Residence time distribution from a continuous Couette flow device

This paper describes an experimental study of residence time distribution (RTD) by pulse response analysis in a continuous Couette flow device with rotating inner cylinder and stationary outer cylinder. The experiments were performed under conditions of (a) negligible and (b) significant influence of molecular diffusion and (c) Taylor vortex flow. Diethylene glycol and water were used as the test fluids with congo red dye and potassium permanganate solution as tracers respectively. A unique RTD described by an analytical expression was observed for experiments with low axial Reynolds number under the condition of negligible influence of molecular diffusion. For most experiments performed under conditions of significant influence of molecular diffusion and Taylor vortex flow regime over the ranges 0 < Ta < 118 and 0.4 < Re < 5.5, the RTD can be described by a dispersion model. The system behaves as a near-plug flow vessel at Ta ≈ 60. The critical Taylor number for this geometry as defined by the minimum dispersion number for a given flowrate is slightly higher than that without axial flow.