液-液循环流化床制取流体冰过程的颗粒形成与运动特性

Drop Formation and Motion Characteristics During Fluid Ice Production in Liquid-liquid Circulating Fluidized Bed

采用水与另一种非相溶载冷液体直接接触换热制取流体冰的液-液循环流化床是一种全新的动态制冰方法,在所建立的循环流化床试验台上针对制冰过程的关键问题——颗粒(液滴、冰颗粒)形成及其运动特性展开研究,研究过程中采用快速摄像与图像处理相结合的方法,获得颗粒形成及其沿程运动过程的图像以及循环流化床不同高度上颗粒的粒径信息。研究发现射流形状、射流长度及其波动的变化规律直接影响形成液滴的粒径大小与均匀性;颗粒的沿程粒径分布具有向粒径增大方向倾斜与移动特征,并随射流液体流量的增大,颗粒的粒径分布范围与倾斜程度增大;颗粒在流化床内沿程运动过程中具有明显的颗粒聚团、聚并与分散现象,且颗粒的聚并现象不可避免,主要出现在流化床0.50 m高度以上,并随射流液体流量增大出现颗粒聚并现象的高度在增高。

Liquid - liquid circulating fluidized bed（LLCFB） is a novel method of dynamic ice - making. The key problems on droplets formation and droplets motion with the height of LLCFB were investigated in the established LLCFB experimental system with a high resolution digital camera and image processing. The images of drop formation and motion and information of drop sizes at different height were obtained. The results show that the shape of jet breakup, jet length, and its fluctuation influence the size and uniformity of drops. Moreover, the particles size distribution displays the sloping and shifting to the larger drop size with the height of LLCFB, and the range of particle sizes and the sloping extent increase with the increase of the jet flow rate. The convergence, coalescence and diffuseness of particles occur in the process of particles motion. In addition, the inevitable coalescence of particles mainly took place over an LLCFB height of 0.5m and this height increased with the increase of the jet flow rate.