Secondary flows known as Dean vortices, that appear in a curved pipe due to centrifugal force, are found to reduce concentration polarisation and fouling and increase membrane permeation rates. The influence of Dean vortices on mass transfer is studied in membrane filtration. The experimental study consists in filtering suspensions of baker's yeast with ultrafiltration hollow fibre membranes, arranged in straight or coiled modules. The effect of different operating parameters is tested: flow velocity, suspension concentration and module geometry. It is found that secondary flow enhances membrane permeation by a factor of up to 5. Moreover, an energy analysis shows that for the same energy consumption, the permeate flux obtained in a coiled module is still far greater than that in a straight module.