Author Topic: Thermal dynamic processes: isobaric, isochoric, isothermal, adiabatic processes  (Read 292120 times)

Fu-Kwun Hwang

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A thermodynamic process may be defined as the energetic evolution of a thermodynamic system proceeding from an initial state to a final state. Paths through the space of thermodynamic variables are often specified by holding certain thermodynamic variables constant.
The pressure-volume conjugate pair is concerned with the transfer of mechanical or dynamic energy as the result of work.

   * An isobaric process occurs at constant pressure (P=constant). An example would be to have a movable piston in a cylinder, so that the pressure inside the cylinder is always at atmospheric pressure, although it is isolated from the atmosphere. In other words, the system is dynamically connected, by a movable boundary, to a constant-pressure reservoir.
  The work done by the isobaric process is $Delta W=int P dV=Pint dV=P(V_f-V_i)= P Delta V$

   * An isochoric process is one in which the volume is held constant (V=constant), meaning that the work done by the system will be zero. It follows that, for the simple system of two dimensions, any heat energy transferred to the system externally will be absorbed as internal energy. An isochoric process is also known as an isometric process or an isovolumetric process. An example would be to place a closed tin can containing only air into a fire. To a first approximation, the can will not expand, and the only change will be that the gas gains internal energy, as evidenced by its increase in temperature and pressure. Mathematically, ?Q = dU. We may say that the system is dynamically insulated, by a rigid boundary, from the environment.

The temperature-entropy conjugate pair is concerned with the transfer of thermal energy as the result of heating.

   * An isothermal process occurs at a constant temperature (T=constant). An example would be to have a system immersed in a large constant-temperature bath. Any work energy performed by the system will be lost to the bath, but its temperature will remain constant. In other words, the system is thermally connected, by a thermally conductive boundary to a constant-temperature reservoir.
 For ideal gas: $Delta W=int P dV=int frac{nRT}{V}dV=nRT int frac{dV}{V}=nRT ln frac{V_f}{V_i}$
 $Delta U=int n C_v dT=n C_vDelta T$.
  $Delta Q=Delta U-Delta W=n C_vDelta T- nRT ln frac{V_f}{V_i}$
 
   * An adiabatic process is a process in which there is no energy added or subtracted from the system by heating or cooling (?Q=0). For a reversible process, this is identical to an isentropic process. We may say that the system is thermally insulated from its environment and that its boundary is a thermal insulator. If a system has an entropy which has not yet reached its maximum equilibrium value, the entropy will increase even though the system is thermally insulated.
 ?Q=dU- ?W=0 so dU=?W.
The first law of thermaldynamically state:
The internal energy change is equal to the heat absorbed minus the work done.
$Delta U= Delta Q -Delta W$
isothermal process: $Delta U=0$, so $Delta Q =Delta W$
 adiabatic process: $Delta Q=0$, so $Delta U =Delta W$
 isochoric process: $Delta W=0$, so $Delta U =Delta Q$
net incoming change= how much you earn -  how much you spend 

if net incoming change=0, how much you spend=how much you earn
if how much you earn=0, net incoming change= how much you spend (-)
if how much you spend=0, net incoming change= how much you earn (+)

The following let you play with different processes:
The work done, heat transfer, internal energy as well as entropy change will be shown when you change parameter with slider bar.



The following is a flash animation for a carnot cycle.
http://www.phy.ntnu.edu.tw/ntnujava/swf/thermal628carnot.swf


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jmscott

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Professor Hwang,
I would like to download this applet, but there does not seem to be the option to download it. Could you help me know how I can download this applet? It is likely right in front of me and I cannot see it. Thank you.

Fu-Kwun Hwang

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It is fixed now. Thank you!

lookang

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Hi prof!

if i make some small changes n post back the xml file, would it be okay with you to recompile it and re post it as the top applet?

i feel kind of weird if i were to post it again under the community board especially it the changes are cosmetic.

This is a good applet. I can feel the usefulness and i can also customized it to suit my learners.

unfortunately i didn't find it when i was teaching from 2000-2007,

strange i didn't see this before.

thanks for all your "free to remix" applets!

You should create a pay-pal button for donations to show appreciation, judging by the number of grateful teachers( i am ONE too) and students here thanking you, you can get some funding for your other expenses. LOL.

« Last Edit: October 16, 2008, 01:57:31 pm by lookang »

Fu-Kwun Hwang

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If you upload xml files to any server (for example the account I gave you at our server) and make link to the xml file.
You can upload xml file to the server and user will be able to download updated files.
If you really need it, I can try to modify the code so that:
File will be replaced when the same filename was attached.

I have been working on project related to open source. I do not need money from users. User can have better use of his/her own money. What I enjoy most are feedbacks/suggestions from users. :-)

lookang

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If you upload xml files to any server (for example the account I gave you at our server) and make link to the xml file.
You can upload xml file to the server and user will be able to download updated files.
If you really need it, I can try to modify the code so that:
File will be replaced when the same filename was attached.

Better not modify, sounds dangerous if i upload wrongly and the version i use in EJS4.0, may cause some problems as u are using EJS 3.47 i think.

I will just upload the xml for your consideration and post in the community board if i think i should :)

glebbugrov

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  Dear Sir!
  I tried thermalPVT applet and find out that during adiabatic process dU=0, dW=0 and T=const.
Is it true?
  Best regards,
  As. professor, Ph.D., Gleb E. Bugrov.


Fu-Kwun Hwang

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Woop! Sorry, it is a bug. I forgot to re-calculate pressure P. so that it was not changed.
It is fixed now.
Thank you!  ;)

glebbugrov

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Sorry, but again during adiabatic process dU=0, dW=0 and T=const.

lookang

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i see the problem now......

http://en.wikipedia.org/wiki/Adiabatic_process
In thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which no heat is transferred to or from the working fluid.

so delta Q = 0.

1st law thermodynamic is delta U = delta Q - delta W , where W is work done by gas.

so delta U = 0 - delta W  imply delta U = - delta W

i did notice the applet is wrong cos
when Adiabatic,
T = constant, which should not be.
i did a simple calculation, PV = uRT,

i notice the u (number of moles of gas) is different/changing if i vary the slider at the bottom "volume".

but if i vary the slider on the right, it is correct!!


maybe to solve the control error, disable the slider "VOLUME" when adiabatic is "TRUE" :)
« Last Edit: November 24, 2008, 06:03:11 pm by lookang »

Fu-Kwun Hwang

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I move T=P*V/nR; from initialize page to constraint page.
The above prolem should be fixed now. (Temperature was not updated in adiabatic process).
Thank you!

lookang

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Excellent applet Prof, Hwang!

thanks for your invaluable quality physics applets.


mirlinda

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Dear Proffesor,


I use your applets for some experiments qith students in high school.

But I need the interface in my language, wish I can modify it using EJS (as you told me in one of my prevoius posts).

But with the Thermal dynamic processes (.jar)  EJS model  modified, I can not package in export folder of EJS.

It appears the following error, HOW CAN I FIX IT?


Warning. Syntax error or custom page chinese:
  Sourced file: inline evaluation of: ``  public void zh_tw () {  l_play="¼½©ñ";  l_init="²M°£";//ªì©l¤Æ";  l_rese . . . '' Token Parsing Error: Lexical error at line 16, column 18.  Encountered: "=" (61), after : ""u00a8tu00b2u00ceu00a7@u00a5\": <at unknown location>

File successfully read thermalPVT.xml
Generating simulation file thermalPVT...
C:EJS_4.2outputusersm.ebibi   hermalPVT.java:241: illegal escape character
  l_dw="?t???@?=0.0 J";  // > Custom.chinese:16


Thank you very much for your help,

Mirlinda


  ^
1 error
Compilation produced an error![/b][/b][/i]

Fu-Kwun Hwang

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The chinese tab in the custom page under model is my own way to translate strings into Chinese.
You can remove
public void zh_tw(){
... // and every code in between
}

but you also need to remove
if(type.equals("zh_tw"))zh_tw();

Then, it should work fine. The problem might due to the Chinese character code in the program, and you java version (OS) did not recognize it.

koclup1580

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thank