Shuji Furui

Bubble behavior and void fraction fluctuation in vertical tube banks immersed in a gas-solid fluidized-bed model

Abstract Heat transfer characteristics of tube-banks immersed in a fluidized bed are dominated by the time averaged as well as fluctuating characteristics of fluidized-particle movement especially in the neighboring region of heat transfer tube. Quantitative flow visualization of the fluidized bed installed vertical tube-banks has been successfully conducted using neutron radiography and image processing technique. The quantitative data of void fraction distribution as well as the fluctuation data are presented. The bubbles formed in the bed rise along by the vertical tubes and observed bubble size is smaller than that in a free bubbling bed without tube-banks. The bubble diameter is well correlated by the modified Mori and Wens correlation. The bubble rise velocity is also well correlated by applying the drift–flux model. These results are consistent for both tested bed materials of Geldards B- and A-particles, while the bubble size is significantly different between two kinds of particles.

Flow visualization of segregation process in a fluidized-bed by neutron radiography

Owing to a wide variety in fluidization properties of particles, segregation phenomena are hardly avoided in industrial fluidized-bed facilities. For the stability and controllability in operation of such fluidized-beds, understanding of the relevant mechanism of particulate segregation is indispensable. This paper describes an experimental observation of the particulate segregation in a binary mixture system visualized successfully by using a neutron radiography (NR). The NR gives real-time information of the segregation process, and this information will be very useful in understanding the segregation mechanism.

Flow Visualization of Bed-Materials in a Fluidized-Bed Heat Exchanger Model by Neutron Radiography

Flow visualization of bed-materials in a fluidized bed was conducted using neutron radiography. The silica sand of the bed-materials are almost transparent for the neutron beam. To have a clear contrast of the visualized image, small amount of sand coated by cadmium sulfate was mixed into the bed-materials. Image processing technique was successfully applied to these images to obtain quantitative data of void fraction distribution.