Mass transfer in 1812 spiral wound modules: Experimental study in dextrose-water nanofiltration

Biotech 1812 spiral-wound elements manufactured by GE Powe&Water have been characterized, operating in NF with aqueous solutions containing 50 g/dm3dextrose at 50 °C and pH = 4. Operative conditions were selected in order to get experimental results of flux and observed rejections highly dependent on feed flow rate, so that a confident mass transfer correlation in the feed side has been obtained. The mass transfer correlation accounts of the feed spacer geometrical characteristics included in the description of the hydraulic diameter. It matches in a surprising manner with the well-known correlation derived from heat and mass transfer analogies in turbulent flow regime, it is in a good agreement with a recently published correlation derived from OSN in 1812 modules, whereas it is heavily in contrast with the widely used Shock and Miquel equation. In addition, the elaboration of the experimental data according to the velocity variation method does not lead to confident results. The correlation here presented can be extended to the simulation of industrial modules operating at feed flow conditions corresponding to Reynolds number in the range from 100 to 700, since it is rather independent of the way in which it was calculated. A critical discussion is also presented about the differences between the values of membrane permeability and of the module permeability and about the role of the “module length to membrane width” ratio in data elaboration. A sensitivity analysis concludes the work, in which authors discuss how the results of module characterization depend on the quality of the mass transfer correlation in the feed side and give some recommendations for a proper elaboration of experimental results.