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.     

基于同步检波的单通道磁感应成像技术研究

磁感应成像在医学领域的应用,由于生物组织的电导率非常小,需要一种测量相位精度高的系统才能满足应用需要。描述了一种基于同步检波的单通道磁感应测量系统,来测量微小相位变化。系统使用模拟开关代替模拟乘法电路,减少直流漂移,增加电路的动态范围。电路中引入了模拟的相移电路,使参考信号和与检测信号相位正交,提高相位测量的灵敏度。研究了单通道系统的稳定度和灵敏度,通过实测电路,该测量系统在1 min内的相位漂移0.001 5°,在1 h内的相位漂移0.006°;并给出电导率变化相应相位变化关系。     

Velocity measurement in solid–liquid flows using an impact probe

The use of a modified impact type of probe for velocity field measurement in the flow of multi-sized (d₅₀=71 μm) particulate slurries is described. The impact probe has a sensor similar to a two hole offset probe but has a modified pressure sensing system which prevents blockage of the probe by the solid particles. The probe system has been successfully used in slurry flows over a wide range of solid concentrations (0–40% by weight) and flow velocities (1.67–2.95 m/s). The data presented in this paper have revealed some special features of velocity distribution in the flow of multi-sized particulate suspensions.     

PIV measurements of two phase velocity fields in aeolian sediment transport using fluorescent tracer particles

This paper presents a method to simultaneously determine the velocity fields of both phases in aeolian sediment transport by means of PIV with fluorescent tracer particles. The fluorescent particles were atomized micron-sized droplets of rhodamine B solution. Specific optical filters were employed to ensure that the fluorescent tracer particles and the sand particles were respectively imaged on two CCD (charge-coupled device) cameras during measurement. A cross-correlation algorithm and image processing were used to obtain vector plots. The experimental results show that the distributions of the averaged velocity u of the wind-sand flow in both phases were concave downward curves on a semilogarithmic figure. The upper parts of the profiles of both phases fitted well with a logarithmic distribution. When sand particle sizes were smaller than or equal to 160 μm, the averaged velocity u of both phases decreased with increasing particle size. The difference between the horizontal velocities (i.e. relative velocity u_r) in both phases of the sand phase increased with increasing particle size and height. In the region where h/δ < 0.25, the momentum transfer between both phases was the most intense, and the effect of the air viscosity on the sand motion played an important role in the transfer. In the region where h/δ > 0.85, the horizontal velocity hysteresis between both phases in each group of samples tended to be constant. For a sand particle diameter of 80-200 μm, Re_r changed linearly with the square root of d_m at the top of the saltation layer.     

A hybrid phase boundary detection technique for two-phase-flow PIV measurements

Particle Image Velocimetry (PIV) measurement accuracy is lower along the phase boundaries of two-phase-flows, because the interrogation windows contain information from both phases. Different seeding density, background intensity, velocity magnitude and flow direction conditions often exist across the boundary, and the cross-correlation-based PIV algorithm selects only the highest correlation peak. The highest correlation peak is either influenced by the wrong phase (across the boundary), or the correctly calculated displacement is erroneously detected as an outlier at a later stage and is subsequently replaced. Phase-separated PIV measurements minimize this problem, and increase accuracy along the boundary by treating each phase separately. This type of measurement requires for each time step; (i) the accurate detection of the phase boundary in consecutive frames, (ii) generation of dynamic phase masks, (iii) an accurate PIV evaluation of each phase and (iv) recombination of the flow fields. In this article, we focus on the first step and test a hybrid phase boundary detection (PBD) technique in three different two-phase-flow configurations which manifest different challenges: The first configuration is the mixing of two liquids in a magnetic micromixer, the second is a combustion experiment where a turbulent, pre-mixed, low-swirl, lifted flame is investigated, and the third is a bubble column reactor where air bubbles are rising in a water tank. The PBD implementation uses a three-step procedure: approximate global thresholding, local Otsu thresholding, and discrimination of image gradients. Comparison of results with and without the use of PBD and phase separation indicate that there are significant measurement accuracy improvements along the boundary.     

Simple installation for measurement of two-phase gas–liquid flow by means of conventional single-phase flowmeters

The paper describes a method of measuring the flow rate of the components of a two-phase gas–liquid mixture. The proposed method ensures the separation of two phases using a rather simple modification of pipeline configuration than using separating vessels to achieve this aim. The two components can then be measured using conventional single-phase flowmeters. The errors of the separating and metering installation are about ±(3–4)% in the flow rate range 3:1.     

基于提升小波时延估计的气液两相流流速测量

利用双截面ERT系统测量气液两相流流速具有高实时性、非侵入测量等优势,并将流速测量问题转化为信号处理中的时延估计问题。由于气液两相流信号大多是非平稳的,因此利用传统互相方法计算时延会出现相关函数曲线多峰值现象,导致流速计算结果严重偏差。为提高流速测量的精度和稳定性,本文出了一种基于提升小波的时延估计算法。该算法基于基小波二次加权理论,利用改进阈值函数提升小波算法对源信号进行去噪,再通过形态学提升小波对互相关计算结果去噪,实现流速精确测量。     

相位式激光测距谱分析鉴相的无偏改进

针对相位式激光测距中的鉴相误差,建立了谱分析鉴相的误差模型,提出了在数据预处理中引入希尔伯特变换来消除相位差估计偏差的测量方法.分析了传统谱分析鉴相的偏差和方差,指出这些测量偏差受初相位的影响,在高速测距中不容忽略.提出了一种无偏改进方法,通过窗函数法设计正弦信号的简易希尔伯特变换器,将离散傅里叶变换的对象转换为解析信号,在仅增加4次加减法运算和2次移位操作的情况下,实现了近似无偏谱分析鉴相.仿真分析和实验验证结果表明,鉴相均值与真实相位差相同;当信噪比为40 dB时,每秒百万次高速鉴相的误差为0.1°;当调制频率为100 MHz时,测距精度达到0.4 mm.实验表明,将希尔伯特变换应用于谱分析鉴相,可实现高准确度相位差测量,并可应用于高速相位式激光测距.     

Micromechanical modeling of dual phase steels

Dual phase (DP) steels having a microstructure consisting of a Ferrite matrix, in which particles of Martensite are dispersed, have received a great deal of attention due to their useful combination of high strength, high work hardening rate and ductility, all of which are favorable properties for forming processes. Experimental investigation into the effect of the harder phase volume fraction, morphology and phase distribution on mechanical properties of the dual phase steels is well established and comprehensive in the literature. In the present work, a micromechanical model is developed to capture the mechanical behavior of such materials, adopting the constitutive behavior of the constituents from the literature. Analytical approaches have been used in the past to model the DP steel material behavior, but theoretical treatments are based on the assumption of uniform deformation throughout the constituents, neglecting the local strain gradients. This assumption contradicts experimental observations, reduces the understanding of the mechanics and mechanism of deformation of such materials. Based on the micromechanical modeling of cells, several idealizations are investigated out of which the axisymmetric model is shown to display intrinsic ability to capture the expected material behavior in terms of the trend of the stress–strain curves with increasing volume fraction of the second phase and in terms of the deformation fields of the constituents.     

Measurement of vertical oil-in-water two-phase flow using dual-modality ERT–EMF system

Oil-in-water two-phase flows are often encountered in the upstream petroleum industry. The measurement of phase flow rates is of particular importance for managing oil production and water disposal and/or water reinjection. The complexity of oil-in-water flow structures creates a challenge to flow measurement. This paper proposes a new method of two-phase flow metering, which is based on the use of dual-modality system and multidimensional data fusion. The Electrical Resistance Tomography system (ERT) is used in combination with a commercial off-the-shelf Electromagnetic Flow meter (EMF) to measure the volumetric flow rate of each constituent phase. The water flow rate is determined from the EMF with an input of the mean oil-fraction measured by the ERT. The dispersed oil-phase flow rate is determined from the mean oil-fraction and the mean oil velocity measured by the ERT cross-correlation velocity profiling. Experiments were carried out on a vertical upward oil-in-water pipe flow, 50 mm inner-diameter test section, at different total liquid flow rates covering the range of 8–16 m³/hr. The oil and water flow rate measurements obtained from the ERT and the EMF are compared to their respective references. The accuracy of these measurements is discussed and the capability of the measurement system is assessed.     

Hybrid analytical–numerical solution for the shear angle in orthogonal metal cutting — Part II: experimental verification

The hybrid analytical–finite element model described in Part I is applied to predict the shear angle for a range of cutting velocity, uncut chip thickness, and two tool orthogonal rake angles. Experimental results and an empirical equation are also presented for the influence of the cutting conditions and cutting tool geometry on the chip–tool contact length. It is shown that there is a linear dependence between the chip–tool contact length/uncut chip thickness ratio and chip thickness/uncut chip thickness ratio over the range of cutting conditions assumed. The increase of the shear angle with the tool orthogonal rake is mostly due to the reduction of the specific shear energy in the primary shear zone and the specific friction energy in the secondary shear zone accompanied by a reduction of the chip–tool contact zone. The uncut chip thickness and cutting velocity influence the shear angle through their effect on the interface temperature and hence on the material flow stress in the secondary shear zone. The change in both parameters does not change significantly the specific shear energy in the primary shear zone. The model results are compared with the experimental results for a work material 0.18% C steel. The agreement between the predicted and experimental results is seen to be exceptionally good.     

The parameters measurement of air–water two phase flow using the electrical resistance tomography (ERT) technique in a bubble column

The air–water two-phase flow is investigated in a bubble column with a height of 2 m and a diameter of 0.282 m by using the Electrical Resistance Tomography (ERT) technique. The flow characterization are measured by applying ERT sensors of three vertical sections with superficial gas velocities in the range 0.027–0.156 m/s. Based on the cross-correlation technique and dynamic gas disengagement (DGD) theory, the bubble Saunter diameters are obtained and the local axial velocity about two phases flow can be calculated. The results show that with increased gas superficial velocity the distribution of bubble size is gradually widespread. Moreover, the local velocity of gas bubble swarm has a center peak distribution with increased gas superficial velocity.     

Fast algorithms for frequency, amplitude and phase evaluation of nonsinusoidal signals with noises

A fast and accurate algorithm for frequency, amplitude and phase estimation of the signals with white Gaussian noises is proposed in this paper. The proposed algorithm need two sample and computation process, one of which is used for frequency estimation in half cycle of the signal and another of which is used for amplitude and phase estimation in another half cycle. The proposed algorithm spends at most 1 cycle. Frequency estimation is based on numerical differentiation, and amplitude and phase estimation is based on fast Fourier Transform. With an initial sample frequency of 512 × 50 Hz, the signal is sampled and the frequency of the signal with white Gaussian noises is estimated at an error of 0.001% over a range of 1 Hz–1000 kHz. With another sample frequency based on the estimated frequency, the signal is once again sampled and the amplitude of the signal is estimated an error of 0.001% over a range of 1 V–320 V and the phase angle of the signal is estimated an accuracy of 0.001% over a range of 0–360. Using Matlab software, the simulation results of the test example are satisfactory.     

Review of certain key issues in indirect measurements of the mass flow rate of solids in pneumatic conveying pipelines

On-line mass flow measurement of particulate solids in pneumatic conveying pipeline is a technically challenging area, where mass flow measurement presents a range of problems. These problems are not normally relevant to a single phase flow, but are always involved in gas–solids two-phase flows, like inhomogeneous distribution of solids over the pipe cross section, irregular velocity profiles, variations in particle size, moisture content, and deposition of fine particles on the inner wall of the pipeline. These variables may affect the response of a solids flow meter in ill-defined ways. All of these make the design and the calibration of solids’ mass flowmeter more difficult. Based on a review of non-invasive mass flow measurements of particulate solids, this paper summarizes and highlights several key issues, which often rely on structures of sensors or measurement methods, in indirect mass flow metering of pneumatically conveyed solids. They are: (i) spatial filtering effect; (ii) averaging effect; (iii) measurement resolution and sensitivity of array structures in tomography sensors.     

波长轮换与相移扫描相结合的表面形貌测量系统

用光学显微干涉法进行表面形貌测量时其深度测量范围的扩大和形貌测量精度的提高是一对矛盾。为此,本文设计出了一种基于波长轮换与相移扫描相结合的三波长表面形貌测量系统,并提出了一种基于椭圆拟合与相位差大小尺度相结合的相位提取与识别算法。将这种算法运用于多波长干涉图像的数据处理,有效地提高了形貌的整体测量精度,并拓展了深度测量范围。实验结果表明:在深度测量范围扩大近15倍的条件下,采用粗糙度国家基准校准的方波多刻线样板得到的表面粗糙度数据与校准数据的相对误差仅为4.12%,表明该系统在一定的深度范围内能够实现表面形貌的高精度测量。另外,针对该系统设计的多波长相位识别算法对环境噪声要求不高,可以支持系统的高噪声或在线测量。     

Measurement range expansion of continuous wave ultrasonic anemometer

This study was conducted to expand the measurement range of a continuous wave ultrasonic anemometer (CWUA) that uses phase difference measurement. A CWUA has a narrower measurement range than conventional ultrasonic anemometers because it can measure the phase difference up to the half-cycle of the used ultrasonic signals. In this study, a method of expanding the measurable range of the phase difference using a phase delay circuit and a frequency divider was developed. Through experiments, it was found that this method doubled or quadrupled the measurement range when the method was used. Furthermore, an algorithm for determining the validity of the measurement data by comparing them with the previous data was implemented with a wind velocity measurement error of less than ±1 μs to solve the problem caused by the use of the frequency divider and to produce a stable measurement system.     

Separation of isochromatics and isoclinics from photoelastic fringes in a circular disk by phase measuring technique

A new polariscope system involving two rotating optical elements and a digital camera for whole field fringe analysis allows automated data to be acquired quickly and efficiently. The developed phase measuring technique that uses eight images through a circular polariscope is presented for the digital measurement of isochromatics and isoclinics, respectively, from photoelastic fringes in a circular disk under diametric compression. Isochromatics can directly be obtained using wrapped isoclinic phases calculated by the arc tangent operator which is the four-quadrant operator from −π to π. It is not required to unwrap isoclinic phases for the calculations of isochromatics. Unwrapped isoclinics are directly determined from isochromatic parameters. Distributions of digitally determined isoclinics are in close agreement to manual measurements. The errors which would appear in unwrapping process of isoclinics can be avoided in the determination of isochromatics.     

Gallium-enhanced phase contrast in atom probe tomography of nanocrystalline and amorphous Al-Mn alloys

Over a narrow range of composition, electrodeposited Al-Mn alloys transition from a nanocrystalline structure to an amorphous one, passing through an intermediate dual-phase nanocrystal/amorphous structure. Although the structural change is significant, the chemical difference between the phases is subtle. In this study, the solute distribution in these alloys is revealed by developing a method to enhance phase contrast in atom probe tomography (APT). Standard APT data analysis techniques show that Mn distributes uniformly in single phase (nanocrystalline or amorphous) specimens, and despite some slight deviations from randomness, standard methods reveal no convincing evidence of Mn segregation in dual-phase samples either. However, implanted Ga ions deposited during sample preparation by focused ion-beam milling are found to act as chemical markers that preferentially occupy the amorphous phase. This additional information permits more robust identification of the phases and measurement of their compositions. As a result, a weak partitioning tendency of Mn into the amorphous phase (about 2 at%) is discerned in these alloys.     

A comparative study of material phase effects on micro-machinability of multiphase materials

In the mechanical micro-machining of multiphase materials, the cutting process is undertaken at a length scale where material heterogeneity has to be considered. This has led to increasing interest in optimising the process parameters for micro-machining of such materials. In this study the micro-machinability of two steels, a predominantly ferrite material (AISI 1005) and a near-balanced ferrite/pearlite microstructure (AISI 1045) was studied. Workpiece sample deformation properties were characterised by nano-indentation testing. Additionally, metallographic grain size evaluation was undertaken for the workpiece microstructures. Surface roughness, workpiece microstructure and burr size for micro-machined parts as well as tool wear were examined over a range of feed rates. The results suggest that for micro-machined parts, differential elastic recovery between phases leads to higher surface roughness when the surface quality of micro-machined multiphase phase material is compared to that of single phase material. On the other hand, for single phase predominantly ferritic materials, reducing burr size and tool wear are major challenges. Thus, the paper elucidates on material property effects on surface and workpiece edge quality during micro-milling.     

基于正弦相位调制的光纤干涉位移测量系统研究

针对全光纤干涉仪工作距离短、测量范围小等问题,提出了一种基于正弦相位调制的全光纤干涉系统,在参考臂通过电光调制器引入的调制参考光,与探头接收到的目标反射光产生干涉。根据锁相放大原理从干涉信号中提取出正交分量后,首先建立由正交分量构成的观测模型,通过卡尔曼滤波对正交分量的幅值和偏置进行迭代估计和修正,降低由相位延迟、调制深度漂移、寄生干扰等导致的幅值漂移和附加偏置;然后利用反正切法对反射光与参考光之间的相位差进行解调。开展了模拟干涉信号的相位解算仿真模拟和位移测量实验。仿真和实验验证了该算法解算相位的有效性。结果表明,该位移测量系统的工作距离可达到20 cm,测量精度为10 nm。