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本实验对不锈钢管内CaCO_3污垢的沉积过程进行了分段研究。测得传热系数后,获得了污垢热阻,并用电镜扫描(SEM)获得了污垢分布随时间的变化.实验结果表明:在不锈钢管内CaCO_3污垢沉积的初始阶段,传热系数增大而非减小,出现负污垢热阻,说明CaCO_3污垢初始阶段的沉积有利于传热,经过一段时间的沉积后才会出现正污垢热阻。电镜扫描(SEM)结果表明,污垢沉积的初始阶段,污垢结晶以星状点分布于管内壁,随着沉积时间的增长星状点变得密实,这种不完全覆盖使得流体在流经污垢时产生扰流,增强了传热效果。随着时间推移,结晶污垢的覆盖面积逐渐增大,污垢热阻逐渐增加,传热系数减小。
In this experiment, the deposition process of CaCO_3 in stainless steel tube was studied in different stages. The measured heat transfer coefficient obtained the fouling resistance and the change of fouling distribution with time by SEM.The experimental results show that in the initial stage of CaCO_3 fouling in stainless steel tube, the heat transfer coefficient increases rather than decreases Small, there is a negative fouling resistance, indicating that the initial stage of CaCO_3 fouling deposition is conducive to heat transfer, after a period of deposition will appear after the fouling resistance. Electron microscopy (SEM) results showed that in the initial stage of fouling, the fouling crystals distributed in the inner wall of the tube with star-shaped dots. As the deposition time increased, the star-shaped dots became dense. This incomplete covering made the fluid flow through the fouling Produce spoiler, enhance the heat transfer effect. With the passage of time, the coverage area of crystalline fouling gradually increases, the fouling thermal resistance gradually increases, and the heat transfer coefficient decreases.