Experimental Study Of Characteristics Of Composite Fouling On Spirally Corrugated Surface

Fouling, as a universal phenomenon in the industrial heat transfer equipment, would cause extreme waste of energy because of the decreasing of the heat transfer efficiency. Thus, it will be much meaningful to study the fouling characteristic of heat transfer surface. Enhanced surface was used in heat transfer equipment widely, and the surface condition has an important influence on the fouling process. The fouling characteristic of spirally corrugated surface often used as a common type of enhanced surface should be investigated in further research. Based on previous work the experimental study of fouling characteristics on spirally corrugated surface was carried out in this paper. The main results are as follows:The effects of spirally corrugated tube's geometric parameters on the crystallization characteristic were investigated by the dynamic monitoring apparatus. The influences of cold water hardness, temperature, velocity on fouling formation were experimentally studied. The results indicated that when the temperature was low, the fouling rate and the fouling resistance increased, and the fouling induction period decreased with increased water hardness. But when hardness got to a limition, the fouling resistance began to decrease. Moreover, when the temperature was high, the fouling resistance for spirally corrugated tubes changed more notable than normal temperature. As the temperature rose, the induction period tended to disappear and the fouling resistance would relevantly increase. When speeding up of water flow, the induction period increased, the fouling resistance and fouling rate reduced at the same time. Furthermore, the fouling resistance and fouling rate increased as the pitch increased. However, the deepening of groove brought on the increase of fouling rate and the decrease of fouling induction period, meanwhile the fouling resistance tended to decrease. Comparing with smooth tubes, the geometric structure had much more complex effect on fouling characters as the flow became confused.Further, experimental study had been done on the MgO particulate fouling and the composite fouling of MgO and CaCO3 in smooth tube and spirally corrugated tubes. As the results indicated, for particulate fouling, the fouling induction period became reduced, and the resistance increased with the increased concentration. As the temperature increased, the fouling rate increased resulting in higher resistance. For spirally corrugated tubes, the fouling induction period increased as the pitch increased, at the same time, the fouling rate and the fouling resistances increased, moreover the resistances were all above those of smooth tubes. For composite fouling, the fouling induction period was not so obvious, the fouling rate and the resistance both increased with the increasing of concentration. As the temperature increased, the fouling rate increased notably, the fouling resistantance increased and approached the asymptotic fouling resistance rapidly. However, there was little difference between the resistances of spirally corrugated tubes and smooth tubes. When the temperature was low, the composite fouling resistance was greater than both particulate and crystallization fouling; the crystallization fouling resistance was the smallest. When the temperature was high, the fouling rate of the composite fouling was the greatest in the initial period; meanwhile, its fouling resistance was the greatest. The crystallization fouling resistance increased most notably as the temperature increased. The result indicated that the comprehensive effect of concentration of fouling ion solution, impurity particles and temperature on fouling process was much more prominent.