OpenFOAM Computational Fluid Dynamic Simulations of Single-Phase Flows in an Advanced-Flow Reactor

Abstract

Computational fluid dynamic (CFD) simulations are carried out for single-phase flow in an advanced-flow reactor (AFR) using the open source software OpenFOAM. Excellent agreement of simulations with experimental pressure drop and residence time distribution (RTD) is obtained. Streamlines, stagnant zones, velocity profiles, and pressure fields are obtained at different flow rates ranging from 5 to 100 mL/min. A change in the flow behavior with the presence of recirculation zones is observed with a 40 mL/min flow rate. The extent of the recirculation zones increases with increasing flow rate from 40 to 60 mL/min and is limited further by the presence of a second cylindrical post inside the heart cell, remaining almost constant in the flow rate range of 60−100 mL/min. The RTD is also determined for all flow rates, and a comparison between different reactor designs (two-post, single-post, and low-flow-reactor-like single-post) is presented. The AFR shows a plug-flow behavior with a small degree of dispersion, which broadens the RTD. Symmetric RTD curves are obtained for the single-post designs, whereas the Gen 1 AFR design experiences asymmetry in the RTD at flow rates in the range between 20 and 60 mL/min. ■ INTRODUCTIONMicroreactors have been demonstrated to provide advantages over conventional process technologies for the synthesis of chemical compounds and kinetic studies at laboratory scale. 1 High heat and mass transfer rates, rapid mixing, and higher selectivities and conversions can be achieved in these microdevices thanks to the small characteristic dimensions, enabling the synthesis of compounds that cannot be synthesized in conventional reactors. In the past years, efforts have been directed toward the application of microreactor technology for production purposes, especially in the pharmaceutical and fine chemicals industry. 2−4 The challenge is how to get the benefit of the transport rates inherent to microreactors while increasing the throughput for production applications. Two approaches to increase production rate are possible: (a) scale-out by parallelization of units and (b) scaleup by increase in channel size and flow rates. Scale-out requires thousands of units to achieve kilogram per minute of production rates and development of very expensive and complex control systems to ensure identical operating conditions in each unit for a perfect and predictable overall reactor performance. In contrast, scale-up by increase in channel size risks losing mass and heat transfer performance. The advanced-flow reactor (AFR) manufactured by Corning, Inc., combines both approaches and is able to yield production rates of 10−300 g/min per module. 5 The AFR is formed by three layers, and the reaction mixture flows through the middle one. The reaction layer has a special design in the form of several rows of heart-shaped cells in series (Figure 1a) that form a sequence of convergent−divergent segments that enhance mass transfer rates. The height for this layer is 1.1 mm, and the minimum width is 1 mm (Figure 1b). T...

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