A gas-focused micro-jet used for sample delivery in femtosecond crystallography was
numerically modelled. We considered a standard micro-nozzle and a nominal flow rate of
gas (helium) 10.8 mg/min (Re^ = 198.1 and We^ = 19.3) and liquid (water) 43.2 µl/min
(Re^ = 111.2 and We^ = 19.0) at Ca = 0.16. The two-phase liquid-gas system was
considered an incompressible ideal mixture in axial symmetry. The rheology of the liquid
was considered in the power law non-Newtonian formulation framework. The focusing gas
was considered ideal. The work deals with Newtonian and non-Newtonian shear thinning (^
from 0 to 0.5) and shear thickening (^ from 1 to 1.5) flow, with ^ = 1.0 ⠙ 10⠒6 m2/s . The
system of equations for conservation of mass and momentum was numerically solved with
the finite volume method. The interface boundary between the gas and the liquid was
determined with the volume of fluid method. Newtonian fluid has a jet diameter of 9 µm,
length of 1538 µm and average velocity of 19.76 m/s. Compared to the Newtonian fluid,
the shear thinning case (^ = 0,5) has a 6 % larger diameter, 59 % shorter jet and a 22 %
slower jet, while the shear thickening liquid (^ = 1,5) has a 33 % larger diameter, 43 %
longer and 40 % slower jet.
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