A plastic liter jug, half filled with water. It has an inlet valve, with a pump. You pump several atmospheres of pressure into the jug.
Wait for the system to equilibrate to room temp. Then open the outlet valve. Let the air escape until equilibration pressure.
What's the interior temp.?
-- Rich
Lower than ambient, although the outlet valve will heat up through friction. But what's the water for?
Cheers
-- Syd
Air saturated with water vapour has slightly different thermodynamics to dry air - the cooling as it expands causes some of the water vapour to condense, releasing its latent heat of vaporisation.
-- Bill Sloman, Sydney
Correct - this is one of the thermodynamic effects I don't calculate in my (1997) water rocket simulator at
Bryan Holt duplicated my math independently, and correlated it with some high-speed video measurements taken by Prof Dean Wheeler at UCB.
Bryan found a couple percent variation in the velocity curves which was only corrected when he added the thermodynamic effect of vapour condensation.
Just thought you'd like to know that Bill's assertion is confirmed by real physical experiments.
Oh, and regarding strength, our tests on PET soft-drink bottles say that typical 2L bottles are safe for 120psi, 1.25L bottles for 160psi, and
600/660ml bottles for 200psi. That's assuming new bottles with the typical wall thickness of about 0.3mm. Smaller diameter bottles are under less hoop stress for the same pressure.As to the original question, google for the adiabatic expansion formula, and adjust for condensation.
Clifford Heath.
Such as hurricanes. ;) Moist processes drive most of the interesting physics in the atmosphere.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant
e
Some experiment. Physicists think big, but calling a hurrican "an experimen t" is a trifle meglomaniac. Then again, our current exercise in digging up and burning every last scrap of fossil carbon we can find to raise the CO2 level in the atmosphere is an even larger scale experiment.
It's a pity that our right-wing nitwits haven't been able to get their head s around the preliminary results, to the extent that they claim that it's n ot working.
-- Bill Sloman, Sydney
Fun! (I've always wanted to build a water/ bottle rocket.)
George H.
Wow, Bill, your trip back to Holland does seem to have refilled your Europeon scorn-and-derision tanks. Go try that stuff down at the local pub in Sydney, and I bet it drains out again pretty fast.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant
s
ur
in
ome
as
riment" is a trifle meglomaniac. Then again, our current exercise in diggin g up and burning every last scrap of fossil carbon we can find to raise the CO2 level in the atmosphere is an even larger scale experiment.
heads around the preliminary results, to the extent that they claim that it 's not working.
"Scorn and derision"? Check out Phil Allison for what you've got to produce for a Sydney audience to register scorn or derision.
What I posted was benign fair comment.
Or have you actually created your own hurricane in the course of one of you r experiments? That really would have been a Clausewitzian extension of dip lomacy by other means. You'd have been lucky to get off with mere scorn and derision if you'd been responsible for such a pontentially destructive phe nomenon.
-- Bill Sloman, Sydney
To absorb the CO2 and make fizzy water at high pressures (OT baybe assumes bottle cannot bust).
There's a Yahoo ML/forum that acts as a support group for addicts. I created it when I closed our majordomo server a decade ago.
Personally I haven't launched in over two years, and even then it was only to scare the crows away - I found they don't like things going booom and then flying close by at 300km/hr. It's a great way to teach physics, however, as there's enough complexity to tickle NASA but an 8yo can still participate. The "Clark Cable" cable tie launcher is pretty easy to make.
No. Why should it drop?
heh Sort of a distraction.
But also motivated by reality. A friend believes he's going to develop a water cooler this way. For bicyclists and hikers -
-- Rich
Joule-Thompson effect.
Not a very effective one. Run the numbers.
-- Bill Sloman, Sydney
You'd certainly need a cool drink after putting in the effort to cool a drink. Best plan is to carry a few sachets of dehydrated ice to drop in as required.
Cheers
-- Syd
A plastic liter jug, half filled with water. It has an inlet valve, with a pump. You pump several atmospheres of pressure into the jug.
Wait for the system to equilibrate to room temp. Then open the outlet valve. Let the air escape until equilibration pressure.
What's the interior temp.?
-- Rich Since you did not specified how many atmospheres of pressure was pumped into
If you fill a canvas bag with water, the water slowly wicks to the outside, where it evaporates, this cools the rest of the water inside. Not sure wh at they are called, but I say them in Australia many moons ago. (I guess t hey work best in a dry climate.)
George H.
Hey near the first line the wiki link says that, "At room temperature, all gases except hydrogen, helium and neon cool upon expansion by the Joule?Thomson process."
Why not those gases too? In grad school I use to drain 2000 psi helium ta nks into the helium liquifier... they got plenty cold on the outside.
George H.
The Joule Thomson effect is purely dependent on the attraction of gas molecules, and when they expand they cool. An ideal gas exhibits no J-T effect. This phenomenon is completely separate to adiabatic expansion where work is done.
Because at higher temperatures hydrogen molecules repulse each other at high pressures, the gas actually heats on expansion. The situation is reversed at lower temperatures where at higher pressures there is an attraction. I'm not sure about Neon and Helium and its notable they are monoatomic noble gases.
A gas only cools if in the course of expanding it does work. Expanding a gas through a nozzle means that the work that could have been done now heats the gas, so we are essentially back at square one, ie nominally at the same temperature (excluding the much smaller J-T effect).
Your tank of high pressure helium would be undergoing adiabatic expansion by the draw of helium to the outside world. The gas inside would be expanding, doing work by expelling helium through a valve, hence cooling.
-- Mike Perkins Video Solutions Ltd
Hi Mike, thanks, more thought will be required. (It's been way too long si nce I did any Thermo.) I don't think the pressurized bottle is best descri bed as the Joule-Thompson (J-T) process.. it's a free expansion.
The above mention helium liquifier did have a J-T throttling valve, but as you say it would only start working down around ~10K where some fraction of the throttled helium would turn into liquid. I spent many nights as a gra d student baby sitting the liquifer and tweaking the J-T valve. George H.
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