Nonlinear pyrolysis layer model for thermal behavior of nonhomogeneous charring materials

Li, Weijie; Huang, Haiming; Xu, Xiaoyan; Zhao, Zhonglong

doi:10.1002/app.42331

Cited by 5 publications

(4 citation statements)

References 27 publications

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“…However, this model does not take into account the real situation between the virgin layer and the char layer, because the density and the enthalpy of pyrolysis gas change with heating time in this stage. In order to analyze the effect of this stage on ablation, Li et al [21,22] established a one-dimensional ablation model including the virgin layer, the pyrolysis layer, the char layer and the ablation layer and the effect of density on ablation was analyzed. It was found that not only external heat flux, moving interfaces and boundary affect the ablation result, but the change in density also affects the ablation, it was shown that the pyrolysis layer is essential in the one-dimensional ablation model.…”

Section: Introductionmentioning

confidence: 99%

Insight into chemical reaction kinetics effects on thermal ablation of charring material

Xiao

Jiang

2022

THERM SCI

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Thermal ablation plays an important role in the aerospace field. In this paper, to study the chemical kinetics effects on heat transfer and surface ablation of the charring ablative material during aerodynamic heating, a charring ablation model was established using the finite element method. AVCOAT5026-39H/CG material, one typical thermal protection material used in thermal protection system, was employed as the ablative material and heated by aerodynamic heating condition experienced by Apollo 4. The finite element model considers the decomposition of the resin within the charring material and the removal of the surface material, and uses Darcy?s law to simulate the fluid flow in the porous char. Results showed that the model can be used for the ablation analysis of charring materials. Then effects of chemical kinetics on ablation were discussed in terms of four aspects, including temperature, surface recession, density distribution, and mass flux of pyrolysis gas. The pre-exponential factor and activation energy have different effects on ablation, while the effect of the reaction order is little. This paper is helpful to understand the heating and ablation process of charring ablative materials and to provide technical references for the selection and design of thermal protection materials.

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Section: Introductionmentioning

confidence: 99%

Insight into chemical reaction kinetics effects on thermal ablation of charring material

Xiao

Jiang

2022

THERM SCI

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“…6 Thermochemo-mechanical phenomenon used in the ablation process dissipates the high heat fluxes by serial endothermic processes in the material and releases gaseous products. [7][8][9] The pyrolytic gasses flow in the direction of the exposed surface through the formed porous and charred solid material. 5,8 At a certain point of heating, the walls of pores become so thin that the exterior layer of the material is split off under the action of external flow pressure (external mechanical erosion) or pores break down by the release of pyrolytic gases (internal mechanical erosion).…”

Section: Introductionmentioning

confidence: 99%

“…The chemical reaction that takes place at 3000 K and above is called sublimation. 9,10 This is a highly endothermic phenomenon, but normally the composite wall does not reach the sublimation temperature and so the chemical reaction with flow gasses is the main chemical ablation contribute. 6 Ablation chart of composite material is shown in Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Thermochemical erosion and thermophysical properties of phenolic resin/carbon fiber/graphite nanocomposites

Sabagh

Ahmad

Bahramian

2016

Journal of Reinforced Plastics and Composites

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The main objective of this work is an experimental investigation and an analytical modeling of ablation and to analyze the thermophysical properties of nanocomposites based on novolac resin/short carbon fiber/graphite nanocrystalline powders in oxyacetylene flame test. The composite consisting of 40 wt.% carbon fiber was prepared as reference sample of which matrix was modified with three different percentages (6, 9 and 12 wt.%) of nano-sized graphite powders as reinforcement. Ablation is calculated by mass balance equation. Some parameters in the ablation modeling are evaluated by simultaneous thermal gravimetric analysis technique. Results of this work show that ablation rates decrease by the addition of graphite powders. The theoretical ablation rates are 33–38% less than the experimental data analyzed by oxyacetylene flame tests. This difference is reasonable because the effect of fluid stream force of oxyacetylene flame that causes the thermomechanical erosion of the surface is omitted in theoretical calculations. Therefore the model only calculates thermochemical erosion. Also, the thermophysical properties change due to heating is analyzed. Moreover, in nanocomposite with 9 wt.% graphite nanopowders, the rate of ablation and thermal diffusivity coefficient decreased by 10% and 50%, respectively, and thermal stability increased by 12% compared to the reference sample.

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“…The pyrolysis of charring ablation materials and the flow of pyrolysis gases in the material can bring off amounts of heat [4][5][6][7]. Meanwhile, the char on the material surface usually ablates because it reacts with the oxygen in the boundary layer behind the shock wave.…”

Section: Introductionmentioning

confidence: 99%

Protection of pyrolysis gases combustion against charring materials’ surface ablation

Huang

Wang

et al. 2016

International Journal of Heat and Mass Transfer

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractCharring ablation materials are widely used for thermal protection systems in a vehicle during hypersonic reentry. The pyrolysis gases from the charring materials can react with oxygen in the boundary layer, which makes the surface ablation rate decrease. The problem of protection of combustion of pyrolysis gases in charring material against surface ablation is solved by the detached normal shock wave relations and the counterflow diffusion flame model. The central difference format for the diffusion term and the upwind scheme for the convection term are used to discretize the mathematical model of the counterflow diffusion flame. Numerical results indicate that the combustion of pyrolysis gases in the boundary layer can completely protect the material surface from recession when the velocity of pyrolysis gases injecting to the boundary layer is higher than the critical velocity. There is an allometric relationship between the critical velocity and Mach number, and the combustion heat has little influence on the temperature distribution originating from the aerodynamic heating. This study will be helpful for the design of the thermal protection system in hypersonic reentry vehicles.

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Nonlinear pyrolysis layer model for thermal behavior of nonhomogeneous charring materials

Cited by 5 publications

References 27 publications

Insight into chemical reaction kinetics effects on thermal ablation of charring material

Insight into chemical reaction kinetics effects on thermal ablation of charring material

Thermochemical erosion and thermophysical properties of phenolic resin/carbon fiber/graphite nanocomposites

Protection of pyrolysis gases combustion against charring materials’ surface ablation

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