Journal of Non-Newtonian Fluid Mechanics 235 (2016) 143–153 Contents lists available at ScienceDirect Journal of Non-Newtonian Fluid Mechanics journal homepage: www.elsevier.com/locate/jnnfm Particles falling through viscoelastic non-Newtonian flows in a horizontal rectangular channel analyzed with PIV and PTV techniques Milad Khatibi ∗ , Rune W. Time, H.A. Rabenjafimanantsoa Department of Petroleum Engineering, University of Stavanger, Stavanger, Norway a r t i c l e i n f o Article history: Received 24 January 2016 Revised 15 August 2016 Accepted 16 August 2016 Available online 17 August 2016 Keywords: Particle fall velocity Non-Newtonian liquids Horizontal flow channel Impingement distance Scaling laws Numerical simulation a b s t r a c t Fall velocity of particles traversing through viscoelastic non-Newtonian flow in a horizontal channel was measured. Aqueous solutions of Poly-Anionic Cellulose (PAC) with two different concentrations 2 and 4 g/l were used as a continuous liquid phase. An experimental setup with a rectangular test section was car- ried out to achieve good optical conditions. Particle image velocity (PIV) and particle tracking velocity (PTV) techniques were used to measure fluid velocity, particle trajectories as well as particle fall veloci- ties. Experiments were also performed for Newtonian fluid (water) as a reference fluid. It was found that the particle fall dynamics is closely related to the fluid rheology as well as the local fluid velocity, shear rate and particle size. The more concentrated the PAC solution the stronger is the drag coupling, and with less spread in particle trajectory. The experimental results were compared with 3D CFD simulations. The effect of parameters which influences the hole cleaning aspects on model prediction was investigated and developed a correlation to predict the settling impingement distance of the particles. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Fall (settling) velocity of particles in fluid flow is a more com- plex quantity than often described in the literature. Through pre- vious studies researchers have mostly investigated the fall velocity (V s ) of particles in an “infinite” chamber [1–5]. This is not realis- tic for many practical industrial applications since there is obvi- ously governed a flow which might even be turbulent in the flow channel (as determined from channel Reynolds number, Re). In this work the particle fall velocity is investigated in non-Newtonian fluid flows, for particles falling perpendicular to the flow direc- tion, where the effects of drilling fluid velocity, shear thinning behavior, and particle size become crucial. This is highly impor- tant for hydraulic conveying of particles in the process systems and to the hole-cleaning (cuttings transportation in the annulus) in the hydrocarbon well drilling [6,7]. An even more accurate de- scription of the fall dynamics is provided when the particle tra- jectory/travelling path as a function of time was recorded using PTV technique. Two PAC solutions with different rheology, mainly shear thinning, were used to measure the fall velocity in applica- tions where such fluids are of importance. Chien [2] found that, ∗ Corresponding author. E-mail address: milad.khatibi@uis.no (M. Khatibi). if the fluid itself is in motion such as annulus flow in the drilling operation, the effect of fluid velocity on the fall velocity can be manifested through the change in the local shear rate ( ˙ γ ). Padhy [8] simulated the settling rate of spherical particles in a cross shear flow of viscoelastic fluid and found that the shear flow was reduc- ing the falling velocity as the drag was increased. In spite of predicting the particle trajectories, there is a partic- ular interest in predicting the impingement distance of particles. The impingement distance is defined as an axial particle displace- ment from the injection position to the impinged position at the bottom of the test section (see Fig. 1). This is practically impor- tant in the hydrocarbon well drilling to track the localized bed height and particle suspension trend. A correlation was developed to predict the impingement distance of particles in the horizontal channel flow. This correlation is validated with the recorded exper- imental data in this study. However, it should be complemented with further experiments and with different heights of the chan- nel. To better understand the effects of parameters affecting the par- ticle fall dynamics, the experimental results were compared with Computational Fluid Dynamics (CFD) simulations with different rheology models. The computational model accuracy and the im- pact of the experimental uncertainty on the numerical prediction were assessed in this study. The commercial code (ANSYS-Fluent) was used to conduct the 3D CFD simulations. http://dx.doi.org/10.1016/j.jnnfm.2016.08.004 0377-0257/© 2016 Elsevier B.V. All rights reserved.