Page 231 - The Mechatronics Handbook

12

Engineering

Thermodynamics

12.1 Fundamentals
Basic Concepts and Definitions • Laws of Thermodynamics
12.2 Extensive Property Balances
Mass Balance • Energy Balance • Entropy Balance • Control
Volumes at Steady State • Exergy Balance
Michael J. Moran 12.3 Property Relations and Data
The Ohio State University 12.4 Vapor and Gas Power Cycles

Although various aspects of what is now known as thermodynamics have been of interest since antiquity,
formal study began only in the early nineteenth century through consideration of the motive power of
heat: the capacity of hot bodies to produce work. Today the scope is larger, dealing generally with energy
and entropy, and with relationships among the properties of matter. Moreover, in the past 25 years
engineering thermodynamics has undergone a revolution, both in terms of the presentation of funda-
mentals and in the manner that it is applied. In particular, the second law of thermodynamics has emerged
as an effective tool for engineering analysis and design.

12.1 Fundamentals

Classical thermodynamics is concerned primarily with the macrostructure of matter. It addresses the
gross characteristics of large aggregations of molecules and not the behavior of individual molecules.
The microstructure of matter is studied in kinetic theory and statistical mechanics (including quantum
thermodynamics). In this chapter, the classical approach to thermodynamics is featured.

Basic Concepts and Definitions
Thermodynamics is both a branch of physics and an engineering science. The scientist is normally
interested in gaining a fundamental understanding of the physical and chemical behavior of fixed,
quiescent quantities of matter and uses the principles of thermodynamics to relate the properties of
matter. Engineers are generally interested in studying systems and how they interact with their surround-
ings. To facilitate this, engineers have extended the subject of thermodynamics to the study of systems
through which matter flows.

System
In a thermodynamic analysis, the system is the subject of the investigation. Normally the system is a
specified quantity of matter and/or a region that can be separated from everything else by a well-defined
surface. The defining surface is known as the control surface or system boundary. The control surface may
be movable or fixed. Everything external to the system is the surroundings. A system of fixed mass is

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