NUMERICAL SIMULATION OF DEPOSITION OF CALCIUM CARBONATE PARTICLES SUSPENDED IN THE TURBULENT COOLING WATER FLOW

Calcium carbonate is predominantly present in cooling tower's water and is usually the principal cause of hard water. This paper applies the modeling technique typically used for aerosol deposition to simulate the deposition process of calcium carbonate nano- and micro-particles suspended in turbulent cooling water flows. The mean turbulent velocity field and the fluctuating velocities are determined by the k-epsilon and RSM turbulence models by simulating the water flow in a typical heat exchanger horizontal tube. Commercial software (ANSYS FLUENT (TM) 12.1.4) is used for turbulence mean flow modeling and the simulation of turbulence fluctuations is performed by stochastic models. Particle deposition velocities are obtained for the particles with diameters in the range 0.01-50 mu m by the k-epsilon and RSM models and compared to the deposition velocities calculated from semi-empirical correlations to investigate the effect of the turbulence model on the deposition velocity. Results show that the proposed numerical model can predict deposition velocity of micro-particles in water accurately and can be useful in determining the range of particle diameters in which the highest deposition velocity occurs. However, for nano-particles, the model's results do not agree with the correlations due to the higher lateral turbulence fluctuations calculated by ANSYS FLUENT (TM) code. The proposed model can be useful for predicting fouling in industrial heat exchangers, for planning operations and cleaning schedules, and proposing efficient filtering processes for lowering deposition rate and cleaning costs.