Humidity and Stove Testing

Always good to have some helpful tips when making stove.
Where to get materials cheap, what tool is best.
How to do a specific task. Anything that will help.
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zelph
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Humidity and Stove Testing

Postby zelph » Sun May 05, 2013 2:50 pm

"CAMARILLO, Calif. (AP) — A flow of damp air from the Pacific Ocean helped firefighters in their battle against a huge wildfire burning through coastal mountains in Southern California.

Fire crews on Saturday worked to create miles of containment lines as the high winds and hot, dry air of recent days were replaced by the normal Pacific air, significantly reducing fire activity."


Over the years I have used more than 12 gallons of denatured alcohol for testing DIY stove designs. 1/2oz/15ml at a time. I stopped counting after the 12th gallon.

I learned early on that low barometric pressure/humid air associated with incoming storm fronts etc. had a direct affect on my tests.

On a dry sunny day a stove design would boil 2 cups of 70 degree water with no problem. Overnite the barometric pressure drops and rain is falling. Same stove tested with same amount of fuel and beginning water temperature and I can't get a boil.

This is just a reminder to new DIY stove designers out there humid conditions have an affect on your tests just as the humid conditions helped firefighters out west put down the fires yesterday.
http://www.woodgaz-stove.com/

sudden
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Re: Humidity and Stove Testing

Postby sudden » Fri May 10, 2013 7:55 am

I wonder if it has something to do with absorbed water diluting the alcohol a bit???
"People are not persuaded by what we say, but rather by what they understand."

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zelph
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Re: Humidity and Stove Testing

Postby zelph » Fri May 10, 2013 9:38 pm

sudden wrote:I wonder if it has something to do with absorbed water diluting the alcohol a bit???


Nobody has explained it to me so I will do some detective work to find out "why" ;)
http://www.woodgaz-stove.com/

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zelph
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Re: Humidity and Stove Testing

Postby zelph » Fri May 10, 2013 11:08 pm

Google is our friend ;)

"Understanding air density and its effects"

By Jack Williams, USATODAY.com
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 a molecular weight of 28 (2 atoms with atomic weight 14) . Another 21% of the air is oxygen, with each molecule having a molecular weight of 32 (2 stoms with atomic weight 16). 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, which replace nitrogen or oxygen, have a molecular weight of 18. (One oxygen atom with atomic weight of 16, and two hudrogen atoms each with atomic weight of 1). 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. (Related: Understanding water in the atmosphere).

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.
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In conclusion we can understand that water vapor in the air acts like all other gasses.. it provides partial pressure proportional to its content in the air. in other words, the moist air will contain less oxygen at the same pressure (the sum of partial pressures being the same, the more water in the air, the less oxygen for combustion).
http://www.woodgaz-stove.com/

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cruiser
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Re: Humidity and Stove Testing

Postby cruiser » Sat May 11, 2013 2:03 pm

Wow. Great explanation. I too previously assumed it was about water being absorbed into the hydrophilic fuel. I would not have guessed it could be about levels of oxygen available for combustion.

I nominate you for honorary PHD.

sudden
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Re: Humidity and Stove Testing

Postby sudden » Sat May 11, 2013 3:07 pm

cruiser wrote:Wow. Great explanation. I too previously assumed it was about water being absorbed into the hydrophilic fuel. I would not have guessed it could be about levels of oxygen available for combustion.

I nominate you for honorary PHD.


seconded.

Very informative article zelph. Makes perfect sense now.
"People are not persuaded by what we say, but rather by what they understand."

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zelph
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Re: Humidity and Stove Testing

Postby zelph » Sun May 12, 2013 9:45 pm

Great, glad it meant something :D Something else I read dealt with "dew" point and how humidity is hard on us when it gets up to 70% humidity. Very difficult for us to breath because of the lack of oxygen in the air. Time to stay indoors with the AC turned on and also the dehumidifier on ;)

If you're out on a hike in those conditions you might just want to take some zero days till the weather gets better.
http://www.woodgaz-stove.com/


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