Numerical simulation and experimental study of the growth characteristics of particulate fouling on pipe heat transfer surface

The problem of particulate fouling accumulating on the heat exchange surface in urban effluent still exists after secondary treatment which deteriorating the heat transfer performance and increasing operational cost. Therefore, it is significant to study the fouling mechanism of particulate fouling on the inner wall of heat exchange tube. In this paper, the effects of flow velocity, particle concentration, inlet temperature, particle size, roughness of pipe wall, viscosity of working fluid and type of particle on the thermal resistance and fouling rate of particulate fouling were investigated by numerical simulation and experimental methods. The results show that the working fluid velocity, particle concentration and particle size are three significant factors that affect the thermal resistance of particulate fouling. The increase of flow velocity causes the asymptotic value of fouling thermal resistance to decrease, while the increase of particle concentration and particle size causes it to increase. To slow down the fouling rate, the flow velocity and inlet temperature should be increased, while the particle concentration, particle size, roughness of pipe wall and viscosity of working fluid should be decreased. The net deposition rate of particles on the heat exchange surface increases with the increasing particle density. However, the effect of particle type isn’t definite, the fouling rates and asymptotic values from small to large are MgO, CaSO4, CaCO3 and SiO2 in this study, which does not increase with the increase of density. The synergistic effect of different kinds of particulate fouling make the asymptotic value of mixed fouling thermal resistance decrease, but it is also related to different particle properties.