fluid pair models
 

hi
i am modeling a domain with 3phases ( i.e. air+water+sediment).
for defining model, i selected continues fluid for air and water and dispersed fluid for sediment in basic setting. in this state cfx want viscosity for sediment. what should i select it?
in fluid pair models tab, should i select free surface for air/water and particle model for water/sediment in interface transfer option ?
in experimental model, sediment don't move but in modeling with cfx sediment go out from end of channel. what is cause of it while velocity is same in both model?