Mechanisms for the removal of calcium phosphate deposits in turbulent flow

This work investigates the mechanisms for the removal of calcium phosphate deposits from stainless steel tubing in turbulent flows. Two types of depos its were analyzed: brushite (dicalcium phosphate dihydrate, DCPD) and a mix ture of DCPD/hydroxyapatite (HAP). Cleaning studies were carried out at pHs ranging from 2.85 to 10. The data were analyzed by means of a mathematical model that incorporates the effects of interfacial dissolution and mass tr ansfer. The results show that the HAP/DCPD cleaning rate is influenced both by the kinetics of the interfacial dissolution and by mass transfer. Withi n the same range of experimental conditions, the rate-limiting mechanism fo r DCPD removal was the abrasion of the solid by shear stresses. In this cas e, the interfacial dissolution process plays the role of decreasing the str uctural integrity of the deposit. These findings show that the removal mech anism of the HAP/DCPD mixture differs significantly from the behavior of in dividual components.