Passive Mixer cum Reactor Using Threaded Inserts: Investigations of Flow, Mixing, and Heat Transfer Characteristics

Abstract

Significant efforts have been and are being spent on developing intensified tubular reactors for continuous manufacturing of fine and specialty chemicals. In this work, we have proposed a new design of passive mixer-cum-reactor for process intensification and development of continuous processes. The mixer/reactor consists of threaded inserts with cone-shaped ends, placed concentrically in the tube such that fluid flows through the annular region between the inserts and the tube. The proposed design is easy to fabricate, maintain, and overcomes the limitations of scale up/scale down compared to most of the commercial passive mixers. The split and recombine of flow around inserts, the swirling effect generated by threads, change in the swirl direction due to change in the direction of screw threads, and pinching effect/expansion at the cone-cone shaped ends realize desired enhancements in mixing and heat transfer. A detailed computational study has been carried out on the mixer-cum-reactor to characterize flow, mixing and heat transfer at different operating conditions using a verified and validated CFD model. Various designs and configurations of threaded inserts were considered: 5-channel, 7-channel and 9-channel, smooth surface (no threading) and smooth surface-extended rear end inserts. The flow, mixing and heat transfer were characterized over the Reynolds number range of 100 to 1600. Structure of the generated swirling flow, effect of pinching/expansion, direction reversal of flow, tracer fraction, temperature and path lines were investigated systematically to gain new insights. Threaded inserts could achieve excellent mixing (>99 % of mixing intensity) and heat transfer (7 times smooth inserts and 20 times without inserts). The presented results will provide a sound basis for selecting appropriate threaded inserts for intensifying mixing and heat transfer in tubular reactors. The work also provides a useful starting point for further work on multiphase flows in a tubular reactor with threaded inserts.

CFD–PBM Numerical Study on Liquid–Liquid Dispersion in the Q-Type Static Mixer

“…A static mixer is widely used in the fine chemicals industry, pharmaceutical industry, polymerization process, biological chemical industry, and other industrial processes due to its excellent mixing performance, compact structure, flexible operation, easy installation, and other characteristics . There have been a lot of reference reports focusing on the effects of the element type and arrangement on pressure drop, residence time distribution, and heat transfer enhancement of single-phase flow in static mixers. − The dispersion mixing process in the static mixer is complex because it includes hydrodynamics, turbulent flow, and physicochemical properties of the multiphase system …”

CFD Analysis of a Kenics Static Mixer with a Low Pressure Drop under Laminar Flow Conditions

“…22 A quantitative comparison of different static mixers indicates that Kenics mixers can achieve a mixing index of above 98%. 12 The influence of varying geometric parameters has been investigated numerically to optimize the mixing performance of Kenics mixers. In the creeping flow regime (Re < 1), Kenics mixers with alternating twist directions of adjacent mixing elements (R−L configuration) are globally chaotic, while segregated islands, which form barriers to mixing, occur in designs with adjacent mixing elements in the same direction (R−R configuration).…”

“…Static mixers are commonly used to enhance mixing in channels through chaotic advection, − resulting in an increase in intermaterial area and a decrease in the diffusion length. Different static mixing elements and configurations − have been used to achieve fluid mixing depending on process requirements and pressure drop. Enhanced mixing in static mixers leads to improved heat transfer. ,, Furthermore, in crystallization studies, supersaturation gradients can be minimized with static mixers, which results in products with a narrower particle size distribution compared to devices without flow switching. − The ideal static mixer is one in which efficient mixing can be achieved with a low pressure drop.…”

“…Different static mixing elements and configurations − have been used to achieve fluid mixing depending on process requirements and pressure drop. Enhanced mixing in static mixers leads to improved heat transfer. ,, Furthermore, in crystallization studies, supersaturation gradients can be minimized with static mixers, which results in products with a narrower particle size distribution compared to devices without flow switching. − The ideal static mixer is one in which efficient mixing can be achieved with a low pressure drop.…”

“…Furthermore, both dispersive and distributive mixing can be enhanced in Kenics mixers by the helical mixing elements. , Dispersive mixing, unlike distributive mixing, which leads to a reduction in the distance between fluid elements, involves size reduction of fluid layers . A quantitative comparison of different static mixers indicates that Kenics mixers can achieve a mixing index of above 98% . The influence of varying geometric parameters has been investigated numerically to optimize the mixing performance of Kenics mixers.…”