Capillary ionic liquid electrospray: beam compositional analysis by orthogonal time-of-flight mass spectrometry

Orthogonal time-of-flight mass spectrometry has been used to characterize the kinetic energy and charged species distributions from an in vacuo electrospray ion source for four different ionic liquids at volumetric flow rates between 0.3 and 3.3 nanolitres per second. In all cases, the mass spectra revealed charged species consisting of singly charged and multiply charged ions as well as two broad, unresolved droplet distributions occurring in the 104 to 106 atomic mass unit per charge range. The mean jet velocity and mean jet breakup potential were established from analysis of the energy profile of the high mass-to-charge droplets. At the jet breakup point, we find the energy loss and the jet diameter flow rate dependence of the electrospray beam to be similar to that determined by Gamero-Castaño (Phys. Fluids, vol. 20, 2008, 032103; Phys. Rev. Fluids, vol. 8, 2021, 013701) for 1-ethyl-3-methylimidazolium bis(trifluromethylsulfonyl)imide at similar volumetric flow rates. Similar trends are observed for all four liquids over the flow regime. A jet instability analysis revealed that jet electrification and viscous effects drive the jet breakup from the case of an uncharged, inviscid jet; jet breakup occurs at droplet and jet radius ratios that deviate from 1.89. Using the analytically determined ratio and the beam profile, different species are modelled to reconstruct the mass spectra; primary droplets constitute only a fraction of the total species present. The populations of the species are discussed.

Reversal and Inversion of Capillary Jet Breakup at Large Excitation Amplitudes

The evolution of the capillary breakup of a liquid jet under large excitation amplitudes in a parameter regime relevant to inkjet printing is analysed using three-dimensional numerical simulations. The results exhibit a reversal of the breakup length of the jet occurring when the velocity scales associated with the excitation of the jet and surface tension are comparable, and an inversion of the breakup from front-pinching to back-pinching at sufficiently large excitation amplitudes. Both phenomena are shown to be associated with the formation of vortex rings and a local flow obstruction inside the jet, which modify the evolution of the jet by locally reducing or even reversing the growth of the capillary instability. Hence, this study provides a mechanism for the well-known breakup reversal and breakup inversion, which are both prominent phenomena in inkjet printing. An empirical similarity model for the reversal breakup length is proposed, which is shown to be valid throughout the considered range of characteristic parameters. Hence, even though the fluid dynamics observed in capillary jet breakup with large excitation amplitudes are complex, the presented findings allow an accurate prediction of the behaviour of jets in many practically relevant situations, especially continuous inkjet printing.

The Natural Breakup Length of a Steady Capillary Jet: Application to Serial Femtosecond Crystallography

One of the most successful ways to introduce samples in Serial Femtosecond Crystallography has been the use of microscopic capillary liquid jets produced by gas flow focusing, whose length-to-diameter ratio and velocity are essential to fulfill the requirements of the high pulse rates of current XFELs. In this work, we demonstrate the validity of a classical scaling law with two universal constants to calculate that length as a function of the liquid properties and operating conditions. These constants are determined by fitting the scaling law to a large set of experimental and numerical measurements, including previously published data. Both the experimental and numerical jet lengths conform remarkably well to the proposed scaling law. We show that, while a capillary jet is a globally unstable system to linear perturbations above a critical length, its actual and shorter long-term average intact length is determined by the nonlinear perturbations coming from the jet breakup itself. Therefore, this length is determined solely by the properties of the liquid, the average velocity of the liquid and the flow rate expelled. This confirms the very early observations from Smith and Moss 1917, Proc R Soc Lond A Math Phys Eng, 93, 373, to McCarthy and Molloy 1974, Chem Eng J, 7, 1, among others, while it contrasts with the classical conception of temporal stability that attributes the natural breakup length to the jet birth conditions in the ejector or small interactions with the environment.

Liquid Film Behavior of Bottoming Liquid Jet in a Shallow Pool Measured by 3D-LIF

When the core meltdown accident occurs in the nuclear plant, molten corium falls into a coolant pool of the lower plenum. It is considered that the molten corium jet is broken up, cooled, and solidified with fuel-coolant interaction (FCI). However, the coolant pool could be a shallow condition by the leakage and evaporation of the coolant. In this situation, it is considered that the corium jet bottoms and spreads without the jet breakup. From the viewpoint of safety, understanding a jet behavior and estimating a cooling behavior are needed. The purpose of this study is to clarify the mechanism of the liquid jet behavior in a shallow pool as the fundamental process for estimating the cooling behavior in the real machine. In this paper, we discuss the spreading behavior of the liquid jet after bottoming. The jet injection experiment was conducted using test fluids. By using the 3D-LIF method, the 3D visualization of the liquid jet was Successfully implemented. From the visualization result, the following behaviors were seen. After bottoming, the jet spread radially with the liquid film. As the jet spreading behavior, the liquid film was rolled up to the inside, and the vortex was formed. After a certain time, the vortex was broken. Then the flow and the number density of the fragment were changed.

Numerical Study of the Micro-Jet Formation in Double Flow Focusing Nozzle Geometry Using Different Water-Alcohol Solutions

The purpose of this work is to determine, based on the computational model, whether a mixture of a binary liquid is capable of producing longer, thinner and faster gas-focused micro-jets, compared to the mono-constituent liquids of its components. Mixtures of water with two different alcohols, water + ethanol and water + 2-propanol, are considered. The numerical study of pre-mixed liquids is performed in the double flow focusing nozzle geometry used in sample delivery in serial femtosecond crystallography experiments. The study reveals that an optimal mixture for maximizing the jet length exists both in a water + ethanol and in a water + 2-propanol system. Additionally, the use of 2-propanol instead of ethanol results in a 34% jet length increase, while the jet diameters and velocities are similar for both mixtures. Pure ethanol and pure 2-propanol are the optimum liquids to achieve the smallest diameter and the fastest jets. However, the overall aim is to find a mixture with the longest, the smallest and the fastest jet. Based on our simulations, it appears that water + 2-propanol mixture might be slightly better than water + ethanol. This study reveals the dominant effect of liquid viscosity on the jet breakup process in a flow focusing nozzles operated under atmospheric conditions.