Compressed Air

Okay, I'll play:

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"You have a 2 liter Soda Bottle."

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There, I did it. I don't feel anything. Am I supposed to? Oh well.

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'....What would the volume of the air be when you reach a pressure of 15 PSI?...'

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Well, that depends on a number of things:

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1. PSIA or PSIG?

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2. Where is this happening?...or alternately what is the initial pressure?

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3. Is there heat transfer through the soda bottle wall? What about heat transfer with the water being introduced?

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4. If someone else does your homework for you, do much credit do you deserve? Are you willing to divide your grade with those who helped?

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PV/nRT = PV/nRT

Assuming you mean psig, a bit less than one liter of air.

Really?

1/2 the volume is 15 psi?

Joe

Ok, here comes the much too literal, pain in the a$$, smart mouth answer .

When I pour water into a two liter soda bottle, the displaced air leaves out the top and remains at a nominal one atmosphere of pressure. A sealed bottle cannot have more water added. It is sealed.

_{Since everyone else answered the intended way I felt somebody had to provide the childish answer. Why not me?}

OK,

What I was thinking was in one of my High Altitude Balloon flights. for a ballast system.

If I had some sort of liquid ballast say alchaol,, In this 2 litre bottle and how much air I would need to leave in the bottle that once I drag it up to near vacuum of say 80K feet, how much air inside would be needed to be able to push the liquid out via a solenoid valve,

If we left the bottle open so air could come in so liquid could go out then the alchaol would just boil away.

Looks like 'm going to have to pre pressureize the bottle above sea level pressures to be able to make use all the liquid is able to be pushed out.

joe

Well now you just raised a whole lot more questions. Here is the first two.

Why alcohol as a ballast and why are you letting it out at 80,000 feet?

To get to 81,000 feet....

We don't want to go below 80K feet, if we are above fine but when we drop below we want to drop some ballast to remain above 80K

why alchol?

cheap, wont freeze at -70C pretty good reasons.

Be careful of which alcohol you select and the purity. As this link points out a 40% solution of isopropyl alcohol will freeze at only -20°C and pure isopropyl will freeze at -89°C. You should also consider the atmospheric pressure drop you anticipate. You don't want you ballast to prematurely leak out.

Giant atmopheric pressure drop, where we go it is probably better than most of the best lab vacuums

0.064729 PSI

P₁V₁/T₁=P₂V₂/T₂

P₁T₂/P₂T₁=V₂/V₁

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P₁=14.7 psia (roughly)

P₂=.0735 psia (to allow some remaining pressure to drive the last water out... make the calculation simple)

T₁= 300 K

T₂= 200 K

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14.7 x 200/(.0735 x 300) = ~133

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V₂/V₁ =~130

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Meaning the liter of air in the soda bottle will want to expand by more than 130 times for that change in pressure (moderated a little for the change in temperature.

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So you could use a lot less than a liter of air.

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Do you know how much presure a soda bottle and the solenoid valve and attachments will withstand at those temps?

AWESOME!!

Now how much liquid could I put in it at sea level,

Then seal her off, and lets say worst case 60K feet, 1.040159PSI

How much liquid could I put in it and be sure it will all come out at 60K feet.

Joe

Either just multiply the previous answer by .0735 and then divide by 1.040159

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or, (even better...)

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Use the formula I provided.

It is really very easy to understand or just plug in the values (Initial pressure times volume divided by absolute temp is equal to final pressure times volume divided by absolute temp).

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... oh, you will need to plug in a new temp if it will not be the -70C (200K) you earlier stated .

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One more important thing.... your concern about being sure will all comes out might be unbalanced compared to your apparent lack of concern about being sure it doesn't all come (suddenly) out prematurely.

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You might want to do some careful testing (like submerged in a tank of water except realistic tests would have to be at a much lower temp) of your soda bottle attachments and solenoid valve, to make sure it can handle at least 30psia when at sea level.

those bottles 30 psi at sea level, well they wouldn't even know they have any pressure in them at that pressure.

Coke confirmed by phone all their plastic 20oz to 2
liter PETE bottles are safety tested at the "industry standard" 150 psi and

some are even tested to 250 psi. Burst happens near the 300 PSI range.

A common "FUN" thing to do is fill a bottle with a little water add some dry ice seal it and wait for it to blow.

The pressure release is pretty impressive. you tube video

http://youtu.be/nZHGK37jBp8

Shredded aluminum foil and muriatic acid works well too!
BOOM!

i always wondered how so many scientist are interested in weather now i get it - there's gonna be thunder and what you just said ((help help))

Ok, so an bottle intact would probably be fine (-70 C makes thing behave differently though...than temps most of us are accustomed to).

The connections to the bottle and the solenoid valve need consideration/evaluation.

I am not sure why you have used a 100 degree K difference in temperature. I would just use a constant temperature and then:

P1V1=P2V2 ==> V2=P1V1/P2

V2=14.7psia x 2 liters/29.7 psia

= 0.9898 Liters as volume at 15 psi guage or 29.7 psi absolute

Because the nominal air temperature drops with altitude.

I would accept that but OP never mentioned altitude. So unless OP comes up with a change in Temperature, I would assume constant Temperature. He actually never mentioned whether it was absolute or gauge pressure so I assume gauge as the 15 psi. Here is another link to pressure tanks and water systems. 100 degrees K or C is still large even at the top of a very high mountain (or is this the balloon altitude). I am too easy confused.

'....I am not sure why you have used a 100 degree K difference in temperature. I would just use a constant temperature and then:.........= 0.9898 Liters as volume at 15 psi guage or 29.7 psi absolute...'

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I am sure that the reason you are not sure, is because you have not read enough of the post to understand the application.

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The reason I used 300 K and 200 K is because those are close to the expected temperatures.

...note that the OP has specified using alcohol to avoid having the fluid freeze..... doesn't that suggest there will be some change in temperature?

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The reason I used standard atmospheric and the pressure expected at 80k ft, is because that is what is specified in the application.

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Mea Culpa. I read post 6 too quick. Thanks.

I think he means a nice single malt, perhaps from the Island of Islay.

I have grave concerns about the evaporation rate and the effect that this will have on the crew and passengers.

BAB

24point384km the nitrogen populates (& oxides) above 2.5...5 up to 40km(cirrus ... i guess) /// + not to the prev. some pictures (i never focused on Earth's atm. too intense)

https://yr11geography.wikispaces.com/file/view/w3.1.jpg/32577067/w3.1.jpg

it's just difficult to find even those (clearity readout usfulness) plots - just incase sored in My Computer

very interesting!

the upper 1's from

Surveys in Geophysics (2006) 27:149-167 © Springer 2006
DOI: 10.1007/s10712-005-3874-9
COMPARATIVE PLANETARY CLIMATOLOGY✩
FREDRIC W. TAYLOR
Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory,
University of Oxford, Oxford, OX1 3PU, England
E-mail: fwt@atm.ox.ac.uk
(Received 4 August 2005; Accepted 5 October 2005)

muhahahaahaahaahaaa

some calculations "must have"

+http://www-pcmdi.llnl.gov/links/links.php

keep interested

We need to know what kind of alcohol ... Vodka, Gin, Bourbon, ...?

Bacardi 151! 75.5% Alcohol.

Well for once a thread turned out to be educational!

Continue on!

Am I missing something? The volume of air doesn't change, it's still 2 litres. Just that compressed to 15 psi it is going to be compressed into roughly 1 litre.

Go metric, Bar is such a lovely unit to do this with.

Why not just have the bottle open to atmosphere and the solenoid valve at the bottom, let it gravity drain?

10 Bar pressure test on a coke bottle, I'm impressed. Always wondered what the pressure was when they blew after we put a little bit of liquid nitrogen in them! Or Mentoes in Diet Coke!

Dear Mr. NSS,

It is very simple.

P1VI/T1 = P2V2/T2

OR P1V1 = wRT1 = P2V2 =wRT2

Take care of correct Units.

dhayanandhan.s

Why not use fine steel shot,like in shotgun shells.It will pour like a liquid when needed,just make sure to keep it dry.It will require less space for same weight,and if dry, freezing is not an issue.

Not likely to hurt anyone due to small size and low mass of the pellets.

and that is the problem,

any moisture and nothing happens, and trying to make 100% moisture blocking design, yet be able to drop some when needed is nearly impossible.

How about placing a tray of (or porous container) caustic soda flakes (or beads) or molecular sieve 7A, or Alumina, that has been pre-dried, shot that has been de-greased and dried carefully in a drying oven? The air in the container would help push the steel shot out when the slider valve is open, so be careful to calibrate the dump against a vaccum... and watch out airliners below, and drones below, etc.

That's a PV=nRT problem, where n & R are constants, so you can use PV/t(initial) = PV/t(final)

Initially pressure = 100kPa (about 15psi), Volume = 2 l, Temp = 300K (about room temp)

Afterwards Pressure = 200kPa (plus 15psi) Volume = X & Temp = 300K (if you want it at room temp)

You can plug the numbers in turn the handle and get the answer. Good luck with rest of the homework.

PSI? not PSIG?

therefore 15 = (2*14.7)/V2

therefore V2 = (2*14.7)/15 = 1.96

Answer 1.96 litres of air at normal Atmos pressure, adjust for variable air pressures.

Regards JD.

Couldn't you just put a solenoid on the top and bottom then fill it all the way with the alcohol? The solenoids would be wired to open simultaneously allowing the alcohol to drain out.

The simplicity in this idea is beautiful!

Yes notrmally could not leave the top open because the alcahaol would boil off.

But lave at top and bottom, is elegant in simplicity.

Joe

'....The simplicity in this idea is beautiful!....'

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Simplicity?

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-instead of one penetration (presumably where is already exists at the mouth of the bottle) now there are two.

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-connections from the bottle to the valve have doubled.

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-two solenoid valves are now required which adds cost, adds non-jettison-able weight, takes up additional space, requires power to activate two valves, risks leakage of two valves, means mass will be jettisoned more slowly, and adds a non-simultaneity factor to the risk of failure.

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This idea isn't terrible, but it certainly isn't elegant in its simplicity either.

Yet, allowing for the possibility the original intention was to use more than one of these "ballast vessels", using 2 valves on one bottle would cut the number of bottles and mounting brackets in half producing an overall reduction in weight. There is also the possibility of utilizing the single opening with a vent tube inside the bottle that could be opened by the second solenoid.

Vent tube inside it going to subject the alcohol to evaporation.

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Since the gas will expand more than 100 times, very little gas is needed in each soda bottle, I doubt a weight or size improvement could be achieved in the manner you suggest.

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Even if neither of the above were concerns (even though they are), the suggested solution is not 'elegant in its simplicity' as previously claimed.

Vent tube inside it going to subject the alcohol to evaporation.

How will this happen if the vent tube is closed until the second solenoid opens?

when you wrote:

'...There is also the possibility of utilizing the single opening with a vent tube inside the bottle that could be opened by the second solenoid....'

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you seemed to be suggesting that complexity of additional valves could be avoided using a vent valve. I clearly misread your statement. You are saying that both drain and vent could enter through the bottle mouth. You definitely have a point there.

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That still leaves twice the connections, twice the valves requiring twice the activation and creating new point of failure in non-simultaneity.

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Workable? sure.

Better? doubtful.

Elegantly simple? no way.

Why are you guys doing this person's homework?

UFG

I think that this is much to do about nothing. I think the most critical factor will be making sure the sealing valve does not react with the liquid ballast, what ever it is. My next concern is the battery and electronics being able to receive a ground signal and drive the solenoid for long enough time to empty the ballast tanks bottles. The battery chemistry will surely change at these temperatures. Then I would worry about debris or moisture contaminants that might freeze and block your outlet nozzle and valve movement at these temperatures.

Worrying about the gas charge pressure in these bottles seems silly with the outside pressure dropping to far less than one PSI. As TNC implied in #13, the pressure inside the bottle will drop from the temperature change. The pressure outside is expected to drop far more than the trapped volume of gas. _{I'll leave it open to the student to ponder why this happens.}

I think that this is much to do about nothing. I think the most critical factor will be making sure the sealing valve does not react with the liquid ballast, what ever it is.

And that is simple by communication with the valve manufacturer.

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My next concern is the battery and electronics being able to receive a ground signal and drive the solenoid for long enough time to empty the ballast tanks bottles.

No Need, even tho this is never a problem when we do send signals to a payload for remote control never in 30 years have had a problem. Plus with the flight this is going in, it will be all automatically controlled all by itself, It will now when it need to drop some.

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The battery chemistry will surely change at these temperatures.

The cells we have been using have served us well, never once have they quit working, Yes they do indeed loose some capacity (about 10%) but have always worked.

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Then I would worry about debris or moisture contaminants that might freeze and block your outlet nozzle and valve movement at these temperatures.

Mousture I will agree with, as far as purity well that is as pure a you make it to be,

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Worrying about the gas charge pressure in these bottles seems silly with the outside pressure dropping to far less than one PSI. As TNC implied in #13, the pressure inside the bottle will drop from the temperature change. The pressure outside is expected to drop far more than the trapped volume of gas.

True, the whole question was if it was filled with no air at all, you would have to rely on the alcahol to boil off from the exposeure to the low pressure to loose the ballast.

But some air, the air would expand to try to equlize the pressure so it pushes out the alchaol.

I was also thinking, 2000 ml volume right?

if I had 1800 ml liquid and 200 ml air in the bottle, at sea level. at 60K feet the 200 ml of air would if allowed to, expand to 2125 ml. yes?

'....True, the whole question was if it was filled with no air at all, you would have to rely on the alcahol to boil off from the exposeure to the low pressure to loose the ballast.

But some air, the air would expand to try to equlize the pressure so it pushes out the alchaol....'

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This actually raises an interesting point, and suggests you shouldn't error on the side of too little air in the bottle (so 200ml should be fine but not much below that).

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Excessive boiling of alcohol because of reduced pressure could cause large drop in temperature at certain points in the system. The temperature may drop below the freezing point of alcohol.

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Having some air pressure in there to maintain pressure and making sure that the valve is somewhat restrictive will help reduce the chance of alcohol freezing upstream of the valve. A restriction downstream of the valve that is somewhat insulated from the valve will help to insure the valve won't freeze open. The shape of that last restriction might become important.

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This also presents a more serious problem for the two valve, drain and vent system suggested below.

The new absolute pressure will be 15,7+15=30.7 psia, so the new volume is 15.7/30.7=0.51 times the "original" volume, or 0.51x2=1.022 liters. This is assuming air is an ideal gas, in fact it is almost ideal. It is also assumed that temperature remains constant.

The applied formula is PV/T=P'V'/T', if T is constant, then PV=P'T', that's to say volume is inversely proportional to pressure. Got it? Any proccess or chemical technician or engineer can explain it with more detail...

Hey NSS,

There has been some speculation around the water cooler, and I figured it would be best if I just asked you directly:

In what capacity do you function in the team who has been doing this for 30 years?

Director? Fabricator? Funder? PR? Legal?...etc..

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Just curious about where/how you fit into the whole scheme of things.

All the Above.

I hope this isn't taken in the wrong way.... I have to ask:

How have you managed to avoid familiarity/proficiency with the Ideal Gas Law while doing this for 30 years? How have known for instance how much gas to put in the balloon? ...etc...seems like this is mission critical knowledge..

Not taken wrong.

I'm used to thinking in lowering pressures and expanding gases way. Pressureing sometimes confuses me.

And if would have just thought of a gas bubble at sea level, and what it would expand to at 60K, I could have easily figured out how large the initial bubble would need to be to expand to 2 litres or more at 60K, and just ignore the liquid in the bottle.

Just had a brain fart,

If there is air in the bottle, there will also be some moisture in the bottle. Perhaps the air should be dried or another gas should be considered.

Since this is not my area of expertise, I can't offer answers, just questions.

is your solenoid (design not detailed) already automated to open at certain altidude ?? after first reaching another higgher altidue - higger than certain - the membranes can trigger stuff you need probably 2 or more tanks to do this (just membranes rods and gears)

"#%&%#/ synchroni Z T

http://www.ncbi.nlm.nih.gov/pubmed/15204440