Investigation on Liquid Breakup Regimes and Atomization Performance of Slinger

甩油盘液体破碎形态及雾化性能研究

覃文隆

（中国飞行试验研究院,西安 710089）

摘要：

在Dahm的研究基础上,对甩油盘的液体形态、雾化性能等进行研究。在圆形出孔中,当液体与壁面之间夹角小于时,表面张力会阻止液体在科氏力作用下聚集到出孔一侧。Dahm提出的判定液柱、液膜形态的公式并不能准确衡量液体的形态,提出排水池假说、相对滑移假说来解释此现象。sub与super与韦伯数相关,当we小是为sub,we大时为sup,而当we在中间状态时无法判定。液体的一次雾化与相应特征长度下的we有关,但二次雾化会产生大量微小液滴,液雾SMD与相应特征长度下We相关系数不大。整体上液雾SMD与We成指数关系,特征长度为出孔内液膜厚度,相关系数接近0.9。

关键词：旋转雾化,甩油盘,液体破碎形态,液雾SMD

     

大容量空气雾化水煤浆喷嘴的实验研究

对空气雾化水煤浆(CWS)喷嘴进行实验研究.提出适合于空气雾化的大容量撞击式水煤浆喷嘴,在实验台上研究结构参数对流量和雾化特性的影响,结合流体力学及雾化理论对喷嘴结构和实验结果进行分析.实验表明,影响喷嘴流量特性（气浆压力和流量间的相互关系）的主要参数有Y型气孔尺寸、混合室直径、浆孔直径、雾化头出口孔尺寸等,其中浆孔直径的变化显著影响浆压;出口孔径、Y型气孔尺寸的影响大于T型气槽宽度和混合室直径的影响;通过多元参数回归得到喷嘴流量特性的半经验方程;索太尔平均粒径(SMD)测量结果显示,较大的Y型气孔能够强化雾化头的雾化作用,改善雾化性能.     

双股射流碰撞雾化特征实验

为改善双股射流碰撞雾化器的雾化性能,基于自行搭建的射流碰撞雾化实验台,采用CCD拍摄技术,研究射流速度、碰撞角度、喷嘴出口内径和黏度对雾化特征的影响.结果表明:随着射流韦伯数和碰撞角度的增大,喷雾角增大,液滴的索太尔平均直径(SMD)减小,且液滴分布更加均匀;喷嘴内径较小时形成的液膜厚度较薄,稳定性差,喷雾角较小,在所研究的范围内,液滴的平均直径不受喷嘴内径的影响;液体黏度越大,液膜越稳定不易破碎,液膜尺寸越大,喷雾角越小,液滴的平均粒径越大;在韦伯数较小时,差异明显,而在较高的韦伯数条件下,差距较小.在进行40%浓度甘油溶液雾化实验时,观察到了液膜翻转现象,从碰撞点往下出现连续多个相互垂直的液膜.因此,增大射流速度、碰撞角度,减小液体黏度,有助于改善雾化性能.     

Spray Characteristics of Non-Circular Nozzle in Air-Assisted Injection System

In order to analyze the spray characteristics of non-circular nozzle holes based on the air-assisted spray system, the spray characteristics of circular and non-circular nozzles were studied under the pressure of 0.2-0.6 MPa and the spray volume of 1000-5000 mL/h. Elliptical nozzle and triangular nozzle are classified as non-circular geometries. The spray cone angle was measured by processing the spray image captured by a CCD camera. The measured spray cone angles of the circular nozzles were an...     

细水雾灭火喷嘴的雾化特性测量

为了改善喷嘴的雾化效果和研究其喷雾过程，对直射式灭火喷嘴进行了加旋芯改进和实验测量.初
步探讨了旋芯式喷嘴的雾化机理，简述了三维相位多普勒粒子测速仪(PDPA)的系统参数、测量原理和测量
过程.施加不同的喷雾压力，分别测量了喷嘴无旋芯和有旋芯时的喷雾锥角并进行比较.在2.5 MPa喷雾压
力时，测量了旋芯式喷嘴喷射的雾滴分别在喷雾中心和边缘处的索太尔雾滴直径(SMD)、轴向速度、径向
速度和切向速度并进行对比.结果表明，与没加旋芯的喷嘴相比，加旋芯的喷嘴有更大的喷雾锥角和更好
的雾化效果，其雾化过程符合稳定性理论规律；在喷雾中心和边缘处，喷雾参数有显著的区别.     

气体搅动对填料塔和喷洒塔的性能影响

气体搅动作用可以强化液-液两相接触和传质性能.在填料塔和喷洒塔中,气体搅动对萃取塔性能的影响有很大的差异.在气体搅动下,通过对填料塔和喷洒塔流体力学性能和传质性能的试验研究,发现填料对气泡和液滴均有破碎作用,因此填料塔的气含率和分散相滞存率均明显高于喷洒塔,传质单元高度和液泛速度则相反;对填料塔和喷洒塔,气体搅动都可以显著提高液-液两相的接触与传质性能.     

间接蒸发冷却用气水雾化喷嘴特性实验研究

为了提高间接蒸发冷却器换热效率,提出了将气-水雾化喷嘴应用于间接蒸发冷却器改进换热器表面水膜的均匀性,实验研究了扇形两相(气-水)喷嘴在不同空气压力和水压下的特性,测出了不同压力时喷嘴雾化角和气水质量流量值,得出了其变化规律,确定出了最佳的喷雾气水压力比和雾化角等参数.     

物联网中LEACH算法的研究与改进

针对物联网节点异构的特点,从时效性要求不同的角度出发,提出一种改进的LEACH路由分簇算法。在传送数据之前,要求节点发送代表数据缓急的脉冲,根据脉冲长度及频率得到节点时效性要求参数,结合参数的大小和传输的数据量,动态分配每轮数据传输的时隙,使得高时效性要求节点分配较长时隙,在相对较短的轮次内完成数据传输。仿真结果表明,高时效性节点优先得到资源,传送时延较小,特别在节点数目众多的条件下,节点的平均传送时延得到降低。     

液态LPG发动机燃料喷射过程的研究

液化石油气(LPG)的喷雾特性对发动机的工作性能有重要的影响。本文采用通过CFD软件FIRE数值模拟了液态LPG的喷雾过程。在模拟过程中确认本文提出的喷雾模型的可行性基础上,特别考虑了闪急沸腾现象对于液态LPG喷射过程的影响。结果表明,对于液态LPG喷射,采用KHRT雾化模型得到的喷雾贯穿距离、索特平均直径(SMD)等模拟结果与实验结果有很好的一致性,闪急沸腾现象对于喷雾贯穿距离、索特平均直径以及温度场的分布有重要影响。     

滴流床反应器典型分配器的结构与性能

分配器的液体分配效果直接影响到滴流床反应过程的表观反应速度、产品收率及催化剂失活速度等,而分配器的性能取决于分配器的几何特征与操作条件。为了更好了解分配器的有关性能,详细分析了泡罩型分配器、垂直管分配器和喷射型分配器等３种典型滴流床反应器的分配器宏观分配性能及其影响因素,并通过试验测定了不同负荷条件下这３种分配器的微观分配性能。结果表明,泡罩型分配器喷淋点密度较小,液体分配效果明显次于喷射型分配器     

Visualization study on atomization characteristics and heat transfer performance of R1336mzz flash spray cooling

Visualization experiments are carried out to investigate the atomization characteristics of R1336mzz flash spray cooling. The influences of superheat, spray distance, and nozzle orifice diameter on spray cooling performance are analyzed experimentally. As the superheat increases, finer droplets and thinner liquid film are observed; this is helpful to improve the two-phase heat transfer efficiency. Enlarging atomization angle under high superheat is also observed for flash spray cooling, and it benefits for reducing the spray distance. It can be found that when the inlet superheat is 19.8°C and the spray distance is 6 mm, the critical heat flux (CHF) reaches 251 W/cm² and the maximum heat transfer coefficient (HTC) reaches 37.4 kW/(m² °C), which are 55% and 11.6% higher than those when the inlet subcooling is 6.9°C and the spray distance is 12 mm, respectively. Using flash spray reduces the spray distance, which benefits for designing compact spray cooling device. In addition, the nozzle orifice diameter has great influence on the cooling performance of flash spray, and the choice of the nozzle depends on the superheat. This study provides a physical insight into the heat transfer enhancement in flash spray cooling.

     

螺旋槽干气密封性能及结构优化研究

建立螺旋角槽的数学模型,利用Fluent分别研究了不同的槽数、转速、入口压力、槽深、气膜厚度对密封性能的影响规律.通过分析对比密封性能参数如静压、开启力、泄漏量等,得出了单螺旋角槽性能最佳的几何结构参数.针对单螺旋角槽存在的问题,提出了一种双螺旋角槽干气密封结构,且计算结果表明:双螺旋角槽可使气动分离效果更明显,当吸力...     

The measurement of internal surface characteristics of fuel nozzle orifices using the synchrotron X-ray micro CT technology

The design of fuel nozzle orifices at micrometer scales is crucial for generating desired fuel spray patterns, and consequently optimizing fuel combustion and emission in internal combustion engines. Although there have been several recent advancements in the characterization of orifice internal geometries, quantitative studies on the orifice internal wall surface characteristics are still challeges due to the lack of effective measuring methods. A new method for quantifying the internal wall surface characteristics of fuel nozzle micro-orifices is presented in this study to achieve a better understanding and prediction of spray characteristics: Firstly, by using the synchrotron X-ray micro CT technology, a three-dimensional digital model of the fuel nozzle tip was constructed. Secondly, a data post-processing technique was then applied to unfold the orifice internal wall surface to a flat base plane. Finally, the conventional surface characteristic quantification techniques can be used to evaluate the wall surface characteristics. Two diesel nozzles with identical orifice geometry design but different hydraulic grinding time were measured using this method. One nozzle was hydro-ground for 2 s while the other was not. The internal wall surfaces of the two orifices were successfully unfolded to base planes and their surface characteristics were respectively analyzed. The surface fluctuation data were perfectly reproduced by a Gaussian distribution function. The standard deviations of the distribution demonstrate the fluctuation range and the distribution of the entire surface fluctuation profiles. As an effective parameter to evaluate the hydraulic grinding process and the spray behaviors, the standard deviation was considered feasible for the analysis of the orifice internal wall surface characteristics.     

Spray Characteristics of Air-Assisted Injector Under Different Ambient Pressures

Spray atomization of liquid fuel plays an important role in droplet evaporation, combustible mixture formation and subsequent combustion process. Well-atomized liquid spray contributes to high fuel efficiency and low pollutant emissions. Gasoline direct injection(GDI) has been recognized as one of the most effective ways to improve fuel atomization. As a special direct injection method, the air-assisted direct injection utilizes high-speed flow of high-pressure air at the injector exit to assist liquid fuel injection and promote spray atomization at a low injection pressure. This injection method has excellent application potential and advantages for high performance and lightweight engines. In this study, the hollow cone spray emerging from an air-assisted injector was studied in a constant volume chamber with the ambient pressures ranging from 5 kPa to 300 kPa. External macro characteristics of spray were obtained using high speed backlit imaging. Phase Doppler particle analyzer(PDPA) was utilized to study the microcosmic spray characteristics. The results show that under the flash boiling condition, the spray will generate a strong flash boiling point which causes the cone shape spray to expand both inwards and outwards. The axisymmetric inward expansion would converge together and form a lathy aggregation area below the nozzle and the axisymmetric outward expansion greatly increases the spray width. The sauter mean diameter (SMD) of flash boiling condition can be reduced to 5 μm compared to the level close to 10 μm in the non-flash boiling condition.     

半淹没式旋转孔板污水取水机水力特性数学模型及运行分析

针对污水源热泵系统中过滤除污装置流量稳定性差、不易调节并影响换热器效率的问题,介绍了新型半淹没式旋转孔板污水取水机,研究了其工作原理,通过建立数学模型分析了污水中污杂物浓度、污水的液面高度、孔板的旋转周期对其过流量、过滤负荷、滤面堵塞系数的影响.结果表明：污水液面高度、孔板旋转周期一定的条件下,污水浓度增加将导致孔板过流量减小,滤面堵塞系数增加;通过调整液面高度和孔板旋转周期可调节由于污水中污杂物浓度变化对孔板过流量的影响,且孔板旋转周期调节效果优于液面高度.     

二维滴流床反应器内分配器与液体分配

作为反应原料的液相在反应器床层中的分配和润湿情况直接影响反应过程的效率、反应产物的质量和收率等 ,而床层内液体分配情况与分配器性能有直接关系。为了更好地了解滴流床反应器内液体分配情况 ,以及液体分配器对床层内液体分配的影响 ,利用二维滴流床反应器可视化图像技术 ,分别考察了使用普通垂直管分配器和喷射型分配器时 ,二维滴流床反应器内的液体分配情况。通过对实验得到的大量图片分析发现 ,液体的初始分配对床层液体分配有很大的影响 ;液体在床层顶部的初始分配状态会在床层中延续很长一段距离 ,因此液体初始分配致关重要 ;喷射型分配器能使液体均匀地喷洒到床层上 ,使液体实现良好的初始分配 ,液体在床层内的分配情况明显优于使用普通垂直管分配器     

波导宽壁缝隙耦合器的全波分析

使用FDTD法对由两正交矩形波导构成的宽壁缝隙耦合器进行了严格的分析.通过对两种类型缝隙(纵向/横向缝隙和斜向缝隙)的分析,得出了耦合器在不同的波导尺寸及频率下散射系数、谐振长度的变化特性,这些结果与矩量法求得的结果完全吻合.还利用得出的特性分析了一种带有短路器的耦合器系统,为缝隙阵天线的综合设计提供参考.     

喷射成形静电作用下雾化过程的理论分析

静电雾化技术可以提高喷射成形雾化质量,但由于雾化过程涉及气液固三相流、流场和电场等多场联合作用等,给试验研究带来了诸多不便.为了深入了解静电作用对喷射成形中金属液射流破碎的雾化过程影响,从理论上分析了静电作用对喷射成形雾化中射流破碎长度、雾滴表面张力和雾化液滴粒径的影响.结果表明：随着静电电压的增加,射流破碎长度将缩小,雾化液滴直径减小;当电压升高到一定值时,破碎长度和雾滴直径趋于稳定.静电力降低了液滴的表面张力,使得雾化动力相对增加,从而有助于提高雾化质量.     

室内CCD立靶光源能量分布均匀性分析

针对室内CCD立靶测试中对背景光源的光强度和均匀性需求,分析普通二极管和贴片灯珠的发光特性,并以贴片灯珠作为最小发光单元建立了三角形布阵模型,通过数学原理推导出了光源阵列的光能量强度分布函数,分析计算出光源结构参数.试验结果表明,采用本设计的光源提高了背景光成像的均匀性,在室内立靶测试中很大程度的提高了目标与背景的对比度,保证了对目标中心像素坐标提取的可靠性和精度,使得系统测量精度优于10mm.     

Experimental Study and Numerical Simulation on Spray Characteristics of New-Type Air-Assist Nozzle

To investigate the spray characteristics of a new-type air-assist nozzle, three-dimensional laser phase Dopper analyzer (PDA) was used to measure the spray parameters. The external flow fields of the nozzle were simulated by means of computational fluid dynamics (CFD). The distributions of the diameter and the axial velocity for the droplets were analyzed respectively. The results indicate that, the mean diameter of the droplets fluctuates along the center axis. The distance between the measurement point and the nozzle increases, the axial velocity of the droplets decreases. The further the measurement point from the center axis is, the smaller the axial velocity of the droplets is. With the increase of the nozzle pressure drop, the axial velocity of the droplets improves while the mean diameter of the droplets is reduced, and the distribution uniformity of the droplets is better for the diameter. The simulation result agrees well with the experimental data. The average deviation ranges from 3.9% to 7.7%.