Microscopic Study of CaCO3 Scaling on Heat Transfer Surfaces.

Abstract

For the purpose of obtaining essential information on scaling in heat exchangers, microscopic observations were made for CaCO3 deposition from a flowing solution onto initially clean heat transfer surfaces. The growth rates of CaCO3 crystals were measured by changing the Reynolds number and supersaturation degree of the bulk solution, materials and temperature of the heat transfer surface. The growth rate was found to be relatively well correlated with the supersaturation degree of the solution adjacent to the surface, deduced from the equilibrium relationships between the species in the calcium carbonate solution. The nucleation rate was also estimated by measuring the change of the cumulative number density of deposited crystals against time. The crystals were formed on the surface at a constant nucleation rate over time, but the factors which dominate the nucleation rate could not be determined.