The flow rate of a steady flow of viscoelastic fluid under a constant pressure gradient in a toroidal pipe of circular cross-section is analytically solved with the White-Metzner constitutive equation by a perturbation method. It is examined how the shear thinning viscosity and elasticity affect the flow rate of the fluid at high shear rate to which former analyses could not be applied.
The analysis shows that the characteristics of the flow in a curved pipe are determined not only by the Dean number but also by the non-dimensional value W
e /√Rwhere W
e is the Weissenberg number and R is the ratio of toroidal radius to cross-sectional one. The results calculated for the ratio f
r of the flow rate in a toroidal pipe to that in a straight pipe under the same pressure gradient in the flow direction at low Reynolds number are asfollows :
(1) In the case of power law fluid in which W
e is zero, f
r decreases with increasing the Reynolds number R
e and with decreasing the viscosity index n. Thus, the resistance in a curved pipe is higher than that in a straight pipe.
(2) The larger W
e gives the larger f
r, thus the pipe resistance is smaller.
(3) The larger R
e and the smaller n give the larger degree of increment of f
r with increasing W
e.
(4) The effect of the elasticity index s, representing the shear thinning elasticity, on f
r is insignificant unless the value of n is small.
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