Renata Jecl

Boundary element method for natural convection in non-Newtonian fluid saturated square porous cavity

Abstract The main purpose of this work is to present the use of the Boundary Element Method (BEM) in the analysis of the natural convection in the square porous cavity saturated by the non-Newtonian fluid. The results of hydrodynamic and heat transfer evaluations are reported for the configuration in which the enclosure is heated from a side wall while the horizontal walls are insulated. The flow in the porous medium is modelled using the modified Brinkman extended Darcy model taking into account the non-Darcy viscous effects. The governing equations are transformed by the velocity–vorticity variables formulation enabling the computation scheme to be partitioned into kinematic and kinetic parts. To analyse the effects of the available non-Newtonian viscosity and to evaluate the presented approach, the power law model for shear thinning fluids ( n n >1) and in the limit for the Newtonian fluids ( n =1) is considered. Numerical model is tested also for the Carreau model adequate for many non-Newtonian fluids. Solutions for the flow and temperature fields and Nusselt numbers are obtained in terms of a modified Rayleigh number Ra ∗ , Darcy number Da , and the non-Newtonian model parameters. The agreement between the results obtained with finite difference method is very good indicating that BEM can be efficiently used for solving transport phenomena in saturated porous medium.

Energy band shape of monolayer metal/organic/metal structures as determined by the capacitance-voltage method

The room-temperature differential capacitance of monolayer metal/organic-semiconductor/metal structures was derived. The derivation was based on two basic assumptions: (a) the rectifying metal/organic-semiconductor junction is characterized by the bias-dependent net excess charge density, induced at the interface, and (b) the charge flow within the organic layer is represented by the space-charge-limited current. The predictions of the derivations were compared to C-U data on an ionized cluster beam Ag-deposited 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on indium-tin-oxide (ITO), Ag∕PTCDA∕ITO, sample obtained at 1 kHz and at room temperature. In addition, thorough analyses of published, room-temperature capacitance-voltage data for Al∕pentacene(60nm)∕ITO, poly(phenylene vinylene) Al∕PPV(200nm)∕ITO, poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene], Ca∕MEH‐PPV(40nm)∕Au, tris-(8-hydroxyquinoline) aluminum, Al∕Alq3(60nm)∕ITO, Ca∕Alq3(60nm)∕ITQ, and Ca∕Alq3(120nm)∕ITO organic-semiconduc...

Heat and Mass Transfer Porous Medium Saturated with Compressible Fluid with Boundary Domain Integral Method

A numerical approach to solve a problem of combined heat and mass transfer in porous medium saturated with compressible fluid is presented. Transport phenomena in porous media is described using the modified Navier-Stokes equations, where for the governing momentum equation the Brinkman extended Darcy formulation is used. Governing equations are solved with the Boundary Domain Integral Method, which is an extension of classical Boundary Element Method.

NUMERICAL SIMULATION OF CONVECTIVE FLOW IN A NON-DARCY POROUS CAVITY FILLED WITH NANOFLUID

Suspensions of nanoscale particles and fluids have been recently subject of intense research, since it was proved that they considerably improve heat transfer capabilities of the fluid which can be crucial in several technological processes. Several applications can be found in the field of porous media flow, such as oil recovery systems, thermal and geothermal energy, nuclear reactors cooling. Since nanofluids are a mixture of a solid and fluid phase, in general, the two phase mathematical model would be the most appropriate to use. However, due to very small size of nanoparticles (1–100 nm) can be assumed, that they behave as a water molecule and a single phase model along with empirical correlations for nanofluid properties can be used. In the present study a convective flow through porous cavity fully saturated with nanofluid is analyzed in detail using the single phase mathematical model based on the Navier-Stokes equations taking into account the non-Darcy parameters. The mathematical model is written at a macroscopic level enabling the simulation of the porous media flow. The solutions are obtained with the in house numerical code based on the Boundary Element Method, which was already proved to have some unique advantages when considering fluid flow problems in different configurations. The effects of the presence of different types of nanoparticles as well as the porous matrix were investigated in detail for different values of governing parameters in order to examine the improved heat transfer characteristics of added nanoparticles.

Assessment of flutter speed on long span bridges

In this paper it is shown how to calculate flutter speed on the example of the Great Belt East Bridge in Denmark. Two numerical approaches are shown for prediction of the aeroelastic phenomena on bridges. In the computational fluid dynamics (CFD) simulation turbulence model based on Reynolds Average Navies Stokes (RANS) approach, two-equation shear stress turbulence (SST) models were chosen. Although the SST model needs more computer resources compared to the k-ω and k-e models, it is still affordable with multi-processing personal computers. In this paper extracted flutter derivatives in the force vibration procedure are shown. Flutter derivatives are later used in the hybrid method of flutter. Final flutter speed was calculated based on flutter derivatives from fluid structure interaction extraction and experimental extraction. Flutter velocity was also determined with a free vibration of deck at the middle of the bridge. The deck section of unit length was clamped into springs and dampers. Flutter speed was reached with time increasing of wind speed until large oscillations occurred. The general procedure of how to formulate the fluid structure interaction and necessary stapes for flutter analysis of the bridge is shown in this paper. Numerically extracted flutter derivatives are compared based on the final flutter speed to experimental measurements of the deck section.

Numerical analysis of fluid flow in a three-dimensional porous enclosure by the Boundary Element Method

In the present paper a three-dimensional numerical code for simulation of porous media flow is presented which is based on the Boundary Element Method (BEM). The most general mathematical model is used to describe momentum, energy and solute transport in porous media which are based upon the general Navier‐Stokes equations valid for the pure fluid flow. The developed numericalalgorithm enables detailed investigation of the fluid flow together with heat and solute transfer under various conditions given with different governing parameters, e.g. thermal and solutal Rayleigh numbers, Darcy number, Lewis number, buoyancy coefficient. In the paper the effectof differentgoverningparameterson the rate of heat, solute and momentumtransferare investigated.Under a certain rangeof parameters,complex flow patternsoccur which exhibitsthe importancefor us to investigatethe problem in three dimensions.

Boundary Domain Integral Method for Double Diffusive Natural Convection in Porous Media Saturated with Compressible Fluid

In the present work, a Boundary Domain Integral Method, which has been already established for the solution of viscous incompressible fluid flow through porous media, is extended to capture compressible fluid flow in porous media. The presented numerical scheme was used for solving the problem of double diffusive natural convection in a square porous cavity heated from a side, while the horizontal walls are maintained at different concentrations. The Brinkman extension of Darcy equation is used to model the flow through porous medium. The velocity‐vorticity formulation is employed enabeling the computation scheme to be partitioned into kinematic and kinetic parts. The results of double diffusive natural convection in porous cavity are presented in terms of velocity, temperature and concentration redistributions.