Development of a Neutron-Radiographic Technique for Investigating Physical Models of Fluidized Beds

This paper describes the results of the application of neutron radiography to the study of a two-phase medium, and the resulting technique can be extended to the study of two-phase flow in a fluidized bed. Neutron radiography allows the nonintrusive visualization of a sand/air bed enclosed in aluminum walls. This capability exceeds what others have been able to observe using conventional optical or radiographic techniques. A static 15 cm thick sand model was constructed and examined by the radiographic technique. The technique employed a collimated thermal column of neutrons, an image intensifier, and conventional photography. To simulate a fluidized bed, spherical voids of several centimeters in diameter were created by placing thin-walled empty aluminum shells in the sand bed. Also, hollow tubes were inserted in the bed. As a function of neutron fluence, high contrast images of the voids inside the 15 cm thick bed were obtained and analyzed. This technique can be extended to the study of dynamic beds by using the neutron source, i.e., the nuclear reactor, in the pulsed mode. Also, contrast agents may be used to extend the range of experimental situation under which high contrast images may be obtained.