Co-flowing streams

In conventional single phase microfluidic systems, flow in the microchaimel is laminar a parabolic velocity profile is established with fluid velocity zero at the channel walls and maximum at the channel center [18, 21] (Fig. 9a). There are two implications to this behavior (1) a reagent sample plug will constantly dissipate along the microchannel, and (2) the mixing of samples could be very slow in co-flow streams. 

Y-junction. Flow rates were tuned so that a two-colored parallel flow was obtained. Then this co-flow stream entered the sheath junction and came into contact with two aqueous streams containing 2 wL% of PVA. The resulting Janus droplets were collected outside the device and cured by heat-induced polymerization, resulting in Janus polymer particles (Figure 18.13, bottom). In a subsequent study, Nisisako et al. [18] pushed further the production of Janus particles by integrating 16 SFMDs... 

Subsequently the catalyst-electrode is immediately exposed to a flowing stream of C2H4 (or CO) in He and an infrared C02 analyzer is used to monitor the mole fraction, yco2> of C02 formed by the reaction of C2FLi (or CO) with adsorbed oxygen. By integrating the peak area one determines the amount N0 (mol O) of O adsorbed on the surface after the desorption time W... 

By changing the flow direction of gas and liquid streams, a co-flow and counterflow guidance is in principle possible however, owing to the low gas velocities usually employed, this makes no practical difference [5],... 

It should be noted that rather than exploiting the proactive aspects of a surface, it is equally valid to mask or negate wall effects by fluidically isolating the sample from the substrate channel wall to eliminate surface effects. This is carried out by using either a co-axial flow to keep the sample in the centre, i.e. away from the walls (Takagi et al. 2004) or in a similar way using multiple flow streams to surround the sample stream to form a sheath (Munson et al. 2004,2005). 

Plain-orifice atomizers are widely used for injecting liquids into a flow stream of air or gas. The injection may occur in a co-flow, a contra-flow, or a cross-flow stream. The best known application of plain-orifice atomizers is perhaps diesel injectors. This type of injectors is designed to provide a pulsed or intermittent supply of fuel to the combustion zone for each power stroke of the piston. As the air in the combustion zone is compressed by the piston to a high pressure, a very high pressure (83-103 MPa) is required to allow the fuel to penetrate into the combustion zone and disintegrate into a well-atomized spray. 

Table 3.2. Classification and Criteria of Breakup Regimes of Round Liquid Jets in Co-flowing Air as Compared to Those of Thin Liquid Sheets and Spherical Droplets in Air Stream 210 ...

Arai and Hashimoto[2611 studied disintegration of a thin liquid sheet in a co-flowing air stream. For a constant sheet thickness, an empirical correlation was derived for the sheet breakup length as ... 

As Kang el al. [3] have reported, counter-flow diffusion flames are located on the oxidizer side when hydrocarbons are the fuel. Appropriate dilution with inert gases of both the fuel and oxidizer streams, frequently used in the co-flow situation, can position the flame on the fuel side. It has been shown [4] that the criterion for the flame to be located on the fuel side is... 

The flow involves fuel, F, issuing from a central slot of width D with an oxidizer, O, co-flow with both streams at the reference temperature, Tq. A global single-step, irreversible, exothermic chemical reaction of the type F + rO —> (1 -f r)P with an Arrhenius reaction rate coefiicient is assumed. A hot layer of combustion products, P, at the inlet serves to separate the fuel and oxidizer streams and acts as an ignition source. The inlet conditions for the velocity, temperature, and composition are shown in Fig. 10.2. The ratio of the inlet velocities of the fuel to oxidizer streams is chosen as 4. Inlet velocity forcing is used to induce early roll-up and pairing of the jet shear layer vortices. 

Figure 23.8 presents axiai pressure distributions for two tests for which air-barbotated kerosene was injected through round (test run No. 11) and elliptic nozzles (test run No. 12) located at the base of fin-pylons in the co-flow direction of the main-stream flow. One can conclude from Fig. 23.8 that the combustion-induced pressure rises for elliptic and round nozzles are nearly the same, i.e., mixing and combustion efficiencies practically remain the same for both t q)es of nozzles. 

This conclusion is confirmed by the calculation of the combustion-induced pressure-area integrals for both types of nozzles (Fig. 23.9). It follows from comparison of Figs. 23.6 and 23.9 that tube-micropylons with injection at an angle of 45° relative to the main-stream air flow direction provide better performance than fin-pylons with co-flow injection. 

For the horizontal variant, counter-, cross- and co-flow injection schemes are given (large arrows). The alternating streams enter the mixing channel in all cases as co-flows (small arrows) [39],... 

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