Mass transfer enhancement in coiled hollow fiber membrane modules

In this study, coiled hollow fiber membrane modules were prepared, and their mass transfer performances were experimentally examined. It was found that, compared with the conventional straight module, the mass transfer in both tube and shell side of the coiled hollow fiber module could be remarkably enhanced. At either side of membrane, the mass transfer coefficient of coiled module was more than two times higher than that of straight module. The improvements in mass transfer can be attributed to the created secondary flows (known as Dean vortices) inside coiled fiber and the promoted turbulence on the shell. Coiled modules of different geometric parameters were employed to study the influences of such factors as wind angle, coiled diameter and internal diameter of fibers on mass transfer. It was found that wind angle had important influence on the fluid condition of the coiled module, and therefore, its mass transfer. The coiled module of wind angle lower than 45° showed better mass transfer performance than the one of wind angle higher than 45°. The fluid dynamics and mass transfer correlations for the coiled tubes of different wind angle were obtained. The exponents of flow velocity and the exponents of modified Dean numbers in these correlations are reasonably higher than their counterparts in the correlations of straight modules. As for the influence of coiled diameter and fiber internal diameter, it was found that the module with smaller coiled diameter or smaller fiber internal diameter gave higher mass transfer coefficient.