Auto-Ignition and Reaction Front Dynamics in Mixtures With Temperature and Concentration Stratification

We review recent developments in the study of the diffusion reaction system of the type A+B→C in which the reactants are initially separated. We consider the case where the A and B particles are initially placed uniformly in Euclidean space at x>0 and x<0 respectively. We find that whereas for d≥2 a single scaling exponent characterizes the width of the reaction zone, a multiscaling approach is needed to describe the one-dimensional system. We also present analytical and numerical results for the reaction rate on fractals and percolation systems.

Download Full-text

Scaling anomalies in reaction front dynamics of confined systems

Physical Review Letters ◽

10.1103/physrevlett.71.3592 ◽

1993 ◽

Vol 71 (21) ◽

pp. 3592-3595 ◽

Cited By ~ 55

Author(s):

Mariela Araujo ◽

Hernan Larralde ◽

Shlomo Havlin ◽

H. Eugene Stanley

Keyword(s):

Reaction Front ◽

Confined Systems ◽

Front Dynamics

Download Full-text

Study of an A+2B--->C Reaction-Diffusion System with Initially Separated Components

MRS Proceedings ◽

10.1557/proc-366-319 ◽

1994 ◽

Vol 366 ◽

Author(s):

Andrew Yen ◽

Raoul Kopelman

Keyword(s):

Reaction Front ◽

Reaction Rate ◽

Reaction Diffusion ◽

Biological Processes ◽

Local Production ◽

Kinetic Behavior ◽

Acetate Trihydrate ◽

Physical Chemical ◽

Global Reaction ◽

Front Dynamics

ABSTRACTThe presence of a reaction front is a characteristic feature of a variety of physical, chemical and biological processes. A chemical reaction exhibits a front (spatially localized region where concentration of product is non zero), provided the diffusing reactants are separated in space. We study the reaction front dynamics of a termolecular A+2B--->C reaction with initially separated components in a capillary. The reaction tetra+2Ni2+--->1:2 complex is used, where ‘tetra’ is disodium ethyl bis(5-tetrazolylazo) acetate trihydrate. We measure and compare with theory the dynamic quantities that characterize the kinetic behavior of the system: the global reaction rate R(t), the location of the reaction center xf(t), the front's width w(t), and the local production rate R(xf,t). The non-classical nature of this dynamical system is confirmed.

Download Full-text

Experimental Study of An A+B→C Reaction-Diffusion System in a Capillary: Crossovers from Reaction to Diffusion-Limited Regimes

MRS Proceedings ◽

10.1557/proc-290-273 ◽

1992 ◽

Vol 290 ◽

Cited By ~ 4

Author(s):

Yong-Eun Koo ◽

Raoul Kopelman ◽

Andrew Yen ◽

Anna Lin

Keyword(s):

Experimental Study ◽

Reaction Zone ◽

Reaction Front ◽

Reaction Rate ◽

Local Reaction ◽

Reaction Diffusion ◽

Theoretical Studies ◽

Boundary Motion ◽

Diffusion Limited ◽

Front Dynamics

AbstractContinuing work on elementary A+B→C reactions in capillaries, we study the reaction front dynamics of xylanol orange with Cr3+ in an effectively one-dimentional system with initially separated reactants. This reaction, in contrast to previously studied systems, is not strictly in the diffusion limited regime. i.e. the probability of reaction between species is not unity. Anamalous behavior not seen in the diffusion-limited case has been observed experimentally for the reaction rate, boundary motion, reaction zone width, and local reaction rate. The observed behavior is consistent with recent theoretical studies.

Download Full-text

Reaction front dynamics of A + B → C with initially separated reactants

Physica A Statistical Mechanics and its Applications ◽

10.1016/0378-4371(92)90521-q ◽

1992 ◽

Vol 191 (1-4) ◽

pp. 168-171 ◽

Cited By ~ 7

Author(s):

Mariela Araujo ◽

Hernan Larralde ◽

Shlomo Havlin ◽

H.E. Stanely

Keyword(s):

Reaction Front ◽

Front Dynamics

Download Full-text

Numerical Investigation of Auto-Ignition Characteristics in Microstructured Catalytic Honeycomb Reactor for CH4–Air and CH4–H2–Air Mixtures

Journal of Energy Resources Technology ◽

10.1115/1.4042825 ◽

2019 ◽

Vol 141 (8) ◽

Author(s):

H. Kayed ◽

A. Mohamed ◽

M. Yehia ◽

M. A. Nemitallah ◽

M. A. Habib

Keyword(s):

Flow Rate ◽

Ignition Temperature ◽

Reaction Front ◽

Equivalence Ratio ◽

Thermal Conditions ◽

Flammability Limits ◽

Transient Conditions ◽

Auto Ignition ◽

Transient Simulations ◽

Ignition Characteristics

Stable ranges of auto-ignition for the microcombustion of CH4 and CH4–H2 mixtures are identified numerically in a platinum-coated microcatalytic honeycomb reactor. Steady and transient simulations under pseudo-auto-thermal conditions were performed to investigate the coupling phenomenon between combustion and heat transfer in such microburner using ANSYS 17.2 coupled with a detailed chemkin reaction mechanism. The model was validated utilizing the available data in the literature on a similar microreactor, and the results showed good agreements. A certain amount of heat is furnished from outside at constant temperature from an external electric furnace to investigate the variations of localized self-ignition temperature while changing the flow rate and mixture strength. It was found that the ignition temperature for CH4–air mixtures is not affected by the mass flow rate. However, the ignition temperature of CH4–H2 air mixtures decreases while increasing the flow rate. The effect of equivalence ratio was studied to demonstrate the variations of flammability limits of the present microreactor. The equivalence ratio required for auto-ignition of CH4–air mixtures was found to be in the range from 0.4 up to 0.85 at a flow rate of 9.5 g/s. The reaction front moved from upstream to downstream under transient conditions matching with the reported experimental behavior in the literature.

Download Full-text