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| Analysis of in tubes particulate fouling characteristic |
| LI Hong-xia, LI Guan-qiu, LI Wei |
| Department of Energy Engineering, Zhejiang University, Hangzhou 310027, China |
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Abstract In order to discover the fouling characteristic inside enhanced tubes, the particulate fouling tests including one smooth tube and three internal repeated rib tubes with different geometry designs were carried out. Foulant in the particulate fouling tests was aluminum oxide and ferric oxide, which had an average diameter of 1.75 μm and 2.11 μm, respectively. The foulant concentration was about 1500 mg/L and the heat flux in the test section was about 13 kW/m2. The experimental results show that the plane tube has the smallest fouling resistance, and the next is rib tube of product code 30/10, 30/20, 15/10. A semi-theoretical model was developed to investigate the main factors of particulate fouling formation from the fouling tests. The fouling model which started from the mass balance model considered the influences of the mass transfer coefficient, wall shear stress, sticking probability and deposit bond strength factor. The model analysis results fit the experimental data well. After some simplifications, the 2D numerical models for the experimental tubes were established, in which volume-control method and standard k-ω model were used. To explain the diversity of anti-fouling performance in different tubes, the influences of velocity field near wall and wall shear stress to the particulate fouling deposition were also discussed. It is found that that the fouling resistance decreases with the increase of the wall shear stress which is affected by the fin distance. The numerical results had reasonable deviations with the experimental data.
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Published: 01 September 2012
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管内颗粒污垢特性分析
为了研究强化管管内污垢特性,选取一组直肋管与光管管内颗粒污垢实验进行了分析,对光管和不同几何设计的3种内置直肋管进行了研究,实验所用颗粒为氧化铝和氧化铁颗粒,平均直径分别为1.75 μm和2.11 μm,质量密度约为1 500 mg/L,实验段的热流密度约为13 kW/m2.实验发现,光管的污垢热阻渐进值最小,其次是型号为30/10,30/20,15/10的直肋管,为此建立了一半理论化模型,对影响颗粒污垢形成的主要因素进行了研究.污垢模型从最常用的质量平衡模型出发,分别讨论了质量传递系数、壁面剪切应力、黏附几率、污垢抗分散强度的影响因素,理论模型与实验结果吻合良好.另外,在进行相应简化后,对实验相应管型进行了二维数值分析，数值分析采用控制容积法和标准kω模型.为解释不同管型在抗垢性能上的差异,讨论了不同管型的近壁面流场分布以及壁面剪切应力对颗粒污垢沉积的影响,发现壁面剪切力越大,污垢热阻值越小,而肋间距是影响壁面剪切力的重要几何参数.数值模拟结果与经验公式和实验结果相比也有合理的偏差.
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