Microchannel inlet

Several flow patterns are observed during condensation inside a microchannel. Figure 9.18 shows representative flow regimes in a microchannel at different locations from the microchannel inlet. Five distinct flow regimes as identified are discussed below. 

To optimize the design of the manifold configuration, a number of numerical calculations were conducted for three types of manifolds shown in Fig. 2.66. Figure 2.67 shows the velocity distribution at 2 mm from the inlet to the microchannels, from which one can conclude that configuration 1 and 2 ensure uniform velocity distribution at the entrance. 

The experimental data obtained in conventional size channels and micro-channels with diameters between 100 pm and 6.0 mm are examined to further elucidate and understand the differences in two-phase flow characteristics between the microchannels and conventional size channels. Since two separate sets of experiments have been conducted using air and water in acrylic channels with diameters between 500 pm and 6.0 mm, and nitrogen gas-water in fused silica channels with diameters between 50 and 500 pm, the authors refer to the former channels as conventional size channels, and the latter channels as micro-channels for convenience. Two different inlet sections were covered in micro-channel experiments, a gradually reducing section and a T-junction. 

Galbiati L, Andreini P (1992) Elow patterns transition for vertical downward two-phase flow in capUlary tubes. Inlet mixing effects. Int Comm Heat Mass Transfer 19 791-799 Garimella S, Sobhan C (2003) Transport in microchannels - a critical review. Ann Rev Heat Transfer 13 1-50... 

The test module consisted of inlet and outlet manifolds that were jointed to the test chip (Fig. 6.20). The tested chip with heater is shown in Fig. 6.21. It was made from a square shape 15 x 15mm and 0.5 mm thick silicon wafer, which was later bonded to a 0.53 mm thick Pyrex cover. On one side of the silicon wafer 26 microchannels were etched, with triangular shaped cross-sections, with a base of 0.21 mm... 

Initially, the reactor was to be built using silicon wafers, 92 but more recent efforts have focused on a stainless steel reactor. The reformer, 7.5 x 4.5 x 11.0 cm (371 cm ), houses up to 15 stainless steel plates (0.5 mm thick) with chemically etched microchannels and heating cartridges. Conventional and laser micromachining techniques were used to fabricate the reformer body. The microchannel dimensions are 0.05 x 0.035 x 5.0 cm . The reactor inlet was carefully designed to allow uniform flow conditions. ... 

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.)... 

Figure 36.2. Left cross section of a microchannel with an inlet port, a channel, an outlet port and integrated gold electrodes. Right a cartridge containing eight parallel microchannels, embedded in a white polymer support, serving as rigidifier, guide and reservoir.

Micropumps based on piezoelectrics are made of pumping chambers that are actuated by three piezoelectric lead zirconate titanate disks (PZT). The pump consists of an inlet, pump chambers, three silicon membranes, three normally closed active valves, three bulk PZT actuators, three actuation reservoirs, flow microchannels, and outlet. The actuator is controlled by the peristaltic motion that drives the liquid in the pump. The inlet and outlet of the micropump are made of a Pyrex glass, which makes it biocompatible. Gold is deposited between the actuators and the silicon membrane to act as an upper electrode. Silver functions as a lower electrode and is deposited on the sidewalls of the actuation reservoirs. In this design, three different pump chambers can be actuated separately by each bulk PZT actuator in a peristaltic motion. 

Surface energy present in a small liquid drop at the inlet reservoir was used to pump the liquid through a PDMS microchannel [398]. 

Kitamori s group has proposed selective chemical surface modification utilizing capillarity (called the capillarity restricted modification or CARM method) (Hibara et al., 2005). In the CARM method, a microchannel structure combining shallow and deep microchannels and the principle of capillarity are utilized. The procedures are shown in Figure 19. A portion of an ODS/toluene solution (lwt%) is dropped onto the inlet hole of the shallow channel, and the solution is spontaneously drawn into this channel by capillary action. The solution is stopped at the boundary between the shallow and deep channels by the balance between the solid-liquid and gas-liquid interfacial energies. Therefore, the solution does not enter the deep channel. It remains at the boundary for several minutes and is then pushed from the deep channel side by air pressure. 

Figure 19 Modification procedures by CARM method, (a) The shallow and deep microchannels have separate inlet holes and contact points in the microchip, (b) A solution containing modification compounds is introduced from the inlet of the shallow microchannel by capillarity, (c) The solution does not leak to the deep microchannel and only the shallow microchannel is modified, (d) The solution is pushed away with air pressure from the deep microchannel. (e) A sectional illustration along the s-s dashed line in (d) (Hibara et al, 2005).

The industrially important nitration of aromatic compounds in a microreactor using two immiscible liquid phases was demonstrated in different studies using either parallel [220] or segmented flow [221]. In all studies, a PTFE capillary microchannel, connected to an inlet junction, was used in which either segmented or parallel flow can be created. The use of PTFE tubing is desirable as it is commercially available and no complicated microfabrication methods are involved. 

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. 

Figure 14 Fabrication procedure for the pile-up microreactor. (1) Photolithography Conventional photolithography/wet etching methods were applied. The back side of the glass plate was covered with polyolefin tape during the HF treatment. (2) Drilling Penetrating holes were drilled at the inlet and outlet ports of the micro-channel circuit. (3) Thermal bonding The required number of glass plates with microchannels and one cover plate were laminated and bonded thermally at 650°C.

Garimella and Bandhauer [32] conducted heat transfer experiments using the same test sections that were used for the pressure drop experiments of Garimella et al. [24, 25, 27, 28] described above. The high heat transfer coefficients and low mass flow rates in microchannels necessitate modifications to the test facility and test procedures described above. For the small zlx required in the test section, the heat duties at the mass fluxes of interest are relatively small. Calculating this heat duty from the test section inlet and outlet quality measurements would result in considerable... 

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