共查询到16条相似文献,搜索用时 531 毫秒
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为研究翼型涡流发生器结构以及布置对换热面污垢的影响,对矩形通道内布置翼型涡流发生器后壁面CaCO3析晶污垢的沉积进行了模拟。计算并分析了在温度为50℃,流速为0.2 m·s-1,浓度为1000 mg·L-1的CaCO3过饱和溶液下,翼形涡流发生器的翼型、攻角和纵向间距等几何因素对表面污垢沉积的影响。结果表明:表面单位面积结垢量随着翼型涡流发生器攻角的增大而减小,随着涡流发生器列间距的增大而增大,当间距为60 mm时达到最大,超过60 mm后表面单位面积结垢量呈现下降趋势。 相似文献
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为了研究涡流发生器的污垢沉积特性,运用Fortran汇编语言自主编程,引用析晶污垢模型模拟了CaSO4溶液流经矩形通道并在矩形楞涡流发生器表面生成污垢的过程。考察了涡流发生器楞的结构尺寸(横向排列间距、纵向高度)以及流动工况(入口速度、壁面温度、工质浓度)对污垢特性的影响。根据模拟数据给出的矩形楞涡流发生器表面CaSO4污垢沉积率、剥蚀率及污垢热阻随时间曲线的变化规律,得到了抑垢效果最佳时的结构尺寸x=40mm、h=0.3H,并总结出污垢沉积过程的影响趋势。通过模拟对比,发现加入涡流发生器后,流通壁面污垢沉积减少,大大提高了换热效率。 相似文献
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为探讨圆形楞涡流发生器结构和布置方式对换热面污垢的影响,采用数值模拟方法研究了布置圆形楞涡流发生器矩形通道内壁面CaSO4析晶污垢的沉积过程,同时计算并分析了入口流体温度为300 K、速度为0.5 m·s-1、浓度为3.0 g·L-1的CaSO4过饱和溶液下圆形楞涡流发生器的楞长、布置方式、半径的大小以及纵向间距等几何因素对表面污垢沉积的影响。结果表明:污垢热阻值随涡流发生器楞长增加先减小后增大,而且在(4/8)H楞长处出现最小值;随涡流发生器列间距增大而增大,当间距超过55 mm后污垢热阻值逐渐趋于光通道的污垢热阻值;随涡流发生器半径增大而减小;相同列间距、半径以及当楞长为(4/8)H时,顺排靠边布置时其污垢热阻值最小。 相似文献
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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。 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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The influence of flow velocity and particle size on the deposition of suspended alumina particles onto heat transfer surfaces was measured with two fouling probes, namely, a heated cylindrical rod in an annulus and a coiled wire in crossflow. Additionally, the response of the fouled probes to such changes as may occur in operating heat exchangers was investigated. The measured influence of flow velocity, wall temperature, bulk temperature, heat flux, particle concentration and particle size on the fouling behaviour as described in this paper and in a companion paper is compared to the predictions of several fouling models from the literature, and recommendations are made for further improvement of these models. 相似文献
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实验研究了水质工况对硫酸钙污垢特性的影响,在管内流速、入口温度、工质浓度、化学方程式和阴离子浓度5个方面分别研究氯离子和硝酸根离子对硫酸钙结垢特性的影响。结果表明,阴离子对硫酸钙污垢的形成有一定的促进作用,但这种促进作用受实验管段流速的影响,流速越大,促进作用越小,与管段入口温度和工质浓度没有明显关系。电镜观察结果显示,含有大量硝酸根离子的硫酸钙溶液在不锈钢圆管内结垢致密且厚重,工质溶液以条状和块状混晶析出硫酸钙晶体,晶体紧密的聚集。含有大量氯离子的硫酸钙溶液在不锈钢圆管内结垢疏松且均匀,工质溶液以条状析出硫酸钙晶体,晶体间没有明显的聚集现象。 相似文献
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采用微观粒子图像测速法(Micro-PIV),实验研究了Reynolds数(Re)=50~800范围内去离子水在微肋直径D=0.4 mm微肋阵内的绕流流场特性,获得了不同Re下错排和顺排微肋阵内的流线分布与速度场,分析了Re与微肋排布方式对旋涡结构、流速分布等流场特性的影响规律。研究结果表明,在Re=50~700范围内,错排和顺排微肋阵内均出现涡结构,当Re=800时错排微肋阵内开始发生旋涡脱落;错排微肋阵内旋涡长度随着Re的增大而增加,而对于顺排微肋阵,在低Re时旋涡长度随着Re的增大而增加,当Re≥300后,旋涡长度保持微肋间距不再增加;顺排微肋阵内主流区顺流速度较错排微肋阵大,而错排微肋阵内横向速度大于顺排微肋阵且最大值比顺排微肋阵高约25%,微肋错排布置增强了流体的掺混。 相似文献
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Fouling and subsequent chemical cleaning are two important issues for sustainable operation of nanofiltration (NF) membranes in water treatment and reuse applications. Fouling strongly depends on the feed water quality, especially the nature of the foulants and ionic composition of the feed water. Consequently, appropriate selection of the chemical cleaning solutions can be seen as a critical factor for effective fouling control. In this study, membrane fouling and chemical cleaning under condition typical to that in water recycling applications were investigated. Fouling conditions were achieved over approximately 18 h with foulant cocktails containing five model foulants namely humic acids, bovine serum albumin, sodium alginate, and two silica colloids in a background electrolyte solution. These model foulants were selected to represent four distinctive modes of fouling: humic acid, protein, polysaccharide, and colloidal fouling. Three chemical cleaning solutions (alkaline solution at pH 11, sodium dodecyl sulphate (SDS), and a combination of both) were evaluated for permeate flux recovery efficiency. The results indicated that with the same mass of foulant, organic fouling was considerably more severe as compared to colloidal fouling. While organic fouling caused a considerable increase in the membrane surface hydrophobicity as indicated by contact angle measurement, hydrophobicity of silica colloidal fouled membrane remained almost the same. Furthermore, a mechanistic correlation amongst cleaning efficiency, characteristics of the model foulants, and the cleaning reagents could be established. Chemical cleaning of all organically fouled membranes by a 10 mM SDS solution particularly at pH 11 resulted in good flux recovery. However, notable flux decline after SDS cleaning of organically fouled membranes was observed indicating that SDS was effective at breaking the organic foulant—Ca2+ complex but was not able to effectively dissolve and completely remove these organic foulants. Although a lower permeate flux recovery was obtained with a caustic solution (pH 11) in the absence of SDS, the permeate flux after cleaning was stable. In contrast, the chemical cleaning solutions used in this study showed low effectiveness against colloidal fouling. It is also interesting to note that membrane fouling and chemical cleaning could permanently alter the hydrophobicity of the membrane surface. 相似文献