Revisiting the Effect of U-Bends, Flow Parameters, and Feasibility for Scale-Up on Residence Time Distribution Curves for a Continuous Bioprocessing Oscillatory Baffled Flow Reactor

Abstract

An oscillatory baffled flow reactor (OBR) has been designed with 60 interbaffled cells. The baffled columns of 40 mm internal diameter together result in a reactor length of 5740 mm. The oscillatory amplitude and frequency were in the range of 2−12 mm and 0.3−2 Hz, respectively. The report investigates the impact of Ubends and the number of reactor sections on axial dispersion for scaleup feasibility. A prediction model using operating parameters has been developed to maximize plug flow conditions using the tanks-in-series (TiS) model. The maximum TiS value was 13.38 in a single column compared to 43.68 in the full reactor at a velocity ratio of 2.27 using oscillatory parameters 8 mm and 0.3 Hz. The mixing efficiency along the reactor was found to decrease after each column at amplitudes <6 mm compared to amplitudes up to 12 mm, where a negligible impact was observed. U-bend geometry had a significant role in the decrease of TiS values.

Characterising flow with continuous aeration in an oscillatory baffle flow reactor using residence time distribution

“…These results correlate with previous RTD studies, reporting that as the velocity ratio increases past an optimal zone the intensity of mixing has a detrimental effect on the level of plug flow. 22,42,48,49…”

“…, in a counter-current direction then the RTD curves would exhibit non-symmetrical curves with a tail at the end implying back mixing is not the case. 42,53…”

“…The true outlet signal ( E ) was calculated by the inverse fast Fourier transformation between the measured inlet and outlet signals as described in eqn (4)A detailed methodology for quantifying the level of plug flow including equations is reported in a previous study. 42 To aid with the clarity of data, the TiS numbers were portrayed against the velocity ratio, itself a dimensionless number, which equates to the ratio between the net flow and the oscillatory flow displayed in eqn (5).…”

“…The range of amplitude and frequency were selected to provide a wide range of velocity ratios and based on previous studies that maximise plug-flow and mass transfer; whereas gas flow was set at the two extremes within the systems capabilities. 3,42 Centre points which were the median of each factor are included with all experiments replicated twice whilst the centre points were replicated 4 times.…”

“…12 This particular system achieved the greatest number of TiS at a velocity ratio of 2.27. 42 Adequate levels of plug flow are described as present in the system when the TiS number is >10. 8,22,31,32 Initial results identified this TiS number at the same parameters without aeration to provide a baseline comparison when aeration is added.…”