Abstract:

In this research, the mechan ism of scale controlling by ultrasonic was revealed through the crystal dynamics and the investigation into the in fluence of ultrasonic on the shape and size of CaCO₃. The results show that the nucleation induction period of CaCO₃ crystals is shortened and the formed velocity of crystal nuclei is inc reased by ultrasonic, which causes a great number of minicrystals promptly to suspend in solution. And, the growth velocity of the crystal is decreased and the deposition of the scale on pipe well is prevented, thus decreasing the amount of scale. Moreover, the cavitation and mechanic l function of ultrasonic result in the increase of scale solubility, destroy the formed scale and make the scale soft fall off. In addition, ultrasonic radiation changes the shape, the size of CaCO₃ crystal and the pileup form of the scale, thus preventing the pipeline from begriming. Experiments in a mill indicate that ultrasonic treatment can not only prevent the scale formation but also remove the formed scale, with an average efficiency of scale controlling up to 76. 4%. Thus, the evaporation in tensity and heat transfer coefficient of the evaporation system is improved.

Key words: ultrasonic, crystal dynamics, calcium carbonate, evaporation intensity, scale controlling