Shadow Method Research Articles

Radial distribution characteristics of droplet size and velocity in annular mist flow around the bluff body

Wet gas is a common gas–liquid flow type in chemical processing. When measuring the gas flow rate and liquid load of wet gas with a vortex flowmeter, the small droplets in the flow can significantly affect the measurement accuracy. The optical shadow method was used to measure the parameters and distribution of droplets around the bluff body in annular mist flow. The experimental results show that the velocity distribution of droplets upstream of the bluff body mainly depends on the gas superficial velocity. After passing through the bluff body, when the liquid loading capacity φl is<0.030, the droplet velocity changes from a concentrated single-peak to an uneven double-peak distribution. However, when φl ≥ 0.041, the droplet velocity distribution recovers to a single-peak distribution. The joint distribution of droplet diameter and velocity indicates that the change in velocity distribution is mainly caused by small droplets within the range of 0 to 20 μm, as large droplets are not easily lifted by vortices but can cause rapid dissipation of vortices. The experimental data quantitatively confirm the momentum transfer and transformation between droplets and the vortex flow field, and describe the motion dynamics of droplets in the flow field through the Stokes number (Stp) to analyze the interaction between droplets and vortices.

Solution of the Inverse Problem of Calculating a Gas–Liquid Injector with a Two-Phase Flow

We consider the possibility of solving the inverse problem of calculating a gas–liquid jet injector with a bubbly two-phase flow structure. The parameters governing the injector operation, such as the pressure difference, the orifice diameter, and the air concentration, are determined for the given value of the mean Sauter diameter. For this purpose, the operation of a mixer with a two-phase working body and injectors of different diameters was experimentally investigated in the bubbly operation regime with a water–air working body. In the experiments the parameters of the phases supplied to the mixer (flow rates, pressures, and temperatures) were measured, together with the pressure ahead of the injector. The dispersity and velocity parameters in the spray were measured using the laser shadow method. The statistics thus gathered allow one to obtain the required correlation dependences which makes it possible to solve the problem formulated.

Experimental study on the lateral migration of a bubble contaminated by surfactant in a linear shear flow

Adding a small amount of surfactant to a gas–liquid two-phase flow can markedly change the dynamic behavior of its bubbles. In this study, the lateral motion of a single bubble (deq = 1.99–3.33 mm, Reb = 200–420) contaminated by surfactant and rising in a linear shear flow is experimentally studied. Sodium dodecyl sulfate (SDS) is chosen as the surfactant with concentrations ranging from 10 to 50 ppm. A curved screen is used to generate a stable linear shear flow, and particle image velocimetry is used to measure the quality of the flow field. Bubble motion parameters, including trajectory, aspect ratio, instantaneous velocity, and terminal velocity, are captured using the shadow method with charge-coupled device cameras. The lift coefficient C L is obtained by a quasi-steady-state analysis. The results show that the presence of surfactant inhibits the lateral migration of bubbles rising in a shear flow and that increasing the SDS concentration and bubble equivalent diameter strengthens this inhibition effect. That is, the C L and the net lateral migration distance decreased with SDS concentration and bubble equivalent diameter. In addition, the variation trends of the quasi-steady drag coefficient, bubble terminal velocity, and bubble oscillation frequency with bubble equivalent diameter and SDS concentration also were analyzed.

Measurement of Spot Diameter and Divergence of Laser Beam by Shadow Method Using Generalized Parameters

Measurement of Spot Diameter and Divergence of Laser Beam by Shadow Method Using Generalized Parameters

Energy Meter Patch Resistance and Welding Spot Anomaly Detection Method Based on Machine Vision

Based on the problems, such as the difficulty of detecting and obtaining evidence of patch resistance replacement and welding spot anomaly in the current field of meter anomaly detection, a patch resistance and welding spot anomaly detection algorithm is proposed based on machine vision. The resistance anomaly detection algorithm combines the K-D tree and Ransac to complete the high-efficiency energy meter registration. It detects the suspected resistance abnormal area through the difference shadow method and then judges the resistance abnormal situation according to the resistance value recognized by the classification network. The welding spot anomaly detection algorithm enhances the feature of the image through saliency detection, then obtains the target information of the welding spot by segmentation, and finally determines the welding spot anomaly condition in combination with the connection domain analysis. Experimental results show that the precision of patch resistance anomaly of this method reaches 95.28%, and the detection time is about 1.52s; the precision of welding spot anomaly reaches 96.74%, and the detection time is about 0.74s. The method can meet the requirements of spot detection accuracy and speed and has good application value.

Study on the effect of focal position change on the expansion velocity and propagation mechanism of plasma generated by millisecond pulsed laser-induced fused silica

In this work, by controlling the positional relationship between the target and the focal point, the surface damage, shock wave phenomenon and propagation mechanism involved in the plasma generation of fused silica by millisecond pulsed laser irradiation at different focal positions were studied. Laser energy is an important experimental variable. The dynamic process of plasma was detected by optical shadow method, and the influence of surface film damage on plasma propagation and the propagation mechanism at different focal positions were discussed. The study found that the plasma induced by the pulsed laser at the focus position within 0–20 μs exploded, the micro-droplets formed around 20 μs. At the same time, a shock wave is formed by the compressed air, the micro-droplets are compressed under the action of the shock wave recoil pressure, and the micro-droplets channel phenomenon is observed in the micro-droplets. The peak velocities of plasma and combustion wave appear earlier in the pre-focus position than in the post-focus position. This research provides a reference for the field of laser processing using fused silica as the substrate.

Investigations of string cavitation and air back suction during injection duration in the scaled-up diesel fuel injection nozzle

The flow inside the diesel fuel injector nozzle is directly associated with the subsequent jet atomization and fuel–air mixture performance, and finally affects the combustion efficiency and emission. In this study, high-speed microscope imaging technology is applied to capture the complex multiphase flow and near-field spray during the process of fuel injection. Besides normal optical experiments for nozzle internal flow and spray, the submerged jet experiment for comparison is also carried out to investigate the phenomenon of air back suction. Combined with the simulation of a three-component multiphase model, the difference between air and cavitation vapor is analyzed. Results show that the submerged jet experiment will not change the internal flow field but can eliminate the influence of air. The shaded area in the hole obtained by the shadow method may be the sucked air or vapor generated by string-type cavitation phase change. Both can coexist in the hole and are closely related to the swirling intensity and the spray structure, respectively. When the needle lift is low, the internal flow field has larger swirling intensity resulting in a kind of hollow spray. The low-pressure region exists in the vortex core, nearly at the axis of the nozzle orifice. The ambient air will be sucked into the orifice to form an air column under the action of pressure difference, which is also easy to occur under low injection pressure. When the needle lift is high, the weak swirl intensity leads to hole-to-hole string cavitation which has weak cavitation intensity and obvious periodicity. At this time, the results of non-submerged and submerged jet experiments are basically the same. In addition, the cavitation bubble near the orifice outlet was observed, for the first time, to move upstream under the action of the pressure difference inside and outside the orifice in the submerged jet experiment. It can be predicted that in the non-submerged jet experiment, the ambient air will be sucked into the orifice to form an air column.

Оценка возможности контроля болтового соединения крышек сосудов с помощью ультразвуковых волн

The aim of the work is to study the applicability of the acoustic method for monitoring the loosening of fasteners on vessel lids, based on the change in signal amplitude during reflection and transmission of ultrasonic waves through the interface between plates. In the course of the work, theoretical dependences of the change in the amplitude of the received signal with a change in the applied pressure were obtained for the case of a flange connection without an additional gasket and in the presence of a gasket made of various materials. It has been established that in the absence of acoustic contact in the flange connection, the amplitude of the signal reflected from the interface is maximum, while in continuous contact it is minimal. The results obtained were verified experimentally using the shadow and echo method of ultrasonic testing. As a result of the study, it was found that the maximum change in the signal amplitude is observed at low frequencies, and when controlled by the shadow method, it is higher than when using the echo method.

Прикатодные плазменные и газодинамические процессы при формировании искрового разряда в воздухе атмосферного давления в промежутке острие-плоскость

Using the method of shadow photographing, the formation of a spark discharge in the "tip (cathode) – plane" interval with a length of 1.5 mm is investigated. Two types of shock waves have been registered – cylindrical, created when the discharge channel expands, and cathode, presumably generated by cathode flares near the surface of the tip electrode. The computational and theoretical consideration of the proposed mechanism is carried out.

Near-cathode plasma and gas-dynamic processes during the formation of a spark discharge in air at atmospheric pressure in the gap point-plane

Using the method of shadow photographing, the formation of a spark discharge in the &amp;quot;tip (cathode)-plane&amp;quot; interval with a length of 1.5 mm is investigated. Two types of shock waves have been registered cylindrical, created when the discharge channel expands, and cathode, presumably generated by cathode flares near the surface of the tip electrode. The computational and theoretical consideration of the proposed mechanism is carried out. Keywords: gas discharge, microstructure, electron temperature, degree of gas ionization.

INTEGRATION METHOD FOR MEASURING QIBLA DIRECTION (COMPARATIVE ANALYSIS OF GOOGLE EARTH AND MIZWALA)

The accuracy of measuring the qibla direction of the mosque in Kendal, Central Java, needs attention from astronomy because the majority of people only know the traditional qibla direction measurement tool namely using a compass and the sun's shadow method. Even though errors in the use of the method will result in inaccurate measurement results and have an impact on the validity of the prayers performed. Therefore, this study compares two methods that are easy for the public to use, namely Google Earth and Mizwala. Google Earth as a method to check the qibla direction and Mizwala as a comparison method to improve Google Earth. Through mathematical qualitative methods with data collection techniques through observation and interviews, it is known that these two methods are the easiest and most accurate to determine the qibla of all mosques. The method of data collection was carried out by calculating and measuring the qibla direction towards 1 mosque and 5 musholla. Although the two methods differ in terms of appearance, that Google Earth uses a satellite network while Mizwala uses the concept of the Sun's shadow, both of them can be used in an easy and integrative way. The result of Mizwala's measurements with Google Earth conclude error tolerance that is a range of minutes of angle. In the end, the two methods can be integrated to help and increase public awareness about the importance of correct qibla direction accuracy.

Link-Blockage Model and AP-Placement Scheme for No-Blockage Link between AGV and AP in Logistics–Warehousing VLC Network

In this paper, the blockage problem of the optical link between AGV (autonomous ground vehicles) and AP (access point) in the logistics–warehousing VLC (visible light communication) network is analyzed. First, based on the random geometric model, a link-blockage model is proposed. Given the position of AGV, AP and obstacle, the blockage state of the VLC link between AGV and AP can be obtained through this model. Then, an AP-placement scheme based on the link-blockage model is proposed. Under this AP placement, AGVs in any position have a reliable link that is not affected by obstacles. During the movement of AGV, the VLC link of AGV will not be interrupted by a random blockage. Finally, the effectiveness of the link-blockage model is demonstrated by the shadow method. In this paper, the link outage probability and the data rate under different AP heights, AP spacings and the number of obstacles are simulated. Simulation results show that the VLC link can keep uninterrupted under the AP placement proposed in this paper.

Optical Methods for Studying Pre-Breakdown Phenomena in Liquid Dielectrics

Three main groups of non-invasive experimental methods (shadow, spectral, and electro-optical) for studying pre-breakdown processes in liquid dielectrics are reviewed. Each of these methods has its own capabilities and allows a limited set of information about the process under study to be obtained. High-speed shooting makes it possible to record emerging objects and trace the dynamics of the processes occurring in the discharge gap. Shadow methods make it possible, by recording changes in the probing radiation in a real-time mode, to obtain information about the course of processes in a liquid, during which a change in the refractive index occurs. However, neither of these two methods allows the obtained data to be linked to the electrical characteristics of the object under study. Spectral research methods make it possible to consider the effect of high voltage on the physicochemical processes occurring in the discharge gap. To do this, it is advisable to combine them with high-speed shooting methods, but the low intensity of the studied radiation and the high speed of the processes add much difficulty to the use of such methods. If the processes occurring at the molecular and atomic levels are set aside, the electro-optical research method remains the only one that links the electrical parameters of the object under study with the obtained optical picture of the processes. Moreover, with a growth in the field strength, additional features appear in the electro-optical pattern due to the the Kerr effect nonlinearity, as a result of which the characteristic processes that precede the breakdown can be noticed. It is shown, using the electro-optical Kerr effect as an example, how the use of modern computer-aided experimental data processing methods helps obtain additional information that was previously inaccessible.

Experimental investigation on the fracture surface features of heat-treated red sandstone containing fissure under constant amplitude low cycle impact using 3D digital reconstruction

Fractured rocks as typical engineering materials are commonly exposed to temperatures and dynamic perturbations. In this paper, constant amplitude low cycle (CALC) impact tests were carried out on red sandstone containing a single fissure (0°, 30°, 60° and 90°) after thermal treatment (25 °C, 200 °C, 400 °C, 600 °C and 800 °C) utilizing a modified split Hopkinson pressure bar (SHPB). Subsequently, the fracture surfaces of the failure specimens were digitally reconstructed based on point cloud data captured by a three-dimensional (3D) laser scanning. And scanning electron microscopy (SEM) was also employed as a complementary tool to study the fracture micromorphology. The fractal and rough features of fracture surfaces based on the box-counting method and image segmentation method were investigated, respectively. Meanwhile, four second-order statistics in the grayscale co-occurrence matrix (GLCM) of the digitized fracture surface after grayscale processing were calculated to describe the fracture surface texture. The best-fit multiple regression models between the fracture surface feature parameters and the interaction of temperatures and fissure angles were constructed and analyzed. Moreover, the relationships between the fracture surface features and the mechanical parameters as well as the intrinsic mechanisms were analyzed and discussed in detail. The results demonstrate that the fractal dimension (DC), joint roughness coefficient (JRC), maximum elevation difference (MD), roughness characterization factor (ω), and GLCM second-order statistics possess specific response patterns to the temperatures and fissure angles. Whether the sensitivity in portraying the fracture surface features to the interaction of temperatures and fissure angles or the reliability of the best-fit multiple regression models, the shadow method based on image segmentation behaves more promisingly. Furthermore, conspicuous correlations can be found between both the feature parameters including the GLCM second-order statistics and the failure strength, strain rate as well as life. The high temperature activates thermal activation mechanisms that alter the potential crack sources and pathways in the grain and rock skeleton, affecting the microscopic fracture face morphology. Finally, the maximum tensile stress at the edge of the prefabricated fissure might be responsible for the angle effect exhibited by the feature parameters.

Experimental and numerical study of Taylor flow in a square minichannel

A numerical and experimental study of Taylor bubbles in a square minichannel with a side of 1 mm has been carried out. A three-dimensional numerical simulation was performed using the volume of fluid method in the open source package OpenFOAM. An experimental study was performed using a high-speed shadow method and automatic processing. The characteristic flow regimes are investigated, with the main attention being paid to the Taylor regime. In the course of the work, the calculated and experimental data were compared, and their good agreement was shown. The distribution of velocities in a liquid and gas, as well as the distribution of the liquid film thickness in a bubble, is studied. The thickness of the liquid film in the corner and the center of the channel is compared with the corresponding well-known correlations. A dependence that describes the thickness of a liquid film in a square channel is proposed. Investigations of the streamline both in the liquid near the bubble and in the bubble itself. It is shown that in the square channel in front of the bubble there are four stable vortexes in the direction of the channel corners. Inside the bubble there is a specific flow from the tail to the nose of the bubble. There is a swirling of the gas in the transverse direction in the bubble.

A disturbance suppression micro-Newton force sensor based on shadow method

The precision of micro-force measurement depends on the force sensor sensitivity and the environmental disturbance magnitude. However, micro-force sensors generally have the poor anti-disturbance ability. Inspired by the shadow formed by water striders walking on water surface under sunlight, a viscoelastic-polymer micro-force (VPMF) sensor based on the shadow method was proposed, which could suppress disturbances effectively due to the high damping ratio of 0.22. The shadow diameter change and the applied force were proportional. The experimental results indicated that the sensitivity could reach 2.15 μN/pixel with a good linear performance. Furthermore, compared with the cantilever, it was capable of the reduction of the disturbance influence by approximately 96.35%. Therefore, the VPMF sensor can be applied to reliable micro-force measurement in complex environments such as industrial sites.

Shadow method retrievals of the atmospheric optical depth above Gale crater on Mars using HRSC images

The ‘Shadow Method’ is a tool to estimate the Atmospheric Optical Depth (AOD) on Mars from the brightness of shadows. This method is derived from the equations of radiative transfer, but there are several important simplifications that together invoke errors of several tens of percent. Work by us and by others show that these errors are largely systematic and can be minimized by adding an empirical ‘Correction-Factor’ to the equations. To quantify this factor, we compared shadow method retrievals from orbiter images with in-situ measurements by the Curiosity rover. We analysed a set of seven images that was taken by DLR's High Resolution Stereo Camera (HRSC) on-board ESA's orbiter Mars Express. The images were taken in seven channels: NIR, red, green, blue, and in three panchromatic stereo channels S1, Nadir, and S2. All these images show Gale crater and the exploration site of the Curiosity rover therein. Comparing the rover measurement of the AOD with shadow method retrievals from 5 close-by regions yielded the following correction factors: 0.53 ± 0.03 for Nadir, 0.60 ± 0.04 for S1, 0.62 ± 0.03 for S2, 0.66 ± 0.03 for NIR, 0.64 ± 0.03 for Red, 0.55 ± 0.03 for Green, and 0.57 ± 0.03 for Blue.We analysed 71 regions with varying altitudes between −4.6 km to +3.8 km and found that, on an average, the AOD decreases with increasing altitude. The available channels yielded the following averages of atmospheric optical depth before applying the correction factor: Nadir: 0.47; S1: 0.46; S2: 0.52; Red: 0.49; Green: 0.53; Blue: 0.57 and NIR: 0.44 while after applying the correction factor we obtain Nadir: 0.89; S1: 0.77; S2: 0.84; Red: 0.77; Green: 0.96; Blue: 1.0 and NIR: 0.67. The Curiosity rover, at an altitude of −4.87 km, measured a ground-truth AOD of 0.88.The shadowed and sunlit comparison regions that were used for this work range in altitudes from −4.6 km to +3.8 km. The AOD decreases with altitude and the decrease yields the following scale heights: S1: 12.5 + 0.48/−0.35 km; nadir: 11.1 + 0.53/−0.33 km; S2: 14.3 + 0.48/−0.44 km; NIR: 11.1 + 0.56/−0.47 km; red: 14.3 + 0.52/−0.49 km; green: 15.6 + 0.62/−0.59 km; blue: 14.3 + 0.44/−0.42 km. For this area and around that time of day, the Mars Climate Database predicts a pressure scale height of 11.6–12.2 km, which agrees well with the scale heights that we derived for Nadir, S1 and NIR. One region (number 42) contained a cloud with an optical depth of up to 0.6—0.8; i.e., around one third of the total AOD of 1.9 ± 0.01 measured for this area. Region 29 showed the highest AOD of our sample.

Structuroscopy of Coils after High-Temperature Mechanical Treatment on the Basis of Measurements of Rayleigh Waves Velocity

For the manufacture of spring springs of rolling stock (wagons, locomotives, cars), bars made of spring steels are used. With high-temperature machining, when winding springs and quenching them, there is a difference in the cooling rates of the inner and outer sides of the spring coils, which leads to a difference in the structural state and affects the durability of the springs. The aim of the work is to study the effect of structural changes in the outer and inner surfaces of spring steel coils after winding and high–temperature machining operations on the measured characteristics of Rayleigh acoustic waves.The propagation velocities of Rayleigh waves in spring-spring steel 60C2A after winding and hightemperature machining operations are investigated. The shadow method and the autocirculation method with piezoelectric converters CTS-19 with a frequency of 5 MHz with a special block design were used for research. The converters provide input and reception of the Rayleigh wave along the inner and outer forming surface of the spring. It is shown that the method of comparing the results of measuring the velocity of Rayleigh waves on a fi base by the coil generator on the inner and outer surfaces of the spring is sensitive to disturbances in the structure of the material and the appearance of defects. An unambiguous relationship of the structural states on the outer and inner sides of the spring with the velocity of the Rayleigh wave is found.As a result of the measurements, a conclusion was made about the significant sensitivity of Rayleigh waves to the structural state of the steel under study. An increase in the wave velocity was detected on the inner surface of the coil in the contact zone with the mandrel relative to the outer side of the coil, signaling incomplete hardening of steel in this zone during high-temperature machining. The relative speed difference in different spring samples is approximately up to 1 % (≈ 30 m/s), which is a significant value for assessing the quality of high-temperature machining.

Влияние пористой полиуретановой перегородки на гидравлические характеристики потока и на распространение фронта пламени в открытом канале

The purpose of the research was to experimentally study the influence of a porous polyurethane partition on the flow parameters and on the flame front propagation in front of the partition upon initiation at the open end of the channel. The flame front velocities were determined in a hydrogen-air mixture at atmospheric pressure in a channel open on both sides with an inner diameter of 20 mm. The ratio between hydrogen and air was varied, so that the molar excess of hydrogen varied from 0.3 (ultra-poor mixture) to 1.0 (stoichiometric composition). The pore size varied within 0.3--2.5 mm, which corresponded to the number of pores per inch in the range of 10--80. The coefficients of hydraulic resistance of a polyurethane partition with an open pore type, depending on the size of the pores and the thickness of the partition, were calculated from the pressure loss when the air flow passes through the porous element. The flame front velocity was determined using the shadow method and high-speed survey. Findings of the research show that the optimal value of the thickness of the porous partition, after which the polyurethane partition begins to show filtration properties, in most cases is approximately equal to twice the pore size and the drag coefficient depends linearly on the total thickness of the partition. In this case, the deficit of the flow velocity with increasing thickness increases according to a power law. A qualitative correspondence between the flame front velocity in front of the porous partition and the flow velocity deficit is shown

Heat transfer enhanced surfaces for horizontal tube falling film evaporator characterized using laser interferometry

The falling film evaporators are a class of heat exchanger that is widely studied. The research for improving the efficiency is still of prime importance because of its widespread applications in many industries such as desalination, food processing, nuclear energy, refrigeration etc. Our motive in this work is to investigate the potential use of heat and mass transfer enhanced surfaces for horizontal tube falling film evaporator to scale up its effectiveness. Four different tube surfaces viz. bare copper tube, Al2O3 thermal spray coated tube, Al2O3 + TiO2 thermal spray coated tube and open cell copper metal foam wrapped tube were taken for the study. Scanning electron microscope, 3D surface profilometer, contact angle metre and energy-dispersive X-ray spectroscopy were utilized to study the surface texture, surface roughness, wettability and composition, respectively. Out of these four surfaces, a total of eight configurations were realized by varying the coating thickness, surface roughness and porosity. A new prototype of horizontal tube falling film evaporator was designed and fabricated with fully wetted flow. An in house developed novel method based on laser interferometry was utilized for the experimental investigation. This non-invasive technique was capable of measuring falling film thickness and falling film interface temperature simultaneously with unprecedented circumferential span. For the film thickness evaluation, an optical shadow method incorporating Otsu’s algorithm with precise interface tracking features was used. Mach–Zehnder Interferometer was employed to visualize the isotherm formation and to quantitatively infer the interface temperature. A 2D CFD study based on VOF model was carried out and found to be in good agreement with experimental as well as theoretical results. Further, the effect of flow rate, feed inlet water and body temperature were explored in detail and analysed statistically.