Liquid mixing oscillating flow

These droplets are then mixed with more air to dry the particles. The rate of droplet formation is equal to the oscillation frequency (/) of the piezoelectric crystal. From the volumetric flow rate of the liquid and the frequency /, the volume of the individual drops and particle diameter can be calculated. 

Houcine et al. (64) used a non-intrusive laser-induced fluorescence method to study the mechanisms of mixing in a 20 dm CSTR with removable baffles, a conical bottom, a mechanical stirrer, and two incoming liquid jet streams. Under certain conditions, they observed an interaction between the flow induced by the stirrer and the incoming jets, which led to oscillations of the jet stream with a period of several seconds and corresponding switching of the recirculation flow between several metastable macroscopic patterns. These jet feedstream oscillations or intermittencies could strongly influence the kinetics of fast reactions, such as precipitation. The authors used dimensional analysis to demonstrate that the intermittence phenomenon would be less problematic in larger CSTRs. 

A micromixer in which the fluid can be stirred by periodically pumping through the side channels is shown in Figure 3.45 [481]. The periodic perturbation applied via the side channel allows liquids A and B to be mixed. Other mixers based on oscillating pressure-pumped flow have also been reported [482,483]. Two droplets (600 pL) were merged and mixed by a push-pull (shuttling) method in a PDMS device consisting of a hydrophobic microcapillary vent (HMCV) [364]. 

Combustion control, both active and passive, heis been used as a tool to minimize combustion-generated oscillations to obtain stable operation, maximize combustion efficiency to improve performance, control temperature distribution, minimize emissions, and improve mixing and residence times to reduce combustor size. Techniques previously used with gaseous fuel combustion have been extended to combustion of liquid fuel of interest. Porous media inserts, counter-current combustors, etc. have been investigated to control flow and temperature within the combustion chamber, aiming at compact combustors with reduced emission. 

To measure an adsorption Isotherm, the oscillation frequency was monitored as the computer adjusted the partial pressure p of Nj In the gas phase over the device at 77 K. This was done by controlling the relative flow rates of a He mix-down stream and a Nj carrier stream. Since He Is nonadsorbing at liquid Nj temperature (16), p -0 for the mix-down stream, while for the carrier stream, p - p, since the device temperature Is maintained at the boiling point of N2. The value of p/p, was incremented every 3 sec from a value of 0 at the start of the run to a value around 0.95 and then back to 0. It was found that two hours for a full adsorption Isotherm was sufficiently slow to maintain adsorption equilibrium (10). 

Let us consider the schematic diagram of the experimental setup (Fig. 11.6). Let Pi denote the pressure in the inner chamber and P2 denote the pressure in the outer chamber containing a liquid of lower density. Fluid flow across the capillary is mainly responsible for generating oscillations. The upward flow is opposed by the viscosity of heavier fluid in the inner vessel, while the downward flow is opposed by buoyancy. The buoyancy depends on the density difference Pi — Pf where Pi and P2 are the densities of heavier liquid and lighter liquid, respectively. This is so since the magnitude of the buoyancy force would depend on the difference of vertical components of fluid force on the upper and lower sides of the capillary. This is turn would depend on the pressure difference sP = Pi-P2. The density of the denser fluid in the capillary due to partial mixing would depend on the pressure difference. 

In all cases, the liquid-liquid interface is observed, during video recordings of flow visualisations of real rollovers, to become unstable whereby upwards penetrative oscillations of the interface build up in vertical amplitude. Elements of the lower layer are mixed into the upper layer, and the liquid-liquid interface migrates slowly downwards. 

---