Environmental Fluid Mechanics 1:
Mass Transfer and Diffusion

Course Script > Ch 1

Chapter 1:  Concepts, definitions, and the diffusion equation

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.




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