Mass transfer improvement by secondary flows: Dean vortices in coiled tubular membranes

A helically wound hollow-fibre (or tubular) membrane module was studied in an oxygenation operation with water flowing in the laminar regime inside the tube. Data are compared with a conventional module where straight hollow-fibre membranes are in parallel alignment. In the former design, the results are analyzed taking into account the formation of secondary flow (Dean vortices) and a new mass transfer correlation is presented. In the latter design, results are consistent with the Lévêque equation. It is shown that the presence of vortices gives better performance in terms of oxygen transfer. Improvement factors were in the range of 2 to 4.