Mixing, settling, and the movement of the interface between the mobile andstationary phases in CCC

In a J-type centrifuge, wave mixing is the primary method of mass transfer between mobile and stationary phases. It is observed centered about the pro ximal key node, while settling is observed centered about the Distal key no de. A hypothesis using the Kelvin-Helmholtz wave stability criteria gives a n explanation of why mixing and settling occur centered around these key no des. The assumption of constant retention means that the stationary phase h as zero linear velocity for all positions within the coil, and that the mob ile linear velocity is constant. Closer examination of the Kelvin-Helmholtz wave stability criteria shows that the relative flow of two phases is impo rtant in creating waves. The interfacial movement can be viewed as a relati ve pumping action between the phases that increases the relative linear vel ocity of the mobile phase at the proximal key node to cause wave mixing. Th e interface can move within one loop of a coil. This can cause wave mixing at the proximal key node and settling at the distal key node when the lower phase is selected as the mobile phase. The analysis presented, is based upon the following techniques: i) radial a nd tangential accelerations for helical wound coils on J-type centrifuges, ii) pressure gradient analysis, iii) Hagen-Poiseuille equation for laminar flow in circular bore tubing, iv) hydraulic mean depth to allow for two pha se flow in circular bore tubing, v) computational numerical integration. A derived equation links the parameters: centrifuge radius (R), beta value, r otational speed (omega), densities of both phases (rho (L), and rho (U),), viscosities of both phases (mu (L) and mu (U)), tubing bore diameter (d), a nd mobile phase volumetric flow rate (Q(m)). It is hoped, that the derived equation can be used to qualitatively predict the effects of changes to the above parameters on CCC.