Novel liquid-flow splitting unit numbering-up of liquid/liquid specifically made for chemical microprocessing

A liquid-flow splitting unit for dividing one main liquid stream into six substreams was developed without the need for active flow regulation. The tool has six fluid connectors that allow the numbering-up of a respective number of microprocess devices for liquid or liquid/liquid processes. One such liquid/liquid process for which the current tool design and tests in particular have been conceived, is the forced precipitation of precious inorganic powders by the segmented flow tubular reactor (SFTR) technique. Such investigations were performed with six micromixers of impinging-jet or interdigital separation layer type attached to the liquid-flow splitting unit. Fluid equipartition is achieved via the action of the microdevices as flow resistors, thereby increasing the pressure drop of the system. Liquid splitting was carried out in a cylindrical liquid tank with one inlet and six outlet holes that also served for pulsation dampening. By CFD simulations the impact of two important geometric parameters of this tank, namely, the height at a given diameter and the position of the inlet hole, on the fluid splitting was studied. In addition, the influence of the injection direction with respect to the normal of the tank was analyzed. It turned out that in the presence of flow resistors (typically generating a pressure drop at about 60 mbar) this impact is negligible, i.e., principally, a large flexibility on design and operation is provided. Without these resistors, the before-mentioned parameters in turn have a large impact that is discussed in detail. Experiments with a liquid-flow splitting unit and six coupled impinging-jet micromixers using water as liquid proved a reasonable fluid distribution with a standard and maximum deviation of the substream flow rates of 4 and 11 %, respectively. These deviations are mainly caused by different pressure drops (Deltap) of the individual impinging-jet mixers as a result of tolerances in the microfabrication method, die sinking muEDM manufacture. Already small differences in the microstructured outlet hole diameters (d = 300 mum) of the impinging-jet mixer have a large influence due to the d(-4) similar to Deltap dependence. Additionally, attaching specially adapted interdigital separation layer micromixers to the liquid-flow splitting unit, a minimum/maximum (standard) deviation of the water distribution below 5 (2) % could be achieved. To obtain this improved result, it was necessary to optimize the choice of material, the design of the microstructure inside the mixer, and the fabrication process.