Dispersion in coiled tubular reactors: A CFD and experimental analysis on the effect of pitch

This work investigates axial dispersion in coiled tubes when the coil pitch is non-negligible compared to the other geometrical parameters. The axial dispersion model (ADM) is used for the description of residence time distributions (RTDs) and an analytical expression for the closed-closed (CC) ADM is presented and used for the analysis of coiled reactors. Correlations, based on validated computational fluid dynamics (CFD) results, are developed to take the coil pitch effect into account. The dispersion coefficient is evaluated numerically and experimentally for different coils, with a good agreement between predicted and observed values. Coiling not only reduces the dispersion significantly with respect to straight tubes, but also the ADM can be applied in a wider region of the common conditions used in practice. The results are summarized in a nomogram that displays applicability regions of the ADM and enables estimation of the dispersion coefficient with a simple graphical procedure.