# Review: Types of Thermodynamic Cycles

## Three Types of Thermodynamic Cycles

1. Power Cycles
- Purpose: produce Ws
- Input: QH
- Waste: QC

2. Refrigeration Cycles
- Purpose: remove QC from the cold reservoir
- Input: Ws
- Waste: QH

3. Heat Pump Cycles
- Purpose: transfer QH to the hot reservoir
- Input: Ws
- Waste: QC

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### Ch 6, Lesson B, Page 3 - Review: Types of Thermodynamic Cycles

• What’s going on inside the system depends on the purpose of the cycle.
• You probably recall the three types of cycles from Lesson 4F, but it has been a while.  So let’s review them.
• The three types of thermodynamic cycles are: power cycles, refrigeration cycles and heat pump cycles.
• In a power cycle, the goal is to produce work.
• In order to accomplish this, we must provide heat from a high temperature reservoir.
• For reasons that will become clear when you understand the 2nd Law, the power cycle cannot convert 100% of the heat it absorbs from the high temperature reservoir into work.
• So, in order to obey the 1st Law, the power cycle must reject some waste heat to the cold reservoir.
• Now a refrigerator has a completely different purpose.  The purpose of a refrigerator is to remove energy, in the form of heat, from a low temperature reservoir.
• In order to accomplish this, the system must receive an input of work.
• In order to operate at steady-state and still obey the 1st Law, the system must reject waste heat to the hot reservoir.
• A heat pump is a lot like a refrigerator because it uses work to make heat flow from a cold reservoir into a hot reservoir.
• The only difference is that in a heat pump the purpose, or desired effect, to transfer heat into the hot reservoir instead of cooling the cold reservoir.
• Now, let’s review how the 1st Law is applied to these cycles and how their performance is measured.
• Then, we can finally dig into the equipment that lives inside the little gray “SYSTEM” circles.