Controlled microfluidics is vital for sample delivery in serial crystallography and serial femtosecond crystallography, where the micro-jets carry dispersed crystals into an X-ray beam. We present a numerical study to assess the performance of such jets with non-Newtonian power-law fluids. An axisymmetric gas dynamic virtual nozzle is considered, where the liquid from an inner feeding capillary is focused by a co-flowing gas from a converging outer capillary. A fixed helium gas flow rate of 10 mg/min and liquid flow rate of 43 µl/min are used in a typical micro-nozzle configuration, resulting in a gas Reynolds number of 130. The Reynolds and Weber numbers for a reference water jet are 90 and 10, respectively. The jet lengths, diameters, and velocities are analysed as a function of the power-law non-Newtonian modification of the reference liquid. A related laminar incompressible multiphase problem is formulated within the mixture framework and solved with the finite volume method and volume of fluid interface treatment. 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). The obtained novel information on the behaviour of non-Newtonian gas-focused micro-jets provides a possible new dimension in tailoring the serial crystallography sample delivery systems.

International journal of multiphase flow 170, 104628 (2024). doi:10.1016/j.ijmultiphaseflow.2023.104628

Published by Pergamon Press, Braunschweig [u.a.]