Modern Engineering Thermodynamics

CHAPTER 6
First Law Open System Applications
CONTENTS
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
6.2 Mass Flow Energy Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
6.3 Conservation of Energy and Conservation of Mass Equations for Open Systems . . . . . . . . . . . . 171
6.4 Flow Stream Specific Kinetic and Potential Energies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
6.5 Nozzles and Diffusers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
6.6 Throttling Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
6.7 Throttling Calorimeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
6.8 Heat Exchangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
6.9 Shaft Work Machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
6.10 Open System Unsteady State Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
6.1 INTRODUCTION
This chapter contains detailed solutions to a variety of classical open system thermodynamic problems. These
solutions use the generalized problem solving procedurediscussedinChapters4and5(seeFigure4.21)and
focus on illustrating the use of the conservation of mass law and the first law of thermodynamics. The availability
of these two basic equations plus many auxiliary formulae means that there are usually more unknowns to
be solved for in open system problems than in closed system problems.
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/B978-0-12-374996-3.00006-3
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