DENSITY GRADIENT COLUMNS - DYNAMIC MODELING FOR LINEAR PROFILES

Rigorous mathematical modeling of the process dynamics associated with the construction and filling of density gradient columns is presented in this article. These models incorporate the hydrostatic driving for ces for fluid flow, friction losses associated with this flow, and the unsteady-state behavior of the liquid levels in the filling vessels a nd in the column itself. Four different filling arrangements are consi dered, corresponding to the density order of the two fluids in the fil ling vessels and two methods for introducing the fluid of varying dens ity into the column. Time requirements for filling of the column and t he resulting calibration curve for liquid density versus height in the gradient column are both obtained as a result of this modeling proced ure. Further, extremely important operating guidelines for the final a chievement of a linear density gradient in the column, which is normal ly the desired objective in most laboratory applications, are derived and presented. Conversely, the causes leading to nonlinear gradients a re elucidated and quantified. (C) 1996 American Institute of Physics.