Effects of Inter-Particle Force on Particle Behavior and Heat Transfer around a Horizontal Tube in a Fluidized Bed

实验研究了颗粒的黏结和后续团聚对水平管内颗粒行为和传热特性的影响。通过改变流化空气的湿度来控制液体桥引起的颗粒间粘结力。通过测量床层压降和目视观察，定量评价了含黏性颗粒流化床的总体行为。采用三种不同的实验方法研究了水平管周围的颗粒行为和传热特性。其中之一是同时测量颗粒行为（空隙率和颗粒速度）和管内同一位置的瞬时局部传热系数。另一种测量方法是使用微型摄像机从管内可视化温度和管内表面的颗粒。利用热敏液晶片对加热管周围的温度分布进行了可视化。并利用神经网络方法计算了换热系数的分布。通过从管内发射激光片，可以观察到颗粒和气泡在管内表面的行为。得到的主要结果如下：随着流化空气相对湿度的增加，颗粒间力增大，管周空隙率增大，管上表面颗粒的运动受到抑制，管周换热系数明显降低。利用由床层压降估计的通道指数，可以很好地与颗粒间力的增加引起的管内总平均换热系数的减小相关联。提出了从管内抛射激光片的可视化方法，该方法能清晰地区分与管内表面接触的颗粒和气泡。少

The effects of cohesiveness and subsequent agglomeration of particles on the particle behavior and heat transfer characteristics around the horizontal tubes were experimentally studied. The inter-particle cohesive forces due to a liquid bridge were controlled by changing the humidity of the fluidizing air. The gross behavior of the fluidized bed with the cohesive particles was quantitatively evaluated by measuring the bed pressure drop and visual observation.Three kinds of experimental method were used to study the particle behavior and heat transfer characteristics around the horizontal tube. One of these is the simultaneous measurement of the particle behavior (void fraction and particle velocity) and the instantaneous local heat transfer coefficient at the same location on the tube surface. The other measuring methods are the visualization of the temperature and the particles on the tube surface from the inside of the tube using a micro-video camera. The temperature profiles around … More the heated tube were visualized by using thermosensitive liquid crystal sheet. And the heat transfer coefficient distributions were calculated from them by Newral network method. The behavior of the particles and the bubbles on the tube surface were visualized by throwing a laser light sheet from the inside.The obtained main results are summarized as following : When the inter-particle forces increased as the relative humidity of the fluidizing air increased, the void fraction around the tube became higher and the movements of the particles on the upper surface of the tube were suppressed, and consequently, the heat transfer coefficient around the tube became significantly lower. The decrease of overall average heat transfer coefficients around the tube by the increase of the inter-particle forces can be well correlated by using the channeling index which is estimated from the bed pressure drop. The new visualization method by throwing the laser light sheet from the inside of the tube was proposed and it can clearly distinguish the particles making contact with the tube surface from the bubble. Less