Transport & Exchange

Question 1

Representative Elemantary Volume (REV)

Answer 1

Small volume in catesian coordinates. It is the volume over which a measurement can be made that will yield a value representative of the whole.
If the concentration changes over time within the REV, the system is considered dynamic or transient.

Question 2

Partial Differential Equation

Answer 2

An equation containing multiple partial derivatives (e.g. spatial and temporal)

Question 3

Advection

Answer 3

Advection is the process by whing a substance is transported through the bulk movement of hte medium in which it is contained. E.g. the movement of air or water, carrying wiht it properties such as temperature, humidity, or dissolved solutes.

Question 4

Molecular diffusion

Answer 4

A physical process in which particles or molecules spontaneously move from regions of higher concentration to areas of lower concentration. This movement results from the intrinsic random motion of particles, known as Brownian motion, and is driven by the tendency to achieve a more uniform distribution of particles, in accorance with the principle of entropy.

Question 5

factors that influence the rate of diffusion include among others:

Answer 5

• The concentration gradient (the difference in concentration between two regions over space)
• Temperature
• The properties of the medium through which the particles are moving

Question 6

Tortuosity

Answer 6

The ratio between the pore space diffusion length (diffusion through penetration into the solid matrix through pores) and the free diffusion length (diffusion in a fluid alone). However, diffusion through the solid matrix is often neglected as it is much smaller than through the fluid alone.

Question 7

Turbulent dispertion

Answer 7

It describes the spreading or mixing of particles, fluid elements, or other substances within a turbulent fluid flow. Turbulence is characterized by chatotic, irregular fluid motion with fluctuations in velocity, pressure, and other flow properties, which significantly enhance mixing throughout the fluid.

Question 8

Mechanical Dispersion

Answer 8

Mechanical dispersion in fluid dynamcis refers to the mixing or spreading of solutes or practicles due to the physical flow characteristcs within the porous medium. (turbulent structures are negligible

Question 9

Key factors influencing mechanical dispersion

Answer 9

• pore size
• shape
• tortuosity

Question 10

Hydrodynamic dispersion

Answer 10

Diffusion and (turbulent and mechanical) dispersion are often grouped into a single effective parameter known as the hydrodynamic dispersion coefficient. Because on a macroscopic scale, these processes are challenging to seperate in practical applications.

Question 11

Reactive transport

Answer 11

Reactive transport refers to the migration and transformation of substances (e.g., solutes or gases) within systems such as soil, groundwater, or surface water bodies, where (bio-)geochemical reactions are essential drivers of change.