两种斜翅管表面碳酸钙垢初始阶段结垢特性

进行了3种强化管在不同碳酸钙溶液浓度和流速下的动态结垢实验,得到碳酸钙浓度、流速和不同管型对碳酸钙析晶垢结垢过程的影响.结果表明,碳酸钙浓度增大,使溶液中均相成核速率和所形成晶核的生长速率增大,使溶液换热表面界面的污垢晶粒浓度和成垢离子浓度均增大,前者使更多的污垢附着换热面,而后者使表面异相成核速率和生长速率增大.流速增大,使光管表面形成的晶核、污垢晶体和污垢热阻均减少,而诱导期延长;使平直和锯齿斜翅管初始成核增多,但诱导期延长,而结垢量和污垢热阻减小.平直和锯齿斜翅管在清洁状态和结垢状态下均具有比光管更大的总换热系数、更小的污垢热阻,尽管结垢量略多.在相同结垢状态下,锯齿斜翅管的结垢量和污垢热阻大于平直斜翅管的,但是,其总换热系数仍大于平直斜翅管.

Characteristics of the Initial Stage of CaCO3 Crystallization Fouling on Two Kinds of Oblique Fin Tube

To investigate the effect of CaCO₃ concentration and velocity on CaCO₃ scaling fouling process on plain,straight oblique and saw-tooth oblique fin tubes,experiments were done at different CaCO₃ concentration,velocity and surface parameter of the three kinds of tubes.The results show that the homogeneous nucleation rate and the growing rate both increase when CaCO₃ concentration increases.This makes the scaling particle concentration and fouling ion concentration increase,the former leads to more scaling on tubes and the later enlarges the heterogeneous nucleation rate and growing rate.Higher velocity decreases the nucleation of scaling,scaling crystal and fouling resistance,but it can prolong the induction period.Higher velocity increases nucleation rates on straight oblique fin tube and saw-tooth oblique fin tube,but the induction period extends and the mass of scaling and fouling resistance decrease.Straight oblique fin tube and saw-tooth oblique fin tube have bigger heat transfer coefficient than plain tube under both clean and fouling conditions in despite of smaller fouling resistance and a little more scaling.Under the same condition,saw-tooth oblique fin tubes have bigger heat transfer coefficient and fouling mass than straightoblique fin tubes,but the total heat transfer coefficient is bigger than that of straight oblique fin tubes.