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Thermal Dissociation (thermal + dissociation)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Comparative study of flame structures and NOx emission characteristics in fuel injection recirculation and fuel gas recirculation combustion system

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2004
Jeong Park
Abstract A numerical study with momentum-balanced boundary conditions has been conducted to grasp the chemical effects of added CO2 to fuel- and oxidizer-sides on flame structure and NO emission behaviour in H2,O2 diffusion flames with varying flame location. A reaction mechanism is proposed to show better agreements with experimental results in CO2 -added hydrogen flames. Oxidizer-side dilution results in significantly higher flame temperatures and NO emission. Flame location is dramatically changed due to high diffusivity of hydrogen according to variation of the composition of fuel- and oxidizer-sides. This affects flame structure and NO emission considerably especially the chemical effects of added CO2. The present work also displays separately thermal contribution and prompt NO emission due to the chemical effects caused by thermal dissociation of added CO2 in NO emission behaviour. It is found that flame temperature and the flame location affect the contribution of thermal and prompt NO due to chemical effects considerably in NO emission behaviour. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Chemical effects of CO2 addition to oxidizer and fuel streams on flame structure in H2,O2 counterflow diffusion flames

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2003
Jeong Park
Abstract Numerical simulation of CO2 addition effects to fuel and oxidizer streams on flame structure has been conducted with detailed chemistry in H2,O2 diffusion flames of a counterflow configuration. An artificial species, which displaces added CO2 in the fuel- and oxidizer-sides and has the same thermochemical, transport, and radiation properties to that of added CO2, is introduced to extract pure chemical effects in flame structure. Chemical effects due to thermal dissociation of added CO2 causes the reduction flame temperature in addition to some thermal effects. The reason why flame temperature due to chemical effects is larger in cases of CO2 addition to oxidizer stream is well explained though a defined characteristic strain rate. The produced CO is responsible for the reaction, CO2+H=CO+OH and takes its origin from chemical effects due to thermal dissociation. It is also found that the behavior of produced CO mole fraction is closely related to added CO2 mole fraction, maximum H mole fraction and its position, and maximum flame temperature and its position. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Ablative heat transfer in a shrinking packed-bed of ZnO undergoing solar thermal dissociation

AICHE JOURNAL, Issue 7 2009
L. O. Schunk
Abstract A transient heat transfer model is formulated for a shrinking packed-bed of reacting ZnO particles exposed to concentrated solar irradiation. The model combines conduction, convection, and radiation heat transfer with simultaneous sintering and reaction kinetics. Validation is accomplished in terms of temperatures and dissociation rates experimentally measured using a solar-driven thermogravimeter with ZnO packed-bed samples subjected to solar flux concentration ratios in the range 1225,2133 suns and surface temperatures in the range 1834,2109 K. Operating conditions are typical of an ablation regime controlled by the rate of radiative heat transfer to the first layers of ZnO undergoing endothermic dissociation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Kinetics of the thermal dissociation of ZnO exposed to concentrated solar irradiation using a solar-driven thermogravimeter in the 1800,2100 K range

AICHE JOURNAL, Issue 6 2009
Lothar O. Schunk
Abstract The two-step H2O-splitting thermochemical cycle based on the Zn/ZnO redox reactions is considered for solar H2 production, comprising the endothermal dissociation of ZnO followed by the exothermal hydrolysis of Zn. A solar-driven thermogravimeter, in which a packed-bed of ZnO particles is directly exposed to concentrated solar radiation at a peak solar concentration ratio of 2400 suns while its weight loss is continuously monitored, was applied to measure the thermal dissociation rate in a set-up closely approximating the heat and mass transfer characteristics of solar reactors. Isothermal thermogravimetric runs were performed in the range 1834,2109 K and fitted to a zero-order Arrhenius rate law with apparent activation energy 361 ± 53 kJ mol,1 K,1 and frequency factor 14.03 × 106 ± 2.73 × 106 kg m,2 s,1. Application of L,vov's kinetic expression for solid decomposition along with a convective mass transport correlation yielded kinetic parameters in close agreement with those derived from experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Thermally dissociable pseudo -polyrotaxane as a supramolecular shrinkage suppressor for epoxy,amine curing system

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2008
Yukio Isobe
Addition of pseudo -polyrotaxanes (PPRtxs) consisting of cyclodextrins (CDs) and amine-terminated polyethers to epoxy,amine curing system remarkably suppressed the volume shrinkage on the curing reaction. The PPRtx underwent thermal dissociation with creation of free volume, which efficiently contributed to the suppression of volume shrinkage. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.] [source]

Structural properties of trimers and tetramers of ribonuclease A

PROTEIN SCIENCE, Issue 10 2001
Arianna Nenci
Abstract Ribonuclease A aggregates (dimers, trimers, tetramers, pentamers) can be obtained by lyophilization from 40% acetic acid solutions. Each aggregate forms two conformational isomers distinguishable by different basic net charge. The crystal structure of the two dimers has recently been determined; the structure of the higher oligomers is unknown. The results of the study of the two trimeric and tetrameric conformers can be summarized as follows: (1) RNase A trimers and tetramers form by a 3D domain-swapping mechanism. N-terminal and C-terminal types of domain swapping could coexist; (2) the secondary structures of the trimeric and tetrameric conformers do not show significant differences if compared with the secondary structure of monomeric RNase A or its two dimers; (3) a different exposure of tyrosine residues indicates that in the aggregates they have different microenvironments; (4) the two trimeric and tetrameric conformers show different susceptibility to digestion by subtilisin; (5) dimers, trimers, and tetramers of RNase A show unwinding activity on double-helical poly(dA-dT) , poly(dA-dT), that increases as a function of the size of the oligomers; (6) the less basic conformers are more stable than the more basic ones, and a low concentration in solution of trimers and tetramers favors their stability, which is definitely increased by the interaction of the aggregates with poly(dA-dT) , poly(dA-dT); (7) the products of thermal dissociation of the two trimers indicate that their structures co ld be remarkably different. The dissociation products of the two tetramers allow the proposal of two models for their putative structures. [source]