In drilling operations, cuttings transport is one of the crucial tasks performed by the drilling fluid. To be able to predict the true volumetric flow rate of the cuttings it is necessary to understand how the momentum is transferred from the fluid to the particles. This has been the subject of research for more than a century. However, there are still open questions. Due to high apparent viscosities of the fluid, cuttings are typically transported under laminar flow conditions. Moreover, the particle equivalent diameters are far from uniform and polydispersed suspensions and non-Newtonian fluids need to be considered. Many empirical correlations have been obtained to predict the transport of cuttings. However, the results are limited to flow systems similar to the ones analyzed. A better understanding of the transport mechanisms would help to obtain more general predictive tools.

In this contribution, we present an experimental setup used to measure fluid velocities and bidispersed particle velocities and position distributions. The particle image velocimetry (PIV) and the particle tracking velocimetry (PTV) methods are used to obtain flow fields of several bidispersed suspensions with varying particle diameter ratio and concentration. The results supply locally averaged fluid and particle velocity profiles and fluctuations of the particle velocities in the axial directions. These allow us to evaluate the effect of polydispersity on momentum transfer. Furthermore, histograms of the particle positions are used to investigate the effect of velocity gradients on the lateral distributions of semi-dilute suspensions. The results will be used for the development and validation of constitutive relations used in multiphase numerical methods such as the two-fluid model.

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