Abstract Summary (Max 250 words)
The impingement of two, free, liquid jets upon one another (free impinging jets) is commonly used for the injection of liquid rocket propellants and for rapid reactions where a wall-free environment is desirable. It is generally assumed that the collision of free impinging jets does not release energy; thus, liquid-phase micromixing has received relatively little attention. However, a recent study [R.J. Demyanovich, Atomization and Sprays, 35(3):1-26 (2025)] has shown that these collisions are dissipative, and the present study employs this finding to study the micromixing striation thickness. Micromixing was investigated by following the progress of an acid-base neutralization accompanied by a change in fluorescence intensity. Micromixing was modeled using a framework that assumes diffusion and reaction of species occur within striations of fixed thickness 2L (2L is fixed because turbulence dies out after a few turnover times of the large energy-containing eddies). A simulation, which included a module for calculating the fluorescence intensity, determined 2L for energy dissipation rates (ϵ) ranging from 1,650 to 2,650,000 W/kg. The experimental results revealed that the impingement zone contained a distribution of striation thicknesses which were well correlated with the local energy dissipation rate. The striation thickness was found to lie within the range of turbulent dissipative scales less than the Taylor microscale but greater than the Kolmogorov microscale. Besides depending on ν⁄ϵ, where ν is the viscosity, the striation thickness is also a function of the large-eddy Reynolds number in the impingement zone.
