In this work, an effective thermal conductivity (ETC) for living tissues, which directly affects the energy transport process, is determined. The fractal scaling and Monte Carlo methods are used to describe the tissue as a porous medium, and blood is considered a Newtonian and non-Newtonian fluid for comparative and analytical purposes. The effect of the principal variables—such as fractal dimensions DT and Df, porosity, and the power-law index, n—on the temperature profiles as a function of time and tissue depth, for one- and three-layer tissues, besides temperature distribution, are presented. ETC was improved by considering high tissue porosity, low tortuosity, and shear-thinning fluids. In three-layer tissues with different porosities, perfusion with a non-Newtonian fluid contributes to the understanding of the heat transfer process in some parts of the human body.
The multiscale modeling of complex fluids under small and large amplitude oscillatory shear flow using non-linear kinetic and transient network models is presented. The kinetics of microstates is analogous to chemical kinetics, which defines the physical macromolecule interaction in a Newtonian fluid, and the concentration of microstates defines a variable maximum length of extension for each microstate. The effect of important parameters like viscosity ratio, chain length, viscoelasticity, kinetic rate constants, for different initial entanglement scenarios (entangled, disentangled and aleatory) are analyzed. The Lissajous curves for the shear stress and the first normal stress difference versus the instantaneous strain or strain-rate are shown. The self-intersection of the Lissajous curves or secondary loops is shown to depend on the kinetic rate constants, the maximum extension length, and the elasticity.
In this work, the dynamics of the bioconvection process of gravitactic microorganisms enclosed in a rectangular cavity, is analyzed. The dimensionless cell and energy conservation equations are coupled with the vorticity-stream function formulation. Then, the effects of the bioconvection Rayleigh number and the heating source on the dynamics of microorganisms are discussed. The results based in streamlines, concentration and temperature contours are obtained through numerical simulations considering eight different configurations of symmetrical and asymmetrical heat sources. It is concluded that microorganisms accumulate in the warmer regions and swim through the cooler regions to reach the surface. They form cells for each heat source, but at high concentrations, they form a single stable cell. The results presented here can be applied to control and to understand the dynamics of microorganisms with discrete heat sources.
A numerical solution for axis-symmetrical fluid flow through a smooth constriction using the alternating direction implicit finite volume method and the fractional-step-method is presented. The wall is modelled with a smooth contraction mapped by a sinusoidal function and the flow is supposed to be axis-symmetric. A pressure boundary condition is set at the inlet and the resulting pressure gradient field drives fluid flow which is always in laminar regime. This study presents results for a non-Newtonian fluid using the Ostwaldde Waele constitutive model. Moreover, a transient network representing three different microstructures, immersed in the fluid, is evolved by viscous dissipation and an isothermal process is considered. The time dependent evolution of the transient network is represented by a set of kinetic equations with their respective forward and reversed constants. The numerical predictions show that, at a fixed Reynolds number, the viscous dissipation and the grade of structure restoration or breakage is influenced by constriction severity due to the energy generated during fluid flow. A 50% reduction in transversal section generates secondary flow downstream and vortex shedding, whereas a 10% and 25% constrictions presents a thin boundary layer and no secondary flow near the constricted wall.
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