CORIOLIS-INDUCED SECONDARY FLOW IN SEDIMENTATION FIELD-FLOW FRACTIONATION

In an attempt to examine the effect of smaller channel breadth in sedimentation field-flow fractionation channels, computer simulations of zone profiles are reported which utilize the complete fully developed flow field obtained from Navier-Stokes calculations. The flow field displays Coriolis-induced secondary flow which results when a moving fluid is rotated regardless of the radius of curvature of the channel. By inclusion of secondary flow in the simulation, it is suggested that channel breadths smaller than those used in commercial fractionators will lead to zone leakage; i.e. a small concentration of particles will be found between the void peak and retained peak. Simulation demonstrates that when channel rotation is in the same direction as flow, zone leakage is enhanced compared with the case where flow and rotation are in opposing directions. To reduce zone dilution, which is found to be linear in channel breadth, it is recommended that channel thickness be reduced because of its 3/2 power dependence on the dilution factor. Smaller channel thickness also allows the channel breadth to be reduced because of the reduction in secondary flow. Concentrations of flow in a circular channel are also given to explain why circular channels fall to perform adequately in sedimentation FFF.