Effect of Nozzle Outlet Type On the Flow Field Velocity and Impact Pressure of High Pressure Water Jet Peening

Water jet peening can effectively improve the fatigue strength of metal materials, and the outlet shape of nozzle greatly affects the effect of water jet peening. In this paper, the effects of nozzle outlet shape on water jet velocity and impact pressure is studied by numerical simulation, and the jet velocity and dynamic pressure for different standoff distances are also discussed. The results show that the water jets of square, circular and triangular nozzles are highly concentrated, and the water jet of elliptical nozzles is the most divergent. The axial velocity attenuation of the square nozzle along the axis is slower than that of the other three nozzles. The water axial velocity of the elliptical nozzle attenuates fastest and the length of the core segment of the water jet is the smallest. Within a certain axial distance, the dynamic pressure area in the central area of the elliptical water jet is obviously larger than that of the other three nozzles, and the effective treatment range is large, which is more suitable for the welding surface strengthening operation.

A new calculation formula to describe the dynamic pressure of water jet peening with elliptical nozzle for high-efficiency treatment

Water jet peening is a good potential method to control welding residual stresses. The water jet with elliptical nozzle can improve the treatment efficiency due to its large treatment area. In this article, the water jet velocity and dynamic pressure for different elliptical nozzle dimensions and standoff distances are discussed by numerical simulation. The results show that when the axial distance is 10 mm, the effective impact diameter of the elliptical nozzle a/b=8–12 is about 2 times or more than that of the circular nozzle. The length of the jet core of the elliptical nozzle is only related to the outlet structure and is independent of the inlet pressure. The correlation between the dimensionless core length of the elliptical water jet and its long and short axes is derived. When the ratio of the major axis to the minor axis is between 7 and 13, the core length of the elliptical water jet is 7–7.5 times that of its minor axis. Combining the suitable treatment area and dynamic pressure, the elliptical nozzle with an axis ratio of 8 is recommended to control the welding residual stress. Finally, a new formula for calculating dynamic pressure distribution is proposed for the elliptical nozzle water jet at different stages.

КІНЕТОСТАТИЧНЕ ДОСЛІДЖЕННЯ ШАРНІРНИХ ПРОСТОРОВИХ МЕХАНІЗМІВ ГАЛТУВАЛЬНИХ МАШИН (ЧАСТИНА 2: ДОСЛІДЖЕННЯ МЕХАНІЗМУ МАШИНИ З ДВОМА РОБОЧИМИ ЄМКОСТЯМИ, ЩО З’ЄДНАНІ ПОСТУПАЛЬНОЮ КІНЕМАТИЧНОЮ ПАРОЮ)

Goal. Kinetostatic study of a statically defined hinged spatial mechanism without excessive (passive) connection of the shredding machine with two working tanks connected by a translational kinematic pair. Method. Radial and axial components of reactions in all rotating and translational kinematic pairs of the hinged statically defined spatial mechanism of the machine for processing of details with two working capacities connected among themselves by translational kinematic pair at its work at idling were determined on the basis of kinetostatic research. The study was performed using the computer-aided design system SolidWorks-2016 computer-aided design system, which performed a 3D model of a shredding machine with two working tanks connected by a translational kinematic pair. Results. 3D modeling of a shredding machine with two working tanks connected by translational kinematic pair in the computer-aided design system SolidWorks-2016 computer-aided design system is performed, maximum values of radial and axial components of reactions in all rotating and translational kinematic pairs of machine are determined, and the influence of total two working tanks for the increase of the maximum values of reactions in the kinematic pairs of the spatial mechanism of the machine. Scientific novelty. For the first time, the relationship between the total wheelbase of two working tanks and the change in the maximum values of reactions (axial and radial) in all rotating and translational kinematic pairs of the shredding machine was established. The allowable range of variation of the total wheelbase of two working tanks is determined, which creates conditions for long-term operation of the machine. Practical significance. It is established that the change of maximum values of radial and axial components of reactions in all rotating and translational kinematic pairs of the spatial mechanism of the galvanizing machine depends on the total axial distance of two working capacities of the machine. The obtained research results can be useful in the design of shredding equipment with complex spatial movement of working tanks.

Single-Walled Carbon Nanotube Synthesis Yield Variation in a Horizontal Chemical Vapor Deposition Reactor

The controlled synthesis of single-walled carbon nanotubes (SWNTs) is essential for their industrial application. This study investigates the synthesis yield of SWNTs, which depends on the positions of the samples on a horizontal chemical vapor deposition (CVD) system. Methane and Fe thin films were used as the feedstock and catalyst for SWNTs synthesis, respectively. A high-resolution scanning electron microscope was used to examine the synthesis yield variation of the SWNTs along the axial distance of the reactor. The morphology and crystallinity of the fabricated SWNTs were evaluated by atomic force microscopy and Raman spectroscopy, respectively. We observed that the highest synthesis yield of the SWNTs was obtained in the rear region of the horizontal reactor, and not the central region. These results can be applied to the synthesis of various low-dimensional nanomaterials, such as semiconducting nanowires and transition metal dichalcogenides, especially when a horizontal CVD chamber is used.

A hybrid computational framework for the simulation of atmospheric pressure plasma jets: The importance of the gas flow model

A hybrid computational framework, consisting of a detailed turbulence flow model, a global model, and a model for the calculation of the electron energy probability function, is developed to predict the density of plasma generated species along the axial distance of plasma jets. The framework is applied to an Ar/O2 plasma in a kINPen 09 device without a shielding gas. A reaction set of 764 reactions and 84 species is considered. The effect of different turbulence flow models, namely the detailed and high cost large eddy simulation (LES) model and the simple and low cost realizable k-ε model, on the densities of plasma generated species is investigated at different values of absorbed power. The effect is not severe on the density of the majority of the species, justified by the small differences in the inputs of the global model, i.e. the volume averaged axial velocity and density of air species (coming from the turbulence flow model). Nevertheless, the differences in the densities of O2(1Σg), O-, O2-, O(1D), O, H, H2(r), H-, N2O(v), H7O3+, H9O4+, H15O7+ and OH- are remarkably affected by the choice of the turbulence flow model and may reach an order of magnitude. The detailed LES model is a proper choice for Ar jets and this is reinforced by the comparison of the results of the framework with atomic oxygen experimental measurements along the axial distance of the jet: the use of the LES model leads to atomic oxygen density closer to the measured one compared to (the use of) the realizable k-ε model. Finally, an evaluation of the assumptions required for the use of global models in plasma jets is performed, demonstrating their validity for the case studied.

Three-Probe Error Separation with Chromatic Confocal Sensors for Roundness Measurement

In this study, three-probe error separation was developed with three chromatic confocal displacement sensors for roundness measurement. Here, the harmonic suppression is discussed first to set suitable orientation angles among three sensors. Monte Carlo simulation is utilized to test the error separation and optimize the orientation angles and off-axial distance. The experimental setup is established using chromatic confocal sensors with a precise rotary platform. The experimental results show that the measured roundness with an orientation-angle combination of (0°, 90.1°, and 178.6°) is much better than that of another nonoptimal selection (0°, 90.4°, and 177.4°). The roundness error is only 0.7% between the proposed measurement system and an expensive ultraprecision roundness meter. Furthermore, it is proven that the eccentricity distance should be decreased as small as possible to improve the measurement accuracy. In sum, this paper proposes a feasible method for roundness measurement with reliable simulations, easily integrated sensors, and an ordinary precision rotary platform.

CFD Simulation Study on the Performance of a Modified Ram Air Turbine (RAT) for Power Generation in Aircrafts

The present paper aims to study the possibility of dispensing an auxiliary power unit (APU) in an aircraft powered by fossil fuels to reduce air pollution. It particularly seeks to evaluate the amount of power generated by the ram air turbine (RAT) using the novel counter-rotating technique while characterizing its optimum axial distance. The ram air turbine (RAT), which is already equipped in aircrafts, was enhanced to generate the amount of energy produced by the APU. The approach was implemented by a CRRAT system. Six airfoil profiles were tested based on 2D models and the best airfoil was chosen for implantation on the RAT and CRRAT systems. The performance of the conventional single-rotor RAT and CRRAT were analyzed using FLUENT software based on 3D models. The adopted numerical scheme was the Navier–Stokes equation with k–ω SST turbulence modeling. The dynamic mesh and user-defined function (UDF) were used to revolve the rotor turbine via wind. The results indicated that the FX63-137 airfoil profile showed a higher performance in terms of the lift-to-drag ratio compared to the other airfoils. The optimum axial distance between the two rotors was 0.087 m of the rotor diameter and the efficiency of the new CRRAT increased to almost 45% compared to the single-rotor RAT.

Supercritical CO2-Assisted Atomization for Deposition of Cellulose Nanocrystals: An Experimental and Computational Study

Nanoparticle spray deposition finds numerous applications in pharmaceutical, electronics, manufacturing, and energy industries and has shown great promises in engineering the functional properties of the coated parts. However, current spray deposition systems either lack the required precision in controlling the morphology of the deposited nanostructures or do not have the capacity for large-scale deposition applications. In this study, we introduce a novel spray system that uses supercritical CO2 to assist the atomization process and create uniform micron-size water droplets that are used as cellulose nanocrystal (CNC) carriers. CNCs are selected in this study as they are abundant, possess superior mechanical properties, and contain hydroxyl groups that facilitate interaction with neighboring materials. We fundamentally investigate the effect of different process parameters, such as injection pressure, gas-to-liquid ratio, the axial distance between the nozzle and substrate, and CNC concentration on the final patterns left on the substrate upon evaporation of water droplets. To this end, we show how tuning process parameters control the size of carrier droplets, dynamics of evaporation, and self-assembly of CNCs, which in turn dictate the final architecture of the deposited nanostructures. We will particularly investigate the morphology of the nanostructures deposited after evaporation of micron-size droplets that has not been fully disclosed to date. Different characterization techniques such as laser diffraction, polarized microscopy, and high-resolution profilometry are employed to visualize and quantify the effect of each process parameter. Numerical simulations are employed to inform the design of experiments. Finally, it is shown that the fabricated nanostructures can be engineered based on the size of the carrier droplets controlled by adjusting spray parameters and the concentration of nanoparticles in the injected mixture. Process parameters can be selected such that nanoparticles form a ring, disk, or dome-shaped structure. Moderate operational conditions, simplicity and time efficiency of the process, and use of abundant and biodegradable materials, i.e., water, CNC, and CO2 promote the scalability and sustainability of this method.

Study on Deposition Motion of Naturally Circulating Particulate Matter in Supercritical Water Based on Factor and Correspondence Analysis

It is very important to study the deposition of particles in natural circulation of supercritical water to ensure the safe and stable operation of supercritical water reactor. The data of natural circulation loop calculated by ANSYS-CFX simulation software were analyzed by factorial analysis method, and the effects of axial distance, initial particle volume fraction, heating power and particle size on particle deposition were obtained. The results show that the contribution rate of particle size to the deposition rate is the largest, about 36.3%, and the contribution rate of initial particle concentration to the deposition rate is about 15.1%; the interaction between axial distance and heating power is the most obvious, and the interaction effect is the pipe temperature distribution. Through correspondence analysis, the main influencing factors of particle deposition rate at each level were analyzed. The results show that: when the deposition rate is small, the small change of axial distance will also have a greater impact on the deposition of particles; when the deposition rate is further increased, the change of initial particle volume fraction will significantly affect the deposition of particles; when the deposition rate is large, the particle size plays a leading role in the deposition of particles. Both of the two analysis methods show that: in the influence on the deposition of particles in supercritical water natural circulation, the influence degree is particle size > concentration > axial distance > heating power. Based on the two analysis methods, an analysis regression model is established and the volume proportion of particles in natural circulation is predicted.

Experimental Investigation of the Transient Pool Boiling Heat Transfer On the Quenching of Vertical Rodlet in Water

Quenching is an important phenomenon in the evaluation of an emergency core cooling system following a hypothetical loss of coolant accident (LOCA) in a nuclear reactor. In the present study, an experimental apparatus is designed and constructed with the purpose of conducting high-temperature transient pool boiling quenching experiments for zirconium (Zr-4) cylindrical test samples. Three thermocouples are inserted in the test sample to investigate the effect of axial distance on the minimum film boiling temperature. The Zr-4 rodlet is heated up to a temperature well above the minimum film boiling temperature (up to 600?), and then plunged vertically in a quiescent pool of subcooled water. A data acquisition system is used to record the temperature of the embedded thermocouples with time. Data reduction is performed by an inverse heat conduction code to calculate the surface temperature and corresponding surface heat flux. A visualization study with a high-speed camera is conducted to record the quenching behavior on the test sample. It is found that the minimum film boiling temperature decreases with the axial distance, while the CHF temperature is relatively insensitive to the axial distance. The film boiling heat transfer coefficient decreases with surface temperature, and seems to be independent of axial distance. The quench front is observed to originate from the bottom and move upwards. It is found that the quench front velocity remains nearly constant in the lower region of the test sample, and significantly increases in the upper region.