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http://hdl.handle.net/10985/21600
Simulation of Wood Combustion in PATO Using a Detailed Pyrolysis Model Coupled to fireFoam
SCANDELLI, Hermes; AHMADI-SENICHAULT, Azita; LACHAUD, Jean; RICHARD, Franck
The numerical simulation of fire propagation requires capturing the coupling between wood pyrolysis, which leads to the production of various gaseous species, and the combustion of these species in the flame, which produces the energy that sustains the pyrolysis process. Experimental and numerical works of the fire community are targeted towards improving the description of the pyrolysis process to better predict the rate of production and the chemical nature of the pyrolysis gases. We know that wood pyrolysis leads to the production of a large variety of chemical species: water, methane, propane, carbon monoxide and dioxide, phenol, cresol, hydrogen, etc. With the idea of being able to capitalize on such developments to study more accurately the physics of fire propagation, we have developed a numerical framework that couples a detailed three-dimensional pyrolysis model and fireFoam. In this article, we illustrate the capability of the simulation tool by treating the combustion of a wood log. Wood is considered to be composed of three phases (cellulose, hemicellulose and lignin), each undergoing parallel degradation processes leading to the production of methane and hydrogen. We chose to simplify the gas mixture for this first proof of concept of the coupling of a multi-species pyrolysis process and a flame. In the flame, we consider two separate finite-rate combustion reactions for methane and hydrogen. The flame evolves during the simulation according to the concentration of the two gaseous species produced from the material. It appears that introducing different pyrolysis species impacts the temperature and behavior of the flame.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/216002021-01-01T00:00:00ZSCANDELLI, HermesAHMADI-SENICHAULT, AzitaLACHAUD, JeanRICHARD, FranckThe numerical simulation of fire propagation requires capturing the coupling between wood pyrolysis, which leads to the production of various gaseous species, and the combustion of these species in the flame, which produces the energy that sustains the pyrolysis process. Experimental and numerical works of the fire community are targeted towards improving the description of the pyrolysis process to better predict the rate of production and the chemical nature of the pyrolysis gases. We know that wood pyrolysis leads to the production of a large variety of chemical species: water, methane, propane, carbon monoxide and dioxide, phenol, cresol, hydrogen, etc. With the idea of being able to capitalize on such developments to study more accurately the physics of fire propagation, we have developed a numerical framework that couples a detailed three-dimensional pyrolysis model and fireFoam. In this article, we illustrate the capability of the simulation tool by treating the combustion of a wood log. Wood is considered to be composed of three phases (cellulose, hemicellulose and lignin), each undergoing parallel degradation processes leading to the production of methane and hydrogen. We chose to simplify the gas mixture for this first proof of concept of the coupling of a multi-species pyrolysis process and a flame. In the flame, we consider two separate finite-rate combustion reactions for methane and hydrogen. The flame evolves during the simulation according to the concentration of the two gaseous species produced from the material. It appears that introducing different pyrolysis species impacts the temperature and behavior of the flame.Computation of the Permeability Tensor of Non-Periodic Anisotropic Porous Media from 3D Images
http://hdl.handle.net/10985/22942
Computation of the Permeability Tensor of Non-Periodic Anisotropic Porous Media from 3D Images
SCANDELLI, Hermes; AHMADI-SENICHAULT, Azita; LEVET, C.; LACHAUD, Jean
The direct proportionality between the flow rate and the pressure gradient of creeping flows was experimentally discovered by H. Darcy in the 19th century and theoretically justified a couple of decades ago using upscaling methods such as volume averaging or homogenization. X-ray computed micro-tomography (CMT) and pore-scale numerical simulations are increasingly used to estimate the permeability of porous media. However, the most general case of non-periodic anisotropic porous media still needs to be completely numerically defined. Pore-scale numerical methods can be split into two families. The first family is based on a direct resolution of the flow solving the Navier–Stokes equations under the assumption of creeping flow. The second one relies on the resolution of an indirect problem—such as the closure problem derived from the volume averaging theory. They are known to provide the same results in the case of periodic isotropic media or when dealing with representative element volumes. To address the most general case of non-periodic anisotropic porous media, we have identified four possible numerical approaches for the first family and two for the second. We have compared and analyzed them on three-dimensional generated geometries of increasing complexity, based on sphere and cylinder arrangements. Only one, belonging to the first family, has been proved to remain rigorously correct in the most general case. This has been successfully applied to a high-resolution 3D CMT of Carcarb, a carbon fiber preform used in the thermal protection systems of space vehicles. The study concludes with a detailed analysis of the flow behavior (streamlines and vorticity). A quantitative technique based on a vorticity criterion to determine the characteristic length of the material is proposed. Once the characterized length is known, the critical Reynolds number can be estimated and the physical limit of the creeping regime identified.
Wed, 13 Apr 2022 00:00:00 GMThttp://hdl.handle.net/10985/229422022-04-13T00:00:00ZSCANDELLI, HermesAHMADI-SENICHAULT, AzitaLEVET, C.LACHAUD, JeanThe direct proportionality between the flow rate and the pressure gradient of creeping flows was experimentally discovered by H. Darcy in the 19th century and theoretically justified a couple of decades ago using upscaling methods such as volume averaging or homogenization. X-ray computed micro-tomography (CMT) and pore-scale numerical simulations are increasingly used to estimate the permeability of porous media. However, the most general case of non-periodic anisotropic porous media still needs to be completely numerically defined. Pore-scale numerical methods can be split into two families. The first family is based on a direct resolution of the flow solving the Navier–Stokes equations under the assumption of creeping flow. The second one relies on the resolution of an indirect problem—such as the closure problem derived from the volume averaging theory. They are known to provide the same results in the case of periodic isotropic media or when dealing with representative element volumes. To address the most general case of non-periodic anisotropic porous media, we have identified four possible numerical approaches for the first family and two for the second. We have compared and analyzed them on three-dimensional generated geometries of increasing complexity, based on sphere and cylinder arrangements. Only one, belonging to the first family, has been proved to remain rigorously correct in the most general case. This has been successfully applied to a high-resolution 3D CMT of Carcarb, a carbon fiber preform used in the thermal protection systems of space vehicles. The study concludes with a detailed analysis of the flow behavior (streamlines and vorticity). A quantitative technique based on a vorticity criterion to determine the characteristic length of the material is proposed. Once the characterized length is known, the critical Reynolds number can be estimated and the physical limit of the creeping regime identified.Development and validation of a local thermal non-equilibrium model for high-temperature thermal energy storage in packed beds
http://hdl.handle.net/10985/24863
Development and validation of a local thermal non-equilibrium model for high-temperature thermal energy storage in packed beds
LIU, Shaolin; AHMADI, Azita; LEVET, Cyril; LACHAUD, Jean
High-temperature thermal energy storage (TES) in packed beds is gaining interest for industrial energy
recovery. The wide range of temperature distributions causes significant variations in thermophysical properties
of the fluid and solid phases, leading to inaccuracies of classical TES models and heat transfer correlations.
The objective of this work is to develop and validate a detailed but pragmatic model accounting for
high-temperature effects. Based on a literature survey spanning over several communities interested in high-
temperature porous media, we propose a generic local thermal non-equilibrium model for granulate porous
media accounting for conservation of mass, momentum and energy (two-equation temperature model). The
effective parameters needed to inform the model are the effective thermal conductivities of the different
phases and the heat transfer coefficient. An experimental-numerical inverse analysis method is employed to
determine these parameters. A dedicated experimental facility has been designed and built to study a model
granulate made of glass bead of 16 mm diameter. Experiments are conducted using the Transient Single-Blow
Technique (TSBT) by passing hot air (ranging from 293 K to 630 K) through cold particles at various mass
flow rates, covering a Reynolds number range of 58 to 252. The new model was implemented in the Porous
material Analysis Toolbox based on OpenFoam (PATO) used to compute the transient temperature fields.
Two optimization algorithms were employed to determine the parameters by minimizing the error between
experimental and simulated temperatures: a Latin Hypercube Sampling (LHS) method, and a local optimization
method Adaptive nonlinear least-squares algorithm (NL2SOL). The results indicate that the value of heat
transfer coefficient ℎ�� in the two-equation model falls in the range of 1.0 × 104 ∼ 1.93× 104 W/(m3 K) under
the given conditions. The axial dispersion gas thermal conductivity was found to be around 5.9 and 67.1 times
higher than the gas thermal conductivity at Peclet numbers of around 55 and 165, respectively. Furthermore,
two improved correlations of Nusselt number (���� = 2+1.54����(�� )0.6�� ��(�� )1∕3) and of axial dispersion gas thermal
conductivity (��������,∥ = 0.00053����(�� )2.21�� ��(�� ) ⋅ ���� ) are proposed and validated for a range of Reynolds number
from 58 to 252. The overall approach is therefore validated for the model granulate of the study, opening new
perspectives towards more precise design and monitoring of high-temperature TES systems.
Thu, 01 Feb 2024 00:00:00 GMThttp://hdl.handle.net/10985/248632024-02-01T00:00:00ZLIU, ShaolinAHMADI, AzitaLEVET, CyrilLACHAUD, JeanHigh-temperature thermal energy storage (TES) in packed beds is gaining interest for industrial energy
recovery. The wide range of temperature distributions causes significant variations in thermophysical properties
of the fluid and solid phases, leading to inaccuracies of classical TES models and heat transfer correlations.
The objective of this work is to develop and validate a detailed but pragmatic model accounting for
high-temperature effects. Based on a literature survey spanning over several communities interested in high-
temperature porous media, we propose a generic local thermal non-equilibrium model for granulate porous
media accounting for conservation of mass, momentum and energy (two-equation temperature model). The
effective parameters needed to inform the model are the effective thermal conductivities of the different
phases and the heat transfer coefficient. An experimental-numerical inverse analysis method is employed to
determine these parameters. A dedicated experimental facility has been designed and built to study a model
granulate made of glass bead of 16 mm diameter. Experiments are conducted using the Transient Single-Blow
Technique (TSBT) by passing hot air (ranging from 293 K to 630 K) through cold particles at various mass
flow rates, covering a Reynolds number range of 58 to 252. The new model was implemented in the Porous
material Analysis Toolbox based on OpenFoam (PATO) used to compute the transient temperature fields.
Two optimization algorithms were employed to determine the parameters by minimizing the error between
experimental and simulated temperatures: a Latin Hypercube Sampling (LHS) method, and a local optimization
method Adaptive nonlinear least-squares algorithm (NL2SOL). The results indicate that the value of heat
transfer coefficient ℎ�� in the two-equation model falls in the range of 1.0 × 104 ∼ 1.93× 104 W/(m3 K) under
the given conditions. The axial dispersion gas thermal conductivity was found to be around 5.9 and 67.1 times
higher than the gas thermal conductivity at Peclet numbers of around 55 and 165, respectively. Furthermore,
two improved correlations of Nusselt number (���� = 2+1.54����(�� )0.6�� ��(�� )1∕3) and of axial dispersion gas thermal
conductivity (��������,∥ = 0.00053����(�� )2.21�� ��(�� ) ⋅ ���� ) are proposed and validated for a range of Reynolds number
from 58 to 252. The overall approach is therefore validated for the model granulate of the study, opening new
perspectives towards more precise design and monitoring of high-temperature TES systems.Experimental investigation and tomography analysis of Darcy-Forchheimer flows in thermal protection systems
http://hdl.handle.net/10985/24903
Experimental investigation and tomography analysis of Darcy-Forchheimer flows in thermal protection systems
LIU, Shaolin; AHMADI, Azita; SCANDELLI, Hermes; LACHAUD, Jean
n thermal protection systems (TPS), Darcy’s law or Darcy-Forchheimer’s law is employed to model the
pyrolysis gas flow within the anisotropic porous ablator depending on the flow regime considered. A key
challenge with using these laws is first, the knowledge of the validity domain of each flow regime in terms of a
critical Reynolds number (������ ). Secondly, the lack of data on macroscopic properties, namely, the permeability
and Forchheimer tensors is particularly challenging for the relevance of the models. The objective of this
work is to contribute to overcoming these challenges by performing experimental and X-ray tomographic
image-based characterization of Calcarb, a commercial carbon preform used for manufacturing TPS. For this
purpose, fluid flow within Calcarb was studied experimentally in the Through-Thickness (TT) and the In-Plane
(IP) directions for Reynolds numbers of 0.05 to 10.46 -representative of the TPS application. Tomography
image-based micro-scale simulations, involving the direct resolution of the Navier–Stokes equations under
both flow regimes, were also performed. Experimental results exhibit the anisotropic nature of Calcarb, namely
through ������ values, corresponding to the Darcy flow regime limit, slightly different in the two directions (������
of 0.31 and 0.43) with measured permeability values of 1.248 × 10−10 m2 and 1.615 × 10−10 m2 for TT and IP
directions respectively. In the Forchheimer regime, experimental Forchheimer coefficients �� were 2.0010 × 105
m−1 (TT) and 1.4948 × 105 m−1 (IP). During the simulation process, a numerical strategy was defined to obtain
the permeability tensor yielding values within 8% of the experimental ones. The comparison of experimental
results vs simulation results in the Forchheimer regime was performed through the analysis of the pressure
gradients as functions of ���� in the ��, ��, and �� directions. The numerical estimations were compared successfully
with experimental measurements, with a discrepancy of 5.2%, for ���� values up to 2.4
Wed, 01 May 2024 00:00:00 GMThttp://hdl.handle.net/10985/249032024-05-01T00:00:00ZLIU, ShaolinAHMADI, AzitaSCANDELLI, HermesLACHAUD, Jeann thermal protection systems (TPS), Darcy’s law or Darcy-Forchheimer’s law is employed to model the
pyrolysis gas flow within the anisotropic porous ablator depending on the flow regime considered. A key
challenge with using these laws is first, the knowledge of the validity domain of each flow regime in terms of a
critical Reynolds number (������ ). Secondly, the lack of data on macroscopic properties, namely, the permeability
and Forchheimer tensors is particularly challenging for the relevance of the models. The objective of this
work is to contribute to overcoming these challenges by performing experimental and X-ray tomographic
image-based characterization of Calcarb, a commercial carbon preform used for manufacturing TPS. For this
purpose, fluid flow within Calcarb was studied experimentally in the Through-Thickness (TT) and the In-Plane
(IP) directions for Reynolds numbers of 0.05 to 10.46 -representative of the TPS application. Tomography
image-based micro-scale simulations, involving the direct resolution of the Navier–Stokes equations under
both flow regimes, were also performed. Experimental results exhibit the anisotropic nature of Calcarb, namely
through ������ values, corresponding to the Darcy flow regime limit, slightly different in the two directions (������
of 0.31 and 0.43) with measured permeability values of 1.248 × 10−10 m2 and 1.615 × 10−10 m2 for TT and IP
directions respectively. In the Forchheimer regime, experimental Forchheimer coefficients �� were 2.0010 × 105
m−1 (TT) and 1.4948 × 105 m−1 (IP). During the simulation process, a numerical strategy was defined to obtain
the permeability tensor yielding values within 8% of the experimental ones. The comparison of experimental
results vs simulation results in the Forchheimer regime was performed through the analysis of the pressure
gradients as functions of ���� in the ��, ��, and �� directions. The numerical estimations were compared successfully
with experimental measurements, with a discrepancy of 5.2%, for ���� values up to 2.4