Page 11 - Entrophy Analysis in Thermal Engineering Systems

CHAPTER ONE

Fundamental concepts

1.1 Thermodynamic properties

In many branches of science, property refers to the condition and
characteristic of a substance under study. The properties of matter are cat-
egorized as mechanical, physical, thermal, etc. The examples include elastic-
ity, yield strength, hardness (mechanical properties); density, melting point,
viscosity (physical properties); thermal conductivity, thermal diffusivity,
specific heat (thermal properties).
In thermodynamics, properties describe the state or condition of a sub-
stance. The basic properties frequently used in thermodynamic calculations
are temperature, pressure, specific enthalpy, specific internal energy, specific
volume, and specific entropy. The thermodynamic properties depend solely
on the state of a given system or substance. They are independent of the path
or process through which the system is brought to that state.
Some of these properties can directly be measured like temperature and
pressure, whereas some properties are unmeasurable such as specific internal
energy and entropy, which are determined using the measurable ones. Fur-
thermore, the unmeasurable properties of two different substances may dif-
fer at identical pressure and temperature. For example, the specific enthalpy
of air at 1atm and 298K is different from the specific enthalpy of water at the
same pressure and temperature.
The properties of a wide range of common substances can nowadays be
found in standard textbooks, web-based software, and commercial software
packages. In thermodynamics, the state of system is said to be fixed if two
independent properties are known. The other properties can then be deter-
mined at the given state with the use of a software or thermodynamic tables.
Note that the two independent properties could be any pair of pressure,
temperature, volume, enthalpy, internal energy, and entropy.
To determine properties required in thermodynamic problems, the
author has found the engineering equation solver (EES) software [1] as a use-
ful tool. A limited free online version of the software is, at the time of writing

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Entropy Analysis in Thermal Engineering Systems 1
https://doi.org/10.1016/B978-0-12-819168-2.00001-5 All rights reserved.