Density gradient columns: Dynamic modeling for linear profiles

Abstract

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 forces for fluid flow, friction losses associated with this flow, and the unsteady-state behavior of the liquid levels in the filling vessels and in the column itself. Four different filling arrangements are considered, corresponding to the density order of the two fluids in the filling vessels and two methods for introducing the fluid of varying density into the column. Time requirements for filling of the column and the resulting calibration curve for liquid density versus height in the gradient column are both obtained as a result of this modeling procedure. Further, extremely important operating guidelines for the final achievement of a linear density gradient in the column, which is normally the desired objective in most laboratory applications, are derived and presented. Conversely, the causes leading to nonlinear gradients are elucidated and quantified.

Refractive-index and density matching in concentrated particle suspensions: a review

“…A density gradient column can be used to that end (Brown et al 1996;Coombs 1981;Oster and Yamamoto 1963;Taylor 1955, 1956), but less expensive techniques are also available. For our experiments, the matching method involved (i) mixing different fluids with a density range close to the PMMA datasheet values and (ii) observing the time needed for the particles to rise or sink.…”