Transport-chemistry coupling in cocurrent and countercurrent flow configurations: Applications to nonlinear dynamics of flames and deposition of membranes in porous media

2003 2003

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Abstract (summary)

The focus of this dissertation is on modeling and analysis of prototype problems of reacting flows interacting with surfaces or in porous media. In particular, flammability limits of gaseous and condensed fuels, complex nonlinear dynamics of flames, and deposition of thin membranes within porous substrates have been studied.

The regime of self-sustained methane-air combustion has been first identified in the parameter space of strain rate-fuel flow rate, for a gaseous diffusion flame. Additionally, the regime of absolute stability, where heat losses at the surface do not extinguish a flame, has also been mapped. It has been found that the critical extinction mass pyrolysis rate is insensitive to thermo-transpo-kinetic details at high values of modified Damköhler numbers, whereas is very sensitive at low values. Selected comparisons with experimental results have been made to validate our numerical predictions.

The regime of oscillatory instabilities in hydrogen-air combustion was systematically mapped for the first time for premixed and diffusion flames. It has been demonstrated that premixed hydrogen-air flames exhibit complex dynamics including chaos at high pressures. The interplay of autocatalytic chemistry with transport, reaction exothermicity, and flow, inherent to distributed flames, has been identified to be the cause for the observed chaotic dynamics.

Finally, a multiscale computational framework for deposition of films within porous substrates is developed and applied to the opposed flow geometry. The model captures transport of reactants through the pores described by the dusty gas model, homogeneous reaction of the organometallic precursor producing an intermediate species, nucleation (treated stochastically), and growth of the film as a moving boundary problem. Adaptive mesh refinement is used to resolve length scales varying from nanometers to one millimeter. The numerical results provide insight into how to confine thin films within substrates and control their thickness. For example, it has been found that the location of the metal deposit within the porous substrate is essentially determined by the relative concentrations of H2 and the organometallic precursor. Additionally, it is shown that the interplay of nucleation and growth kinetics determines the morphology of the deposit at short time scales.

Indexing (details)

Chemical engineering
0542: Chemical engineering
Identifier / keyword
Applied sciences; Deposition; Flames; Membranes; Nonlinear dynamics; Porous media
Transport-chemistry coupling in cocurrent and countercurrent flow configurations: Applications to nonlinear dynamics of flames and deposition of membranes in porous media
Gummalla, Mallika
Number of pages
Publication year
Degree date
School code
DAI-B 64/01, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
9780493997049, 0493997040
Vlachos, Dionisios G.
University of Massachusetts Amherst
University location
United States -- Massachusetts
Source type
Dissertations & Theses
Document type
Dissertation/thesis number
ProQuest document ID
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
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