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。     

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。     

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。     

不同工况下冲孔矩形翼涡流发生器的纳米氧化镁颗粒污垢特性

为了研究不同工况情况下冲孔矩形翼涡流发生器的纳米氧化镁颗粒的污垢特性,通过实验对比了冲孔矩形翼涡流发生器和未冲孔矩形翼涡流发生器的污垢特性,探讨了水浴温度、工质质量浓度及工质流速对颗粒污垢的影响。实验结果表明:相同工况下,冲孔矩形翼涡流发生器较未冲孔涡流发生器具有更优的抑垢效果;随着水浴温度的升高,污垢热阻渐近值增加,而且结垢速率也增大;污垢热阻渐近值随着工质质量浓度的增加而增大,结垢速率有略微提升;随着工质流速的增大,污垢热阻渐近值和结垢速率均降低。     

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.     

污水换热器污垢生长特性试验研究

污水换热器污垢是影响污水冷热源应用的主要因素.了解污垢的形成规律是污水换热器应用与研究的基本要求.基于工程现场实验,通过热阻法测定污水换热器管程内污垢的热阻变化模型Rf(θ)=8×10-4[1-exP(-θ/188)].提出了污垢形成过程有效热阻与有效总传热系数的概念.并通过热阻模型提出了渐进型污垢形成过程的压降模型△(△p)=A-Bexp[-t/t0).为进一步的研究与应用提供了理论基础.     

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。     

原生污水源热泵换热器流态化在线除垢与磨损实验的研究

为考察除垢对原生污水源热泵换热器传热与磨损的影响,文章采用模型实验方法,以自制原生污水换热器为实验模型,以粒径为2～3 mm,体积分数分别为3%,5%的沙粒和聚四氟乙烯颗粒为流态化除垢粒子,研究流态化在线除垢法对原生污水换热器的除垢效果,以及对换热管的磨损程度。实验结果表明:利用流态化在线除垢法对结垢污水换热器进行除垢的效果明显;分别采用体积分数为3%,5%的沙粒和聚四氟乙烯颗粒对结垢污水换热器进行除垢后,污水换热器的换热系数分别提升了38.27%,39.72%,22.77%和38.87%,污垢热阻分别降低了64.91%,68.99%,46.79%和64.21%,各工况下换热管的磨损面积比分别为17.72%,46.37%,2.45%和4.1%。通过分析对比实验结果得到,聚四氟乙烯颗粒体积分数为5%的工况适合对污水换热器进行除垢。     

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。     

非清洁水源热泵系统换热器除污方法研究

非清洁水源热泵系统中,污水换热器换热面的污染问题导致流动阻力增大,换热系数降低,已成为污水源热泵发展的主要技术障碍之一.本文分析了现存的几种在线物理清洗方法应用于污水换热器除垢的局限性,基于污水换热器污垢的特点,针对管壳式换热器提出了适合于污水换热器去污方法,即小水量强力轮替冲洗部分换热管工艺,介绍了强力自冲洗换热器结构和原理,分析了其经济可行性.     

一种现场测定土壤源热泵岩土热物性的新方法

利用现有土壤源热泵实验台测定了岩土热物性参数,采用传热学反问题的方法对实验数据进行分析。测试过程中从岩土取热,U型地埋管换热器形成一个线热汇,使其在测试过程中与热泵实际运行时的工作状态相接近,测试更准确,节省测量过程的耗电量。以每个采样时刻作为计算节点,取平均值作为计算结果。测定结果显示岩土导热系数为3.2W/(m·K),回填材料导热系数为2.0W/(m·K),岩土热扩散率为0.85×10~(-6)m~2/s。可靠性分析表明:其标准误差分别为0.08W/(m·K),0.04W/(m·K)和0.039×10~(-6) m~2/s。     

Application of a heat pump system using untreated urban sewage as a heat source

Untreated urban sewage contains large amounts of thermal energy; and its temperature is suitable as a heat source in heat pumps for the heating and cooling of buildings. However, it is not widely used in heat pump systems due to the problem of filth. This paper presents an untreated sewage source heat pump (USSHP) system in which auto-avoiding-clogging equipment is used to continuously capture suspended solids in the sewage. Thus, the block problems caused by filtration and fouling in the heat exchanger tubes can be efficiently resolved in this system. In an actual engineering application, the characteristic parameters of USSHP system are tested under typical operating conditions for heating status. Based on the test results, the performances of the USSHP system are examined. The results indicate that the thermal resistance of the convective heat transfer and fouling on the sewage side in the sewage exchanger is 80% of its total thermal resistance. The COP of the heat pump unit and the COP of the USSHP system are 4.3 and 3.6, respectively.     

Particulate Fouling and On-Line Cleaning of Ferric Oxide Particles in Internally Enhanced Tubes

This paper describes the results of accelerated particulate fouling tests performed on three enhanced tubes and a plain tube. The tests were performed using ferric oxide as the foulant material. Three enhanced tubes included 25 start, 10 start helically ribbed tube and a ripple tube. Effect of the water velocity (1.2–1.7 m/s) on fouling resistance was investigated. The maximum fouling resistance occurred in the 25 start helically ribbed tube (about 8.0 × 10^?5 m²K/W after 100 hours). For the 10 start helically ribbed tube, the fouling resistance was relatively small (less than 1.8 × 10^?5 m²K/W). The rippled and plain tubes show almost negligible fouling resistance. High velocity flushing was effective for all the tubes except for the 25 start helically ribbed tube. On-line brush cleaning maintained the fouling resistance below 1.8 × 10^?5 m²K/W for all tubes. The fouling concentrations used in the tests were significantly higher than would be expected in commercial heat exchangers. Also, the velocity range investigated was lower than would be expected in heat exchanger operation.     

城市原生污水换热器的能效分析

结垢是影响城市原生污水换热器热工性能的主要原因.以壳管式污水换热器为例,在分析了污垢对换热器性能影响的基础之上,提出了换热器由于传热温差和流动阻力引起的不可逆有效能损失的计算方法,以及污水换热器不可避免(火用)损失的定义及计算方法.分析结果为污水换热器的工程应用和科学研究提供了理论基础.     

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.     

Study of the performance of physical water treatment with a solenoid coil to prevent mineral fouling. Part 1: Effect of a side-stream filtration

The purpose of the present study was to investigate the effect of physical water treatment (PWT) with a solenoid coil on the fouling prevention in a heat exchanger with cooling-tower water. Five different tests were conducted in a concentric-tube heat exchanger at 12 cycles of concentration: no-treatment, PWT only, PWT plus 10% filtration, PWT plus 40% filtration, and 10% filtration only. A small flow velocity of 0.83 m/s and a high heat flux of 22.5x10⁴ W/m² were chosen to accelerate the fouling in the heat exchanger. The fouling resistance in the case with PWT plus 40% filtration was approximately 78% less than that in the no-treatment case.     

壳管式海水换热器污垢状况的火用评价方法研究

分析了壳管式海水换热器管程结垢后换热强度及流动压降变化对换热器火用损失的影响,提出了一种利用(火用)损失系数评价换热器污垢状况的方法.该方法比通过检测污垢热阻评价换热器污垢状况的方法更全面,更简捷.     

Experimental Study of Fouling Resistance in Twisted Tube Heat Exchanger

This paper discusses fouling of a twisted tube heat exchanger under different conditions of fluid velocity and heat input. The fluid velocity was varied from 0.5 to 2.0 m/s, whereas the heat input to the heat exchanger was varied from 200 to 800 W. The experimental results show that for low fluid velocity of 0.5 m/s, the fouling resistance showed noticeable variation with respect to heat input, whereas for high velocity ranges, that is, 1.0–2 m/s, the variation in fouling resistance is less. The fouling in twisted tube steadily increases with time for different values of heat input from 1000 min onward for fluid velocity in the range from 1.0 to 2.0 m/s. It is also observed that fouling resistance curves overlap for various values of heat input. During the initial 1000 min of the test duration, the maximum fouling in a twisted tube heat exchanger decreases with increase in fluid velocity from 1.0 to 2.0 m/s. This behavior of the fouling rate can be attributed to the fact that at higher fluid velocity, flow becomes turbulent, and this in turn flushes the fouling particles. The time-series correlations for the fouling resistance are found to be logarithmic in nature.     

Effect of Geometry and Flow Conditions on Particulate Fouling in Plate Heat Exchangers

This article describes particulate fouling experiments performed on small-scale and full-scale plate heat exchangers for three different corrugation angles (30 deg, 45 deg and 60 deg). The velocity effect has been studied as well as the particle type and concentration effects. The test duration ranges between 20 and 1,500 h in order to reach asymptotic behavior. The results clearly indicate that the corrugation angle has a major influence on the asymptotic fouling resistance. Increasing the corrugation angle leads to lower values for the fouling resistance. Furthermore, for a given corrugation angle, the asymptotic fouling resistance is inversely proportional to the velocity squared. Finally, the asymptotic fouling resistance is proportional to the particle concentration. Fouling mitigation can be obtained by taking into account at the design stage the heat exchanger geometry and fluid velocity.     

Influence of phosphorus on ash fouling deposition of hydrothermal carbonization sewage sludge fuel via drop tube furnace combustion experiments

Phosphorus effect on ash fouling deposition produced during combustion process of sewage sludge solid fuel is a very important factor. Previous studies have only focused on decrease of the ash melting temperature and increase of slagging and sintering by phosphorus content. Therefore, research regarding combustion fouling formation and its effect on temperature reduction of deposit surface by phosphorus content is insufficient. Ash fouling is an important factor, because ash in the combustion boiler process deposits on the surface of heat exchanger and interferes with heat exchange efficiency. In particular, temperature reduction of heat exchanger surface via fouling should be considered together with fouling deposition, because this is related to the heat exchanger efficiency. Synthetic ash, phosphorus vaporization, and drop tube furnace experiments were performed to investigate effect of phosphorus on ash fouling formation and temperature reduction of deposit surface under combustion condition. Phosphorus was highly reactive and reacted with ash minerals to produce mineral phosphate, which promoted ash fouling deposition during the combustion experiments. In contrast, the occurrence of sintering on deposited fouling resulted in formation of a large hollow structure, which alleviated the temperature reduction on the deposit surface. Phosphorus content had a substantial correlation with fouling deposition behavior and influenced reduction in the surface temperature of the heat exchanger, because it led to generating low temperature mineral phases.