Chapter 1

Definition and Basic Concepts

Thermodynamics is defined as the science of energy. Originally derived from Greek words : therme (heat) and dynamics (power) – descriptive of early attempts at conversion of heat into power. Modern interpretation includes all aspects of energy and energy transformations, power generation, refrigeration, and the relationships among properties of matter.

There are two approaches in thermodynamics studies: (1) classical thermodynamics – a macroscopic approach where the whole system is viewed as one entity. It does not require knowledge of behavior of individual particles. It is the direct and easy method of solving engineering problems, (2) statistical thermodynamics – is a microscopic approach based on average behavior of large groups of individual particles. It is rather involved. In this course, the classical approach is adopted.

Many engineering systems and applications apply the principles of thermodynamics – refrigerator, air-conditioning system, water heater, computer, TV, internal combustion engines, rockets, jet engines, power plants and many more.

1.1

Dimensions and Units

A physical quantity is characterized by dimensions, and dimensions have units.

There are seven primary or fundamental dimensions:

Dimension

Length

Mass

Time

Temperature

Electric current

Amount of light

Amount of matter

SI Unit meter (m) kilogram (kg) second (s) kelvin (K) ampere (A) candela (cd) mole (mol)

English Unit pound-mass (lbm) foot (ft) second (s) rankine (R)

SI unit is based on decimal relationship between units. The standard prefixes in SI units :

Multiple

1012

109

106

103

102

101

10-1

10-2

10-3

10-6

10-9

10-12

Prefix tera, T giga, G mega, M kilo, k hecto, h deka, da deci, d centi, c milli, m micro, nano, n pico, p

2

Secondary or derived dimensions are expressed in terms of the fundamental dimensions, for example: velocity V = (length)/(time) and