内置螺旋弹簧换热管污垢性能的实验研究

建立污垢热阻实验系统,对光管和内置螺旋弹簧换热管进行污垢热阻实验,研究不同水质硬度、流体温度、流速对污垢形成过程的影响,比较两者的污垢性能。实验表明:随着水质硬度的提高,结垢速率加快,诱导期缩短,污垢热阻增加,但增至某硬度时,渐进污垢热阻出现下降现象;随着流体温度的提高,诱导期趋于消失,结垢速率加快,渐进污垢热阻增大;随着流速的提高,结垢速率减慢,诱导期延长,渐进污垢热阻减小。通过内置螺旋弹簧换热管与光管污垢热阻的对比,表明内置螺旋弹簧换热管具有一定的抗垢作用。     

对管式换热器黏液形成菌生物污垢特性的实验研究

为了探讨黏液形成菌在管式换热器中的污垢特性,以某电厂循环冷却塔塔底黏泥中分离纯化后得出的黏液形成菌为研究对象,利用污垢动态模拟实验系统,采用对比实验的研究方法得到了不同入口温度、流速及体积浓度条件下黏液形成菌在不锈钢光管换热器中的污垢特性。结果表明:黏液形成菌的结垢过程存在诱导期。随着入口温度的升高,诱导期缩短,污垢热阻达到渐近值所需时间减少。在实验温度范围内,入口温度为30℃时污垢热阻渐近值最大,35℃时次之,25℃时最小;随着流速的增加,污垢热阻达到渐近值所需时间减少,污垢热阻渐近值减小;随着体积浓度的增加,诱导期会延长,结垢速率加快,污垢热阻渐近值增大。     

影响换热面结垢诱导期的表面特性研究

换热面结垢是一个普遍存在的问题,而结垢诱导期的长短对污垢形成过程具有重要的影响,即使在相同实验条件下,不同材料换热面的结垢诱导期仍相差较大.因此本文通过对附着在换热面上的半球形污垢晶核进行受力分析,发现污垢晶核与换热面之间的附着力对其结垢诱导期长短起决定性作用,然后根据颗粒与平板间附着力模型,计算了污垢晶核与具有不同表面能的换热面间附着力,并与相应的结垢诱导期进行对比.结果表明:结垢诱导期的长短与换热面的表面能、污垢晶核与换热面间的附着力及表面粗糙度尺度有关.     

板式换热器黏液形成菌生物污垢特性的实验研究

为探讨黏液形成菌在板式换热器里的结垢规律,对不同流速、温度及体积分数下黏液形成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,黏液形成菌的污垢热阻渐近值逐渐减小;随着温度的升高,黏液形成菌结垢的诱导期缩短,并且达到稳定的时间增加,在实验温度范围内,污垢热阻渐近值在35℃时最大;而随着细菌体积分数的增加,污垢热阻值呈现明显幅度的增长。     

板式换热器颗粒污垢特性的实验研究

以纳米氧化镁颗粒溶液为实验工质,进行了板式换热器颗粒污垢特性的实验研究,分析了颗粒质量浓度、颗粒粒径、流速和低温介质温度对颗粒污垢热阻的影响.结果表明:板式换热器颗粒污垢无明显诱导期存在,结垢速率和污垢热阻渐进值均随颗粒质量浓度的增大而增大,且增大幅度逐渐减小;颗粒粒径对污垢热阻的影响较明显,在相同质量浓度下,颗粒粒径越小,结垢速率越快,且污垢热阻越大;流速对污垢热阻的影响较为复杂,高流速下的结垢速率略大于低流速下,且高流速下达到稳定时的污垢热阻渐进值小于低流速下;低温介质温度对颗粒污垢热阻的影响不明显.     

钛管CaCO_3污垢特性的实验研究

实验研究了钛管的污垢特性,并和不锈钢管、紫铜光管的污垢特性进行了比较.结果表明,钛管的污垢诱导期随着浓度的增大而增大,随着流速的增大而减小;但污垢热阻值随着浓度和流速的变化规律较复杂.在同种工况下,钛管的诱导期比不锈钢管短、却比铜管长,污垢热阻渐近值比铜管小、却比不锈钢管大,说明了钛管的抗垢性能虽好于铜管,但比不锈钢管差.     

基于污水换热器污垢不同生长阶段的除垢试验研究

为了提高污水换热器的除垢效果,文章以管壳式污水换热器为研究对象,以沙粒作为除垢粒子,以污垢热阻变化率表征除垢效果,在利用烘干灼烧失重法、能谱分析法和微观结构分析法分析污垢成分的基础上,运用污垢热阻法进行除垢试验研究。通过试验研究了在污垢生长的诱导期、生长期和渐近期3个阶段除垢对污垢热阻值的影响。试验结果表明:管壳式污水换热器管内污垢的主要成分为含水量较高的有机物;结垢工况下,污垢热阻渐近值为0.74×10^-3(m^2·K)/W;在污垢生长的诱导期、生长期和渐近期进行除垢后,污垢热阻渐近值分别为0.4×10^-3,0.42×10^-3,0.6×10^-3(m^2·K)/W,与结垢工况相比,污垢热阻渐近值分别降低了45.9%,43.2%,18.9%,除垢工况下污垢热阻增长速率较结垢工况明显减缓。     

换热器结垢工况下换热系数变化的分析研究

介绍了换热器污垢热阻的数学模型，包括污垢沉积模型和剥蚀模型。分析了换热器结垢工况下的换热系数的变化，重点研究了时间、流体雷诺数Re和流体—污垢界面温度Ts对换熟系数K的影响，以及在结垢诱导期内换热系数K的变化。得到了冷却水流速与污垢热阻之间的关系式，界面温度Ts与污垢热阻和换热系数之间关系的示意图，并得出了诱导期内的换热系数K大于结垢过程的其他四个阶段的结论。最后，阐述了分析结果对工程的实际指导意义。     

1000MW直接空冷机组凝汽器污垢热阻对热经济性影响特性研究

直接空冷机组运行一段时间后,其散热器管内、外污垢热阻会对机组的热经济性产生一定的影响.以某1 000MW直接空冷机组为例,取污垢热阻的变化范围为0～0.001m2·K/W,用η-NTU建立了机组排汽压力的管内、外污垢热阻数学模型.分析了热负荷一定的情况下,不同环境温度、迎面风速下,散热器管内、外污垢热阻对排汽压力的影响特性.结合当地经济因素,比较了不同管内、外污垢热阻阻值对机组年运行费用的影响程度,为机组的经济运行提供了参考.     

不同金属材料与海水温度对海水结垢影响的实验研究

针对海水换热结垢现象进行了实验研究。对比了镀锌铁片、黄铜、紫铜和不锈钢4种金属在海水中的结垢特征,以及4种金属表面结垢量的变化。实验结果显示,不同金属在海水中的污垢形貌及结垢量不同,镀锌铁片的结垢量最大,紫铜表面腐蚀较为严重,结垢量最小。对海水污垢进行了XRD(X-Ray Diffraction)和EDX(Energy Dispersive XRay)物相分析,结果显示,不同金属材料表面形成的海水污垢的物相组成不同,镀锌铁片表面的污垢成分主要是锌的腐蚀产物,而不锈钢表面的污垢成分主要为氢氧化镁。比较了镀锌铁片和黄铜在80℃和60℃海水中的结垢量变化,镀锌铁片污垢随着海水温度的上升而下降,而黄铜污垢随着海水温度的上升而上升。     

炉管内聚合物结垢规律测试研究

建立了管内聚合物结垢热阻测试试验台。采用对比法对管内聚合物热阻进行了测试研究,分析聚合物结垢的影响因素。测试结果表明:聚合物浓度越高,聚合物结垢层越厚,热阻也越大;随着混合液温度的升高,管内聚合物垢层及热阻都呈现逐步增大的趋势;随着管内聚合物溶液流速的提高,聚合物热阻下降。     

Effect of Condensable Species on Particulate Fouling

The flue gases emanating from the combustion of fuels or gasification process invariably comprise particulate matter and many chemical species in vapor form. The temperature of the flue gases gradually reduces when passing through different sections of heat exchanger, such as the superheater, evaporator, and so on. If the temperatures of the heat exchanger tube surface and the gas phase are favorable for condensation, the chemical species in the vapor form will condense on the particles and on the tube surface. The particle deposition behavior under these conditions is drastically different from the one observed in dry particulate fouling. In order to model the particle deposition under such circumstances, it is important to evaluate the criteria for particle adhesion to the surface. Impaction experiments of particles impacting a surface coated with a thin liquid film and particles that are coated with a liquid film impacting over a dry surface are performed to evaluate the limiting parameters under which a particle sticks to the surface without rebounding. The effects of liquid viscosity, liquid film thickness, and interacting material properties are evaluated. The experimental results are compared to the results of existing models and a suitable model for fouling is proposed. Controlled fouling experiments are performed for varying liquid films coated over a deposition tube under various process conditions to mimic the condensation effects on fouling. The results are compared with detailed impaction experiments.     

垃圾渗滤液浓缩用MVR蒸发管内CaCO3结垢过程数值分析

基于圆管立式降膜蒸发传热传质的相关理论,建立了其管内CaCO3结垢过程的数学模型,并应用于垃圾渗滤液浓缩用机械蒸汽再压缩（MVR）立式降膜蒸发管内CaCO3结垢过程研究,得到了各结垢参数在不同结垢阶段的变化规律。结果表明：结垢初期,蒸发管内CaCO3的沉积速率远大于剥蚀速率,净存速率较大,污垢层厚度、污垢热阻快速增加,使得蒸发管总传热系数快速减小,进而引起蒸发器的蒸发量、浓缩比快速减小;结垢中期,CaCO3的净存速率变小,污垢增加变缓,各结垢参数变化趋势由急变缓;结垢末期,CaCO3的净存速率趋近于零,污垢不再增加,各结垢参数趋于稳定;相比蒸发管入口,出口液膜溶液的流量小、CaCO3浓度高,结垢更严重,且受整个蒸发管结垢的影响,液膜溶液流量、CaCO3浓度变化较大,各结垢参数变化更迅速,更早趋于稳定。     

换热表面结垢对U型管蒸汽发生器传热性能的影响分析

U型管蒸汽发生器的壳侧沉积了来自二回路系统中的腐蚀产物,结垢导致热量聚积在金属换热管上,容易造成垢下热点腐蚀,危害设备安全。为了明确结垢对蒸汽发生器传热性能的影响,本研究基于仿真平台APROS建立了U型管蒸汽发生器的分布式模型,并根据已公开论文中的数据进行了模型准确性验证;推导了污垢热阻与表面换热系数之间的关系式,分析了不同结垢厚度、位置对U型管蒸汽发生器换热区域的传热管壁面温度、流体温度、传热系数、热流密度等的影响程度。研究结果表明：随着结垢程度的加剧,蒸汽发生器的换热效率不断降低,出口蒸汽品质不断下降;结垢对沸腾段换热效率的影响比对过冷段换热效率的影响更大。     

温度对纳米氧化镁颗粒污垢特性的影响

为了探讨温度对纳米氧化镁颗粒污垢结垢特性的影响,通过改变循环工质入口温度和水浴温度实验研究了温度对纳米颗粒污垢在交叉缩放椭圆管中的结垢特性,并通过静置沉降实验验证了入口温度对循环工质聚沉情况的影响。结果表明,循环工质入口温度和水浴温度对纳米颗粒污垢特性都有显著的影响。随着循环工质入口温度的升高,污垢热阻渐近值明显减小,并且污垢热阻达到渐近值的时间缩短。随着水浴温度的升高,污垢热阻渐近值也随之减小,但是达到渐近值的时间略有增加。     

恒热流时污垢对管内对流换热过程热力学性能影响的分析

基于热力学第一、二定律,在恒热流工况下分析了污垢对管内对流换热过程热力学性能的影响,提出了一项在恒热流工况下反映污垢对管内流换热过程热力学性能影响的指标-无因次熵产相对增加数;讨论了管内流体雷诺数（无污垢时）和无因次热流密度等参数对无因次熵产相对增加数的影响。研究结果表明,该指标不仅能反映污垢对管内传热过程的影响,而且能反映污垢对管内流动过程的影响,而由污垢层导热所引起的熵产在管内传热过程总的熵产中占有重要的地位,同时,还把结果与恒壁温时的有关结果进行了比较。     

Numerical investigation of fouling on cross-flow heat exchanger tubes with conjugated heat transfer approach

Although fouling on heat exchanger tubes is extensively investigated, due to the lack of energy resources, the effects of fouling on heat exchangers is still an important area of study and gaining more and more attention every day. In this study we investigated the effects of fouling on heat transfer and flow structures numerically for cross-flow heat exchanger tube geometry. The distributions of temperature, heat transfer coefficient and heat flux at the surface of fouling were obtained for single and double layer fouling cases. In the analysis, Reynolds number and the blockage ratio were fixed to 100 and 0.1 respectively. We used ANSYS software in our analyses and compared some of our results with the literature.     

Fouling thresholds in bare tubes and tubes fitted with inserts

Maya crude oil fouling reveals a straightforward dependency of initial fouling rate on surface temperature but a rather complex dependency on velocity in bare tubes, the initial fouling rate showing a maximum and then decreasing significantly towards zero as the velocity is increased. Surface shear stress clearly is an important parameter. CFD simulation of fluid flow in a tube fitted with a hiTRAN® insert reveals a complex distribution of surface shear stress. To compare the insert situation with the bare tube, an equivalent velocity concept is introduced on the basis that at a given average velocity the fluid flow results in the same average wall shear stress regardless of whether the tube is bare or is fitted with an insert. Using the equivalent velocity concept, the fouling data obtained using both a bare tube and a tube fitted with inserts can be correlated using a single model. Moreover, the fouling threshold conditions below which fouling is negligible, can be predicted for both situations.     

Study of the Effect of Fin-and-Tube Heat Exchanger Fouling on its Structural Performance

This paper presents the thermal and structural analysis of high temperature fin-and-tube heat exchanger. Water flowing in tubular space and flue-gas flowing in the intertubular space, were considered as working fluids. The effect of limescale fouling on thermal and structural performance of heat exchanger was studied. The analysis considered an industrial heat exchanger, which failure occur from time to time. The expert inspection, after the failure indicated the existence of fouling layer within the heat exchanger tubes. In order to understand the reasons of heat exchanger failure, a detailed fluid flow analysis (both in the tubular and intertubular spaces) was performed. The analysis indicated that the silicate limescale fouling layer with thermal conductivity of 0.35 W/(mK) and thickness up to 1.5 mm existing in the tube, may increase the tube wall temperature even more than 150°C. The study also includes the impact of outer tube wall surface fouling with thickness of 0.2 mm and heat transfer coefficient of 2 W/(mK). As a result, the compressible stresses may increase over three times compared to the situation where the tube wall fouling does not exist.