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 Funger
MutantApendanges
Registered: 08/20/02
Posts: 190
Loc: State of insanity
Last seen: 16 years, 5 months
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 Where to measure humidity 
#1251927 - 01/27/03 03:00 AM (21 years, 2 months ago) |
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I someone had a growing chamber that was about 4 feet high, with a humidifier blowing in humid air from the top, where (top, bottom, or middle) would be the most accurate place to put a humidity sensor? How does humid air fill an enclosed space?
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 G a n j a
Pictish and proud
Registered: 12/03/02
Posts: 7,860
Loc: Zone ate
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 Re: Where to measure humidity [Re: Funger]
#1251951 - 01/27/03 03:15 AM (21 years, 2 months ago) |
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Middle 
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Anno
Experimenter
Registered: 06/17/99
Posts: 24,166
Loc: my room
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Re: Where to measure humidity [Re: Funger]
#1251970 - 01/27/03 03:25 AM (21 years, 2 months ago) |
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>How does humid air fill an enclosed space?
Most humid air is on top.
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GratefulDread
Never pass up anopportunity topee.
Registered: 10/21/02
Posts: 366
Last seen: 19 years, 7 months
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Re: Where to measure humidity [Re: Anno]
#1251994 - 01/27/03 03:40 AM (21 years, 2 months ago) |
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Wouldn't the extra weight of the water particles make the humid air naturally follow gravity and be more concentrated in the bottom?
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Before you criticize someone, you should walk a mile in their shoes.
That way, when you criticize them, you're a mile away and you have their shoes.
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TekNut
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Registered: 01/01/03
Posts: 382
Loc: TX Gulf Coast
Last seen: 13 years, 11 months
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Here is some interesting information. I would have thought humid air was heavier due to it being more dense ....
Understanding air density and its effects
In simple terms, density is the mass of anything divided by the volume it occupies. As you go higher, the air's density decreases. On this page you'll find information on the effects of lower air density ? such as caused by going to high altitudes ? on humans, the science of air density, how humidity affects air density ? you might be surprised ? and the affects of air density of aircraft,
Related information Understanding air pressure
Understanding water in the atmosphere
Understanding density altitude
Calculating air density
Table showing the standard atmosphere
Graphic How high, low air pressure affect weather
Effects of lower density on humans
If you go high enough, either by climbing a mountain or going up in an airplane that does not have a pressurized cabin, you will begin feeling the effects of lower air pressure and density.
As air pressure decreases oxygen continues to account for about 21% of the gasses in the air as it does at seal level. But, there is less oxygen because there is less of all of the air's gasses. For instance, by the time you go to 12,000 feet the air's pressure is about 40% lower than at sea level. This means that with each breath you are getting about 40% less oxygen than at the lower altitude.
These effects aren't felt in airliners because the cabins are pressurized to keep the air density inside about the same as it would be about 6,000 or 7,000 feet above sea level.
The links below have more information about the effects of lower air density:
Princeton U.: High Altitude: Acclimatization and Illnesses
WebMD: Altitude sickness
High-Altitude Medicine Guide
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The science of air density
The air's density depends on its temperature, its pressure and how much water vapor is in the air. We'll talk about dry air first, which means we'll be concerned only with temperature and pressure.
The molecules of nitrogen, oxygen and other gases that make up air are moving around at incredible speeds, colliding with each other and all other objects. The higher the temperature, the faster the molecules are moving. As the air is heated, the molecules speed up, which means they push harder against their surroundings. If the air is in a balloon, heating it will expand the balloon, cooling it will cause the balloon to shrink as the molecules slow down. If the heated air is surrounded by nothing but air, it will push the surrounding air aside. As a result, the amount of air in a particular "box" decreases when the air is heated if the air is free to escape from the box. In the free atmosphere, the air's density decreases as the air is heated.
Pressure has the opposite effect on air. Increasing the pressure increases the density. Think of what happens when you press down the handle of a bicycle pump. The air is compressed. The density increases as pressure increases.
Altitude and weather systems can change the air's pressure. As you go higher, the air's pressure decreases from around 1,000 millibars at sea level to 500 millibars at around 18,000 feet. At 100,000 feet above sea level the air's pressure is only about 10 millibars. Weather systems that bring higher or lower air pressure also affect the air's density, but not nearly as much as altitude.
We see that the air's density is lowest at a high elevation on a hot day when the atmospheric pressure is low, say in Denver when a storm is moving in on a hot day. The air's density is highest at low elevations when the pressure is high and the temperature is low, such as on a sunny but extremely cold, winter's day in Alaska.
Humidity and air density
Most people who haven't studied physics or chemistry find it hard to believe that humid air is lighter, or less dense, than dry air. How can the air become lighter if we add water vapor to it?
Scientists have known this for a long time. The first was Isaac Newton, who stated that humid air is less dense than dry air in 1717 in his book, Optics. But, other scientists didn't generally understand this until later in that century.
To see why humid air is less dense than dry air, we need to turn to one of the laws of nature the Italian physicist Amadeo Avogadro discovered in the early 1800s. In simple terms, he found that a fixed volume of gas, say one cubic meter, at the same temperature and pressure, would always have the same number of molecules no matter what gas is in the container. Most beginning chemistry books explain how this works.
Imagine a cubic foot of perfectly dry air. It contains about 78% nitrogen molecules, which each have an atomic weight of 28. Another 21% of the air is oxygen, with each molecule having an atomic weight of 32. The final one percent is a mixture of other gases, which we won't worry about. Molecules are free to move in and out of our cubic foot of air. What Avogadro discovered leads us to conclude that if we added water vapor molecules to our cubic foot of air, some of the nitrogen and oxygen molecules would leave ? remember, the total number of molecules in our cubic foot of air stays the same. The water molecules that replace nitrogen or oxygen have an atomic weight of 18. This is lighter than both nitrogen and oxygen. In other words, replacing nitrogen and oxygen with water vapor decreases the weight of the air in the cubic foot; that is, it's density decreases.
Wait a minute, you might say, "I know water's heavier than air." True, liquid water is heavier, or more dense, than air. But, the water that makes the air humid isn't liquid. It's water vapor, which is a gas that is lighter than nitrogen or oxygen.
Compared to the differences made by temperature and air pressure, humidity has a small effect on the air's density. But, humid air is lighter than dry air at the same temperature and pressure.
I hope this was educational!
Peace,
-TekNut- 
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Anno
Experimenter
Registered: 06/17/99
Posts: 24,166
Loc: my room
Last seen: 4 days, 22 hours
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Re: Where to measure humidity [Re: TekNut]
#1252068 - 01/27/03 04:11 AM (21 years, 2 months ago) |
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TekNut
********
Registered: 01/01/03
Posts: 382
Loc: TX Gulf Coast
Last seen: 13 years, 11 months
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Re: Where to measure humidity [Re: Anno]
#1252111 - 01/27/03 04:25 AM (21 years, 2 months ago) |
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 very funny. Exact same source!
The really amazing thing to consider is the fact that The Shroomery has TONS of information here. I'm truly amazed at all the good info and very incredible, and helpful people in the know!
I wish I lived next door to you Anno! 
Peace,
-TekNut-
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GratefulDread
Never pass up anopportunity topee.
Registered: 10/21/02
Posts: 366
Last seen: 19 years, 7 months
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Re: Where to measure humidity [Re: Anno]
#1252113 - 01/27/03 04:26 AM (21 years, 2 months ago) |
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And now I know
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Before you criticize someone, you should walk a mile in their shoes.
That way, when you criticize them, you're a mile away and you have their shoes.
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ClosetCase
but only inwinter
Registered: 01/22/03
Posts: 295
Loc: Somewhere rubbing my nugs...
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 Re: Where to measure humidity [Re: TekNut]
#1252883 - 01/27/03 09:18 AM (21 years, 2 months ago) |
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oh all this air on me is so heavy. hard to move. why'd you have to tell me that, it's like a big heavy blanket is on me
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"as your attourney I advise you to rent a very fast car with no top, and you'll need the cocaine.."
"well.. why not? I mean if anything's worth doing, it's worth doing right. THIS IS THE AMERICAN DREAM IN ACTION"
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