Papers by DAniel Barragán
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Physical Chemistry Chemical Physics, 2019
The surface temperature is computed for a heterogeneous catalytic reaction model,namely the oxida... more The surface temperature is computed for a heterogeneous catalytic reaction model,namely the oxidation of carbon monoxide on platinum. The surface temperature was found using non-equilibrium thermodynamic theory, a theory which...
Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales
Para el estudio de los niveles de disipación de materia y energía (producción global de calor-ent... more Para el estudio de los niveles de disipación de materia y energía (producción global de calor-entropía) que acompañan la aparición de estructuras espacio-temporales estacionarias (autoorganización), hemos desarrollado una teoría termodinámica de los procesos irreversibles. Las estructuras emergen de un arreglo bidimensional de reactores químicos acoplados, que se encuentran en un estado estacionario oscilatorio homogéneo, después de haber propagado un estímulo químico. Estas estructuras permanecen en el tiempo y en el espacio a expensas de una continua disipación de materia y energía (estructuras disipativas). En el marco de la teoría termodinámica de los procesos irreversibles se investigan los niveles de disipación que acompañan la aparición de las estructuras a medida que el sistema evoluciona en función de parámetros dinámicos (bifurcación), de acople (difusión) y de la magnitud de la perturbación. La teoría termodinámica, los modelos químicos y los resultados obtenidos son gene...
Journal of the Brazilian Chemical Society, 2005
No presente estudo apresentamos a dependência do tempo de indução da reação Belousov-Zhabotinsky ... more No presente estudo apresentamos a dependência do tempo de indução da reação Belousov-Zhabotinsky (BZ) em função da concentração inicial do ácido malonico, bromato e cerium. Os resultados mostram que o tempo de indução aumenta com o aumento da concentração de bromato e tal comportamento não coincide com o mecanismo proposto para as reações BZ. Propomos então que uma competição cinética entre a bromação do ácido malonico e a oxidação dos ácidos bromomalonico e malonico seja o caminho para entender este mecanismo. Cáculos usando modelos GTF e MBM apoiam a proposição sugerida. In this paper we present the dependence of the induction time of the Belousov-Zhabotinsky reaction (BZ) on the initial concentrations of malonic acid, bromate and cerium. The experimental results show that the induction time gets larger with bromate increasing and this behaviour does not agree with the mechanistic explanations based on the models proposed for the BZ reaction. We propose that a kinetic competition between the bromination of malonic acid and the oxidation of bromomalonic and malonic acids is a way to understand this behaviour. Model calculations using the GTF and MBM models support the propose explanation.
Con el propósito de minimizar la velocidad de producción de entropía-disipación termodinámicadura... more Con el propósito de minimizar la velocidad de producción de entropía-disipación termodinámicadurante un proceso químico, la segunda ley de la termodinámica se aplica al estudio de una máquina térmica sujeta a procesos isotérmicos de expansión-compresión. Se determina la magnitud del coeficiente global de transferencia de calor (W m-2 K-1) del pistón que minimiza la disipación termodinámica cuando éste es conducido por la reacción química AB, representada en régimen oscilatorio por el modelo termocinético de Sal'nikov. Palabras clave: optimización basada en la segunda ley la termodinámica, velocidad de producción de entropía, disipación termodinámica, modelo de Sal'nikov, oscilador termocinético.
DYNA
Modeling and computational simulation of the carbon monoxide oxidation process, taken as a key sy... more Modeling and computational simulation of the carbon monoxide oxidation process, taken as a key system to analyze the importance of the dynamic description of active sites into the process yield, are presented in this work. To this aim, the formalism of transport phenomena and population balances are used to implement a realistic model that involves heat exchange, transfer of mass and momentum, chemical reaction, and catalyst deactivation. The model is solved numerically, and the analysis is made by comparing isothermal pseudo-steady state approximation with non-isothermal non-steady state assumption for the catalytic cycle. The results show the advantage of considering the interface explicitly into the model since temporary changes of the reactive complex as well as the active sites of the catalyst have a great influence over the reaction yield. By considering this fact, the reaction description is made in a more proper way.
Revista …, 1998
Se presenta un recuento histórico de los hechos más destacados, relacionados con el estudio de re... more Se presenta un recuento histórico de los hechos más destacados, relacionados con el estudio de reacciones químicas oscilantes. Se ilustran y discuten algunos de los conceptos más importantes en el campo de estas reacciones.
Química Nova, 2015
AN APPROACH FOR INTRODUCING THE EFFECT OF MOLECULAR SHAPE IN THE TEACHING OF CHEMICAL REACTIVITY.... more AN APPROACH FOR INTRODUCING THE EFFECT OF MOLECULAR SHAPE IN THE TEACHING OF CHEMICAL REACTIVITY. We address the concept of steric effect in the pursuit of establishing quantitative correlations between reactivity of molecules and their molecular shape. To this end, a set of series of S N 2 reactions were modeled to compute the energy barrier height and the molecular volume, atomic charges and dipole moment of molecules. We introduced the Kappa index to characterize the shape of molecules. Quantitative correlations between the change in the energy barrier with properties of molecules and Kappa index were presented and discussed.
Physica A: Statistical Mechanics and its Applications, 2018
h i g h l i g h t s • Kinetics and energetics depend significantly on the nature of the intermedi... more h i g h l i g h t s • Kinetics and energetics depend significantly on the nature of the intermediate state. • Fluxes depend strongly on the reaction coordinate at early times of the process. • Lost work differs in the mesoscopic and quasi-stationary approaches. • Sequential processes may improve their kinetics and energetics simultaneously.
Producción De Entropía en Un Modelo Autocatalítico No-Isotérmico Perturbado Con Pulsos De Analito
In this article, the thermodynamic analysis of a non-isothermic Lotka-Volterra type chemical osci... more In this article, the thermodynamic analysis of a non-isothermic Lotka-Volterra type chemical oscillator perturbed with analyte pulses is presented. Starting from a simple reaction mechanism ofthree elementary steps, with two instabilities, plus a fourth step that represents the perturbative effect, a mathematical model based on the law of mass action and in the balance of energy, in closed container and pseudo-adiabatic, is constructed. In this case the variation of the kinetic constants with the temperatureaccording to the Arrhenius model is considered. The numerical solution of the model allows to study the dynamics and thermodynamics based on the second law. The system responds to the perturbation by evolving into a new stable limit cycle path, so that the initial concentration of the analyte pulse correlates withdefined values of entropy production and energy efficiency. Additionally, it is observed for certain valuesof the control parameters, the magnitude of the perturbation a...
Revista Colombiana de Química, 2010
Se propone un método para la interpretación de mecanismos complejos de reacción, el cual es aplic... more Se propone un método para la interpretación de mecanismos complejos de reacción, el cual es aplicado a la simulación del mecanismo de Gyórgyi-Field, (GF) desarrollado para la reacción química oscilante de Belousov-Zhabotinsky (BZ). El método basado en la ley de acción de masas y en el principio de independencia y coexistencia de los pasos elementales, reproduce el comportamiento oscilatorio en la concentración de los intermediarios de reacción.
Revista Colombiana de Química, 2010
Se describe la estructura general de un programa desarrollado para la captura y procesamiento de ... more Se describe la estructura general de un programa desarrollado para la captura y procesamiento de datos calorimétricos y potenciométricos. Se destaca su utilidad a través del estudio de diferentes sistemas químicos como: evaluación de la entalpia de protonación del THAMHCI, seguimiento cuantitativo de la concentración del ion bromuro y del par redox Ce(III)/Ce(IV) durante el transcurso de la reacción química oscilante de Belousov-Zhabotinsky, y cuantificación de la entalpia de reacción con piridina de los sitios ácidos superficiales en una muestra de carbón estándar.
The Role of Energy and Matter Dissipation in Determining the Architecture of Self-Assembled Structures
The Journal of Physical Chemistry B
We show how the architecture of self-assembled structures can be determined from the knowledge of... more We show how the architecture of self-assembled structures can be determined from the knowledge of the energy and matter dissipation inherent to its formation. When the amount of dissipation quantified by the total entropy produced in the process is represented in terms of parameters which describe the shape of the assembled structures, its extremes correspond to structures found in experimental situations such as in gelation and Liesegang ring formation. It is found that only a small amount of extra energy is needed to yield smooth changes in the form of the assembled structures. The connection found between the entropy produced and the type of structures formed may constitute a selection criterion which shows why a set of disordered units may gives rise to a determined self-assembled structure.
Ingeniería e Investigación, 2009
Para un sistema con una fuente interna de generación de calor se analizan, en el marco de la term... more Para un sistema con una fuente interna de generación de calor se analizan, en el marco de la termodinámica de los procesos irreversibles, las ecuaciones evolutivas que describen la transferencia de calor según la ley de enfriamiento de Newton. A partir del balance de flujo de entropía ...
Journal of the Brazilian Chemical Society, 2018
Traditionally, thermokinetic and chemical oscillations have been studied independently, but in ce... more Traditionally, thermokinetic and chemical oscillations have been studied independently, but in cellular media recent studies have shown that cell's temperature is not uniform. Thus, on this context it is possible to inquire about the influence of thermal effects on chemical oscillatory behavior and vice versa. To this end, in this paper we propose a dynamical model based on a modified Sal'nikov oscillator that can address both kinds of oscillatory behavior (thermokinetic and chemical). We found that the system modeled can jump from thermal oscillations to mixed chemical-thermal oscillations through a transition or bifurcation parameter. Thermokinetic oscillations are well defined in a limit cycle, while chemical-thermal oscillations appear in the form of a burst. The model could be useful in explaining biochemical energy recovery under cellular stress conditions.
Propagation Failure In An Array of Oregonator Cells and Irreversible Thermodynamics of An Assembly of Discrete Systems
J. Phys. Chem. A, 2002
In this paper we report on a numerical study of wave propagation and its failure in a one-dimensi... more In this paper we report on a numerical study of wave propagation and its failure in a one-dimensional array of coupled chemical cells and irreversible thermodynamics of the array. The Oregonator model for the Belousov−Zhabotinsky reaction is used to model the chemical reactions. In ...
Revista UIS Ingenierías, Jan 5, 2018
El ensamble de estructuras se observa desde la escala molecular hasta la cosmológica. El ensamble... more El ensamble de estructuras se observa desde la escala molecular hasta la cosmológica. El ensamble de componentes discretos fundamentales puede llevar a la formación de una amplia variedad de estructuras, desde simples hasta complejas. En este trabajo estudiamos el ensamble de bloques moleculares fundamentales que forman trímeros nosimétricos en la mesoescala. El proceso de ensamble se modela mediante un sistema de ecuaciones tipo Fokker-Planck acopladas en la frontera. El modelo matemático se resuelve en un espacio de estados, donde las trayectorias dan información de la probabilidad de formar diferentes trímeros por difusión a través de una barrera de potencial de energía no simétrica. Los resultados muestran que las condiciones de frontera no-homogéneas y la configuración de la barrera de potencial determinan cual estructura ensamblada, trímero, tiene la mayor probabilidad de formarse.
Recebido em 12/4/12; aceito em 26/8/12; publicado na web em 29/11/12 AN APPROACH FOR EXPLAINING C... more Recebido em 12/4/12; aceito em 26/8/12; publicado na web em 29/11/12 AN APPROACH FOR EXPLAINING CHEMICAL TRANSFORMATIONS. A methodology is proposed for explaining one of the central questions in the teaching of general chemistry courses to freshman students: why do chemical transformations occur? The answer to this question is based on thermodynamics but we propose arriving at an answer in a more intuitive way by using computational tools in a bid to increase the motivation of students for learning chemistry.
Induction Period In the BrO 3-, Ce (III), H 2 SO 4, Oxalic Acid and Ketone Oscillating Reaction
Physical Chemistry Chemical Physics, 1999
Induction period in the Ce(III), oxalic acid and BrO 3 , H 2 SO 4 , ... Igal Berenstein, Jesu s ... more Induction period in the Ce(III), oxalic acid and BrO 3 , H 2 SO 4 , ... Igal Berenstein, Jesu s Agreda and Daniel Barraga n* ... Universidad Nacional de Colombia, Facultad de Ciencias, Departamento de Qu mica, Bogota , Colombia. E-mail: dbarrag=ciencias.ciencias.unal. ...
A Criterion for the Formation of Nonequilibrium Self-Assembled Structures
The Journal of Physical Chemistry B
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Papers by DAniel Barragán