A riser with high density has unique behavior as compared with conventional circulating fluidized bed. With increase of cross-sectional solids fraction, the radial profiles of solids fraction,and particle velocity bec...A riser with high density has unique behavior as compared with conventional circulating fluidized bed. With increase of cross-sectional solids fraction, the radial profiles of solids fraction,and particle velocity become significantly non-uniform. The objective of this paper is to develop unique internals that can improve the poor distribution of solids fraction and particle velocity. The experiments are conducted at a high-density riser with 0.186 m ID and 9.0 m in height. FCC particle with particle density 1398 kg·m -3 and average particle size of 54 μm as fluidized material. The apparatus was operated under typical conditions of high-density riser. Two-dimensional LDV and optical fiber density sensor are used to measure the particle velocity and solids concentration in the high-density riser. The radial solids concentration profile in the high-density riser is significantly changed with internals added in the riser. The solids concentration profile downstream the bluffs is much flatter than without internals case. The particle measurement shows that the core-annular structure is destroyed. Transient signal analysis shows that the particle turbulent intensity increases several times near the wall region. The addition of internals reduces the average solids concentration near the internals, while the solids circulating rate changes insignificantly with the addition of internals. The internals can make the radial solids concentration and particle velocity profile uniform downstream the riser, but the length that shows improvement of gas-solids flow in the riser by the internals is about 0.8 m.展开更多
为了深入探讨北京冬季云降水的微物理特征,提高雷达反演冬季固态降水的精度和冬季降水的预报水平,利用PARSIVEL(Particle Size and Velocity)降水粒子谱仪所观测的冬季降水粒子谱,结合地面显微镜粒子图像和云雷达数据,对比分析了北京海...为了深入探讨北京冬季云降水的微物理特征,提高雷达反演冬季固态降水的精度和冬季降水的预报水平,利用PARSIVEL(Particle Size and Velocity)降水粒子谱仪所观测的冬季降水粒子谱,结合地面显微镜粒子图像和云雷达数据,对比分析了北京海坨山地区冬季过冷雨滴、霰粒、雪花、混合态降水的粒子谱和下落速度特征,得到主要结论如下:(1)霰粒降水过程的云顶最高,整层的含水量最大,低层的退偏振比(LDR)最小,粒子更接近于球形;降雪过程的云顶最低,云中含水量最少,低层的退偏振比较大;混合态降水过程的雷达回波强度和高度特征介于两者之间,但低层的退偏振比最大;(2)在云中上升或下沉气流及湍流的影响下,过冷雨滴、霰粒和雪的下落速度均对称分布于各自理论下落末速度曲线的两侧。因此可根据粒子浓度相对于其直径和速度分布的中轴线位置,判断出该段降水过程中的主要粒子形态;(3)冬季雪花、霰粒和混合态降水粒子下落速度分布的散度较雨滴更大,其原因是由于冷云降水过程的粒子形态复杂,且固态粒子下落过程中更容易受破碎、聚并和凇附等微物理过程影响;(4)在4种降水类型中,雪的平均直径和离散度最大,雨滴最小;混合态降水粒子的总数浓度最大,雨滴的总数浓度最低,并且4种降水类型的粒子数浓度、平均直径和离散度均随降水强度的增大而增大。展开更多
文摘A riser with high density has unique behavior as compared with conventional circulating fluidized bed. With increase of cross-sectional solids fraction, the radial profiles of solids fraction,and particle velocity become significantly non-uniform. The objective of this paper is to develop unique internals that can improve the poor distribution of solids fraction and particle velocity. The experiments are conducted at a high-density riser with 0.186 m ID and 9.0 m in height. FCC particle with particle density 1398 kg·m -3 and average particle size of 54 μm as fluidized material. The apparatus was operated under typical conditions of high-density riser. Two-dimensional LDV and optical fiber density sensor are used to measure the particle velocity and solids concentration in the high-density riser. The radial solids concentration profile in the high-density riser is significantly changed with internals added in the riser. The solids concentration profile downstream the bluffs is much flatter than without internals case. The particle measurement shows that the core-annular structure is destroyed. Transient signal analysis shows that the particle turbulent intensity increases several times near the wall region. The addition of internals reduces the average solids concentration near the internals, while the solids circulating rate changes insignificantly with the addition of internals. The internals can make the radial solids concentration and particle velocity profile uniform downstream the riser, but the length that shows improvement of gas-solids flow in the riser by the internals is about 0.8 m.
文摘为了深入探讨北京冬季云降水的微物理特征,提高雷达反演冬季固态降水的精度和冬季降水的预报水平,利用PARSIVEL(Particle Size and Velocity)降水粒子谱仪所观测的冬季降水粒子谱,结合地面显微镜粒子图像和云雷达数据,对比分析了北京海坨山地区冬季过冷雨滴、霰粒、雪花、混合态降水的粒子谱和下落速度特征,得到主要结论如下:(1)霰粒降水过程的云顶最高,整层的含水量最大,低层的退偏振比(LDR)最小,粒子更接近于球形;降雪过程的云顶最低,云中含水量最少,低层的退偏振比较大;混合态降水过程的雷达回波强度和高度特征介于两者之间,但低层的退偏振比最大;(2)在云中上升或下沉气流及湍流的影响下,过冷雨滴、霰粒和雪的下落速度均对称分布于各自理论下落末速度曲线的两侧。因此可根据粒子浓度相对于其直径和速度分布的中轴线位置,判断出该段降水过程中的主要粒子形态;(3)冬季雪花、霰粒和混合态降水粒子下落速度分布的散度较雨滴更大,其原因是由于冷云降水过程的粒子形态复杂,且固态粒子下落过程中更容易受破碎、聚并和凇附等微物理过程影响;(4)在4种降水类型中,雪的平均直径和离散度最大,雨滴最小;混合态降水粒子的总数浓度最大,雨滴的总数浓度最低,并且4种降水类型的粒子数浓度、平均直径和离散度均随降水强度的增大而增大。
