为了研究生物质气化过程中流化床物料的流化状态,搭建了生物质流化床试验系统。以空气为流化介质,对石英砂进行流化试验,并在考虑物料颗粒间碰撞的基础上,基于DEM(discrete element method)模型对流化床床层区域空间内颗粒流动特性进行...为了研究生物质气化过程中流化床物料的流化状态,搭建了生物质流化床试验系统。以空气为流化介质,对石英砂进行流化试验,并在考虑物料颗粒间碰撞的基础上,基于DEM(discrete element method)模型对流化床床层区域空间内颗粒流动特性进行数值模拟。结果表明:当床层物料堆积密度、温度一定时,对应颗粒直径分别为0.56,0.35,0.18 mm的石英砂临界流化风速分别为0.017,0.065,0.170 m/s,物料粒径越小,达到流化状态所需要的流化风速也越小;数值模拟结果与试验结果相比,平均误差为23.1%,临界风速的预测与试验结果基本一致,这表明计算模型对于鼓泡状的两相流动状态有较好的预测效果。展开更多
The famous ’Hu Line’, proposed by Hu Huanyong in 1935, divided China into two regions(southeast and northwest) of comparable area size but drastically different in population. However, the classic Hu Line was derive...The famous ’Hu Line’, proposed by Hu Huanyong in 1935, divided China into two regions(southeast and northwest) of comparable area size but drastically different in population. However, the classic Hu Line was derived manually in absence of reliable census data and computational technologies of modern days. It has been subject to criticism of lack of scientific rigor and accuracy. This research uses a GIS-automated regionalization method, termed REDCAP(Regionalization with Dynamically Constrained Agglomerative Clustering and Partitioning), to reconstruct the demarcation line based on the 2010 county-level census data in China. The results show that the logarithmic transformation of population density is a better measure of attributive homogeneity in derived regions than density itself, and produces two regions of nearly identical area size and greater contrast in population. Specifically, the revised Hu Line by Hu Huanyong in 1990 had the southeast region with 94.4% of total population and 42.9% of total land, and our delineation line yields a southeast region with 97.4% population and 50.8% land. Therefore, the population density ratio of the two regions is 27.1 by our line, much higher than the ratio of 22.4 by the Hu Line, and thus outperforms the Hu Line in deriving regions of maximum density contrast with comparable area size. Furthermore, more regions are delineated to further advance our understanding of population distribution disparity in China.展开更多
To understand the mechanism of premixed flame quenching by porous media,a zonal hybrid RANS/LES model was employed,in which the LES flow solver was used to resolve the large turbulent structures within the non-porous ...To understand the mechanism of premixed flame quenching by porous media,a zonal hybrid RANS/LES model was employed,in which the LES flow solver was used to resolve the large turbulent structures within the non-porous region,while RANS was applied to porous media zone.The predicted results were compared with previous experimental data.And it was evident that the premixed flame propagation rates and structure as well as quenching behaviors were reproduced by this numerical approach with a better accuracy.Due to the inherently higher heat transfer coefficients between the solid and gas phases in porous media,the gas phase temperature has been decreased rapidly.However,upstream obstacles can cause the flame propagating faster and thus reduce the axial gas temperature gradients,resulting in the invalidity of the operation of premixed flame quenching.By comparison with the case without upstream obstacle,the values of reaction rate attained in the case with three pairs of obstacles are higher,which makes a positive impact on the flame passing through the porous medium.In addition,the porous media with greater pore density has an excellent flame quenching property mainly owing to both the larger volumetric heat transfer and higher quenching temperature.展开更多
This study uses six censuses (1953,1964,1982,1990,2000,and 2010) at the county level since the foundation of the People’s Republic of China to examine the changes of population density pattern in China's Mainland...This study uses six censuses (1953,1964,1982,1990,2000,and 2010) at the county level since the foundation of the People’s Republic of China to examine the changes of population density pattern in China's Mainland over time.Based on the Gini coefficient,the change of disparity in population density followed a “U-shaped” trend,i.e.,decreasing during 1953–1982 and increasing during 1982–2010.The shrinking disparity in the pre-reform periods was largely attributable to various ill-conceived political movements,and the enlarging gap in population growth rates in the post-reform era reflected a natural outcome of urbanization,which will continue in the foreseeable future.In addition,this research employs a GIS-automated regionalization method,REDCAP,to uncover a natural demarcation line like the classic “Hu Line” that divides China into two regions of similar area sizes but a strong contrast in population.The results show that the regionalization-derived lines were largely consistent with the Hu Line over time.Therefore,the disparity between the high-density southeast and low-density northwest regions is likely due to differing physical environments that form a natural barrier.Any public policy to overcome this barrier at a large scale is destined to be a vain attempt.展开更多
文摘为了研究生物质气化过程中流化床物料的流化状态,搭建了生物质流化床试验系统。以空气为流化介质,对石英砂进行流化试验,并在考虑物料颗粒间碰撞的基础上,基于DEM(discrete element method)模型对流化床床层区域空间内颗粒流动特性进行数值模拟。结果表明:当床层物料堆积密度、温度一定时,对应颗粒直径分别为0.56,0.35,0.18 mm的石英砂临界流化风速分别为0.017,0.065,0.170 m/s,物料粒径越小,达到流化状态所需要的流化风速也越小;数值模拟结果与试验结果相比,平均误差为23.1%,临界风速的预测与试验结果基本一致,这表明计算模型对于鼓泡状的两相流动状态有较好的预测效果。
文摘The famous ’Hu Line’, proposed by Hu Huanyong in 1935, divided China into two regions(southeast and northwest) of comparable area size but drastically different in population. However, the classic Hu Line was derived manually in absence of reliable census data and computational technologies of modern days. It has been subject to criticism of lack of scientific rigor and accuracy. This research uses a GIS-automated regionalization method, termed REDCAP(Regionalization with Dynamically Constrained Agglomerative Clustering and Partitioning), to reconstruct the demarcation line based on the 2010 county-level census data in China. The results show that the logarithmic transformation of population density is a better measure of attributive homogeneity in derived regions than density itself, and produces two regions of nearly identical area size and greater contrast in population. Specifically, the revised Hu Line by Hu Huanyong in 1990 had the southeast region with 94.4% of total population and 42.9% of total land, and our delineation line yields a southeast region with 97.4% population and 50.8% land. Therefore, the population density ratio of the two regions is 27.1 by our line, much higher than the ratio of 22.4 by the Hu Line, and thus outperforms the Hu Line in deriving regions of maximum density contrast with comparable area size. Furthermore, more regions are delineated to further advance our understanding of population distribution disparity in China.
基金supported by the National Natural Science Foundation of China(Nos.51174115,51604095)the Research Foundation of Education Bureau of Henan Province of China(No.14A410007)the research fund of Henan Key Laboratory for Green and Efficient Mining&Comprehensive Utilization of Mineral Resources
文摘To understand the mechanism of premixed flame quenching by porous media,a zonal hybrid RANS/LES model was employed,in which the LES flow solver was used to resolve the large turbulent structures within the non-porous region,while RANS was applied to porous media zone.The predicted results were compared with previous experimental data.And it was evident that the premixed flame propagation rates and structure as well as quenching behaviors were reproduced by this numerical approach with a better accuracy.Due to the inherently higher heat transfer coefficients between the solid and gas phases in porous media,the gas phase temperature has been decreased rapidly.However,upstream obstacles can cause the flame propagating faster and thus reduce the axial gas temperature gradients,resulting in the invalidity of the operation of premixed flame quenching.By comparison with the case without upstream obstacle,the values of reaction rate attained in the case with three pairs of obstacles are higher,which makes a positive impact on the flame passing through the porous medium.In addition,the porous media with greater pore density has an excellent flame quenching property mainly owing to both the larger volumetric heat transfer and higher quenching temperature.
文摘This study uses six censuses (1953,1964,1982,1990,2000,and 2010) at the county level since the foundation of the People’s Republic of China to examine the changes of population density pattern in China's Mainland over time.Based on the Gini coefficient,the change of disparity in population density followed a “U-shaped” trend,i.e.,decreasing during 1953–1982 and increasing during 1982–2010.The shrinking disparity in the pre-reform periods was largely attributable to various ill-conceived political movements,and the enlarging gap in population growth rates in the post-reform era reflected a natural outcome of urbanization,which will continue in the foreseeable future.In addition,this research employs a GIS-automated regionalization method,REDCAP,to uncover a natural demarcation line like the classic “Hu Line” that divides China into two regions of similar area sizes but a strong contrast in population.The results show that the regionalization-derived lines were largely consistent with the Hu Line over time.Therefore,the disparity between the high-density southeast and low-density northwest regions is likely due to differing physical environments that form a natural barrier.Any public policy to overcome this barrier at a large scale is destined to be a vain attempt.
