Modern Engineering Thermodynamics

CHAPTER 5
First Law Closed System Applications
CONTENTS
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
5.2 Sealed, Rigid Containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
5.3 Electrical Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
5.4 Power Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
5.5 Incompressible Liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
5.6 Ideal Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
5.7 Piston-Cylinder Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
5.8 Closed System Unsteady State Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
5.9 The Explosive Energy of Pressure Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
5.1 INTRODUCTION
In this chapter, we present a series of detailed engineering analyses of the application of the first law of thermodynamics
to closed systems. This material demonstrates good thermodynamic problem solving technique
through a variety of worked examples. In the first three examples that follow, the numbered steps in the solution
are the same as the steps shown in Figure 4.21. As we continue with the examples and the reader becomes
more familiar with the technique, we condense the solutions by omitting the description of each solution step.
In so doing, we also introduce some flexibility into the technique.
SUMMARY OF THE THERMODYNAMIC PROBLEM SOLVING TECHNIQUE
Begin by carefully reading the problem statement completely through.
Step 1. Make a sketch of the system and put a dashed line around the system boundary.
Step 2. Identify the unknown(s) and write them on your system sketch.
Step 3. Identify the type of system (closed or open) you have.
Step 4. Identify the process that connects the states or stations.
Step 5. Write down the basic thermodynamic equations and any useful auxiliary equations.
Step 6. Algebraically solve for the unknown(s).
Step 7. Calculate the value(s) of the unknown(s).
Step 8. Check all algebra, calculations, and units.
Sketch ! Unknowns ! System ! Process ! Equations ! Solve ! Calculate ! Check
Modern Engineering Thermodynamics. DOI: 10.1016/B978-0-12-374996-3.00005-1
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