Stability of Couette flow of liquids with power law viscosity |
| |
Authors: | M Jastrzębski H A Zaidani S Wroņski |
| |
Institution: | (1) Institute of Chemical and Process Engineering, Warsaw University of Technology, 1 Warynskiego Street, 00-645 Warsaw, Poland;(2) Bright Star Technical University, Brega, Libya |
| |
Abstract: | The stability of the Couette flow of the liquid with the power law viscosity in a wide annular gap has been investigated theoretically in this work with the aid of the method of small disturbances. The Taylor number, being a criterion of the stability, has been defined using the mean apparent viscosity value in the main flow. In the whole range of the radius ratio, R
i
/R
o
and the flow index, n, considered (R
i
/R
o
0.5, n = 0.25–1.75 ), the critical value of the Taylor number Ta
c
is an increasing function of the flow index, i.e., shear thinning has destabilizing influence on the rotational flow, and dilatancy exhibits an opposite tendency.In the wide ranges of the flow index, n > 0.5, and the radius ratio, R
i
/R
o
> 0.5, the wide-gap effect on the stability limit is predicted to be almost the same for non-Newtonian fluids as for Newtonian ones. The ratio on the critical Taylor numbers for non-Newtonian and Newtonian fluids: Ta
c
(n) and Ta
c
(n = 1) obey a generalized functional dependence: Ta
c
(n)/Ta
c
(n = 1) = g(n), where g(n) is a function corresponding to the solution for the narrow gap approximation.Theoretical predictions have been compared with experimental results for pseudoplastic liquids. In the range of the radius ratio R
i
/R
o
> 0.6 the theoretical stability limit is in good agreement with the experiments, however, for R
i
/R
o
< 0.6, the critical Taylor number is considerably lower than predicted by theory. |
| |
Keywords: | Flow stability Couette flow Taylor vortices power law viscosity |
本文献已被 SpringerLink 等数据库收录! |
|