垂直下降管内陶瓷球流动与传热的试验

Experimental study on the flow behavior and heat transfer of ceramic balls in a vertical descendant tube

为研究下降管式生物质热裂解反应器内陶瓷球的流动与换热规律,在一内径60 mm,长1.6 m的垂直管上利用粒子图像测速仪进行了陶瓷球流场测试和1.0、1.2、1.4 kg/min质量流量下90℃陶瓷球与室温空气的对流换热试验,分析出了陶瓷球在下降管内的滞留时间和陶瓷球与空气对流换热系数的计算方法。流场试验表明:轴向速度随下降距离增大而增大;任意下降距离处,在靠近管壁半径的15%距离内,陶瓷球的轴向速度逐渐增大,直至达到最大值后不再变化; 边壁附近的径向速度变化较大,中心速度基本为零。换热试验表明:不同陶瓷球流量下的对流换热系数基本相同,利用 Ranz-Marshall公式计算出的换热系数比理论分析计算的小;根据理论计算的换热系数和试验数据,回归出的努谢尔数与雷诺数的关系式为:Nup=2.0 +2Rep0.3712Pr1/3;在60～550℃范围内,利用回归式计算的换热系数与空气温度成线性关系,并随温度升高而增大。

The velocity field distribution of ceramic balls flow was measured with Particle Image Velocimetry(PIV)and the convective heat exchange experiments between ceramic balls of 90℃and the air of room temperature wereconducted in a verticle descendant tube(Diameter 60 mm,lengh 1.6 m)for discovering the ceramic balls flow behavior and heat transfer principles of the biomass pyrolysis descendant tube reactor.The residence time of the ceramic balls in the vertical descendant tube and the heat exchange coefficient w...