Experimental Study of the Particulate Dirt Characteristics on Pipe Heat Transfer Surface

The systematic study of the particulate dirt characteristics on heat exchanging surface can provide theoretical guidance for defouling. In this paper, four main compositions of particulate dirt in the treated city sewage (i.e., CaCO3, MgO, CaSO4 and SiO2) are selected as the research objects. The effects of different working conditions, characteristics of particles on the growth rules of particulate dirt and the synergistic fouling by different particles are researched by thermal resistance method experimentally, while the microstructures of the dirt are observed by Scanning Electron Microscope (SEM). The asymptotic values of both dirt thermal resistance and the scaling rate decrease with the increasing of working fluid velocity, while the two asymptotic values increase with the increasing particle size and particle concentration. Although the working fluid import temperature shows a weaker influence on the thermal resistance, but the increase of working fluid import temperature can retard the fouling rate. Among the stable values of the thermal resistances of four types of fouling, SiO2 is the largest and MgO is the smallest. The synergistic fouling by different types of particles results in the denser structure of mixed fouling.