1,721,034 research outputs found
Artificial Compressibility Based CBS Scheme for the Solution of the Generalized Porous Medium Model
No full textIn this work, the authors present an artificial compressibility (AC) version of the characteristic-
based split (CBS) algorithm for the numerical solution of flow through a fluidsaturated
porous medium. In this study, a fully matrix-inversion-free version of the CBS
algorithm is used for the first time to solve the generalized porous medium flow equations
for forced-, free-, and mixed-convection problems. The efficiency, the accuracy, and the
steady-state convergence of the AC-CBS algorithm are verified through comparison with
numerical and analytical solutions available in the literature. The advantages of the proposed
AC-CBS scheme include easy parallelization and implementation procedure
A stable explicit fractional step procedure for the solution of heat and fluid flow through interfaces between saturated porous media and free fluids in presence of high source terms
No full textIn this paper, porous medium-free fluid interface problems in the presence of high source terms are studied
for the first time by using a stable, accurate and efficient Artificial Compressibility (AC) Characteristic-
Based Split (CBS) algorithm. The interest in the AC-CBS scheme has increased, as its matrix-inversion
free procedure offers the possibility of an easy and efficient parallelization. The present algorithm, recently
introduced for the solution of porous media flows, presented some difficulties in solving complex interface
problems. In this paper, the AC-CBS scheme has been specifically developed to overcome such difficulties
and produce an accurate, stable, and efficient solution for the generalized porous medium flow equations
for forced, free, and mixed convection through interfaces. In order to obtain the present results, a stability
analysis for the AC-CBS scheme for the solution of problems with high source terms is carried out for
the first time. The efficiency and the accuracy of the AC-CBS algorithm are verified through comparison
with analytical, numerical, and experimental data available in the literature. The authors consider three
different types of interface benchmark problems: (i) forced convection in a horizontal channel; (ii) mixed
convection in a vertical channel; and (iii) natural convection in a vertically divided cavity
A novel single domain approach for numerical modelling Solid Oxide Fuel Cells
No full textPurpose – The purpose of this paper is to describe two- and three-dimensional numerical modelling
of solid oxide fuel cells (SOFCs) by employing an accurate and stable fully matrix inversion free finite
element algorithm.
Design/methodology/approach – A general and detailed mathematical model has been developed
for the description of the coupled complex phenomena occurring in fuel cells. A fully matrix inversion
free algorithm, based on the artificial compressibility (AC) version of the characteristic-based split
(CBS) scheme and single domain approach have been successfully employed for the accurate and
efficient simulation of high temperature SOFCs.
Findings – For the first time, a stable fully explicit algorithm has been applied to detailed multidimensional
simulation transport phenomena, coupled to chemical and electrochemical reactions, in
fluid, porous and solid parts of a SOFC. The accuracy of the present results has been verified via
comparison with experimental and numerical data available in the literature.
Originality/value – For the first time, thanks to a stabilization analysis conducted, the AC-CBS
algorithm has been successfully used to numerically solve the generalized model, applied in this
paper to describe transport phenomena through free fluid channels and porous electrodes of SOFCs,
without the need of further conditions at the fluid-electrode interface
High Rayleigh number natural convection in rectangular cavities with different aspect ratios solved by using a stabilized finite element algorithm
No full textIn this work, high Rayleigh number natural convection has been solved for the first time by using a stabilized Artificial Compressibility (AC) Characteristic Based Split (CBS) algorithm. The authors have carried out a stability analysis, based on the order of magnitude analysis of all the terms present in the conservation equations, in order to solve problems in presence of very large source terms. A new benchmark problem for high Rayleigh number natural convection in rectangular cavities with different aspect ratios has been detected by the authors. This new benchmark case is the only one for which experimental data are available. The stabilized AC-CBS scheme is successfully used to solve the present benchmark problem. The efficiency and the accuracy of the AC-CBS algorithm are verified through comparison with the experimental data for the new benchmark problem and with the numerical solutions available in the literature for well known problems. The interest in the AC-CBS scheme has increased since it offers the possibility of an easy and efficient parallelization procedure
A geothermal Downhole heat exchanger model based on an equivalent porous medium approach
No full textThe paper presents a numerical procedure for the simulation of heat and fluid flow in a low enthalpy geothermal energy system, using a generalised model for porous media flow and an equivalent porous medium approach for macroscopic description of the heat exchanger. The results obtained are validated against the experimental data available for a geothermal reservoir in the island of Ischia in Italy, which were available from previous work of one of the authors. The comparison shows that the proposed procedure can be successfully used for the simulation of this type of problems
A stabilized finite element algorithm for the solution of SOFC problems
No full textIn this work, a new stabilized finite element algorithm, using a single domain approach for the solution of mass and energy transport phenomena in solid oxide fuel cells is presented. The proposed numerical procedure is based on the Artificial Compressibility (AC) Characteristic Based Split (CBS) scheme. The stability analysis carried out by the authors for the first time is based on the order of magnitude analysis of all the terms present in the conservation equations. The stability limits speed up the simulation process enormously. Furthermore, the single domain approach allows the application of the present method to the simulation of a whole cells stack
Numerical performance assessment of a novel Darrieus-style VAWT with auxiliary straight blades
No full textDomestic Vertical Axis Wind Turbines (VAWT) are able to operate also when the wind speed is low and can be installed in the open spaces of housing areas. The Darrieus turbine is the most promising since it is characterized by higher efficiency, even if for applications at higher wind speeds with respect to Savonius VAWTs. Several researchers try to optimize the aerodynamics of the Darrieus rotors, allowing wind turbines to start rotation even in the presence of low wind speeds. In this paper the authors propose a numerical investigation of the flow field around a 1:4 scaled model of a pair of blades installed on an innovative Darrieus-type VAWT. A Reynolds Averaged Navier-Stokes-based CFD model was validated on the basis of the wind tunnel data, and the scaled turbine performance was analysed by numerically evaluating the effect of different geometric configurations and rotation angles on the turbine torque coefficients. The results of the simulations confirmed the capabilities of the proposed configuration to give valuable performance even for low wind speeds
New solutions for axial flow convection in porous and partly porous cylindrical domains
No full textIn this work, fully explicit numerical solutions for axial flow convection in cylindrical domains, completely
or partially filled with a fluid saturated porous medium, are presented. Laminar natural convection
in a vertical porous annulus and in a vertical annulus with a centrally located heat generating solid or
porous rod, and laminar forced convection in a pipe partially filled with a porous medium are numerically
simulated. Novel stability conditions are carried out for the axisymmetric version of the Artificial Compressibility
(AC) Characteristic Based Split (CBS) algorithm, based on finite elements, in order to effectively
solve the above problems. The results presented in this paper are validated against experimental
and numerical data available from the literature. The problem taking into account the presence of the
porous rod in the vertical annulus has been presented here for the first time
Design of a Calibration System for Heat Flux Meters
No full textAccurate heat flux measurements are needed to gain a better knowledge of the thermal performance of buildings and to evaluate the heat exchange among various parts of a building envelope. Heat flux meters (HFMs) are commonly used both in laboratory applications and in situ for measuring one-dimensional heat fluxes and, thus, estimating the thermal transmittance of material samples and existing buildings components. Building applications often requires heat flux measurements below 100 W center dot m(-2). However, a standard reference system generating such a low heat flux is available only in a few national metrology institutes (NMIs). In this work, a numerical study aimed at designing an HFM calibration apparatus operating in the heat flux range from 5 W center dot m(-2) to 100 W center dot m(-2) is presented. Predictions about the metrological performance of such a calibration system were estimated by numerical modeling exploiting a commercial FEM code (COMSOL(A (R))). On the basis of the modeling results, an engineered design of such an apparatus was developed and discussed in detail. The system was designed for two different purposes: (i) for measuring the thermal conductivity of insulators and (ii) for calibrating an HFM with an absolute method (i.e., by measuring the applied power from the heater and its active cross section) or by a relative method (i.e., by measuring the temperature drop across a reference material of known thickness and thermal conductivity). The numerical investigations show that in order to minimize the uncertainty of the generated heat flux, a fine temperature control on the thermal guard is needed. The predicted standard uncertainty is within 2% at 10W center dot m(-2) and within 0.5% at 100 W center dot m(-2)
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