A Model for Predicting the Erosion Rate Induced by the Use of a Selective Catalytic Reduction Denitrification Technology in Cement Kilns Flue Gas

Selective catalytic reduction(SCR)is a technology by which nitrogen oxides are converted with the aid of a catalyst into diatomic nitrogen and water.It is known that the catalyst can be easily eroded if a cement kiln with a high-dust content is considered.To understand this process,numerical simulations have been carried out considering a single catalyst channel in order to study the collision and erosion of fly ash and catalysts at meso scale.Based on a response surface methodology,the effects of five factors on the erosion rate have been studied,namely,the catalyst particle velocity,the particle size,the particle concentration,the incidence angle and the catalyst porosity.The results show that the influence of particle velocity,particle size and particle concentration is statistically significant and the particle size and incidence angle have a significant effect on the erosion rate.A quadratic polynomial prediction model for the erosion rate of honeycomb catalysts in cement kiln SCR reactors is finally proposed to support the future optimization of these systems.

An Experimental and Numerical Study on the Cleaning of Pleated Bag Filters Using Low-Pressure Pulsed-Jets

Pulsed-jet cleaning is recognized as the most efficient method to regenerate bag dust collectors traditionally used in industrial processes to control the emission of particulates.In this study,non-woven needle felt filter bags with and without a film coating material have been analyzed considering different geometries(different number N of pairs of pleated filter bag sides)in the frame of dedicated low-pressure pulsed-jet cleaning experiments.The flow structure inside the bag and the response characteristics of its wall have also been analyzed numerically through a computational fluid-dynamics/structural-dynamics(CFD-CSD)unidirectional fluid-solid coupling method.As shown by the experiments,the peak pressure(P_(0))on the wall of the filter bag with N=8 and 12 is higher,which indicates dust can be removed more effectively in these cases.The peak pressure on the wall increases first and then decreases along the direction of the bag length,while the peak pressure of the pleated filter bag with nonwoven needled felt film coating is greater than that without film coating.A comprehensive analysis of the time variation of acceleration,deformation,strain,stress and other factors,has led to the conclusion that the pleated filter bag with N=12 would be the optimal choice.

含GNs甲醇-水二元工质热虹吸管的动力电池散热特性研究

动力电池工作温度过高和温差过大都会导致其性能快速衰退,有效的热管理系统应将电池最高温度和电池模块表面温差控制在允许范围内。基于石墨烯纳米颗粒的甲醇-水二元混合工质热虹吸管的传热特性研究结果,选用充液率50%、石墨烯含量0.02wt%的甲醇-水二元工质热虹吸管为换热器件,搭建电池热管理实验测试装置,研究了模拟电池在1,1.5,2 C三种放电倍率下的散热性能,与自然对流和强制风冷散热进行对比。结果表明,热管散热方式三种放电倍率对应的电池最高温度分别为28.89,32.12及35.76℃;热管散热方式平均升温速率最低,在2 C放电倍率时仅为0.525℃/min;2 C放电倍率下热管散热系统相比风冷散热方式温度下降了22.48%,相比自然对流温度下降了49.13%;三种放电倍率下热管散热系统的散热效率最高,且均超过了70%。研究结果可为热管散热系统应用于电池热管理系统提供理论依据和数据支撑。

Effect of interaction between different CeO_(2)plane and platinum nanoparticles on catalytic activity of Pt/CeO_(2)in toluene oxidation

The plane exposure of support vitally affects the catalytic performance of the catalyst.In this work,CeO_(2)nanorods((110)plane exposure),nano-octahedrons((111)plane exposure)and nano-cubes((100)plane exposure)were prepared as the supports of Pt/CeO_(2)samples to investigate the effect of CeO_(2)plane exposure on total toluene oxidation.Characterizations reveal that the(110)plane of CeO_(2)is more helpful to the dispersion of Pt species,followed by(111)face.The improved dispersion of Pt species can enhance the metal-supports interaction,which promotes the electron transfer of CeO_(2)carrier to Pt nanoparticles and the adsorption-activation of O_(2),thereby facilitating the total oxidation of toluene via the Langmuir-Hinshelwood(L-H)mechanism.Therefore,Pt/CeO_(2)-r(nanorods)sample expresses excellent catalytic performance of toluene oxidation.Finally,the procedure of toluene total oxidation was studied by in-situ diffuse reflectance infrared Fourier transform(DRIFT)spectroscopy.We expect that this work can contribute to the development of an effective sample for the decomposition of volatile organic compounds(VOCs).

圆管内氧化石墨烯MPCM悬浮液对流传热实验研究

由于氧化石墨烯(GO)的高热导率特性,将其添加至相变微胶囊颗粒内,以提高以其为基材制备的悬浮液的热导率,从而进一步强化传热。分别测试了纯水、5wt%相变微胶囊悬浮液(MPCMS)、5wt%和10wt%复合氧化石墨烯的相变微胶囊悬浮液(GO-MPCMS)的传热特性,分析讨论了壁面热流密度、雷诺数(Re)等参数的影响。结果表明,由于相变过程的影响,圆管壁面和流体温度分布呈现上升、平直、上升的变化规律;相同实验条件下,当工质为悬浮液时壁面温度与流体温度比纯水低;颗粒浓度和GO均对传热产生较大影响,相同质量分数(5wt%)时,添加GO时可使稳定后的局部努塞尔数(Nux)进一步提升8个百分点,颗粒质量分数由5wt%增至10wt%时,Nux又增加了20个百分点;与纯水相比,同时考虑GO和微胶囊颗粒的影响,相同实验条件下,相变微胶囊悬浮液平均努塞尔数(Nu)可提升1.0~2.0倍。

高湿黏性颗粒在PTFE滤料表面的沉积规律研究

过滤过程中颗粒物在滤料上的沉积形貌对除尘器过滤性能及清灰频率的确定至关重要。为深入了解颗粒物在聚四氟乙烯(PTFE)滤料表面的沉积规律,搭建了一套过滤实验系统,基于该实验系统对比了过滤时间、粉尘浓度、过滤风速和含水率对颗粒单位面积沉积质量及粉尘层平均厚度的影响,探究了两种沉积速率的适用性及高湿黏性颗粒的黏附效率,并推导了不同含水率粉尘层的厚度分布模型。通过建立沉积粉尘层内部颗粒间的受力模型,对颗粒的受力运动情况进行分析,后续沉积颗粒自身重力对先前沉积颗粒的压缩作用不可忽略,颗粒的运动趋势由上层粉尘层重力、气流对颗粒的曳力及颗粒间黏附力共同决定。实验结果表明,高湿粉尘较干燥粉尘单位面积沉积质量有所降低,随着粉尘含水率增大,粉尘层平均厚度和单位面积沉积质量呈先减小后增大的趋势;高湿粉尘的沉积受颗粒间黏附力大小的影响,粉尘含水率为10%时质量沉积速率和黏附效率最小;粉尘含水率为9%和13%时粉尘层均匀性较干燥粉尘层下降,当高湿颗粒间的黏附力可以抵抗上层重力的压缩作用时颗粒滑动减少,粉尘层结构均匀。含水率为10%~12%时粉尘层均匀性稳定,且含水率为10%时最佳。

Y型褶式洁净滤袋多元结构参数对其过滤阻力影响的CFD模拟研究

为研究褶式滤袋褶数增加引起的褶间距变化对滤袋过滤性能的影响,提出一种新型Y型褶式滤袋,研究了多元几何特性对过滤压降的影响。利用GeoDict软件构建聚酯纤维滤料三维过滤介质模型,用于Y型褶式滤袋的宏观数值模拟研究,基于响应曲面法探究Y型结构下褶式滤袋多元结构参数对其过滤性能的影响。研究结果表明,Y型褶式滤袋相较于常规8,16褶滤袋过滤压降均有所降低。Y型褶式滤袋(褶数NY=8,开口角α=30°,内凹直径d=228 mm)的过滤面积相较于常规8褶滤袋增加58.04%,出口速度分布均匀性提高21.23%;其出口速度分布均匀性相较于常规16褶滤袋提高28.51%。Y型褶式滤袋的最优结构参数为NY=12,α=20.17°,d=240.18 mm,过滤压降达到最小值136.67 Pa。

CFD–DEM simulation of particle deposition characteristics of pleated air filter media based on porous media model

In this study, the three-dimensional physical model of pleated air filtration media was simplified to porous media model, and the calculation parameters of porous media were obtained based on experimental data. The model of V-shaped pleated air filter media is constructed, the height of the media pleat is 50 mm and the pleat thickness is 4 mm, the pleat angle is 3.7°. The Hertz-Mindlin contact model was modified by Johnson Kendall Roberts (JKR) adhesion contact model. The deposition process of particles in media was simulated based on computational fluid dynamics (CFD) theory and discrete element method (DEM). Results show that the CFD–DEM coupling method can be effectively applied to the macro research of pleated air filter media. The particles will form dust layer and dendrite structure on the fiber surface, and the dust layer will affect the subsequent air flow organization, and the dendrite structure will eventually form a “particle wall”. The formation of the “particle wall” will prevent the particles from moving further in the fluid domain, which makes area of pleated angle become the “low efficiency” part about the particle deposition. Compared with area of pleated angle, the particles are concentrated in the opening area and the middle area of the pleated to agglomerate and deposit.

Numerical investigation of non-spherical particle deposition characteristics on filter media

In the building environment,PM2.5 seriously affects people’s health and quality of life,so it is necessary to study the particle deposition characteristics.In addition,it is essential for a thorough investigation of the dust removal mechanism to understand the non-spherical particles deposition characteristics.The stacking angle experiment was used to calibrate the discrete element simulation parameters.And four simulation methods(CFD-DPM,CFD-DEM,API interface loading drag model based on EDEM software and EDEM simulation)were used to numerically simulate the non-spherical particles deposition characteristics.The optimal simulation method EDEM was applied to study the non-spherical particles deposition characteristics in filter media,which saves the calculation time obviously.On this basis,the particle parameters on the particle deposition characteristics of filter media were investigated.The results show that the deposition rate of non-spherical(special shape)particles with the same volume is basically consistent on the filter media,hence it is more realistic that the dust actual shape is simplified into the triangular-shaped particles.As the particle size increases,the number of deposited particles on the filter media decreases.And the larger the particle size,the more dispersed the distribution.It has a significant impact on the number of particles deposited on the filter media when the particle velocity is 0.1 m/s.The particle deposits to the lower part of the filter media in the form of a parabola and deviates from the outlet seriously at 0.1 m/s.Moreover,it has little effect on the number of particle deposition at the other velocities,and most particles are deposited on the upper part of the filter media with the increase of particle velocity.

细小槽道换热器内相变微胶囊悬浮液对流传热DPM模拟

基于离散相模型,采用颗粒比热容随温度变化分段函数描述颗粒的相变过程,模拟了相变微胶囊悬浮液在细小槽道换热器内的对流传热特性,考察了不同入口流量时换热器进出口压差及温差的变化规律,并与纯水进行比较,分析了换热器内部及加热面温度分布,研究了换热器典型通道修正的局部努赛尔数Nux＊沿流动方向的变化规律.结果表明,相变微胶囊悬浮液在换热器内的压损随流量变化规律与纯水一致,较纯水有所增大;引入相变微胶囊颗粒减缓了加热面和流体温度升高的速率,使换热器出口及加热面的温度比纯水低;受进出口位置影响,换热器内温度呈现中间通道低、向两侧逐渐升高的分布规律.不同通道的Nux＊沿流动方向的变化规律存在一定差异,部分通道内相变材料完全融化,而部分通道内相变材料尚未完全融化就流出换热器.需改进换热器进出口位置或对换热器内部结构进行优化设计以获得较好的流量分配特性,从而改善换热效果.

丙烯酸树脂-正十二烷醇相变微胶囊制备及性能表征

微胶囊化相变材料具有储能密度高、相变温度近似恒定、便于储存和输运等特点,在热能储存、输运和利用领域具有广泛的应用前景。本工作采用悬浮聚合法辅以超声辐照手段合成了以正十二烷醇为芯材、丙烯酸树脂为壳材的新型高相变潜热相变微胶囊(MEPCM)颗粒。用扫描电子显微镜(SEM)、傅里叶红外光谱仪(FT-IR)、差式扫描量热仪(DSC)、热重分析仪(TGA)和激光粒度仪(LPSA)等设备对微胶囊性能进行了表征。结果表明,所制相变微胶囊呈较规则球体,粒径为638.14~1478.65 nm,中位径d50为933.91 nm。冷却过程中微胶囊芯呈两种不同的结晶过程,囊芯含量为43%,与设计值50%较接近,包覆率达86%,熔化相变潜热为93.31 kJ/kg;包覆后的相变材料融化温度为22.26℃,过冷度从4.61℃降至2.13℃。壳材不与芯材反应。MEPCM质量降低起始温度略高于纯正十二烷醇,封装可改善相变材料的热稳定性,该相变微胶囊具有良好的潜热储存能力和较快的温度变化响应速度。

柜式空调微通道蒸发器换热性能测试

设计并搭建了柜式空调用微通道蒸发器的性能实验测试平台,测试了微通道蒸发器扁管进出口端温度分布及蒸发器进出口温差、压差、输入功率、制冷量和系统能效比随环境舱温度(18~23℃)升高的变化,并与常规管翅式蒸发器进行了对比。结果表明,微通道蒸发器具有较好的制冷剂流量分配特性,提高了空调出风口温度分布均匀性;由于微通道蒸发器制冷剂充注量低于管翅式蒸发器,且流程也相对缩短,相同工况下,微通道蒸发器进出口压差比管翅式蒸发器降低了33.9%,输入功率降低了4.12%,制冷量提升了2.95%,系统能效比最高提高了6.69%。

氧化石墨烯改性的正十二烷醇相变微胶囊的制备及性能测试

微胶囊化相变材料具有储能密度高、相变恒温、便于储存或运输等特点,在热能储存、输运和利用等领域具有广阔的应用前景。针对传统相变微胶囊含有甲醛及低导热率等问题,以正十二烷醇为芯材、以丙烯酸树脂为壳材,在超声辐照条件下采用悬浮聚合的方法制备了相变微胶囊颗粒,并通过添加氧化石墨烯进行改性。采用扫描电子显微镜(SEM)、傅里叶变换红外光谱(FT-IR)、差式扫描量热仪(DSC)、热重分析仪(TG-DTA)等对其进行测试表征。FT-IR测试结果表明氧化石墨烯的添加并未影响相变微胶囊的基本化学结构。结果表明,氧化石墨烯的引入使微胶囊颗粒粒径增大,且对其外观形貌产生较大影响。相变微胶囊的热性能和稳定性得到改善,相变潜热增加到135.6 kJ/kg,提升了45%,封装率提升到62%。

制冷剂充注量对微通道蒸发器换热性能影响的实验研究

以微通道换热器作为柜式空调蒸发器,设计并加工了微通道蒸发器(MCE,扁管和翅片均为铝材),搭建实验测试系统。研究了三种入口形式(Z-Inlet,Y-Inlet,U-Inlet)、五种制冷剂充注量(800~1600 g)下微通道蒸发器的表面温度分布、制冷量(Q)、输入功率(P_(in))和能效比(EER),并与管翅式换热器(FTE,铜管-铝翅片)进行对比分析。结果表明,Z-Inlet形式MCE内部制冷剂行程基本相同,流量分配较均匀,其表面温度分布比较均匀,换热效果最佳;Z-Inlet形式MCE的制冷量和EER最高,与另外两种形式相比,制冷量和EER最高分别提高了8.8%和5.7%;MCE的制冷量和EER比FTE大,制冷量平均超出了11%,最高达13.3%(约600 W),EER平均提升了9.36%,最大约为12.4%;此外MCE的EER达到峰值对应的制冷剂充注量与FTE相比减少了200 g。

基于层次分析法的新型滤筒除尘器性能指标权重分析

以内部具有锥体结构的新型滤筒除尘器为研究对象,以滤料特性、粉尘负荷、过滤风速、喷吹压力、清灰方式和新型滤筒结构参数为性能评价因子,基于层次分析法建立新型滤筒除尘器性能评价因子分析的递阶层次结构模型,根据Delphi专家调查法建立各层次的判断矩阵,通过计算对影响新型滤筒除尘器选型的主要性能指标除尘效率、压力损失、清灰效果、处理风量及经济性等进行权重分析.结果表明,各性能评价指标对新型滤筒除尘器性能的影响权重为滤料特性＞新型滤筒结构参数＞粉尘负荷＞过滤风速＞清灰方式＞喷吹压力,各性能指标对新型滤筒除尘器选型影响的相对权重为除尘效率＞经济性＞压力损失＞清灰效果＞处理风量.

电热水器内部结构优化及储能特性研究

将相变储能技术应用于电热水器,并通过添加石墨纳米颗粒改善相变材料的导热特性,对其储能过程进行调节,可以起到"移峰填谷"的作用。建立了四种不同结构的电热水器三维模型,模拟了电热水器内部速度场与温度场分布特性。考察了进出口水管结构、电加热管布置方式、保温层结构等因素对热水器内部流场及传热特性的影响,研究了不同储能层厚度对电热水器储能的影响。结果表明,水平加热管与垂直加热管相比,加热过程中加热效率提高了2.2%;进水管管径增大1.5倍,热水输出率提升了17.9%;加入相变材料可在相同保温时间内(36 h)使水温最大提高10.6%。