Change of crystal size and interplanar spacing of CaCO3 in adherent and non-adherent scale by forced-convection heat transfer

A simple device to simulate circulating cooling water was used to study the dynamic reactions of two scale types. Water velocity, which ranged from 0.401 to 1.338 m/s, was adopted to study the effects on crystal size and interplanar spacing of adherent and non-adherent scale. The adherent scale was deposited on copper pipe surface. By using X-ray diffraction, the results suggest that the crystal size of calcite and aragonite in adherent scale increased by ca. 200–300 Å and 100–200 Å, respectively, when compared with that of corresponding non-adherent scale. As water velocity increased, the crystal size of adherent scale increased, while the crystal size of non-adherent scale remained essentially unchanged. Analysis of the change of crystal size and mass fraction showed that stronger hydraulic force was needed to remove calcite, as compared with the removal of aragonite. The data also confirmed that the interplanar spacing of adherent scale was smaller than that of non-adherent scale, as a result of saturation and temperature.