共查询到19条相似文献,搜索用时 125 毫秒
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壁流式柴油机颗粒过滤体捕集性能的实验研究 总被引:1,自引:0,他引:1
过滤压降和过滤效率是评价过滤体性能的重要指标.实验室搭建了捕集柴油机颗粒的发动机台架.通过台架实验,研究了过滤体结构参数对过滤体性能的影响.研究结果表明;随过滤体长度的增加,过滤压降逐渐减小,初始过滤效率先缓慢增加,后急剧下降;增加过滤体的孔隙率有利于降低过滤体初始压降和压降增长率;孔隙率较低的过滤体具有较高的初始过滤效率,但在颗粒层过滤阶段,孔隙率对过滤效率的影响不明显;颗粒层的沉积结构特性受过滤速度的影响,颗粒层比阻与颗粒层堆积厚度乘积的变化率随过滤速度的变化呈非线性关系变化. 相似文献
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运用CFD和DEM方法,建立三维随机填充固定床颗粒层除尘过滤模型,颗粒之间的接触采用"搭桥法"进行处理。数值计算得到的压降结果与实验值、关联式吻合较好,压降与床层厚度近似呈线性关系。在此基础上,数值研究了除尘效率与颗粒床床层厚度、气体流速、粉尘粒径、气流温度及流动方向的关系。粉尘粒径大于5μm时,增加床层厚度,增大气体流速,均可以有效地增加除尘效率。而粉尘粒径大于5μm时,在圆筒壁面恒热流密度冷却的条件下,气流温度越高,除尘效率越低。流动方向与重力方向相同时,可提高除尘效率。并拟合了分级除尘效率与St数的关系式,当St0.009时,分级除尘效率为一定值,当St≥0.009时,分级除尘效率随着lg(St)的增加呈线性增加的趋势。 相似文献
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《工程热物理学报》2017,(6)
基于可视化湿颗粒流化床实验系统,研究了多种Geldart-D类颗粒在不同含液量时的流动特性变化规律,包含流型、床层压降、最小流化速度。实验结果表明:1)在湿流化床内,颗粒出现聚团结块行为,气泡呈现不规则形状;湿颗粒流化过程的稳定性较干颗粒床明显下降,床内近壁面区域易出现局部沟流。2)固定床阶段,由于空隙率的增加,相同气速条件下,湿颗粒床层压降低于干颗粒;基于厄贡公式,得出了湿颗粒固定床床层压降的计算方法。3)湿颗粒的最小流化速度U_(mf)高于干颗粒,且随粒径d_p的增加而增加;导出了预测D类湿颗粒最小流化速度的半经验公式,Re_(mf)=0.279.Ar~(0.5),该式计算结果与实验测量结果偏差小于15%。 相似文献
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颗粒有序堆积多孔介质对流换热实验研究 总被引:4,自引:0,他引:4
本文采用"瞬态单吹反问题研究方法"对颗粒有序堆积多孔介质内的强制对流换热进行了实验研究。详细研究了颗粒堆积方式变化对多孔介质内对流换热的影响,并对均匀与非均匀颗粒堆积多孔介质内的对流换热特性进行了对比分析。研究表明:通过对颗粒进行合理有序堆积,可以使相应多孔介质内的压降显著降低,其综合换热效率明显提高;通过拟合获得了颗粒有序堆积多孔介质内的宏观流动换热实验关联式,其形式与传统经验公式(Ergun公式和Wakao公式)一致,但部分模型参数值远低于传统经验公式。 相似文献
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Two types of asbestos fiber, chrysotile and amosite, form filter cakes of different permeabilities while having a similar degree of dispersion. The filter cake resistance depends on the disperse phase characteristics and the conditions of cake formation. The main reason for the effects mentioned is different particle flexibility influenced by the specific structure of each type of asbestos particle. The flexible chrysotile fibers in the cake form dense and rigid, amosite, porous deposits. An increase in the velocity of the suspended chrysotile particles, caused by pressure difference and agitation, results in significant differences in filter cake resistance. 相似文献
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Schmidt Jörg Guesdon Christine Schomäcker Reinhard 《Journal of nanoparticle research》1999,1(2):267-276
Engineering aspects of the preparation of palladium nanoparticles in non-ionic w/o-microemulsions are examined. In order to achieve reproducible synthesis conditions a semi-batch reactor with a standardized design is used. Influences of the stirring rate and of different ways of concentration control on the product properties are observed. For reproducible synthesis it is important to establish appropriate and defined preparation conditions. Monodisperse palladium particles of around 5nm size are obtained by adding the microemulsion containing the palladium salt at a constant feed rate to the precharged microemulsion containing the reducing agent. A quantitative kinetic model is proposed to describe particle formation in microemulsions. Unknown parameters of the model have been estimated by independent examinations or can be achieved by fitting to the experimental data. 相似文献
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Towata A Sivakumar M Yasui K Tuziuti T Kozuka T Iida Y 《Ultrasonics sonochemistry》2007,14(6):705-710
The paraffin particles were prepared by quenching process after sonicating the solution of paraffin and water at 80 °C. The resultant paraffin particles were then used as template for the preparation of macroporous zirconia materials. For this, zirconium normal butoxide (ZNB) modified with triethanolamine (TEA) was first hydrolyzed by water containing the dispersed paraffin particles with the surfactant, Sodium di(2-ethylhexyl) sulfosuccinate. This resulted in the formation of a slurry consisting of hydrolyzed sol and paraffin particles. After centrifugation, a cake packed with hydrated sol and paraffin particles were obtained which was then subjected to heat treatment. The sample obtained after heat treatment contained finely dispersed pores in the size range from 40 nm to 2 μm. Moreover, using the present approach it has also been observed that, change in pore size of zirconia wall is possible with a change in size of the paraffin particles. Thus, the present approach is a novel way of producing porous materials as the particle size of the template could be changed and templates become hard when they were molded as compared to the conventional methods in which there is no change in phase for the templates under 100 °C. 相似文献
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Yan Wang Robert W. Besant Richard W. Evitts Allan T. Dolovich 《Particle & Particle Systems Characterization》2006,23(5):399-407
When a water‐soluble granular fertilizer, such as potash fertilizer, is wetted and then dried, clumps or cakes often form in the material. A centrifugal loading method has been developed to determine cake strength in a ring of potash fertilizer. This method determines the area‐average tensile stress at the speed of the centrifuge when the specimen fractures. The cake strength was measured for a series of tests in which the initial moisture content and drying time of each sample was varied. The results show that the cake strength increases linearly with greater initial moisture content. It was also found that a slower drying process produces a stronger cake. 相似文献
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Accurate, repeatable heat transfer and pressure-drop measurements have been made for condensation of CFC-113 with downflow inside enhanced microfin tubes and tubes containing twisted-wire inserts. In the latter case measurements have also been made for CFC-113/air mixtures. The heat transfer rate was calculated from the coolant flow rate and temperature rise, the latter measured using a 10-junction thermopile with careful attention paid to adequate coolant mixing and isothermal immersion of the thermopile leads. The surface temperature was found from thermocouples embedded in the tube wall. One plain tube, nine microfin tubes (with different fin heights, helix angles, and number of fins), and four twisted-wire inserts (with different wire densities) were tested. Enhancement ratios (i.e., vapor-side heat transfer coefficient for the enhanced tube divided by that for a smooth tube at the same vapor-side temperature difference and vapor inlet velocity) between 1.6 and 5.6 for the microfin tubes and between 1.2 and 1.6 for the twisted-wire inserts were found, with values depending on vapor-side temperature difference, vapor inlet velocity, and air inlet mole fraction in the case of CFC-113/air mixtures. The microfin tubes showed moderate pressure-drop penalties of around 50% compared to the plain tube, while the twisted-wire inserts showed increasing pressure-drop penalty with increasing wire density. 相似文献
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基于界面极化与静电场理论建立了聚醚砜复合超滤膜表面污染层与溶液体系的介电解析模型. 应用参数敏感性分析和介电测量研究了体系中浓差极化层与滤饼层的厚度与电导率对超滤体系介电弛豫的影响机制. 结果表明超滤过程中浓差极化层能快速建立,而滤饼层的形成是一个增长与剥蚀的动态过程;并且浓差极化层与滤饼层的电学性质是影响超滤体系介电谱的关键因素. 比较介电测量与模拟结果证实了建立的超滤体系介电解析模型能够有效可靠地描述与解释超滤体系产生介电驰豫的机制. 相似文献
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Heinz Umhauer Stefan Berbner Gunnar Hemmer 《Particle & Particle Systems Characterization》2000,17(1):3-15
Based on previous experience, an optical particle counter has been designed which allows the direct measurement of the size and concentration of dust particles in gas flows at high temperatures. The instrument features a new optical measuring volume definition together with a signal control to avoid border‐zone error effects. The instrument has a free working distance of 200 mm. Hence it is possible to make true in situ measurements in pipe flows with a cross‐section of ca. 60 cm2 and additionally to protect the device against heat and dust precipitation on the optical windows. The instrument was initially used to examine the separation behaviour of cake‐forming rigid ceramic barrier filters at temperatures up to 1000 °C. In particular, the fractional efficiencies and the time‐related concentration changes on the clean gas side caused by a pulse jet cleaning event could be determined. The results obtained so far demonstrate that ceramic barrier filters show basically the same behaviour as conventional filters, but possess a substantially higher separation efficiency at a corresponding higher pressure drop (fractional penetration values between 10−5 and 10−9 depending on the type of filter material and the cake formation). 相似文献
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