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Old 08-18-2011, 07:21 AM   #31
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the water will boil at a lower temp at the upper altitudes. as far as the propane usage, i would expect a lower usage. i know u need a certain number of BTUs to get it to the boiling point then more are required to make it boil. in air conditioning, a lower pressure...vacuum is used to boil the water from lines at ambient temps. if u were just trying to get the air out, u could just purge with freon.
ur tire pressure, i would expect to increase because the gauge measures the difference between the pressure of the tire and the pressure of the atmosphere. sense i didn't check my tire pressure when i was in the upper elevations a few years ago. i can't say how much they changed. doubt if it was very much.
the one that puzzled me was the chips. we did buy chips in Montana that had a normal size bag. when we left the area, the bags expanded. we ate the chips before we got home so i don't know what size the bag would have been here (8' above sea level).
we thought we were driving to a lower elevation. the atmospheric pressure should have collapsed them. only thing i can come up with is that we actually went up from glacier.
the O2 continent of the air changes. it's been too long ago that i heard how we react to lower content. seems like around 20% we show changes. 16% i believe we loose consciousness. i really don't remember the numbers but was impressed with how small the reduction was.
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Old 08-19-2011, 03:20 AM   #32
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The oxygen percentage does not change, it remains constant at 21%, nitrogen being the majority of the remaining air.

The volume of air does change, this is explained in Boyle's law. As altitude increases, the air expands which decreases the number of molecules present, it does not affect the percentage, rather the quantity of the molecules, oxygen and nitrogen equally.

Air is a gas and is compressable, and it has weight, therefore, the higher the stack (or weight) of air, the more it is compressed. Thus, at sea level, the air is compressed more than say at 10,000 feet. A sealed, yet not rigid container will expand as you rise from sea level into the mountains, this is because the partial pressure (or weight) is less on the outside of the container. A rigid container, such as a pop can, may not show the difference until you try to open it, then it may burst and spray.

Oxygen in the lungs is affected by this partial pressure, as it takes pressure for the oxygen to pass across the membranes and picked up by the red blood cells, therefore at higher altitudes it is more difficult to take up oxygen, both the quantity of oxygen molecules in a breath of air is less (still 21%), and less partial pressure to "push" the oxygen across the membranes.

Confusing.... yes
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Old 08-19-2011, 08:16 AM   #33
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Confusing yes

But totally correct. Tires can be considered rigid containers in this example. They are fixed volume containers. Even flat (without holes obviously) the interior volume does not change.

They are not like balloons. The pressure in a balloon is the same as outside air pressure (a minor increase due to the stretch of the rubber for purists) and the volume adjusts accordingly.

With a tire, it as air is pushed in the pressure goes up because the tire can NOT expand. That is why over pressurized tires to not make good contact with the road. The center of the tread bulges outward but to maintain the volume the sidewall lifts the outside of the tread off the road.
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Old 09-07-2011, 11:13 PM   #34
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And here is another thing, we are at 6500 feet and the click click thing on the stove works I can see the sparks but it will not light, we have to light it with the BBQ lighter, it was working fine at our last campsite 2500 feet.

Or am I loosing it?

This wine tastes real good at this altitude too

Here we are back down at sea level and the stove top igniter (click think) works every time on the first click! Lou where are you, explain if this is coincidence, science or my imagination, please put me out of my misery
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Old 09-07-2011, 11:51 PM   #35
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The oxygen percentage does not change, it remains constant at 21%, nitrogen being the majority of the remaining air.

The volume of air does change, this is explained in Boyle's law. As altitude increases, the air expands which decreases the number of molecules present, it does not affect the percentage, rather the quantity of the molecules, oxygen and nitrogen equally.

Air is a gas and is compressable, and it has weight, therefore, the higher the stack (or weight) of air, the more it is compressed. Thus, at sea level, the air is compressed more than say at 10,000 feet. A sealed, yet not rigid container will expand as you rise from sea level into the mountains, this is because the partial pressure (or weight) is less on the outside of the container. A rigid container, such as a pop can, may not show the difference until you try to open it, then it may burst and spray.

Oxygen in the lungs is affected by this partial pressure, as it takes pressure for the oxygen to pass across the membranes and picked up by the red blood cells, therefore at higher altitudes it is more difficult to take up oxygen, both the quantity of oxygen molecules in a breath of air is less (still 21%), and less partial pressure to "push" the oxygen across the membranes.

Confusing.... yes
understand. same percentage just lower density.

the membrane exchange is out of my league. always thought of it as the content of the air in the lungs and blood stream trying to reach a balance. much like having a volume of pure O2 and another volume of CO2, if u put them together, they would reach a balance.
i ran some test on the O2 being exhaled (many yrs ago) and if i remember right it was abt 18%. i've slept sense then so i don't remember the exact number, just remembered there was a lot more O2 in there than i thought.
Partial pressure was always difficult for me to see. the sum of the individual pressures and their % (i believe that is supposed to be mole % but that is really above me) will be the pressure of the vapor. our fractionator tower worked on that principle but it was easier for me to see that raising temp or lowering pressure made the gas heavier.
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Old 09-08-2011, 09:13 AM   #36
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Here we are back down at sea level and the stove top igniter (click think) works every time on the first click! Lou where are you, explain if this is coincidence, science or my imagination, please put me out of my misery
While the percentage of oxygen remains constant at about 21% up to FL700 (70,000 feet), the atmospheric pressure drops rapidly above 2500 feet.

Altitude sickness - Wikipedia, the free encyclopedia

Air - Altitude, Density and Specific Volume

At a "Standard Day Temperature" the pressure at Sea Level is about 100 kPa; at 2500 feet it drops to 92 kPa (8% of the air is gone); at 6500 feet it has dropped to 80 kPa (or 20% of the air is gone - a point at which "Altitude sickness" can occur); above 8000 feet (76kPa or about 25% of available air is gone) some humans begin to need supplemental oxygen to live normally. Above 10,000 feet everyone will need supplemental oxygen to live normally. This is why smokers get headaches on long airline flights; the airlines keep the cabin at a pressure equal to 8000 feet.

With 80% of available oxygen gone at 6500 feet, you will have an "over rich" mixture at the gas nozzles (holes too big for the altitude) and the normal sparker will be too close to the "nearly pure propane" outlet of the burner. The lighter will ignite the gas further from the burner where it has had a chance to mix with the available oxygen.

You might have noticed a large space between the metal burner and the "base" of the flame. That space is much smaller at sea level.
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Old 09-08-2011, 09:53 AM   #37
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Shouldn't be putting air in your tires while flying either! The tator chip grease may allow you to slip and fall! Then a blood pressure check won't help.
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Old 09-08-2011, 11:19 AM   #38
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While the percentage of oxygen remains constant at about 21% up to FL700 (70,000 feet), the atmospheric pressure drops rapidly above 2500 feet.

Altitude sickness - Wikipedia, the free encyclopedia

Air - Altitude, Density and Specific Volume

At a "Standard Day Temperature" the pressure at Sea Level is about 100 kPa; at 2500 feet it drops to 92 kPa (8% of the air is gone); at 6500 feet it has dropped to 80 kPa (or 20% of the air is gone - a point at which "Altitude sickness" can occur); above 8000 feet (76kPa or about 25% of available air is gone) some humans begin to need supplemental oxygen to live normally. Above 10,000 feet everyone will need supplemental oxygen to live normally. This is why smokers get headaches on long airline flights; the airlines keep the cabin at a pressure equal to 8000 feet.

With 80% of available oxygen gone at 6500 feet, you will have an "over rich" mixture at the gas nozzles (holes too big for the altitude) and the normal sparker will be too close to the "nearly pure propane" outlet of the burner. The lighter will ignite the gas further from the burner where it has had a chance to mix with the available oxygen.

You might have noticed a large space between the metal burner and the "base" of the flame. That space is much smaller at sea level.
Thanks Lou, as always an excellent an appropriate answer
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Old 09-08-2011, 11:23 AM   #39
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Shouldn't be putting air in your tires while flying either! The tator chip grease may allow you to slip and fall! Then a blood pressure check won't help.
Tator chip grease is less slippery at altitude, had that one worked out already
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Old 09-08-2011, 10:47 PM   #40
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By direct observation, I can thell you that the individual serving size of Lay's potato chips burst at about 11,000 feet.

When I was at Boeing, I went on a goodly number of customer acceptance test flights. The profile was always the same. If we went out in a morning, the cafeteria provided box lunches for everyone on board, including a bag of chips.

One of the tests is a cabin de-pressurisation to show that all the oxygen masks deploy correctly. The co-pilot reads off the cabin altitude as the test progresses. At about 11,000 feet cabin altitude you hear a series of popping noises from the lunch boxes - potato chip bags bursting.
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