【作者】 张仲彬；

【导师】 徐志明；

【作者基本信息】 华北电力大学（河北） ， 热能工程， 2009， 博士

【摘要】 换热设备污垢是工业生产中普遍存在的问题。由于污垢形成过程极其复杂，影响因素众多，而且污垢严重影响传热效率，造成能源的极大损失和浪费。因此，成为传热学界十分关注而又没能完全解决的主要问题之一。本文对换热表面的碳酸钙污垢进行了较为系统的研究。概括起来主要有以下几方面工作：首先，建立了污垢实验台，采用对比实验的研究方法，测试了四种强化管（弧线管、波纹管、缩放管Ⅰ和缩放管Ⅱ）在清洁状态下的传热特性和阻力特性，分别得出管内强制对流换热关联式和阻力关联式。然后利用配置不同硬度的人工硬水或添加氧化镁颗粒的溶液作为循环工质，在相同流速、管外水浴温度、管内工质入口温度的条件下，分别对上述四种强化管与各自对应光管进行了污垢特性的对比实验，得出了各自污垢热阻和诱导期随时间的变化关系。实验结果表明，四种强化管具有结垢速度慢、诱导期长、污垢热阻渐近值小等优点，而且在结垢前后都具有良好的强化传热性能。其次，本文对几种材料表面的粗糙度、接触角、表面能、材料表面与液体之间的界面能进行了测量和计算。考察了上述几种表面特性参数对污垢形成的影响。同时，对几种不同固体材料表面在清洁和结垢条件下作了图像分析。研究结果表明材料表面特性对污垢形成有较大影响，材料的表面能越低，污垢沉积量越小。而粗糙度、接触角、固体材料与液体间的界面能对污垢形成的影响没有找到明显规律。最后，本文应用计算流体力学软件，对圆管内的CaCO₃污垢形成过程进行了数值模拟。根据CaCO₃的浓度变化，得到CaCO₃析晶污垢的沉积率、剥蚀率随时间的变化规律。在不考虑污垢诱导期的情况下，得到污垢热阻随时间的变化规律。模拟结果和实验数据吻合得较好，证实了模拟结果的可靠性。更多还原

【Abstract】 Heat exchanger fouling is a common problem in industry. Fouling deposition is usually very intricate process, as there are lots of factors affecting the fouling accumulation. It affects on heat transfer, and causes the extreme waste of energy and economic losses. So fouling has aroused peoples’ attentions in the domain of heat transfer but is still an unsolved problem. This dissertation discussed the fouling process of calcium carbonate on heat transfer surface. A series of theoretical and experimental studies were carried out systematically in this work. The main achievements of the dissertation are as follows:Firstly, an on-line monitoring apparatus of fouling thermal resistance was developed. Tests had been undergone to achieve the heat transfer and friction performances of four types of enhanced tubes （arc line tube, corrugated tube, convergent-divergent tubes I and convergent-divergent tubes II） under clean conditions. Dimensionless correlations for forced convection heat transfer and friction factor inside the above four types enhanced tubes were obtained from the test results. Moreover, the comparative fouling experiments were carried out between the above four types enhanced tubes and their respective corresponding plain tubes. The experimental working fluid was man-made hardness water or MgO particles solution, and the experiments were done under the conditions of the same liquid velocity, temperature at the water tank outside the tubes and inlet temperature of the working fluid inside the tubes. The relations between fouling resistances of all these tubes and time were gained from the results of the comparative fouling experiment. The experimental results showed that four enhanced tubes had lower deposition rate, longer induce period and smaller asymptotic fouling thermal resistances. Moreover, four enhanced tubes significantly enhanced the heat transfer under both clean and fouled conditions.Secondly, the formation of fouling is closely related with the characteristic of heat transfer surface. So the parameters of surface, such as surface roughness, contact angle, surface energy and interfacial energy were measured and calculated. The effects of all these parameters on the formation of fouling were studied by the fouling experiments of several different types coat surfaces. At the same time, the SEM micrographs of surfaces were analyzed on clean and fouled condition. The experimental results showed that there was an important impact of the material’s surface energy upon fouling formation, but there was not distinct regularity in other parameters. Overall, low surface energy of coat surfaces had advantage in anti-fouling effect.Finally, the numerical simulation of CaCO₃ fouling was carried out by using the CFD software to plain tube. Base on the change of CaCO₃ concentration, the deposition rate and the removal rate of the CaCO₃ fouling with time were achieved. By ignoring the induction period, the fouling resistance with time was also obtained from the fouling sediment mass. At the same time, in order to confirm the correctness of the computed results, the experimental confirmation was carried out, and predicted values agreed with the computed results.更多还原