Virtual Nozzle Research Articles

The kinetic energy transfer analysis between the gas and the liquid in flow-focusing of the micro-jet

The present study uses computational fluid dynamics to analyse the kinetic energy transfer from the gas to the liquid phase, considering the significant influence of surface tension. The considered situation is the gas dynamic virtual nozzle, where the co-flowing gas focuses and accelerates the liquid jet. The experimentally validated half-space three-dimensional gas-liquid mixture model addresses the unsteady, incompressible, isothermal, Newtonian, low-turbulent two-phase flow. The continuity, momentum and the k-ω SST turbulence model are employed to resolve the fluid flow. The numerical solution is based on the finite volume method and volume of fluid approach with a geometric reconstruction scheme for tracking the gas-liquid interface. The total pressure of the gas, an indication of its energy, is tracked along streamlines and analysed spatially and temporarily. It is found that around 50 % of the focusing gas energy is transferred to the liquid jet before its breakup for the nozzle with Weber number 3.5, and gas and jet Reynolds number 1842 and 108, respectively. The linear regression between jet length and energy transfer efficiency is discovered. The presented methodology represents an essential tool for analysing and understanding the energy transfer process between the focusing gas and the liquid jet.

Simulation of non-Newtonian gas-focused micro-jets in chocked gas flow regime

Stable liquid jets are crucial for successful serial crystallography experiments. They are produced from gas dynamic virtual nozzles (GDVNs), where the liquid from an inner capillary is focused by a co-flowing gas from an outer converging capillary. Our previously investigated non-Newtonian jets with incompressible and compressible focusing gas under atmospheric conditions were extended towards compressible chocked gas under vacuum conditions. An axisymmetric GDVN was considered with a fixed gas flow rate of 15 mg/min and liquid flow rate of 40 µl/min. A mixture formulation of the laminar compressible multiphase problem was solved within finite volume method and volume of fluid framework. The jet lengths, diameters, velocities, and temperatures were analysed as a function of the power-law non-Newtonian modification of reference water. It is observed that the jets under vacuum conditions are thinner for Newtonian and shear-thickening fluids than those in the atmosphere. The jet length increases from shear-thinning to shear-thickening rheology but is not affected by the pressure. The shear produced at the nozzle outlet is similar for both pressure conditions but increases in downstream directions for vacuum conditions. Gas expanding into vacuum cools by ~100-150 K while the temperature of the liquid jet drops only by a few K.

Kilohertz droplet-on-demand serial femtosecond crystallography at the European XFEL station FXE.

X-ray Free Electron Lasers (XFELs) allow the collection of high-quality serial femtosecond crystallography data. The next generation of megahertz superconducting FELs promises to drastically reduce data collection times, enabling the capture of more structures with higher signal-to-noise ratios and facilitating more complex experiments. Currently, gas dynamic virtual nozzles (GDVNs) stand as the sole delivery method capable of best utilizing the repetition rate of megahertz sources for crystallography. However, their substantial sample consumption renders their use impractical for many protein targets in serial crystallography experiments. Here, we present a novel application of a droplet-on-demand injection method, which allowed operation at 47 kHz at the European XFEL (EuXFEL) by tailoring a multi-droplet injection scheme for each macro-pulse. We demonstrate a collection rate of 150 000 indexed patterns per hour. We show that the performance and effective data collection rate are comparable to GDVN, with a sample consumption reduction of two orders of magnitude. We present lysozyme crystallographic data using the Large Pixel Detector at the femtosecond x-ray experiment endstation. Significant improvement of the crystallographic statistics was made by correcting for a systematic drift of the photon energy in the EuXFEL macro-pulse train, which was characterized from indexing the individual frames in the pulse train. This is the highest resolution protein structure collected and reported at the EuXFEL at 1.38 Å resolution.

Research on hydrogen leakage and diffusion mechanism in hydrogenation station

As a clean, efficient and sustainable energy carrier, hydrogen energy has been accepted as one of the main directions of future energy development. In this paper, a hydrogenation station providing compressed hydrogen outside was adopted as the research object. Based on finite element method and virtual nozzle model, the influence of leakage of main equipment in hydrogenation station on the distribution of combustible hydrogen was investigated, including hydrogen storage tank group, tube trailer, compressor chamber and hydrogenator. The results showed that the shape and volume of the combustible hydrogen cloud generated by the leak were influenced by obstacles, hydrogen storage pressure, and wind velocity. The disturbance of external wind and the decrease in hydrogen storage pressure will have a positive impact on the reduction of leaked volume. The diffusion of combustible hydrogen clouds can be exacerbated by complex structure of obstacles, while partition wall in the adopted hydrogenation station model can limit the combustible hydrogen cloud in the process area. These conclusions can provide guidance and reference for the risk prevention measures of hydrogenation station.

Numerical modelling and experimental validation of dripping, jetting and whipping modes of gas dynamic virtual nozzle

PurposeThis study aims to develop an experimentally validated three-dimensional numerical model for predicting different flow patterns produced with a gas dynamic virtual nozzle (GDVN).Design/methodology/approachThe physical model is posed in the mixture formulation and copes with the unsteady, incompressible, isothermal, Newtonian, low turbulent two-phase flow. The computational fluid dynamics numerical solution is based on the half-space finite volume discretisation. The geo-reconstruct volume-of-fluid scheme tracks the interphase boundary between the gas and the liquid. To ensure numerical stability in the transition regime and adequately account for turbulent behaviour, the k-ω shear stress transport turbulence model is used. The model is validated by comparison with the experimental measurements on a vertical, downward-positioned GDVN configuration. Three different combinations of air and water volumetric flow rates have been solved numerically in the range of Reynolds numbers for airflow 1,009–2,596 and water 61–133, respectively, at Weber numbers 1.2–6.2.FindingsThe half-space symmetry allows the numerical reconstruction of the dripping, jetting and indication of the whipping mode. The kinetic energy transfer from the gas to the liquid is analysed, and locations with locally increased gas kinetic energy are observed. The calculated jet shapes reasonably well match the experimentally obtained high-speed camera videos.Practical implicationsThe model is used for the virtual studies of new GDVN nozzle designs and optimisation of their operation.Originality/valueTo the best of the authors’ knowledge, the developed model numerically reconstructs all three GDVN flow regimes for the first time.

Advanced manufacturing provides tailor-made solutions for crystallography with x-ray free-electron lasers.

Serial crystallography at large facilities, such as x-ray free-electron lasers and synchrotrons, evolved as a powerful method for the high-resolution structural investigation of proteins that are critical for human health, thus advancing drug discovery and novel therapies. However, a critical barrier to successful serial crystallography experiments lies in the efficient handling of the protein microcrystals and solutions at microscales. Microfluidics are the obvious approach for any high-throughput, nano-to-microliter sample handling, that also requires design flexibility and rapid prototyping to deal with the variable shapes, sizes, and density of crystals. Here, we discuss recent advances in polymer 3D printing for microfluidics-based serial crystallography research and present a demonstration of emerging, large-scale, nano-3D printing approaches leading into the future of 3D sample environment and delivery device fabrication from liquid jet gas-dynamic virtual nozzles devices to fixed-target sample environment technology.

Analyzing the gas temperature of a hydrogen jet fire in a compartment with the Fire Dynamics Simulator

This study presents a method to simulate hydrogen jet fire using the Fire Dynamics Simulator (FDS). To avoid modeling an actual nozzle, high-speed Lagrangian particles released from a virtual nozzle are introduced to simulate released hydrogen. The capability of this FDS model to predict gas temperature is validated by comparing simulation results with five existing experiments in a rectangular steel compartment with an open end. The effects of relevant parameters prescribed in the FDS model on the gas temperature are also analyzed, including numerical parameters (auto-ignition exclusion zone, offset, particle count, and grid) and physical parameters (particle velocity, spray angle, and auto-ignition temperature). The results show that gas temperatures near the nozzle are sensitive to these parameters. Based on the grey relational analysis, the auto-ignition temperature is the least important parameter to predict gas temperatures, while the grid is the most significant parameter for gas temperatures near the ceiling.

Experimental capabilities for liquid jet samples at sub-MHz rates at the FXE Instrument at European XFEL.

The Femtosecond X-ray Experiments (FXE) instrument at the European X-ray Free-Electron Laser (EuXFEL) provides an optimized platform for investigations of ultrafast physical, chemical and biological processes. It operates in the energy range 4.7-20 keV accommodating flexible and versatile environments for a wide range of samples using diverse ultrafast X-ray spectroscopic, scattering and diffraction techniques. FXE is particularly suitable for experiments taking advantage of the sub-MHz repetition rates provided by the EuXFEL. In this paper a dedicated setup for studies on ultrafast biological and chemical dynamics in solution phase at sub-MHz rates at FXE is presented. Particular emphasis on the different liquid jet sample delivery options and their performance is given. Our portfolio of high-speed jets compatible with sub-MHz experiments includes cylindrical jets, gas dynamic virtual nozzles and flat jets. The capability to perform multi-color X-ray emission spectroscopy (XES) experiments is illustrated by a set of measurements using the dispersive X-ray spectrometer in von Hamos geometry. Static XES data collected using a multi-crystal scanning Johann-type spectrometer are also presented. A few examples of experimental results on ultrafast time-resolved X-ray emission spectroscopy and wide-angle X-ray scattering at sub-MHz pulse repetition rates are given.

A numerical study of gas focused non-Newtonian micro-jets

The present numerical study assesses the jet length, diameter and velocity of various non-Newtonian power-law fluids of a gas dynamic virtual nozzle. A related two-phase flow problem is formulated within the mixture framework and solved with the finite volume method and volume of fluid interface treatment in axisymmetry. The process parametric range allows the incompressible laminar flow assumption. A comprehensive jet characteristics analysis is carried out in a typical micro-nozzle configuration for a range of shear-thinning to shear-thickening fluids with power law indices 0.5 ≤ n < 1.5, gas mass flow rate of 10 mg/min and liquid volumetric flow rate of 43 µl/min, resulting in a gas Reynolds number of 130 with Reynolds and Weber numbers for a reference water jet being 90 and 10, respectively. It is observed that jets from shear-thinning fluids (0.5 ≤ n < 1.0) tend to be thicker, longer, and slower when compared with the shear-thickening fluids (1.0 < n ≤ 1.5). A dripping-jetting phase diagram of the nozzle is constructed by varying the power law index, gas and liquid flow rates in the range 0.9–1.1, 5–15 mg/min and 5–50 µl/min, respectively. It is observed that the area of stable jetting decreases with the increase of the power law index. The obtained novel information on the behaviour of non-Newtonian gas-focused micro-jets provides a possible new dimension for tailoring the serial crystallography sample delivery systems where the micro-jets carry dispersed crystals into an X-ray beam.

Nasal steroid spray simulations using measured spray characteristics in healthy and rhinitic nasal passages

Intranasal corticosteroid sprays (ICSs) are frequently prescribed for allergic rhinitis (AR), which is the fifth most common chronic disease in the United States. This study aimed to investigate how the intranasal distribution of ICSs is affected by spray characteristics, patient use factors, and anatomical variation. Three-dimensional reconstructions of the nasal cavity were created from computed tomography (CT) scans of one healthy subject and one AR patient. A virtual spray nozzle was positioned in the nasal vestibule according to package insert instructions and subtracted from the nasal airspace. Hybrid tetrahedral-prism meshes were created and spray simulations were conducted in ANSYS Fluent™ with inspiratory airflow present and spray characteristics from in vitro experiments. Changes in regional corticosteroid deposition with variations in spray product, actuation force, inhalation rate, spray cone angle, nozzle insertion depth, nozzle position, and nasal side were assessed. The simulation results demonstrated that, in both models, target site deposition was mostly affected by changes in nozzle position and anatomy (left vs. right nostril). In the healthy subject, target site deposition increased with a higher actuation force, higher inhalation rate, and smaller nozzle depth, but was not significantly affected by changes in the spray cone angle. In the AR patient, target site deposition was not significantly different for changes in actuation force, inhalation rate, nozzle depth, or cone angle. The findings of this numerical study suggest that the intranasal distribution of ICSs is influenced mostly by nozzle position and nasal anatomy.

Gas Dynamic Virtual Nozzle Sprayer for an Introduction of Liquid Samples in Atmospheric Pressure Ionization Mass Spectrometry.

Electrospray may exhibit inadequate ionization efficiency in some applications. In such cases, atmospheric-pressure chemical ionization (APCI) and photoionization (APPI) can be used. Despite a wide application potential, no APCI and APPI sources dedicated to very low sample flow rates exist on the market. Since the ion source performance depends on the transfer of analytes from the liquid to the gas phase, a nebulizer is a critical component of an ion source. Here, we report on the nebulizer with a gas dynamic virtual nozzle (GDVN) and its applicability in APCI at microliter-per-minute flow rates. Nebulizers differing by geometrical parameters were fabricated and characterized regarding the jet breakup regime, droplet size, droplet velocity, and spray angle for liquid flow rates of 0.75-15.0 μL/min. A micro-APCI source with the GDVN nebulizer behaved as a mass-flow-sensitive detector and provided stable and intense analyte signals. Compared to a classical APCI source, an order of magnitude lower detection limit for verapamil was achieved. Mass spectra recorded with the nebulizer in dripping and jetting modes were almost identical and did not differ from normal APCI spectra. Clogging never occurred during the experiments, indicating the high robustness of the nebulizer. Low-flow-rate APCI and APPI sources with a GDVN sprayer promise new applications for low- and medium-polar analytes.

Numerical and experimental investigation of gas flow field variations in three-dimensional printed gas-dynamic virtual nozzles

Gas-dynamic virtual nozzles (GDVNs) play a vital role in delivering biomolecular samples during diffraction measurements at X-ray free-electron laser facilities. Recently, submicrometer resolution capabilities of two-photon polymerization 3D printing techniques opened the possibility to quickly fabricate gas-dynamic virtual nozzles with practically any geometry. In our previous work, we exploited this capability to print asymmetric gas-dynamic virtual nozzles that outperformed conventional symmetric designs, which naturally leads to the question of how to identify the optimal gas-dynamic virtual nozzle geometry. In this work, we develop a 3D computational fluid dynamics pipeline to investigate how the characteristics of microjets are affected by gas-dynamic virtual nozzle geometry, which will allow for further geometry optimizations and explorations. We used open-source software (OpenFOAM) and an efficient geometric volume-of-fluid method (isoAdvector) to affordably and accurately predict jet properties for different nozzle geometries. Computational resources were minimized by utilizing adaptive mesh refinement. The numerical simulation results showed acceptable agreement with the experimental data, with a relative error of about 10% for our test cases that compared bell- and cone-shaped sheath-gas cavities. In these test cases, we used a relatively low sheath gas flow rate (6 mg/min), but future work including the implementation of compressible flows will enable the investigation of higher flow rates and the study of asymmetric drip-to-jet transitions.

An experimental study of liquid micro-jets produced with a gas dynamic virtual nozzle under the influence of an electric field.

The results of an experimental study of micro-jets produced with a gas dynamic virtual nozzle (GDVN) under the influence of an electric field are provided and discussed for the first time. The experimental study is performed with a 50% volume mixture of water and ethanol, and nitrogen focusing gas. The liquid sample and gas Reynolds numbers range from 0.09-5.4 and 0-190, respectively. The external electrode was positioned 400-500μm downstream of the nozzle tip and an effect of electric potential between the electrode and the sample liquid from 0-7kV was investigated. The jetting parametric space is examined as a function of operating gas and liquid flow rates, outlet chamber pressure, and an external electric field. The experimentally observed jet diameter, length and velocity ranged from 1-25μm, 50-500μm and 0.5-10m/s, respectively. The jetting shape snapshots were processed automatically using purposely developed computer vision software. The velocity of the jet was calculated from the measured jet diameter and the sample flow rate. It is found that micro-jets accelerate in the direction of the applied electric field in the downstream direction at a constant acceleration as opposed to the standard GDVNs. New jetting modes were observed, where either the focusing gas or the electric forces dominate, encouraging further theoretical and numerical studies towards optimized system design. The study shows the potential to unlock a new generation of low background sample delivery for serial diffraction measurements of weakly scattering objects.

Fabrication of self-assembled core-sheath microfibers via formulation of alginate-based bioinks

Core-sheath microfibrous structures are widely used in various tissue engineering applications and drug delivery systems. However, the fabrication of the various core-sheath structures using a 3D printing process supplemented with a coaxial nozzle has been challenging due to the center positioning of the core nozzle enclosed in the bigger shell nozzle. In this work, we developed a new 3D printing process using an alginate-based bioink (a mixture of photo-crosslinkable hydrogel and alginate) and its in situ crosslinking process within a single glass nozzle of the 3D printer. By manipulating the alginate weight fraction, UV intensity, flow rate, and nozzle moving speed, we could fabricate various self-assembled core-sheath structures (straight, wavy, and crimped microfibers in the core region of the structure) in which the photocrosslinked hydrogel resided in the core, and alginate was positioned in the sheath region, like a virtual coaxial nozzle.

Electrically stimulated droplet injector for reduced sample consumption in serial crystallography

With advances in X-ray free-electron lasers (XFELs), serial femtosecond crystallography (SFX) has enabled the static and dynamic structure determination for challenging proteins such as membrane protein complexes. In SFX with XFELs, the crystals are typically destroyed after interacting with a single XFEL pulse. Therefore, thousands of new crystals must be sequentially introduced into the X-ray beam to collect full data sets. Because of the serial nature of any SFX experiment, up to 99% of the sample delivered to the X-ray beam during its “off-time” between X-ray pulses is wasted due to the intrinsic pulsed nature of all current XFELs. To solve this major problem of large and often limiting sample consumption, we report on improvements of a revolutionary sample-saving method that is compatible with all current XFELs. We previously reported 3D-printed injection devices coupled with gas dynamic virtual nozzles (GDVNs) capable of generating samples containing droplets segmented by an immiscible oil phase for jetting crystal-laden droplets into the path of an XFEL. Here, we have further improved the device design by including metal electrodes inducing electrowetting effects for improved control over droplet generation frequency to stimulate the droplet release to matching the XFEL repetition rate by employing an electrical feedback mechanism. We report the improvements in this electrically triggered segmented flow approach for sample conservation in comparison with a continuous GDVN injection using the microcrystals of lysozyme and 3-deoxy-D-manno-octulosonate 8-phosphate synthase and report the segmented flow approach for sample injection applied at the Macromolecular Femtosecond Crystallography instrument at the Linear Coherent Light Source for the first time.

High‐pressure under‐expanded hydrogen leakage model considering gas‐wall friction loss

AbstractThe integral model is used to predict the concentration field, only suitable for low‐pressure leakage, while the virtual nozzle model is widely used in high‐pressure leakage but ignores the friction between the hydrogen and the tube wall during the leakage. We modified the virtual nozzle model by adding the gas‐wall friction loss term to the momentum conservation equation. A theoretical model of a high‐pressure under‐expanded jet is proposed by combining the integral model with the improved virtual nozzle model, which was validated by a series of helium (instead of hydrogen) dispersion in an unenclosed environment. And then the high‐pressure hydrogen leakage system was set up to investigate hydrogen concentration along the centerline of the jet was measured under different pressures. Results show that the mole fractions along with the axial distance all comply with the hyperbolic decay law. Within the range of 40 cm &lt; z &lt; 100 cm, at other pressures of 1, 2, 4 MPa, the minimum deviations of high‐pressure under‐expanded hydrogen leakage prediction model and experiments are 1.67%, 1.37%, 1.33%, respectively. The study is adequately precise to predict high‐pressure leakage concentration and also gives ideas about the installation position of the hydrogen sensor in engineering.

3D printed devices and infrastructure for liquid sample delivery at the European XFEL.

The Sample Environment and Characterization (SEC) group of the European X-ray Free-Electron Laser (EuXFEL) develops sample delivery systems for the various scientific instruments, including systems for the injection of liquid samples that enable serial femtosecond X-ray crystallography (SFX) and single-particle imaging (SPI) experiments, among others. For rapid prototyping of various device types and materials, sub-micrometre precision 3D printers are used to address the specific experimental conditions of SFX and SPI by providing a large number of devices with reliable performance. This work presents the current pool of 3D printed liquid sample delivery devices, based on the two-photon polymerization (2PP) technique. These devices encompass gas dynamic virtual nozzles (GDVNs), mixing-GDVNs, high-viscosity extruders (HVEs) and electrospray conical capillary tips (CCTs) with highly reproducible geometric features that are suitable for time-resolved SFX and SPI experiments at XFEL facilities. Liquid sample injection setups and infrastructure on the Single Particles, Clusters, and Biomolecules and Serial Femtosecond Crystallography (SPB/SFX) instrument are described, this being the instrument which is designated for biological structure determination at the EuXFEL.

A novel method for the evaluation of ejector based on a virtual nozzle and two indexes

This paper presents a novel method for ejector evaluation by developing a virtual nozzle, which provides the ejector’s maximum ability to overcome its back pressure and the minimum constant cross-section area based on two newly-derived evaluation indexes. The method was developed based on the assumption that the total energy and the ratio of dynamic enthalpy to total energy before normal shock of the virtual nozzle are the same as those of the real ejector. Under the condition that the initial state of the virtual nozzle is the same as that of the primary fluid of the ejector, two evaluation indexes, which include the relative pressure ratio and the relative area ratio, were derived to indicate the extent to which the ability to overcome back pressure and area demand deviate from the benchmark obtained from the virtual nozzle. Using the new method, the case studies of ejector evaluation were carried out involving with theoretical data of 13 refrigerants selected as working fluid of ejector and experimental data of four refrigerants. And the relationship between the two indexes was expressed by a high-accuracy fitting correlation equation that was validated by both theoretical calculation and experimental data and was found meaningful.

A multipurpose end-station for atomic, molecular and optical sciences and coherent diffractive imaging at ELI beamlines

We report on the status of a users’ end-station, MAC: a Multipurpose station for Atomic, molecular and optical sciences and Coherent diffractive imaging, designed for studies of structure and dynamics of matter in the femtosecond time-domain. MAC is located in the E1 experimental hall on the high harmonic generation (HHG) beamline of the ELI Beamlines facility. The extreme ultraviolet beam from the HHG beamline can be used at the MAC end-station together with a synchronized pump beam (which will cover the NIR/Vis/UV or THz range) for time-resolved experiments on different samples. Sample delivery systems at the MAC end-station include a molecular beam, a source for pure or doped clusters, ultrathin cylindrical or flat liquid jets, and focused beams of substrate-free nanoparticles produced by an electrospray or a gas dynamic virtual nozzle combined with an aerodynamic lens stack. We further present the available detectors: electron/ion time-of-flight and velocity map imaging spectrometers and an X-ray camera, and discuss future upgrades: a magnetic bottle electron spectrometer, production of doped nanodroplets and the planned developments of beam capabilities at the MAC end-station.

Recent Advances and Future Perspectives on Microfluidic Mix-and-Jet Sample Delivery Devices.

The integration of the Gas Dynamic Virtual Nozzle (GDVN) and microfluidic technologies has proven to be a promising sample delivery solution for biomolecular imaging studies and has the potential to be transformative for a range of applications in physics, biology, and chemistry. Here, we review the recent advances in the emerging field of microfluidic mix-and-jet sample delivery devices for the study of biomolecular reaction dynamics. First, we introduce the key parameters and dimensionless numbers involved in their design and characterisation. Then we critically review the techniques used to fabricate these integrated devices and discuss their advantages and disadvantages. We then summarise the most common experimental methods used for the characterisation of both the mixing and jetting components. Finally, we discuss future perspectives on the emerging field of microfluidic mix-and-jet sample delivery devices. In summary, this review aims to introduce this exciting new topic to the wider microfluidics community and to help guide future research in the field.