The Effect of Radiation and Turbulence on Heat Transport in Combustion in Porous Media

2007 ◽  
Author(s):  
Marcelo J. S. de Lemos
Keyword(s):  
Porous Media ◽  
High Efficiency ◽  
Reaction Rates ◽  
Equation Model ◽  
Test Case ◽  
Process Industries ◽  
Porous Burner ◽  
Reliable Temperature ◽  
Double Decomposition ◽  
Flow Variables

Combustion in inert porous media has been extensively investigated due to the many engineering applications and demand for developing high efficiency power production devices. The growing use of efficient radiant burners can be encountered in the power and process industries and, as such, proper mathematical models of flow, heat and mass transfer in porous media under combustion can benefit the development of such engineering equipment. This paper proposes a new mathematical model for computing temperature and flow variables inside a porous burner. A new concept called “double-decomposition” is used to represent all transported variables. A set of governing equations is presented and the numerical solution method proposed is discussed. Computations are carried out for a test case considering a simple one-energy equation model and one-step reaction rates. Simulations are presented comparing the inclusion of turbulence and radiation transfer in the model. It is shown that for high Re flows, inclusion of turbulence is as important as modeling radiation for obtaining reliable temperature distribution within the porous material.

Simulation of Combustion in Porous Media With a Two-Energy Equation Model

2011 ◽  
Author(s):  
Marcelo J. S. deLemos ◽  
Jose´ E. A. Coutinho
Keyword(s):  
Porous Media ◽  
Flame Front ◽  
Control Volume ◽  
Numerical Technique ◽  
Simple Algorithm ◽  
Equation Model ◽  
Gas Temperature ◽  
Inlet Velocity ◽  
Excess Air ◽  
Porous Burner

This work presents numerical results for two-dimensional combustion of an air/methane mixture in inert porous media using turbulence and radiation models. Distinct energy equations are considered for the porous burner and for the fuel in it. Inlet velocity and excess air-to-fuel ratio are varied in order to analyze their effects on temperature and flame front location. The macroscopic equations for mass, momentum and energy are obtained based on the volume average concept. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted non-orthogonal coordinate system. The SIMPLE algorithm was used to handle the pressure-velocity coupling. Results indicate that for high excess air values, the gas temperature peaks are reduced. Also, for the same conditions the flame front moves towards the exit of the burner. Results also indicate that the same flame front behavior occurs as the inlet velocity increases.

Experimental Validation of Non-Fourier Thermal Response in Porous Media

2001 ◽  
Author(s):  
A. G. Agwu Nnanna ◽  
K. T. Harris ◽  
A. Haji-Sheikh
Keyword(s):  
Heat Flux ◽  
Porous Media ◽  
Experimental Validation ◽  
Thermal Response ◽  
Lag Time ◽  
Equation Model ◽  
Thermal Parameters ◽  
Solid Matrix ◽  
Microscale Model ◽  
Short Time

Abstract An experimental validation of non-Fourier behavior in porous media due to short time thermal perturbation is presented. The governing energy equation is formulated based on the two-equation model and the non-Fourier model. This formulation leads to the emergence of four thermal parameters: lag-time in heat flux τq, lag-time τt in temperature due to interstitial heat transfer coefficient h, and lag-time in the transient response of the temperature gradient τx in the heat flux equation. These parameters account for the microstructural thermal interaction between the fluid and neighboring solid matrix as well as the delay time needed for both phases to approach thermal equilibrium. An experimental verification of the microscale model was performed under standard laboratory conditions. The values of the aforementioned thermal parameters were determined to compute the fluid and solid temperatures. Results predicted from three models (classical Fourier, non-Fourier, and experimental) were compared. It indicates an excellent agreement between the non-Fourier and the experimental model, and a significant deviation of Fourier prediction from the experimental results.

Thermal Analysis of Multijet Impingement Through Porous Media to Design a Confined Heat Management System

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Carlos Zing ◽  
Shadi Mahjoob
Keyword(s):  
Porous Media ◽  
High Efficiency ◽  
Solid Phase ◽  
Electronics Cooling ◽  
Jet Impingement ◽  
Fluid Phase ◽  
Volume Averaging ◽  
High Heat Flux ◽  
Base Temperature ◽  
Heat Management

Thermal management has a key role in the development of advanced electronic devices to keep the device temperature below a maximum operating temperature. Jet impingement and high conductive porous inserts can provide a high efficiency cooling and temperature control for a variety of applications including electronics cooling. In this work, advanced heat management devices are designed and numerically studied employing single and multijet impingement through porous-filled channels with inclined walls. The base of these porous-filled nonuniform heat exchanging channels will be in contact with the devices to be cooled; as such the base is subject to a high heat flux leaving the devices. The coolant enters the heat exchanging device through single or multijet impingement normal to the base, moves through the porous field and leaves through horizontal exit channels. For numerical modeling, local thermal nonequilibrium model in porous media is employed in which volume averaging over each of the solid and fluid phase results in two energy equations, one for solid phase and one for fluid phase. The cooling performance of more than 30 single and multijet impingement designs are analyzed and compared to achieve advantageous designs with low or uniform base temperature profiles and high thermal effectiveness. The effects of porosity value and employment of 5% titanium dioxide (TiO2) in water in multijet impingement cases are also investigated.

A two-energy equation model for conduction and convection in porous media

2001 ◽  
Vol 44 (22) ◽  
pp. 4375-4379 ◽  
Author(s):  
Akira Nakayama ◽  
Fujio Kuwahara ◽  
Masazumi Sugiyama ◽  
Guoliang Xu
Keyword(s):  
Porous Media ◽  
Energy Equation ◽  
Equation Model ◽  
Convection In Porous Media

scholarly journals A Laser-Based Heating System for Studying the Morphological Stability of Porous Ceria and Porous La0.6Sr0.4MnO3 Perovskite during Solar Thermochemical Redox Cycling

Energies ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5935
Author(s):  
Kangjae Lee ◽  
Jonathan R. Scheffe
Keyword(s):  
Heat Flux ◽  
Large Scale ◽  
High Efficiency ◽  
Heating System ◽  
Sample Surface ◽  
Reaction Rates ◽  
Chemical Kinetic ◽  
Redox Cycling ◽  
Radiative Heating ◽  
Morphological Stability

Thermochemical processes are considered promising pathways to utilize solar energy for fuel production. Several physico-chemical, kinetic and thermodynamic properties of candidate oxides have been studied, yet their morphological stability during redox cycling under radiative heating is not widely reported. Typically when it is reported, it is for large-scale directly irradiated reactors (~1–10 kWth) aimed at demonstrating high efficiency, or in indirectly irradiated receivers where the sample surface is not exposed directly to extreme radiative fluxes. In this work, we aimed to emulate heat flux conditions expected in larger scale solar simulators, but at a smaller scale where experimentation can be performed relatively rapidly and with ease compared to larger prototype reactors. To do so, we utilized a unique infrared (IR) laser-based heating system with a peak heat flux of 2300 kW/m2 to drive redox cycles of two candidate materials, namely nonstoichiometric CeO2-δ and La0.6Sr0.4MnO3-δ. In total, 200 temperature-swing cycles using a porous ceria pellet were performed at constant pO2, and 5 cycles were performed for both samples by introducing H2O vapor into the system during reduction. Porous ceria pellets with porosity (0.55) and pore size (4–7 μm) were utilized because of their similarity to other porous structures utilized in larger-scale reactors. Overall, we observed that reaction extents initially decreased along with the decrease in reaction rates up to cycle 120 because of the change in structure and sintering. In the case of H2O splitting, ceria outperformed LSM40 in total H2 production because of the low pO2 during oxidation, where the oxidation of LSM40 is less favorable than that of ceria.

Evaluation of Lattice Boltzmann Method for Reaction-Diffusion Process in a Porous SOFC Anode Microstructure

2012 ◽  
Author(s):  
Hedvig Paradis ◽  
Bengt Sundén
Keyword(s):  
Porous Media ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Reaction Diffusion ◽  
Reaction Rates ◽  
Transport Processes ◽  
Microscopic Level ◽  
Reaction Diffusion Equation ◽  
Interaction Sites ◽  
Boltzmann Method

In the microscale structure of a porous electrode, the transport processes are among the least understood areas of SOFC. The purpose of this study is to evaluate the Lattice Boltzmann Method (LBM) for a porous microscopic media and investigate mass transfer processes with electrochemical reactions by LBM at a mesoscopic and microscopic level. Part of the anode structure of an SOFC for two components is evaluated qualitatively for two different geometry configurations of the porous media. The reaction-diffusion equation has been implemented in the particle distribution function used in LBM. The LBM code in this study is written in the programs MATLAB and Palabos. It has here been shown that LBM can be effectively used at a mesoscopic level ranging down to a microscopic level and proven to effectively take care of the interaction between the particles and the walls of the porous media. LBM can also handle the implementation of reaction rates where these can be locally specified or as a general source term. It is concluded that LBM can be valuable for evaluating the risk of local harming spots within the porous structure to reduce these interaction sites. In future studies, the information gained from the microscale modeling can be coupled to a macroscale CFD model and help in development of a smooth structure for interaction of the reforming reaction and the electrochemical reaction rates. This can in turn improve the cell performance.

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