Transport mechanisms

Introduction
Molecular diffusion in a medium
Transfer accross phase boundaries
Examples for application
Advective and dispersive transport
References and links

Selftest
Problems
     Problem 1
           Hint
           Answer
     Problem 2
           Hint
           Answer
     Problem 3
           Answer
     Problem 4
     Problem 5

Problem 4

Horstmann and McLachlan (1998;  Journal link  Download paper) have shown that PCBs with 6 or more chlorines do not reach equilibrium between the forest canopy and the atmosphere as a source. Try to find out what the dominating resistance is!

Use the following numbers: The major compartment of the plant for accumulating non-polar compounds such as PCB is the wax layer at the outside of needles and leafs. Assume that this layer is 1 µm thick. The laminar boundary layer on the air side is about 1 cm thick. Assume the following numbers for a heptachlorobiphenyl: a diffusion coefficient of 10-10 cm/sec in the wax; a partition coefficient Kwax/air of 10-10 (L/L) for a diffusion coefficient in air of 0.04 cm2/sec.

 

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