The objective of the present paper is to validate experimentally the mass transfer simulations presented in a previous paper by the same authors [J. Membr. Sci. 208 (2002) 289]. In the present study, mass transfer coefficients were obtained by the limiting current method. The results from CFD simulations were successfully validated by experiments. The experiments confirm that the geometric parameters of spacers have a considerable influence on mass transfer at a given cross-flow power consumption. Comparison of the experiments with different non-woven spacers shows that there is an optimal spacer geometry, which agrees with those of the optimal spacer obtained by CFD simulations. The experiments also indicate that the woven and non-woven spacers perform equally well. Since all commercial net spacers investigated in this study had non-optimal spacer geometries, they showed lower mass transfer coefficients at a given cross-flow power consumption than the optimal spacer. (C) 2003 Elsevier B.V. All rights reserved.