Joscha Hoppe

Thank you very much for the answers!
Rob you were right, but the viscosity change i got was wrong since the whole viscosity changed with time and that was not what i wanted.
The viscosity is supposed to change since the fluid exceed a certain temperature. It is supposed to be a simulation of a polymerization process, where the viscosity increases with time. Therefore the after cooling down the viscosity doesnt change. 
I read that i might need a UDS for it, but i would like to know if there is a more simple way.