Author Topic: Molecular Model for an Ideal Gas  (Read 495411 times)

lookang

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Re: Molecular Model for an Ideal Gas
« Reply #45 on: December 29, 2010, 09:26:25 am »
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1455.0
This simulation is remixed to address the real life values.
I introduce some constants to make the simulation reflect real numbers.

Maybe can introduce this simulation :)

ahmedelshfie

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Re: Molecular Model for an Ideal Gas
« Reply #46 on: February 08, 2011, 06:50:11 pm »
Here is Molecular Model by paul Falstad.
http://www.falstad.com/gas/

« Last Edit: February 08, 2011, 06:52:22 pm by ahmedelshfie »

surya316

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Re: Molecular Model for an Ideal Gas
« Reply #47 on: March 17, 2011, 02:12:33 pm »
Dear Professor ,
Can you please email  me  the 2nd collision simulation source code where you kept the volume constant. I tried downloading the files directly but it tells me that the files are corrupted. Do help me out

Fu-Kwun Hwang

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Re: Molecular Model for an Ideal Gas
« Reply #48 on: March 17, 2011, 03:08:38 pm »
Please provide the message where you found the simulation.
I do not know which one you need.

naive

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Re: Molecular Model for an Ideal Gas
« Reply #49 on: March 01, 2012, 09:04:26 am »
Hi Fu-Kwun Hwang,
Bernoulli's equation (ignoring gravity) can be illustrated with a straight tube connected to a tapering tube connected to another straight tube, with pistons in the straight tubes.
question 1: can this be simulated with an ideal gas between the pistons?
question 2: is Bernoulli's equation  true for an ideal gas?
thanks for thinking about this.

Fu-Kwun Hwang

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Re: Molecular Model for an Ideal Gas
« Reply #50 on: March 01, 2012, 09:43:24 pm »
Bernoulli's equation :
Do you mean : $P+   frac{1}{2}ho v^2+ho g h=$constant

Quote
question 1: can this be simulated with an ideal gas between the pistons?
Could you describe your model in more detail? I can not catch your ideas.

Quote
question 2: is Bernoulli's equation  true for an ideal gas?

The Bernoulli's principle is valid for incompressible flows (e.g. most liquid flows) and also for compressible flows (e.g. gases) moving at low Mach numbers

naive

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Re: Molecular Model for an Ideal Gas
« Reply #51 on: March 03, 2012, 06:32:32 am »
hi!
you have the equation. let's ignore the third (gravitational) term.

i hope this diagram clarifies ( " * " outlines a 3-section tube, " + " outlines the pistons.):
* * * * * * * * *
   + *
   + *
   + * * * * * * * * * * * * *
   + +
   + gas enclosed +
   + +
   + * * * * * * * * * * * * *
   + *
   + *
   * * * * * * * * *
basically, we're changing the shape of an ideal gas, keeping the volume the same. but we're looking at the process while it is happening, not a "before" and "after" situation.
it's not clear that we can ignore the temperature.
nor is it clear that the pressure on one piston is the same as the pressure on the wall of its corresponding straight tube section.
nor is it clear that the density in the straight tube sections is the same.

i thought a simulation might help see what's happening. i have no idea if anyone has done this.

thanks again.


naive

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Re: Molecular Model for an Ideal Gas
« Reply #52 on: March 03, 2012, 06:39:17 am »
sorry!

my diagram got screwed up in the posting. spaces got deleted. i don't know how to correct this.

Fu-Kwun Hwang

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Re: Molecular Model for an Ideal Gas
« Reply #53 on: March 03, 2012, 07:21:25 am »
You can add text in between [code] and [/code]  to keep space in the text. (I have already modified your text for you. :-)

Bernoulli's equation is valid for steady fluid which can be represented by stream lines.

It is a different situation you have pistons on both side of the tube: this is a closed system.

We can use fluid model to simulate gas flow when the mean free path is much smaller than the size of the tube. (fluid dynamics)

The molecular model can be used when the mean free path is smaller than the size of the tube, and this is a good time to use particles to simulate the situation.  (However, a lot of computational power is needed: to simulate large number of particles!)

ptnk_triz

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Re: Molecular Model for an Ideal Gas
« Reply #54 on: July 12, 2012, 11:22:31 pm »
Hello Prof Hwang,

Could you tell me the relation of the number of collision and pressure in your ideal gas model?

How can you calculate pressure exactly?

Fu-Kwun Hwang

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Re: Molecular Model for an Ideal Gas
« Reply #55 on: July 12, 2012, 11:37:40 pm »
If you are talking about the simulation at the first post: then the umber of particles are 200 as default and can be changed from user input.
The pressure was calculated by momentum change per second.
Because there are limited number of particles so that the pressure change over time.
In real case, it will be more than $10^{19}$particles per center meter square.
 

ptnk_triz

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Re: Molecular Model for an Ideal Gas
« Reply #56 on: July 12, 2012, 11:51:29 pm »
The pressure is calculated by the momentum change per second. Can you tell me the equation?

The momentum is the average momentum of all the particles?

Do you think, could we find any relation betweens the number of collision of particles on the wall and the pressure?

I just know that : p = F / A

I dont know the relation of p and momentum, could you write down the relation.

Fu-Kwun Hwang

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Re: Molecular Model for an Ideal Gas
« Reply #57 on: July 13, 2012, 12:25:16 am »
From the simulation, I can calculate how many particle collide with the wall per second,
Wih velocity and mass, the momentum can be calculated.

 $vec{F}=frac{dvec{P}}{dt}=frac{d (mvec{V})}{dt}$

and Pressure $P=frac{F}{A}$  normal component of the momentum need to be calculated to from the pressure.

diinxcom

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Re: Molecular Model for an Ideal Gas
« Reply #58 on: December 14, 2014, 07:00:31 pm »
-*-
Bookmarking this thread post. I will read latter