For size-dependent growth rate of crystals

a simplified model: is derived

where G is the linear growth rate of crystals

L and L0 are characteristic lengths of crystals and nuclei respectively

G∞

and β are model parameters

G∞

being the linear growth rate of extremely large crystals

and β characteristic length of crystals for which linear growth rate equals G∞/2. Equations for crystal size distribution (CSD)

suspension density MT and dominant crystal size LD are given. Compared with previous models

most of which are empirical

this model shows a comparable or better fit to the published CDS data for ammonium alum and potash alum. The calculated values of MT agree well with experimental results.