炼焦煤成焦过程中微观结构演变规律的研究进展

炼焦煤在热塑性阶段发生复杂的化学反应会导致微观物理化学结构剧烈变化从而影响焦炭质量,因此深入探究炼焦煤成焦过程中微观结构演变规律对于阐明结焦机制、指导配煤炼焦、生产高质量的焦炭具有重要意义。阐述成焦过程中微观结构的演变过程,综述炼焦煤成焦过程中微观结构演变规律,表明煤—焦微观物理化学结构变化会影响宏观热塑性,而焦炭模型的建立有利于从微观角度认识焦炭的宏观性质。通过综述炼焦煤成焦过程中微观结构演变规律可得出如下结论:宏观热塑性与煤、焦微观物理化学结构的转变过程密切相关,即其与矿物质、预热速率、煤岩组成以及炼焦煤本身的结构有关;炼焦煤在成焦过程中发生了复杂的微观物理化学结构变化,热塑性阶段孔隙率总体呈现出减小—上升—再减小的过程,芳烃缩合度不断上升,脂肪族碳氢含量不断下降,且炼焦煤性质和炼焦工艺也会对与煤成焦过程中微观结构的转变过程造成影响;焦炭结构的形成与煤—焦物理化学结构的变化有关。目前对于煤—焦微观结构的演变规律具有一定认知,但煤成焦过程是在时间和空间上同时进行的动态过程,而大多数研究只针对其中1个维度进行研究,在全面模拟成焦过程方面需进一步加强研究。

Simulation of the Microphysical Processes and Effect of Latent Heat on a Heavy Rainfall Event in Beijing

An extraordinary rainstorm that occurred in Beijing on 21 July 2012 was simulated using the Weather Research and Forecasting model. The results showed that:(1) The two precipitation phases were based on a combination of cold cloud processes and warm cloud processes. The accumulated conversion amount and conversion rate of microphysical processes in the warm-area phase were all much larger than those in the cold front phase.(2) 72.6% of rainwater was from the warm-area phase. Rainwater mainly came from the melting of graupel and the melting of snow, while the accretion of cloud water by rain ranked second.(3) The net heating rate with height appeared as an overall warming with two strong heating centers in the lower and middle layers of the troposphere and a minimum heating center around the melting layer. The net heating effect in the warm-area phase was stronger than that in the cold front phase.(4) Warm cloud processes contributed most to latent heat release, and the thermal effect of cold cloud processes on the storm in the cold front phase was enhanced compared to that in the warm-area phase.(5) The melting of graupel and snow contributed most to latent heat absorption, and the effect of the evaporation of rainwater was significantly reduced in the cold front phase.

Modelling of grain boundary impurity segregation during high temperature plastic deformation

A modified theoretical model is proposed to predict the grain boundary segregation of impurity atoms during high temperature plastic deformation. The model is based on the supersaturated vacancy-impurity complex created by plastic deformation and involves quasi-thermodynamics and kinetics. Model predictions are made for phosphorus grain boundary segregation during plastic deformation in ferrite steel. The results reveal that phosphorus segregates at grain boundaries during plastic deformation. At a given temperature, under a certain strain rate the segregation increases with increasing deformation amount until reaching a steady value, and at the same deformation amount it increases with increasing strain rate. The predicted results are compared with the available experimental values, indicating that there is a reasonable agreement between the theoretical predictions and the experimental observations.

Study on Wood Drying Properties under Vacuum-floating Pressure

Using Masson pine as specimens, when drying mediums are overheated steam and hot-air respectively, preheating characteristics of wood under vacuum-floating pressure drying are discussed by measurement of internal temperature field and variation of moisture content during period of preheating. The relationship between drying medium conditions and drying rate of wood reveals that, firstly, compared with process of air-drying, time needed to be preheated under vacuum-floating decreased dramatically, meanwhile,the magnitude of condensation on the surface is relatively larger. Secondly, drying rate of wood under vacuum-floating pressure increases coupled with temperature of medium, reduction of absolute pressure,and raise of fluctuation rate of pressure. The sequence of factors contribution to drying rate is listed as following: temperature of medium (t) > fluctuation rate of pressure (f)> absolute pressure (p).