灰分对冷凝式换热器换热特性的影响研究

灰分广泛存在于锅炉尾部烟气和各类干燥乏气中,在烟气/乏气余热回收环节是不可忽视的因素。本文以含灰分烟气/乏气的余热和水回收问题为研究背景,采用含灰分湿空气模拟烟气/乏气,对含灰分湿空气的换热特性展开实验研究,获得了换热系数随时间的变化规律并观察了积灰形态。实验研究发现:在含灰分的情况下,湿空气对流冷凝换热系数随时间的增加先减小后维持稳定,呈现指数规律变化。相比较于干空气,湿空气换热系数达到稳定状态所需时间较长、降低幅度较大,积灰严重且主要集中于上部管束。     

规则结构多孔填料塔两相流动特性实验研究

本文以空气和水为工质,对规则结构多孔填料塔的气-液逆向流动特性进行了可视化实验,研究了填料塔内气一液两相流动规律.实验结果表明:当液体流量一定时,随着气体流量的增加,压力损失增大;当气体流量一定时,随着液体流量的增加,气相压力损失增加.根据实验结果提出了采用水力雷诺数、韦伯数和无量纲流动参数的填料塔内气-液两相流动阻力系数实验关联式.     

含微细颗粒混合气体竖直槽道内冷凝换热特性实验研究

用氮气、水蒸气和褐煤煤粉模拟褐煤烟气混合气体,在水蒸气质量分数为30%,褐煤煤粉颗粒粒径小于70μm,颗粒浓度为0.13~1.37 g/m3,混合气体雷诺数为24331的参数范围下,对含微细颗粒混合气体在竖直槽道内的冷凝换热特性进行实验研究,分析微细颗粒浓度和粒径对混合气体冷凝换热特性的影响。研究结果表明:颗粒在冷凝液膜内伴随冷凝液的流动而运动,换热最终达到稳定状态;随着混合气体中颗粒粒径和颗粒浓度的增大,混合气体显热换热强度减弱。     

ZrO_2-水纳米流体管内层流流动特性的实验研究

实验研究了粒径为50 nm,质量分数为0.2%,0.4%,0.8%,1.2%的ZrO_2-水纳米流体分别在弯管和直管内的流动特性以及纳米流体的稳定性.实验结果表明:通过加入分散剂使纳米流体稳定性得到显著提高,在相同温度的层流状态下,弯管的流动阻力系数大于直管.纳米流体的黏度随着质量分数的增大而增大,在相同Re下,纳米流体在层流区内阻力系数随纳米流体质量分数的增加而增大.     

Ar/H2O大气压等离子体射流放电特性

为了研究水蒸气体积分数对大气压等离子体射流放电机理及放电效率的影响,进而产生高活性低温等离子体并优化其效率。通过对大气压氩水等离子体射流的电压电流波形和Lissajous图形等电气特性的测量及发射光谱和发光图像等光学特性诊断,研究了不同水蒸气体积分数时,等离子体射流的放电特性。通过计算放电功率、传输电荷量、电子激发温度、分子振动温度和分子转动温度等主要放电参量,研究了它们随水蒸气体积分数的变化趋势,并结合放电机理对所得实验结果进行分析。结果表明,Ar/H2O等离子体射流除了产生N2和Ar,还有OH和O,气体温度在525~720 K之间变化,为典型的低温等离子体;随着水蒸气体积分数的增加,等离子体羽喷出管口的长度减小,放电功率减小,发光强度减弱,转动温度和振动温度增加;相同功率下,水蒸气体积分数为0.5%时,产生的OH达到最大。     

印刷电路板通道的高温传热和阻力特性研究

印刷电路板换热器是超高温气冷堆等高温能量利用与回收领域中极具潜力的备选强化传热技术之一,本文通过数值模拟方法对典型Z字形印刷电路板(PCHE)传热通道的传热和阻力特性开展了相关研究。计算结果表明:层流模型可以较好地获得Z字形PCHE通道的阻力和传热性能,Z字形PCHE通道的阻力系数大于半圆管直通道的阻力系数;当热侧和冷侧通道流体入口温度均不发生改变时,增加两侧流体的质量流量,通道内的阻力系数随之减小,传热效率也稍微减小;当两侧流量及冷侧入口温度均不发生改变时,提高热侧通道入口温度,通道内阻力系数成线性增大,传热效率也随之提高。     

气液固三相浆态床流型转变特性的试验研究

建立了高0.8 m,截面为0.1 m×0.01m的可视化浆态床实验系统,采用空气、水和玻璃粉作为浆态床中气液固三相,研究了颗粒粒径为58~75μm和106~150μm,固相体积分数为3%和9%时的宏观流动特性。试验获得了不同物料体系下的床层压降随气体雷诺数的变化规律,同时得到了颗粒浓度对流型转变气速的影响。找到均匀流流型向过渡流型转变的第一转变点和从过渡流型向非均匀流型转变的第二转变点的取值范围。结果表明:三相体系的压差值随着气体雷诺数的增大而趋于一个稳定值,颗粒粒径增大会使体系压差值增大;固体颗粒浓度的增加,会使第二转变点取值减小,而颗粒粒径对流型转变气速影响很小.同相浓度的增加,会加快三相体系的失稳,在更低的气速下进入到非均相湍动流动状态中.     

改良干法压裂液摩擦阻力特性实验研究

对改良的干法压裂液这种非牛顿流体的摩擦阻力特性的正确认识,关系着干法压裂技术的有效实施.为此,本文在大型高压泡沫压裂液实验回路上,考察了在模拟实际施工条件下的改良干法压裂的摩擦阻力特性.实验表明:改良后的干法压裂液摩擦阻力系数随压力、温度的升高和泡沫质量的增加而增大,随流速的增加而减小.在实验范围内,温度对摩擦阻力系数的影响不大.实验得到了改良的干法压裂液摩擦阻力系数与广义雷诺数的关联式,平均计算误差为9.19%.     

超临界CO2-丙烷混合物管内传热特性数值研究

采用SST k-w湍流模型对超临界CO₂/丙烷混合工质水平管内的传热特性进行数值模拟研究。管径d=4 mm,加热段L₂=800 mm;混合工质浓度配比为100/0、95/5、90/10、85/15、80/20、75/25;质量流速为150～250 kg·m^?2·s^?1;热流密度为30～40 kW·m^?2,入口温度293 K,入口压力7.5～30 MPa。随着丙烷浓度的增加,CO₂/丙烷二元混合工质的临界压力降低,临界温度升高,丙烷浓度从5%增加到25%,换热系数峰值降低6.19%～31.45%,但增加丙烷浓度可提高拟临界温度后的换热效果。P=7.5～8.5 MPa,换热系数有明显峰值;P=20～30 MPa,换热系数变化规律无明显峰值,并随压力的升高而减小。混合工质的换热系数随质量流速的增大而增大。同一流体温度所对应的换热系数,随着热流密度的增加而减小。     

超临界CO2-丙烷混合物管内传热特性数值研究

采用SST k-w湍流模型对超临界CO₂/丙烷混合工质水平管内的传热特性进行数值模拟研究。管径d=4 mm,加热段L₂=800 mm;混合工质浓度配比为100/0、95/5、90/10、85/15、80/20、75/25;质量流速为150～250 kg·m^?2·s^?1;热流密度为30～40 kW·m^?2,入口温度293 K,入口压力7.5～30 MPa。随着丙烷浓度的增加,CO₂/丙烷二元混合工质的临界压力降低,临界温度升高,丙烷浓度从5%增加到25%,换热系数峰值降低6.19%～31.45%,但增加丙烷浓度可提高拟临界温度后的换热效果。P=7.5～8.5 MPa,换热系数有明显峰值;P=20～30 MPa,换热系数变化规律无明显峰值,并随压力的升高而减小。混合工质的换热系数随质量流速的增大而增大。同一流体温度所对应的换热系数,随着热流密度的增加而减小。     

Condensation Characteristics of Flue Gas/Steam Mixtures with Fine Lignite and Ash Particles along Horizontal Finned Tube Bundles

The condensation behavior for a gas/steam mixture with fine lignite particles and lignite ash particles is experimentally investigated as the particles flow over horizontal finned tube bundles. The effects of the gas velocity, inlet temperature of cooling water, excess air coefficient, and particle dimension are discussed. The total mass flow rate of the condensate and the condensation heat transfer coefficient for flue gas including particles are higher than those of flue gas excluding particles when Reynolds number is higher than 2,300. The area covered by ash depositions tends to grow from the leeward toward the windward side with increasing particle diameter.     

煤粉燃烧过程中灰膜形成比例实验研究

煤焦颗粒燃烧过程中,灰膜形成显著影响其燃烧特性。因此,本文借助高温沉降炉研究了61~75,75~90和90~125μm三种粒径黄陵烟煤在1273和1673 K温度下的燃烧特性与灰膜形成比例;借助扫描电镜(SEM)详细观测空心微珠颗粒内部结构,提出灰膜比例计算公式,并分析温度,粒径和碳转化率对灰膜比例的影响。结果表明,高温下大部分灰分在焦炭烧尽阶段以灰膜形式存在。灰膜比例随温度和碳转化率增加而增加,随煤粉粒径增大而减小。高温下灰分用于形成灰膜比例相对较高,这为煤焦燃尽阶段的低反应性提供了合理的解释。煤焦颗粒动态燃烧过程中灰膜形成比例随燃烧工况变化而变化。该研究为煤焦颗粒燃烧动力学模拟灰膜比例选择提供了关键数据支撑。     

电感耦合等离子体发射光谱法测定烟道灰中的铟

铟是一种银白色稀有稀散金属,在地壳中的平均质量分数为0.000 01%,为了准确测定烟道灰样品中低含量的铟,通过对样品成分的初步分析,确定实验中溶解样品所用的酸及其比例。依次逐步加入HCl, HNO3, HF和HClO4(V∶V∶V∶V=15∶5∶2∶2),将样品完全溶解后,冷却至室温并移入分液漏斗,在HBr介质中,以溴化铵做盐析剂(溶液体积控制在25 mL左右);移取25 mL乙酸乙酯作为萃取剂和稀释剂,萃取液直接导入配备有机进样系统的电感耦合等离子体原子发射光谱仪(ICP-AES),选择In 230.606 nm为分析谱线,对烟道灰样品中的铟进行测定,从而建立了电感耦合等离子体原子发射光谱法(ICP-AES)测定烟道灰样品中铟的方法。实验样品溶解后,采用萃取分离法消除基体元素及共存元素的干扰。通过对萃取酸度、萃取剂、萃取方法、盐析剂、分析谱线等条件试验,确定了最优的实验条件。铟的质量浓度在0.25~4.00 mg·L^-1范围内与其发射强度呈线性关系,校准曲线线性相关系数为0.999 3,检出限为0.03 mg·L^-1,测定结果的相对标准偏差(n=11)小于5%,回收率在92%~102%之间。按照上述试验步骤测定5个烟道灰样品中的铟含量,其测定结果与ICP-MS法比较吻合。另外,与现有的分析方法(EDTA滴定法、分光光度法、原子吸收光谱法、 X射线荧光光谱法、电感耦合等离子体原子发射光谱法及质谱法等)相比,该法具有简便,快速,灵敏,准确度较高的优点,可用于铟含量在0.000 8%~0.10%之间烟道灰样品的批量检测。     

燃煤飞灰物理化学特性及其润湿机理研究

以小龙潭电厂燃煤飞灰及其不同粒径范围的分级灰为对象,采用X射线荧光光谱、X射线衍射、离子色谱、Zeta电位、扫描电镜等实验方法研究了飞灰的物理化学特征.同时采用沉降实验、表面张力实验研究了三种不同润湿剂对飞灰的润湿性能.研究发现,溶液对飞灰的润湿能力不仅取决于其气液界面张力,还与飞灰的组成、表面电位以及形貌特征密切相关.亲水性物质含量的增加,颗粒表面电荷与润湿剂分子间的静电吸引,颗粒表面的棱角孔隙等均可以促进其润湿;温度越高飞灰润湿性能越好,且温度对飞灰润湿过程影响较大,温度较高(60℃)时润湿剂种类及浓度对飞灰润湿过程的影响不明显.     

ICP-OES分析低钙粉煤灰在NaOH溶液中离子浸出规律

低钙粉煤灰潜在的火山灰活性释放缓慢限制了其大规模利用,通过碱激发提高粉煤灰中Si4+,Al3+和Ca2+等离子浸出率对于加快低钙粉煤灰活性释放具有积极作用。采用电感耦合等离子体发射光谱、傅里叶变换红外光谱、X射线衍射和扫描电子显微镜分别测试和分析了5种浓度NaOH溶液对低钙粉煤灰激发过程中Si4+,Al3+和Ca2+的浸出规律、化学基团变化、水化产物生成及微观形貌演化。结果表明：碱激发作用显著提高了低钙粉煤灰中Si4+,Al3+和Ca2+浸出率,三种离子浸出率大小为：Si4+＞Al3+＞Ca2+,其中Si4+和Al3+浸出率随NaOH浓度增加而增加,随浸出时间延长呈对数规律升高;Ca2+由于在NaOH溶液中生成Ca(OH)₂沉淀,其浸出率大小表现为在水中高,在NaOH溶液中低。红外光谱清晰地表征出低钙粉煤灰受碱激发作用后化学基团在指纹区(波数1 300 cm-1以下)的变化,且随碱激发时间的延长和碱浓度的增加变化愈加明显。水化产物和微观形貌的结果显示出粉煤灰颗粒表面受到碱侵蚀发生解聚,在OH-催化下,硅铝单体分子重新排列形成硅酸盐和铝酸盐低聚络合物,通过亲核取代反应形成铝硅酸盐的低聚态溶胶,并进一步与碱金属阳离子通过配位键或静电键的作用缩聚形成水化凝胶类产物。采用ICP-OES测试粉煤灰中离子浸出率可作为评价粉煤灰火山灰活性的一种快速和准确的方法。     

Biomass fly ash deposition in an entrained flow reactor

Fly ash deposition on boiler surfaces is a major operational problem encountered in biomass-fired boilers. Understanding deposit formation, and developing modelling tools, will allow improvements in boiler efficiency and availability. In this study, deposit formation of a model biomass ash species (K₂Si₄O₉) on steel tubes, was investigated in a lab-scale Entrained Flow Reactor. K₂Si₄O₉ was injected into the reactor, to form deposits on an air-cooled probe, simulating deposit formation on superheater tubes in boilers. The influence of flue gas temperature (589 – 968°C), probe surface temperature (300 – 550°C), flue gas velocity (0.7 – 3.5?m/s), fly ash flux (10,000 – 40,000?g/m²h), and probe residence time (up to 60?min) was investigated. The results revealed that increasing flue gas temperature and probe surface temperature increased the sticking probability of the fly ash particles, thereby increasing the rate of deposit formation. However, increasing flue gas velocity resulted in a decrease in the deposit formation rate, due to increased particle rebound. Furthermore, the deposit formation rate increased with probe residence time and fly ash flux. Inertial impaction was the primary mechanism of deposit formation, forming deposits only on the upstream side of the steel tube. A mechanistic model was developed for predicting deposit formation in the reactor. Deposit formation by thermophoresis and inertial impaction was incorporated into the model, and the sticking probability of the ash particles was estimated by accounting for energy dissipation due to particle deformation. The model reasonably predicted the influence of flue gas temperature and fly ash flux on the deposit formation rate.     

Deformation and Fracture Behavior of PP/Ash Composites

In the present work, the deformation and fracture behavior of PP/ash composites with different ash content was investigated. The effect of a silane coupling agent was also analyzed. From uniaxial tensile tests, an increase in the stiffness with ash content was found as a result of the incorporation of the stiffer filler within the PP matrix. On the other hand, a decrease in tensile strength and strain at break with filler loading was observed. This result was attributed to the increased number of debonded large particles with filler content, which subsequently led to the formation of critical-size flaws. On the other side, the composites displayed higher values of fracture parameters than the matrix as a result of the development of a particle induced toughening mechanism. However, fracture properties were also found to decrease with ash content. This could be attributed to the increase in the number of critical-size flaws that induced premature failure. The incorporation of a silane coupling agent in the formulations led to composites with slightly improved tensile and fracture properties. This was probably due to improved interaction between PP and ash in the first case and a better dispersion of ash particles in the matrix and/or changes in the crystallization behavior of PP, in the latter case.     

减少二氧化碳对LIBS检测飞灰中未燃碳含量影响的研究

通常热力发电厂将飞灰中未燃碳的含量作为评价锅炉燃烧效率的重要指标,通过测量飞灰中未燃碳的含量来评价煤粉燃烧的充分程度,进而实现优化燃烧、提高机组效率。基于激光诱导击穿光谱技术(LIBS)无接触、快速响应、高灵敏度、可以在线测量等特点,备用来测量飞灰中未燃碳的含量。由于烟气中CO₂气体的存在,碳谱线强度会随CO₂浓度的变化而改变。为了减少CO₂气体对飞灰未燃碳测量结果的影响,提出并设计了具有二级旋风分离器的LIBS测量飞灰未燃碳含量实验系统,飞灰从给粉机流出后通过二级旋风分离器进入测量腔体,脉冲激光经过透镜作用于飞灰样品进而产生等离子体。LIBS系统采用双中心波长光谱仪,可测得飞灰中C,Si,Mg,Fe,Ca和Al等主要元素谱线,同时高分辨率通道可分辨出相邻C和Fe的元素谱线,可以在获得充分的飞灰光谱信息的同时保证了测量的精度。实验结果表明该系统可有效分离和收集飞灰颗粒,减少CO₂气体对测量结果的干扰,为LIBS技术的工程应用提供了更准确的依据。     

Utilization of Fly Ash Nanofluids in Two-phase Closed Thermosyphon for Enhancing Heat Transfer

This study investigates how fly ash nanofluids affect the thermal performance of a two-phase closed thermosyphon at various states of operation. The utilization of nanofluids obtained from X₂O₃-type oxides, such as Al₂O₃, Fe₂O₃, or CuO, on the improvement of two-phase closed thermosyphon performance was reported in a number of studies in the literature. The present study experimentally demonstrated the effect of using a nanofluid obtained from fly ash comprised of various types of metal oxides in varying ratios on improving the performance of a two-phase closed thermosyphon. The fly ash was obtained from the flue gas that was captured in the cyclones of the Yatagan thermal power plant (Turkey). Triton X-100 (Dow Chemical Company) dispersant was used in the study to produce the 0.2% (wt) fly ash/water nanofluid via direct synthesis. A straight copper tube with an inner diameter of 13 mm, outer diameter of 15 mm, and length of 1 m was used as the two-phase closed thermosyphon. The nanofluid filled 33.3% (44.2 ml) of the volume ofthe two-phase closed thermosyphon. Three heating power levels (200, 300, and 400 W) were used in the experiments with three different flow rates of cooling water (5, 7.5, and 10 g/s) used in the condenser for cooling the system. A increase of 26.39% was achieved in the efficiency of the two-phase closed thermosyphon when 4% (wt) fly ash containing nanofluid was used to replace deionized water at a heat load of 200 W and with a cooling water flow rate of 5 g/s.     

激光能量对飞灰颗粒流中未燃碳LIBS检测影响研究

飞灰含碳量是评价锅炉燃烧效率的重要指标之一,对其进行在线测量有助于实时进行燃烧优化调整,从而提高整个机组的经济性和安全性。利用螺杆式给粉机搭建飞灰颗粒流含碳量测量台架,将脉冲激光直接作用于飞灰颗粒流,形成等离子体,利用激光诱导击穿光谱技术测量飞灰颗粒流中的含碳量信息。重点研究了激光能量对飞灰颗粒流中未燃碳有效激发和测量的影响规律。研究结果显示,在40～130 mJ能量的脉冲激光作用下,碳谱线强度随着激光能量的增大线性增强,而其信噪比则先增加后趋于稳定,无效光谱的剔除率则呈下降趋势。本实验条件下,激光能量在90～100 mJ之间,可得到较强的等离子体发射信号和较优的光谱数据利用率。因而激光能量与颗粒流的激发状态、碳元素特征谱线强度等密切相关。合理的激光能量有利于保证飞灰颗粒流的有效稳定激发,并获得具有良好信噪比的等离子体光谱信号。