Use of sensitivity analysis to describe an endothermic/exothermic reaction system

AIChE Journal ◽  
1992 ◽  
Vol 38 (3) ◽  
pp. 461-465 ◽  
Author(s):  
D. R. van der Vaart ◽  
H. R. van der Vaart
Keyword(s):  
Sensitivity Analysis ◽  
Exothermic Reaction ◽  
Reaction System

Core Scale FEM Modeling of Thermochemical Fracturing on Cement Cube Samples

2021 ◽  
Author(s):  
Zeeshan Tariq ◽  
Ayman AlNakhli ◽  
Abdulazeez Abdulraheem ◽  
Mohamed Mahmoud
Keyword(s):  
Sensitivity Analysis ◽  
Global Economy ◽  
Oil And Gas ◽  
Peak Pressure ◽  
Exothermic Reaction ◽  
Cohesive Zone Modeling ◽  
Fem Modeling ◽  
Breakdown Pressure ◽  
Multiple Fractures ◽  
Micro Cracks

Abstract Brownfields and depleting conventional resources of fossil fuel energy are not enough to fulfill the tremendously increasing energy demands around the globe. Unconventional oil and gas resources are creating a huge impact on the enhancement of the global economy. Tight rocks are usually located in deep and high-strength formations. In this study, numerical simulation results on a new thermochemical fracturing approach is presented. The new fracturing approach was implemented to reduce the breakdown pressure of the unconventional tight formations. The hydraulic fracturing experiments presented in this study were carried out on ultra-tight cement block samples. The permeability of the block samples was less than 0.005mD. Thermochemical fracturing was carried out by a thermochemical fluids that caused a rapid exothermic reaction which resulted in the instantaneous generation of heat and pressure. Different salts of nitrogen such as sodium nitrite and ammonium chloride were used as a thermochemical fluid. The instantaneous generation of the heat and pressure caused the creation of micro-cracks. The fracturing results revealed that the novel thermochemical fracturing was able to reduce the breakdown pressure in ultra-tight cement from 1095 psi to 705 psi. The reference breakdown pressure was recorded from the conventional fracturing technique. A finite element (FEM) analysis was conducted using commercial software ABAQUS. In FEM, two approaches were used to model the thermochemical fractures namely, cohesive zone modeling (CZM) and concrete damage plasticity models (CDP). The sensitivity analysis of peak pressure and time to reach the peak pressure is also presented in this study. The sensitivity analysis can help in better designing thermochemical fluids that could lead to the maximum generation of micro-cracks and multiple fractures.

scholarly journals Simplification of Carbon Bond Mechanism IV (CBM-IV) under Different Initial Conditions by Using Concentration Sensitivity Analysis

Molecules ◽  
2019 ◽  
Vol 24 (13) ◽  
pp. 2463 ◽  
Author(s):  
Le Cao ◽  
Simeng Li ◽  
Ziwei Yi ◽  
Mengmeng Gao
Keyword(s):  
Sensitivity Analysis ◽  
Reaction Mechanism ◽  
Initial Conditions ◽  
Model Simulation ◽  
Computing Time ◽  
Reaction System ◽  
Carbon Bond ◽  
Reduced Mechanism ◽  
Concentration Sensitivity ◽  
Bond Mechanism

Carbon Bond Mechanism IV (CBM-IV) is a widely used reaction mechanism in which VOCs are grouped according to the molecular structure. In the present study, we applied a sensitivity analysis on the CBM-IV mechanism to clarify the importance of each reaction under two different initial conditions (urban and low-NO scenarios). The reactions that exert minor influence on the reaction system are then screened out from the mechanism, so that a reduced version of the CBM-IV mechanism under specific initial conditions can be obtained. We found that in a typical urban condition, 11 reactions can be removed from the original CBM-IV mechanism, and the deviation is less than 5% between the results using the original CBM-IV mechanism and the reduced mechanism. Moreover, in a low-NO initial condition, two more reactions, both of which are nitrogen-associated reactions, can be screened out from the reaction mechanism, while the accuracy of the simulation is still maintained. It is estimated that the reduction of the CBM-IV mechanism can save 11–14% of the computing time in the calculation of the chemistry in a box model simulation.

Study of different Carbon Bond 6 (CB6) mechanisms by using a concentration sensitivity analysis

2021 ◽  
Vol 21 (16) ◽  
pp. 12687-12714
Author(s):  
Le Cao ◽  
Simeng Li ◽  
Luhang Sun
Keyword(s):  
Sensitivity Analysis ◽  
Early Stage ◽  
Reaction System ◽  
The Other ◽  
Peroxy Radicals ◽  
Nox Formation ◽  
Carbon Bond ◽  
Surface Emission ◽  
Concentration Sensitivity ◽  
The Difference

Abstract. Since the year 2010, different versions of the Carbon Bond 6 (CB6) mechanism have been developed to accurately estimate the contribution to air pollution by the chemistry. In order to better understand the differences in simulation results brought about by the modifications between different versions of the CB6 mechanism, in the present study, we investigated the behavior of three different CB6 mechanisms (CB6r1, CB6r2 and CB6r3) in simulating ozone (O3), nitrogen oxides (NOx) and formaldehyde (HCHO) under two different emission conditions by applying a concentration sensitivity analysis in a box model. The results show that when the surface emission is weak, the O3 level predicted by CB6r1 is approximately 7 ppb higher than that predicted by CB6r2 and CB6r3, specifically due to the change in the sink of acyl peroxy radicals with high-order carbons (i.e., species CXO3) in the mechanism and the difference in the ozone dependence on the isoprene emission. In contrast, although CB6r1 estimates higher values of NOx and HCHO than the other two mechanisms at an early stage of the simulation, the levels of NOx and HCHO estimated by these three CB6 mechanisms at the end of the 7 d simulation are mostly similar, when the surface emission is weak. After the increase in the surface emission, the simulated profiles of O3, NOx and HCHO obtained by CB6r2 and CB6r3 were found to be nearly the same during the simulation period, but CB6r1 tends to estimate substantially higher values than CB6r2 and CB6r3. The deviation between the O3 levels provided by CB6r1 and the other two CB6 mechanisms (i.e., CB6r2 and CB6r3) was found to be enlarged compared with the weak-emission scenario because of the weaker dependence of ozone on the emission of isoprene in CB6r1 than those in CB6r2 and CB6r3 in this scenario. Moreover, HCHO predicted by CB6r1 was found to be larger than those predicted by CB6r2 and CB6r3, which is caused by an enhanced dependence of HCHO on the emission of isoprene in CB6r1. Regarding NOx, it was found that CB6r1 gives a higher value than the other two mechanisms, which is caused by the relatively stronger connection between the NOx prediction and the release of NO and NO2 in CB6r1 due to the change in the product of the reaction between isoprene and NO3 in CB6r1. Consequently, more emitted NOx is involved in the reaction system denoted by CB6r1, which enables a following NOx formation and thus a higher NOx prediction of CB6r1.

Oscillatory Reactions

2006 ◽  
Author(s):  
John Ross ◽  
Igor Schreiber ◽  
Marcel O. Vlad
Keyword(s):  
Chemical Reactions ◽  
Negative Feedback ◽  
Exothermic Reaction ◽  
Reaction System ◽  
Chemical Species ◽  
Heat Removal ◽  
Solid Catalyst ◽  
Distinct Property ◽  
Present Context ◽  
Flow Through

Oscillating chemical reactions have the distinct property of a periodic or aperiodic oscillatory course of concentrations of reacting chemical species as well as temperature. This behavior is due to an interplay of positive and negative feedback with alternating dominance of these two dynamic effects. For example, an exothermic reaction produces heat that increases temperature, which in turn increases reaction rate and thus produces more heat. Such a thermokinetic effect is thus autocatalytic and represents a positive feedback. When run in a flow-through reactor with a cooling jacket, the autocatalysis is eventually suppressed if the reactant is consumed faster than it is supplied. At the same time, the excess heat is being removed via the jacket, which tends to quench the system. The latter two processes are inhibitory and represent a negative feedback. If the heat removal is slow enough so as not to suppress entirely the autocatalysis, but fast enough for temperature to drop before there is enough reactant available via the feed to restore autocatalysis, then there are oscillations in both temperature and concentration of the reactant. Examples of these thermokinetic oscillations are combustion reactions, which typically take place either in homogeneous gaseous or liquid phase or in the presence of a solid catalyst, thus representing a heterogeneous reaction system. Of more interest in the present context are reactions where thermal effects are often negligible, or the system is maintained at constant temperature, as is the case with homogeneous chemical reactions taking place in a thermostated flow-through reactor, as well as biochemical reactions in living cells and organisms. Autocatalysis can easily be realized in isothermal systems, where instead of a heat-producing reaction there will typically be a closed reaction pathway, such that species involved are produced faster by reactions along the pathway than they are consumed by removal reactions. As an example, let us examine the well-known Belousov–Zhabotinsky (BZ) reaction of bromate with malonic acid catalyzed by cerium ions in acidic solution.

scholarly journals Model of the nonlinear reaction system with autocatalysis and autoinhibition: Stability of dynamic states

2012 ◽  
Vol 66 (5) ◽  
pp. 637-646 ◽  
Author(s):  
Stevan Macesic ◽  
Zeljko Cupic ◽  
Ljiljana Kolar-Anic
Keyword(s):  
Sensitivity Analysis ◽  
Hopf Bifurcation ◽  
Network Analysis ◽  
Self Regulation ◽  
Reaction System ◽  
Model System ◽  
Economic Systems ◽  
Nonlinear Reaction ◽  
Stoichiometric Network Analysis ◽  
Theoretical Analyses

Self-regulation, achieved through positive (autocatalytic) or negative (autoinhibitory) feedback is commonly encountered in natural, technological and economic systems. The dynamic behavior of such systems is often complex and cannot be easily predicted, necessitating mathematical modelling and theoretical analyses. The aim of this work is to analyze the dynamics of a minimal model system with autocatalytic and autoinhibitory steps coupled through the same species, in order to understand under which critical condition the system loses stability and passes through an Andronov-Hopf bifurcation. The analysis used was improved stoichiometric network analysis (SNA) in combination with bifurcation and sensitivity analysis.

Steady-State Modeling of Pt-Catalyzed H2 Combustion in a Monolithic Reactor: From Micro- to Macro-kinetics

2016 ◽  
Vol 14 (1) ◽  
pp. 373-381 ◽  
Author(s):  
Qi Su ◽  
Xiao-Ling Zha ◽  
Jin Xu ◽  
Wei-Fang Yu
Keyword(s):  
Steady State ◽  
Kinetic Modeling ◽  
Hydrogen Oxidation ◽  
Exothermic Reaction ◽  
Reaction System ◽  
Surface Species ◽  
Parametric Sensitivity ◽  
Composition Effects ◽  
Steady State Model ◽  
Pt Catalyzed

AbstractMicro-kinetic modeling of Pt-catalyzed hydrogen oxidation in a monolithic reactor was carried out for various feed temperatures. The monolith behavior was described by a simplified steady-state model that avoids surface species enthalpy evaluation and does not have temperatures as unknowns. A simplified pseudoarch length method was used to obtain the multiple solution branches for this typical exothermic reaction system. Based on parametric sensitivity and surface species distribution analyses of the micro-kinetic modeling results, macro-kinetic models that involve only gas concentrations were derived and were used to explain the composition effects on ignition temperature.

Nuclear Reactions in Deuterium Titanium

1990 ◽  
Vol 48 (2) ◽  
pp. 134-135
Author(s):  
D.M. Vanderwalker
Keyword(s):  
Nuclear Reactions ◽  
Ion Beam ◽  
Exothermic Reaction ◽  
Pure Titanium ◽  
Fundamental Interest ◽  
Transmission Electron ◽  
Iodide Titanium ◽  
A Cell ◽  
After Hours ◽  
Quantity Of Heat

There is a fundamental interest in electrochemical fusion of deuterium in palladium and titanium since its supposed discovery by Fleischmann and Pons. Their calorimetric experiments reveal that a large quantity of heat is released by Pd after hours in a cell, suggesting fusion occurs. They cannot explain fusion by force arguments, nor can it be an exothermic reaction on the formation of deuterides because a smaller quantity of heat is released. This study examines reactions of deuterium in titanium.Both iodide titanium and 99% pure titanium samples were encapsulated in vacuum tubes, annealed for 2h at 800 °C. The Ti foils were charged with deuterium in a D2SO4 D2O solution at a potential of .45V with respect to a calomel reference junction. Samples were ion beam thinned for transmission electron microscopy. The TEM was performed on the JEOL 200CX.The structure of D charged titanium is α-Ti with hexagonal and fee deuterides.

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