压力条件对旋流槽数不同的离心式喷嘴液膜破碎及雾化的影响研究

利用粒子动态分析仪和高速摄影系统,研究不同注压下的锥形液膜流动、破碎及雾化特性,分析不同注压下液膜流动速度对液膜破碎的作用以及喷雾质量参数的变化规律,并结合相应试验数据求解了锥形液膜的色散方程,验证了注压对液膜破碎的影响.结果表明,随着注入压力增大,喷嘴流量增大,喷嘴液膜破碎长度下降,喷雾锥角先增加后趋于稳定,雾场SMD(索特尔平均直径)减小,雾滴流动速度增大,液膜切向速度对锥形液膜的作用效果显著;旋流槽数的增加使液膜速度增加,喷雾锥角减小,雾滴流速增大,雾场浓度增加且均匀性更好;通过求解色散方程得到了液膜表面波增长率,从理论的角度说明旋流槽数的增加使液膜表面波增长率增加,导致锥形液膜破碎长度减小.     

切削液油雾形成机制及影响因素的实验研究

对切削液油雾产生的机制进行理论分析,并对切削液油雾形成的影响因素进行实验研究。实验在密闭的车床内进行,利用车床的供液系统采用浇注式供给磨削液,在油雾产生密集区域内安装有磨削液雾滴粒径的测量装置,该装置中的共聚焦显微镜可观察切削液雾滴在空气中的分布,精确扫描单颗雾滴的形态轮廓,通过计算机可计算出雾滴的分布和直径尺寸。分别控制主轴转速和切削液流量,探究对所形成的油雾浓度和平均直径的影响。实验结果表明:金属加工过程中主轴转速和切削液流量对切削液油雾特性的影响显著,随着主轴转速的增加,油雾的平均直径减小,而油雾浓度却呈上升趋势;随着切削液流量的增加,油雾的平均直径变大,并且油雾浓度同样呈上升趋势。     

MQL外圆车削数值模拟及流场分析

基于流体力学理论及流体分析软件FLUENT建立了最小量润滑(MQL)外圆车削模型,模拟了MQL喷雾射流过程,分析了车削后刀面楔形区的流体压强及静压力的分布特性,分析了MQL喷雾形态,结果表明:MQL压缩空气较强的气压和较高的流速对楔形区的流场有很大的影响;楔形区的流场特性对MQL切削液雾滴的运动和渗透有着较大的影响,楔形区的负压差能够促进切削液喷雾的运动,切削液雾滴粒径在集中在(1~20)μm之间,并按一定的规律分布。这对MQL切削参数及雾滴回收装置的研究有一定的参考意义。     

喷雾粒径测试方法分析及比较

喷雾粒径是对喷雾效果评价的重要参数,雾滴效果的好坏对于农业喷洒灌溉、内燃机的效率、航空航天有着重要的意义。因此针对不同喷雾测试方法得到的喷雾数据分析比较,分别以水敏纸法、油盘法和激光粒度仪法在0.3MPa喷雾压力的条件下对5种喷头分别进行雾滴粒径测定的数据比较;液滴评判系统和马尔文测量法在相同孔径不同压力下测得的雾化特性参数比较。分析结果表明：户外的喷雾场测试中使用水敏纸法是较好的选择;随着数字图像处理技术的发展而诞生的液滴尺寸判读系统可以作为实验室喷雾场测试方法的一种很好的补充。     

最小量润滑的车削数值模拟及流场分析

利用Fluent软件建立最小量润滑的端面车削模型,模拟MQL喷雾射流的过程,分析主后刀面楔形区域的流场特性及MQL喷雾形态。结果表明:MQL喷雾过程中,在压缩空气较强的气压和较高的流速下,切削楔形区被分为减压区和增压区;楔形区域的流场特性直接影响着切削液雾滴的运动和渗透,在减压区的负压差利于喷雾的运动,增压区则有阻碍作用;对MQL参数合理的优化可减少切削液喷雾流入周围空气。     

阀芯结构对双流体喷雾粒子特性的影响

为了研究阀芯结构对双流体喷雾粒子特性的影响,提升喷雾效果,运用相位多普勒粒子分析仪（PDPA）对不同阀芯结构的双流体喷雾雾滴粒径、轴向速度以及雾滴数目进行了测试,并对测量结果进行了分析和讨论。结果表明：随着轴向距离的增大,雾滴索特平均直径(SMD)、算术平均直径(AMD)呈先增大后趋于平缓的趋势,轴向速度以及湍流脉动速度均呈减小趋势,雾滴数目呈先增大后减小的趋势;随着气液压力比的增大,SMD呈先增大后减小的趋势,而AMD、轴向速度以及雾滴数目均呈减小趋势;阀芯的喉口直径、出口直径的减小均有利于喷雾效果的提升,但同时导致速度稳定性变差;当喉口直径为1.5mm、出口直径为2.5mm时,与原始阀芯结构相比,雾滴数目和雾滴轴向速度分别增大了82.43%和22.31%,SMD和AMD分别减小了52.18%和21.47%,综合喷雾效果得到了大幅提升。     

基于FLUENT的采煤机螺旋滚筒内喷雾性能研究

井下工作面粉尘不仅影响工人身体健康,而且容易引发粉尘爆炸等安全事故。螺旋滚筒的内喷雾系统在解决粉尘污染产生问题上起着至关重要的作用,因此设计出具有良好性能的内喷雾系统的螺旋滚筒至关重要。以MG325采煤机为依托,采用Pro/E和GAMBIT建立该采煤机截割机构及其工作面有限元模型,选用双湍流流动数学模型构建滚筒内喷雾数学模型,通过FLUENT对内喷雾系统外流场进行仿真分析,分别分析喷雾压力、喷嘴口径、扩散角和喷雾入射角对雾滴粒径、运动速度等雾化效果的影响。研究表明:当喷雾压力为5 MPa、喷嘴口径为1.2 mm、扩散角为60°、内喷雾入射角为15°时,喷雾效果最佳。分析结果为提高采煤机螺旋滚筒喷雾降尘效率提供了明确的量化依据,为喷雾系统的设计提供了新的理念和方法。     

风送液力式超低量喷雾装置内流场的模拟分析

风送液力式喷雾技术有利于促进低量喷雾技术的推广应用。利用FLUENT软件对喷雾装置内流场进行模拟分析,分析结果表明风送液力式喷雾装置有利于细化雾滴并减少细小雾滴的漂移,因此给其应用提供了理论依据。     

农用航空喷雾系统的试验与研究

<正>一、喷头选择大多数飞机喷药都用液力式喷头。可选的喷头类型有空心锥雾喷头、扇形雾喷头、离心雾化器等。其中前者为地面作业常用喷头,不再赘述。1.扇形喷头带有一个附加孔的锥雾喷头可以产生很大的雾滴,可用于那些对飘移要求很严格的场合。对飘移要求严格的地方,也常选用一种有多个小喷孔、向后折射的喷头,一般用于喷洒除草剂。(1)扇形喷嘴基本喷雾类型扇形喷嘴种类及喷雾     

喷射压力对生物柴油混合燃料喷雾特性的影响

基于KH-RT液滴破碎模型对定容燃烧弹内生物柴油-正丁醇混合燃料的喷雾贯穿距离、喷雾锥角、索特平均粒径、速度场以浓度场进行数值模拟,通过定容燃烧弹试验台架获取的生物柴油-正丁醇混合燃料的喷雾特性对数值模型进行验证,结果表明:随着喷射压力的增加,BD70N30混合燃料的喷雾贯穿距和喷雾锥角增加;索特平均粒径降低;雾束中心...     

Modeling of diesel spray impingement on a flat wall

To understand the transient behavior of droplets after impingement in a diesel engine, a numerical model for diesel sprays impinging on a flat wall is newly developed by the proposition of several mathematical formulae to determine the post-impingement characteristics of droplets. The new model consists of three representative regimes such as rebound, deposition and splash. The gas phase is modeled in terms of the Eulerian conservation equations, and the dispersed phase is calculated using a discrete droplet model. To validate the new model, the calculated results are compared with several experimental data. The results show that the new model is generally in good agreement with the experimental data. Therefore, it is thought that the new model is acceptable for the prediction of transient behavior of wall sprays.     

An experimental study on the performance of air/water direct contact air conditioning system

Direct contact air conditioning systems, in which heat and mass are transferred directly between air and water droplets, have many advantages over conventional indirect contact systems. The purpose of this research is to investigate the cooling and heating performances of direct contact air conditioning system for various inlet parameters such as air velocity, air temperature, water flow rate and water temperature. The experimental apparatus comprises a wind tunnel, water spray system, scrubber, demister, heater, refrigerator, flow and temperature controller, and data acquisition system. The inlet and outlet conditions of air and water are measured when the air contacts directly with water droplets as a counter flow in the spray section of the wind tunnel, and the heat and mass transfer rates between air and water are calculated. The droplet size of the water sprays is also measured using a Malvern Particle Analyzer. In the cooling conditions, the outlet air temperature and humidity ratio decrease as the water flow rate increases and as the water temperature, air velocity and temperature decrease. On the contrary, the outlet air temperature and humidity ratio increase in the heating conditions as the water flow rate and temperature increase and as the air velocity decreases.     

Droplet interaction of adiabatic dense sprays

The effect of the droplet interactions which arise in the interior of dense sprays is examined by considering the vaporization of a single droplet in a confined region or “bubble”. In the present study the temporal variation of vaporization was determined at two levels of approximation, such as “film analysis” and “quasi-steady analysis”. Thermodynamic analysis was used to determine the final equilibrium conditions which must be satisfied by the unsteady solutions. The results of these two approximate approaches to the unsteady problem were found to be in good agreement providing support for the use of the relatively simple film theory and clearly indicated that the d²-vaporization law cannot be applied in dense sprays. It was shown that the transition between complete and incomplete evaporation is very sensitive to the initial air temperature and to the ratio of the mass of the liquid to the air. In order to gain a preliminary indication of the effect of spray size distribution on the vaporization process the film analysis was extended to sprays with a bimodal droplet size distribution, and it was found that then the kinetics of vaporization also depends on the ratio of the mass of the smaller to that of the larger droplets.     

Influence of Cavitation on the Working Surfaces of the Cylinder–Piston Group in a Diesel Engine during Maintenance

Russian Engineering Research - When a diesel engine runs on water–fuel emulsion, carbon deposits break down on account of microimpact by the fuel droplets in the emulsion. The evaporation of...     

The influence of humidity on the fretting behaviour of PVD TiN coatings

The influence of the relative humidity (RH) in ambient air on the friction and wear behaviour of PVD TiN coatings subjected to contact vibrations against corundum and bearing steel (100Cr6) counterbodies has been investigated. The fretting experiments were performed in the gross-slip regime on TiN coatings produced by three different PVD processes. The results indicate two basic friction characteristics. At low relative humidity (RH < 10%), the friction force is in the range of the normal force whereas it is less than one third of the normal force in atmospheres of high relative humidity (RH > 80%). A transition from high to low friction was observed during the course of experiments performed in atmospheres of medium relative humidity. The duration of the high friction phase in such transitions was found to depend on fretting parameters such as the normal force and the vibration frequency. This humidity dependence of the friction force was found for both counterbody materials. The size of the damaged surface area as well as the volumetric wear on the TiN coatings were found to be largest at low relative humidity. Fretting damage occurs over a smaller area but extends more into the depth at high relative humidity. The size of the fretted surface area induced on TiN is larger for Cr-steel than for corundum counterbodies.     

Extraction of sizes and velocities of spray droplets by optical imaging method

In this study, an optical imaging method was developed for the measurements of the sizes and velocities of droplets in sprays. Double-exposure single-frame spray images were captured by the imaging system. An image processing program was developed for the measurements of the sizes and positions of individual particles including separation of the overlapped particles and particle tracking and pairing at two time instants. To recognize and separate overlapping particles, the morphological method based on watershed segmentation as well as separation using the perimeter and convex hull of image was used consecutively. Better results in separation were obtained by utilization of both methods especially for the multiple or heavily-overlapped particles. The match probability method was adopted for particle tracking and pairing after identifying the positions of individual particles and it produced good matching results even for large particles like droplets in sprays. Therefore, the developed optical imaging method could provide a reliable way of analyzing the motion and size distribution of droplets produced by various sprays and atomization devices.     

The influence of temperature and humidity on the sensitivity of torque transducers

This paper presents a study of the effect of temperature and relative humidity on the sensitivity and the characteristics of torque transducers such as residual zero torque, reversibility and creep. Temperature and humidity coefficients of the sensitivity take positive as well as negative values. Linear dependence is found between the influence of temperature/relative humidity and the applied load. For some torque transducers, under temperature change the sensitivity has a transient overshoot reaching up to 3 times the steady amplitude. Also there is a small effect of temperature/relative humidity on the transducer’s parameters such as residual zero torque, reversibility and creep. Equations are presented to predict the effect of temperature/relative humidity changes on the sensitivity of torque transducers.     

Studies on droplet-turbulence interactions

The present study focuses on numerical modeling for droplet dispersion by turbulence and turbulence modulation by droplets. To account for the dense spray effects, modulation models, a droplet collision model, and the Reitz’s wave instability breakup model are incorporated into a state-of-the-art multiphase all-speed transient flow solution procedure. A parcel probability density function(PDF) approach is implemented to improve the efficiency in droplet dispersion calculations. The numerical results indicate that the present parcel PDF model has the capability to realistically represent turbulent dispersion in dilute and dense sprays with improved efficiency over the delta function stochastic separated flow(SSF) model. Comparative performance of the existing turbulence modulation models are discussed in detail.     

胡萝卜切片热风干燥对流传质系数的估算

将逆数值方法应用于物性测试,通过建立胡萝卜的内部水分扩散模型,把反映物料干燥过程动态特性的实验含水率曲线与物料颗粒内部的水分扩散相结合,确定胡萝卜在脱水过程中的对流传质系数。同时研究了厚度、半径、干燥温度和相对湿度对胡萝卜切片对流传质系数的影响。结果表明,对流传质系数不是一个常数。对流传质系数随厚度和干燥温度的增大而增大; 随相对湿度的减小而减小; 半径的增大对其无明显影响。     

Spray structures and vaporizing characteristics of a GDI fuel spray

The spray structures and distribution characteristics of liquid and vapor phases in non-evaporating and evaporating Gasoline Direct Injection (GDI) fuel sprays were investigated using Laser Induced Exciplex Fluorescence (LIEF) technique. Dopants were 2% fluorobenzene and 9% DEM A (diethyl-methyl-amine) in 89% solution of hexane by volume. In order to study internal structure of the spray, droplet size and velocity under non-evaporating condition were measured by Phase Doppler Anemometry (PDA). Liquid and vapor phases were visualized at different moments after the start of injection. Experimental results showed that the spray could be divided into two regions by the fluorescence intensity of liquid phase: cone and mixing regions. Moreover, vortex flow of vapor phase was found in the mixing region. About 5μn diameter droplets were mostly distributed in the vortex flow region. Higher concentration of vapor phase due to vaporization of these droplets was distributed in this region. Particularly, higher concentration of vapor phase and lower one were balanced within the measurement area at 2ms after the start of injection.