Alternative Geometric Arrangements of the Nozzle Outlet Orifice for Liquid Micro-Jet Focusing in Gas Dynamic Virtual Nozzles.

Božidar Šarler,Saša Bajt,Rizwan Zahoor

doi:10.3390/ma14061572

Abstract

Liquid micro-jets are crucial for sample delivery of protein crystals and other macromolecular samples in serial femtosecond crystallography. When combined with MHz repetition rate sources, such as the European X-ray free-electron laser (EuXFEL) facility, it is important that the diffraction patterns are collected before the samples are damaged. This requires extremely thin and very fast jets. In this paper we first explore numerically the influence of different nozzle orifice designs on jet parameters and finally compare our simulations with the experimental data obtained for one particular design. A gas dynamic virtual nozzle (GDVN) model, based on a mixture formulation of Newtonian, compressible, two-phase flow, is numerically solved with the finite volume method and volume of fluid approach to deal with the moving boundary between the gas and liquid phases. The goal is to maximize the jet velocity and its length while minimizing the jet thickness. The design studies incorporate differently shaped nozzle orifices, including an elongated orifice with a constant diameter and an orifice with a diverging angle. These are extensions of the nozzle geometry we investigated in our previous studies. Based on these simulations it is concluded that the extension of the constant diameter channel makes a negligible contribution to the jet’s length and its velocity. A change in the angle of the nozzle outlet orifice, however, has a significant effect on jet parameters. We find these kinds of simulation extremely useful for testing and optimizing novel nozzle designs.

Highlights

Serial femtosecond crystallography (SFX) [1] at X-ray free electron lasers (XFELs) is providing new capabilities for time-resolved macromolecular crystallography
A gas dynamic virtual nozzle (GDVN) model, based on a mixture formulation of Newtonian, compressible, two-phase flow, is numerically solved with the finite volume method and volume of fluid approach to deal with the moving boundary between the gas and liquid phases
The considered GDVN micro-nozzles operate in choked-flow mode [10]

Summary

Introduction

Serial femtosecond crystallography (SFX) [1] at X-ray free electron lasers (XFELs) is providing new capabilities for time-resolved macromolecular crystallography. The XFEL pulses from the Linac Coherent Light Source (SLAC, Menlo Park, CA, USA) are delivered with a frequency of 120 Hz while the pulse frequency of the European XFEL (Schenefeld, Germany) can be as high as 4.5 MHz. The XFEL pulses from the Linac Coherent Light Source (SLAC, Menlo Park, CA, USA) are delivered with a frequency of 120 Hz while the pulse frequency of the European XFEL (Schenefeld, Germany) can be as high as 4.5 MHz When such X-ray laser pulses interact with the jet carrying the samples they produce shock waves, which can damage protein crystals and influence the data collection at MHz rates [2,3]. The natural environment of protein crystals is water or a buffer liquid This is why they are injected into the X-ray beam via a liquid jet. This liquid produces unwanted background that often obstructs diffraction patterns

Methods

Results

Conclusion