# Lesson Preview

In Lesson 6A, we learned that the 1st Law does not tell us everything we need to know about thermodynamic processes.

We need to develop an understanding of the 2nd Law of Thermodynamics in order to address issues relating to spontaneity, equilibrium and efficiency.

Before we study the 2nd Law, however, it will be most helpful if we get a better understanding of the nature of the three types of cycles: Power Cycles (or Heat Engines), Refrigeration Cycles and Heat Pump Cycles.

In this lesson, we will learn how individual devices or processes work together to carry out the three different types of cycles.

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### Ch 6, Lesson B, Page 1 - Lesson Preview

• In the previous lesson, we learned some pretty compelling reasons that we need to understand the 2nd Law.
• I hope you were convinced !
• But it turns out that we need to know more about heat engines and power cycles if we are to understand some aspects and implications of the 2nd Law.
• So, before we introduce the 2nd Law in all its glory, we will take a closer look at heat engines.
• In fact, we will show how to assemble a heat engine from the equipment that you studied in Lesson 5C.
• The key pieces of equipment are turbines, compressors, pumps and heat exchangers.
• Pumps are new to you, but not really.  Pumps are a lot like compressors.  They use shaft work to increase the pressure in a flowing fluid.  The main difference is that a pump works on a liquid and a compressor works on a gas.
• Anyway, in the next few pages, we’ll see how we can put these devices together to create a system that will carry out thermodynamic cycles.
• Flip the page and let’s get started.