Dual Role of Viscosity During Start-Up of a Maxwell Fluid in aPipe

Based on the exact solution of start-up flow of Maxwell fluids in a long circular straight pipe, the effect of viscosity on the time of flow establishment is analysed. It is found that the viscosity of Maxwell fluids plays a dual role. A key parameter is the dimensionless relaxation time λ. For 0 < λ < 0.0432, the viscosity mainly plays the same role as in Newtonian fluids, and the time of flow establishment decreases with the increasing viscosity; for λ > 0.0432, the viscosity mainly plays a role of strengthening the oscillation, and the time of flow establishment increases with the incremental viscosity.