Jet Impingement Angle Research Articles

A Study on Erosion of Alumina Wafer in Abrasive Water Jet Machining

Abrasive water jet machining is considered as a promising technique in hard and brittle material processing. This paper studies the erosion performance of the alumina ceramics in the different process parameters. In the erosion experiments, alumina ceramics wafers were eroded by the abrasive waterjet machining. The single factor experiments were carried out to understand the effect of different process parameters (jet impact angle, standoff distance, water pressure, abrasive particle diameter) on the material removal rate (MRR), the removal depth and surface roughness (Ra). The experimental results can provide guidance for alumina ceramics abrasive water jet cutting and polishing.

Toward the design of low flow-rate multijet impingement spray atomizers

When setting the baseline for discussing options toward a more efficient use of water resources, one of the drivers for decoupling economic growth and environmental impact is the development of resource-efficient innovations and instruments. One of such fields of interest is the design of water efficient showerheads, which provide a good shower experience, while consuming low flow rates (<3l/min), and potentiating energy savings for heating water. As a step forward in this challenge, the approach followed in this work is motivated by the need to develop tools for designing tailored sprays toward a high degree of efficiency in water usage. However, in order to design tailored sprays, it is important to establish a proper relation between the atomizer’s geometric configuration, operating conditions and the desired characteristics for the spray droplets (size and velocity). Therefore, this work focus on this tailoring through a multijet impingement atomization strategy using 2 and 3 impinging jets. An investigation is reported on the parametric effects on the dynamic characteristics of droplets of jet-impingement angle (40–90°) and pre-impingement distances (2.5–7.5mm), for a range of jet Weber numbers (20<Wej<500). The size of droplets is measured by image analysis, and their velocity by a Particle Tracking Velocimetry algorithm. The results evidence the similarities between droplet characteristics of sprays produced by 2- and 3-impinging jets, although the geometric effects induced by the jets’ impingement angle are more relevant for the 3-impinging jets spray, while negligible for the 2-impinging jets spray. Moreover, empirical correlations for the arithmetic (d10) and Sauter (d32) mean diameters, normalized by the jet diameter (dj), as well as drop velocity normalized by the jet velocity (ud/uj) are devised as tools for designing tailored multijet impingement sprays for low-flow rate water applications.

Cavity filling water control below aerator devices

With the rapid development of high dam projects within China, the dragon-drop-tail spillway tunnel is introduced and widely used. In view of the high water head and the large flow velocity on the dragon-drop-tail section, aerator devices are usually placed for the cavitation damage control. For the device placed in its initial position, it is a serious concern to design a suitable flow regime of the cavity and to control the cavity filling water due to the large flow depth and the low Froude number through this aerator. In this study, the relationships between the geometries of the aerator device and the jet impact angle of the lower trajectory of the flow are theoretically analyzed with/without a local slope. Nine test cases with different geometries are designed, the effectiveness of the filling water control is experimentally investigated under different operation conditions, and two criteria of the local slope design are proposed. It is concluded that the cavity flow regime and the filling water can be improved if a small impact angle and some suitable geometries of the local slope are designed.

A study of the micro-machining process on quartz crystals using an abrasive slurry jet

An investigation of the micro-channelling process on a quartz crystal using an abrasive slurry jet is presented. An experimental study is conducted first to understand the material removal process, surface quality as well as the effect of process parameters on the channelling performance, namely the material removal rate, channel depth, top channel width and channel wall inclination angle. It is found that a good micro-channel top edge appearance and bottom surface finish can be produced on quartz crystal by employing smaller particles with a relatively small jet impact angle, but at the sacrifice of material removal rate. Predictive models for material removal rate and micro-channel depth are then developed using a combination of the dimensional analysis method and the particle impact erosion theories, where the squeeze film effect on the impact erosion is considered. The models are verified experimentally and it is found that the model predictions are in good agreement with the corresponding experimental data.

Prediction of Flow and Oxygen Transfer by a Plunging Water Jets with Genetic Expression Programming (GEP) Models

A plunging water jet passing through the surrounding air entrains a large amount of air bubbles into a pool and forms a large submerged two-phase (gas–liquid) contacting area. This process is called air entrainment or aeration by a plunging water jets. In this study, the flow characteristics such as volumetric air entrainment rate, bubble penetration depth and oxygen transfer efficiency are evaluated based on five major parameters which describe air entrainment at the plunge point: the nozzle diameter, jet length, jet velocity, nozzle length-to-diameter ratio and jet impact angle. This paper presents gene expression programming (GEP) model, which is an extension to genetic programming, as an alternative approach to modeling of the flow characteristics such as the bubble penetration depth, air entrainment rate and oxygen transfer efficiency by plunging water jets. New formulations for prediction of the flow characteristics in the plunging water jet system are developed using GEP and regression models.

Experimental Analysis of Flow Characteristics from Different Circular Nozzles at Plunging Water Jets

A plunging water jet passing through the surrounding air entrains a large amount of air bubbles into a pool and forms a large submerged two-phase (gas–liquid) contacting area. This process is called air-entrainment or aeration by plunging water jets. Numerous studies were conducted with circular nozzles. This paper presents experimental investigation of flow characteristics of truncated and non-truncated circular nozzles. The flow characteristics such as volumetric air entrainment rate, bubble penetration depth and oxygen transfer efficiency are evaluated based on four major parameters which describe air entrainment at the plunge point: the nozzle diameter, jet length, jet velocity, and jet impact angle. In addition, new predictive equations are developed for the flow characteristics of truncated and non-truncated circular nozzles. Experimental results showed that truncated and non-truncated circular nozzles have very different flow characteristics. The truncated circular nozzles indicated a rather high quality with respect to bubble penetration depth, volumetric air entrainment and oxygen transfer. In aeration application, the truncated circular nozzles can be preferred due to different flow characteristics.

Multi-Linear Regression Based Prediction of Mass Transfer by Multiple Plunging Jets

The paper aims to compare the performance of vertical and inclined multiple plunging jets and to model and predict their mass transfer capacity by multi-linear regression based approach. The multiple vertical plunging jets have jet impact angle of θ = 90; whereas, multiple inclined plunging jets have jet impact angle of θ = 60. The results of the study suggests that mass transfer is higher for multiple jets, and inclined multiple plunging jets have up to 1.6 times higher mass transfer than vertical multiple plunging jets under similar conditions. The derived relationship, based on multilinear regression approach, has successfully predicted the volumetric mass transfer coefficient (KLa) from operational parameters of multiple plunging jets with a correlation coefficient of 0.973, root mean square error of 0.002 and coefficient of determination of 0.946. The results suggests that predicted overall mass transfer coefficient is in good agreement with actual experimental values; thereby, suggesting the utility of derived relationship based on multi-linear regression based approach and can be successfully employed in modeling mass transfer by multiple plunging jets. Keywords—Mass transfer, multiple plunging jets, multi-linear regression.

A predictive model on air entrainment by plunging water jets using GEP and ANN

Plunging water jet flow situations are frequently encountered in nature and environmental engineering. A plunging liquid jet has the ability to provide vigorous gas-liquid mixing and dispersion of small bubbles in the liquid, and enhances mass transfer rate by producing larger gas-liquid interfacial area. This process is called air-entrainment or aeration by a plunging water jet. Advances in field of Artificial Intelligence (AI) offer opportunities of utilizing new algorithms and models. This study presents Artificial Neural Network (ANN) and Gene-Expression Programming (GEP) model, which is an extension to genetic programming, as an alternative approach to modeling of volumetric air entrainment rate by plunging water jets. A new formulation for prediction of volumetric air entrainment rate by plunging water jets using GEP is developed. The GEP-based formulation and ANN approach are compared with experimental results, Multiple Linear/Nonlinear Regressions (MLR/NMLR) and other equations. The results have shown that the both ANN and GEP are found to be able to learn the relation between volumetric air entrainment rate and basic water jet properties. Additionally, sensitivity analysis is performed and it is found that nozzle diameter is the most effective parameter on the volumetric air entrainment rate among water jet velocity, jet length and jet impact angle.

A Study on Erosion Performance of Monocrystalline Silicon in Ultrasonic Vibration-Assisted Abrasive Water Jet Machining

Ultrasonic vibration-assisted machining (UVAM) is an effective and promising technology for processing hard and brittle materials, it has been explored in many experimental and theoretical investigations. In this paper, a study on the erosion performance of monocrystalline silicon with UVAM is presented and discussed. In the erosion experiments, monocrystalline silicon wafers were eroded by the abrasive water jet machine assisted with an ultrasonic vibration system. A contrast experiment was carried out firstly to study the influence of the ultrasonic vibration, and then an orthogonal experiment investigation was carried out to understand the effect of process variables (the abrasive particle diameter, jet impact angle, standoff distance, abrasive mass flow rate and ultrasonic vibration power) on the depth of erosion and material removal rate (MRR). The experimental results revealed that ultrasonic vibration-assisted abrasive water jet erosion (UVA-AWJE) can obviously improve the depth of the erosion and MRR compared with those in traditional AWJE and the variation trends of the effect of the abrasive particle diameter, jet impact angle, standoff distance and abrasive mass flow rate on the erosion performance in UVA-AWJE are very similar to those effect in the traditional AWJ machining.

A Visualization Study of the Radial-Mode Abrasive Waterjet Turning Process for Alumina Ceramics

A visualization study of the radial-mode abrasive waterjet (AWJ) turning process on an alumina ceramic is presented to gain an understanding of cutting front development process and hence the material removal mechanisms. A statistically designed experiment is conducted to study the effects of process parameters on the development of the cutting front, considering the change of water pressure, nozzle feed speed and nozzle tilt angle. It is found that the most significant parameters affecting the cutting front development are feed speed and water pressure. Further, the actual jet impact angle is dependent on both the water pressure and feed speed, but at higher water pressures the actual impact angle tends to become independent of feed speed, while water pressure becomes the dominating factor.

An investigation into the radial-mode abrasive waterjet turning process on high tensile steels

Abstract A study of the radial-mode abrasive waterjet (AWJ) turning process is presented and discussed. An experimental investigation is carried out first to understand the material removal process and mechanisms as well as the effect of process variables (feed speed, water pressure, abrasive mass flow rate, nozzle tilt angle, and rotational surface speed) on the depth of cut, material removal rate (MRR) and surface roughness when turning an AISI4340 high tensile steel. It is found that this cutting mode is advantageous for high MRR, as compared to the traditional offset-mode turning, through the maximum use of jet energy for material removal as well as employing the optimum jet impact angle and high workpiece surface speed. The most efficient conditions to maximize depth of cut are found to be at the normal jet angle, higher water pressure, higher surface speed and lower feed speed. Yet, lower surface speed is not good for either MRR or surface quality. At high surface speeds, increasing the depth of cut always comes at the expense of poorer surface quality. In order to estimate the depth of cut on a mathematical basis, a dimensional analysis has then been conducted and a model for the depth of cut has been developed and verified. The model predictions are found to be in good agreement with the experimental results with an average error of 0.2%.

Characteristics of abrasive slurry jet micro-machining: A comparison with abrasive air jet micro-machining

Abrasive slurry jet micro-machining (ASJM) uses a well-defined jet of abrasive slurry to erode features in a solid target. Compared with abrasive water jet machining (AWJM), the present ASJM system operates at pressures that are roughly two orders of magnitude lower and uses a premixed slurry of relatively low concentration. The objective of the present study was to gain a better understanding of the mechanics of erosion in ASJM by comparing its performance in the micro-machining of holes and channels in borosilicate glass with that of abrasive air jet micro-machining (AJM), a process that is simpler and relatively well understood. A new ASJM system was developed and used to machine blind holes and smooth channels of relatively uniform depth that did not suffer from the significant waviness previously reported in the literature. The effect of particle velocity, particle concentration, jet traverse speed and jet impact angle were examined. A direct comparison of ASJM and AJM results was possible since novel measurements of the crushing strength of the aluminum oxide abrasive particles used in both experiments proved to be unaffected by water. Brittle erosion was shown to be the dominant material removal mechanism in both ASJM and AJM in spite of the significant flow-induced decrease in the local impact angles of many of the particles in ASJM. A new model of the rapid particle deceleration near the target surface helped explain the much smaller erosion rates of ASJM compared with those in AJM. The modeling of the erosion process during the micro-machining of channels showed that the effect of the local impact angle at the leading edge of the advancing jet was much more significant in ASJM than in AJM, primarily due to the narrower focus of the jet impact zone in ASJM. The differences in the water and air flow fields and associated particle trajectories were used to explain the steeper side walls and flatter bottoms of the holes and channels machined with unmasked ASJM compared to those with masked AJM. The respective structures of the water and air jets also explained the much sharper definition of the edges of these features using ASJM compared with maskless AJM. The results of the study show that ASJM can be used to accurately micro-machine channels and holes with a width of 350–500μm and an aspect ratio of 0.5–1.3 without the use of masks.

Finite element modelling of overlapping abrasive waterjet milled footprints

Successful automatic simulation of the resulting surface obtained by abrasive waterjet (AWJ) milling is dependent on the ability to model the overlapped jet footprints. In this article an attempt has been made to develop a finite element (FE) model to simulate the overlapping AWJ milled footprints over a range of step-over distances, water pressures and traverse speeds at 90° jet impingement angle. A methodology has been proposed by which multiple overlapped AWJ milling passes can be simulated without being computationally extremely expensive. The FE results are validated by comparing the simulated footprints and erosion rates with the corresponding experimental data. The workpiece material is modeled as Ti6Al4V, an extensively used material in the aerospace industry, and the abrasive particles are modeled as garnet which is a commonly used abrasive during AWJ machining. The model provides the opportunity to study and improve the mass distribution of the abrasive particles around the jet central axis. The simulated footprints and erosion rates obtained when overlapping the jet footprints are shown to be in good agreement (with maximum errors under 15%) with the experimental data. The results of this research are quite encouraging while taking into account the possible sources of errors within the experimental data (e.g. non-constant pressure, particles sizes and fragmentation).

NUMERICAL STUDY OF A HOT-AIR-BASED AIRCRAFT WING ANTI-ICING SYSTEM USING THE BOX-BEHNKEN DoE APPROACH

This article proposes the use of the Box-Behnken design of experiment (DoE) methodology to study an aircraft anti-icing system. The anti-icing system consisted of a piccolo tube with round apertures for producing air jets inside a wing. Mass flow, jet to wall distance, and jet impact angle were varied, starting from an initial design, in order to maximize heat transfer effectiveness. A conjugate heat transfer procedure from commercial CFD software was used to solve for cold air external flow, compressible internal flow, and thermal conduction in the airfoil skin. The DoE methodology was validated using a single impinging jet. A quadratic model of the heat transfer effectiveness of the anti-icing system was then built using the methodology and the maximal value was sought.

Mathematical modelling of abrasive waterjet footprints for arbitrarily moving jets: Part II—Overlapped single and multiple straight paths

Controlled-depth abrasive waterjet machining (milling) is considered as a niche technology, capable of generating complex geometries in any material regardless of its properties. The key enabler of waterjet milling is the development of a model for predicting the jet footprint. The authors' previous work reported on a geometrical model for a single footprint of a free-moving jet for various impingement angles upon the target surface. Firstly, the present work identifies ways to make the single jet footprint models accurate for low jet impingement angles that are likely to occur when footprints are overlapped. Then, the paper presents for the first time a validated model that predicts the surface micro-geometry for overlapped footprints (jet with step-over movement), and an analysis of error propagation for predicting the material removed in successive layers. The modelling approach has proved its validity by being able to predict the surfaces obtained from single and multiple (i.e. layered) overlapped footprints with low errors, i.e. <6% and <9% respectively. The importance of the development of the model (dependent on feed velocity, tilt angle and stepover of the jet) for surface micro-geometry resulting from overlapped jet footprints research resides in (i) ability to simulate real controlled-depth waterjet machining when jet kinematics follows a raster path; (ii) it opens up the possibility of generating complex part geometries by adjusting the trajectory and velocity of the jet and thus the development of accurate and flexible CAM software for waterjet milling to support this technology.

1204 気中ウォータジェットを用いたフォトレジスト除去に関する実験的検討 (噴流衝突角度と試料水の効果について)(GS01-1 流体工学,オーガナイズドセッション 7:「最新工作機械」)

1204 気中ウォータジェットを用いたフォトレジスト除去に関する実験的検討 (噴流衝突角度と試料水の効果について)(GS01-1 流体工学,オーガナイズドセッション 7:「最新工作機械」)

An Experimental Study of the Abrasive Water Jet Micro-Machining Process for Quartz Crystals

An experimental study of the machining process for micro-channels on a brittle quartz crystal material by an abrasive slurry jet (ASJ) is presented. A statistical experiment design considering the major process variables is conducted, and the machined surface morphology and channelling performance are analysed to understand the micro-machining process. It is found that a good channel top edge appearance and bottom surface quality without wavy patterns can be achieved by employing relatively small particles at shallow jet impact angles. The major channel performance measures, i.e. material removal rate (MRR) and channel depth, are then discussed with respect to the process parameters. It shows that with a proper control of the process variables, the abrasive water jet (AWJ) technology can be used for the micro-machining of brittle materials with high quality and productivity.

Micro-grooving on quartz crystals by an abrasive air jet

An investigation of the micro-grooving performance of abrasive air jet (AAJ) on quartz crystals is presented and discussed. An experimental study was carried out first to understand the effect of process parameters on the major grooving performance measures such as groove depth, groove width, kerf taper, and surface roughness. Plausible trends for these grooving performance measures with respect to the various process variables, such as air pressure, nozzle traverse speed, jet impact angle, and abrasive mass flowrate, are discussed. It is found that AAJ is an effective technology for micromachining of quartz crystals and the grooving performance can be improved or optimized by selecting the process parameters properly. Predictive models are then developed for quantitatively estimating the micro-grooving performance. The models are finally verified by an experiment. It shows that the model predictions are in good agreement with the experimental results under the corresponding conditions.

An analytical model for top width of jet footprint in abrasive waterjet milling: a case study on SiC ceramics

In two-axis/five-axis macro/micro milling with abrasive waterjets (AWJs), the ‘top width of the jet footprint' is one of the critical measures that determine the dimensional accuracy of the part to be manufactured. In two-axis milling, the top width of the jet footprint is influenced by operating parameters such as the diameter of the focusing nozzle, the jet plume divergence in air, the standoff distance, and the jet feed rate, and in complex shape machining using five-axis milling, it is also influenced by the jet impingement angle, i.e. the angle between the jet axis and the horizontal workpiece plane. Hence, in this work, an analytical (i.e. geometrical) model for the top width of the jet footprint was proposed and tested on silicon carbide (SiC) workpeices by considering the diameter of the focusing nozzle, the jet plume divergence in air, the standoff distance, and jet impingement angle. The influence of jet feed rate was included in the model by the use of a parameter defined as the ‘effective jet plume divergence'. SiC workpieces were considered in this study, since they offer a reduction in the ‘noise' created by plastic deformations thus creating an appropriate environment for the calibration of the proposed geometrical model. Moreover, with its low machinability and chipping/fracture tendency, a SiC workpiece represents a good case study on niche applications of AWJs for manufacturing high-value-added products made of advanced materials. Assessment of the proposed model was carried out by comparing the top width of the jet footprint predicted by the proposed model with the experimental values obtained at various jet impingement angles in the range 40—90° at both high and low jet feed rates. From the results, it was observed that the top width of the jet footprint decreases gradually with an increase in jet impingement angle. Although the actual jet plume divergence does not change with the jet feed rate, the effective jet plume divergence, i.e. the divergence that can initiate erosion, decreases at higher jet feed rates. Furthermore, it was found that the prediction error slightly increases at shallower jet impingement angles owing to the instability in the leading portion of the jet structure and this is significant at higher jet feed rates.

3D plunge pool scour with protection measures

Plunge pool scour phenomena are well-known for destructive action at the base of hydraulic structures. An experimental study was conducted at the Hydraulic Laboratory of the University of Pisa, Italy, to investigate the hydraulics of 3D plunge pool scour in presence of simple protection measures. The main geometrical scour hole parameters were investigated and various relationships are proposed for different flow conditions. These parameters include the maximum dynamic scour hole depth, the maximum scour hole width and the location of the scour hole initiation point. Equations for all these parameters are presented in terms of the basic scour variables including the jet densimetric Froude number, jet impact angle, tailwater elevation above the originally horizontal sediment bed level and the protection permeability and longitudinal positions of the protection. Moreover, a scour hole typology and relationships for the non-dimensional longitudinal scour hole profile in presence of the protection are also given.