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

Study of A+B-4C and A+2B–C Reaction-Diffusion System with Initially Separated Components

MRS Proceedings ◽

10.1557/proc-407-119 ◽

1995 ◽

Vol 407 ◽

Author(s):

Andrew Yen ◽

Raoul Kopelman

Keyword(s):

Dynamical System ◽

Reaction Front ◽

Reaction Rate ◽

Reaction Diffusion ◽

Biological Processes ◽

Local Production ◽

Kinetic Behavior ◽

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. The reaction exhibits a front, provided that the diffusing reactants are separated in space. We study the reaction front dynamics of both A+B→C bimolecular and A+2B→C termolecular reactions with initially separated components in a capillary. We measure and compare with theory and simulations 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(xft). 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

Experimental Study of a Reaction-Diffusion System in a Capillary: Complex Behavior of a Seemingly Simple System

MRS Proceedings ◽

10.1557/proc-366-389 ◽

1994 ◽

Vol 366 ◽

Author(s):

Anna Lin ◽

Andrew Yen ◽

Yong-Eun Koo ◽

Raoul Kopelman

Keyword(s):

Reaction Front ◽

Reaction Rate ◽

Capillary Tube ◽

Xylenol Orange ◽

Reaction Diffusion ◽

Reaction Diffusion System ◽

Diffusion System ◽

Product Concentration ◽

Global Rate ◽

Global Reaction

ABSTRACTWe study a reaction-diffusion system within the confines of a thin capillary tube. Xylenol orange and Cr 3+ are introduced into a capillary tube from opposite ends and meet in the middle forming a reaction front. Unequal initial concentrations of the reactants causes the center of the reaction front to move in time. Characteristics of the front such as the width of the reaction zone, w, the position of the center of the front, xf, the global reaction rate, R, and the local reaction rate, r(xf,t) are determined by continuously monitoring the product concentration in space vs. time. We observe crossover of the global rate from classical to non-classical behavior and a splitting of the reaction front.

Download Full-text

REACTION-FRONT DYNAMICS IN A+B→C WITH INITIALLY-SEPARATED REACTANTS

Fractals ◽

10.1142/s0218348x93000423 ◽

1993 ◽

Vol 01 (03) ◽

pp. 405-415 ◽

Cited By ~ 8

Author(s):

S. HAVLIN ◽

M. ARAUJO ◽

H. LARRALDE ◽

A. SHEHTER ◽

H.E. STANLEY

Keyword(s):

Reaction Front ◽

Reaction Rate ◽

Reaction System ◽

Diffusion Reaction ◽

Dimensional System ◽

Scaling Exponent ◽

One Dimensional ◽

Recent Developments ◽

The One ◽

Front Dynamics

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

Crossover Time Behavior in a+b⃗c And a+2b⃗c Reaction-Diffusion Front Systems in a Capillary

MRS Proceedings ◽

10.1557/proc-543-237 ◽

1998 ◽

Vol 543 ◽

Author(s):

Sung Hyun Park ◽

Andrew Yen ◽

Zhong-You Shi ◽

Raoul Kopelman

Keyword(s):

Reaction Rate ◽

Early Time ◽

Reaction Diffusion ◽

Time Behavior ◽

Explicit Dependence ◽

Diffusion Front ◽

Front Width ◽

Time Regime ◽

Global Reaction ◽

Mechanism Of The Reaction

AbstractThe crossover time from the early-time regime to the asymptotic regime for the A+B⃗+C reaction-diffusion system with initially separated reactants has been derived analytically by matching the rate expressions for the two regimes. The crossover time expression thus obtained shows an explicit dependence on the rate constant (k) and the initial reactant concentrations (ao, bo). For the A+2B⃗C system we performed computer simulations using two different methods. Crossover behaviors for the global reaction rate and reaction front width have been observed for both methods. The crossover time depends on the mechanism of the reaction.

Download Full-text

Physical-Chemical and Thermodynamic Analyses of Ethanol Steam Reforming for Hydrogen Production

Journal of Fuel Cell Science and Technology ◽

10.1115/1.2217957 ◽

2006 ◽

Vol 3 (3) ◽

pp. 346-350 ◽

Cited By ~ 11

Author(s):

Antonio Carlos Caetano de Souza ◽

José Luz-Silveira ◽

Maria Isabel Sosa

Keyword(s):

Hydrogen Production ◽

Steam Reforming ◽

Production Efficiency ◽

Physical Chemical ◽

Steam Reforming Of Ethanol ◽

Thermodynamic Conditions ◽

High Production ◽

Exergetic Analysis ◽

Global Reaction ◽

Technical Features

Steam reforming is the most usual method of hydrogen production due to its high production efficiency and technological maturity. The use of ethanol for this purpose is an interesting option because it is a renewable and environmentally friendly fuel. The objective of this article is to present the physical-chemical, thermodynamic, and exergetic analysis of a steam reformer of ethanol, in order to produce 0.7Nm3∕h of hydrogen as feedstock of a 1kW PEMFC. The global reaction of ethanol is considered. Superheated ethanol reacts with steam at high temperatures producing hydrogen and carbon dioxide, depending strongly on the thermodynamic conditions of reforming, as well as on the technical features of the reformer system and catalysts. The thermodynamic analysis shows the feasibility of this reaction in temperatures about 206°C. Below this temperature, the reaction trends to the reactants. The advance degree increases with temperature and decreases with pressure. Optimal temperatures range between 600 and 700°C. However, when the temperature attains 700°C, the reaction stability occurs, that is, the hydrogen production attains the limit. For temperatures above 700°C, the heat use is very high, involving high costs of production due to the higher volume of fuel or electricity used. The optimal pressure is 1atm., e.g., at atmospheric pressure. The exergetic analysis shows that the lower irreversibility is attained for lower pressures. However, the temperature changes do not affect significantly the irreversibilities. This analysis shows that the best thermodynamic conditions for steam reforming of ethanol are the same conditions suggested in the physical-chemical analysis.

Download Full-text

Controlling chemical dosing for sulfide mitigation in sewer networks using a hybrid automata control strategy

Water Science & Technology ◽

10.2166/wst.2013.525 ◽

2013 ◽

Vol 68 (12) ◽

pp. 2584-2590 ◽

Cited By ~ 7

Author(s):

Yiqi Liu ◽

Ramon Ganigué ◽

Keshab Sharma ◽

Zhiguo Yuan

Keyword(s):

Control Strategy ◽

Control Method ◽

Biological Processes ◽

Control Performance ◽

Hybrid Automata ◽

Sewer Pipe ◽

Physical Chemical ◽

Iron Salts ◽

Pumping Stations ◽

Sewer Networks

Chemicals such as magnesium hydroxide (Mg(OH)2) and iron salts are widely used to control sulfide-induced corrosion in sewer networks composed of interconnected sewer pipe lines and pumping stations. Chemical dosing control is usually non-automatic and based on experience, thus often resulting in sewage reaching the discharge point receiving inadequate or even no chemical dosing. Moreover, intermittent operation of pumping stations makes traditional control theory inadequate. A hybrid automata-based (HA-based) control method is proposed in this paper to coordinate sewage pumping station operations by considering their states, thereby ensuring suitable chemical concentrations in the network discharge. The performance of the proposed control method was validated through a simulation study of a real sewer network using real sewage flow data. The physical, chemical and biological processes were simulated using the well-established SeweX model. The results suggested that the HA-based control strategy significantly improved chemical dosing control performance and sulfide mitigation in sewer networks, compared to the current common practice.

Download Full-text