气液双介质喷嘴雾化特性的影响因素研究

目的 气液双介质喷嘴的应用是烟叶加料工艺的关键因素之一,通过采用现有的模拟手段实现加料过程的高精化,为优化实验奠定基础。方法 文中以外混式双介质喷嘴为研究对象,通过构建基于DPM的数值模型,研究不同蒸汽入口压力与针阀位置对喷嘴雾化的气动性能与粒径特性的影响规律。结果 研究表明,喷嘴出口通流面积越大,气流高速区离喷嘴越近,但蒸汽与料液的速度最大值并未有较大变化,此时液滴喷射距离由远变近,喷射半角由小变大。随着蒸汽压力的增大,气流速度以及高速区长度变大,蒸汽压力为0.1 MPa时,气流速度的最大值与蒸汽压力为0.4 MPa时的相差近25%;不同压力下喷射角变化范围较小,为21.5°~23.5°;除此之外,喷雾束变集中,定向性变好,有助于控制其在烟叶表面喷射的均匀性。结论 对于较近的烟叶墙,采用较大流通截面积的喷嘴结构有利于均匀地覆盖烟叶墙,相反,对于较远的烟叶墙,则适合采用较小流通截面积的结构。适当地提高压力有利于提高料液喷洒的均匀性,减少料液的浪费,提高烟丝制备的工艺水平。     

压力型雾化喷嘴射流喷雾气-液两相流数值模拟

为了研究喷雾压力和环境气流速度对射流喷雾的雾化效果及喷雾雾场的均匀性的影响,基于流体力学理论,建立压力型喷嘴喷雾的数值计算模型,利用计算流体动力学软件Fluent对喷雾雾场进行气-液两相流数值模拟研究,并通过大量的数据统计定量分析雾滴粒径的分布情况。结果表明:在喷射压力一定时,风速越大雾滴飘移能力越强,风速过大或过小都将严重影响雾化雾场的均匀性;在一定范围内喷射压力越大,雾化效果越好,所形成的雾滴平均粒径越小。     

低压环境下喷雾特征实验研究北大核心CSCD

对蒸馏水分别通过压力雾化喷嘴和直流喷嘴喷射到低压环境的喷雾过程进行了实验研究,分析了环境压力、工质温度、工质流量对压力雾化喷嘴喷雾锥角和直流喷嘴喷雾瞬态特征的影响。实验结果显示,当采用压力雾化喷嘴时,环境压力越低,工质初始温度越高,喷雾锥角越大;工质流量越大,工质冲转旋转叶片速度越快,喷雾锥角也越大。当采用直流喷嘴时,环境压力越低,工质温度越高,工质流量越大,液柱出现破碎所用的时间越短。直流喷嘴的喷雾现象表现为随时间生长的过程,喷雾形态经历了液柱—液柱破碎—液柱完全雾化的过程。工质温度、环境压力直接影响工质的过热度,来影响闪蒸的剧烈程度,从而改变喷雾形态。     

低压环境下喷雾特征实验研究

对蒸馏水分别通过压力雾化喷嘴和直流喷嘴喷射到低压环境的喷雾过程进行了实验研究,分析了环境压力、工质温度、工质流量对压力雾化喷嘴喷雾锥角和直流喷嘴喷雾瞬态特征的影响。实验结果显示,当采用压力雾化喷嘴时,环境压力越低,工质初始温度越高,喷雾锥角越大;工质流量越大,工质冲转旋转叶片速度越快,喷雾锥角也越大。当采用直流喷嘴时,环境压力越低,工质温度越高,工质流量越大,液柱出现破碎所用的时间越短。直流喷嘴的喷雾现象表现为随时间生长的过程,喷雾形态经历了液柱—液柱破碎—液柱完全雾化的过程。工质温度、环境压力直接影响工质的过热度,来影响闪蒸的剧烈程度,从而改变喷雾形态。     

基于激光粒度仪测量油品喷雾粒径的方法研究

为了测量油品喷雾过程的雾化性能,通过对喷嘴雾化粒径的指标和雾化粒径测定方法的分析,利用激光粒度仪及粒径发生装置设计喷嘴雾化实验系统,并对实验系统的工作原理进行描述;在不同喷雾压力下测定煤基柴油特征平均粒径dv10、dv50、dv90、d[3,2]、d[4,3]数据。结果表明:柴油雾化过程分为形成阶段、扩散阶段、稳定阶段;喷雾压力越大,雾滴特征平均粒径dv10、dv50、dv90、d[3,2]、d[4,3]参数值越小,雾化效果越好,并且随着喷雾压力的增大,液滴雾化粒径减小的趋势变缓。     

平口喷嘴的真空射流雾化模拟分析

基于breakup和collsin液滴破碎模型采用Fluent和Gambit软件对平口喷嘴的真空射流雾化进行了模拟,研究了环境压力、喷射压力和喷嘴直径等参数对射流雾化结构和液滴索特平均直径(Sauter mean diameter,SMD)的影响.结果表明:①随着环境压力的降低,喷射束宽度减小,射流贯穿距离和SMD增加.当环境压力小于0.01 MPa时,各雾化性能参数的变化幅度减小;②环境压力和喷嘴直径一定,随着喷射压力的增加,喷射束宽度呈先快速后缓慢增加的趋势,而射流贯穿距离近似线性增加,SMD值变化不明显;③喷嘴直径越小,喷射束宽度和射流贯穿距离越大,SMD值越小,射流雾化效果越好,更易制备出光滑致密的聚合物薄膜.     

喷雾冷却系统中雾化特性影响因素研究

为研究喷雾式蒸发冷却超级计算机中喷射压力和喷嘴口径对喷雾雾化质量的影响,采用相位多普勒粒子分析仪(PDPA)对成雾状况做了精确测量,分析了雾化参数——雾滴速度、雾滴粒径与喷雾压力、喷嘴口径之间的关系。研究发现:喷雾的粒径分布呈现中间小、两边大的趋势,喷雾速度呈现中间大,两边小的趋势。随着喷雾压力的增加,喷雾的Sauter平均直径(SMD)逐渐变小,雾滴粒径分布趋向均匀,同时喷雾的平均速度变大。随着喷嘴口径的减小,雾滴粒径逐渐变大,速度则先增大后减小。平均SMD与喷雾压力P之间呈指数减小,平均速度V与喷雾压力P之间呈线性关系。平均SMD与喷嘴口径和压力有很好的二元线性关系。     

低出口压力下喷嘴内部空化流动模拟分析

采用Ansys Fluer软件并基于Schnert与Sauer空化模型,对出口压力小于10 Pa平口喷嘴内部的空化流动进行了模拟,研究了喷射压力和喷嘴直径对喷嘴内部蒸汽体积和湍动能分布的影响.结果表明,高喷射压力(10 MPa)对喷嘴内部蒸汽体积的作用减弱,喷射压力为10 MPa时,喷嘴出口径向上的蒸汽体积大于其它喷射压力下的蒸汽体积,可获得较好的空化效果;喷嘴内的湍动能随喷射压力的增加而增加;喷嘴直径对喷嘴内部的空化流动有很大的影响,喷嘴直径越小所产生的空化流动越强烈,对比其它直径的喷嘴,直径为0.1mm的喷嘴在出口处的蒸汽体积和湍动能较大,有助于雾化质量的提高.     

雾化法制备锌粉技术研究

用自行设计的限制式雾化喷嘴为核心的雾化装置,研究了在喷嘴关键结构参数（输液管的直径、喷嘴狭缝尺寸、喷射角等）一定的条件下,雾化压力及熔融温度对液锌的雾化效果的影响。结果表明,当雾化介质为Ｎ２,压力为０．４０～０．５０ＭＰａ,液锌温度为６５０℃时,液锌可以获得较好的雾化效果,通过显微镜观察和电镜扫描,发现制备的锌粉大部分为不规则形状。     

大豆蛋白液喷雾场粒度分布变化

目的研究大豆蛋白液喷雾场粒度分布的变化规律,为选择一个合适的蔬菜纸喷涂面提供实验数据,以期得到质量好的蔬菜复合纸覆膜。方法将大豆蛋白喷涂雾化场网格化,使用粒度仪分别测量各个区域的粒径和粒度占比分布。结果雾化场轴向距离从H=10 cm处的95μm左右,到H=15 cm处的85μm左右,到H=20 cm处的65μm左右,再到H=30 cm处的45μm左右,最大粒径占比范围逐渐降低;雾化场径向距离从L=4 cm处的40~50μm,到L=8 cm处的35~40μm,到L=12 cm处的35~40μm,再到L=16 cm处的30~35μm,最大粒径占比范围也逐渐降低;在相同的喷涂气压、喷涂液压下,随着轴向距离的增加,大豆蛋白液液滴粒径分布范围的减小,大粒径大豆蛋白液液滴的比例逐渐减少,粒径分布朝着小粒径方向靠拢,大豆蛋白液液滴粒径分布曲线越来越陡峭;在喷涂气压、喷涂液压不变的情况下,仅仅改变大豆蛋白液的粘度,在相同的喷雾场位置随着大豆蛋白液粘度的减小,粒度分布朝小粒径方向靠拢,小粒径大豆蛋白液液滴比例逐渐减小。结论喷涂气压越大、大豆蛋白液粘度越小,雾化效果越好,而喷涂液压对雾化效果影响不大;大豆蛋白液喷雾场液滴的粒径分布随着喷雾贯穿距离的增加,小粒径液滴所占比例逐渐增加,粒径分布曲线朝小粒径方向发展,同时随着垂直与喷雾轴心线径向距离的增加,小粒径液滴所占百分比也增加,粒径分布曲线朝着小粒径方向发展。     

大豆蛋白喷涂液雾化粒子场实验

目的研究大豆蛋白喷涂液雾化场的粒度分布,及喷涂过程中喷涂参数对大豆蛋白液雾化液滴粒径的影响,从而在蔬菜复合纸覆膜成型过程中选择最优喷涂参数。方法利用激光粒度仪测量不同喷涂参数下大豆蛋白液喷涂雾化场的粒度分布,并通过数据分析软件Origin研究喷涂参数对大豆蛋白液喷涂雾化粒度的影响。结果喷涂参数相同时,喷涂雾化场中随着轴向距离的增加,大豆蛋白液液滴粒径先显著减小后趋于稳定;喷涂雾化场中同一轴向位置随着径向距离的增加,大豆蛋白液液滴粒径呈减小趋势。在喷涂雾化场同一测量点,随着喷涂气压的增大,大豆蛋白液液滴粒径逐渐减小;喷涂液压对大豆蛋白液液滴粒径没有显著影响。结论喷涂气压为0.2 MPa,喷涂液压为0.16 MPa,喷涂雾化场轴向30 cm平面内,大豆蛋白液雾化液滴粒径较小且均匀。     

The influence of cavitation on the flow characteristics of liquid nitrogen through spray nozzles: A CFD study

Spray cooling with cryogen could achieve lower temperature level than refrigerant spray. The internal flow conditions within spray nozzles have crucial impacts on the mass flow rate, particle size, spray angle and spray penetration, thereby influencing the cooling performance. In this paper, CFD simulations based on mixture model are performed to study the cavitating flow of liquid nitrogen in spray nozzles. The cavitation model is verified using the experimental results of liquid nitrogen flow over hydrofoil. The numerical models of spray nozzle are validated against the experimental data of the mass flow rate of liquid nitrogen flow through different types of nozzles including the pressure swirl nozzle and the simple convergent nozzle. The numerical studies are performed under a wide range of pressure difference and inflow temperature, and the vapor volume fraction distribution, outlet vapor quality, mass flow rate and discharge coefficient are obtained. The results show that the outlet diameter, the pressure difference, and the inflow temperature significantly influence the mass flow rate of spray nozzles. The increase of the inflow temperature leads to higher saturation pressure, higher cavitation intensity, and more vapor at nozzle outlet, which can significantly reduce mass flow rate. While the discharge coefficient is mainly determined by the inflow temperature and has little dependence on the pressure difference and outlet diameter. Based on the numerical results, correlations of discharge coefficient are proposed for pressure swirl nozzle and simple convergent nozzles, respectively, and the deviation is less than 20% for 93% of data.     

基于二值化灰度图像的大豆蛋白液喷雾相对雾化程度的研究

目的 为了更直观的评估大豆蛋白液喷雾雾化程度,辅助筛选出有效扇形面积更大、缺陷更少的喷雾,有助于研究喷雾场的雾化均匀性,以期得到均匀一致的大豆蛋白膜。方法 选取合适的阈值后,对粒子图像速度场仪（Particle Image Velocimetry,PIV）拍摄的图像进行二值化处理,划定喷涂有效区域,利用二值化图像计算喷涂雾化场区域在喷涂有效区域内的点位数占比,将数值定义为相对雾化程度,改变稠度系数、喷涂参数,研究相对雾化程度的变化趋势。结果 低稠度系数的大豆蛋白液喷雾相对雾化程度受喷涂参数的影响较小,并保持在90%以上;中高稠度系数的大豆蛋白液喷雾相对雾化程度随着喷涂流量的增加而减小,随着液压、气压的增大有增大的趋势,随着气液比的增加先增大后减小。结论 基于二值化的PIV图像处理可以有效地辅助评估大豆蛋白液喷雾场的均匀性。     

Effect of water supply pressure on atomization characteristics and dust-reduction efficiency of internal mixing air atomizing nozzle

As a new type of nozzle, the internal mixing air atomizing nozzle has been widely used in the field of dust reduction via spraying. In this study, the effect of water supply pressure on the atomization characteristics and dust-reduction efficiency of the internal mixing air atomizing nozzle was investigated. Firstly, the FLUENT software was used to simulate the flow field inside and outside the nozzle under different water supply pressures. The numerical simulation results showed that as the water supply pressure increased, the internal pressure and water flow velocity in the mixing chamber of the nozzle increased while the air flow rate decreased sharply, resulting the continuous decrease in the relative velocity between gas and liquid. Meanwhile, as the water supply pressure increased, the fragmentation scale of the liquid jet at the outlet of the nozzle was prolonged and the atomization of the liquid was limited. Secondly, based on the custom-developed dust reduction experimental system via spraying, the atomization characteristics of the nozzle were investigated. According to the experimental results, when the water supply pressure increased, the water flow rate and air flow rate of the nozzle had exponential increase and decrease, respectively. As the water supply pressure increased, the range, droplet volume fraction, droplet size, and velocity all increased, while the atomization angle first increased and then decreased. Finally, the dust reduction experiment via spraying was performed under different water supply pressures. The results showed that with the increase of water supply pressure, the dust-reduction efficiency for both the total dust and the respirable dust first increased and then decreased.     

雾化特性及系统参数对闭式喷雾冷却系统性能的影响

搭建了以R22为冷却介质的闭式喷雾冷却实验台,通过更换3种不同的喷嘴,分析对比了不同喷嘴类型和喷雾高度下传热性能的变化规律。实验结果表明:选择喷嘴时必须同时考虑喷雾流量和雾化角度的影响;雾化角较小的喷嘴在低高度下适用性较好。同时,研究了系统参数如过冷度和充注压力对喷雾冷却传热性能的影响,得出过冷度对喷雾冷却性能有一定促进作用,但过冷度越大,促进效果越弱;表面传热系数和表面温度均随充注压力的升高而升高,因此高充注压力不适用于需严格控制温度的表面冷却。     

Numerical study of liquid nitrogen cavitating flow through nozzles of various shapes

The cavitating flow of cryogenic liquid through a spray nozzle is influenced by many factors, such as unique thermophysical properties of cryogenic liquid, the inflow temperature and the complicated geometrical structure of the spray nozzle. The geometrical parameters of liquid nitrogen spray nozzles have a profound impact on cavitating flow which in turn affects spray atomization characteristics and cooling performance. In present study, CFD simulations are performed to investigate influence of the nozzle geometry on the liquid nitrogen cavitating flow. The mixture model is used to describe the liquid-vapor two phase flow, and both the cavitation and evaporation are considered for the phase change. The predictions of mass flow of liquid nitrogen spray are validated against experimental results. The effects of geometric parameters, including the outlet orifice diameter and the length of nozzle, the inlet edge angle of orifice, the inlet corner radius of orifice, the orifice shape and different positions of swirl vanes, are investigated under a wide range of pressure difference and inflow temperature. The results show that the effects of geometric parameters on cavitating flow show different trends under subcooled conditions compared with saturated temperature conditions. The flow characteristics are more affected by the changes of the inlet edge angle, the inlet corner radius, and the orifice shape. The insert of swirl vanes has an effect on the distribution of the cavitated vapor within the orifice, but it has little influence on flow characteristics. The results could enrich our knowledge of liquid nitrogen cavitating flow in spray nozzles of various shapes.     

Investigation of atomization concepts for large‐scale flame spray pyrolysis (FSP)

Flame spray pyrolysis (FSP) is a versatile process for the production of inorganic nanoparticles featuring the advantage that the reagents are directly dissolved in the liquid fuel that is atomized to form the burning flame. A majority of previous studies on flame spray pyrolysis is focused on the formation and growth processes of the nanoparticles but neglect the preceding step of precursor atomization and spray formation. In this work an atomization concept for large‐scale nanoparticle production by flame spray pyrolysis is presented. A pressure swirl nozzle is applied for creating a liquid hollow cone, and in a second step, different dispersion gas nozzles are utilized to enhance the atomization of the liquid phase and to influence the spray cone formation and geometry. The relevant parameters influencing the atomization process (dispersion gas feed rate, liquid feed rate) are investigated (for air, water) in non‐burning (cold) spray conditions in order to access the utilization of the different atomizer concepts for the flame spray pyrolysis‐process. Measurements are conducted by applying high speed camera imaging (HSC), particle image velocimetry (PIV) and laser diffraction spectroscopy (LDS). Computational fluid dynamics (CFD) revealed further insight into the gas entrainment and the trajectory of droplets within the spray. Results show that the liquid volume flow rate (and thus the productivity of the process) may be increased significantly while still maintaining an appropriate droplet size compared to the conventional atomization process conditions in flame spray pyrolysis reactors.     

Numerical study of cryogenic micro-slush particle production using a two-fluid nozzle

The fundamental characteristics of the atomization behavior of micro-slush nitrogen (SN₂) jet flow through a two-fluid nozzle was numerically investigated and visualized by a new type of integrated simulation technique. Computational fluid dynamics (CFD) analysis is focused on the production mechanism of micro-slush nitrogen particles in a two-fluid nozzle and on the consecutive atomizing spray flow characteristics of the micro-slush jet. Based on the numerically predicted nozzle atomization performance, a new type of superadiabatic two-fluid ejector nozzle is developed. This nozzle is capable of generating and atomizing micro-slush nitrogen by means of liquid-gas impingement of a pressurized subcooled liquid nitrogen (LN₂) flow and a low-temperature, high-speed gaseous helium (GHe) flow. The application of micro-slush as a refrigerant for long-distance high-temperature superconducting cables (HTS) is anticipated, and its production technology is expected to result in an extensive improvement in the effective cooling performance of superconducting systems. Computation indicates that the cryogenic micro-slush atomization rate and the multiphase spraying flow characteristics are affected by rapid LN₂-GHe mixing and turbulence perturbation upstream of the two-fluid nozzle, hydrodynamic instabilities at the gas-liquid interface, and shear stress between the liquid core and periphery of the LN₂ jet. Calculation of the effect of micro-slush atomization on the jet thermal field revealed that high-speed mixing of LN₂-GHe swirling flow extensively enhances the heat transfer between the LN₂-phase and the GHe-phase. Furthermore, the performance of the micro-slush production nozzle was experimentally investigated by particle image velocimetry (PIV), which confirmed that the measurement results were in reasonable agreement with the numerical results.     

蒸发式冷凝器喷嘴流量均匀性数值研究

喷嘴出口流量均匀性对蒸发式冷凝器的换热效果有直接影响。本文用FLUENT软件对40种不同工况下喷淋系统内的水流情况进行数值模拟,并比较和研究影响喷嘴出口流量均匀性的主要因素。结果表明,结构对称可使各喷淋管的喷嘴出口流量分布基本相同;小直径喷嘴的出口流量均匀性良好;喷嘴直径较大时,随总喷淋量的增大,喷嘴出口流量的差异也增大;加装压力平衡管后,喷嘴出口流量均匀性会提高。