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《化工进展》2017,(3)
为研究过冷流动沸腾状态下的颗粒污垢特性,在竖直向上的环形流动通道内,以纳米氧化镁颗粒悬浮液作为实验工质,通过改变工质浓度、热流密度和质量流量等得到不同工况下的颗粒污垢特性,并利用契尔顿-柯尔本类比建立了不同工况下的污垢分析模型。结果表明:由于壁面温度较高,过冷流动沸腾状态下颗粒污垢结垢迅速;工质浓度增加增大了流体与壁面间的浓度差,污垢热阻渐近值和结垢速率随着工质浓度增大显著增加;随着热流密度的增加,传质增强,污垢热阻渐近值增大;增加质量流量使壁面剪切力变大,污垢热阻渐近值出现轻微的下降;随着工质入口温度的提高,增强了气泡的剥蚀作用,污垢热阻渐近值与结垢速率下降明显。 相似文献
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换热设备颗粒污垢一般指悬浮在流体中的固体颗粒在换热面上的积聚。开发了一种Ni-P-TiO2防垢型复合改性表面,并将之用于板式换热器抑制纳米MgO颗粒污垢在换热表面的积聚。基于搭建的板式换热器颗粒污垢热阻动态监测实验系统,研究了不同冷却水流速(0.1~0.3 m/s)、入口温度(30~40℃)及纳米MgO浓度(100~400 mg/L)对Ni-P-TiO2复合改性换热表面抑垢特性的影响。结果表明,随着流速的增加,污垢热阻渐近值减小了27.85%~34.41%;随着冷却水入口温度的升高,污垢热阻渐近值减小了25.15%~39.14%;随着MgO颗粒浓度的增加,热阻渐近值减小了26.15%~45.36%。结合Ni-P-TiO2复合改性表面的表面能分析了其表面的抑垢性能,发现制备的Ni-P-TiO2复合改性表面的表面能与纳米MgO颗粒污垢层的表面能相接近,符合Zhao提出的“最优表面能”抑垢理论。与常规板式换热器不锈钢表面相比,Ni-P-TiO2复合改性表面不仅抑制了颗粒污垢的积聚,还降低了颗粒污垢的固着强度,使得积聚其上的颗粒污垢更容易被剥离换热表面,实现了换热表面持久高效抑垢。 相似文献
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为了探究三角翼涡流发生器的纳米氧化镁颗粒污垢特性, 选用粒径为50 nm的氧化镁颗粒配制的胶体溶液为研究对象, 研究了在不同水浴温度、颗粒浓度、流速、三角翼间距以及不同布置等工况下三角翼涡流发生器的污垢特性。结果表明:三角翼涡流发生器具有抑垢特性, 水浴温度、浓度、流速对其抑垢能力及结垢速率均有影响, 水浴温度升高、颗粒浓度降低以及工质流速升高都会导致三角翼的抑垢能力增强。三角翼不同列间距的抑垢能力随着布置方式的改变而改变, 采用均匀分布布置形式时40 mm列间距的抑垢能力最强, 而采用同列数布置时80 mm列间距的抑垢能力最强。 相似文献
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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。 相似文献
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The influence of particle size on particulate fouling rates during convective sensible heat transfer to liquids has been investigated. Experiments have been carried out using aluminum oxide particles with nominal diameters ranging from 0.06 μm to 15 μm, suspended in an organic solvent for a wide range of concentrations. The observed influence of particle size on the asymptotic fouling resistance is compared with the predictions of the Watkinson–Epstein model. The results of this comparison suggest that, in addition to the changes of mass transfer coefficient with increasing particle size, reduced adhesion forces between particles and wall and increasing removal forces have to be considered as well. Additionally, the influence of different particle/fluid combinations was investigated. Experiments were performed with aluminum oxide particles suspended in isopropanol, isobutanol or water, and with kaolin particles suspended in water. 相似文献
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建立了丁胞管物理模型,采用标准k-ε方程和SIMPLE算法,研究了丁胞管内CaSO4流体的污垢特性,分析了结构与运行工况对丁胞管内CaSO4污垢特性的影响。结果表明,丁胞的顺排叉排对于污垢热阻渐进值影响极小。高Reynolds数时,与光管的污垢热阻相比,丁胞的存在会减小污垢热阻值;而在低Reynolds数时,相对深度较小的丁胞反而会增大污垢热阻值。丁胞的相对深度与丁胞的相对密度对于污垢热阻值均有较大的影响,在丁胞深度为0.8时,丁胞管的抑垢效率为1.150。在丁胞的相对密度为5.30时,其抑垢效率为0.730。丁胞管抑垢率随着进口流速增长而增大,随着工质浓度增长而减小,随着壁面温度的增长而减小。 相似文献
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In order to study the effect of heat flux and inlet temperature on the fouling characteristics of nanoparticles, and to further reveal the fouling mechanism for insights into proper operating conditions, γ-Al_2O_3/water suspensions were chosen as the subject of this research. The particulate fouling characteristics of γ-Al_2O_3/water suspensions on the surface of stainless steel have been experimentally studied by varying the heat flux and the inlet temperature under single-phase flow and subcooled-flow boiling conditions. The results show that in the condition of single-phase flow, the asymptotic value of fouling resistance decreases with increasing of heat flux and inlet temperature. The asymptotic value of fouling resistance under single-phase flow is much higher than for the subcooled-flow boiling condition. The effect of heat flux on the fouling resistance under the two flow states has an inverse relationship, and there exists a minimum value of fouling resistance between these two states. For subcooled-flow boiling, the asymptotic value of fouling resistance increases with increasing heat flux, whereas the effect on fouling resistance by the inlet temperature is negligible. 相似文献
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研究松花江水在换热过程中,主要水质参数对表面污垢热阻的影响程度,分别测定3种管型在换热过程中水质参数的变化情况,所选管型分别是光管、交叉缩放椭圆管和不连续双斜向内肋管,水质参数为pH、碱度、电导率、溶解氧、钙离子浓度和亚铁离子浓度.应用灰色关联方法,将水质数据和污垢热阻数据进行关联分析得出,两种强化管的水质参数关联顺序相同.其中的两种参数与污垢热阻呈现同向变化趋势,其余参数与污垢热阻呈现反向变化的趋势.强化换热管不但对水质参数的变化产生影响,而且对关联程度也有影响. 相似文献
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An experimental study was conducted to investigate the fouling process of calcium carbonate on the heat transfer surface, during forced convective heat transfer. The dynamic monitoring apparatus of fouling resistance was set up for the present experiments. The fouling behavio(s were examined under different factors including fluid velocity, hardness,alkalinity, solution temperature, and wall temperature. Asymptotic fouling curves varying with time were obtained. The fouling rate and asymptotic fouling resistance increased and the induction periods were shortened with the fluid velocity decreasing, hardness andalkalinity increasing, and solution temperature and heat transfer surface temperature increasing. Thecomponents of fouling that formed on the heat transfer surface included crystallization fouling and particulate fouling. The thermal performance parameter of fouling,ρfhf, varied from 380 to 2600 kg·W·(m^4·K)^-1, increasing with growing velocity and decreasing solution temperature, hardness or alkalinity. Furthermore, the thermal conductivity of fouling, λf, varied from 1.7 to 2.2 W·(m·K)^-1 . 相似文献
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扭曲扁管在蒸发器中的运行特性实验研究 总被引:1,自引:0,他引:1
对扭曲扁管与普通直管在蒸发器工况下的传热、流动阻力和污垢特性进行了对比实验研究。实验采用45 mm×3 mm的普通直管和由同种直管制成的扭曲扁管,扭曲扁管导程St分别为450,550,650 mm。通过实验,研究了Re和St对各特性的影响。结果表明,在实验Re数条件下,管壁污垢热阻增长呈渐近线型特性,扭曲扁管渐近污垢热阻为直管的0.15—0.29倍,流动阻力系数为直管的1.48—1.63倍。实验还得出,实验扭曲扁管的强化传热作用随着St减小而增大,扭曲扁管的传热系数在洁净状态下为直管的1.29—1.51倍,在运行8 h后,由于扭曲扁管具有较强的抑垢作用,传热系数趋近为直管的1.96—2.79倍。 相似文献