Analysis of turbulence and surface growth models on the estimation of soot level in ethylene non-premixed flames

Soot prediction in a combustion system has become a subject of attention, as many factors influence its accuracy. An accurate temperature prediction will likely yield better soot predictions, since the inception, growth and destruction of the soot are affected by the temperature. This paper reported the study on the influences of turbulence closure and surface growth models on the prediction of soot levels in turbulent flames. The results demonstrated that a substantial distinction was observed in terms of temperature predictions derived using the k-ε and the Reynolds stress models, for the two ethylene flames studied here amongst the four types of surface growth rate model investigated, the assumption of the soot surface growth rate proportional to the particle number density, but independent on the surface area of soot particles, ƒ(As) = ρNs , yields in closest agreement with the radial data. Without any adjustment to the constants in the surface growth term, other approaches where the surface growth directly proportional to the surface area and square root of surface area, ƒ(As) = As and ƒ(As) = √As, result in an under- prediction of soot volume fraction. These results suggest that predictions of soot volume fraction are sensitive to the modelling of surface growth

Progress towards synthetic modelling of humic acid: Peering into the physicochemical polymerization mechanism

Oxidative copolymerization of gallic acid (GA) and protocatechuic acid (PA) at 1:1 ratio provides a water soluble humic-acid-like polycondensate (HALP) which mimics fundamental physicochemical and spectroscopic properties of natural humic acid (HA). The redox potential (Eh) of polymerization plays a determinative role on the physicochemical, spectroscopic and H-binding properties of the HALP as well as on the mass yield. Trends have been systematically mapped and analyzed for two Eh values, e.g. 0mV (HALP_0) and 100mV (HALP_100). HALP_100 has physicochemical properties, prevailing aliphatic structure, which resemble those of fulvic acids (FAs) or soil-type HAs. HALP_0 has a prevailing aromatic/phenol structure which resembles lignite-like HAs. Ionic strength had a significant impact on the charge and H-binding properties of the HALP_100. Donnan volume (VD) estimates show that HALP_100 has a more expanded structure. A molecular model is suggested for the polymerization reactions in connection with the observed macromolecular, spectroscopic and H-binding characteristics of the HALPs and natural HAs. © 2011 Elsevier B.V

Interfacial Hydrogen Atom Transfer by nanohybrids based on Humic Acid Like Polycondensates

Novel nanohybrid materials were prepared by covalent grafting of a polyphenolic polymer [Humic Acid Like Polycondensate (HALP)] on SiO2 nanoparticles. Four nanohybrids were so-produced, using four different types of SiO2 i.e. three Aerosil flame-made nanoparticles with nominal specific surface area of 50, 90 and 300m2/g, herein codenamed OX50, A90, A300 respectively, plus a colloidal SiO2[S300] with SSA=300m2/g. The antioxidant activity of the SiO2-HALP nanohybrids was evaluated by assessing their kinetics for Hydrogen Atom Transfer [HAT] to DPPH radicals. When normalized per same HALP concentration, bigger NPs SiO2[OX50]-HALP NPs can scavenge 280μmoles of DPPH radicals per gram of HALP, while [A90]-HALP and [A300]-HALP NPs can scavenge 514 and 832μmoles of DPPH radicals per gram of HALP, respectively. The colloidal SiO2[S300]-HALP can scavenge fewer DPPH radicals (252 μmoles) per gram of HALP. Based on detailed kinetic data it is shown that (i) surface grafted HALPs perform 300% better HAT than non-grafted HALP in solution. (ii) By controlling the particle type and grafting-loading, we can control/optimize the HAT performance: when grafted on the appropriate SiO2 surface the HALP macromolecules are able to quench up to 0.8mmoles of DPPH-radical per gram of HALP

On the mechanism of action of thiamin enzymes, crystal structure of 2- (α-hydroxyethyl)thiamin pyrophosphate (HETPP). Complexes of HETPP with zinc(II) and cadmium(II)

The crystal structure of the 2-(α-hydroxethyl) thiamin pyrophosphate (LH2) was solved by X-ray diffraction. Crystallographic data: space group F2dd, a=7.922(4) Å, b=33.11(2) Å, c=36.232(10) Å, V=9503(9) Å3, z=16. Metal complexes of the general formula K2[M(LH)Cl2]2 (M=Zn2+, Cd2+) were isolated from methanolic solutions and characterized by elemental analysis, IR, Raman, and 13C CP MAS NMR spectra. They were also characterized by 13C NMR, 31P NMR, 113Cd NMR, ES-MS, and 1H NMR ROESY spectra in D2O solutions. The data provide evidence for the bonding of the metals to the N(1’) atom of the pyrimidine ring and to the pyrophosphate group. The free ligand and the metal-coordinated ligand adopt the S conformation. Since thiamin cofactor, substrate, and metal ions are present in our system, the extracted results directly refer to thiamin catalysis and possible functional implications are correlated and discussed