Channel-based flow fields

Of course other channel-based flow-field designs are possible. In general attention has to be paid to the temperature gradient and good water removal. How fields with meandering channels involve the risk of liquid water collecting in the bends. 

The liquid alone pattern showed no entrained bubbles or gas-liquid interface in the field of view. The capillary bubbly flow, in the upper part of Fig. 5.14a, is characterized by the appearance of distinct non-spherical bubbles, generally smaller in the streamwise direction than at the base of the triangular channel. This flow pattern was also observed by Triplett et al. (1999a) in the 1.097 mm diameter circular tube, and by Zhao and Bi (2001a) in the triangular channel of hydraulic diameter of 0.866 mm. This flow, referred to by Zhao and Bi (2001a) as capillary bubbly... 

An emerging class of emulsification methods is not based on imposing an overall flow field, but rather by making individual droplets on the mouths of membrane pores or micro-engineered channels. Characteristic is that the flow fields applied are much milder energy consumption is much lower, while the droplet sizes are strongly dependent on the shape and dimensions of the pores or micro-channels. A number of processes belong to this class ... 

Industrial processes are at this moment predominantly based on the first class (using intense flow fields). The second class based on membranes or micro-channels seems to have large potential for making more complex products for example, monodisperse emulsions or double emulsions. The third class is used in the production of foods, but also in other industries where emulsions need to be made in which the dispersed phase has a high viscosity compared to the continuous phase. 

Flow field-flow fractionation (flow FFF or FIFFF) is one of the FFF subtechniques in which particles and macromolecules are separated in a thin channel by aqueous flow under a field force generated by a secondary flow. As with other FFF techniques, separation in FIFFF is based on the applied force directed across the axis of separation flow. In FIFFF, this force is generated by cross-flow of liquid delivered across the channel walls. In order to maintain the uniformity of cross-flow moving in a typical rectangular channel, two ceramic permeable frits are used as channel walls and the flow stream enters and exits through these walls. The force applied in FIFFF is a Stokes force that depends only on the sizes of sample components. 

As seen in Figure 32-12, p. 379, a solution passing through two ceramic frits serves to provide the cross-flow field. The particles are retained on a semipermeable membrane. The field is a pressure field formed by the liquid flowing between the frits. According to J.C. Giddings Science, 260, 1456, 1993), "The sample particles are carried to the channel accumulation zone with the cross flow. Each species then diffuses into an equilibrium based zone of a specific... 

The base substrate is FR4 or PI with a copper layer with a thickness of 70 pm. The polymer layer has thickness of 50-100 pm. In the Cu layer the flow field structure is patterned. This patterning technology is a two-stage etch process. In the first step the channels for the H2 distribution were realised. In the second step the current collector structure was patterned. 

The oscillatory deep-channel rheometer described by Nagarajan and Wasan (227) can be used to examine the rheological behavior of liquid/liquid interfaces. The method is based on monitoring the motion of tracer particles at an interface contained in a channel formed by two concentric rings, which is subjected to a well-defined flow field. The middle liquid/liquid interface and upper gas/liquid interface are both plane horizon tal layers sandwiched between the adjacent bulk phase. The walls are stationary while the base moves. In the instrument described for dynamic studies of viscoelastic interfaces the base oscillates sinusoidally. This move ment induces shear stresses in the bottom liquid that are transmitted to the interface. The interfaces are viewed from above through a microscope attached to a rotary micrometer stage which is coaxial to the cylinders. 

The converging-diverging channel geometry for which Guzman and Amon [31] computed flow fields was also considered by Wang and Vanka [43]. They computed the flow and temperature field in an elementary cell of the channel based... 

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