Author Topic: Carnot Cycle (Heat Engine)  (Read 521263 times)

Fu-Kwun Hwang

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Carnot Cycle (Heat Engine)
« on: January 29, 2004, 09:34:33 pm »
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This java applet show you the physics processes of a Carnot heat engine.
Carnot cycle is a four stage reversible sequence consisting of
1. adiabatic compression
2. isothermal expansion at high temperature T2
3. adiabatic expansion
4. isothermal compression at low temperature T1
5. back to stage 1 and continue.

1. Set the starting point (Press, Volume) of the adiabatic compression process:
    The program will show the piston position and related information
      as you move the mouse inside the P-V region.

    Click the mouse to set the initial P-V value.
    Before you set up the initial P-V value, you can click the horizon line and drag it to change the Max. pressure (Pmax).
    Move the mouse to P=1 atm, and V=22.4(liter), and check out the value of PV/(nR).
    Do you know how many mole of gas is inside the chamber?


2. Set the starting point for the isothermal compression process:
    click the mouse button again (within the possible region).

3. Press Start button to start the animation, Press Reset to reset the conditions.
    Click + to increase speed of animation  , click - to slow it down (Each click change the time scale by 1.25)
    Click RIGHT mouse button to stop the animation, click it again to resume.

    The efficiency of the heat engine will be displayed.
    Different color for the gas volume represent its temperature.
    Color of the piston:
      Red : contact with heat reservoir at high T2.
        Yellow bar within the gas volume is proportional to heat flow (In).

      Green: contact with heat reservoir at low T1.
        Yellow bar within the piston region is proportional to heat flow (Out).
        (Total length of the yellow bar is the maximum heat flow during isothermal
        expansion process, some of the heat were release during the isothermal compression process.)

      Blue : adiabatic process¡C


4. Cp/Cv is the ratio of the specific heat of the gas at constant pressure to that at constant volume.
    You can enter any value larger than 1. (Be reasonable, OK!)
    It will reset the program automatically.


5. While the animation is suspended, move your mouse within the PV-diagram to view the (P, V) values.

The following information are extracted from www.grc.nasa.gov/WWW/K-12/airplane/carnot.html



Thermodynamics is a branch of physics which deals with the energy and work of a system. Thermodynamics deals with the large scale response of a system which we can observe and measure in experiments. As aerodynamicists, we are most interested in the thermodynamics of propulsion systems and high speed flows. To understand how a propulsion system works, we must study the basic thermodynamics of gases.

Gases have various properties that we can observe with our senses, including the gas pressure p, temperature T, mass, and volume V that contains the gas. Careful, scientific observation has determined that these variables are related to one another, and the values of these properties determine the state of the gas. A thermodynamic process, such as heating or compressing the gas, changes the values of the state variables in a manner which is described by the laws of thermodynamics. The work done by a gas and the heat transferred to a gas depend on the beginning and ending states of the gas and on the process used to change the state.

It is possible to perform a series of processes, in which the state is changed during each process, but the gas eventually returns to its original state. Such a series of processes is called a cycle and forms the basis for understanding engines. The Carnot Cycle is one of the fundamental thermodynamic cycles and is described on this web page. We will use a p-V diagram to plot the various processes in the Carnot Cycle. The cycle begins with a gas, colored yellow on the figure, which is confined in a cylinder, colored blue. The volume of the cylinder is changed by a moving red piston, and the pressure is changed by placing weights on the piston. We have two heat sources; the red one is at a nominal 300 degrees, and the purple one is at 200 degrees. Initially, the gas is in State 1 at high temperature, high pressure, and low volume.

  * The first process performed on the gas is an isothermal expansion. The 300 degree heat source is brought into contact with the cylinder, and weight is removed, which lowers the pressure in the gas. The temperature remains constant, but the volume increases. During the process from State 1 to State 2 heat is transferred from the source to the gas to maintain the temperature. We will note the heat transfer by Q1 into the gas.
  * The second process performed on the gas is an adiabatic expansion. During an adiabatic process no heat is transferred to the gas. Weight is removed, which lowers the pressure in the gas. The temperature decreases and the volume increases as the gas expands to fill the volume. During the process from State 2 to State 3 no heat is transferred.
  * The third process performed on the gas is an isothermal compression. The 200 degree heat source is brought into contact with the cylinder, and weight is added, which raises the pressure in the gas. The temperature remains constant, but the volume decreases. During the process from State 3 to State 4 heat is transferred from the gas to heat source to maintain the temperature. We will note the heat transfer by Q2 away from the gas.
  * The fourth process performed on the gas is an adiabatic compression. Weight is added, which raises the pressure in the gas. The temperature increases and the volume decreases as the gas is compressed. During the process from State 4 to State 1 no heat is transferred.

At the end of the fourth process, the state of the gas has returned to its original state and the cycle can be repeated as often as you wish. During the cycle, work W has been produced by the gas, and the amount of work is equal to the area enclosed by the process curves. From the first law of thermodynamics, the amount of work produced is equal to the net heat transferred during the process:

W = Q1 - Q2

The Carnot Cycle has performed as an engine, converting the heat transferred to the gas during the processes into useful work. A similar Brayton Cycle explains how a gas turbine engine works, and an Otto Cycle explains how an internal combustion engine works.


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topic23
« Reply #1 on: January 30, 2004, 06:03:21 pm »
From: "Franco Di Liberto" <francesco.diliberto@na.infn.it>
To: <hwang@phy03.phy.ntnu.edu.tw>
Subject: Carnot Engine applet
Date: Fri, 7 Jan 2000 15:56:12 +0100

Dear Hwang
I appreciate very much your java applet on Carnot Engine.
I note, anyway, that the P,V values which are shown at the top are =
interchanged (are shown the V,P values) and moreover that the (ingoing =
and outgoing )bar proportional to heat flow is ...Yellow.
I suggest (to be perfect!) that you extend the range of V values to =
include 22,4 liters (the volume occupied by a mole) and (setting =
n=3D1 in PV=3DnRT) show also the Temperatures.
Finally it would be nice that one could stop the animation and read =
(step by step) the P,V values
 and (during the adiabatics) also the T values .=20

Thank you and Happy new Year
Sincerely yours

Francesco di Liberto
I.N.F.M., I.N.F.N. and Dipartimento di Scienze Fisiche
Universita di Napoli Federico II
Pad 19 Mostra D'Oltremare
80125 Napoli- Italia
Tel: +39817253424, Email: diliberto@na.infn.it

Fu-Kwun Hwang

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Re: Carnot Cycle (Heat Engine)
« Reply #2 on: March 05, 2007, 03:52:26 pm »
It is the PV-diagram. So the vertical axis is P, and horizontal axis is V.
Right click the mouse button in the simulation region will toggle simulation on/off.
Temperature is shown as PV/(nR).

bazu

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Re: Carnot Cycle (Heat Engine)
« Reply #3 on: March 20, 2007, 10:52:56 pm »
i am unable to see ur model of any topic plz tell me how i can hv a view of it.

Fu-Kwun Hwang

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Re: Carnot Cycle (Heat Engine)
« Reply #4 on: March 21, 2007, 09:59:33 pm »
This applet was created many years ago with JDK1.0.2. You need to see the source code to find out the model.
Actually, it is a standard model in any physics text book. We can discuss it if you want.

For those applets created with EJS, you can click load ejs as signed applet to see the model.
(You will be asked to grant the permission to load EJS into your computer, then the program will be run in a browser and you will see all the variables and equations used in the simulation in a GUI)
Please check out applets from another category: Easy Java Simulations (2001- )

Fu-Kwun Hwang

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baloch.2008

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Re: Carnot Cycle (Heat Engine)
« Reply #6 on: October 27, 2008, 04:09:57 pm »
how i can download this carnot cycle pic

lookang

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Re: Carnot Cycle (Heat Engine)
« Reply #7 on: October 28, 2008, 04:29:08 pm »
This is a flash animation, not a pic like u said.

 I am using Firefox so go download it and follow this simple method without those pay $$ for swf downloaders.

1. Saving Flash files from Firefox

Firefox for Newbies
a. Click Tools - Page Info
b. Click the Media Tab on the Page Info Windows
c. The media tab has a complete list (with preview) of Images, CSS Files and Shockwave Flash files that were downloaded by the Firefox browser while rendering (loading) the page.
d. Scroll down the list and locate the swf file.
e. Click the "Save As" button. Select some directory on your hard drive and save the file (No need for a third-party plug-in)

It is easy right?

Reference:
http://labnol.blogspot.com/2005/11/save-flash-from-firefox-and-ie.html

diandra

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Re: Carnot Cycle (Heat Engine)
« Reply #8 on: December 17, 2008, 10:43:04 am »
i also cannt get those flash file,
i've tried to follow ur step by step,,but theres just background,, n icons file
huge thanx

Fu-Kwun Hwang

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Re: Carnot Cycle (Heat Engine)
« Reply #9 on: December 17, 2008, 10:12:33 pm »
I have no trouble finging those swf files from popuped toolbar/pageinfo window (switch to media tab and you will find many files).

enalice

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Re: Carnot Cycle (Heat Engine)
« Reply #10 on: February 27, 2009, 12:23:02 pm »
Why refrigeration cycle is called reverse carnot cycle?







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« Last Edit: February 27, 2009, 12:28:52 pm by enalice »

Fu-Kwun Hwang

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Re: Carnot Cycle (Heat Engine)
« Reply #11 on: February 27, 2009, 01:48:00 pm »
The physics processes of a Carnot heat engine.
Carnot cycle is a four stages reversible sequence consisting of
1. adiabatic compression
2. isothermal expansion at high temperature T2
3. adiabatic expansion
4. isothermal compression at low temperature T1
5. back to stage 1 and continue.
It is moving in clockwise direction as shown in the applet.


The above process get heat (QH-QC)as input to do work W.

Refrigeration cycle is reversed : get input from electric power to cool the system (heat transfer from lower temperature to higher temperature). It is moving in counter-clockwise direction.
1. adiabatic expansion
2. isothermal expansion at low temperature T1
3. adiabatic compression
4. isothermal compression at high temperature T2
5. back to stage 1 and continue.
 
Input Work W and reverse the direction of Heat flow Tc->TH (W=QH-QC )

casedetails

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Re: Carnot Cycle (Heat Engine)
« Reply #12 on: April 03, 2009, 08:59:58 am »
Thanks Fu-Kwun Hwang.  Those flash animations really make a big difference when trying to understand these cycles.  I once worked with my physics professor in my University days to make such flash animations.

Marc M
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« Last Edit: April 03, 2009, 09:07:54 am by casedetails »

arnaldroy23

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Re: Carnot Cycle (Heat Engine)
« Reply #13 on: April 13, 2009, 03:34:50 pm »
May i know Why refrigeration cycle is called reverse carnot cycle? I didn't get it clear...

Thanks Fu-Kwun Hwang.  Those flash animations really make a big difference when trying to understand these cycles.  I once worked with my physics professor in my University days to make such flash animations.

Marc M
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« Last Edit: April 13, 2009, 03:40:20 pm by arnaldroy23 »

Fu-Kwun Hwang

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Re: Carnot Cycle (Heat Engine)
« Reply #14 on: April 13, 2009, 07:34:54 pm »
The carnot is a clockwise direction of cycle:
1. isothermal expansion at higher temperature Th
2. adiabatic expansion to lower temperature Tc
3. isothermal compression at lower temperature Tc
4. adiabatic compression back to higher temperature Th
Net thermal energy during each cycle is convert to work.

However, rreversed carnot cycle is

1. isothermal expansion at lower temperature Tc
2. adiabatic  compression to higher temperature Th
3. isothermal compression at higher temperature Th
4. adiabatic expansion back to lower temperature Tc

Net energy is required to move heat flow from lower temperature to higher so that the refrigerator can be cooler than outside.