Experimental study of mixing enhancement of viscous liquids in confined impinging jets reactor at low jet Reynolds numbers

• The mixing performance in a CIJR is studied with PLIF.
• Influences of viscosity and excitation on mixing enhancement are investigated.
• The mixing at low Re can be effectively enhanced by excitation.
• Compared with Re, the fluid viscosity has an insignificant impact on the mixing.

Mixing performance of water and glycerol–water solution in a confined impinging jets reactor (CIJR) with and without excitation was experimentally studied using planar laser induced fluorescence (PLIF) at 100≤Re≤500. The effects of the jet Reynolds number (Re), fluid viscosity and excitation on the oscillation behaviors and mixing performance in CIJR have been qualitatively and quantitatively investigated. Results show that for Re≤100 the flow is segregated with poor mixing; for Re≥150 the flow evolves to an oscillation regime with strong mixing. Compared with the Reynolds number, the fluid viscosity has an insignificant effect on the mixing in CIJR. The mixing in CIJR at low jet Reynolds number can be effectively enhanced by excitation with low frequency, as a periodic oscillation is induced by the pulsed inflow, which further causes the continuous folding and stretching of the impingement plane. The enhancement of mixing is strengthened with the increase of excitation amplitude and is weakened with the increase of excitation frequency.