O2 it can't hold as much water, which is why in certain cases drilling more holes in a shotgun FC increases the RH?
Edited by sansa (12/27/09 09:07 PM)
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Czo
Neophyte


Registered: 08/19/09
Posts: 79
Loc: Colorado
Last seen: 2 years, 6 months
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Re: Low RH suggests high CO2? [Re: sansa]
#11728552 - 12/27/09 09:14 PM (15 years, 23 days ago) |
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I notice at the end, you mention shotgun FC, which is what I'll assume you are using. The risers are so air can hit the perlite, causing extra evaporation and maintaining that high RH. As for your direct question/hypothesis of CO2 holding humidity worse than O2, I don't know.
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anonjon
Partially Right

Registered: 11/03/08
Posts: 6,322
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Re: Low RH suggests high CO2? [Re: sansa]
#11728613 - 12/27/09 09:22 PM (15 years, 23 days ago) |
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Air does not hold water like a sponge. The greatest factor affecting rh in your terrarium is surface area. When pan sits on perlite its blocking a bunch of surface area.
C02 and 02 do not 'hold' water. Water vapor is an entity unto itself. Relative Humidity, RH, is strictly a relationship between the potential vapor pressure of water in the given space and the actual vapor pressure of water in the given space.
So the variables at play are temperature, time, and the amount of h20 present.
We hold the volume as a constant and can safely ignore the pressure of other gasses like nitrogen, oxygen, carbon dioxide. Water vapor pressure is independent of them.
-------------------- The above post is fictional, hypothetical, or downright nonsensical.
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sansa

Registered: 11/17/09
Posts: 647
Last seen: 10 years, 4 months
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Re: Low RH suggests high CO2? [Re: anonjon]
#11728710 - 12/27/09 09:39 PM (15 years, 23 days ago) |
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OK, I think I see my mistake. Water is not actually dissolved in the air, the air is there in addition to the water vapor.
From wikipedia...
http://en.wikipedia.org/wiki/Relative_humidity
Quote:
A common misconception
Often the notion of air holding water vapor is presented to describe the concept of relative humidity. However, air simply acts as a transporter of water vapour and is not a holder of it. Therefore, relative humidity is wholly understood in terms of the physical properties of water alone and thus is unrelated to this concept.[2][3] In fact, water vapor can be present in an airless volume and therefore the relative humidity of this volume can be readily determined.
The misconception that air holds water is likely the result of the use of the word saturation which is often misused in descriptions of relative humidity. In the present context the word saturation refers to the state of water vapor,[4] not the solubility of one material in another.
The thermophysical properties of water-air mixtures encountered at atmospheric conditions are reasonably approximated by assuming they behave as a mixture of ideal gases. For many practical purposes the assumption that both components (air and water) behave independently of each other is reasonable. Therefore the physical properties of an air-water mixture can be estimated by considering the physical properties of each component separately.
I'm not quite clear on this part: "When pan sits on perlite its blocking a bunch of surface area."
I've only got a few holes on the bottom of the shotgun FC, when it was on the tray and blocked up I can see how that would prevent CO2 from escaping out the bottom but I don't see how that affects the surface area? The perlite inside the FC is still sitting on the bottom of the plastic, I'm not sure about which surface area you mean?
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Bugzy
Magician



Registered: 03/18/09
Posts: 436
Last seen: 11 years, 4 months
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Re: Low RH suggests high CO2? [Re: sansa]
#11728823 - 12/27/09 09:56 PM (15 years, 23 days ago) |
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What are you using? sounds like a shotgun. In that case I believe anonjon was reffering too your tray covering your perlite, which takes away surface area from the evaporating perlite.
-------------------- American by Nature.... unamerican by Law
"Out of all the things I've lost, I miss my mind the most."
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RogerRabbit
Bans for Pleasure



Registered: 03/26/03
Posts: 42,214
Loc: Seattle
Last seen: 1 year, 10 months
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Re: Low RH suggests high CO2? [Re: sansa]
#11728891 - 12/27/09 10:12 PM (15 years, 23 days ago) |
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Quote:
sansa said: My RH was also barely above 75%. I propped it back up on the risers and checked it a few minutes later and the RH is back in the 90's.
Does CO2 hold less humidity than O2? I'm wondering why increasing the flow of air on the bottom would raise the RH?
It's because of the engineering behind a shotgun terrarium. The majority of air enters through the bottom holes, and then rises up through the perlite as it travels to the fruiting part of the tub. As the air passes through the perlite, it absorbs moisture, raising the humidity. RR
-------------------- Download Let's Grow Mushrooms
semper in excretia sumus solim profundum variat
"I've never had a failed experiment. I've only discovered 10,000 methods which do not work."
Thomas Edison
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anonjon
Partially Right

Registered: 11/03/08
Posts: 6,322
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Re: Low RH suggests high CO2? [Re: Bugzy]
#11730188 - 12/28/09 06:48 AM (15 years, 23 days ago) |
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Quote:
Bugzy said: What are you using? sounds like a shotgun. In that case I believe anonjon was reffering too your tray covering your perlite, which takes away surface area from the evaporating perlite.
Yeah, i misunderstood the op's original question.
-------------------- The above post is fictional, hypothetical, or downright nonsensical.
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