Modeling liquid-side particulate fouling in internal helical-rib tubes

This paper provides accelerated particulate fouling data in five 15.54 mm I.D. copper, helically ribbed tubes taken at different concentrations and velocities. The ranges of geometric parameters were number of rib starts (18–45), helix angle (25–45°), and height (0.33–0.55 mm). Aluminum oxide particles with 3.0μm average particle diameters were used as foulant. These geometries provide a new class of internal enhancement that is typical of commercially enhanced tubes presently used in water chillers. A semi-theoretical model is developed. The model, with experimentally determined efficiency index [(j/jp)/(f/fp)[(j/jp)/(f/fp), where j=StPr2/3j=StPr2/3, the ff is a friction factor, the subscript pp refers to smooth surface] by the tube manufacturer, can predict the fouling behavior of helically ribbed tubes. There are two series of correlations of the ratio of fouling factor based on different reference tube: linear correlation and nonlinear correlation. The ratio of enhanced-to-plain tube fouling factor nonlinearly increases with increasing the efficiency index and the ratio of the enhanced-to-enhanced tube 4 fouling factor linearly increases with increasing the efficiency index. The enhanced tube 4 with number of rib starts (10), helix angle (45 °), and height (0.43 mm) is the most popular helically ribbed tube in current operating chillers.The semi-theoretical analysis of dividing a fouling factor ratio into a fouling process index and an efficiency index significantly simplifies the fouling analysis.