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.
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.
