Microreactors fluid flow

The distinctive fluid flow, thermal and chemical kinetic behavior, observed in microreactors, as well as their size and energy characteristics, contribute to their usefulness in diverse applications [1-3] including ... 

Monophasic fluid flow in capillary-scale ducts is characterized by a low Reynolds number, the flow in capillary-scale microreactors is generally laminar and transport... 

Figure 4-12 shows (a) a microreacior with heat exchanger and (b) a microplant with reactor, valves, and mixers. Heat. Q, is added or taken aw ay by the fluid flowing perpendicular to the reaction channels a.s shown in Figure 4-12(a). Production in microreactor systems can he increased simply by adding more units in parallel. For example, the catalyzed reaction... 

Patents related in process control in microreactor are largely focused on achieving high regulation in flow distribution and ensured operations. How distribution control for liquid-liquid reactions and reducing the pressure fluctuations of a fluid flowing in microreactors are major points to achieve the precise process control in microreactors. 

In the course of the fast growing development of microfluidic devices like Lab-on-a-Chip, microreactors, and micro heat pipes, it is essential to develop effective systems for measuring the temperature distribution in the microscale. For example, for observing the heat transfer in microchannel flows, it is a matter of particular interest to know both the temperature distribution along the wall and the temperature distributirHi in the fluid flow. Conventional methods for temperature measurements are based on thermocouples and resistance thermometers which have a minimum size of about 10 pm and which always interfere with the system to be measured. Contactless methods for measuring temperature, e.g., infrared thermography, have many... 

Ahmed-Omer, B., Barrow, D., and Wirth, T. (2007) Effect of segmented fluid flow, sonication and phase transfer catalysis on biphasic reactions in capillary microreactors. Chem. Eng. J, 135 (Suppl. 1), S280-S283. 

Fig. 1 Microreactor (Institut fur Mikrotechnik, Mainz (IMM)) left sketch of fluid flows. Right picture of the whole reactor block...

Design rules for microreactors have already been formulated and many aspects are generally well understood. Heat and mass transfer in single-phase fluid flow in microchannels has been extensively studied during the last 15 years, and it was demonstrated that classical engineering correlations for calculation of heat and mass transfer coefficients can be used. For example, for fully developed laminar flow, the Nusselt number is a constant... 

Owing to the high degree of parallelization, the scale-up of the microreactor is relatively simple as long as the equipartition of the fluid flow through the channels is achieved. 

The uniform and well-defined fluid flow conditions of microreactors also provide opportunities to better control the dynamics of nanomaterial synthesis. Kroon et cd. [102] studied the eSects of mixing on the coagulation processes of CdS NPs vrithout a stabilizer using simple predpitation reaction of CdN03 and Na2S. Their results indicate that the use of a static micromixer and laminar flow reactor could produce a dispersed CdS NP solution that is stable for hours. In contrast, the batch reactor... 

Choi et al. [104] synthesized ZnO NCs using a continuous-flow microreactor system. The growth mechanism and stability of ZnO NCs were studied by varying the pH value of the aqueous solution and flow conditions. It was found that external forces from convective fluid flow could affect the assembly of ZnO NCs and result in different shapes at pH 13. The ZnO NC assemblies formed particular structures such as a tactoid structure or a semispherical structure via an attachment growth mechanism. The assembly results from a competing interaction between electrostatic force caused by surface charge of NCs and external force from convective fluid flow. This study shows that the external forces from convective fluid flow could be applied to fabricate assembly of functional metal oxides with complex architectures in a continuous-flow microreactor system. 

Hsing et al. [66] presented simulations of two- and three-dimensional fluid flows, thermal fields, and chemical species concentrations in microreactors for the Pt-catalyzed NH3 oxidation in the T-shaped microreactor. Simulations and experiments showed good agreement and reactions were mass transfer limited. Therefore, it is not possible to obtain kinetic information, that is, details of the kinetic mechanism from the simulation data. Nevertheless, the comparison of predicted and experimental data demonstrates that it is possible to accurately predict and understand transport phenomena in microreactors, which is often difficult to obtain with macroscopic systems because of flow distributors, baffles, and turbulence. 

A distinctive feature of microreactors is the microchannels for fluid flow. MMRs are mainly characteristic of such microchannels with anchored catalysts for reactions and miniature membranes to perform separation, which are formed on the porous ceramic or metal supports. Based on the configuration and architecture of the reactor, MMRs can be classified into two categories plate type and tubular type. 

When the membrane tube is reduced in diameter to a certain level, that is, ID < 1 mm, it becomes a hollow fiber and the fiber lumen may take on the effect of a microchannel on the fluid flow. The catalyst can be coated on the inner surface of the hollow fiber or impregnated inside the porous wall, while the separation is achieved by the porous hollow fiber itself or by the membrane formed on the outer surface of the hollow fiber, as shown in Figure 8.5. Such catalytic hollow fiber membranes can easily be fabricated into MMRs, called hollow fiber membrane microreactors (HFMMRs). 

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