THE USE OF FRACTAL DIMENSION TO QUANTIFY THE EFFECT OF SURFACE ROUGHNESS ON FILM MASS TRANSFER ENHANCEMENT

Experimental results from previous work, contained in a companion paper by Van Vliet and Weber (1988), have shown qualitatively that the external film transfer coefficient for adsorption on particulate adsorbents is very dependent on the roughness of the mass transfer surface. Until recently a suitable method to quantify surface roughness was not available. Experimental data of film mass transfer coefficients of various activated carbons, carbonaceous adsorbents, and polymeric adsorbents are investigated. It is shown that film mass transfer is enhanced by the effect of surface roughness. The fractal dimensions of the adsorbent particle surfaces are determined and are shown to be linked to the degree of mass transfer enhancement. This suggests that the external mass and heat transfer enhancement properties of a rough surface are related to its fractal dimension.