Abstract
The present experimental study addresses the flow of a Yield Stress Fluid with some elasticity (Carbopol gel) in a square duct. The behaviour of two fluids with lower and higher yield stress is investigated at multiple Reynolds numbers $Re^* \in$ (1, 200) and Bingham numbers $Bi \in$ (0.01, 0.35). A secondary flow consisting of eight vortices is observed to recirculate the fluid from the corners to the core. Their extent and intensity grows with increasing $Re^*$. The second objective of this study is to explore the change in flow in the presence of particles. Almost neutrally-buoyant finite-size spherical particles with duct height, $2H$, to particle diameter, $d_p$, ratio of 12 are used at two volume fractions $\phi$ = 5 and 10\%. Particle Tracking Velocimetry (PTV) is used to measure the velocity of these refractive-index-matched spheres, and PIV to extract the fluid velocity. Simple shadowgraphy is also used for qualitatively visualising the development of the particle distribution along the streamwise direction. The particle distribution pattern changes from being concentrated at the four corners, at low flow rates, to being focussed along a diffused ring between the center and the corners, at high flow rates. The presence of particles induces streamwise and wall-normal velocity fluctuations in the fluid phase; however, the primary Reynolds shear stress is still very small compared to turbulent flows. The size of the plug in the particle-laden cases appears to be smaller than the corresponding single phase cases. Similar to Newtonian fluids, the friction factor increases due to the presence of particles, almost independently of the suspending fluid matrix. Interestingly, predictions based on an increased effective suspension viscosity agrees quite well with the experimental friction factor for the concentrations used in this study.
Highlights
We have presented an experimental study of the flow of an elastoviscoplastic fluid, Carbopol gel, at two different concentrations – one with a high yield stress and the other with a low yield stress – and studied the laminar single-phase flow and the flow in the presence of finite-size spherical particles at relatively high concentrations inside a square duct
Mean and fluctuating velocities and concentration fields have been measured using a combination of particle image velocimetry (PIV) and PTV; these optical techniques have been possible due to the refractive-index matching of the fluid–particle mixture
The experimental pressure drop is in agreement, over the range of flow rates considered, with the laminar friction factor based on the semi-empirical Reynolds number Re∗ (see (1.1)) by Liu & Masliyah (1998)
Summary
Ancey (2007) and Chambon, Ghemmour & Naaim (2014)) Before yielding, they have solid-like properties e.g. they can sustain shear stress and deform elastically, whereas after yielding they behave like a fluid. It is used to assess the shelf life of paints, keep particulate fillers from settling in many consumer products and dictates whether bubbles remain trapped in cement (Singh & Denn 2008). The latter is an important factor in the structural integrity of buildings
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call