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Thermodynamics: Processes and Cycles

Processes and Cycles

When a system moves from one state of equilibrium to another state of equilibrium this in known as a process. As a system goes from one state of equilibrium it follows what is called the path. Typically during thermodynamics analysis an engineer would ideally like to have the path be in a state of quasi equilibrium. This means that system will stay close to an equilibrium state as it follows the path. Now this is an ideal process, and in a real process this would not happen. The only way for this to occur in real life is the process has to occur at a very slow rate.

For a process to occur the system is gaining something or loosing something in relation to its properties. There are few ideal processes that you should know about. The first ideal process is the isothermal process. During the isothermal process the temperature will remain constant within the system as the process occurs. The next ideal process is called the isobaric process. For an isobaric process to occur, the pressure in the system will remain constant during the process. Finally, the next ideal process is the adiabatic process. For an adiabatic process occur there cannot be any heat gain or loss as the cycle occurs. The reason why these are ideal is because one of the properties are allowed to remain constant making it easier to analyze the process.

Finally, as you start to combine processes that will bring the system back to its original state you have created a thermodynamic cycle. There are many different types of thermodynamic cycles, such as the Carnot Cycle. The Carnot cycle is known as the ideal cycle, meaning it is impossible to create a cycle that is more efficient then the Carnot Cycle. The Carnot Cycle is made of two isothermal processes and two adiabatic processes. Refer to figure to below to view a P-V diagram of the Carnot Cycle.

Carnot Cycle

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