simulate a erosion from a "dirtlayer" in a retangular duct, using the multiphase
 

Hello,

first of all i am a absolute beginner in CFD and StarCCM+!

issue:
the flow cell (retangular duct) is in one section "contaminated" with maltose-extract. i want to simulate the erosion of the extract under different flow velocities.

Questions:
1. I choose the eulerian multiphase modell, because there are no particles in the extract (sugar), only mass transfer, diffusion an convection are important. Can i add the "fluid-film-modell" addtionally, respectively which modell i can use?
2. the contaminated area in the duct is a square with following dimensions: 3cm*1cm*0,2cm. How can i define this area? Maybe with a surface injector, or with field function?

I hope you can help me,
best regards,
Felix