Modeling oscillatory fouling in enhanced tubes in cooling tower systems

摘要

This paper is concerned with the development of a new approach to model the fluctuation of fouling in general. The proposed modeling concept is to split a property into a mean variable and a fluctuating variable. The goal is to investigate the oscillatory characteristic of fluctuating fouling resistance. Long-term fouling data collected from seven 15.54 mm ID copper, helically ribbed tubes with water velocity at 1.07 m/s in a cooling tower system were used to present oscillatory behaviors. An uncertainty analysis indicates that a minimum water temperature difference of 3.0℃ between inlet and outlet of each test tube is needed to observe the oscillatory behavior of fouling data. The frequency of fluctuation is independent of tube interior geometries on which fouling deposit develops; the amplitude of fluctuation is related to tube interior geometries and is a function of the ratio of rib pitch to rib height. There are two ranges of amplitude of fluctuation of fouling characteristics based on internal dimensions: linear range and non-linear range. A series of semi-theoretical amplitude correlations as a function of the ratio of rib pitch to rib height were developed. They were applicable to different internally ribbed geometries within the dimensional range in the study.