Investigation of induction period and morphology of CaCO3 fouling on heated surface

The accumulation of unwanted crystalline deposits (fouling) reduces the efficiency of heat exchanger considerably. In order to mitigate fouling, many measures have been taken including the use of low-energy surface and antifoulant. In this investigation, the CaCO3 fouling experiments in both cooling water and pool-boiling systems were performed, the induction period as well as the removal of fouling was studied, and the fouling morphology was also investigated by scanning electron microscopy and atomic force microscopy (AFM). Compared with the copper surface, the self-assembled monolayers low-energy surface can prolong the induction period of fouling in the cooling water system. The induction period increases with decreasing initial surface temperature and fluid velocity. When the heat flux is fixed in different experiments, an increase in the fluid velocity will result in a decrease in the initial surface temperature. Under this condition, owing to the interactional effects between surface temperature and fluid velocity, the induction period increases with increasing fluid velocity. The removal experiments were carried out both in the induction period and in the post-induction period. The results show that only in the induction period can the fouling resistance be reduced owing to the weaker adhesion strength of fouling. In the presence of antifoulant polyacrylic acid (PAA), the crystal forms are changed and the fractal dimensions of CaCO3 morphologies increase for both the cooling water and the pool-boiling systems. AFM images show that the steps are bunched for CaCO3 formed in the pool-boiling system, and in the presence of PAA, the step spacing is widened compared to the case in the absence of PAA. (C) 2002 Elsevier Science Ltd. All rights reserved.