A computational investigation of microjet focusing with secondary fluid and compressible gas

Zahoor, Rizwan (author), Bajt, Saša (author), Šarler, Božidar (author)

Double-flow focusing nozzles (DFFNs) are used to produce liquid microjets for sample delivery in serial femtosecond crystallography (SFX), where crystallized samples are dispersed in a primary liquid jet and delivered into the x-ray beam path. Such jets are generated by focusing a primary liquid jet with a coaxial secondary liquid and outer gas. Precise control of microjet stability and morphology is crucial for efficient sample delivery. This study presents a comprehensive numerical model of double-flow focused liquid jets from a DFFN, where the liquid phase consists of water and ethanol, and the focusing gas is helium. An axisymmetric, Newtonian, compressible, two-phase gas– liquid and two-component water–ethanol model is formulated and solved using the finite-volume method and volume-of-fluid framework. The water–ethanol mixing and resulting changes in density, viscosity, and surface tension as a function of ethanol concentration and tem perature are simulated using the Jouyban–Acree model. The jet characteristics as a function of material mixture properties, focusing-gas compressibility, and temperature are investigated numerically. A parametric analysis is performed over the typical SFX operating range, varying the water and ethanol flow rates from 0 to 20 ▫$\mu$▫l/min and the helium gas flow rate from 0 to 20mg/min. Jet stability, diameter, length, and velocity are analyzed. The influence of local mixture properties, mapped onto the Ca–We plane, reveals transitions between viscous-dominated and inertia-driven jetting regimes. The predicted jet diameters are consistent with the Young–Laplace equation and scal ing expression. The findings provide a physical insight required for the virtual design of DFFNs.

• Language: English
• Keywords: serial crystallography, double-flow-focusing, jet-length
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 15 str.
• Numbering: Vol. 38, iss. 8, art. 082003
• PID: 20.500.12556/RUL-185590
• UDC: 532.57
• ISSN on article: 1089-7666
• DOI: doi.org/10.1063/5.0342127
• COBISS.SI-ID: 287497987
• Publication date in RUL: 11.08.2026

Record is a part of a journal

• Title: Physics of fluids
• Shortened title: Phys. fluids
• Publisher: American Institute of Physics
• ISSN: 1089-7666
• COBISS.SI-ID: 18986023

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: serijska femtosekundna kristalografija, fokusiranje z dvojnim tokom, dolžina curka