Experimental Study On Heat Transfer And Fouling Characteristics Of Spirally Corrugated Tube

Fouling, as a universal phenomenon in nature, exists in a wide range of various fields in the social production and daily life, especially in the industrial heat transfer equipment. So we must take into account the effect of fouling factors when using the enhanced heat transfer technology because of the low thermal conductivity of fouling. Therefore, it will create very important practical significance that we carry out the experimental study on the fouling characteristic of enhanced heat transfer surface. In view of this, this thesis investigated the work effect of different kinds of spirally corrugated tubes of different geometries from the two aspects, heat transfer and fouling characteristics.First of all, on the basis of theoretical calculation for the spirally corrugated tubes before, we chose a trustworthy empirical formula, and investigated the heat transfer characteristics of spirally corrugated tubes associating with the experimental data. Then comparing of the results of theoretical calculations and experimental data, it indicated that the error in heat balance of hot and cold water were both less than 10%, thus it can be seen the experimental data was trustworthy.Secondly, we studied the heat transfer effect of spirally corrugated tubes at different water flow rate and inlet temperature of cold water, and then we found that heat transfer coefficient of spirally corrugated tubes is about from 0.94 to 1.45 the smooth tubes, decreases as the pitch increases, and increase with the groove depth. At the same time we investigated the effects to the fouling characteristic in the four kinds of spirally corrugated tubes, which hardness, fluid velocity, and temperature of cold water produced, through experimental research on the dynamic monitoring apparatus. The tests showed that the fouling resistance in the surface of the spirally corrugated tubes also increased when the water hardness increased from 300mg/L to 500mg/L , but when the water hardness reached 750mg/L, the thermal resistance was below the one when the hardness is 500mg/L, and the temperature of cold water rose from 22.5℃to 44℃, the fouling resistance would relevantly increased; When speeding up the cold water velocity from 1.2m/s to 1.64m/s, the fouling resistance would reduced accordingly, but when the velocity slow down from 1.2m/s to 0.9m/s, the fouling resistance in the surface of certain kinds of tubes would also reduced. Meanwhile, this paper took an analysis for the geometric parameters of spirally corrugated tubes. It concluded that the fouling characteristics of different kinds of spirally corrugated tubes varied differently along with the change of geometric parameters under the same condition. As a result, we found that the spirally corrugated tube (P = 3mm, e = 1mm) had the best performance in heat transfer and fouling resistance under our experimental conditions. Finally, we compared fouling resistance of the spirally corrugated tubes and the smooth tubes under the same condition, then it turned out that it was the geometric structure of spirally corrugated tubes affected the flow field and temperature field quite evidently, while the fouling characters reflected differently completely, at a high temperature and high hardness, the anti-fouling characteristics of spirally corrugated tubes were much more obviously, and the fouling resistance should be able to reach 51.9 %. However, for some kinds of tubes, it stimulated scaling on the heat transfer surface.