水煤浆气力式静电雾化喷嘴设计及雾化流场形貌

借鉴已有的常规水煤浆气力式雾化喷嘴的研究与应用成果,设计了新型的气力式静电雾化喷嘴。在此基础上搭建了以环电极感应充电方式的水煤浆静电雾化实验台,利用激光粒子成像速度仪(PIV)上的CCD相机对其静电雾化流场的形貌进行实验观察,获取其荷电射流雾化角度随外加电场增加的变化情况;并利用激光粒子动态分析仪(PDA)系统分别获得流场轴线上以及轴线150 mm处横截面的透浆率随环电极电压的变化情况。实验结果表明:在感应电场的作用下,荷电喷雾流场随外加电场的增加而扩展,射流雾化角在42°—65°变化,且随充电电压的上升略呈一定的指数规律增加;水煤浆雾滴在射流轴线附近聚集的现象得以改善,浆滴在雾炬空间的弥散愈加均匀,可在一定程度上解决水煤浆雾炬核心区贫氧燃烧的难题。     

乙醇在微尺度单电极燃烧器内的雾化与燃烧

采用荷电喷雾燃烧技术是促进微尺度下液体燃料稳定燃烧的重要方法。使用乙醇为燃料,在新型结构的喷嘴内径为0.8 mm微尺度单电极燃烧器内,进行了荷电雾化与燃烧特性的实验研究。结果表明:荷电雾化会随喷嘴电压升高而出现4种模式,对应的荷质比在脉动模式下最低,到达锥-射流模式后出现跃升,在锥-射流模式下最为稳定。荷电雾化后的乙醇在燃烧器网格处稳定燃烧,火焰温度随着当量比增大先上升后下降。火焰温度在当量比=1.0时达到最高值,且随电压增大而上升。锥-射流模式下,当量比=1.0时,燃烧效率可达89%,燃料转换效率可达90%。稳定的雾化模式以及合适的当量比,对燃烧效果具有较大的改善作用。     

液液静电雾化特性

对水静电雾化弥散于玉米油的液-液雾化过程进行了实验研究。通过拍照对雾滴形态进行了观察。观察表明,不同电压下液-液雾化会呈现出滴状和云状雾化两种较为典型的雾化形态,在两种形态下液滴具有不同的形貌和运动特点,本文给出了两种雾化形态的出现条件及特征描述。通过Winner99颗粒图像分析仪及雾滴尺寸的分布理论,对不同静电电压下雾滴直径的分布规律进行了定量分析。研究结果表明,液-液静电雾化中雾滴的直径分布服从Rosin-Rammler分布规律。随着电压的升高,雾滴直径分布趋向均匀,雾化细度得到改善。与在空气中雾化有所不同,液-液雾化中雾滴分布的概率密度曲线峰值两边呈现出显著的不对称性,小液滴数尺寸分布较窄而大雾滴数的尺寸分布较宽。随着电压的升高,大雾滴尺寸分布有所变窄,概率密度曲线趋近对称。     

双流体喷嘴雾化特性实验

双流体雾化降温冷却技术是将气体和液体在喷嘴内部直接混合,在高压射流作用下直接雾化,雾化的小液滴气化时带走热量,从而降低工作区域温度。喷雾冷却降温系统广泛应用于养殖、高精度建筑及机械切削加工中刀具的冷却等。影响喷雾降温冷却的关键因素是雾滴粒径和雾滴运动速度。雾滴粒径越小,其总表面积越大,易于蒸发、气化,从而产生良好的降温效果;而雾滴运动速度加快则可以进一步加快工作区域的换热过程。文章利用相位多普勒粒子动态分析仪(PDA)对4种不同喷孔直径的喷嘴进行了较为详细的实验研究,获得了影响雾滴粒径和雾滴运动速度的重要因素,得到了双流体雾化喷嘴工作的最佳压力与孔径组合,为喷雾冷却降温的研究奠定了基础。     

不同雾滴要求下气力式雾化喷嘴的最佳气耗率

为探讨和分析最佳气耗率与液体流量变化之间的规律,采用液体旋流式气力雾化喷嘴分别对水和水煤浆进行雾化特性试验,以雾滴索太尔平均直径和粒径分布作为主要判断指标,根据不同的应用场合对雾滴的不同要求,确定了最佳气耗率的选取标准。结果表明,不同内径的气力式雾化喷嘴在其液体流量(负荷)改变时,均对应有不同的最佳气耗点。最后,回归拟合了雾化工质为水的该喷嘴最佳气耗率经验公式,经对比与实验数据基本吻合。     

静电喷雾技术理论与应用研究进展

静电喷雾技术为新型农药使用技术,对农药利用率、环境保护以及药液在靶标上的分布等具有重要作用。对静电喷雾的原理与特点,荷电方式,静电雾化,雾滴荷电效果及运行、沉积过程进行了深入阐述,论述了静电喷雾技术、药械的研究进展,提出当前静电喷雾技术理论与应用过程中存在的问题和解决方法,对未来可能的发展趋势进行了展望。     

电晕放电喷雾荷电特性

静电喷雾广泛应用于工业各个领域,如静电喷涂、静电雾化燃烧、静电雾化除尘等,其应用效果与喷雾荷电特性密切相关。为获得更佳荷电效果,本文探究了电晕荷电过程中感应电流对液滴真实荷电电流的影响,通过改变荷电电压、电极间距、电极环直径及液体流量等,实验研究了各因素变化对喷雾荷质比、电荷衰减及液滴粒径的影响。结果表明：相比于感应荷电,电晕荷电过程不稳定但能获得更佳的荷电效果,液滴荷质比随荷电电压的增加而先减小后增大,随电极环直径的增加而先增大后减小,随电极间距的增大而增大,电极环直径80mm,电极间距40mm能获得最佳荷电效果;荷电液滴带电量会随输运距离增加而泄漏衰减,相同距离下液滴通过电晕放电带有电荷后衰减更快;液滴带电后能够降低液体表面张力,随着液滴荷电量的增加,雾化液滴粒径有所降低。     

国内外水煤浆喷嘴研究进展

本文从水煤浆喷嘴结构及使用寿命,水煤浆的雾化特性及雾滴测量技术等几个方面,对近几年国内外水煤浆燃烧及气化喷嘴的研究成果和发展现状进行了综述,意在促进我国水煤浆雾化喷嘴的研究。这无疑将对我国水煤浆雾化喷嘴结构研究和提高使用寿命等起到积极的推动作用。     

假塑性流体雾化研究：Ⅰ.雾化特性的研究

本文采用二流式气动喷嘴，通过激光衍射粒径分布测量系统对假塑性流体料液的雾化特性进行了试验研究，得到了物料特性（主要指粘度）和操作参数（主要指气液质量比和空气速度）以及喷嘴液气出口面积比对雾滴平均直径和尺寸分布参数的影响，并进行回归，得到预测雾滴平均直径及尺寸分布参数的关联式。     

生物柴油雾化特性仿真模拟及实验研究

为了研究风量对地沟油生物柴油在旋流喷嘴中雾化特性的影响规律,本文采用Fluent数值模拟与实验相结合的方法,在供给不同一二次风量的条件下,对地沟油生物柴油进行雾化过程分析。结果表明,在等温等压条件下,控制进入燃油燃烧器的总气量为定值429L/min时,不同一二次风量对油束雾滴的索特平均直径（D₃₂）、雾滴速度、雾化锥角和雾化贯穿距有较大的影响。随着一次风量的增大,雾滴的破碎时间变短,D₃₂逐渐减小,速度逐渐增大;雾化贯穿距和雾化锥角呈现先增大后减小的趋势,一次风量50L/min时达到最大值;且湍动能与一次风量大小成正比关系。风量对D₃₂影响存在一定限度,当一次风量达到30L/min时,D₃₂基本趋于稳定。对不同粒径的雾化液滴数量统计分析,得到了生物柴油的不同粒径数量密度分布及拟合经验公式,颗粒直径主要集中在25～75μm之间。     

带点火功能的水煤浆烧嘴及应用

简要介绍开发研制的带点火功能的水煤浆烧嘴,由此使水煤浆气化采用水冷壁气化炉成为可能.可以进一步提高水煤浆气化炉的温度,以适应于高灰熔点的煤种.该烧嘴已成功应用于山西丰喜肥业集团.     

Mathematical Modeling of Drying of Liquid/Solid Slurries in Steady State One-Dimensional Flow

ABSTRACT

A mathematical model of simultaneous mass, heat and momentum transfer for two-phase flow of a gas and a solid/liquid slurry was developed. The model was applied to calculation of the drying process of coal-water slurry droplets in a gas medium in a steady one-dimensional flow. The model was based on the well-known two-stage drying process for slurry droplets. After the first period of drying, in which the evaporation rate is controlled by the gas phase resistance, the evaporating liquid diffuses through the porous shell (crust) and then, by convection, into the gas medium. Inside the dry external crust of the drop, a wet central core forms, which shrinks as evaporation proceeds. The temperature of the slurry droplet rises. The process ends when the temperature of the dry outer crust reaches the coal ignition temperature in the case of combustion or when the moisture of the particle reaches the final required moisture. The developed model was based on one-dimensional balance equations of mass, energy and momentum for the liquid/solid and gas phases. The system of governing equations was represented by first-order differential equations and solved simultaneously. The numerical solution of the governing equations was obtained using Gear's method. The model permitted calculation     

Mathematical Modeling of Drying of Liquid/Solid Slurries in Steady State One-Dimensional Flow

A mathematical model of simultaneous mass, heat and momentum transfer for two-phase flow of a gas and a solid/liquid slurry was developed. The model was applied to calculation of the drying process of coal-water slurry droplets in a gas medium in a steady one-dimensional flow. The model was based on the well-known two-stage drying process for slurry droplets. After the first period of drying, in which the evaporation rate is controlled by the gas phase resistance, the evaporating liquid diffuses through the porous shell (crust) and then, by convection, into the gas medium. Inside the dry external crust of the drop, a wet central core forms, which shrinks as evaporation proceeds. The temperature of the slurry droplet rises. The process ends when the temperature of the dry outer crust reaches the coal ignition temperature in the case of combustion or when the moisture of the particle reaches the final required moisture. The developed model was based on one-dimensional balance equations of mass, energy and momentum for the liquid/solid and gas phases. The system of governing equations was represented by first-order differential equations and solved simultaneously. The numerical solution of the governing equations was obtained using Gear's method. The model permitted calculation     

铝–油酸/正庚烷基纳米浆体燃料液滴着火燃烧特性

采用液滴悬挂法研究了正庚烷液滴、油酸/正庚烷混合燃料液滴、含20wt%纳米铝粉的铝–油酸/正庚烷基纳米浆体燃料液滴在不同温度下(600~800℃)的着火燃烧特性。用高速摄像机观测液滴进入管式电阻炉后的着火燃烧过程,使用热电偶记录液滴周围的气相温度变化,同时通过对应的温度曲线计算液滴的着火延迟时间。结果表明,纳米铝粉和油酸的添加均能降低正庚烷液滴的着火延迟时间。随温度升高,正庚烷、油酸/正庚烷混合燃料、铝–油酸/正庚烷基纳米浆体燃料液滴的着火延迟时间显著降低,但变化趋势逐渐趋于平缓。铝–油酸/正庚烷基纳米浆体燃料液滴的着火延迟时间与环境温度满足阿累尼乌斯方程。与纯正庚烷、油酸/正庚烷混合液滴的燃烧过程相比,铝–油酸/正庚烷基浆体燃料液滴的燃烧过程有显著差异,其燃烧经历3个阶段：正庚烷稳定燃烧阶段、正庚烷微爆炸阶段和表面活性剂微爆炸阶段。铝–油酸/正庚烷基浆体燃料液滴燃烧时间延长,火焰熄灭后又复燃,且燃烧过程中发生剧烈的火焰形变和铝颗粒溅射现象,大部分铝以团聚体形式在第三阶段完成氧化还原反应。     

水煤浆流化悬浮高效洁净燃烧技术研究与应用

在深入研究的基础上,作者提出了水煤浆流化悬浮高效洁净燃烧新技术,并进行了工程实践。该技术可用于新型系列水煤浆流化悬浮高效洁净燃烧锅炉的开发,并将各种型式的低效链条炉排锅炉、往复炉排锅炉、煤粉锅炉、鼓泡流化床锅炉、燃油锅炉改造成先进水煤浆流化悬浮高效洁净燃烧锅炉。文中介绍了该技术的特点与原理及工程实践。     

Disruptive burning of precursor/solvent droplets in flame‐spray synthesis of nanoparticles

Flame spray pyrolysis is an established technique for synthesizing nanoparticles in the gas phase through aerosol combustion of precursor/solvent droplets. The combustion characteristics of isolated micron‐sized precursor/solvent droplets are investigated experimentally. Pure solvent droplets burn uniformly and classically quasisteady, whereas precursor/solvent droplets manifest disruptive combustion behavior. The fast onset of droplet disruption, which occurs only for solutions with dissolved metal precursors, is not due to solid‐particle precipitation within the droplet. Instead, the mechanism of disruptive droplet burning is similar to that of slurry droplets, consisting of three main steps: (1) diffusion‐controlled burning of the high‐volatile solvent, (2) viscous‐shell formation due to decomposition of the low‐volatile metal precursor, and (3) subsequent disruption due to heterogeneous nucleation. The time sequence of the three steps depends on the concentration and decomposition characteristics of the metal precursor, shortening with increased concentration and higher incremental decomposition temperature. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4553–4566, 2013     

采用高压静电雾化法制备W/O乳化液的实验研究

采用静电雾化方法进行了W/O玉米油乳化液制备的实验研究,在雾化流量2.8~15 mL/min、电极施加电压5.2~11 kV的条件下,用Winner99颗粒图像测试仪测试了所制乳化液的离散相滴径,分析了施加电压及雾化流量对平均滴径及滴径分布的影响. 结果表明,静电雾化法可制备离散相滴径比搅拌法更均匀的乳化液,离散液滴平均滴径约为28 mm且绝大多数液滴直径为20~40 mm,其稳定性明显优于搅拌法所制乳化液. 乳化液离散相滴径与施加电压及雾化流量密切相关,电压增大、雾化电流增大,乳化液离散相滴径急剧减小,滴径分布变窄. 流量增大,单位时间内液滴携带及输运的电量增大,故雾化电流增大;但液滴荷积比随流量增大而减小,故滴径变大,滴径分布变宽. 高电压、低流量有助于获得稳定性更好的乳化液.     

精细水煤浆在小型高速内燃机上的燃烧理论分析

根据在内燃机气缸内燃烧水煤浆的试验,计算了精细水煤浆的热值;通过对汽缸内热力分析,得出精细水煤浆燃烧可以完全满足汽缸内的工况要求,同时分析了精细水煤浆在气缸内的燃烧过程。     

Effects of NTO Oxidizer Temperature and Pressure on Hypergolic Ignition Delay and Life Time of UDMH Organic Gel Droplet

Organic gel propellants are promising candidates for a variety of rocket motor and scramjet applications, since they are intrinsically safe and provide high performance. It is well known that organic gel fuel droplets exhibit distinct combustion characteristics compared with conventional liquid fuel droplets, and furthermore an understanding of the ignition delay and lifetime of these droplets is critical to the improvement of combustor design. In this work, investigations of the combustion of unsymmetrical dimethylhydrazine (UDMH) organic gel droplets in different nitrogen tetroxide (NTO) oxidizing atmospheres were conducted using two sets of experimental apparatus. The combustion characteristics under different conditions of temperature and pressure were compared and analyzed based on the flame shapes observed during experimentation. From these trials, an unsteady combustion model was developed and used for the numerical simulation of spray‐sized UDMH organic gel droplet combustion in an NTO atmosphere. The hypergolic ignition and burning characteristics of the organic gel droplets under conditions simulating either engine startup or steady state combustion were compared, and changes in ignition delay and droplet lifetime with ambient temperature and pressure were analyzed. The experimental and numerical results show that the UDMH organic gel droplets exhibit periodic swell‐burst behavior following the formation of an elastic film at the droplet surface. Each droplet burst results in fuel vapor ejection and flame distortion, the intensity of which declines with increasing ambient pressure. However, the swell‐burst period is extended with increasing ambient pressure, which results in potential flameout. Under conditions of low temperature and pressure similar to those at engine startup, the ignition delay and lifetime of spray‐sized gel droplets decrease with increasing temperature or pressure, although there is a sharp increase in droplet lifetime when the ambient pressure reaches a critical value associated with flameout. The ignition delay was found to be a rate‐limited phenomenon linked to the droplet heating rate. The proportion of ignition delay and droplet lifetime due to droplet heating‐up decreased with increasing temperature or decreasing pressure. Conversely, at high temperatures and pressures simulating the engine’s steady state operating conditions, the droplets were observed to flameout after several swell‐burst periods and both ignition delay and lifetime decreased monotonically with increasing temperature or pressure. The ignition delay time was determined to be rate‐limited by gas phase chemical reactions and contributed very little to the overall droplet lifetime compared with the engine startup condition.