Tj. Heindel et Jl. Monefeldt, OBSERVATIONS OF THE BUBBLE DYNAMICS IN A PULP SUSPENSION USING FLASH X-RAY RADIOGRAPHY, Tappi journal, 81(11), 1998, pp. 149-158
A better understanding of bubble dynamics in an air/water/fiber suspen
sion is important to many paper processing areas, including flotation
deinking and gaseous bleaching. However, using conventional visualizat
ion techniques to view gas bubbles in pulp suspensions is nearly impos
sible because these systems are opaque at consistencies relevant to th
e paper industry. Therefore, alternative tools and techniques must be
developed to characterize bubble behavior in these complex systems. In
this study, flash X-ray radiography (FXR) is used to visualize air fl
ows in a suspension of unprinted old newspaper (ONP) at various consis
tencies and air injection rates. FXR provides stop-motion images of ai
r bubbles rising through the opaque ONP suspension. The technique is e
ffective because air has a significantly different X-ray attenuation c
oefficient than water or wood pulp, which have similar attenuation coe
fficients. Qualitative observations of these air/water/fiber flow cond
itions are reported and compared with those obtained in a simple air/w
ater system. The radiographic images reveal that agas flow characteris
tics are substantially altered in the presence of fibers. The results
demonstrate that gas flows in a simple air/water system are not the sa
me as those in an air/water/fiber system.