CHAP. 10: TRANSPORT PROCESSES [CONTENTS] 330
Chapter 10
Transport processes
This chapter deals with thermal conductivity, viscosity and diffusion. All these phenomena
relate to the transport of a certain physical quantity in a system. Diffusion involves mass
transport from one part of a system to another; viscosity concerns the transfer of molecules
momentum in flowing gas or liquid; thermal conductivity relates to transport of molecules
thermal energy.
10.1 Basic terms
10.1.1 Transport process.
In a system which is not in the state of thermodynamic equilibrium, spontaneous processes
occur under unchanging external conditions which in the end lead to equilibrium [see1.4.1,
1.4.2,1.4.4]. During a transport process the value of the observed quantity changes with time
at a certain location in the system. The observed quantity may be amount of substance, energy
or momentum.