Three-phase flow, microchannels

S)-ibuprofen by means of ionic liquid flow within a microfluidic device. (B, Bottom) Photographs of the three-phase flow in the microchannel (a) center near the inlets of the microchannel, (b and c) arc of the microchannel, and (d) center near the outlets of the microchannel. Flow rates of the aqueous phase and the ionic liquid flow phase in (a-d) were 1.5 and 0.3 mL/h, respectively. (Reprinted from Huh, Y.S., Jun, Y.S., Hong, Y.K., Hong, W.H., and Kim, D.H., /. Mol. Catal. B, 43, 96-101, 2006. Copyright 2006 Elsevier. With permission.)... 

To further stabilize multiphase flow, the liquid-liquid interface can be created at the boundary formed at a constricted opening [427]. Moreover, guide structures (5 pm high) were fabricated in a microchannel (20 pm deep) to stabilize a three-phase flow, as shown in Figure 3.16. These structures were etched on quartz using... 

Figure 3 Photographs of the multiphase laminar flow in the microchannels (a) confluence of water and m-xylene (b) phase separation part (c) confluence of HCI, organic phase, and NaOH and (d) three-phase flow.

In the latter (washing) area, the m-xylene phase containing the Co chelates and the coexisting metal chelates from the former (reaction and extraction) area is interposed between the HC1 and NaOH solutions, which were introduced through the other two inlets at a constant flow rate. Then a three-phase flow, HCl/m-xylene/NaOH, forms in the microchannel. The decomposition and removal of the coexisting metal chelates proceed along the microchannel in a similar manner as described above. Finally, the target chelates in m-xylene are detected downstream by TLM. 

The advantages of this approach compared with conventional methods are simplicity and omission of troublesome operations. The acid and alkali solutions cannot be used simultaneously in the conventional washing method, but this becomes possible by using three-phase flow in the microchannel. This chemical processing corresponds to the integration of eight MUOs on a microchip, two-phase formation, mixing and reaction, extraction, phase separation, three-phase... 

Figure 2 Flow maps of T-junction microchannels. (A) Liquid/liquid two-phase flow in a T-junction microchannel, whose cross-section is 0.52 x 0.2 mm for the main channel and 0.27 x 0.2 mm in for the side channel. The solid dots are from the experiment with water/2 wt% spanSO-dodecane and the hollow dots are from the experiment with octane/3 wt% SDS (sodium dodecyl sulfonate)—water. (B and D) Gas/liquid two-phase and gas/liquid/liquid three-phase flows in a cross-junction microchannel. (C) Liquid/ liquid/liquid three-phase flows in a cross-junction microchannel in a flow-focusing microfluidic device. Panels (B and D) These figures are adapted from Wang et al (2013b) with permission of Wiley. Panel (C) Reprinted from Nieetal (2005) with permission of American Chemical Society.

Wang K, Qin K, Lu YC, et al Gas/liquid/hquid three-phase flow patterns and bubble/ droplet size laws in a double T-junction microchannel, ALCHEJ 61 1722—1734, 2015a. 

A different design for three-phase systems was proposed by Kobayashi et al. [120]. The authors immobilized a palladium catalyst on the glass wall of a capillary and operated the microchannel reactor such that an annular flow pattern was obtained, which is characterized by a liquid film on the wall (Figure 16). The hydrogenation of benzalacetone was used as a model reaction to demonstrate the general applicability of this concept. The authors could achieve an effective interaction between H2, substrate, and the palladium catalyst as a result of the large interfacial area and the short diffusion path in the narrow space. 

Phase separation improvements are based on either surface modification, fluid property control, or physical separation. Studies have shown that organic liquid membranes can be developed in a microchannel device using surface modification [207,208]. An organic liquid membrane consists of an organic phase with aqueous phases on either side. An analyte can be extracted from the aqueous phase, into the organic phase and then back-extracted into the second aqueous phase. These three phases can flow stably within a single microchannel, but better separation of the three phases is possible with surface modification of the organic phase channel (Fig. 7.16). 

Many important technological processes involving flow, transport and chemical reactions take place on or near fluid-solid or fluid-fluid interfaces. Both equilibrium properties of a fluid and transport coefficients are modified in the vicinity of interfaces. The effect of these changes is crucial in the behavior of ultra-thin fluid films, fluid motion in microchannels, etc. It is no less important in macroscopic phenomena involving interfacial singularities, such as rupture, coalescence and motion of three-phase contact lines. 

Multilayer parallel flows can also be formed in microstructured devices and increase the interfacial area, allowing efficient extraction. Hibara et al. had developed a device for three-layer flow [12]. The inlet of the device is branched into three ways. A water-ethyl acetate-water interface is formed in a 70p,m wide and 30 im deep channel (Pyrex glass). The interface is stable and maintained for a distance of more than 18 cm. As an example of application, the liquid-liquid extraction of a codi-methylaminophenol complex in the microchannel was performed. The solvent extraction process of the complex into m-xylene in the multilayer flow was found to reach equilibrium in 4 s, whereas it took 60 s in a simple two-phase extraction. 

The three-layer flow is extended to rapid transport of analytes through an organic liquid membrane [13]. Figure 12.4 shows the experimental setup and a photograph of microchannels near the phase confluence point. In the continuous laminar flow... 

This chapter focuses on description of microstructured reactors for gas-solid, gas-liquid, and three-phase processes, flow regimes, mass transfer considerations for various configurations of microchannels, design criteria, and evaluation of each reactor type. Special attention is devoted to Taylor flow in microchannels, as this flow regime is the most adapted for practical engineering applications. 

Kikutani, Y., Hisamoto, H., Tokeshi, M., Kitamori, T., Micro wet analysis system using multi-phase laminar flows in three-dimensional microchannel network Lab-chip 2004, 4, 328-332. 

The pressure drops for the three different microchannels are compared in Fig. 4.8 for a constant ionic liquid flow rate of Qil = 2.26 cm h. Because of the small differences in the diameters of the three channels, to enable the comparisons the data have been non-dimensionalised by dividing the two-phase pressure drop with that of the ionic liquid flowing alone in the channel (q). 

Flow Cytometer Lab-on-a-Chip Devices, Fig. 6 Micromachined impedance flow cytometer (a) side schematic view of the microchannel showing a particle passing over three electrodes (A, B, and C). The impedance signal is measured differently (Zac - Zbc). As the distance between two measurement areas and time separating the signal spikes are known, the speed of the particle can be calculated, and (b) signal in-phase amplitude of 2,000 erythrocytes and ghost cells recorded simultaneously for two frequencies [9]... 

In order to transport fluids in microfluidic systems with a liquid flow layer and a pneumatic control layer, a pneumatic pump typically consists of three pneumatic actuators (pneumatic microvalves) in the pneumatic control layer and a microfluidic channel in the liquid flow layer, as schematically shown in Fig. 1 [1]. The two layers are separated by an elastic membrane, such as a film of PDMS materials. The time-phased deflection of elastic membranes at the top of pneumatic actuators along the microchannel length can generate a peristaltic effect which drives the fluid from the inlet to outlet along the microfluidic channel in the liquid flow layer. The deflection of elastic membranes and the actuatirm... 

When the operation of a solenoid valve makes one of the three pneumatic actuators on the microchip connected with the compressed air source, as shown in Fig. 4a, the pressure in the pneumatic actuator will rise up and the elastic membrane will deflect propelling liquids and consequently shutting down the flow in the liquid flow channel. When the operation of a solenoid valve makes a pneumatic actuator connected with the atmosphere, as shown in Fig. 4b, the pressure in the pneumatic actuator will equal to the atmospheric pressure. The elastic membrane will release and the actuator stops working. The time-phased deflection of three elastic membranes along the microchannel length can be realized by the sequence actuation of three external pneumatic solenoid valves. Since each solenoid valve in the supporting system is connected directly to one actuator on the microfluidic chip. 

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