Coiled configuration for flow inversion and its effect on residence time distribution

Abstract

Flatter velocity profiles and more uniform thermal environments are extremely desirous factors for improved performance in flow reactors and heat exchangers. One means of achieving this in laminar flow systems is to use mixers and flow inverters. These improve performance but at higher initial and operating costs. This paper introduces a new and more effective device for flow inversion which is achieved by changing the direction of centrifugal force in helically-coiled tubes. Transient response experiments carried out under the conditions of both negligible and significant molecular diffusion reveal drastic narrowing of the residence time distribution (RTD). The effectiveness of the present device can be assessed by the fact that even at a Dean number of 3 the value of dispersion number as low as 0.0013 is obtained under the condition of significant diffusion, and in the case of negligible diffusion the value of dimensionless time at which the first element of tracer appears at the outlet is as high as 0.85.

Residence-time distributions for chaotic flows in pipes

“…This theory can also provide an explanation for the observed steep gradients in residencetime distributions observed in experiments by Saxena and Nigam. 4 In their apparatus with helically coiled cells, steeper gradients have been observed when more cells were present. We have shown that this corresponds to the uniformization of time averages within a chaotic zone in the cross-section.…”

Design of a Continuous Tubular Cooling Crystallizer for Process Development on Lab‐Scale

“…Due to the flow on the circular pathway, centrifugal forces act on the fluid, shifting the maximum flow velocity of the laminar flow profile to the outer side of the wall. Thereby, Dean vortices are induced, which can significantly intensify radial mixing [40]. This effect can be further enhanced using the CFI design.…”

“…This effect can be further enhanced using the CFI design. By bending the tubular helix after a certain number of turns with a 90°angle, Dean vortices have to be reformed and change the direction [40]. The Reynolds number (Eq.…”

Process intensification in green synthesis

“…Saxena and Nigam [126] developed an innovative device based on the principle of fl ow inversion. The working principle of the coiled fl ow inverter (CFI) is multiple fl ow inversion which is effectively achieved by changing the direction of centrifugal force by 90 ° in coiled tubes.…”