Using pseudorandom axial oscillations of concentric cylinders to measure the viscoelastic properties of fluids

A pair of concentric cylinders, where the inner cylinder is moved axially t hrough the outer fixed cylinder, is used to measure the dynamic viscoelasti c properties of a fluid which occupies the annulus between them. A micro-Fo urier rheometer is used to cause the inner cylinder to undergo small amplit ude, band-limited pseudorandom oscillations in the axial direction, with si multaneous measurement of the instantaneous resistance force due to the flu id. The magnitude and phase of the force signal are used to calculate the s torage and loss moduli G'(omega), G"(omega) as functions of oscillation fre quency omega. Tests performed on two types of silicone oil show fair agreem ent with results conducted with the parallel plate squeezing flow geometry.