Essential Questions: Transport Flashcards
Which basic properties are crucial for transport?
Melting point, boiling point, vapor pressure, water solubility, mobility (Koc), Henry’s Law constant, diffusion coefficient (Kd)
These properties are usually connected for distribution and transport.
What are two fundamentals ways to look at diffusion?
Random: Random motion starts from a specific place, which then can go in different directions. In this sense, it is similar to Brownian motion.
Deterministic: This is what we normally use in engineering. Follows Fick’s First law.
At which spatial scale is diffusion of particular importance?
It is particularly important when we look at the microscale. Moreover, it is important in the following media:
- In air.
- In porous media as it is across small distances where we have advection and turbulence.
- In stagnant medium, interfaces, and bottlenecks, in which there is only diffusion.
How can you estimate the diffusion coefficient of a given chemical in water?
Either by using the molar mass or the molar volume (which is more accurate).
What does ΔC*D give?
This formula calculates the flux, which is based on Fick’s First Law.
What are the differences in diffusion coefficients between gas, liquid, and solid? Which is highest?
The ranking is: soil < water < air
Solids, it is a bit difficult as it depends on what kind of solid it is. Time-scale: It can take years to reach a certain point.
Gas: Diffusion is much faster in gas. Here, the time-scale is in minutes or hours.
What is co-transport?
Co-transport takes place when compounds bind to things like molecules, particles, or microorganism. It is associated with a vector that transports the compound. The most important part of this is that this vector/carrier moves faster than the compound and, in that sense, the mobility of the compound is increased.
Can you give 3 examples of co-transport?
1) In air: dust, birds, soot-particles (e.g. PAHs from woodstoves)
2) In sea: Animals such as whales or salmons migrate over long distances. Another one to consider is ships.
3) In groundwater: Compounds bind to colloids as they are small enough to go through (colloid facilitated transport). This will not happen for particles.
Can you give an example of biological co-transport?
Microorganisms: The condition is that the carrier moves faster than the free compound.
Can you give an example of antropogenic co-transport?
Transport of goods and waste e.g. freight ship or in the discarded waste.
What is eddie diffusion?
- Eddie diffusion is random movement with the media rather than through the media.
- Turbulence follows the law of random movement (molecular diffusion is not important in this case).
- Diffusion is when the compound is moved without turbulence.
