Search results for " Enthalpy"
showing 10 items of 31 documents
Medium enthalpy geothermal systems in carbonate reservoirs, the Western Sicily example.
2013
The multidisciplinary and integrated review of existing data (mainly acquired during oil exploration), specifically reread for geothermal purposes, and the integration with new data acquired in particular key areas, such as the Mazara Del Vallo site in the southern part of western Sicily, allowed us to better understand this -regional scale- medium-enthalpy geothermal system (with measured temperatures up to 100 °C), to reconstruct the modalities and peculiarities of fluids circulation, and to evaluate the geothermal potentialities of western Sicily. We suggest that these findings could be taken as exemplificative of the behavior of low-to medium enthalpy geothermal systems hosted in carbon…
A Chemical Index Inspired by Biological Plastic Evolution: Valence-Isoelectronic Series of Aromatics
2004
Plastic evolution is a new perspective of the evolutionary process conjugating the effect, on one hand, of the acquired characters and, on the other, of the relationships that emerge among the principle of evolutionary indeterminacy, the principle of morphologic determination, and natural selection. Plastic evolution is applied to design the coordination index Ic. Ic is used to characterize the valence-isoelectronic series of cyclopentadiene, benzene, toluene, and styrene and compared to charge indices for dipole moment. The parameters needed to calculate Ic are minus the standard enthalpy of formation T, molecular surface area S, and molecular weight W. With the exception of the O heteromo…
A Solar Pond for Feeding a Thermoelectric Generator or an Organic Rankine Cycle System
2017
The world energy demand is continuously growing, which means an increase in consumption for all modern fuels or stronger effort on the development and improvement of renewable technologies. Moreover, Developing Countries claims more energy and they have often wide unutilized or unusable lands. The solar energy represents a useful opportunity for these Countries. The Solar Pond is both a solar collector and a thermal storage for long period and is suitable to use in wide sunny areas. Solar pond technology is able to supply heat for several applications requiring low-grade thermal energy or for electrical power production. In order to produce electrical energy from solar ponds it is necessary…
The role of atomic static displacements in binary-alloy formation
2003
Abstract A microscopic approach to considering the influence of local atomic static displacements (LASD) on binary alloy thermodynamic properties has been developed. The explicit expression for the free energy of a disordered alloy is derived within the collective variables method. The LASD are shown to promote formation of a disordered alloy. The theory is illustrated by numerical calculations performed for alloys of the Ca–Ba system. Dependence of the alloy formation heat on temperature and concentration obtained numerically agrees perfectly with the experimental data.
Metal complex-DNA binding: Insights from molecular dynamics and DFT/MM calculations.
2012
Molecular dynamics (MD) simulations, followed by density functional theory/molecular mechanics (DFT/MM) calculations, provided a detailed structure of the binding site between the cationic metallointercalator (dipyrido [3,2-a:2',3'-c]phenazine)(glycinato)copper(II), [Cu(gly)(dppz)](+), and the two dodeca-deoxynucleotide duplexes [dodeca(dG-dC)]2 and [dodeca(dA-dT)]2. Three simultaneous DNA binding types were detected in the fully optimized DFT/MM structures: 1) metal coordination through exocyclic oxygen atoms of nitrogen bases; 2) intercalation of the dppz chromophore between stacked Watson-Crick AT-AT and GC-GC bases; and 3) hydrogen bonding between the glycinato ligand and amine groups o…
Speciation of Al3+ in fairly concentrated solutions (20 to 200 mmol L-1) at I = 1 mol L-1 (NaNO3), in the acidic pH range, at different temperatures.
2011
AbstractThe hydrolysis of Al3+ was studied in aqueous 1 mol L−1 NaNO3 solution at different concentrations (20–200 mmol L−1) and temperatures (283.15–343.15 K) by potentiometry (ISE-H+, glass electrode). Many different speciation models were considered in the calculations and it was found that the best model is represented by the following species: Al(OH)2+, Al(OH)45+, Al13(OH)327+. Hydrolysis constants and enthalpy changes at different temperatures are reported.
Towards highly accurate ab initio thermochemistry of larger systems: benzene.
2011
The high accuracy extrapolated ab initio thermochemistry (HEAT) protocol is applied to compute the total atomization energy (TAE) and the heat of formation of benzene. Large-scale coupled-cluster calculations with more than 1500 basis functions and 42 correlated electrons as well as zero-point energies based on full cubic and (semi)diagonal quartic force fields obtained with the coupled-cluster singles and doubles with perturbative treatment of the triples method and atomic natural orbital (ANO) triple- and quadruple-zeta basis sets are presented. The performance of modifications to the HEAT scheme and the scaling properties of its contributions with respect to the system size are investiga…
Cyclooctadienine — hoch gespannte C 8 H 8 ‐Kohlenwasserstoffe
1985
Mit Hilfe der MNDO-Methode werden die energiearmsten Konformationen der vier strukturisomeren Cyclooctadienine 1–4 berechnet. Aus ihren Bildungswarmen ΔHf konnen durch Bezug zu den Cyclooctatrienen 5 und 6 die geometrischen Ringspannungen Eg abgeschatzt werden. Als experimentelle Sonde fur die Ringspannung dienen die UV-, IR (Raman)- und 13C-NMR-Spektren. Cyclooctadienynes — Highly Strained C8H8-Hydrocarbons Applying the MNDO-method the conformations with lowest energy of the isomeric cyclooctadienynes 1–4 are calculated. The geometrical ring strains Eg can be evaluated from the enthalpies of formation ΔHf in relation to the cyclooctatrienes 5 and 6. UV, IR (Raman) and 13C NMR spectra serve…
Titanocene Selenide Sulfides Revisited: Formation, Stabilities, and NMR Spectroscopic Properties
2019
[TiCp2S5] (phase A), [TiCp2Se5] (phase F), and five solid solutions of mixed titanocene selenide sulfides [TiCp2SexS5−x] (Cp = C5H5−) with the initial Se:S ranging from 1:4 to 4:1 (phases B–E) were prepared by reduction of elemental sulfur or selenium or their mixtures by lithium triethylhydridoborate in thf followed by the treatment with titanocene dichloride [TiCp2Cl2]. Their 77Se and 13C NMR spectra were recorded from the CS2 solution. The definite assignment of the 77Se NMR spectra was based on the PBE0/def2-TZVPP calculations of the 77Se chemical shifts and is supported by 13C NMR spectra of the samples. The following complexes in varying ratios were identified in the CS2 solutions of …
Enthalpies of formation of isoprene’s major oxidation byproducts
2005
Abstract The theoretical enthalpies of formation ( Δ f H 298 . 15 ∘ ) of methyl vinyl ketone (MVK, CH 2 CHC(O)CH 3 ), methacrolein (MACR, CH 2 C(CH 3 )CHO), and the radical products formed in their corresponding OH radical oxidations have been calculated with DFT (MPW1K/6-31+G(d,p)) and multilevel (MCCM-UT-CCSD(T)//MPW1K/6-31+G(d,p)) methods. The bond dissociation energies ( BDE , DH 298 . 15 0 ) of the H-atoms that can be abstracted from the MVK and MACR molecules, and the C–O forming bonds of the OH addition products are also calculated. The regioselectivity of the global reaction is discussed in terms of bond strength.