Page 16 - Bird R.B. Transport phenomena

Chapter 0

The Subject of Transport

Phenomena

§0.1 What are the transport phenomena?
§0.2 Three levels at which transport phenomena can be studied
§0.3 The conservation laws: an example
§0.4 Concluding comments

The purpose of this introductory chapter is to describe the scope, aims, and methods of
the subject of transport phenomena. It is important to have some idea about the struc-
ture of the field before plunging into the details; without this perspective it is not possi-
ble to appreciate the unifying principles of the subject and the interrelation of the
various individual topics. A good grasp of transport phenomena is essential for under-
standing many processes in engineering, agriculture, meteorology, physiology, biology,
analytical chemistry, materials science, pharmacy, and other areas. Transport phenom-
ena is a well-developed and eminently useful branch of physics that pervades many
areas of applied science.

§0.1 WHAT ARE THE TRANSPORT PHENOMENA?
The subject of transport phenomena includes three closely related topics: fluid dynam-
ics, heat transfer, and mass transfer. Fluid dynamics involves the transport of momentum,
heat transfer deals with the transport of energy, and mass transfer is concerned with the
transport of mass of various chemical species. These three transport phenomena should,
at the introductory level, be studied together for the following reasons:
• They frequently occur simultaneously in industrial, biological, agricultural, and
meteorological problems; in fact, the occurrence of any one transport process by it-
self is the exception rather than the rule.
• The basic equations that describe the three transport phenomena are closely re-
lated. The similarity of the equations under simple conditions is the basis for solv-
ing problems "by analogy."
• The mathematical tools needed for describing these phenomena are very similar.
Although it is not the aim of this book to teach mathematics, the student will be re-
quired to review various mathematical topics as the development unfolds. Learn-
ing how to use mathematics may be a very valuable by-product of studying
transport phenomena.
• The molecular mechanisms underlying the various transport phenomena are very
closely related. All materials are made up of molecules, and the same molecular