Coflow

M. K. Kim, S. H. Won, and S. H. Chung, Effect of velocity gradient on propagation speed of tribrachial flames in laminar coflow jets, Proc. Combust. Inst. 31 901-908,2007. 

More recently, experimental studies have been carried out using a similar device but with an annular external hot coflow of burned gases that allowed one to operate within a much larger velocity range. Chen et al. [26] and more recently Chen and Bilger [27,28] have studied the perturbations that the smallest scales of turbulence can impose to the local flamelet structures. Those studies are of paramount importance, first because they have allowed to get deeper insights into the local structure... 

Calculated species mole fractions, temperature, and heat-release rate across a gaseous n-heptane diffusion flame (18 mm o.d., fuel velocity 0.1 cm/s) in coflowing air (velocity 10.7cm/s) at a height of 10.8mm inly. 

Walsh, K.T., Fielding, J., Smooke, M.D., and Long, M.B., Experimental and computational study of temperature, species, and soot in buoyant and non-buoyant coflow laminar diffusion flames, Proc. Combust. Inst., 28, 1973, 2000. 

In Chapter 8.1, F. Takahashi presents candle and laminar jet diffusion flames highlighting fhe physical and chemical mechanism of combustion in a candle and similar laminar coflow diffusion flames in normal gravity and in microgravity. This apparently simple system turns out to be very complex, and thereby its study is of greaf importance for the understanding of diffusion flame fundamentals. 

However, many reactions of commercial interest have chemistry, mechanical, or system requirements that preclude the use of cross-flow reactors. Processes cannot use a cross-flow orientation primarily because of high temperatures and the need to internally recuperate heat such as steam methane reforming (SMR) [12, 13] and oxidation reactions [14]. Counter- and coflow devices require a micromanifold to dehver sufficiently uniform flow to each of the many parallel channels. 

For premixed fuel-air systems, results are reported in various terms that can be related to a critical equivalence ratio at which the onset of some yellow flame luminosity is observed. Premixed combustion studies have been performed primarily with Bunsen-type flames [52, 53], flat flames [54], and stirred reactors [55, 56], The earliest work [57, 58] on diffusion flames dealt mainly with axisymmetric coflow (coannular) systems in which the smoke height or the volumetric or mass flow rate of the fuel at this height was used as the correlating parameter. The smoke height is considered to be a measure of the fuel s particulate formation and growth rates but is controlled by the soot particle bumup. The specific references to this early work and that mentioned in subsequent paragraphs can be found in Ref. [50],... 

Work on coflowing Wolfhard-Parker burners [59,60], axisymmetric inverse coflowing configurations (oxidizer is the central jet) [61, 62], and counterflow... 

Figure 17. Mole fraction of water vapor, hydrogen, and oxygen in the gas channels at a cell potential of 0.72 V, at a temperature of 80 °C, and in a coflow arrangement. The local current density is shown by the solid line. (Reproduced with permission from ref 15. Copyright 1993 The Electrochemical Society, Inc.)...

The 2-D models also allow for different effects to be studied in depth. For example, the simulations show that, as mentioned above, countercurrent flow yields better performance than coflow due to water recycling. This is something that a 1-D... 

Cl) Constant flow 2 B, Dc, Ib, S, W Also extended to coflowing stream... 

N. Sullivan, A. Jensen, P. Glarborg, M.S. Day, J.F. Grcar, J.B. Bell, CJ. Pope, and RJ. Kee. NO Formation and Ammonia Conversion in Laminar Coflowing Non-premixed Methane-Air Flames. Combust. Flame, in press, 2002. 

Since selectivity is a function of the local permeate flux, and thus the local transmembrane pressure, selectivity can be further improved by maintaining a nearly uniform and low transmembrane pressure throughout the ultrafiltration module. Following the early work from Sandblom, HPTFF technology uses, when required, a cocurrent permeate flow that is accomplished by the addition of a coflow loop and pump on the permeate side. 

Early work on premixed Bunsen flames and coflowing diffusion flames [69-71] was repeated in experiments where the temperature was controlled by varying... 

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