Alessandro Mauro

High Rayleigh Number Laminar-Free Convection in Cavities: New Benchmark Solutions

The fully matrix-inversion-free artificial compressibility (AC), characteristic based split (CBS) algorithm is used to produce a stable and accurate solution for high Rayleigh number natural convection in rectangular cavities. Two benchmark problems are solved using the AC-CBS scheme: the classical differentially heated (DH) cavity, and a cavity subject to temperature boundary conditions on its sides, which is proposed here as a new benchmark. For the DH cavity problem, the dependence of the solution on the computational grid is highlighted, and it is shown how the horizontal velocity is more sensitive than the other calculated quantities. For the newly proposed benchmark, the numerical results are compared to experimental data that has recently appeared in the open literature.

Transient Thermal Analysis of Natural Convection in Porous and Partially Porous Cavities

In this article, the authors numerically investigate dynamic heat transfer related to free convection in porous and partially porous cavities, paying particular attention to the dependence of velocity and temperature fields on Rayleigh (Ra) number, porous layer permeability, and cavity aspect ratio (AR), the ratio between its height and width. Heat and fluid flows inside the cavity are described by using the generalized porous medium model, and the governing equations were numerically solved using the artificial compressibility version of the characteristic-based split scheme. The proposed model was first applied to the simulation of heat and fluid flows in a square porous cavity, and an excellent agreement was found between the results obtained and the data available in the literature. The analysis was then extended, here for the first time, to transient natural convection in partly porous cavities, with AR equal to 4:1 and 8:1 for different Ra and Darcy (Da) numbers. The mean Nusselt (Nu) number was calculated as a function of cavity geometrical characteristics, porous layer permeability, and fluid properties.

Artificial compressibility based CBS solutions for double diffusive natural convection in cavities

Purpose – The purpose of the paper is to numerically simulate steady‐state thermo‐solutal convection in rectangular cavities with different aspect ratios, subject to horizontal temperature and concentration gradients, and validate the results against numerical and experimental data available from literature.Design/methodology/approach – The fully explicit Artificial Compressibility (AC) version of the Characteristic Based Split (CBS) scheme is adopted to solve double diffusion (DD) problems. A stabilization analysis is carried out to efficiently solve the problems considered in the present work. The thermal and solutal buoyancy forces acting on the fluid have been taken into account in case of aiding and opposing flow conditions.Findings – The stability limits derived by the authors for the thermo‐solutal convection assume a fundamental role to efficiently solve the DD problems considered. In the cases characterized by higher Rayleigh number the convergent solution is obtained only by employing the new st...

Artificial Compressibility-Based CBS Scheme for the Solution of the Generalized Porous Medium Model

In 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 fluid-saturated 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.

High Order Explicit Solutions for the Transient Natural Convection of Incompressible Fluids in Tall Cavities

The performance of the artificial compressibility (AC) version of the characteristic based split (CBS) scheme for the solution of transient free convection in tall cavities is analyzed. A dual time-stepping procedure is used to recover the transient solution. The true transient term is discretized explicitly up to the fourth order of approximation, with consequent possibility to adopt larger true time-steps and to gain in accuracy and computing efficiency. In order to obtain the present results, the novel stability analysis recently developed by the authors for the steady-state AC-CBS scheme is here extended to the transient algorithm. Cavities with three different aspect ratios have been considered: 8:1, 10:1, and 16:1. The obtained results have been compared with the analytical and numerical data available in the literature.

A novel single domain approach for numerical modelling solid oxide fuel cells

Purpose – 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 multi‐dimensional 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 ...

New benchmark solutions for transient natural convection in partially porous annuli

Purpose – The purpose of this paper is to focus on the numerical analysis of transient free convection heat transfer in partially porous cylindrical domains. The authors analyze the dependence of velocity and temperature fields on the geometry, by analyzing transient flow behavior for different values of cavity aspect ratio and radii ratio; both inner and outer radius are assumed variable in order to not change the difference ro-ri. Moreover, several Darcy numbers have been considered. Design/methodology/approach – A dual time-stepping procedure based on the transient artificial compressibility version of the characteristic-based split algorithm has been adopted in order to solve the transient equations of the generalized model for heat and fluid flow through porous media. The present model has been validated against experimental data available in the scientific literature for two different problems, steady-state free convection in a porous annulus and transient natural convection in a porous cylinder, sh...

The Effect of Temperature Changes in Vitreoretinal Surgery.

Purpose Recent studies on temperature control in biology and medicine have found the temperature as a new instrument in healthcare. In this manuscript, we reviewed the effects of temperature and its potential role in pars plana vitrectomy. We also examined the relationship between intraocular pressure, viscosity, and temperature in order to determine the best balance to manipulate the tamponades during the surgery. Methods A literature review was performed to identify potentially relevant studies on intraocular temperature. Physics equations were applied to explain the described effects of temperature changes on the behavior of the endotamponades commonly used during vitreoretinal surgery. We also generated an operating diagram on the pressure–temperature plane for the values of both vapor–liquid equilibrium and intraocular pressure. Results The rapid circulation of fluid in the vitreous cavity reduces the heat produced by the retinal and choroidal surface, bringing the temperature toward room temperature (22°C, deep hypothermia). Temperature increases with endolaser treatment, air infusion, and the presence of silicone oil. The variations in temperature during vitreoretinal surgery are clinically significant, as the rheology of tamponades can be better manipulated by modulating intraocular pressure and temperature. Conclusions During vitreoretinal surgery, the intraocular temperature showed rapid and significant fluctuations at different steps of the surgical procedure inside the vitreous cavity. Temperature control can modulate the rheology of tamponades. Translational Relevance Intraoperative temperature control can improve neuroprotection during vitreoretinal surgery, induce the vaporization of perfluorcarbon liquid, and change the shear viscosity of silicone oil.

The Finite Element Method: DiscretizationAnd Application To Heat Convection Problems

In this chapter, we give an overview of the finite element method and its applications to heat and fluid flow problems. An introduction to weighted residual approximation and finite element method for heat and fluid flow equations are presented. The characteristic–based split (CBS) algorithm is also presented for solving the incompressible thermal flow equations. The algorithm is based on the temporal discretization along the characteristics, and the high-order stabilization terms appear naturally from this kind of discretization. The artificial compressibility (AC) and the semi-implicit (SI) versions of the CBS scheme are presented and some examples are also given to demonstrate the main features of both the schemes.

Modeling and optimization of an incinerator plant for the reduction of the environmental impact

Purpose – The purpose of this paper is to optimize the performance of an incinerator plant in terms of NO emissions and temperature of particles 2 s after the last air injection, which must be above 850°C as established from the Directive 2000/76/EC of the European Parliament and of the Council – December 4, 2000 on dioxins formation in waste incineration plants. Design/methodology/approach – Investigation is made by coupling proper models developed within three commercial software environments: FLUENT, to reproduce the thermodynamic field inside the combustion chamber of the incinerator plant taken into account, MATLAB, to evaluate the position and temperatures of the particles 2 s after the last air injection, MODEFRONTIER, to change both the secondary air mass flow rate and the equivalent heat transfer coefficient of the refractory walls to fulfill the conflicting objectives of reducing the NO formation and increasing the mean gases temperature as required by the Directive. Findings – The investigation...