Abstract
Partial differential equations were developed to model material and momentum balances inside a hollow fine reverse osmosis (RO) fibre. Equations were discretized by orthogonal collocation. An approximate analytical solution was obtained by applying the one point collocation method in the radial and the axial directions. Simple expressions were then derived for the recovery and product concentrations. Results were compared with those obtained by using a higher order collocation method. Application of the results to the design and operation of RO plants is discussed.