Effect of visco-plastic and shear-thickening/thinning characteristics on non-Newtonian flow through a pipe bend

Abstract

This study investigates the influence of the rheological parameters on the unyielded zone, pressure drop, and secondary flow pattern of non-Newtonian fluid like fresh cement mortar through a pipe bend with different curvatures. The regularized Herschel–Bulkley model is employed in the framework of lattice Boltzmann method to model the effects of the visco-plastic and shear-thickening/thinning characteristics with variations on the yielding stress σ0 and the power-law index n. The sharper curvature, higher power-law index contributes to a smaller and more asymmetric unyielded zone and even vanishes for curvature radius Rc=1D and n = 1.4, as the width and distribution of plug region are governed by the comparison between yielding stress and shear stress. The increased yielding stress and power-law index lead to an increase in the total pressure drop and additional pressure loss; however, their variations with respect to the curvature radius display an opposite trend. The intensity of the helical secondary flow in the elbow, primarily governed by the competition between the centrifugal and viscous force, is reduced to about one quarter when σ0 and n increase from 0 Pa and 0.6 to 50 Pa and 1.4.

Which Is an Appropriate Quadratic Rheological Model of Fresh Paste, the Modified Bingham Model or the Parabolic Model?

“…To study the rheological behavior of fresh cementitious materials using the parabolic model, the significance of the rheological parameters in the parabolic model should be analyzed. The parabolic model has two rheological parameters to describe the yield stress and viscosity of a fluid, which is similar to the Bingham model [5,6], and the third parameter describes the shear thickening or shear thinning. Therefore, three rheological parameters in the parabolic model need to be analyzed.…”

“…In the nonlinear rheological model, there are two concepts describing viscosity: apparent viscosity and differential viscosity [6,17]. Apparent viscosity indicates the slope of the line drawn from any point on the rheological curve to the origin of the coordinate.…”

“…The rheological expression of the Bingham model is simple. Two parameters in the Bingham model represent the yield stress and plastic viscosity of fresh cementitious materials [5,6]. With the comprehensive use of mineral admixtures and chemical admixtures, the rheological behavior of fresh cementitious materials deviates gradually from those described by the Bingham model [7][8][9][10][11][12].…”

“…In recent years, many studies [13][14][15][16] have shown that fresh cementitious materials exhibit shear thickening or shear thinning. Shear thickening or shear thinning describes the increase or decrease, respectively, in the apparent viscosity of a fluid with the increase in the shear stress [6,17]. The apparent viscosity of fresh cementitious materials with shear thickening or shear thinning is not constant, which corresponds to a nonlinear relationship between the shear stress and shear strain rate under the steady flow state.…”

Improved color-gradient method for lattice Boltzmann modeling of two-phase flows

“…LBM received a growing interest motivated by its scalability and its low dissipation properties, making it particularly well-suited for acoustic long distance dispersion problems 20 . It has been applied to a wide range of applications such as, reservoir permeability [21][22][23] , combustion flows 24 , blood flow 25 , boiling flow 26 , thermocapillarity flows 27 , non-Newtonian flows 28 , magneto-hydrodynamic flows 29 , cryogenic flows 30 , etc.…”