Modern Engineering Thermodynamics

4 CHAPTER 1: The Beginning
HOW IS THERMODYNAMICS USED IN ENGINEERING?
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Mechanical engineers study the flow of energy in systems such as automotive engines (Figure 1.2), turbines, heat
exchangers, bearings, gearboxes, air conditioners, refrigerators, nozzles, and diffusers.
Electrical engineers deal with electronic cooling problems, increasing the energy efficiency of large-scale electrical power
generation, and the development of new electrical energy conversion technologies such as fuel cells.
Civil engineers deal with energy utilization in construction methods, solid waste disposal, geothermal power generation,
transportation systems, and environmental impact analysis.
Materials engineers develop new energy-efficient metallurgical compounds, create high-temperature materials for engines,
and utilize the unique properties of nanotechnology.
Industrial engineers minimize energy consumption and waste in manufacturing processes, develop new energy
management methods, and improve safety conditions in the workplace.
Aerospace engineers develop energy management systems for air and space vehicles, space stations, and planetary
habitation (Figure 1.4).
Biomedical engineers develop better energy conversion systems for the health care industry, design new diagnostic and
treatment tools, and study the energy flows in living systems.
All engineering fields utilize the conversion and use of energy to improve the human condition.
1.3 GETTING ANSWERS: A BASIC PROBLEM SOLVING
TECHNIQUE
Unlike mechanics, which deals with a relatively small range of applications, thermodynamics is truly global and
can be applied to virtually any subject, technology, or object conceivable. You no longer can thumb through a
book looking for the right equation to apply to your problem. You need a method or technique that guides you
through the process of solving a problem in a prescribed way.
In Chapter 4, we provide a more detailed technique for thermodynamics problem solving, but for the present,
here are seven basic problem solving steps you should know and understand.
1. Read. Always begin by carefully reading the problem statement and try to visualize the “thing” about which
the problem is written (a car, engine, rocket, etc.). The “thing” about which the problem is written is called
the system in thermodynamics. This may seem simple, but it is key to understanding exactly what you are
analyzing.
2. Sketch. Now draw a simple sketch of the system you visualized and add as much of the numerical
information given in the problem statement as possible to the sketch. If you do not know what the “thing” in
the problem statement looks like, just draw a blob and call it the system. You will not be able to remember all the
numbers given in the problem statement, so write them in an appropriate spot on your sketch, so that they
are easy to find when you need them.
3. Need. Write down exactly what you need to determine—what does the problem ask you to find?
4. Know. Make a list of the names, numerical values, and units of everything else given in the problem
statement. For example, Initial velocity = 35 meters per second, mass = 5.5 kilograms.
5. How. Because of the nature of thermodynamics, there are more equations than you are accustomed to
working with. To be able to sort them all out, you need to get in the habit of listing the relevant equations
and assumptions that you “might” be able to use to solve for the unknowns in the problem. Write down all
of them.
A BASIC PROBLEM SOLVING TECHNIQUE
1. Carefully read the problem statement and visualize what you are analyzing.
2. Draw a sketch of the object you visualized in step 1.
3. Now write down what you need to find, that is, make a list of the unknown(s).
4. List everything else you know about the problem (i.e., all the remaining information given in the problem statement).
5. Make a list of relevant equations to see how to solve the problem.
6. Solve these equations algebraically for the unknown(s).
7. Calculate the value(s) of the unknown(s), and check the units in each calculation.
Read → Sketch → Need → Know → How → Solve → Calculate