Introduction

Thermodynamics involves the storage, transformation, and transfer of energy.

Energy is stored as internal energy (due to temperature), kinetic energy (due to

motion), potential energy (due to elevation), and chemical energy (due to chemical

composition); it is transformed from one of these forms to another; and it is transferred

across a boundary as either heat or work. We will present equations that

relate the transforma tions and transfers of energy to properties such as temperature,

pressure, and density. The properties of materials thus become very important.

Many equations will be based on experimental observations that have been presented

as mathematical statements, or laws: primarily the fi rst and second laws of

thermodynamics.

The mechanical engineer’s objective in studying thermodynamics is most often

the analysis of a rather complicated device, such as an air conditioner, an engine, or

a power plant. As the fl uid fl ows through such a device, it is assumed to be a continuum

in which there are measurable quantities such as pressure, temperature, and

velocity. This book, then, will be restricted to macroscopic or engineering thermodynamics.

If the behavior of individual molecules is important, statistical thermodynamics

must be consulted.