Optical properties of carbonized sporinite in vitrinite/sporinite blends

A study is made of the morphological and optical properties of a blend of concentrated sporinite and vitrinite macerals (equal parts) from the same coal carbonized between 400–900 °C at 5 °C/min under nitrogen. Two coals of different rank were used and the results compared with properties of unblended carbonized sporinites. Coke from a blend of low-rank vitrinite and sporinite produced a two-phase optical texture, whereas coke from the medium-rank vitrinite and sporinite mixture produced a three-phase optical texture. A ‘Transitional Zone’ of optical texture was observed at interfaces between carbonized vitrinite and sporinite, this zone being wider for the coal of higher rank. The increase of bireflectance in oil with carbonization temperature of the sporinite in the blends was lower than for the carbonized unblended sporinite, caused by a reduction in fluidity of sporinite with blending. The decrease of refractive index for sporinite carbonized > 600 °C in the blends was lower than that of the unblended sporinite.     

Effect of freezing on the dynamic mechanical response of hardened cement paste down to −60°C

The dynamic mechanical response (the internal friction, tanδ, and the E-modulus) in the temperature range from −60°C to 0°C reveals a sharp modulus change and a shallow tanδ peak. This “capillary transition” occurs only in specimens suspected of having capillary water; its strength is both a function of moisture content and the pore structure. The E-T curve in the transition region for a number of saturated specimens is fitted by an empirical equation; the parameters of this equation are correlated with the capillary porosity, defined in the conventional manner. One of these parameters is interpreted in terms of a maximum pore size. A theory is outlined for interpreting the E-T curve in terms of thermodynamic, composite mechanics, and pore structure parameters. The discovery of the “capillary transition” has made available a new technique for investigating the various, rather complicated aspects of the process of freezing within a porous solid.     

Effect of prolonged heating on the optical properties of vitrinite

Vitrinites ranging from sub-bituminous to anthracitic rank have been heated at 150 and 350 °C for residence times extending up to 32 weeks. Devolatilization vacuoles develop in all the vitrinites at 350 °C, apart from the anthracitic. Occasional small vacuoles formed in the vitrinites of coking rank at 150 °C are most probably related to gas evolution from liptinites. Slight rounding of the margins of vitrinite particles of coking rank at 350 °C indicates softening, while heating at the longest residence time has been sufficient to allow vitrinites of coking rank to undergo ‘active decomposition’. Mosaic structures have developed at temperatures as much as 125 °C below those normally attributed to the formation of such structures in short-term laboratory carbonization experiments on vitrinites of the same rank. Again, apart from the vitrinites of anthracitic rank, the reflectance of vitrinites shows a rise at 150 and 350 °C that would continue beyond the longest residence time used. At 350 °C a large part of the reflectance increase occurs during the first week of heating. The reflectance data and the derived refractive and absorptive indices indicate that with sufficiently long residence times, changes that are more fundamental than ‘molecular stripping’ must take place, probably involving condensation reactions that introduce increased coplanarity into the vitrinite molecules. The implication of these data to thermal metamorphism of coals and to the normal coalification process is briefly discussed.     

The Impact of Ventilation Rate and Partition Layout on the VOC Emission Rate: Time-Dependent Contaminant Removal

A numerical study has been carried out to predict the indoor air quality in a newly painted partitioned office and to assess the effect of ventilation rate and partition layout on the pre-ventilation time required to allow the contaminant concentration level to drop to an acceptable level. The air-flow pattern, the time history of the average contaminant concentration level in the occupied zone, and the pre-ventilation time were computed by a CFD code with a K-ε turbulence model. A displacement ventilation system, with different operating conditions, was used to remove contaminants in the office. The VB emission model, developed by Guo and Tichenor (1992), has been improved to include the influence of non-uniform concentration distribution on contaminant emission rate from the paints. The average contaminant (VOC) concentration levels in the occupied zone and in each chamber were recorded hourly until the average concentrations in the office were less then 0.0005 g/m³. It has been found that the non-uniform concentration distri- bution greatly influences the decay rate of VOC emissions. The time required for the average concentration in each chamber to reach the threshold level is different, since they are non-uniform. The time differences between the chambers having the highest and lowest concentrations were 3 to 8 hours. The results also show that the time required to reduce the concentration in the occupied zone to the threshold level is dependent on the partition layout. For the same ventilation rate, the required time is approximately 4-8 hours longer when using a side layout than when using a central layout.     

Reducing Dangerous Effects of Unsymmetrical Dimethylhydrazine as a Liquid Propellant by Addition of Hydroxyethylhydrazine—Part I: Physical Properties

In this work, the effect of low volatile hydroxyethylhydrazine (HEH) as a solute on unsymmetrical dimethylhydrazine (UDMH) has been studied in order to reduce harmful effects of UDMH vapors. Desirable physical properties of binary mixtures UDMH/HEH have been measured and compared to pure UDMH. These properties include boiling point, viscosity, density, and vapor pressure that are important for using binary mixtures of UDMH/HEH as less dangerous liquid propellants. Due to the formation of strong hydrogen bonding between UDMH and HEH, the volatility of UDMH has been reduced appreciably upon the addition of HEH. It is indicated that the measured physical properties may deviate significantly compared to corresponding predicted values. Binary mixtures of UDMH/HEH can also react spontaneously in contact with nitrogen tetroxide (NTO) and red fuming nitric acid (RFNA), so they can be called hypergolic propellants.     

Two-stage flow-shop scheduling problem with non-identical second stage assembly machines

This paper addresses the two-stage assembly flow-shop problem (TSAFP) with multiple non-identical assembly machines in second stage with the objective function of makespan minimization. This problem is a generalization of previously proposed problems in TSAFP. Mathematical mixed-integer linear programming model of this problem is defined, and for it being NP-hard, a hybrid SA heuristic is proposed. The heuristic is proved to solve the problem in reduced time with negligible error. To validate the proposed method, a real-life example is presented and solved in which the efficiency of the proposed heuristic is shown.     

圆形封闭水箱非稳态数值模拟

采用数值方法对圆形封闭水箱内放置两根加热管的二维流动传热进行了非稳态数值模拟,探讨了Ra数从104到107四种情况和封闭水箱的加热管不同摆放位置下的流动和换热;对流场和温度场进行了分析,讨论了不同情况下加热管平均努赛尔数(Nuavg)的变化情况。数值模拟结果表明,随着Ra数增大水箱内的流动表现出了很大变化,决定了传热是导热或者是对流;两个水平加热管在水箱存在最佳的放置距离,这样可以使自然对流情况下的换热达到最好。     

Optimization of ventilation systems in office environment,Part II: Results and discussions

Whether one considers the issues related to office workers' well-being and productivity or the issues from an energy and environmental perspective, there are clear evidences in favor of improving the quality of office environment. Part I of this paper proposed a simulation-based optimization approach by using computational fluid dynamics (CFD) techniques in conjunction with genetic algorithm (GA), with the integration of an artificial neural network (ANN) for response surface approximation (RSA) and for speeding up fitness evaluations inside GA loop. In this part, the results from data preparation for ANN model construction, ANN training and testing, and sensitivity analysis (regarding the impact of weighting factors in the objective function on the optimization results) are presented. Final optimization results indicate that the present choices of objective function and optimization approach are able to result in great improvement in the design and operation of ventilation systems in an office environment, with the goal of enhancing the thermal comfort and indoor air quality (IAQ) without sacrificing the energy costs of ventilation.