A predictive model of hollow fiber reverse osmosis systems is developed using the equivalent annulus assumption. The fraction of feed recovered Φ depends on five parameters. Optimum values exist for the ratio of the inside to outside fiber radius ri/ro and for the outside fiber radius ro. For dilute systems, a simple closed form expression is obtained for Φ which enables one to determine optimum values easily.

The effects of pressure, temperature, flow rate, concentration, viscosity of the feed, system length, membrane rejection parameter, and number of fibers are studied. Countercurrent is superior to concurrent operation.