【作者】 常宝英；

【导师】 马重芳；

【作者基本信息】 北京工业大学 ， 热能工程， 2002， 硕士

【摘要】 结垢一直是工业上一个普遍令人头痛的问题，结垢会减少有效容量、降低生产效率、消耗燃料，从而造成巨大的经济损失。据调查，仅美国发电厂每年因冷却塔水垢问题导致的经济损失就高达100万美元。而我国每年因水垢引起的机件报废，直接损失也达十多亿元，而且污垢问题严重时甚至会危及人机安全。因此，对结垢问题的研究至关重要。现有的化学清洗方法不仅污染环境，而且会大大降低设备的使用寿命。但使用电磁场来进行减垢、抗垢时却可以避免这些问题，因而这一技术始终是研究者关注的重点。 本文仅从实验的角度来对电磁结垢、抗垢技术进行热态实验研究，概括起来，主要包括以下几项工作： 1、在原有的电磁抗垢、减垢实验装置上增设了换热段。 2、进行了系统检测实验，其中包括热态热平衡实验和单相管内强制对流换热实验，以便验证实验系统的可行性。 3、通过改变磁场频率、实验介质硬度等过程参数从污垢热阻以及换热系数的角度来进行了实验研究和理论分析。实验结果表明： (1) 没有经过电磁处理时，污垢热阻随着时间的增加而增加，换热系数随着时间的增加而减小；一旦经过电磁场的处理，污垢热阻开始时仍呈上升趋势，经过一段时间以后，便逐渐下降，换热系数的变化与此正好相反，即在实验开始时呈下降趋势，后来逐渐上升；当实验时间延长时，发现污垢热阻及换热系数在实验开始时的变化趋势与前面的实验结果基本相同，但到后来，二者的数值则分别均趋于稳定。 (2) 在其它实验条件不变的情况下，若仅改变电磁场的频率，发现当频率为700赫兹左右时除垢效果最佳。 北京工业大学工学硕士学位论文一 （3）在其它实验条件不变的情况下，发现污垢热阻随着硬度的增加而增力口。 4、在循环实验中分别将经过电磁处理的污垢晶体和未经过电磁处理的污垢晶体在扫描电镜下进行观察和分析后发现，电磁抗垢技术的机理的本质在于电磁技术改变了污垢晶体的形态，即由结构致密型易结垢的霸石改变为结构松散型不易结垢的方解石，这一结论与冷态实验研究的结论一致。更多还原

【Abstract】 Fouling is a difficult problem in the industry all the time, because it reduces effective capacity, decreases productivity, consumes the fuel and accordingly results in tremendous economic loss. It is investigated that the economic loss that fouling of cooling tower of power houses causes every year in the Unite States is one million dollar and the direct loss which work reject caused by scale every year in China induces is more ten hundred million. Furthermore, fouling even endangers the safety of people and machine. So it is very important to study descaling. However, the existing chemical cleanout not only causes pollution, but also reduces the nature life of equipments. Electronic anti-fouling technology does not bring these problems, so researchers give it more attention.This paper performs the thermal experiment about electronic anti-fouling. The primary work is as following.1 > A heat transfer test section is designed and established on the basis of the existing experimental device of Electronic Anti-fouling .2> Some preparative experiments which include thermal balance experiments and forced convection heat transfer tests in the circular tube are done in order to validate the feasibility of the experimental system.3 ? We did the experiments and academic analysises from the point of view of fouling resistance and heat transfer coefficient by changing the coefficients such as the frequency of magnetic field, hardness of experimental liquid and so on. The experimental results are as follows:(1) Without EAF the fouling resistance increase along with addition of timeand change of the heat transfer coefficient is just contrary to the result. However, with EAF fouling resistance still enhances at the beginning of experiment and later, it gradually minishes after experiment has started for some time. Of course, the change of heat transfer coefficient still is contrary to the outcome. But when experiment lasts longer time, fouling resistance and heat transfer coefficient change in the same trend as the fore results at the beginning of the experiment. However, They all go to the tranquilization until the last.(2) Under the same experimental condition as ever but changing the frequency of magnetic field, we discover that descaling is the best when the frequency of magnetic field is 700 Hz.(3) Under the same experimental condition as ever but changing hardness of experimental liquid, we discover that fouling resistance reduces along with the increase of hardness of experimental liquid.4 According to the observation of scale specimen under a scanning electron microscope, we discover that the mechanism of electromagnetic anti-fouling is to change the shape of fouling crystal. In other words, harder and denser aragonite is changed into incompact calcite under the action of magnetic field. The conclusion is consistent with the past experimental results.更多还原