Heat Transfer and Residence Time Distribution in Plug Flow Continuous Oscillatory Baffled Crystallizers

Abstract

Heat transfer coefficients in a continuous oscillatory baffled crystallizer (COBC) with a nominal internal diameter of 15 mm have been determined as a function of flow and oscillatory conditions typically used under processing conditions. Residence time distribution measurements show a near-plug flow with high Peclet numbers on the order of 100–1000 s, although there was significant oscillation damping in longer COBC setups. Very rapid heat transfer was found under typical conditions, with overall heat transfer coefficients on the order of 100 s W m–2 K–1. Furthermore, poor mixing in the COBC cooling jacket was observed when lower jacket flow rates were implemented in an attempt to decrease the rate of heat transfer in order to achieve more gradual temperature profile along the crystallizer length. Utilizing the experimentally determined overall heat transfer coefficients, a theoretical case study is presented to investigate the effects of the heat transfer rate on temperature and supersaturation profiles and to highlight potential fouling issues during a continuous plug flow cooling crystallization.

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

“…They found that the attained oscillatory amplitude is halved at the outlet when 11 U-bends and 22 columns are used. 12 From previous computational fluid dynamic (CFD) evaluations (data not shown and unpublished), the Ubend is suspected to have more of an influence on oscillatory dampening than that of the baffle constrictions. This is due to momentum changes and collision of eddies along a nonsymmetrical pathway around U-bend radii and fluid traveling at different distances.…”

“…These plots are similar to figures made of other multipass OBR setups, exhibiting minimal axial dispersion. 12,33 3.4. Scaling the OBR for Bioprocesses.…”

“…One biotechnology company currently operates a commercial OBR for their production of enzymes, but due to confidentiality, they have not disclosed the reasons for using the OBR. 7 Other laboratory-scale demonstrations that have successfully enhanced the production rate or performance include crystallization, 12 fermentation processes, 2 and production of biofuel, 13 polymers, 10 and microalgae. 14 Continuous flow technologies are appealing to the bioprocessing industry due to the potential in reducing footprint, waste, cost, and energy compared to the batch process 15 but are yet to reach industrial expectations.…”

“…OBRs are suitable for bioprocesses due to their increased production per unit volume, 9 low shear rates reducing stress on cells, 16 uniform and controllable mixing independent of net flow allowing controllable residence time, 17 and improved scale-up capabilities. 12 OBR technology relies on periodically spaced baffles within columns, in which oscillation is applied either by reciprocating baffles 10 or by fluid pulsations. 18 As the fluid oscillates back and forth against the constrictions, eddies are formed on either side of the baffle.…”

Optimal Operation of an Oscillatory Flow Crystallizer: Coupling Disturbance and Stability

“…Accordingly, an oscillatory flow crystallizer (OFC) has been considered to be a promising candidate to avoid mechanical agitation effects, − as it can generate recirculation flow and vortex through the combination of a reactor structure and oscillation process . This unique flow can create a series of well-mixed volumes, which is beneficial to control mass and heat transfer. − Furthermore, the appropriate residence time in the OFC can also improve the quality of the crystals produced. It is certain that the employment of the OFC for crystallization can reach the requirement of flow field mixing; however, the principle on how to balance the relationship between the stable environment and appropriate disturbance has rarely been reported.…”