Modeling of pyrolysis of straight-run naphtha in a large-capacity type SRT-VI furnace

The problem of modeling pyrolysis of naphtha in a modern SRT-VI large-capacity furnace from ABB Lummus Global (USA) was examined. Curves of the yield of basic products as a function of the composition of the feedstock and pyrolysis regime were obtained with the experimental data and physicochemical characteristics of the process. The model is intended for predicting the composition of pyrolysis gas and controlling the pyrolytic process in an active plant. __________ Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 3, pp. 37–42, May–June, 2008.     

Simulation and experimental studies on plasma temperature, flow velocity, and injector diameter effects for an inductively coupled plasma

An inductively coupled plasma (ICP) is analyzed by means of experiments and numerical simulation. Important plasma properties are analyzed, namely, the effective temperature inside the central channel and the mean flow velocity inside the plasma. Furthermore, the effect of torches with different injector diameters is studied by the model. The temperature inside the central channel is determined from the end-on collected line-to-background ratio in dependence of the injector gas flow rates. Within the limits of 3% deviation, the results of the simulation and the experiments are in good agreement in the range of flow rates relevant for the analysis of relatively large droplets, i.e., ～50 μm. The deviation increases for higher gas flow rates but stays below 6% for all flow rates studied. The velocity of the gas inside the coil region was determined by side-on analyte emission measurements with single monodisperse droplet introduction and by the analysis of the injector gas path lines in the simulation. In the downstream region significantly higher velocities were found than in the upstream region in both the simulation and the experiment. The quantitative values show good agreement in the downstream region. In the upstream region, deviations were found in the absolute values which can be attributed to the flow conditions in that region and because the methods used for velocity determination are not fully consistent. Eddy structures are found in the simulated flow lines. These affect strongly the way taken by the path lines of the injector gas and they can explain the very long analytical signals found in the experiments at low flow rates. Simulations were performed for different injector diameters in order to find conditions where good analyte transport and optimum signals can be expected. The results clearly show the existence of a transition flow rate which marks the lower limit for effective analyte transport conditions through the plasma. A rule-of-thumb equation was extracted from the results from which the transition flow rate can be estimated for different injector diameters and different injector gas compositions.     

Lateral conductivity of <Emphasis Type="Italic">p</Emphasis>-type doped Si/Ge island structures

Numerical calculations of the conductance in structures with doping modulated along the current-flow direction are carried out taking into account band offsets at the interfaces between high-and low-resistivity regions. It is found that such structures exhibit S-shaped current-voltage characteristics; in the limiting case, there should be a negative-conductance region, with the abruptness of the heterojunction between the narrow-and wide-gap sections of the structure and the doping level being the critically important parameters in the theory. p-type Si/Si_1?x Ge _x island structures with different sizes of islands and different band offsets were grown by molecular-beam epitaxy. Theoretical results are compared with the data on lateral conductance of the grown structures.     

DFT Quantum-Chemical Calculation of Thermodynamic Parameters and DSC Measurement of Thermostability of Novel Benzofuroxan Derivatives Containing Triazidoisobutyl Fragments

New derivatives of benzofuroxan containing triazidoisobutyl fragments, opening the way for the creation of highly effective compositions with an increased value of energy characteristics, were synthesized for the first time. Such compounds are also an excellent platform for further modification and for the preparation of new biologically-active compounds containing tetrazole and triazole fragments. Calculations of heats of formation performed with the DFT (density functional theory) method showed that the studied compounds are high-energetic density ones, the enthalpies of formation of which are comparable to the enthalpies of formation of similar benzofuroxan derivatives and exceeds experimental enthalpy of formation of CL-14 (5,7-diamino-4,6-dinitrobenzofuroxan). The analysis of DSC indicates a sufficiently high thermal stability of the synthesized azidobenzofuroxans, which are acceptable for their use as components in the creation of highly efficient compositions with an increased value of energy characteristics.     

Low-loss, high-permittivity composites made from graphene nanoribbons

A new composite material was prepared by incorporation of graphene nanoribbons into a dielectric host matrix. The composite possesses remarkably low loss at reasonably high permittivity values. By varying the content of the conductive filler, one can tune the loss and permittivity to desirable values over a wide range. The obtained data exemplifies how nanoscopic changes in the structure of conductive filler can affect macroscopic properties of composite material.     

Quasi-hydrodynamic simulation of the conductivity of heavily doped nanosize layered heterostructures in high electric fields

The electrical conductivity of nanosize-layered heterostructures in high electric fields is studied using the methods of mathematical simulation based on the equation of energy balance. It is shown that a characteristic feature of the corresponding current-voltage characteristics is a peak of the differential conductance, whose position and magnitude are determined by the heterobarrier height and steepness, as well as by the doping level of the structure. A physical model is suggested that accounts for the shape of the calculated characteristics by the combined effect of the electrostatic reduction in the heterobarrier height and the increase in the electronic temperature in the vicinity of the injecting heterointerfaces.