Effect Of Stand-off Distance Research Articles

Effect of industrial scale stand-off distance on water jet break-up, cleaning and forces imposed on soil layers

The effect of stand-off distance (the distance between a stationary nozzle and a soiled surface, L) on cleaning by a water jet generated by a 3mm nozzle (diameter, dN) was studied. Two nozzle gauge pressures, pN=2.0bar and 4.0bar, giving jet Reynolds numbers of ReJet=43800 and 61600, were investigated, for four soils with different cleaning behaviour (petroleum jelly, ketchup, mustard, starch+diatomaceous earth). For long times, of tc=10min and 20min, the area cleaned increased with L due to jet break-up increasing the area exposed to impact.For soils which are easy to clean (here ketchup) at shorter time scales (tc≤0.1min) a stand-off distance of L=2m gave optimal cleaned area. Soils which are hard to clean required small stand-off distances with short cleaning times.The cleaning results are compared with jet break-up, impact force and impact pressure results presented by Fuchs et al. (2018). Jet break-up gives a larger impact area which results in a more efficient cleaning for most soils. However, results of the cleaned area only correspond to measurements of jet impact area in the case of soils that are not swellable and hard to clean.Binding forces within the soils were determined with a micromanipulation apparatus. Results show that the basic cleaning behaviour of the soils can also be determined on a laboratory scale without using a water jet. This allows the prediction of cleaning behaviour without extensive cleaning tests as well as preselection of cleaning devices.

Computational Study of Partially Covered Hartmann Whistle in a Sonic-Underexpanded Jet

The present study investigates the use of Hartmann whistle as an effective passive flow control device by partially covering the entire area between the jet exit and cavity inlet using a cylindrical shield, numerically. The passive flow control is accomplished by allowing the pulsating jet to exit through two small openings in the shield: (i) near the cavity inlet, (ii) away from the cavity inlet. The studies are performed for various S/Dj values of 1.43, 2.86 and 4.28, (where S is the stand-off distance and Dj is the jet diameter). The velocity vectors indicate the jet regurgitance showing inflow/outflow phases as well as flow diversion features near the cavity mouth. The Mach contours show shock-structures as well as the flow deceleration and re-acceleration zones. It shows that the resonant oscillations are primarily driven by jet regurgitance at smaller stand-off distances but at higher stand-off distances they are mainly driven by fluid column oscillations in the shock cells, shield, as well as in the cavity regions. It also shows that the stand-off distance is a key parameter that controls the strength of shock as well as regurgitant/fluid column, oscillations. An empirical formula developed using dimensional analysis reveals that the resonance frequency of the partially covered Hartmann whistles can be obtained using the classical Helmholtz resonator analogy with the stagnation sound speed, size of the flow control openings, shield height, stand-off distance and cavity length as parameters. Thus, this paper adequately illustrates the effect of stand-off distance as well as flow control openings in modifying the shock as well as regurgitant/fluid column, oscillations in a partially covered Hartmann whistle for attaining the effective flow control .

Study of extrudability and standoff distance effect during nanoclay-enabled direct printing

Nanoclay-enabled self-supporting printing has been emerging as a promising filament-based extrusion fabrication approach for different biomedical and engineering applications including tissue engineering. With the addition of nanoclay powders, liquid build materials may exhibit solid-like behavior upon extrusion and can be directly printed in air into complex three-dimensional structures. The objective of this study is to investigate the effect of nanoclay on the extrudability of N-isopropylacrylamide (NIPAAm) and the effect of standoff distance on the print quality during nanoclay-enabled direct printing. It is found that the addition of nanoclay can significantly improve the NIPAAm extrudability and effectively eliminate die swelling in material extrusion. In addition, with the increase of standoff distance, deposited filaments change from over-deposited to well-defined to stretched to broken, the filament width decreases, and the print fidelity deteriorates. A mathematical model is further proposed to determine the optimal standoff distance to achieve better print fidelity during nanoclay-enabled direct printing. Based on the extrudability and standoff distance knowledge from this study, NIPAAm–Laponite nanoclay and NIPAAm–Laponite nanoclay–graphene oxide nanocomposite hydrogel precursors are successfully printed into a three-layered one-dimensional responsive pattern, demonstrating the good extrudability and print quality during nanoclay-enabled printing under optimal printing conditions.

Investigation of stand-off distance effect on structure, adhesion and hardness of copper coatings obtained by the APS technique

The outbreak of the disease and infection in the hospital environment and medical equipment is one of the concerns of modern life. One of the effective ways for preventing and reducing the complications of infections is modification of the surface. Here, the handmade atmospheric plasma spray system is used for accumulating copper as an antibacterial agent on the 316L stainless steel substrate, which applies to hospital environment and medical equipment. As a durable coating with proper adhesion is needed on the substrate, the effect of stand-off distance (SOD) which is an important parameter of the spray on the microstructure, the hardness and adhesion of the copper coating on the 316L stainless steel were investigated. The structure and phase composition of copper depositions were investigated using scanning electron microscopy and X-ray diffraction. The adhesion and hardness of depositions are evidenced using the cross cut tester and Vickers hardness tester, respectively. The findings confirm that the voids in the coatings increase with increasing SOD, which leads to decreasing the hardness of coatings and also the adhesion strength between depositions and substrate. In addition, by increasing the SOD, the oxygen content and the size of grains in the lamellae (fine structure) of coatings also increase.

Experimental study on the deformation and damage of cylindrical shell-water-cylindrical shell structures subjected to underwater explosion

Experimental investigations were carried out on Q235 steel cylindrical shell-water-cylindrical shell (CWC) structures subjected to near field or contact underwater explosion loading. All the tests were conducted in an artificial water pool detonating 50 g charge weight of trinitroluene (TNT) explosive. Corresponding plastic deformation of the CWC structures were measured for different structural parameters and standoff distances. Three major deformation modes including seven typical subdivided deformation characteristics were classified and analyzed considering the effect of standoff distance, shell thickness and water interlayer thickness. Microscopic analysis was performed using the SEM method to further compare two typical subdivided fracture modes with the combination of the macroscopic deformation features.

Abrasive jet drilling of glass sheets: Effect and optimisation of process parameters on kerf taper

This article reports an investigation of the influence of process parameters on the obtainable dimensional accuracy when drilling glass using abrasive jet machining. In particular, holes were drilled out of glass sheets, and the effects of standoff distance, nozzle diameter, particle grain size and applied pressure on the kerf taper were examined. An artificial neural network technique was used to establish a precise model of kerf taper as a function of the process parameters. The proposed model was then optimised, and the conditions to minimise the kerf taper were identified using a genetic algorithm. The results revealed that standoff distance has a major effect on kerf taper, and it proved possible to substantially reduce the kerf taper by applying an axial feed to the nozzle so that the standoff distance is kept constant during the machining process.

Effect of Stand-Off Distance on the Mechanical and Metallurgical Properties of Explosively Bonded 321 Austenitic Stainless Steel - 1230 Aluminum Alloy Tubes

In this research, the effect of stand-off distance on the interfacial mechanical and metallurgical properties of explosively bonded 321 austenitic stainless steel to 1230 aluminum alloy tubes was investigated. Interfacial microstructure was evaluated by optical microscopy and scanning electron microscope. Also, Microhardness tests were also carried out. The results show that with increasing of stand-off distance from 1 mm to 2.5 mm, thickness of intermetallic compounds at the interface increased from 3.5 µm to 102.3 µm, and also shape of interface was transited from smooth to wavy. The microhardness of the sample with 1 mam stand-off distance was 650 HV that increased to 927 HV in the sample with 2.5 mm stand-off distance which is related to intermetallic amount. The proportional amount of strength were 103.2 MPa and 214.5 MPa in the above samples respectively.

Titanium Dioxide Coating Prepared by Use of a Suspension-Solution Plasma-Spray Process

Titanium dioxide coatings were prepared from titanium isopropoxide solution containing nano TiO2 particles by use of a plasma-spray process. The effects of stand-off distance on coating composition and microstructure were investigated and compared with those for pure solution precursor and a water-based suspension of TiO2. The results showed that the anatase content of the coating increased with increasing stand-off distance and the rate of deposition decreased with increasing spray distance. Anatase nanoparticles in solution were incorporated into the coatings without phase transformation whereas most of the TiO2 in the precursor solution was transformed into rutile. The microstructure of preserved anatase particles bound by rutile improved the efficiency of deposition of the coating. The amount of anatase phase can be adjusted by variation of the ratio of solution to added anatase TiO2 nanoparticles.

Laser Spot Welding of Thermoplastic and Ceramic: An Experimental Investigation

Laser welding of dissimilar materials classes has vast potential in a variety of applications due to the non-contact nature of the process. This study investigates the effects of CO2 laser process parameters on the characteristics of spot welded joint between ceramic and thermoplastic. Using a full-factorial design an experimental investigation is carried out studying the effect of welding parameters (laser exposure, number of spots, stand-off distance) on the tensile strength and the diameter of spot weld. The study reveals an increase of joint tensile strength with the increase in the number of spots and the duration of exposure. However at low laser power, the effect of stand-off distance on the spot weld diameter is found to be inconclusive. Optimal process parameters are estimated using the multi-objective optimization on the basis of ratio analysis. The analysis shows that the higher number of spots and the longest duration of laser exposure result in optimal weld characteristics. Alongside these conditions, a larger stand-off distance is seen to have beneficial impact on the weld characteristics.

Abrasive waterjet micro-piercing of borosilicate glass

Abrasive water jet (AWJ) machining of delicate materials is difficult due to the large pressures that commonly result in large-scale chipping and other target damage. The damage occurs mostly during the initial piercing operations when the jet flow creates a large stagnation pressure at the jet to surface interface at the bottom of blind holes. This paper examined the parameters that affect target damage during piercing operations in borosilicate glass. The effects of stand-off distance (SOD), dwell time and pressure for three nozzles sizes were compared. A novel aspect of the study is the use of a prototype 254μm micro-abrasive waterjet machining (μAWJM) nozzle. The results of a parametric analysis identified machining configurations that resulted in the reduction of chipping and hole size, and an improved hole circularity. This paper also proposed and assessed two methods for the reduction of exit pierce chipping using the μAWJM nozzle. A finite element analysis showed that the use of stacked borosilicate glass plates reduced the exit stresses associated with through piercing, thus reducing the amount of exit hole chipping. An μAWJM/AJM (micro-abrasive waterjet machining/abrasive jet machining) hybrid operation was also shown to considerably reduce exit chipping and exit hole size.

Autodyn-2D Simulation of Shaped Charge Jet Formation and Penetration Mechanism into Multi-Layered Shielded Target

In this work, the shaped charge jet formation depends on different parameters which can has effect on jet behavior such as jet velocity, breakup and penetration. Jet radius or liner thickness, shell thickness, liner material density, α angle and stand-off distance are evaluated in purpose to investigate their effect on performance of shaped charge jet velocity and jet breakup phenomena, also we investigate the effect of stand-off distance on shaped charge jet penetration into steel target. We also studied the performance of some protective shields materials in order to assure more protection for vehicle structure against shaped charge jet penetration. For that, different materials were used as armors such as: kevlar epoxy, polyethylene, glass epoxy, steel-1006 and Al2O3 ceramic. These protective shields were evaluated in order to show their performance against shaped charge penetration into target. To do so, adopted explicit dynamic analyzing program Autodyn basing on finite element were used to simulate shaped charge jet formation and penetration. Autodyn-2D simulationshighlight the efficiency of our work comparing with the experiments done in literature and Birkhoff’s theory. In other terms, increasing in shell thickness, alpha angle and liner densityenhance jet breakup time, protective shields layered armor of steel-1006, steel 1006 with polyethylene and steel-1006 with Al2O3ceramic give more protection for structure against shaped charge jet penetration comparing with others armors.

Mechanism and experimental investigation of ultra high pressure water jet on rubber cutting

The recycle and reuse of rubber materials has become a global environment problem with the fast increasing amount of waste rubber. Compared to traditional recycle methods, ultra high pressure water jet, as a fast developing tool of cool cutting, can be used in recycling rubber materials without damaging the internal organization structure of materials. This paper investigates ultra high pressure jet cutting rubber in mechanism and experiment. Different from metallic materials and brittle materials, rubber materials are cut by the force of shear and tensile under the impinging of ultra high pressure water jet and the erosion of high speed water flow with rubber powder. The overall structure of kerf is Y shape. The upper section of Y shape is caused by shear, the middle section is resulted from both shear and tensile, and the bottom section is a result of the erosion and the tensile. The results of experiment show: (1) a significant linear correlation between cutting depth and pump pressure;(2) 2.0 mm/s is the optimal transverse velocity under the current experiment condition;(3) the cutting depth has a decreasing tendency with the stand-off distance increased. It can be concluded from orthogonal analysis that pump pressure has a signification effect on cutting depth, nozzle transverse velocity is not remarkable, and the effect of stand-off distance is not obvious.

Hydrodynamics of fluid around a collapsing bubble in the spark bubble droplet generation process

Summary This article aims to study in detail the bubble oscillation near confined free surfaces and the ensuing droplet formation using a combined boundary element-finite difference method. Three configurations are considered: (i) the bubble oscillation near a circular aperture made in a flat plate, (ii) the bubble oscillation inside and near the top opening of a vertical cylinder and (iii) the bubble oscillation between a perforated flat plate and a horizontal solid boundary. The effects of standoff distance on the bubble dynamics and on the surrounding fluid dynamics are examined. Completely different bubble shapes, free surface motions, jetting patterns and pressure distributions under different standoff distances could be observed in the present work. In addition, it was found that for the configurations (i) and (iii), the bubble reentrant jet is always directed away from the free surface. For the cylinder case, however, a critical standoff distance was found for which the pressure distribution in the fluid above and below the bubble are the same and the bubble takes the shape of an hourglass at the time of jet impact. For subcritical standoff distances the bubble reentrant jet is always away from the free surface. However, for supercritical standoff distances the direction of the reentrant jet is interestingly directed towards the free surface. Finally, the effect of plate and cylinder configurations on the resulting droplet dynamics was investigated. It was found that the driving force for the droplet formation is the initial velocity induced by the bubble reentrant jet rather than the pressure difference inside the liquid. Besides, in the cylinder case the droplet size is smaller and its pinch-off happens earlier than the plate case.

Effects of Standoff Distance and Particle Size on Quality of NiCoCrAlY Coating by Cold Spraying

According to the gas dynamic property of cold spraying, the distance from the outside of nozzle to the substrate has great influence on the coating quality including the thickness of coating and the deposition effeciency. Meanwhile, the effects of particle size on coating quality are of the utmost importance. The influences of two parameters above on the quality of the NiCoCrAlY coating on the magnesium substrate by the experiments of the cold gas dynamic spraying were discussed in this study. The results of the experiments showed that, based on the fact that other parameters were not changed, when the standoff distance was more than 50mm, there were no complete coatings on the surface of the substrate, and its thickness was asymmetrical. When the standoff distance was 25mm, the thickness was homogeneous, and the oxygen content was only 1.3%. Also, when the particle size was 5~50μm, the coating quality was better.

Study on the Effect of Standoff Distance on Processing Performance of Alumina Ceramics in Two Modes of Abrasive Waterjet Turning Patterns

Abrasive waterjet (AWJ) turning is an emerging technology, which plays an important role in machining cylindrical parts with the distinct advantages of negligible thermal effects and extremely low cutting force. This paper presents an experimental study of abrasive waterjet turning (AWJT) of Al2O3ceramics. The machining process and performance in terms of the depth of penetration (DOP), surface roughness (Ra) and actual impact angle (β) are discussed to understand the effect of standoff distance (SOD) on the processing performance at two different turning modes. Based on the results of these investigations, there is a significant change ofDOPandRaat differentSODin radial mode turning and the optimalSODof gaining maximumDOPand the minimumRais about 5.5mm.However, theDOPis nearly independent on theSODin offset mode turning. SmallerRaandDOPcan be obtained in offset mode. Furthermore, the results indicate that the roundness error of cylinder parts is probably improved with the properSODinterval in radial mode turning and it is suitable for machining cylinder part with considerably different radial size. The offset mode turning as the next operation after radial mode turning is recommended to process workpiece with excellent roundness. In this way, by understanding the effect ofSODon processing alumina ceramics, the paper establishes a good basis for developing strategies for optimizing processing parameters in order to generate the desired part geometry and achieve better surface quality.

Effect of standoff distance on the reconstruction of in-duct velocity field and regeneration of pressure field

Identification of in-duct acoustic source characteristics is essential in the design of fluid machinery system for reducing and predicting the flow-generated noise. To this end, the inverse estimation method can be employed by using the measured sound field and matrix formulation for wave propagation within a duct. In this paper, the effect of the distance between source and measurement plane is investigated. At each standoff distance, pressures are measured at three planes with two different spacings to widen the estimation frequency range, and measurements are conducted with three different standoff distances. Modal decomposition is applied to estimate modal amplitudes, and the result is used to reconstruct the velocity field at the source plane and to obtain the regenerated pressure field at the measurement planes. It is shown that the modal amplitude identified by measured pressure field at the short standoff distance, i.e., at nearfield, can yield an accurate reconstructed velocity field of the source and regenerate the pressure field with smaller error, which is similar to the other inverse techniques such as equivalent source method and nearfield acoustical holography. A field reduction example by suppressing some parts of source velocity field is shown for demonstrating the effectiveness of the method.

Effects of standoff distance on porosity, phase distribution and mechanical properties of plasma sprayed Nd–Fe–B coatings

Fabrication of components that require magnetic parts such as in micro motors and micro generators demands an alternative to micro machining processes that are costly and time consuming. In this study, Nd–Fe–B coatings with an average thickness of 200μm were deposited onto stainless steel substrates by an atmospheric plasma spray technique using amorphous feedstock powder of spherical morphology. The microstructure of the coatings shifted from lamellar to spherical in nature as standoff distance (SOD) increased. The total porosity of the coatings exhibited a minima with respect to SOD and ranged from 1.8 to 8.2%. Two distinct phases; i.e., the Nd-rich and Fe-rich phases, were observed and imply phase separation during the plasma spray process. Occurrence of phase separation was argued to arise due to metastable phase formation and non-equilibrium solidification. The Fe-rich phase increased with increasing SOD due to longer in-flight time allowing non-equilibrium solidification to occur. The presence of two phases results in a bimodal Weibull distribution for Vickers hardness data. However, Weibull plots for Knoop hardness and elastic modulus show monomodal behaviour. The correlation between the degree of data scattering, as reflected by the Weibull modulus, with porosity and phase percentage was determined.

Effect of Stand-Off Distance on Impact Pressure of High-Speed Water Jet Injected in Water

This study is to measure the impact pressure of high-speed water jet injected in water at the stand-off distance from the nozzle exit. The high-speed water jets are generated by the impact of a projectile, which known as impact acceleration method, launched by Horizontal Single Stage Power Gun. The maximum averaged jet velocity of about 374.24 m/s in water was generated in this experiment. The impact pressure of high-speed water jet in water at the stand-off distance 15, 20, 30 and 40 mm from the nozzle exit was measured by the PVDF pressure sensor. Moreover, the impact phenomena of the jet were visualized by a high-speed video camera with shadowgraph optical arrangement. From the pressure sensor, two peak over-pressures are always observed in this experiment. From visualization, it was found that the two peak over-pressures of 24 GPa and 35 GPa at x = 15 mm were generated by the jet and the bubble impact, respectively. The peak over-pressure decreases exponentially as the stand-off distance between the PVDF pressure sensor to the nozzle exit increases. Moreover, the jet and the bubble impact on the PVDF pressure sensor, shock waves, and bubble deformation were obviously observed in this study.

Removal of Hydrogen Sulfide from Gas Stream Using a Novel Metal Membrane Prepared by Wire Arc Spraying

In this research, we have demonstrated the feasibility of fabrication of a novel metal membrane by wire arc spraying. The feedstock wires were made of carbon steel (1.1% C, 1.9% Mn, and 1.8% Cr). The effects of stand-off distance between the gun and the substrate and the pressure of atomizing gas on the oxides, the porosity and mean pore size of the prepared membranes were studied. The SEM micrograph showed that the prepared membranes are asymmetrically porous. They were not uniform. The performance of prepared membranes was elucidated using gas stream containing hydrogen sulfide. The membranes with higher porosity exhibited gas permeability. Hydrogen sulfide reacts with the available iron in the membrane and produces iron sulfide and hydrogen. Hydrogen sulfide was considerably removed from the gas stream. The EDX test on the reacted membrane indicated that FeS covered the active surface of the metal membrane.

喷嘴工件距对激光切缝中气体流场的影响

喷嘴工件距对激光切缝中气体流场的影响