Fouling in enhanced tubes using cooling tower water Part II: combined particulate and precipitation fouling

This work addresses fouling in a family of seven internally helically ridged tubes, which have different ridge heights, helix angles, and a number of ridge starts. Of specific interest are long term, combined precipitation and particulate fouling (P&PF) in cooling tower systems, and accelerated particulate fouling. The comparison of the P&PF and accelerated particulate fouling data shows a unique relationship. This allows one to infer the relative long-term P&PF performance of different enhanced tube geometries from accelerated particulate fouling data. For a small number of ridge starts (less than 25) and helix angles below 35 degrees, the fouling resistance is proportional to the heat transfer coefficient (or the mass transfer coefficient, via the heat-mass transfer analogy). However, for a large number of starts and high helix angles (e.g., 45 degrees), the fouling factor is considerably higher than one would predict, based on the mass transfer coefficient. It appears that this occurs because of low shear stress (affecting the foulant removal rate) in the interfin region. Recommendations are offered on geometries that will avoid high fouling penalty. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.