A flow method for measuring difusion coefficients in power law fluids

Laminar Flow Dissolution and Diffusion in Non-Newtonian Fluid

“…The present observation of decrease in the diffusivity with polymer addition is thus in agreement with these findings. Similarly, the observed absence of the effect of shear rate on the diffusivity is also in agreement with the findings of others (2,12,28,30).…”

“…The results for aqueous CMC solution are compared with the published data in Table III. The present values are in good agreement with the results of Hansford and Litt ( 12), Deo and Vasudeo (28), and Mishra and Singh (30), but differ from that of Astarita (7). According to Deo and Vasudeo, the higher value reported by Astarita is due to the use of erroneous solubility data.…”

“…Out of the various experimental methods used by the previous workers, the diffusion cell (8,14,20), interferometric technique (6), laminar jet (3,5,18,19), membrane technique (4,9), polarographic (16), refractometric (13,15), and stagnant medium (1,10,17) techniques are ineffective in showing the effect of shear rate, if any, on the diffusivity. The results obtained with flow methods, such as falling films and wetted walls (11,23,26,27), rotating cones, disks, and spheres (12,21,22,24,25,29,30), dispersion in flowing fluids (28), and dissolution during flow along inclined planes and through tubes (2,7) show no effect of shear rate in the range investigated. This point, however, needs further attention because the shear rate range covered in most of these studies is narrow.…”

Diffusion coefficient in aqueous polymer solutions

“…Out of the various methods used by previous workers, the diffusion-cell, interferometric, membrane, polarographic, refractometric, and other stagnant-medium techniques are Ineffective in showing the effect of shear rate, if any, on the molecular diffusivity in polymer solutions (3). Thus flow techniques like laminar jet (4-7), falling films and wetted walls (8-10), rotating cones, disks, and spheres (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21), dispersion in flowing fluid stream (22), and dissolution during laminar flow along plates and through tubes (3,23,24) have been extensively used for the measurement of molecular diffusivity in polymer solutions. In many of these the experimental conditions were such that mass transfer occurred in a constant-velocity (or zero-shear) field (4)(5)(6)(7)(8)(9)(10).…”

“…Consequently, the influence of shear rate on the molecular diffusivity could not be assessed from these studies. Remaining techniques (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24), however, do indicate that the molecular diffusivities remain unaffected in a finite shear field. Some of the flow techniques, which have been successfully used with gases, are unsuitable for solid solutes.…”