Rod Climbing and Normal Stresses in Heavy Crude Oils at Low Shears

G. A. Nunez, G. S. Ribeiro, A. S. Arney, J. Feng and D. D. Joseph

*J. Rheol.* **38**, 1251-1270 (1994)

**Abstract** - This paper gives the results
of a study of the nonlinear viscoelastic behavior of three heavy crude oils
from California and Venezuela. A linear combination of normal stress coefficients
at zero shear is expressed in terms of the quantity (the climbing constant)
used to measure the height of rise on a rotating rod. Measurements of the
climbing constants are given for the crude oils. Values of both the first
and the second normal stress coefficients at zero shear are determined by
the climbing constant when another combination of the two coefficients is
known. In principle, the required information can be obtained by back
extrapolation of the first normal stress difference, by back extrapolation
of the dynamic modulus or by back extrapolation of the ratio of the second
to first normal stress difference. Back extrapolation of data can be achieved
when measurements are available at shear rates low enough to enter onto the
second-order plateau of the functions generated by different instruments.
Examination of previously published data for well-characterized solutions
suggests that second-order rheology is most readily obtained in rod
climbing.