Flux Density of Salt in Horizontal Tube: How Does Advection Affect Transfer?

[kathyt.25]

Homework Statement

What is the flux density of salt in a horizontal tube, 10cm in length, connecting seawater (salinity 30g/L) to a tank of freshwater (salinity ~0) assuming no advection occurs?

Homework Equations

J (g/m²s) = C (g/m³) x V (m/s)

The Attempt at a Solution

C = 30g/L * 1L/0.01m³ = 3000g/m³
The calculation is obviously really simple, but I'm not sure what to use for time when calculating velocity (m/s). I'm given the length 10cm, but I'm assuming time has something to do with the statement "assuming no advection occurs". I feel like I'm overlooking some basic assumption.

 

[ehild]

What is advection? How can the salt be transferred through the tube?

ehild