Convective mixing of miscible liquids in a rotor-stator spinning disk reactor

Convective mixing of two miscible liquids injected into a rotor-stator spinning disk reactor (RS-SDR) has been studied using an LIF technique and CFD simulations. The fluids are ammonia water and fluorescein ammonia water solutions. The RS-SDR has a rotor 100 mm in diameter and a thin circular cavity 0.10-0.15 mm in height between the rotor and stator. Laminar flow conditions for rotation speeds up to 120 rpm and total flow rates up to 8 mL/min are considered. The fluorescein solution is injected from the second off-center hole into the cavity filled with the ammonia water supplied from the central hole. The LIF technique visualizes a spiral streak pattern formed downstream of the second injection hole. This streak pattern is analyzed to calculate the local mixedness of the two fluids. It is determined that the mixedness increases for lower flow rates, while it is less sensitive to rotation speed and cavity height. The CFD simulations indicate that the spiral streak pattern is deformed and stretched in the radial direction to form a densely layered structure of the two fluids. The development of the mixedness along the streak pattern is correlated well with Re-inlet/Re-cavity, where Re-inlet and Re-cavity are the Reynolds numbers for the injected flow and the azimuthal flow in the cavity, respectively. This Reynolds number ratio is shown to be related to the Rossby number and the position and radius of the second injection hole. The proposed correlation is based on a linear combination of injection mixing and rotation mixing. The mixedness decreases with Re-inlet/Re-cavity because the injection mixing decreases with Re-inlet while the rotation mixing increases with Re-cavity.