Controlled centrifugal instabilities (called Dean vortices) resulting from flow in helical tubes have been used to reduce concentration polarization and membrane fouling during nanofiltration. These vortices enhance back-migration of solute through convective flow away from the membrane-solution interface and allow fur increased membrane permeation rates. Based on the theory of Dean vortex flow, a new prototype vortex generating tubular nanofiltration element was designed. Two sets of nanofiltration modules were constructed; a linear module and a new module containing hollow fibers wrapped around rods of small diameter in helical geometry. Optimization of the design is discussed with respect to the diameter and thickness of the hollow fibers. Axial pressure drop and energy consumption measurements for the helical module agreed very well with available correlations for various experimental conditions. Water permeabilities for the helical modules were similar to those of the conventional linear modules. No significant effect of pH was observed on the water permeability.