فهرست مطالب razieh habibpour

Release and dispersion of toxic and flammable gases in atmosphere is one of the most important incident in safety of the processes. Risk analysis with the aim of prevention from harm and damage usually carries out by software packages, which are based on the field experiments and mathematical models.

In order to derive dispersion models and evaluate existing models, some different experiments are done. Experiments of the gas release and gas dispersion are in two categories, experiments which took place in wind tunnels and which are field experiments. Kit Fox, Thorney Island and coyote are some of the most famous field experiments. PERP group and EMU tests are major experiments in wind tunnels.  In many of studies, gas dispersion was investigated in the open places in absence or presence of obstacles because most of the industrial accident happens in open places. Others are also taking place in indoors and large buildings. Early, simple models such as box models, steady state plume and integral models were proposed. Thereafter, group models like Lagrangian models and Lagrangian- Gaussian models were evinced. One of the other approach is using more complex and computational methods. Fluid dynamics methods are designed and developed for this purpose. The models of the heavy gas dispersion can be categorized to four major group. The first is simple and experimental models. intermediate and integral or shallow layer models include box models, steady state / general steady state plume models, one dimensional integral models is located in the next. The third group is advanced and lagrange models. The last and latest models are computational fluid dynamic models: RANS, LES and DNS

Different gases, distinct release scenarios are studied in researches. As another effective parameter on the path of gas dispersion, topology of release location can be mentioned which is investigated in field experiments and simulations.

in order to use and refer the field   experiments and models as an evaluation, desired scenarios’ condition should be as close as possible to the models or experiments’ condition. These conditions could be such as type of gas, terrain and topology of release path, puff or plume release and other environment and physical conditions.

First-principle calculations were carried out to investigate the adsorption of CO over Cun nanoclusters. The structural, spectroscopic and electronic properties like optimized geometries, HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy levels, binding energy, adsorption energy, vibrational frequency and density of states (DOSs) of the pure Cun nanoclusters, and CunCO complexes in their ground state were thoroughly analyzed. The CO adsorbed on the Cun nanoclusters showed a stretch frequency at 1950-2052 cm-1, which was red-shifted relative to that of gas-phase CO (2143 cm-1). This red-shift was believed to arise from the charge transfer from the Cu metal d states to the CO antibonding 2π* level. The CO adsorption on the Cu nanoclusters was chemisorption in nature with the Cu–C bond length (adsorption height) in the range of 1.85-1.92 Å.

An ab initio study has been performed for the electronic, spectroscopic, and chemical properties of the most stable configuration of the (CdO)n nanoclusters by employing B3LYP-DFT/LanL2DZ method. Different isomers were optimized to obtain structural stability and numerous chemical parameters such as dipole moment, ionization potential, etc. We report here the vibrational frequencies of the most stable configuration of (CdO)n nanoclusters. We found that, the highest vibrational frequencies of each (CdO)n nanoclusters arise from the asymmetrical stretching vibrations while the lower frequencies correspond twisting, bending and the out-of-plane vibrations of Cd and O atoms. Our results show that, the (CdO)2 nanocluster with the ring structure and the smallest HOMO-LUMO gap (HLG = 1.897) has the smallest hardness (ɳ = 0.95) and consequently is expected to has the highest chemical reactivity.

In this study, the structures, the IR spectroscopy, and the electronic properties of AunCum (n≤5) bimetallic clusters were studied and compared with those of pure gold and copper clusters using the generalized gradient approximation (GGA) and exchange correlation density functional theory (DFT). The study of an O2-AunCum system is important to identify the promotion effects of each of the two metals and their effect in catalysts, sensors, energy sources, or many other applications. This study also demonstrated that the O2 molecule preferred to adsorb at the Cu site rather than at the Au site in bimetallic clusters. O2 adsorption at a bridge site is energetically more favored over the other sites (1- both oxygen atoms are bonded to the same substrate atom 2- O2 is connected to a Cu atom through a single bond) for oxygen adsorption on these clusters. Further, it was concluded that after the adsorption of the O2 molecule on the bimetallic clusters, the Au-Cu interaction is strengthened and the O-O interaction is weakened; the reactivity improvement of the oxygen molecule was clear.