Abstract
Oscillatory baffled reactors (OBRs) have attracted much attention from researchers and industries alike due to their proven advantages in mixing, scale-up, and cost-effectiveness over conventional stirred tank reactors (STRs). This study quantitatively investigated how different mixing indices describe the mixing performance of a moving baffle OBR using computational fluid dynamics (CFD). In addition, the hydrodynamic behavior of the reactor was studied, considering parameters such as the Q-criterion, shear strain rate, and velocity vector. A modification of the Q-criterion showed advantages over the original Q-criterion in determination of the vortices’ locations. The dynamic mesh tool was utilized to simulate the moving baffles through ANSYS/Fluent. The mixing indices studied were the velocity ratio, turbulent length scale, turbulent time scale, mixing time, and axial dispersion coefficient. We found that the oscillation amplitude had the most significant impact on these indices. In contrast, the oscillatory Reynolds number did not necessarily describe the mixing intensity of a system. Of the tested indices, the axial dispersion coefficient showed advantages over the other indices for quantifying the mixing performance of a moving baffle OBR.
Highlights
Mixing is key to many chemical industries since it can positively affect reaction yield, mass and heat transfer, and product uniformity
Our goal was to perform a comprehensive study of the mixing performance and hydrodynamic oscillation frequencies and oscillation amplitudes (Table 1) for the series of studies
Several mixing indices and hydrodynamic parameters of operating conditions was based on their feasibility in experimental works accomplished far, were employed, and the performance wasphase justified usingphase) hydrodynamic datafrom obtained from in the literature
Summary
Mixing is key to many chemical industries since it can positively affect reaction yield, mass and heat transfer, and product uniformity. Chemical industries and researchers require reactors that improve mixing, which results in a more efficient production process in terms of reaction time and the quality of product [1]. OBR baffle designs are usually of the single orifice variety, but they may be perforated plates and disc-and-donut [3,4]. This type of reactor can be either batch or continuous, with two methods of imparting motion to fluid: (a) through stationary baffles with moving fluid or (b) through moving baffles. In stationary baffled OBRs, fluid oscillates by means of a diaphragm, piston, Processes 2020, 8, 1236; doi:10.3390/pr8101236 www.mdpi.com/journal/processes
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