Abstract:

In order to study the scale-resisting properties and scale-resisting mechanism of spirals inserted in tubes, the effects of three spirals inserted into heat exchange tubes at different flow rates on fouling thermal resistance and total heat transfer coefficient were experimentally studied. Meanwhile, the particle size and porosity of fouling were quantitatively characterized from a microscopic perspective to obtain the microstructure distribution of fouling. The results show that, under the experimental conditions, with the increase of flow velocity, the fouling resistance of the interpolation spiral decreases by 63%, the heat transfer coefficient decreases by more than 20%, and the interpolation spiral with a pitch of 20 mm has the best scaling performance. The particle size and porosity of dirt gradually increase from the near wall area to the surface area, and there is a clear crystal transition feature between the dirt layers. The porosity of the surface area and transition area of the fouling layer increases with the increase of flow velocity, and the change of the internal structure of the fouling by the characteristics of the interpolation spiral flow field is the fundamental reason for the difference in scale-resisting properties.

Key words: fouling, spiral insert, scale-resisting properties, microstructure, heat transfer, porosity

摘要：

为研究管内插螺旋阻垢性能及阻垢机理，实验研究了不同流速下换热管内插三种螺旋对污垢热阻、总传热系数的影响，同时从微观角度，对污垢粒径、孔隙率进行量化表征得到污垢微观结构分布规律。结果表明：在实验条件范围内，随流速增大内插螺旋污垢热阻渐进值最大降幅为63%，传热系数稳定值较未结垢时均降低20%以上，且节距为20 mm的内插螺旋具有最好的除垢性能；污垢从近壁面区到表面区粒径、孔隙率逐渐升高，污垢层间具有明显晶型过渡特征；污垢层表面区与过渡区孔隙率随流速增大进一步增大，内插螺旋流场特征改变污垢内部结构是阻垢性能出现差异的根本原因。

关键词: 结垢, 内插螺旋, 阻垢性能, 显微结构, 传热, 孔隙率