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Gas Expansion, please help.

by timman_24
Tags: expansion
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timman_24
#1
Dec15-03, 09:46 AM
P: 52
I am doing a physics problem in my High School class and I cannot find the answer to this:

How much does water expand when changing from a liquid to a solid. Is there a percent? Example, when a gallon of water fully evaporates how much space does the vapor take up?

Thanks alot!
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suyver
#2
Dec15-03, 10:33 AM
suyver's Avatar
P: 265
It depends on things like pressure, temperature and density of the liquid. But as a rule of thumb: 1 liter liquid becomes roughly 1000 liters of gas.
radagast
#3
Dec15-03, 11:02 AM
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P: 460
As far as the expansion of water going from liquid to ice, it's somewhere on the order of about 10%.

timman_24
#4
Dec15-03, 11:52 AM
P: 52
Gas Expansion, please help.

Nah, I'm talking about the expansion of the liquid to the gaseous form...

Thanks guys, I might have more questions later.
hemmul
#5
Dec17-03, 09:13 AM
P: n/a
Actually, there is not enough information provided to answer the stated question.

You see, the real gases roughly obey Van-der-Vaal's law, which links it's state parameters: Pressure, Volume and Temperature. From this law it follows, that in vacuum the gas, due to a very small forces of attraction between its atoms, takes the certain volume. Also, it is impossible (because of the finite size of the atoms) to shrink the gas in less than a certain small volume

Now, when the water evaporates:
1) in vacuum the vapour will fill the volume predicted by Van-derVaal's law, which can be easily derived from his equation of state
2) in some matter, say air, you must also consider the outer pressure, and so on + use the law of partial pressures to find the partial pressure of the vapour in the air, and substituting it in Van-der-Vaal's equation derive the expression for the volume.

Concerning the expansion of water, going into ice, it is slighty different question, but really the difference is about 10% because the density of ice is 900 kg/m^3 and of water 1000 kg/m^3.

NOTE:
In practice, if the volume of a vial with liquid is initially closed, the vapour will fill the whole volume. This assumption is used to solve the majority of thermodynamics problems. It is absolutely true for the ideal gas, where they neglect the potential energy of interaction of gas atoms, and their size, thus using the equation of ideal gas instead of Van-der-Vaal's equation.
hope that helped!
you can use
scinceworld.wolfram.com for more information of Van-der-Vaal's equation (sorry, i am not sure in spelling in this name)
timman_24
#6
Dec17-03, 02:57 PM
P: 52
Yes it helped alot actually. Let me be less vague about my question. My project so far is to make an energy balance of a normal gas engine. There is a twist though. There is a patent (#5,156,114 ) that states that a Rudolf Gunnerman claims there is a way for a gasoline engine to run off of 20% fuel and 80% water. It produces comparable power also. The water dissociates and the Hydrogen burns and the oxygen helps the burn. Anyways I am trying to account for all the energy in the system.

Here is where I am at. When the water runs through the fuel rail (fuel injected motor) it is in liquid form but is hotter then the threshold for evaporation,, but the pressurization of the rail keeps it in the liquid phase. When the water is ejected into the cylinder it is not as pressurized and turns to vapor form. I am trying to see what equation to use to get the pressure in the cylinder and compare that to the compression ratio. I am trying to see how much it raises the compression ratio of the engine, because the compression ratio effects the output power. Also heat is absorbed through the cylinder to vaporize the water. I am seeing how much heat is used in the process.
Hopefully I am making some sense...
timman_24
#7
Dec17-03, 02:58 PM
P: 52
Oh also the patent is #5,156,114 if anyone is interested. Just go to www.uspto.gov and search the number...
obstinatus_iter
#8
Jul11-04, 03:33 AM
P: 1
i was wondering if there is an equation for the expansion of pressurized gas , specifically helium, i need to know how long it would take for a gas to expand to a specific volume.


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