where XG and nG are the parameters of the function. Another function which has been widely used to represent particle size distribution is the log-normal distribution function (Prasher, 1987):
where b is the steepness constant¼1=(2 ln2rg), rg is the size ratio corresponding to the 84% cumulative undersize mass fraction (X84) and the 50% cumulative undersize mass fraction (X50), XM is the mode of the size distribution and w is the model parameter. Regression of all three models mentioned above with experimental particle size distribution data to determine the model parameters have been well detailed in Prasher (1987) and Manohar and Sridhar (2001).