Course
Script > Ch 1
Chapter
1: Concepts, definitions, and the diffusion equation
(PDF)
Environmental fluid mechanics is the study of fluid mechanical processes that affect the fate
and transport of substances through the hydrosphere and atmosphere at the local or regional
scale (up to 100~km). At larger scales we must account for the Earth's rotation through the
Coriolis effect, and this is the subject of geophysical fluid
dynamics. In general, the substances of interest are mass, momentum
and heat. More specifically, mass can represent any of a wide variety of passive and reactive tracers,
such as dissolved oxygen, salinity, heavy metals, nutrients, and many others. Part~I of this textbook,
"Mass Transfer and Diffusion," discusses the passive process affecting the fate and
transport of species in a homogeneous natural environment. Part~II,
"Stratified Flow and Buoyant
Mixing," incorporates the effects of buoyancy and stratification
to deal with active mixing problems.
This chapter introduces the concept of mass transfer (transport)
and focuses on the physics of diffusion. Because the concept of diffusion is fundamental to this part of the course, we single it
out here and derive its mathematical representation from first principles to the solution of the governing partial differential
equation. The mathematical rigor of this section is deemed appropriate so that the student gains a fundamental and
complete understanding of diffusion and the diffusion equation. This
foundation will make the complicated processes discussed in the remaining chapters tractable and will start to build the
engineering intuition needed to solve problems in environmental fluid mechanics.
See Lecture
1, Lecture 2, and
Lecture 3.
