Advanced Materials Research Vols. 560-561

Abstract: To acquire better understanding of the early ignition phenomena in 100mm ignition simulator loaded with packed propellant bed, a theoretical model of ignition gas flow through rigid porous media is developed. Three pressure gauges are installed in the lateral side of ignition simulator for chamber pressure measurements after ignition. The pseupropellant loaded in the chamber is similar to the standard 13/19 single-base cylindrical propellant in size. It is composed of rigid ceramic composite with low thermo conductivity. It is assumed that the pseupropellant bed is rigid in contrast to the previous elastic porous media assumption. The calculated pressure values can be verified by the experimental data well at the low loading density of pseupropellant bed of 0.18 g/cm³. However, there is still error between the experimental and calculated results in the early pressure peak position close to the ignition primer when the loading density of pseupropellant bed increases to 0.73 and 1.06g/cm³, due to the change of local permeability of pseupropellant bed at high loading density, which is assumed a constant in the model for the modeling easily. The calculations can enable better understanding of physical processes of ignition gas flow in the ignition simulator loaded with the pseupropellant bed.

Abstract: This paper addresses the potential of molecular dynamics simulation for structure–property correlations in rubber. This is an important topic within a multi-scale framework to rubber blends. For that purpose, the Mechanical Properties of NR(Natural rubber)/TPI(Gutta percha) are studied by Molecular dynamics simulation method. The result indicates that the NR/TPI’s properties have been improved significantly. Compared to the pure TPI, the rubber blends’ Modulus and rigidity decrease while flexibility and strength are enhanced. Based on these, the pair correlation functions are discussed, the best simulation technique identified in this study reveal the nature of interactions between the components of the blends.

Abstract: Based on mass conservation and Fick’s diffusion law, a model for describing the nutrient release from coated urea particles was proposed. This model was verified by the release data of three novel paraffin- rosin coated urea in distilled water. The results indicate that the model is effective in describing and predicting the delivery behaviors for a diffusion-controlled coated- urea and their correlation coefficients R2 are 0.9976, 0.9973 and 0.9984, respectively. The model shows that the nutrient release rate for coated urea is direct proportion to effective diffusion coefficient Deff, inverse proportion to diameter’s square of urea granule and inverse proportion to the coating thickness.

Abstract: Abstract. Parallel reaction is a common reaction of chemical kinetics, and there are two types of parallel reactions according to the reaction orders equivalence: parallel reactions with same reaction orders and parallel reactions with different reaction orders. For the reason that the reaction orders are different, the chemical kinetic numerical computation and kinetic model parameters estimating of parallel reactions with different reaction orders is more complicated than parallel reactions with same reaction orders. In this paper, the 4th order Runge-Kutta method was employed to solve the numerical computation problems of complex ordinary differential equations, which was the chemical kinetic governing equations of parallel reactions with different reaction orders, and also, the Richardson extrapolation and Least Square Estimate were employed to estimate the kinetic model parameters of parallel reactions with different reaction orders. A C++ program has been processed to solve the problem and has been tested by an example of parallel reactions with different reaction orders.

Abstract: Theoretical multiscale model of nitride semiconductor nanostructure is proposed. The model combines various computational methods such as density functional theory, molecular dynamics and kinetic Monte Carlo. As a first step of implementation of proposed approach ab initio calculations of structural and electronic properties of two different structures InN/Si and AlN/AlGaN/GaN heterostructures were carried out. In particular, the influence of oxygen on InN/Si adhesion energy was studied. AlN, GaN, Al_xGa_1-xN (x=0.33) spontaneous and piezoelectric polarizations as well as sheet carrier concentrations at GaN/AlGaN interface were calculated. Obtained value for sheet carrier concentration at GaN/AlGaN interface is close to experimental data.

Abstract: Molecular dynamic simulation for Co cluster deposition on Si substrate was investigated in this work. The surface roughness and the interface mixing will be evaluated for the deposited film quality under different incident energies and substrate temperatures. The effect of thermal annealing on the ability of gap filling will be discussed by a slip vector. The results indicate that the incident energy has dominant effect on the surface roughness, and there is a minimum surface roughness value around the incident energy of 8 eV. However, the substrate temperature has little effect on the surface roughness. For interface mixing, the simulation indicates the easy diffusion of Co atoms into Si substrate. However, increasing either the incident energy or the substrate temperature could not change much the mixing conditions. As for the ability of gap filling, it is clear that the thermal annealing does improve this ability and obtains better surface roughness and interface mixing.

Abstract: Adding tubes on the bottom of delayed coking furnace is an useful measure for enhancing the throughput, but the distance between tubes and burners is too small to conform design standard. The security of these bottom tubes is uncertain. The processes of turbulence, combustion and heat transfer in the furnace were simulated by numerical method. Detailed information of velocity field, temperature field and heat flux was obtained. The heat transfer of tubes in entrainment zone of jet flame was investigated. The possibility of tube oxidation and hot spot was also discussed. Results show that the bottom tubes are security, which located in the low temperature field and the range of heat flux is 22~45 kW/m². The results are in good agreement with industrial testing data.

Abstract: Power generator used as one of the main parts of a power plant, plays a big role in power ‎generation. Its high performance in continuous power generation is very important. Parameters of ‎temperature, insulating materials quality and performance of its cooling system affect on its ‎efficiency and lifetime. Cooling gas temperature monitoring can help us control it in the suitable ‎range, and as the gas is circulated inside the generator area, it can help scientists to find probable ‎defects of the system [1]. Organic insulating materials used in big power generators, degrade and ‎overheat after working long time, or because of electrical defects, and cause thermal decomposed ‎sub micron products entrained in the gas stream coolant of power generator [2]. By sampling and ‎chemical analysis of cooling gas detection of sub micron decomposition products is possible. ‎Therefore it is possible to prevent some unexpected troubles in different parts of generators like ‎stator core, rotor or stator winding [4]. This paper contains design and development of a system for ‎simulating of insulating material and coatings thermal decomposition with the same atmosphere as ‎generators, named Pyrolyzer, which has a hot plate to pyrolysis electrical insulating materials, and ‎on other hand decrease the temperature of the inside atmosphere to room temperature. And then ‎explains pyrolysis of insulators, sampling of cooling gas impurities, analysis of impurities by GC-‎MS, and identification of the overheat products, in order to use them as patterns and witnesses of ‎condition monitoring analysis of power generators.‎

Abstract: It is time-consuming to dry the caffeine colloid got from caffeine methylation liquid after evaporating crystallization and cooling crystallization. To solve this problem, the laboratory equipment is designed to simulate vacuum rotating dryer to dry the caffeine colloid. Through the single-factor experiment and orthogonal experiment, the suitable dry conditions are determined as follows: the heating temperature is 110 °C; the vacuum degree is 0.09 MPa; the stirring speed is 250 rpm. The drying time under the optimal process conditions is reduced to 1.01hours.

Abstract: A mathematical model describing the transient hydrodynamic behaviours is introduced to predict the effect of magnetic field intensity and process parameters in magnetically stable fluidized beds (MSFBs). Computational fluid dynamics (CFD) code Fluent 6.2 has been used to investigate the hydrodynamics of a gas-solid MSFB operated with fine particles. The model is incorporated into simulations based on an Eulerian approach. In the simulations, the closure models describing the hydrodynamics of the solids phase are directly affected by the behavior of magnetic field intensity. The simulations are compared with experiments at different gas Reynolds numbers (ReG = uGdp/vG) and magnetic field intensity (Er = 3μ0MpH/2gdpρp). The agreement obtained between the simulation results and experimental data for local solid holdup is good at lower ReG and Er values.