Mixing instantaneous devices

Also discussed are precipitation specific experimental techniques, such as supersaturation measurements, constant composition (CC) method, instantaneous mixing devices, maximum (critical) growth rate experiments, and sizing. Due to the intrinsic difficulties with the direct supersaturation measurements and the microsecond characteristic time scale of precipitation reaction and nucleation, the CC method is used to study the precipitation kinetics. For the same reasons, the critical growth experiments are used to delineate the domain of the reactant feed rate that assures a renucleation-free process and a unimodal CSD. 

In scaling-up this process, appropriate reactor design was conducted elaborately by the results of several tests. The following two points are characteristic of the scale-up. One is the development of catalyst suitable for fluid beds. Selectivity should not decrease by the increase of hydrocarbon concentration. Also, reaction rate of the secondary reaction should be small. These problems were solved by the development of rather simple P-V catalyst (K2, K3). Another device is the instantaneous mixing inlet mechanism for hydrocarbon and air. By this, activity decline of the catalyst can be prevented (T12). Thus a process has been developed which is equally as profitable as the benzene process. 

The improvement in accuracy achieved by the complex closures compared to the simpler ones can also be questionable. Osenbroch ]67] and Mortensen ]60] successfully applied the combined particle image velocimetry (PIV)/planar laser induced fluorescence (PLIF) technique to measure the instantaneous velocity and reacting species concentration in mixing devices like a mixing channel, pipe, and multi-functional channel reactor. The measured... 

In this work, measurements of the mean velocity and the turbulent fluctuations in the flows generated by the two impellers were confined to the center line of the radial jet since this is the zone where the flow is most strongly influenced by the impeller style. Turbulent flow parameters were determined using a DISA Electronics Laser Anemometer System. As the name implies, this is an optical device that measures the instantaneous velocity at a point. The technique is linear which allows accurate flow measurements at very high turbulence levels such as found in mixing vessels. Since there is no probe, there are no flow disturbances and the measurement is independent of fluid properties. The anemometer used in this work was sensitive to the direction of the instantaneous velocity. 

This electrode is constituted of a glass tube, maintained in a vertical position, of which the central passageway (10-70 pm in diameter), allows the transfer of mercury between a reservoir and the capillary tip, where very small droplets are formed. This dropping-mercury electrode is immersed in an unstirred solution containing the target analyte mixed with a support electrolyte. The surface of the droplet of mercury increases until it falls (around 4-5 s). The fall is most often provoked by a device producing a small impact on the electrode. Instantaneously, a new droplet, identical to the previous one, is formed presenting a fresh uncontaminated surface. 

The numerics in Table 16.2 make two points. One is that turbulence is difficult to achieve at the mesoscale and nearly impossible to achieve in micro- and nanoscale devices. The other point is that diffusion becomes so fast at the microscale that cross-channel (e.g., radial) mixing is essentially instantaneous for all but the very fastest reactions. Thus composition and temperature will be approximately uniform in the cross-channel direction. The solutions to the convective diffusion equations in... 

This method is typically valid when effluent concentrations are measured. When using a measurement device that allows the measurement of pore-water concentrations, other boundary conditions apply to the advection equation and Equation 15.12is not valid anymore (Kreft and Zuber, 1978 van Genuchten and Parker, 1984). Attention must also be paid to experimental artifacts arising from specific laboratory devices. For example, if injection is performed in a volume of water outside of the column (like a device to maintain the piezometric head), the actual injection condition is not an instantaneous step variation. Due to mixing with the volume of water, the injection is actually exponential. Not accounting for such effects can result in a serious bias in the estimated values of dispersivity (Novakowski, 1992). 

Controlled release is important in agriculture, especially for insect control. One common example involves the pheromones, sex attractants released by insects. If you mix this attractant with an insecticide, you can wipe out all of one sex of a particular insect pest. A device for releasing one pheromone is shown schematically below. This pheromone does not subline instantaneously, but at a rate of... 

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