Micro flow field

Leo, H.L., He, Z.M., Ellis, J., and Yoganathan, A., Micro flow fields in the hinge region of CarboMedics bileaflet mechanical valve design. / Jhorac Cardiovasc Surg, 2002.124 p. 561-74. 

Fig. 16 Performance characteristics of cells. Patterning of micro flow field...

In this work, the MeOH kinetic model of Lee et al. [9] is adopted for the micro-channel fluid dynamics analysis. Pressure and concentration distributions are investigated and represented to provide the physico-chemical insight on the transport phenomena in the microscale flow chamber. The mass, momentum, and species equations were employed with kinetic equations that describe the chemical reaction characteristics to solve flow-field, methanol conversion rate, and species concentration variations along the micro-reformer channel. 

Strictly, chemical micro processing, in addition to being a device field based on micro channels, is a means to use micro flows, which is oriented not at one, but rather at a multitude of purposes. Process intensification, also strictly, is a concept (but specifying no concrete means) and apparatus for a specific purpose (see above). 

Micro Total Analysis Systems (pTAS) are chip-based micro-channel systems that serve for complete analytics. The word Total refers to the monolithic system character of the devices, integrating a multitude of miniature functional elements with minimal dead volumes. The main fields of application are related to biology, pharmacology, and analytical chemistry. Detailed applications of pTAS systems are given in Section 1.9.8. Recently, pTAS developments have strongly influenced the performance of organic syntheses by micro flow (see, e.g., [29]). By this, an overlap with the micro-reactor world was made, which probably will increase more and more. 

Also a simulation of the flow field in the methanol-reforming reactor of Figure 2.21 by means of the finite-volume method shows that recirculation zones are formed in the flow distribution chamber (see Figure 2.22). One of the goals of the work focused on the development of a micro reformer was to design the flow manifold in such a way that the volume flows in the different reaction channels are approximately the same [113]. In spite of the recirculation zones found, for the chosen design a flow variation of about 2% between different channels was predicted from the CFD simulations. In the application under study a washcoat cata-... 

Figure 2.46 Section of a micro channel with electrodes embedded in the channel walls (left). When an electric field is applied along the channel, different flow patterns may be created depending on the potential of the individual electrodes. The right side shows the time evolution of an ensemble of tracer particles initially positioned in the center of the channel for a flow field alternating between the single- and the four-vortex pattern shown on the left [144].

This sheet micro flow reactor (Figure 4.32) was used for investigating spatially two-dimensional effects in reaction media using agar gel induced by electric fields [68]. This device utilizes an adapted Petri dish which comprises a rectangular channel... 

The most commonly utilized embedded sensor for temperature distribution mapping is the thermocouple. Wilkinson et al.130 developed a simple, in-situ, and noninvasive method of measuring the temperature distribution of a fuel cell with micro-thermocouples. In this study, thermocouples were located in the landing area of the flow field plates (in contact with the GDL of the MEA) of a fuel cell. The temperature data taken at different locations along the flow channel was then used to find each temperature slope, which in turn were related through mathematical equations to the local current density of each location. Thus, the current density distribution in the fuel cell was determined by simple temperature measurements. The results of this approach are discussed in more detail in Section... 

The structure of the experimental SCISR is the same as that shown in Fig. 10.2 for convenience of operation it is without cover. The propellers are driven by two motors of stable speeds and with a stepless-speed-adjustable device. Highly accurate micro pressure probes of Model XCQ-062 made by the Kulite Corporation are used for measuring the pressure fluctuation. The outside diameter of the probes is 1.6 mm, which is very small in comparison with the dimensions of the reactor so that their influence on the flow field can be negligible. In addition, the inherent frequency of the probes is 330 kHz, much higher than those to be measured, and thus complete fluctuation signals can be detected without any loss. 

Figure 1.114 Schematic of the cyclone mixer design (left) and streamline indicating the rotational flow field in the cyclone micro mixer [109] (by courtesy of Kluwer Academic Publishers).

Behavior of the fluids in the microfabricated channels are different from those in the millimeter scale channels. Miniaturization of micro flow devices opens a new research field, microfluidics which represents the behavior of the fluid in the micro channel [8]. Since the Reynolds number in the micro channel is usually below 200, the flow is laminar and special design concepts are necessary for the fluidic elements of mixers, reaction coils etc. in the pTAS. Some components of flow switches and fluid filters were developed using laminar flow behavior. 

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 ... 

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