How to calculate spread parameter in Rosin-Rammler model
 

Dear guys,
I am modeling separation of gas-solid flow in a cyclone using fluent. I am going to using Rosin-Rammler particle distribution model in fluent. In fact I have the particle distribution as shown in attached figure but unfortunately I do not know how to calculate "Spread parameter" for an existing particle distribution. Please help me to calculate that.

The user guide and theory manual contain all the info you need to do this calculation. I actually just did this the other day.