Effect of droplet size on the droplet behavior on the heterogeneous surface

Journal of Mechanical Science and Technology - The characteristics of a three-dimensional hemispherical droplet on a heterogeneous surface were studied using the Lattice Boltzmann method (LBM). The...     

高压加热器疏水系统的液位自动调整

介绍用液位自动调整器代替T940H-10型调整阀对B25-90/10-1型和C50-90/13-1型汽轮机高压疏水系统改进的情况.分析了改进前存在的问题,介绍了自动调整器的工作原理,在减小端差、稳定水位、无需人员操作以及降低检修费用等方面取得良好效果.     

Experimental analysis of the yield criterion for a hard asperity sliding on a soft flat surface

The validity of the theoretical yield criterion proposed previously for a hard asperity on a soft flat surface in abrasive friction process was examined by the experiments in the scanning electron microscope with model asperities. The asperity specimens with six asperity angles were made of SUS304 (18Cr-8Ni austenitic stainless steel) and four types of S45C (0.45% C steel). Mating flat specimens were made of S45C and two types of 6-4 brass. The hardness ratio of those frictional pairs ranged from 0.17 to 0.91.The experimental results gave good agreement with the proposed theoretical predictions, i.e. if the asperity angle is smaller than a critical asperity angle which is determined by the hardness ratio between the asperity and the mating flat surface, the tip of the asperity deforms plastically despite its being harder than the mating flat surface.     

Dynamic behavior of a droplet on a moving wall

A two-dimensional immiscible droplet deformation phenomenon on a moving channel bottom wall is simulated using the lattice Boltzmann method. We considered the effect of the initial static contact angle, the capillary number, and the size of the droplet on the dynamic behavior of the moving droplet. When the initial static contact angle is less than 90°, the moving droplet is deformed and stretched, resulting in increasing width and decreasing height of the droplet. This is due to the hydrophilic (wetting) characteristic of the channel’s bottom wall. However, when the initial static contact angle is larger than 90°, the deformed and stretched droplet on the moving channel bottom wall is broken up, and is then pinched off or detached from the moving channel bottom wall, depending on the initial static contact angle and capillary number. This is due to the hydrophobic (non-wetting) characteristic of the wall.     

一种绝缘体表液体自动测试系统

提出一种绝缘体表液体自动测试系统的设计方案,在保证系统测试性能的同时能够大幅降低设计成本。通过对系统数据采集数据转换,以及系统控制部分的工作与设计原理的分析,设计三种相邻电容传感器,讨论分析传感器设计关键参数,并给出了最终设计参数;简单解释了测量数据转换部分和控制部分的系统设计思想。实验部分采用有限元仿真技术模拟了电容传感器的性能;通过阻抗分析仪对测得的数据进行分析、比对、讨论了测量噪声对系统检测的影响,并提出解决方法;实验结果表明,电容探测传感技术应用于绝缘体表液体自动测试系统中的可行性与重要性,设计的系统硬件部分能够实现自动探测分级报警功能。     

Tribological behavior and surface analysis of magnetized sliding contact XC 48 steel/XC 48 steel

We have studied the tribological behavior of a XC 48 steel/XC 48 steel sliding couple in the presence of an A.C. magnetic field. Experiments were conducted on a pin-on-disc tribometer in ambient atmosphere under an applied normal load P=62.85 N and sliding speed v=0.38 m/s. The magnetic field was applied to the pin and remained constant during each test. Experimental results showed that the presence of a magnetic field around the tribocontact modifies the tribological behavior through changes of the mechanical properties of the subsurface. The surface microhardness increases in magnetic field and modifies the tribocontact rheology. The modifications induced in the contact surface and subsurface of XC 48 steel, by the magnetic field H=0 to 8 kA/m after 30 min of sliding, were analyzed by Vickers microhardness measurement, scratch testing with acoustic emission detector, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).     

A dynamic measurement system for evaluating dry bio-potential surface electrodes

In this paper, a dynamic measurement system (DMS) is presented for assessing performance of wearable and dry bio-potential surface electrodes (DBSEs) in air, especially motion artifacts. A pair of perforated membranes is assembled on the two ends of the barrel which contains electrolyte to simulate surface of the skin. The pressure of electrode/membrane can be controlled and measured, one of electrodes can move on membrane by the motion controller. Experimental results show maximum coefficient of variation (CV) of electrical impedance spectra (EIS) and dynamic open circuit potential variation (DOCP, so-called motion artifacts) of gold electrode pair are, respectively, 4.3% and 7.2% in continuous measurements, 12.6% and 22% in discontinuous measurements, the pressure and the length of motion track between electrode and membrane are strongly linear correlation with DOCP variations. EIS and DOCP of five types of electrodes were measured on DMS and their parameters of equivalent circuit (EC) of EIS and DOCP variation show larger is equivalent capacitance in electrode/electrolyte interface, less is DOCP variation. DOCP variations of two batches of electrode performed respectively on DMS and on skin have approximate 0.64 of Pearson correlation coefficient. In general, the DMS provides a powerful tool to investigate the mechanism of DOCP variation and evaluates the static or dynamic performance of electrodes. However, parameters of EC model by fitting EIS can predict the motion artifact and help the design of electrode and its integrated wearable garments.     

Theoretical analysis of the plastic yielding of a hard asperity sliding on a soft flat surface

When a hard material slides on a soft material, wear occurs generally on the soft material surface. Wear can also occur on the harder material but the conditions for this have not yet been elucidated.As plastic deformation of contact points is an important factor in the generation of wear particles, the condition under which the plastic yielding of each material occurs simultaneously and the condition under which the hard asperity yields before the soft flat surface were analysed theoretically. The analysis indicates that there is a critical value, which depends on the hardness ratio and the shear stress on the interface, for the top angle of the asperity. If the top angle of an asperity is less than this critical value, the asperity can yield plastically despite its being harder than the mating surface.     

Study on droplet formation with surface tension for electrohydrodynamic inkjet nozzle

Droplet ejection from an electrohydrodynamic (EHD) inkjet nozzle depends on many factors such as an onset voltage, liquid conductivity, surface tension, etc. Since the surface tension has an influence on the contact angle between the nozzle surface and the liquid droplet, the surface tension change should be investigated for the control of the droplet ejection. In this study, surfactant, which can weaken the surface tension force, was used to analyze the effect of the surface tension. Furthermore, hydrophobic coating of the nozzle surface was considered as another factor for the droplet ejection. Also, a flow visualization technique was developed to observe the droplet formation and ejection from the EHD inkjet nozzle by various surface tension values.     

Experimental study of droplet splashing phenomena on hydrophobic micro-and micro/nano-textured surfaces

Journal of Mechanical Science and Technology - Droplet splashing phenomena are observed experimentally on the well-designed hydrophobic micro and micro-/nano-textured surfaces. The critical Weber...     

Thermomechanical analysis of elastoplastic medium in sliding contact with fractal surface

The effects of mechanical and thermal surface loadings on deformation of elastic–plastic semi-infinite medium were analyzed simultaneously by using the finite element method. Rigid rough surface of a magnetic head and smooth surface of an elastic–plastic hard disk were chosen to perform a comprehensive thermo-elastic–plastic contact analysis at the head–disk interface (HDI). A two-dimensional finite element model of a rigid rough surface characterized by fractal geometry sliding over an elastic–plastic medium was then developed. The evolution of deformation in the semi-infinite medium due to thermomechanical surface loading is interpreted in terms of temperature, von Mises equivalent stress, and equivalent plastic strain. In addition to this, the effects of friction coefficient, sliding, and interference distance on deformation behavior were also analyzed. It is shown that frictional heating increases not only the contact area but also the contact pressure and stresses.     

Tribological behavior of boundary lubricated sliding surfaces using three different spacing of surface profiles

The ball-on-disk type sliding tests with boundary lubricated steels were carried out to verity the effect of initial spacing in surface profiles on wear and scuffing. Three kinds of surface spacing, which are closely related with initial surface micro-cracks on sliding surfaces, were produced onAISI 1045 steel surfaces using different grinding and polishing processes. Frictional forces and time to scuffing were measured, and the shape and amount of wear particles were analyzed to compare the with original surface profiles. From the tests, it was confirmed that the size of wear particles are related closely to the original spacing of the surface profile. The time to failure and amount of wear were sensitive to the surface spacing. The wider surface spacing shows much longer sliding life and smaller amount of wear than the others. Time to scuffing was increased with increasing surface profile spacing. The size of wear particles increased while the wear and wear rateK were decreased with an increase in surface spacing. After the sliding tests, surface cracks of inner parts of the wear track formed due to scuffing were observed and compared among the specimens having the different surface spacing.     

制造系统柔性评价方法研究

深入分析评价制造系统柔性的基本要求,并介绍柔性熵的概念,建立评价系统柔性的数学模型。通过实例分析,证明该模型对评价制造系统柔性有一定的价值。     

Prediction of wear in a sliding system

In previous publications, the author and his co-workers have presented two models concerning wear prediction in sliding systems. The first model, the zero-wear model, enables one to predict analytically the amount of sliding required to produce wear of the order of the surface finish. The second model, the measurable-wear model, enables one to predict how wear, which is greater than the surface finish, will increase with increasing amounts of sliding. With the model for measurable wear, however, it was not possible to predict analytically how the wear would depend on other parameters of the system (e.g., load, material constants, etc.).This paper explores the possibility of using the zero-wear model, in conjunction with the measurable-wear model, to predict these dependencies. The results of this combined model were compared with experimental data obtained for several different sliding systems; good agreement was found between the theoretical calculations and experimental data.     

Adaptive calibration of a capacitance tomography system for imaging water droplet distribution

A highly sensitive electrical capacitance tomography (ECT) system based on an HP4284 impedance analyser has been developed and used to quantify low concentration multi-phase flows in wet gas separation processes. The system hardware provides high accuracy (0.05%) and high resolution (10⁻¹⁷ F). The sensor was calibrated in an environmental chamber with solid samples of known permittivity over ranges of temperature and humidity. Adaptive calibration and adjacent electrode pair correction techniques were applied to image very low concentration profiles. This paper describes the techniques used and presents the experimental results obtained from a test flow rig called Twister, which has been designed to separate liquid droplets from wet gas streams. The test results over a range of operating conditions (20–95% humidity) demonstrate that the ECT system is capable of reconstructing clear images of the droplet distribution inside Twister. Changes as small as 1 gWater/kgAir in the form of liquid droplets were detectable. It has also been shown that the concentration of the condensable phase can be estimated quantitatively within 20% in comparison with the reference measurements.     

引信产品可生产性评价系统的研究

分析了目前引信设计忽视可生产性评价的现状,提出了引信产品可生产性评价的指标体系,包括可制造性和可装配性的评价指标体系,建立了引信可生产性的模糊评价模型,最后给出了引信可生产性评价系统的体系结构和实现方法。     

An investigation on sliding wear behavior of PVD coatings

Ti-6Al-4V alloy rubbing against aluminum-bronze 630 was evaluated in this work. High velocity oxygen fuel (HVOF) WC-10%Co-4%Cr thermal sprayed and TiN, CrN and DLC physical vapor deposition (PVD) coatings were applied to increase titanium substrate wear resistance. Pin-on-disk tests were performed with a normal force of 5 N and at a speed of 0.5 m/s, with a quantitative comparison between the five conditions studied. Results showed higher wear resistance for Ti-6Al-4V alloy DLC coated and aluminum-bronze 630 tribological pair and that the presence of graphite carbon structure acting as solid lubricant was the main wear preventing mechanism.     

Transfer of semicrystalline polymers sliding against a smooth steel surface

The interrelationships between transfer and wear in polymers were studied using a pin-disk-type wear testing apparatus. The wear rates of polymers except polytetrafluoroethylene (PTFE) were high for up to about the first 100 revolutions of the disk and decreased gradually until the steady low wear rates which generally occurred after about 2000 revolutions. However, PTFE exhibited an almost constant high wear rate throughout the wear process. The thickness of transferred polymer increased rapidly with increasing number of revolutions in the initial wear stage but after about several hundred revolutions remained constant. A coherent transfer film was formed in most parts of the friction track after about 100 revolutions. It was found that polymer wear could occur in polymers sliding on a transferred polymer layer. All polymers except PTFE exhibited smaller wear rates when sliding on the transferred layer. The load dependence of the thickness was very small compared with that of the wear rate. PTFE produced a very dense and coherent transferred layer compared with that of other polymers. However, there was no clear relationship between friction and the thickness of the transferred polymer layer.     

Characteristics of auto-ignition and micro-explosion behavior of a single droplet of water-in-fuel

The characteristics of auto-ignition and micro-explosion behaviors of a single fuel droplet have been investigated experimentally with varying droplet sizes, ambient temperature, and water content. The fuel used for this experiment was pure n-decane, which was emulsified with several water content varied from 10% to 30% to compare the effects of water content in the emulsified fuel. Imaging with a high-speed digital camera was adopted to measure the ignition delay and flame life-time, as well as to observe micro-explosion behavior. The increase of droplet size and furnace temperature causes a decrease of the ignition delay time. The flame life-time is augmented as the droplet size increases, however it doesn’t seem to be affected by the ambient temperature relatively. As the water content increases, the ignition delay increases and the micro-explosion behavior is strengthened. The start timings of micro-explosion and fuel puffing are compared for different droplet sizes and the amount of water content.