Herschel–Bulkley fluid

About: Herschel–Bulkley fluid is a research topic. Over the lifetime, 1946 publications have been published within this topic receiving 49318 citations.

Experimental characterization of the fluid dynamics in an in‐vitro system simulating the peristaltic movement of the stomach wall

Abstract: The difficulty in experimentally characterizing the dynamics of gastric contents during digestion has limited the knowledge required to understand and model the kinetics of food disintegration. The goal of this work was to experimentally characterize, in a closed system, the peristaltic flow of fluids with different rheological properties. An experimental apparatus was developed to reproduce the general characteristics of gastric motility, while supporting the use of a non-intrusive flow measurement technique (Particle Image Velocimetry). The apparatus consisted of a polycarbonate chamber with one neoprene wall that was continuously deformed by vertically moving a stainless steel cylinder at a speed of 3.5 mm/s. The fluid dynamics of three Newtonian fluids (water, and water solutions of 10% and 95% corn-syrup) and two shear thinning fluids (water solutions of 0.15% and 0.50% CMC) were investigated. In addition, the effect of the occlusion ratio (30, 45 and 60%) on the fluid dynamics of water within the system was analyzed. Experimental results showed that the loci of maximum velocity were present in the section corresponding to the location of the hump peak. As the viscosity of the Newtonian fluid increased, higher and more localized retropulsive velocities developed. However, these differences were not observed in the dynamics of shear thinning fluid flows. As the viscosity of the fluid increased, a more ordered flow developed, but no differences were found with respect to maximum values of shear rates or vorticity. The differences in the overall flow behaviour of the two CMC solutions were even less noticeable, but they both exhibited lower shear rates and vorticities than the Newtonian fluid. By decreasing the compression ratio of the hump, the maximum water velocity within the system decreased by 45%, while the maximum values of shear and vorticity decreased by 18% and 23%, respectively. This work showed the significant effect of the rheological properties of the flow on the fluid-dynamics within a closed system due to the peristaltic deformation of its wall. From a boarder perspective, this work demonstrated the relevance of acquiring a good characterization of the rheology of gastric contents to fully characterize the fluid- mechanical forces involved in food digestion.

Effects of variable fluid properties on natural convection of MHD fluid from a heated vertical wavy surface

Abstract: In the present paper, the influence of temperature-dependent fluid properties, density, viscosity and thermal conductivity on MHD natural convection flow from a heated vertical wavy surface is studied. It is assumed that, the fluid density and the thermal conductivity vary as exponential and linear functions of temperature, respectively. However, the fluid viscosity is assumed to vary as a reciprocal of a linear function of temperature. The model analysis used here is more relevant to liquid flow. Using the appropriate variables, the wavy surface are transformed into a flat one. The transformed boundary layer equations are solved numerically, using implicit-Chebyshev pseudospectral method, for several sets of values of the physical parameters, namely, the temperature dependent fluid properties parameters, the magnetic parameter, the amplitude-wavelength ratio parameter, and the Prandtl number. The numerical values obtained for the velocity, temperature, shearing stress, and the Nusselt number are presented through graphs and tables for several sets of values of the parameters. The effects of the physical parameters on the flow and heat transfer characteristics are discussed. The results were compared with numerical solutions of previous works. The present results are found to be in good agreement.

Blood flow of an Oldroyd-B fluid in a blood vessel incorporating a Brownian stress

Abstract: The mechanical behavior of non-Newtonian fluids can be modeled by several constitutive differential equations. The Oldroyd model is viewed as one of the successful models for describing the response of a subclass of polymeric liquids, in particular the non-Newtonian behavior exhibited by these fluids. In this paper, we are concerned with the study of the unsteady flows of an incompressible viscoelastic fluid of an Oldroyd-B type in a blood vessel acting on a Brownian force. First we derive the orientation stress tensor considering Hookean dumbbells on Brownian configuration fields. Then we reformulate the three-dimensional Oldroyd-B model with the total stress tensor which consists of the isotropic pressure stress tensor, the shear stress tensor, and the orientation stress tensor. Finally we present the numerical simulations of the model and analyze the effect of the orientation stress tensor in the vessel.

Conjugate transfer of heat and mass in unsteady flow of a micropolar fluid with wall couple stress

Abstract: This is an attempt to investigate the unsteady flow of a micropolar fluid with free convection caused due to temperature and concentration differences. Micropolar fluid is taken over a vertical plate oscillating in its own plane. Wall couple stress is engaged at the bounding plate together with isothermal temperature and constant mass diffusion. Problem is modelled in terms of coupled partial differential equations together with some physical conditions and then written in non-dimensional form. Exact solutions are determined using the Laplace transform method. For convenience, they are expressed in simplified form using exponential functions and complementary error functions. Using computational software MATHCAD, analytical results of velocity, temperature, microrotation and concentration are plotted in graphs and discussed for various embedded parameters. Results of skin friction, wall couple stress, rate of heat transfer (Nusselt number) and rate of mass transfer (Sherwood number) are also evaluated. Present results of micropolar fluid are graphically compared with published results of Newtonian fluid. It is found that micropolar fluid velocity is smaller than Newtonian fluid.

Falling film flow of a viscoelastic fluid along a wall

Abstract: In this paper, we study the heat transfer in the fully developed flow of a viscoelastic fluid, a slag layer, down a vertical wall. A new constitutive relation for the stress tensor of this fluid is proposed, where the viscosity depends on the volume fraction, temperature, and shear rate. For the heat flux vector, we assume the Fourier's law of conduction with a constant thermal conductivity. The model is also capable of exhibiting normal stress effects. The governing equations are non-dimensionalized and numerically solved to study the effects of various dimensionless parameters on the velocity, temperature, and volume fraction. The effect of the exponent in the Reynolds viscosity model is also discussed. The different cases of shear-thinning and shear-thickening, cooling and heating, are compared and discussed. The results indicate that the viscous dissipation and radiation (at the free surface) cause the temperature to be higher inside the flow domain. Copyright © 2013 John Wiley & Sons, Ltd.