Reynolds number and impeller diameter effects on instabilities in stirred vessels

Leveraging Dissolution by Autoinjector Designs

Chemical warfare or terrorism attacks with organophosphates may place intoxicated subjects under immediate life-threatening and psychologically demanding conditions. Antidotes, such as the oxime HI-6, which must be formulated as a powder for reconstitution reflecting the molecule's light sensitivity and instability in aqueous solutions, dramatically improve recovery-but only if used soon after exposure. Muscle tremors, anxiety, and loss of consciousness after exposure jeopardize proper administration, translating into demanding specifications for the dissolution of HI-6. Reflecting the patients' catastrophic situation and anticipated desire to react immediately to chemical weapon exposure, the dissolution should be completed within ten seconds. We are developing multi-dose and single-dose autoinjectors to reliably meet these dissolution requirements. The temporal and spatial course of dissolution within the various autoinjector designs was profiled colorimetrically. Based on these colorimetric insights with model dyes, we developed experimental setups integrating online conductometry to push experiments toward the relevant molecule, HI-6. The resulting blueprints for autoinjector designs integrated small-scale rotor systems, boosting dissolution across a wide range of viscosities, and meeting the required dissolution specifications driven by the use of these drug products in extreme situations.

Experimental Study and Detached Eddy Simulation of the Macro-Instability in an Eccentric Stirred Tank

The turbulent flow in stirred tank is highly complicated and anisotropic, especially when the macro-instability (MI) are involved. In this work, the numerical simulation method of the eccentric agitation was established based on the detached eddy simulation (DES) model to study the MI in an eccentric stirred tank. The turbulent flow in the eccentrically located Rushton turbine stirred tank was numerically investigated. The rotation of the impeller was simulated by the transient sliding mesh (SM) method. The effect of eccentricity, impeller Reynolds number and impeller-tank diameter ratio were studied in order to quantify the MI frequency. PIV experiments were performed to validate the DES results and frequency analyses were applied to the obtained time series of the velocity recordings. It was found that the flow field in eccentrically stirred tank are highly unsteady and is subject to MI with varying period less than 10 blade passage period. Good agreements have been found between the DES and PIV results, both indicate that the dominant frequency of MI increases linearly with the Reynolds number, increases with the impeller-tank diameter ratio and decreases with the eccentricity. According to the agreements between the experimental and simulation results, it can be concluded that the combination of DES and SM is suitable for the prediction of the MI phenomenon in stirred tanks.