Mauricio Giraldo

Evaluation Of Strong Shear ThinningNon-Newtonian Fluid Flow UsingSingle Domain DR-BEM

The dual reciprocity method (DRM) has been successfully employed along with the boundary element method (BEM) to simulate non linear flow phenomena such as convective momentum transport and shear thinning fluids. In the latter however, domain partitioning has been necessary to achieve convergence when the power law index is below 0.8. This paper shows how a single domain DR-BEM formulation for non Newtonian low Reynolds number flows can be implemented in order to obtain accurate results for lower values of the power law index. Some of the characteristics of this implementation are the use of quadratic elements and an iterative solution of the non linear system of equations using a modified Newton–Raphson method. Along with the implementation, two radial inelastic non Newtonian flow: couette mixing and slit flow. Solutions obtained are also compared to results from a multi-domain dual reciprocitymethod (MD-DRM) for equal meshes. Results showed that using the abovementioned strategies, single domain DR-BEM can accurately predict the flow field in inelastic non Newtonian flow for values of the power law index as low as 0.5. It is also worth noting that the accuracy of the single domain strategy was shown to be higher than MD-DRM, although the latter clearly reduced computational resource consumption.

Boundary element solution of thermal creeping flow in a nano single mixer

In order to employ continuum models in the analysis of the flow behaviour of a viscous Newtonian fluid in micro scale devices, it is necessary to consider at the wall surfaces appropriate slip boundary conditions instead of the classical non-slip condition. The slip behaviour in the case of micro fluid flow of rarefied gases is associated with the combined effect of reduction in momentum transfer due to the reduction in the number of molecules (shear creep) and the thermal creep or transpiration, which as a consequence of inequalities in temperatures, forces the fluid to slide over a surface from colder to hotter regions. In this work a boundary integral equation formulation for Stokes slip flow, based on the normal and tangential projection of the Green’s integral representational formulae for the Stokes velocity field, which directly incorporates into the integral equations the local tangential shear rate and heat flux at the wall surfaces, is presented. The tangential heat flux is evaluated in terms of the tangential gradient of the temperature integral representational formulae presenting singularity of the Cauchy type, which are removed by the use of an auxiliary field. These formulations are used to simulate a Single rotor mixer and analyze the combined effect of both shear and thermal creep effects over mixer performance.

Modeling and Simulation of a Co-Current Rotary Dryer Under Steady Conditions

A model which joins the overall design algorithm of a rotary dryer with the drying kinetics equations derived from experimental data and with a finite segment algorithm is implemented in order to verify the dryer dimensions obtained from a basic sizing procedure. Total energy and mass balances and well-known correlations for the overall heat transfer coefficient are employed to develop it. Moreover, a one-dimensional finite segment model is solved to obtain the length profiles of temperature and water content for the air and solid phases. An experimental correlation for the mass transfer coefficient between solid and air phases is included in the finite segment model. The chosen heat transfer unit number for the basic sizing is verified with the outlet temperature and water content calculated by the finite segment scheme.

Critical Sources of Aerodynamic Resistance in a Medium Distance Urban Train: a CFD approach

In this article, the aerodynamic behavior of a commuter train operating at average speeds is evaluated, by means of computational fluid dynamics; the main goal is to identify the main aerodynamic drag sources. The study consist of two phases; the first one is the aerodynamic analysis of the current train using certain mesh parameters and the turbulence model – to obtain a real condition of operation, with this analysis was obtained the total power consumption corresponding to the value of the aerodynamic drag thrown by the simulation process. These results were qualitatively compared with experimental data in order to validate the simulation process. The second part is the identification and analysis of the main aerodynamic drag zones that the Metro system generate in its interaction with the air, to make a preliminary evaluation of a few modifications that allowed the reduction in the drag in these critical

Control volume-radial basis function method for two-dimensional non-linear heat conduction and convection problems

An improvement to the traditional Finite Volume Method (FVM) for the solution of boundary value problems is presented. The new method applies the local Hermitian interpolation with Radial Basis Functions (RBF) as an interpolation scheme to the FVM discretization. This approach, called the Control Volume-Radial Basis Function (CV-RBF) method, uses an interpolation scheme based on the meshless Symmetric method, in which the numerical solution is approximated by employing the governing equation and the boundary condition operators. The RBF implemented is the Multiquadric (MQ) with a shape parameter found experimentally. The two-dimensional solutions to the Dirichlet problem for linear heat conduction, heat transfer in the Poiseuille flow and the non-linear conduction situations are obtained by the CV-RBF method. The numerical results are in agreement with the corresponding analytical and numerical solutions found in the literature.

Boundary Integral Equation Approach for Stokes Flow with Non‐Linear Slip Boundary Condition

The numerical simulation of microfluid flow through the solution of governing equations based on continuum models has to be done under the consideration of appropriate slip boundary conditions to account for the velocity jump at the solid‐fluid interface. The linear model proposed by Navier states a relation between the tangential shear rate and the fluid‐wall velocity differences and has been successfully used in reproducing the characteristics of many types of flows (e.g. slit flows, rotating curved mixers, microbearings, among others), where the shear rate at solid‐fluid interfaces remains linear because of the geometry smoothness. Despite this, there are some situations for which this linear dependency fails leading to unrealistic behaviour and an expression for the slip condition at a solid‐liquid interface establishing the variation in the slip length in terms of the square root of the tangential shear rate needs to be used. This work employs a boundary integral equation formulation for Stokes slip ...

Convective Heat Transfer in Nanofluids: A Computational Approach

Nanofluids are a novel strategy to increase heat transfer characteristics of fluids by the addition of solid particles with diameters below 100 nm. Experimental measurements have shown that this approach can greatly increase heat conductivity, even above that predicted by Maxwell’s theory. This paper shows a direct numerical simulation of the flow and thermal behaviour of a nanofluid loaded with alumina nanoparticles. The Boundary Element Method is used given its capabilities to deal with moving boundary problems. Results showed strong convective currents caused by the presence of the nanoparticles, which in time increase total heat flow in the cavity.