Ultraviolet Disinfection:  Similitude in Taylor−Couette and Channel Flow

Abstract

The inactivation data for Escherichia coli are recorded for the three reactor geometries of Taylor-Couette flow and flow between either concentric cylinders or a square channel. All of the data are shown to be correlated with the assumption of plug flow. In particular, the effects of nonuniform radiation levels are accounted for by integration across the fluid channel as done previously. However, a new correction factor is introduced that is shown to be inversely proportional to the laminar, velocity boundary thickness to account for the effects of a concentration boundary layer of surviving pathogen. It has also been demonstrated that the common problems of nonuniform radiation levels and concentration boundary layer effects in UV reactors are largely eliminated with the use of Taylor-Couette flow. Moreover, the repetitive exposure of fluid parcels to a small number of lamps in the rotating Taylor-Couette flow decreases maintainance requirements compared to the hydrodynamic equivalent of cross-flow over a tube bank or lamp array. Over a 3-log reduction in the inactivation of E. coli was demonstrated compared to a conventional channel with the same radiation dosage. Moreover, greater than a 2-log reduction was evident compared to flow through concentric cylinders.

Actinometric and biodosimetric evaluation of UV-C dose delivery in annular, Taylor–Coutte and coiled tube continuous systems

“…The hydrodynamics of the TC reactor can be improved by applying rotation to the inner cylinder. The onset of the toroidal vortices was observed for the critical Taylor number Tac > 41 (Forney et al., 2003). The occurrence of the circumferential vortices within the annular gap greatly improves the mixing conditions and UV photon exposure of the treated liquid by repetitive refreshing of the UV irradiated quartz surface.…”

“…The treatment at the Ta = 0 resulted in the formation of the laminar CP flow pattern. For Ta = 0, the thickness of the velocity boundary layer ( θ ) can be calculated as half of the gap width between cylinders (Forney et al., 2003). In the present study, CP flow was characterized by θ = 1.65 × 10 −3 m, which constituted 50% of the gap width ( b = 0.0033 m).…”

“…In the present study, CP flow was characterized by θ = 1.65 × 10 −3 m, which constituted 50% of the gap width ( b = 0.0033 m). Such hydrodynamic condition is characterized by non-uniform exposure of the tested liquid to the UV photons and low concentration of the absorbing species near the surface of irradiated quartz cylinder (Forney et al., 2003).…”

Photon Absorption in Modified Taylor−Couette Flow: Theory and Experiment

“…To account for the variation in C with radius, that is, the distance from the surface of the reactor or stator, eq 4 has been modified to where β ∝ K /δ and δ is the boundary layer thickness next to the stator. , …”

“…In the second, the UV inactivation of E. coli is recorded. The procedure is similar to that used in an earlier study which considered a smooth rotor at low rotation rates and with laminar Taylor−Couette flow. , In the present experiments, the simultaneous application of UV and cavitation is considered at large rotation rates, that is, at large Reynolds and Taylor numbers, under conditions of continuous flow within the Taylor−Couette design. Such conditions are similar to those found in a continuous stirred tank reactor or CSTR …”