On the viscosity of a fluidized system

Summary By considering a fluidized state to be similar to a fluid with a given density, which depends on the voidage, a rough order of magnitude for the apparent shear viscosity of the fluid was found from a simple study of bubble motion in the fluidized state. A value for the viscosity of about 10 poise, or less, was found, which is in line with more recent suggested values.Using an expression for the continuum shear viscosity and bubble rise velocity given by the author previously a dependence of the bubble velocity on the voidage was indicated which showed that in fluidized states the velocity of rise increased with increasing voidage. This is in keeping with experimental observation.It should be noted both from the above and previous work in this area that the concept of a fluidized state as a simpleNewtonian fluid is limiting. With aNewtonian concept, however, considerable quantitative information has been found. This, not unexpectedly, has been in the area which might be described as the inviscid fluidized state.I would like to thank Mr,B. A. Partridge of the Chemical Engineering Division, Atomic Energy Research Etablishment, Harwell, England, for kindly supplying details of some of the experimental work quoted above and for the careful criticism and the time he gave to some of my ideas on the viscosity of a fluidized system.