论由循环水动态模拟试验估算极限污垢热阻

在大量动态模拟试验的基础上,分析了采用Kern—Seaton模式,以试差法求解极限污垢热阻R_f~*的任意性问题。提出用一个可进行线性回归的、能反映出诱导期的指数函数R_f=R_f~*e-A/t-to,来描述污垢增长的规律。经将60轮动态模拟数据用TI—59可编程序计算器处理表明,这个指数函数比Kern—Seaton的R_f=R_f~*(1-e-Bt)更符合实验数据。采用新的模式,就能由实验所得的R_(f1)和相应的t_i直接计算出极限污垢热阻R_f~*。     

板式换热器冷却水污垢热阻预测的偏最小二乘回归法

搭建板式换热器冷却水污垢热阻实验台,测得不同时间、流速和温度下天然循环冷却水（松花江水）中铁离子、氯离子、细菌总数、pH值、溶解氧、浊度、电导率等水质参数,随机取一组实验的水质参数作为输入变量,建立换热器冷却水污垢热阻预测的偏最小二乘回归模型,对板式换热器的污垢热阻进行预测。整个实验过程中,热水进口温度为43.5～44.5℃,冷却水进口温度为21.5～22.5℃,流速为0.104 m·s-1,当温度和流速发生变化时,则重新采取数据。经过计算,确立本模型应提取4个潜变量,由此建立了板式换热器冷却水污垢热阻预测模型。预测结果和实验结果最大相对误差在5.11%以内。结果表明偏最小二乘回归算法的污垢模型预测精度高,所建预测模型是合理可行的。     

入口温度对换热器污垢热阻的影响及其修正

为提高污垢热阻测量精度,在分析污垢热阻温差监测法的基础上,研究了循环冷却水入口温度对换热器污垢热阻的影响。通过对污垢热阻测量模型参数进行推算,利用最小二乘法原理对污垢热阻数据进行处理,确定了在线测量污垢热阻的修正方法。修正前污垢热阻数据表明了循环冷却水入口温度与换热器污垢热阻之间呈反比例的关系。针对无垢和有垢两种情况,分别对污垢热阻测量模型进行了修正,结果表明:对于某电厂现场数据和实验室数据,修正效果均使污垢热阻测量值更加准确,证明了修正公式的可靠性。     

冷却水系统中的污垢热阻及金属腐蚀速度的在线监测

研究了冷却水系统中污垢热阻及腐蚀速度的在线监测方法;研制了能模拟冷却水流动和传热状态,并消除自腐蚀电位漂移和溶液IR降影响的冷却水污垢热阻及腐蚀速度在线监测装置;同时开发出相应的软件使整个测量和数据处理过程实现了计算机自动控制。实验结果表明:该装置能真实地在线反映换热器结垢和腐蚀变化情况。     

Ca2+环境下水质参数变化对板式换热器铁细菌微生物污垢的影响

换热设备微生物污垢形成机制和影响因素复杂,污垢数据和规律的获取难度较大。本文采用搭建的板式换热器循环冷却水实验系统,获得了加入Ca²⁺后板式换热器冷却水铁细菌微生物污垢热阻数据,研究了加入Ca²⁺后不同运行工况下冷却水水质参数（OD、pH、电导率）的变化,进一步分析了水质参数变化对微生物污垢生长带来的影响。结果表明,加入Ca²⁺后微生物污垢热阻渐变化明显。随着低温循环冷水进口温度增加,含有Ca²⁺和铁细菌的循环冷却水OD逐渐降低,pH则逐渐升高,电导率减小,微生物污垢热阻逐渐降低;随着流体速度的增加,循环冷却水OD则升高,pH降低,电导率增大,但流速的增大同样加剧了冷却水对通道壁面的剥蚀作用,导致微生物污垢热阻随流速增逐渐下降。     

Ca~(2+)环境下板式换热器微生物污垢特性

为了研究Ca2+环境下微生物的污垢特性,通过人工配比方法加入Ca Cl2与铁细菌,对板式换热器循环冷却水系统在不同温度、速度和铁细菌浓度下的污垢特性进行了实验研究。结果表明:在Ca2+环境下污垢热阻高于纯铁细菌污垢热阻,且温度越高污垢热阻渐近值越小,流体速度越大污垢热阻渐近值越小,铁细菌浓度越大污垢热阻渐近值越大。     

介绍一种冷却水污垢沉积评价装置—FEU

<正> 美国Nalco化学公司最近介绍一种冷却水系统现场污垢评价装置——FEU。它可用来测定污垢量、污垢类型及污垢热阻。并且也能分析微生物的种类。用以对冷却水系统加药处理效果的评价,并能同时与空白水进行对比。作为评定配方试验用。     

再论由循环水动态模拟试验估算极限污垢热阻

一、引言动态模拟试验是评选冷却水化学处理配方和研究传热与表面污垢问题的主要手段。鉴于用Kern—Seaton 模式,以两点法求解极限污垢热阻的不足,前文已经     

水质参数对交叉缩放椭圆管污垢的影响

采用对比的实验方法对交叉缩放椭圆管与光管的污垢热阻进行了分析,并重点研究了冷却水（松花江水）水质参数对污垢产生的影响。实验结果表明：在低流速时,交叉缩放椭圆管的污垢热阻渐近值比光管低,且没有明显的诱导期;实验中冷却水水质参数的变化对污垢影响明显。并深度分析了水质参数随时间的变化及水质参数变化对强化换热表面污垢特性的影响,为换热器提高换热效率提供了参考。     

U形管式换热器CaCO_3型污垢热阻变化趋势预测研究

用自制的实验装置模拟工业U形管式换热器Ca CO3型污垢的形成过程,通过计算机采集系统对实验数据进行记录和分析,采用灰色Verhulst模型对污垢热阻随时间的变化趋势进行预测并取得了良好的效果。该研究结果为U形管式换热器污垢热阻研究提供了实验和预测依据。     

再论估量冷却水成垢的新模型

20世纪80年代初，在60轮冷却水动态模拟试验的基础上，用回归分析的方法，得出了一个描述冷却水成垢的新模型Rf＝Rf*e^-A/t-to。对在美国Oregon州立大学所做的31轮冷却水动态模拟试验的结果采用新计算技术，进行了分析，再次证实了Rf＝Rf*e^A/t-to模型的可靠性。其中，引进了常数to来表征实验中经常出现的诱导期，并可较方便地进行线性回归．以得出具有相对比较价值的Rf*。     

Effect of alkalinity on the scaling of simulated cooling tower water

The scaling behavior of simulated cooling tower water on a heat transfer surface was investigated. The alkalinity was the main parameter investigated. The fouling vs. time curves were fitted to the equation which was derived from a simple model of the fouling process. Correlation coefficients ranging from 0.81 to 0.987 were obtained in fitting the data to the model. No particular pattern was observed for delay times and they appeared not to have a significant influence on the asymptotic fouling resistance. The latter is a complex function of the alkalinity but generally increases with alkalinity for the conditions of the experiment. Scale strength appears to be a strong function of the non-calcium carbonate components of the scale.     

交叉缩放椭圆管颗粒污垢特性的实验分析

为探讨纳米氧化镁颗粒在交叉缩放椭圆管内部的污垢规律,本文选用纳米氧化镁颗粒配置纯胶体溶液为研究对象,对不同颗粒直径、颗粒浓度、工质流速和温度工况下交叉缩放椭圆管的污垢特性进行了实验研究,并通过扫描电镜观察其结垢表面。结果表明：交叉缩放椭圆管纳米颗粒污垢下无明显诱导期;在相同的工况下,颗粒粒径越小,结垢速率越快,污垢热阻渐近值越大;随着颗粒浓度的增加,结垢速率加快,污垢热阻渐近值明显增大;随着流速的增加,污垢热阻渐近值和结垢速率都有所降低;污垢热阻渐近值随着实验管段入口温度的升高而降低。     

板式换热器混合微生物污垢特性的实验研究

为探讨铁细菌与黏液形成菌混合微生物污垢的结垢特性,进而为微生物污垢阻垢和抑垢的研究打下基础。本文以微生物污垢中最常见的铁细菌和黏液形成菌为研究对象,实验研究了板式换热器中两种细菌在形成混合微生物污垢时相互协同抑制的关系以及不同工况下的结垢特性。结果表明,微生物污垢存在明显诱导期,铁细菌的污垢热阻渐近值约为2×10^-4m²·K/W,黏液形成菌的污垢热阻渐近值约为1.2×10^-4m²·K/W,铁细菌相比黏液形成菌有较强的致垢能力,1∶1比例混合菌的热阻值介于二者之间;无论哪种细菌量占据主导时,它们之间的互相协同作用会促使混合污垢的致垢能力增强。30℃时混合菌的热阻渐近值低于35℃时的情况,达到渐近值的时间约为35℃时的2倍;流速对混合菌污垢特性的影响明显,流速为0.1m/s时的污垢热阻渐近值约为0.15m/s时的2倍,达到渐近值的时间约为0.15m/s时的2.7倍。     

板式换热器铁细菌生物污垢特性的实验分析

为探讨铁细菌在板式换热器里的污垢规律,对不同流速、温度及浓度下铁细菌在板式换热器内的污垢特性进行了实验研究。结果表明：随着流速的增加,铁细菌的污垢热阻渐近值逐渐减小;随着温度的升高,铁细菌的结垢诱导期明显缩短,结垢速率加快,污垢热阻的渐近值呈减小的趋势;而随着浓度的增加,污垢热阻值呈现明显的增长。     

基于Kern-Seaton模型结合Capdeville生物膜增长体系建立的微生物污垢模型

为研究换热设备生物污垢的形成过程,将Capdeville生物膜增长体系引入Kern-Seaton模型,建立了一个新的微生物污垢模型。采用铁细菌和管式换热装置对模型进行了实验验证。结果表明：除诱导期外,新建的微生物污垢热阻模型的计算数据和实验数据的相对误差小于20%。     

缩放管传热与污垢特性的实验研究

采用对比实验的方法,对两种缩放管及其对应光管的流动阻力、传热特性和污垢特性进行了研究。实验结果表明,缩放管的性能与其结构尺寸有关,两种缩放管的流动阻力系数明显高于光管。在加速结垢实验中,缩放管表现出良好的抗垢性能,具有结垢诱导期长、污垢热阻渐近值小的优点,而且缩放管平均传热系数都优于光管,在结垢前后都有良好的强化传热性能。     

Induction Time in Crystallization Fouling on Heat Transfer Surfaces

This work deals with the induction period in crystallization fouling on heat transfer surfaces. While the crystal growth period can be calculated, the influencing effects in the initial stage of crystallization fouling are not fully understood and quantified so far. To identify the factors influencing the induction time, experiments with calcium sulfate were performed on modified surfaces. As surface parameters the free surface energy, roughness and topography were determined by drop shape analysis and/or AFM. The visual information by microscopic studies with a SEM shows different behavior in the initial stage of crystallization on modified surfaces at constant process conditions. These microscopic findings could be verified with induction times of fouling experiments, leading to a prediction of the induction time based on surface parameters and supersaturation of the salt solution.     

Investigation of induction period and morphology of CaCO3 fouling on heated surface

The accumulation of unwanted crystalline deposits (fouling) reduces the efficiency of heat exchanger considerably. In order to mitigate fouling, many measures have been taken including the use of low-energy surface and antifoulant. In this investigation, the CaCO₃ fouling experiments in both cooling water and pool-boiling systems were performed, the induction period as well as the removal of fouling was studied, and the fouling morphology was also investigated by scanning electron microscopy and atomic force microscopy (AFM). Compared with the copper surface, the self-assembled monolayers low-energy surface can prolong the induction period of fouling in the cooling water system. The induction period increases with decreasing initial surface temperature and fluid velocity. When the heat flux is fixed in different experiments, an increase in the fluid velocity will result in a decrease in the initial surface temperature. Under this condition, owing to the interactional effects between surface temperature and fluid velocity, the induction period increases with increasing fluid velocity. The removal experiments were carried out both in the induction period and in the post-induction period. The results show that only in the induction period can the fouling resistance be reduced owing to the weaker adhesion strength of fouling. In the presence of antifoulant polyacrylic acid (PAA), the crystal forms are changed and the fractal dimensions of CaCO₃ morphologies increase for both the cooling water and the pool-boiling systems. AFM images show that the steps are bunched for CaCO₃ formed in the pool-boiling system, and in the presence of PAA, the step spacing is widened compared to the case in the absence of PAA.     

Optimal design of a heat exchanger undergoing reaction fouling

The design of heat exchangers which resist fouling is examined. It is shown that for asymptotic reaction fouling in a uniform wall temperature exchanger with outlet fluid temperature kept constant, it is possible to obtain an optimum combination of exchanger size and tube-side temperature. This optimum minimises the amount of fouling in the system. An equation which gives a good approximation to the optimum is derived, and its limitations discussed.