Measurement of the flow behavior index of Newtonian and shear-thinning fluids via analysis of the flow velocity characte
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Measurement of the flow behavior index of Newtonian and shear‑thinning fluids via analysis of the flow velocity characteristics in a mini‑channel Shadi Ansari1 · Md. Ashker Ibney Rashid1 · Prashant R. Waghmare1 · David S. Nobes1 Received: 20 June 2020 / Accepted: 21 September 2020 © Springer Nature Switzerland AG 2020
Abstract An in-situ measurement technique to determine the rheology of a fluid based on the experimentally measured velocity profile of a flow in a mini-channel is introduced. The velocity profiles of a Newtonian and different shear-thinning fluids along a rectangular channel were measured using shadowgraph particle image velocimetry (PIV). Deionized water and different concentrations of a polyacrylamide solution were used as Newtonian and shear-thinning fluids, respectively and were studied at different Reynolds numbers. The flow indices of the fluids were determined by comparing the experimental velocity profile measurements with developed theory that takes into account the non-Newtonian nature of the fluids rheology. The results indicated that the non-Newtonian behavior of the shear-thinning fluid intensified at lower Reynolds numbers and it behaved more as a Newtonian fluid as the Reynolds number increased. A comparison between the power law index determined from experimental monitoring of the velocity profile at different Reynolds numbers and measurements from a rheometer reflected good agreement. The results from the study validate the new approach of the rheology measurement of Newtonian and non-Newtonian flows through straight, rectangular crosssection channels. The proposed approach can be further utilized using other methods such as X-ray PIV to characterize the rheology of non-transparent fluids and in general, for all non-Newtonian fluids. Keywords Velocity profile · Mini-channel flow · Rheological properties · Non-newtonian flow · PIV
1 Introduction In industrial applications for efficient transport of fluids or characterizing the motion of carried materials such as microorganisms in biological application [1] or components in drug delivery [2], a clear understanding of the carrying fluid’s rheology is needed [3]. The rheology of the fluid determines the flow parameters such as flow velocity and pressure field. Knowledge of rheological properties of the fluid flow behavior helps to obtain better understanding of the resultant pumping energy required for fluid transport [4], the energy required to transport the material [5] or the potential locations of the material deposition in a flow passage [6]. Hence, the quantification of
rheological properties of the fluid in a continuous manner would be beneficial to understand the flow phenomena both for a single-phase flow or for flows carrying suspended particles. Ex-situ rheological measurement techniques, such as a rotational rheometer [7] are currently the conventional approach for quantifying the rheological properties of the fluid. In these measurements, the bulk rheology of the fluid is measured by variation of shear rate and the shea
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