MODELING CONCENTRATION POLARIZATION IN REVERSE-OSMOSIS SPIRAL-WOUND ELEMENTS

The effect of feed water how rate on the concentration-polarization of magnesium sulfate, sodium chloride, and sodium selenate in reverse os mosis (RO) spiral-wound elements was investigated and modeled. Experim ents were performed with 40 in. long and 2.5 in. in diameter spiral-wo und elements tested with feed solutions of the single electrolyte magn esium sulfate, and a mixture of sodium chloride and sodium selenate as major and trace components, respectively. The feed flow rates investi gated ranged from 1.12 to 13.5 L/min, corresponding to Reynolds number s from 25 to 300. The element was modeled by dividing it into n identi cal subelements, each separated into two compartments, feed channel an d product water carrier, by the RO membrane. The feed channel compartm ent of each subelement was assumed to be an ideal continuous-flow stir red tank reactor (CSTR). Model predictions correlated generally well w ith experimental observations. Predicted product water flow rates and solute concentrations were within 12 and 24%, respectively, of corresp onding experimental values.