Electrical impedance tomography (EIT) is used to investigate the net migrat
ion of particles in a suspension undergoing pressure-driven flow through a
tube at low Reynolds number. A low frequency electrical current is applied
to the flowing suspension by two flush-mounted electrodes on the pipe wall
to create a potential field which is sampled by other pairs of flush-mounte
d electrodes. A numerical inversion of the data, which takes into account t
he geometry and symmetry of the problem, gives the conductivity variation w
ithin the flow. An image of the suspension particle volume fraction in the
tube is then formed using a relationship between the local conductivity and
local suspension concentration. Consistent with particle shear migration o
f a concentrated suspension at low Reynolds number, the images from experim
ental data show a net migration of particles toward the centerline of the t
ube. The images of a 0.25 volume fraction suspension at the lowest Reynolds
number examined compare favorably to an existing continuum theory of parti
cle shear migration. Other images from experiments at higher, but still sma
ll Reynolds numbers, and at volume fractions of 0.25 and 0.40 are also pres
ented. The particle migration measured with the relatively inexpensive EIT
at the latter condition is in very good agreement with the particle distrib
ution measured with magnetic resonance imaging by Hampton et al. [J. Rheol.
41, 621 (1997)]. (C) 1999 American Institute of Physics. [S1070-6631(99)03
208-0].