where, A=2ldp,
B=2gDm
and 
Equation (33) is a hyperbolic function which has a minimum value of (H) for a particular value of (u). Thus, a maximum efficiency will obtained at a particular linear mobile phase velocity.
An example of an HETP curve obtained in practice showing this hyperbolic relationship is given in figure 11.
Figure 11. HETP Curve for Hexamethylbenzene
