Numerical analysis of cooling tower water fouling in enhanced tubes

This paper provides particulate and precipitation fouling data in five 15.54 mm I.D. copper, helically ribbed tubes taken at the condition of Re=16000 and 800 ppm concentration. The geometries of the helical-rib tubes provided a class of internal enhancement that is typical of commercially enhanced tubes presently used in water chillers, and the ranges of geometric parameters were number of rib starts (10 to 30), helix angle (25 to 45), and height (0.40 to 0.55 mm). A semi-theoretical model was developed to investigate the main factors of fouling formation from the fouling tests. The fouling model which started from the mass balance model considered the influences of the mass transfer coefficient, wall shear stress, sticking probability and deposit bond strength factor. The model analysis results fit the experiment data well. 3D numerical models for the experimental tubes were established, in which volumecontrol method and standard k-ω model were used. To explain the diversity of anti-fouling performance in different tubes, the influences of velocity field near wall to the cooling tower fouling deposition were also discussed. It is found that the fouling resistance increases with the increase of the number of starts and helix angle. The numerical results had reasonable deviations with the experimental data