Rapid rheological characterization of a viscoelastic fluid based on spatiotemporal flow velocimetry

• A new method to characterize viscoelastic fluids in transient shear is proposed.
• Use of Particle tracking velocimetry and ultrasound velocity profiling are compared.
• Triadic relation among shear rate, shear strain, and shear stress are easily obtained.
• From the “Flow Surface” a variety of characteristics in rheology is visualized.

A method to characterize viscoelastic fluids in transient shear is proposed based on spatiotemporal flow velocimetry. Particle tracking velocimetry and ultrasound velocity profiling are functionally applied to obtain shear rate and shear strain of a fluid within a Couette system. The ratio of the cylinder radii is set large differently from ordinary Couette systems so that shear stress and shear strain in their designed ranges are available without changing the rotational speed. Simultaneously performing a torque measurement of the rotating cylinder with flow velocimetry, the spatiotemporal fluid response is converted into a triadic relation among shear rate, shear strain, and shear stress. The relationship is graphically represented as a “flow surface” in the three-dimensional parameter space. For an aqueous polyacrylamide solution, the elementary features, such as yield stress, shear wave, and shear-thinning trend, of the viscoelastic fluid reflected in the flow surface are read off. Finally, the experimental flow surface is directly applied for momentum conservation equation to simulate the viscoelastic flow structure as a demonstration.