Chapter 10 Exam 3 Review Questions

What does volumetric flux represent and what are its units?

it’s the amount of fluid moving through an area per time (vol/area * time)

units: m**3/(m**2*s)

True or False: the dispersion coefficient E accounts for diffusion and dispersion.

True

True or False: Diffusivity in a liquid increases with molecular size.

False

True or False: Diffusivity is a property of a mass species only and not the medium

False

True or False: Dispersion cannot be present in the absence of flow.

True

True or False: Hydraulic potential in Darcy’s Law includes applied pressure and matric pressure.

True

How does diffusivity change with temperature and why?

An increase in temperature increases diffusivity because at higher temperatures, molecules have a higher KE, so they move around faster therefore diffusing faster

How is the governing equation for mass transfer?

Using mass balance (conservation) and Fick’s Law

What are the different modes of mass transfer?

• molecular diffusion

• capillary diffusion

• bulk flow through porous media

• dispersion

• convection

Define molecular diffusion.

spontaneous movement of mass (solid, liquid, gas) down a concentration gradient due to random molecular movement

Define capillary diffusion.

movement of mass due to capillary action in a porous medium

Define bulk flow through porous media.

bulk movement of a fluid in a porous media due to hydraulic forces (pressure, matric forces, gravity)

Define dispersion.

spreading of fluid from its bulk flow path (similar effects to molecular diffusion, bud different mechanisms; due to turbulence in fluid)

Define convection.

addition of bulk flow to diffusion or dispersion