Cold Spray Nozzle Research Articles

Optimization of particle acceleration parameters of special cold spray nozzles via neural network and genetic algorithm

Optimization of particle acceleration parameters of special cold spray nozzles via neural network and genetic algorithm

Nozzle fouling in cold spray: Material transfer between Ni particles and WC-Co substrates at shallow impact angles and elevated surface temperatures

Experimental and theoretical investigations of nozzle clogging in WC-Co cold spray nozzles using nickel powder were conducted. Computational fluid dynamics (CFD) was used to show that the highest particle impact kinetic energy density occurs just downstream of the nozzle throat, where clogging is common. CFD also showed particles impact the nozzle wall at angles between 0.3°–5°, with smaller particles having higher velocities and temperatures. An experimental setup was used to investigate the effects of substrate temperature, surface roughness, and incidence angles on material deposition. Scanning electron microscopy revealed nickel particles smeared on the substrate surface, with more deposition on smoother surfaces. Energy dispersive X-ray spectroscopy (EDS) showed more nickel deposited at higher substrate temperatures and lower impact angles. Finite element simulations indicated nickel powder reaches temperatures above its melting point while sliding along the WC-Co substrate and predicted localized melting. Particle smearing is identified as the cause of nozzle clogging based on experimental and simulation results.

Optimal Design of a Cold Spray Nozzle for Inner Wall Coating Fabrication by Combining CFD Simulation and Neural Networks

AbstractRecently, the low-pressure cold spray (LPCS) technique has been used to fabricate superhydrophobic polymer coatings on metallic substrates, suggesting a significant potential in engineering applications. This study aims to design a spiral LPCS nozzle to coat the pipe’s inner wall with superhydrophobic polymer. The design goal is to achieve the maximum particle velocity in a confined (limited) space, assuming that the powder can enter the feeding tube through the Venturi effect. Achieving these two goals simultaneously using only computational fluid dynamics (CFD) simulation is challenging. Therefore, the CFD simulation was combined with the neural network (NN) method to design the new spiral nozzle. During training, the effects of the NN models and algorithms were investigated. The results showed that the feedforwardnet model combined with the trainbr or trainlm algorithm (from MATLAB 2016b software), presented a minimal error for particle velocity or gas flux prediction, respectively. The trained NN correlates the nozzle parameters (i.e., mean coil diameter, spring lift angle, and expansion ratio) and its performances (i.e., particle velocity and gas flux in the powder feeding tube). As a result, the optimal spiral nozzle was determined based on the design goal of maximum particle velocity and suitable gas flux in the powder feeding tube. Furthermore, the effect of each nozzle parameter on the particle velocity and gas flux in the powder feeding tube was analyzed. The cold spray experiment confirmed that the designed spiral nozzle could fabricate Perfluoroalkoxy alkane (PFA) coatings.

Optimization of Cold Spray Nozzles Based on the Response Surface Methodology

Spraying technical parameters are important factors that affect spraying efficiency. Most studies on spraying technical parameters use single-factor methods to study the speed of spray particles, and few scholars have studied the joint influence of multiple factors. This article uses gas temperature, particle size, and gas pressure as independent variables, and the independent variables interact. The design-expert method was used to establish a linear regression equation model of the velocity of sprayed Al and Cu particles at the Laval exit and the velocity before deposition with the substrate, and the response surface analysis method was used to predict the optimal spraying parameters of Al and Cu particles. The study found the contribution rate of three factors to particle velocity: the prediction of particle velocity at the exit of the Laval nozzle and before deposition with the substrate was realized; the error between the predicted value of particle velocity and the actual value obtained by simulation is less than 1.6 %, indicating that the speed linear regression equation established is effective and reliable in predicting the simulation results; the optimal spraying parameters and particle speeds of Al and Cu particles were obtained through response surface analysis.

Analysis of spray particles entrance of Right-angle cold spray nozzle based on CFD

Cold spray technology is a solid-state deposition technology, and the nozzle is an important part of the cold spray system. This article proposes a right-angle nozzle. The characteristic of this nozzle is that it can change the flow direction of the gas flow inside the nozzle to realize spraying on the surface of special parts; the acceleration of particles by the right-angle nozzle with different particle entrances is studied. The results show that the outlet center velocity of the right-angle nozzle with a circular throat section is greater, the viscous boundary layer effect is better, and the effective circulation area is larger; the maximum airflow velocity near the outlet of the right-angle nozzle at the particle entrance A is 663.4m/s; it can also effectively avoid the deposition of particles inside the right-angle nozzle, thereby reducing the loss of kinetic energy during the acceleration of particles in the right-angle nozzle; the research on the structure of the new right-angle cold spray nozzle can provide reference for the nozzle of cold spray technology Opinion.

A contoured nozzle design method for effective cold spray metal coating

In cold spraying, a uniform particle distribution of uniform velocity is desirable to achieve a good quality deposition pattern. Whereas many cold spray facilities use conical convergent-divergent nozzles for accelerating the particles, this paper evaluates a contoured axisymmetric nozzle design to enhance the process efficiency. The performance of a conventional conical cold spray nozzle is compared with that of a new axisymmetric nozzle designed with a smooth throat and contoured for a parallel outflow. The new nozzle profile is obtained by the application of two aerospace design codes based on the Method of Characteristics. A two-way coupled Eulerian-Lagrangian Computational Fluid Dynamics formulation is used, where the continuous phase steady motion is predicted by solving the Reynolds-Averaged Navier-Stokes equations with the Shear Stress Transport k-ω model. A Discrete Phase Model computes the motion of the particles carried by the jet. The numerical predictions show that the new nozzle shape delivers a more radially uniform deposition. A higher particle velocity is also obtained at the same operating conditions used by the industry standard nozzle, which is desirable for good particle bonding to the substrate.

Study of a Cold Spray Nozzle Throat on Acceleration Characteristics via CFD

Cold spray technology can obtain coatings in a solid state, suitable for deposition protection, repair, and additive manufacturing. In order to further expand the application areas of cold spraying nozzles, especially the inner surface of the components or areas where a Straight-line conical nozzle cannot be applied, because the study of the throat of the nozzle with the angle will directly reduce the total length of the nozzle (the horizontal direction), hence, the spray with the angle will show its advantage. This study discusses the influence of the throat structure of the conical cold spray nozzle on the acceleration characteristics, including the throat’s size, length, and angle. The results show the following. Firstly, under the premise of keeping the shrinkage ratio and divergence ratio unchanged at normal temperature, the throat diameter is between 2–6 mm in size, and the maximum growth rate exceeds 20 m/s. When the throat exceeds 6mm, the growth rate of the outlet slows down, and the growth rate is only 8 m/s. Secondly, the length of the throat has little effect on the acceleration characteristics, the total range fluctuated from 533 to 550 m/s, and 11 mm length of the throat is the closest to 0mm. Additionally, the 90° throat angle has the least effect on the acceleration characteristics. Finally, the particle trajectory is affected by inlet pressure, injection pressure, particle size, and other factors.

Particle–Substrate Transient Thermal Evolution During Cold Spray Deposition Process: A Hybrid Heat Conduction Analysis

A hybrid analytical heat conduction model was developed to predict the transient thermal evolution at the particle–substrate interface during the deposition of cold spray process. First, three-dimensional heat conduction model based on classical diffusion approach was developed to predict the transient surface temperature of the substrate. To that end, the traveling wave solution technique was utilized in order to take into account the effect of the movement of the cold spray nozzle. The results of the analytical model were validated with the experimentally measured surface temperature which was obtained by employing a low-pressure cold spray unit to generate the impingement of a compressed air jet on a flat substrate. The analytical model was further utilized to investigate the effect of the non-dimensional characteristic velocity of the traveling heat source on the surface temperature profile of the substrate. It was found that both the maximum surface temperature and the spatial variation of surface temperature profile of the substrate decreased as the non-dimensional characteristic velocity increased. The mathematical model was further extended by developing a one-dimensional hyperbolic (non-Fourier) heat conduction model to predict the temperature rise at the particle–substrate interface during the cold spray deposition process. In order to validate the results of the hybrid model, a three-dimensional finite element model was developed in ABAQUS to simulate the thermal and dynamic behavior of a single particle upon impact. The results of the hybrid analytical model for the temperature at the particle–substrate interface were compared to the results of the numerical model, and good agreement was found. It was concluded that by coupling the classical diffusion theory and hyperbolic heat conduction approach, the proposed hybrid analytical model can be utilized to predict the transient temperature of the particle–substrate interface during the cold spray deposition process a priori before experimentation.

The associated effect of powder carrier gas and powder characteristics on the optimal design of the cold spray nozzle

ABSTRACT During cold spray, the temperature of the particle carrier gas is at room temperature, which is lower than the preheated propulsive gas and affects the mixed gas temperature and particle acceleration. This study is investigating the associated effect of the powder carrier gas and powder characteristics on the optimal design of the nozzle using numerical simulations. The results show that the heat exchange of mixed gas stabilizes, and temperatures of mixed gas and particles are higher in the nozzle when a larger inlet diameter and a longer convergent section are used. In addition, particle impact velocity is inversely related to its size and density. Therefore, heavier particles require longer divergent lengths and larger expansion ratios for a longer acceleration distance and increased kinetic energy. The nozzle geometry can be designed depending on the selected particles and the chosen propulsive gas, for a maximum particle impact velocity.

CFD Simulations of Feeder Tube Pressure Oscillations and Prediction of Clogging in Cold Spray Nozzles

Cold spray is an additive manufacturing method in which powder particles are accelerated through a supersonic nozzle and impinged into a nearby substrate. This method produces deposits with advantageous attributes, namely with low porosity and low residual stresses, which nearly match those of the bulk material. One challenge with cold spray is nozzle clogging, which occurs when particles bond to the inside of the nozzle, altering the cross-sectional area, increasing roughness on the nozzle inner surface, and causing a drop in the gas velocity, ultimately resulting in a lower quality deposit. Clogging puts certain combinations of materials and operational parameters out of practical reach. A CFD model of the cold spray nozzle is developed to study the flow of metal particles in the cold spray process, and we determine that the two-phase particle-laden flow from the feeder tube is inherently transient. CFD simulations demonstrate that pressure fluctuations in the particle feed system can cause the particles to disperse in the nozzle and ultimately lead to some particles bonding with the nozzle wall. The degree of clogging is found to be strongly dependent on the amplitude of these upstream pressure fluctuations and seemingly independent of the pressure oscillation frequency.

One-Dimensional Analysis on the Gas/Particle Flows of Cold Spray Nozzle with Carrier Gas Injection in the Diverging Part

One-Dimensional Analysis on the Gas/Particle Flows of Cold Spray Nozzle with Carrier Gas Injection in the Diverging Part

The role of particles flow characteristics in the performance of cold spray nozzles

Cold Spray(CS) is an emerging process, attracting much interest both as a coating and additive technique due to its solid-state nature and high deposition rates. The key element of any CS apparatus is the supersonic nozzle. The work presented here, for the first time, will explore in detail the relationship between particle flow, and its acceleration in the nozzle using Computational Fluid Dynamics and experimental measurements obtained with a Particle Tracking Velocimetry apparatus. We have developed modelling parameters capable to accurately predict the particle flow exit speed and space distribution, leading to considerably improved nozzle performances.

Numerical assessment of miniaturized cold spray nozzle for additive manufacturing

Purpose Application of cold spray technology may exhibit significant benefits for the additive manufacturing process, particularly for producing intricate objects. To ascertain the feasibility of such an application, this paper aims to present a numerical investigation of the effect of scaling down a convergent-divergent (de Laval) nozzle, which is typically used in the cold spray industry, on the compressible flow parameters and thermal characteristics. Design/methodology/approach The Navier–Stokes equations and energy equation governing compressible flow are numerically solved using a finite volume method with a coupled solver. The conjugate heat transfer technique is used to couple fluid and solid heat transfer domains and predict the local heat transfer coefficient between the solid and fluid. The use of various RANS turbulence models has also been investigated to quantify the effect of the turbulence model on the simulation. Findings The numerical results reveal that the flow and thermal characteristics are altered as the convergent-divergent nozzle is scaled down. The static pressure and temperature profiles at any section in the nozzle are shifted toward higher values, while the Mach number profile at any section in the nozzle is shifted toward a lower Mach number. The turbulent kinetic energy at the nozzle exit increases with the scaling down of the nozzle geometry. This study also provides convincing evidence that the adiabatic approach is still suitable even though the temperature of the nozzle wall is extremely high, as required for industrial application. Results indicate that it is feasible to use the available capabilities of the cold spray technology for additive manufacturing after scaling down the nozzle. Originality/value The idea of adopting cold spray technology for additive manufacturing is new and innovative. To develop this idea into a viable commercial product, a thorough understanding of the flow physics within a cold spray nozzle is required. The simulation results discussed in this paper demonstrate the effect that scaling down of a convergent-divergent nozzle has on the flow characteristics in the nozzle.

Characterization of the interacting gas-particle dynamic system in cold spray nozzles in dimensional and non-dimensional form

In order to study fundamental particle and gas dynamic behavior in the cold spray process, a simplified model was created assuming all dependent process parameters to vary in the streamwise x-coordinate only. This model resulted in a coupled system of ordinary differential equations describing gas and particle interactions in terms of basic conservation principles for mass, momentum and energy within a converging-diverging nozzle. The system of ordinary differential equations along with a prescribed set of initial conditions for all dependent variables at x = 0, forms an initial value problem which was integrated in the x-direction using a 4th order Runge-Kutta method to determine the velocity and temperature of the gas and particle phases. The numerical solutions from the model were then validated by comparison with steady, axisymmetric, two-dimensional computational models incorporating the relevant PDE's using the CFD software. To obtain additional insight into the dynamic and thermal behavior of the coupled system, applicable scales were chosen to cast the simplified dimensional governing equations in non-dimensional form. One of the significant results of this simplified one-dimensional study is the parameterization that falls out naturally from the scaled equations, thus conferring a more general means to characterize (in non-dimensional terms) the relative gas-particle momentum and energy exchange in higher dimensional problems. From the scaled results it was also discovered that there is no advantage in using lighter, more expensive carrier gases such as helium to accelerate larger, heavier particles, and thus considerable cost savings can result through the use of compressed air.

Particle velocity and dispersion of high Stokes number particles by PTV measurements inside a transparent supersonic Cold Spray nozzle

The complexity of technical applications involving particle-laden gas flows often impedes a holistic understanding of the interplay of underlying physical aspects. The usual approach is to isolate phenomena and study them individually, forcing researchers to ignore realistic circumstances. An example is the coating formation process Cold Spray (CS), in which high Stokes number particles are accelerated in a supersonic nozzle and free jet. Along the flow, the particle laden gas undergoes extreme changes, e.g. in velocity, temperature and volume fraction, through a series of interconnected flow events for a poly-disperse distribution of particle sizes. A consequence of this complexity is an under-representation of research on the fluid-mechanics in this field. This manuscript aims to build a bridge between empirical testing in CS and more fundamental aspects of the relevant fluid mechanics: Parameters associated with the multi-phase character of the process are not yet well understood. In this sense, the particle mass loading is often ignored, so are particle-particle interactions and the strong variations of local conditions. Previous work has indicated that there is no conclusive understanding of the phase interaction mechanisms in CS beyond high-Mach number drag laws. In order to start filling this gap, the first experiment for the direct observation of the particle behaviour within a CS nozzle is designed. Rectangular de-Laval nozzles are manufactured from quartz glass and particle tracking velocimetry (PTV) is used to obtain particle velocities and positions at the injection zone, throughout the nozzle and in the supersonic jet under varying operating conditions. This study firstly reports the direct measurement of particle injection, acceleration, and dispersion in CS. It suggests physical explanations based on a statistical evaluation of the observed data and forms the basis for more fundamental understanding of CS fluid mechanics.

Analytical study of the heat transfer coefficient of the impinging air jet during cold spraying

A semi-empirical analytical model was developed to determine the convective heat transfer coefficient of an impinging air jet generated by a cold spraying nozzle. A low-pressure cold spraying unit was utilized to produce hot air jets that impinged upon a flat substrate surface. An infrared camera was used to measure the surface temperature of the substrate at different time intervals. A method involving Green's functions was employed to solve a transient two-dimensional heat conduction problem to obtain an expression for the temperature distribution within the substrate. By coupling the analytical results of temperature distribution and experimental surface temperature data, the radial variation of the non-dimensional heat transfer coefficient of the impinging air jets upon the substrate was estimated. The results showed that the maximum values of the heat transfer coefficient were present close to the stagnation point of the air jets. It was found that the heat transfer coefficient was independent of the time that the cold spray nozzle remained stationary over the substrate surface. It was found further that by increasing the stand-off distance of the nozzle, the radial variations of the heat transfer coefficient became negligible, compared to those for small stand-off distances. The close agreement between the experimental results and the predictions of the model suggested that the estimated heat transfer coefficient of the cold spray gas jet can be used to estimate the surface temperature of the substrate at any time.

CFDEM modelling of particle heating and acceleration in cold spraying

Cold spraying is a promising approach for the processing of refractory metals. A powder material is accelerated and heated in the gas flow of a supersonic nozzle to velocities that are sufficient to obtain cohesion of the particles to a substrate due to plastic deformation. The cohesion behavior of the particles is mainly determined by their velocity and temperature. These are controlled by the pressure and temperature of the gas at the nozzle entrance. A correlation of the process parameters gas pressure and temperature with the particle velocity and temperature is possible based upon numerical simulations. In this contribution a CFDEM simulation model for particle heating and acceleration based on OpenFOAM and LIGGGHTS is presented. CFDEMcoupling combines computational fluid dynamic (CFD) calculation of the gas flow based on the finite volume method with a description of the particles based on the discrete element method (DEM). The predictions of the simulation model are verified based on an analytical description of the cold spray nozzle and validated by experimentally measured particle velocities. Based on this experimental validation the drag model of Koch and Hill appears best suited for a CFDEM modelling of cold spraying.

Analysis of Jet Characteristics Among Various Cold Spray Nozzles

This research is conducted mainly to analyze the jet characteristics of various cold spray nozzles. This study presents the theoretical and practical aspects of Cold Spray process modeling, discusses multiple numerical analysis research areas, and determines the significant parameters to be considered while developing a custom cold spray setup and exhibits analysis-based correlations. The simulations were performed on some meshes of different density using the SST turbulent model in Star CCM+ solver. For the first time, in this work, the jet characteristics inside a step drilled nozzle was presented; Furthermore, shock diamond formation was found inside the divergent section of step drilled nozzle which strongly influence the flow regime with sharp fluctuations. The comprehensive comparison between step drilled nozzle, conical nozzle and curved nozzle indicates that curved nozzle results in slightly higher nozzle exit velocity. However, results have suggested that the curved nozzle can achieve much higher velocities by optimizing the nozzle length.

A Study on the Estimation of Mixed-Mean Gas Temperature using Gas Dynamic Method in Cold Spray Nozzle (In Case of Carrier-Gas Partly Mixed with Process Gas at Nozzle Throat)

A Study on the Estimation of Mixed-Mean Gas Temperature using Gas Dynamic Method in Cold Spray Nozzle (In Case of Carrier-Gas Partly Mixed with Process Gas at Nozzle Throat)

Deposition of aluminum powder by cold spray micronozzle

Spatial resolution of cold spray depends on the exit dimension of converging-diverging nozzle used for particle acceleration. Typical diameter of cold spray nozzle lies in the range between 4 and 10 mm. In this study, micronozzle with 0.5 mm throat diameter and 1 mm exit diameter is applied for cold spray deposition of aluminum powder. Numerical simulation and experimental velocity measurements demonstrate that aluminum particles could be accelerated to the velocity sufficient for coating deposition if room temperature helium is applied as working gas. The diameter of spraying spot in this case does not exceed 1.7–1.8 mm that is significantly lower than for standard cold spray nozzle. However, the density and the bond strength of obtained aluminum coating are significantly lower than those for standard cold spray aluminum deposits.