What is a Thermodynamic Cycle?

Ch4, Lesson F, Page 1 - What is a Thermodynamic Cycle?

• You may recall the definition of a thermodynamic cycle from Chapter 1.
• Hopefully it is a bit more meaningful to you now.
• A system completes a thermodynamic cycle when it undergoes two or more processes and returns to its initial state.
• This may seem silly to you at first, but cycles are at the heart of many important applications of thermodynamics.
• Try the roll-overs while I tell you about some important applications of thermodynamic cycles.
• For example, the water and steam used in fossil fuel and nuclear power plants operates in a Power Cycle to produce work which is used to generate electrical power.
• The refrigerant used in the refrigerator in your kitchen flows though a series of devices that make up a Refrigeration Cycle.
• Household refrigerators and thermal power generation are both examples of closed, vapor cycles.
• They are closed cycles because the working fluid is reused.  It does not enter and leave the system
• These cycles are vapor cycles because both the steam in the power plant and the refrigerant in the refrigerator are condensed and vaporized during the cycle.
• An automobile engine and a jet airplane engine are examples of open, gas cycles.
• These engines are open because the working fluid, air, flows into the system and out of the system as the cycle proceeds.
• These engines are gas cycles because the air remains in the gas phase at all times.  It never condenses to the liquid phase.
• OK, now you have a general idea of what a thermodynamic cycle is and how it can be used industrially.  Now, let’s apply the 1st Law to a thermodynamic cycle.