Liquid Metal Jet Research Articles

Jet on demand—A pneumatically driven molten metal jetting method for printing crack-free aluminum components

Additive manufacturing (AM) of many traditional aluminum alloys is difficult due to hot cracking during cooling, which motivates investigating alternative AM methods that can mitigate this challenge. Here we demonstrate a new pneumatically driven molten metal jetting (MMJ) AM technique which uses a longer pressure pulse width to produce a jet of liquid metal that reaches the heated build plate. The “jet on demand” technique is utilized to build Al-6061 parts on heated build plates. Due to the large thermal mass contained in each jet, excellent adhesion is observed between droplets and layers while still maintaining dimensional control to produce parts with high relative densities (>98%). While as-printed parts exhibit different microstructure and hardness than traditional Al-6061, both microstructure and hardness are restored to traditionally processed values through a traditional T6 heat treatment. Microhardness values of 104 HV were obtained for printed Al-6061, which compares well to wrought properties. We observe that high build plate temperatures allow for lower solidification rates and eliminate hot cracking. These results point to a method for additively manufacturing traditional aluminum or other alloys that cannot currently be additively manufactured due to hot cracking.

Exploring spatial beam shaping in laser powder bed fusion: High-fidelity simulation and in-situ monitoring

Laser beam shaping is a novel and relatively unexplored method for controlling the melt pool conditions during metal additive manufacturing (MAM) processes, but even so it still holds good promise for achieving site-specific tailored properties. In this work, a comprehensive numerical and experimental campaign is carried out to explore this subject within metal laser powder bed fusion (LPBF). More specifically, a multiphysics numerical model is implemented for simulating the heat and fluid flow conditions during LPBF of Ti6Al4V using arbitrary circular beam shapes with various power distributions spanning from a pure Gaussian beam to a pure ring beam profile. The model is subsequently coupled with cellular automata to describe the beam shape effects on the microstructure evolution. Model validation is carried out in a two-fold manner. First, we compare the predicted melt pool cross-section with the one from ex-situ single track experiments, and we find a deviation of less than 9 % in melt pool dimensions. Secondly, advanced in-situ X-ray monitoring is carried out to unravel the melt pool dynamics and we find that the predicted morphology closely matches the in-situ X-ray results. Moreover, it is shown that at lower laser power, a bulge of liquid metal forms at the center of the melt pool when employing ring profiles, and this is ascribed to the absence of recoil pressure at the center of the ring beam. Furthermore, increasing the laser power seems to destabilize the melt pool regime, as the central bulge transforms into a liquid metal jet that periodically collapses and breaks up into hot spatter. Based on the results, we believe that our multiphysics modelling methodology, opens up new pathways for predicting how laser beam shaping influences porosity, surface roughness as well as microstructure formation in LPBF processes.

Experimental study of liquid aluminum droplet breakup characteristics based on a Drop-on-demand (DOD) magnetohydrodynamic actuation

In magnetohydrodynamic (MHD) drop-on-demand (DOD) actuation, Lorentz force generated in different excitation stages are exerted on the liquid metal jet to form a "push-pull" mechanism, which is crucial for generating accurate and repeatable metal droplets. In this study, the important parameters of the excitation current waveform in the magnetohydrodynamic (MHD) process, including the influence of the excitation voltage pulse width ratio and current amplitude on the velocity, energy, volume, and breakup length of aluminum droplets are studied. The conversion process of surface energy and kinetic energy during the formation and fall stage of liquid droplets is analyzed. The results show that the negative and positive excitation voltage pulse width ratio of the MHD pump has a significant effect on the droplet velocity, breakup time, size, and sphericity. The amplitude of the excitation current and Hartmann number has a significant impact on the generation of stable droplets. The results show that the single droplet ejection state can be achieved within the Ha number between 319.5 and 391.1. As the Ha number increases, the volume, length, kinetic energy and surface energy of the droplets at breakup time also increase. The size of droplets can be adjusted by changing the amplitude of excitation waveform.

In-lab X-ray particle velocimetry for multiphase flows: Design principles and demonstration of O(1 kHz) XPV

We combine X-ray-specific tracer particles, a photon counting detector, and a liquid metal jet anode X-ray source to achieve O(1 kHz) X-ray imaging speeds in the laboratory, 15× faster than previous comparable studies with O(50 μm) tracers. To examine the limits of this measurement technique we conduct three experiments: 2D and 3D X-ray particle velocimetry (XPV) of Poiseuille pipe flow, 3D XPV of flow around a Taylor bubble, and 3D scalar mixing with a laminar jet. These experiments demonstrate the performance improvement achievable by combining the aforementioned elements, the applicability to multiphase flows and deforming systems, and the potential to capture scalar and vector quantities simultaneously. Most importantly, these experiments are conducted with a laboratory-scale system, showing that in-lab X-ray particle velocimetry techniques are now becoming usable for a wider range of flows of interest. Furthermore, the design of XPV experiments is discussed to clarify the trade offs between achievable imaging speed, domain size and spatiotemporal resolution.

An experimental investigation of the dynamic response of a liquid metal jet subjected to nanosecond laser ablation

The dynamic response of a micrometer-sized gallium–indium (Ga-In) jet in nitrogen subjected to intense Neodymium-doped Yttrium Aluminum Garnet (Nd: YAG) laser pulses with energy ranging from 0.35 to 5.0 mJ per pulse is investigated experimentally. The rapid deformation of the jet was visualized using timed-delayed stroboscopic shadowgraphy. The laser pulse disrupts the jet to form a gap, and the length of the gap grows according to a logarithm relationship with respect to the dimensionless time normalized a characteristic timescale τ, which is determined by the pulse energy Ep. The ablation impulse bends and flattens the jet into a thin curved film that resembles a wind-blown sail. The area of the sail increases with t6/5Ep13/15, where t is time. The sail eventually breaks up into fine mist. Additionally, we found that the laser-blast-induced initial bending velocity of the jet could be predicted using the semi-empirical laser-ablated propulsion model for an In-Sn droplet of tens of micrometers.

Mass log-stable distribution of fragments in liquid–liquid jet fragmentation based on a two-step cascade between viscous shear instability and Rayleigh–Taylor instability

This work is devoted to the study of liquid-liquid fragmentation. It contains both an experimental part and a theoretical part. In the experimental part, a low-melting point liquid metal jet is injected into a water pool. High-speed shadowgraph method is used to measure the jet velocity and to observe the dynamics of the fragmentation. Thereafter, the solidified fragments are sieved and weighted allowing to measure their mass distribution according to their size. The mass Probability Density Function (PDF) is then fitted using log-stable laws, generalization of log-normal laws. In the theoretical part, it is shown how it is possible to compute the shift parameter of the stable law considering that the droplets are mainly generated by a boundary layer stripping mechanism. Actually the computation relies on a viscous shear instability mechanism (different from classical Kelvin–Helmholtz instability) sometime called “gradient instability”. The width of the distribution (or more precisely its scale parameter) is computed assuming a cascade mechanism between this first wave instability and a secondary Rayleigh–Taylor mechanism applied on the generated wave. The model is then compared to present experimental results and previously published results obtained in the field of nuclear safety studies (Fuel-Coolant Interaction or FCI). Two fitting parameters are then identified. The agreement is good when phase change and solidification effects can be neglected and qualitatively good (i.e. fitting parameters need to be modified) when these effects cannot be neglected.

Experimental and numerical analysis of impingement temperature effect on the sacrificial plate's hole formation during nuclear severe accident

Liquid metal breaching onto a metal plate is an important aspect that needs to be considered in the nuclear severe accident analysis. This relates to the downward relocation of molten material to the supporting system such as sacrificial grid plate and lower head while accident happened. The molten core material impinged the sacrificial grid plate which was quenched before interacted with reactor pressure vessel. The present study aims to investigate the dynamic behaviors of holes formation due to liquid metal jet impingement onto a metal plate at initial temperatures 423 K, 473 K, and 523 K. The experiments and numerical simulation were performed with molten Wood's Metal and 5 mm thickness of Lead Bismuth Eutectic plates. The modified Moving Particle Semi-Implicit method was used to perform the numerical calculation based on the particle movement. The results showed that the plate was locally melted by the heat supplied from the liquid metal jet and induced the penetration. A larger amount of liquid metal stayed, then liquid metal pool was formed when the liquid temperature jet was lower. The temperature variation resulted unsignificant change of hole size diameter on both surfaces. The formed hole sizes in the plate's top and bottom surfaces were around 5.7–14 mm and 3.7−5 mm, respectively. The required time for the liquid metal penetration was shorter when the liquid metal temperature was higher. The increase of conduction heat transfer during the solidification of liquid metal could decrease the Nusselt number at the stagnation zone. The findings show that the experiment and numerical results can predict the sacrificial grid plate's hole formation and dynamic mechanism within critical time of molten core material impingement.

Experimental study of submerged liquid metal jet in a rectangular duct in a transverse magnetic field

A liquid metal flow in the form of a submerged round jet entering a square duct in the presence of a transverse magnetic field is studied experimentally. A range of high Reynolds and Hartmann numbers is considered. Flow velocity is measured using electric potential difference probes. A detailed study of the flow in the duct's cross-section about seven jet's diameters downstream of the inlet reveals the dynamics, which is unsteady and dominated by high-amplitude fluctuations resulting from the instability of the jet. The flow structure and fluctuation properties are largely determined by the value of the Stuart number ${{N}}$ . At moderate ${{N}}$ , the mean velocity profile retains a central jet with three-dimensional perturbations increasingly suppressed by the magnetic field as ${{N}}$ grows. At higher values of ${{N}}$ , the flow becomes quasi-two-dimensional and acquires the form of an asymmetric macrovortex, with high-amplitude velocity fluctuations reemerging.

Study of a negatively buoyant jet of liquid metal in a density-stratified ambient

Negatively buoyant jet of liquid metal (lead bismuth eutectic, LBE) at a low Prandtl number issued to a confined density-stratified ambient is investigated using large eddy simulation (LES). The Reynolds number and the densiometric Froude number of the jet are respectively Re = 8240, Fr = 29. The statistics demonstrate the features of the jet, such as the buoyancy effect and the presence of multiple shear layers. The misalignment between the turbulent heat flux and the temperature gradient implies that standard turbulence models are not suitable for such a flow.The low Prandtl number convection is compared with that of water at unity Prandtl number to investigate fluid similarity. The terminal penetration depth of the jet, mean velocity and temperature, and temperature fluctuations are analyzed. The velocity development of the LBE jet demonstrates the same behavior as that of the water jet, but the centerline variations of the mean temperature and the temperature fluctuations demonstrate the strong intensity of molecular diffusion in heat transport in LBE. The momentum and the thermal boundary layers at the side wall are compared with a similarity solution for laminar flow. The temperature distribution compares well with experimental data, demonstrating that the simulation returns satisfactory results.

Thermal fatigue analysis of structures subjected to liquid metal jets at different temperatures in the Gen-IV nuclear energy system

In the Generation-IV (Gen-IV) nuclear reactor system, the liquid metal cooled fast reactor is regarded as a promising reactor type, especially the sodium-cooled fast reactor (SFR). It is necessary to investigate the thermal striping of liquid metal jets and the thermal fatigue behavior of adjacent structures at the core outlet of a liquid metal cooled fast reactor where coolant at different temperatures is mixed and causes thermal fatigue of adjacent structures. In this work, a fluid-structure coupling model and thermal fatigue assessment methodology are proposed and employed to study the thermal fatigue of structures subjected to liquid mental jets at the core outlet of the SFR. The temperature field and velocity distribution of the fluid, as well as the deformation and thermal stress of structures are obtained. The transient load and thermal fatigue damage of the structure at different locations are also calculated and analyzed. The fatigue damage factor of the structure is less than 1.0. The max deformation is predicted and a relatively large von Mises stress is located in the junction of central column and control rod guide tube, as well as the area of geometric structure mutation.

Experimental Demonstration of the Thin-Film Liquid-Metal Jet as a Charge Stripper.

For high-power heavy ion accelerators, the development of a suitable charge stripper, which can handle intense beams, is essential. This Letter describes the first experimental demonstration of a heavy ion liquid lithium charge stripper. A 10-20 μm thick liquid lithium jet flowing at >50 m/s was formed and confirmed stable when bombarded by various heavy ion beams, while increasing the charge state of the incoming beams to the desired charge state range. This demonstration proved the existing power limitation with the conventional strippers can be overcome by the liquid-metal stripper, opening completely new possibilities in high-power accelerator development.

Can laboratory x-ray virtual histology provide intraoperative 3D tumor resection margin assessment?

Purpose: Surgery is an essential part of the curative plan for most patients affected with solid tumors. The outcome of such surgery, e.g., recurrence rates and ultimately patient survival, depends on several factors where the resection margin is of key importance. Presently, the resection margin is assessed by classical histology, which is time-consuming (several days), destructive, and basically only gives two-dimensional information. Clearly, it would be advantageous if immediate feedback on tumor extension in all three dimensions were available to the surgeon intraoperatively. Approach: We investigate a laboratory propagation-based phase-contrast x-ray computed tomography system that provides the resolution, the contrast, and, potentially, the speed for this purpose. The system relies on a liquid-metal jet microfocus source and a scintillator-coated CMOS detector. Our study is performed on paraffin-embedded non-stained samples of human pancreatic neuroendocrine tumors, liver intrahepatic cholangiocarcinoma, and pancreatic serous cystic neoplasm (benign). Results: We observe tumors with distinct and sharp edges having cellular resolution ( ) as well as many assisting histological landmarks, allowing for resection margin assessment. All x-ray data are compared with classical histology. The agreement is excellent. Conclusion: We conclude that the method has potential for intraoperative three-dimensional virtual histology.

Crack Formation in Chill Block Melt Spinning Solidification Process: A Comparative Analysis Using OpenFOAM®

The application of FeSiB family magnetic materials in the electrical or electronic industry has significantly increased owing to the development of amorphous and nanocrystalline metallic glasses using melt spinning and chill block melt spinning technology, which involves a rotating metal wheel with a high rotation speed. With this technique, a thin ribbon is obtained owing to the jet of liquid metal expelled from a casting nozzle at high pressure and temperature over the outer surface of the wheel. The cooling rates that can be achieved lead to disorder in the crystalline lattice of the metal, which is dependent on the chemical composition. As soon as the material jet is expelled by the nozzle, turbulence can occur in the solidification puddles. This generates defects and cracks in the solidification profile. In this study, numerically simulated ad hoc events in OPENFOAM® are comparatively examined using a real process.

Study of a Negatively Buoyant Jet of Liquid Metal in a Density-Stratified Ambient

Study of a Negatively Buoyant Jet of Liquid Metal in a Density-Stratified Ambient

Stability analysis of a liquid-metal jet loaded with an axial current

Stability analysis of a liquid-metal jet loaded with an axial current

Measurement of velocity in swirling flows of liquid metals in the presence of a magnetic field

Studies of the dynamics of a round submerged jet of liquid metal in a transverse magnetic field. The experiments were performed in the range of Reynolds numbers up to 1000 and Hartmann numbers up to 1300 using a probe technique for measuring velocity using potential sensors. Detailed three-dimensional flow structures are visualized using a direct numerical simulation method independent of the experiment. The paper presents data on the averaged velocity field and statistical characteristics of the flow, reproducing the complex nature of a substantially unsteady flow, in which zones of reverse fluid flows are detected and a significant heterogeneity of the velocity field is observed.

Flat liquid metal jet affected by a transverse magnetic field

A liquid metal flat jet immersed in a square duct under the influence of a transverse magnetic field is studied experimentally. Two cases are considered: when the applied magnetic field is oriented parallel (coplanar field) or perpendicularly (transverse field) to the initial plane of the jet. The main goal of the study is to investigate the mean flow characteristics and the stages of the jet's transformation. Signals of streamwise velocity at different locations are measured, which allows us to determine average velocity profiles and spatial-temporal characteristics of the velocity field. The two considered configurations are directly compared under the same flow regimes, with the same equipment. Figs 8, Refs 11.

CFD analysis and experimental measurements of the liquid aluminum spray formation for an Al–H2O based hydrogen production system

The paper proposes a combined approach between numerical modeling and experimental measurements for the analysis of a cogeneration system based on the reaction of liquid aluminum and water steam. Scrap aluminum is used for hydrogen production and the primary one is employed as an energy carrier to transport the energy from the alumina reduction system to the site of the suggested plant. The analysis focuses on the liquid aluminum injection phase immediately downstream the nozzle.High frequency thermo-cameras are employed to qualitatively assess the thermal behaviour the liquid aluminum jet. Fast imaging techniques are used to capture the multiphase flow pattern of the liquid metal jet during the injection phase.The experimental results are used to validate a 2D multi-phase CFD approach. The computational fluid dynamics model of the injection phase is created and used to extend the measurements and deepen the understanding of the thermo-fluid dynamics behaviour of the system. In particular, the influence of different nozzles diameters and different injection pressures on the liquid aluminum jet is investigated.A modular approach is adopted for the domain subdivision in order to represent accurately all the geometrical features, while the volume of fluid approach is used to model the multi-phase flow distribution in the real geometry under actual operating conditions. Finally, a good agreement between the measurements and the calculations is found.

Increasing the sensitivity of micro X-ray fluorescence spectroscopy through an optimized adaptation of polycapillary lenses to a liquid metal jet source

The combination of optimally adapted polycapillary lenses and highly brilliant liquid metal jet sources leads to significant enhancement in the sensitivity for transition metals using laboratory μXRF.

High-resolution Imaging by Using Liquid MetalJet Microfocus and Nano-focus X-ray Sources

High-resolution Imaging by Using Liquid MetalJet Microfocus and Nano-focus X-ray Sources