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Isothermal & adiabatic processes

by ElmorshedyDr
Tags: adiabatic, isothermal, processes
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ElmorshedyDr
#1
Mar28-14, 04:19 PM
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I'll start with what I know: when work is done on an ideal gas its internal energy increases and some of the work is used to increase the volume of the container if the walls are movable, and I know that when a gas does work its internal energy decreases by a value equivalent to F.d, I have been gaining good information about the gas laws for several days so I could advance to low temperature physics, but when I reached the adiabatic and isothermal processes, 8couldn't clearly understand their concepts. I know their definitions because I read it lots of times on the internet, but I can't understand the mechanism of achieving both processes practically.

I hope someone could give me a good explanation with simple clear examples. Thanks
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Simon Bridge
#2
Mar28-14, 08:37 PM
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The processes are their definitions. The thermodynamic processes you learn are mathematical idealizations used to help model real physical processes.

If you found the definitions online, then some of the same sources should have also given you examples.
i.e. letting air out of a pressure container (i.e. a pneumatic tire) would realize an adiabatic decompression.
(which is to say the process is "well modeled" by an adiabatic process)

Another common example is the compression stroke in a 4-stroke engine.

Isothermal is usually given as a cylinder with a plunger immersed in a heat bath - pull on the plunger very slowly. But you can also think of boiling water in air or pumping up a tire - slowly.
http://www.physicsforums.com/showthread.php?t=149876
... the process has to be slow to make sure that heat can flow into the system fast enough to maintain the temperature.

Also see:
http://faculty.wwu.edu/vawter/Physic...alProcess.html

Since these are common - perhaps you have a problem with the examples, or you do not know how they are physically implemented?
ElmorshedyDr
#3
Mar29-14, 02:03 PM
ElmorshedyDr's Avatar
P: 403
Quote Quote by Simon Bridge View Post
The processes are their definitions. The thermodynamic processes you learn are mathematical idealizations used to help model real physical processes.

If you found the definitions online, then some of the same sources should have also given you examples.
i.e. letting air out of a pressure container (i.e. a pneumatic tire) would realize an adiabatic decompression.
(which is to say the process is "well modeled" by an adiabatic process)

Another common example is the compression stroke in a 4-stroke engine.

Isothermal is usually given as a cylinder with a plunger immersed in a heat bath - pull on the plunger very slowly. But you can also think of boiling water in air or pumping up a tire - slowly.
http://www.physicsforums.com/showthread.php?t=149876
... the process has to be slow to make sure that heat can flow into the system fast enough to maintain the temperature.

Also see:
http://faculty.wwu.edu/vawter/Physic...alProcess.html

Since these are common - perhaps you have a problem with the examples, or you do not know how they are physically implemented?

if a container of gas of movable walls was to be placed in a room, and then work is done on the gas, the temperature of the gas increases slightly and some work is used up to increase the volume so the temperature decreases (before thermal equilibrium) the overall result is a decrease or an increase in the temperature??


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