The Experts below are selected from a list of 128541 Experts worldwide ranked by ideXlab platform

Weijie Li - One of the best experts on this subject based on the ideXlab platform.

  • a new mechanism of surface ablation of Charring materials for a vehicle during reentry
    Applied Thermal Engineering, 2016
    Co-Authors: Weijie Li, Haiming Huang, Xiaoliang Xu
    Abstract:

    Abstract Coupled thermal/fluid/chemical analysis for the surface ablation of Charring materials in a vehicle during hypersonic reentry has been conducted. The pyrolysis layer model is presented to simulate the thermal responses of the material, the relations of the normal shock wave are adopted to obtain the aerodynamic parameters in the boundary layer, and the counterflow diffusion model considering chemical mechanisms of hydrocarbons is proposed to solve the combustion of the pyrolysis gases. Meanwhile, the gas-solid chemical reactions of surface char are coupled with the thermal responses, the aerodynamic parameters and the combustion of the pyrolysis gases. The new equations of surface ablation for the Charring materials are discretized by the central and the up-wind difference formats. A coupled mechanism of surface ablation is simulated by using our computer codes. Numerical results indicate that the consumption of oxygen in the combustion of the pyrolysis gases can protect Charring materials from the surface ablation in some degree. Furthermore, selecting Charring materials with larger activation energy and smaller frequency factor can effectively improve the thermal protection performance of Charring materials. This study will be helpful for the design of the thermal protection system in reentry vehicles.

  • a nonlinear pyrolysis layer model for analyzing thermal behavior of Charring ablator
    International Journal of Thermal Sciences, 2015
    Co-Authors: Weijie Li, Haiming Huang, Ye Tian, Zhe Zhao
    Abstract:

    Abstract Understanding the pyrolysis phenomena experienced by Charring ablators used in thermal protection systems for manned reentry vehicles is crucial for their design. A one-dimension nonlinear pyrolysis layer model without surface recession has been developed to explore the thermal behavior of Charring ablator when subjected to an aerodynamic hyper-thermal environment. The Charring ablator in this model consists of three distinct zones: char, pyrolysis and virgin material. The heat and mass transfer, the two moving interfaces and the temperature-dependent thermal properties in Charring materials undergoing pyrolysis are considered in the formulation of the model. The governing differential equations are derived, and its implicit finite difference formulations are programmed in MATLAB. Examples are given to demonstrate the effectiveness and accuracy of this model. The thermal response of Charring material with antioxidants is also predicted under actual service conditions.

  • effects of gradient density on effective heat capacity of Charring ablative material for re entry vehicles
    International Journal of Numerical Methods for Heat & Fluid Flow, 2015
    Co-Authors: Weijie Li, Hailing Yu, Haiming Huang, Xiaoliang Xu
    Abstract:

    Purpose – The effective heat capacity is a key index to estimate the thermal protection performance of Charring ablative materials in reentry vehicles subjected to aerodynamic heat loads. The purpose of this paper is to investigate the effects of gradient density on the effective heat capacity. Design/methodology/approach – Based on the Fourier law and the pyrolysis interface model, the authors establish the governing equations for the transient heat conduction with variable density, and then simulate one-dimensional transient thermal behavior of a homogeneous and three types of non-homogeneous Charring ablative material in reentry capsules by using the implicit numerical method. Findings – The moving rate of pyrolysis interface and the surface temperature of Charring ablative material depend on not only the surface heating history, but also the gradient density. And the gradient density can improve the insulation performance of Charring materials, e.g. the effective heat capacity in the bilinear design i...

Xiaoliang Xu - One of the best experts on this subject based on the ideXlab platform.

  • a new mechanism of surface ablation of Charring materials for a vehicle during reentry
    Applied Thermal Engineering, 2016
    Co-Authors: Weijie Li, Haiming Huang, Xiaoliang Xu
    Abstract:

    Abstract Coupled thermal/fluid/chemical analysis for the surface ablation of Charring materials in a vehicle during hypersonic reentry has been conducted. The pyrolysis layer model is presented to simulate the thermal responses of the material, the relations of the normal shock wave are adopted to obtain the aerodynamic parameters in the boundary layer, and the counterflow diffusion model considering chemical mechanisms of hydrocarbons is proposed to solve the combustion of the pyrolysis gases. Meanwhile, the gas-solid chemical reactions of surface char are coupled with the thermal responses, the aerodynamic parameters and the combustion of the pyrolysis gases. The new equations of surface ablation for the Charring materials are discretized by the central and the up-wind difference formats. A coupled mechanism of surface ablation is simulated by using our computer codes. Numerical results indicate that the consumption of oxygen in the combustion of the pyrolysis gases can protect Charring materials from the surface ablation in some degree. Furthermore, selecting Charring materials with larger activation energy and smaller frequency factor can effectively improve the thermal protection performance of Charring materials. This study will be helpful for the design of the thermal protection system in reentry vehicles.

  • effects of gradient density on effective heat capacity of Charring ablative material for re entry vehicles
    International Journal of Numerical Methods for Heat & Fluid Flow, 2015
    Co-Authors: Weijie Li, Hailing Yu, Haiming Huang, Xiaoliang Xu
    Abstract:

    Purpose – The effective heat capacity is a key index to estimate the thermal protection performance of Charring ablative materials in reentry vehicles subjected to aerodynamic heat loads. The purpose of this paper is to investigate the effects of gradient density on the effective heat capacity. Design/methodology/approach – Based on the Fourier law and the pyrolysis interface model, the authors establish the governing equations for the transient heat conduction with variable density, and then simulate one-dimensional transient thermal behavior of a homogeneous and three types of non-homogeneous Charring ablative material in reentry capsules by using the implicit numerical method. Findings – The moving rate of pyrolysis interface and the surface temperature of Charring ablative material depend on not only the surface heating history, but also the gradient density. And the gradient density can improve the insulation performance of Charring materials, e.g. the effective heat capacity in the bilinear design i...

Haiming Huang - One of the best experts on this subject based on the ideXlab platform.

  • a new mechanism of surface ablation of Charring materials for a vehicle during reentry
    Applied Thermal Engineering, 2016
    Co-Authors: Weijie Li, Haiming Huang, Xiaoliang Xu
    Abstract:

    Abstract Coupled thermal/fluid/chemical analysis for the surface ablation of Charring materials in a vehicle during hypersonic reentry has been conducted. The pyrolysis layer model is presented to simulate the thermal responses of the material, the relations of the normal shock wave are adopted to obtain the aerodynamic parameters in the boundary layer, and the counterflow diffusion model considering chemical mechanisms of hydrocarbons is proposed to solve the combustion of the pyrolysis gases. Meanwhile, the gas-solid chemical reactions of surface char are coupled with the thermal responses, the aerodynamic parameters and the combustion of the pyrolysis gases. The new equations of surface ablation for the Charring materials are discretized by the central and the up-wind difference formats. A coupled mechanism of surface ablation is simulated by using our computer codes. Numerical results indicate that the consumption of oxygen in the combustion of the pyrolysis gases can protect Charring materials from the surface ablation in some degree. Furthermore, selecting Charring materials with larger activation energy and smaller frequency factor can effectively improve the thermal protection performance of Charring materials. This study will be helpful for the design of the thermal protection system in reentry vehicles.

  • a nonlinear pyrolysis layer model for analyzing thermal behavior of Charring ablator
    International Journal of Thermal Sciences, 2015
    Co-Authors: Weijie Li, Haiming Huang, Ye Tian, Zhe Zhao
    Abstract:

    Abstract Understanding the pyrolysis phenomena experienced by Charring ablators used in thermal protection systems for manned reentry vehicles is crucial for their design. A one-dimension nonlinear pyrolysis layer model without surface recession has been developed to explore the thermal behavior of Charring ablator when subjected to an aerodynamic hyper-thermal environment. The Charring ablator in this model consists of three distinct zones: char, pyrolysis and virgin material. The heat and mass transfer, the two moving interfaces and the temperature-dependent thermal properties in Charring materials undergoing pyrolysis are considered in the formulation of the model. The governing differential equations are derived, and its implicit finite difference formulations are programmed in MATLAB. Examples are given to demonstrate the effectiveness and accuracy of this model. The thermal response of Charring material with antioxidants is also predicted under actual service conditions.

  • effects of gradient density on effective heat capacity of Charring ablative material for re entry vehicles
    International Journal of Numerical Methods for Heat & Fluid Flow, 2015
    Co-Authors: Weijie Li, Hailing Yu, Haiming Huang, Xiaoliang Xu
    Abstract:

    Purpose – The effective heat capacity is a key index to estimate the thermal protection performance of Charring ablative materials in reentry vehicles subjected to aerodynamic heat loads. The purpose of this paper is to investigate the effects of gradient density on the effective heat capacity. Design/methodology/approach – Based on the Fourier law and the pyrolysis interface model, the authors establish the governing equations for the transient heat conduction with variable density, and then simulate one-dimensional transient thermal behavior of a homogeneous and three types of non-homogeneous Charring ablative material in reentry capsules by using the implicit numerical method. Findings – The moving rate of pyrolysis interface and the surface temperature of Charring ablative material depend on not only the surface heating history, but also the gradient density. And the gradient density can improve the insulation performance of Charring materials, e.g. the effective heat capacity in the bilinear design i...

Zhe Zhao - One of the best experts on this subject based on the ideXlab platform.

  • a nonlinear pyrolysis layer model for analyzing thermal behavior of Charring ablator
    International Journal of Thermal Sciences, 2015
    Co-Authors: Weijie Li, Haiming Huang, Ye Tian, Zhe Zhao
    Abstract:

    Abstract Understanding the pyrolysis phenomena experienced by Charring ablators used in thermal protection systems for manned reentry vehicles is crucial for their design. A one-dimension nonlinear pyrolysis layer model without surface recession has been developed to explore the thermal behavior of Charring ablator when subjected to an aerodynamic hyper-thermal environment. The Charring ablator in this model consists of three distinct zones: char, pyrolysis and virgin material. The heat and mass transfer, the two moving interfaces and the temperature-dependent thermal properties in Charring materials undergoing pyrolysis are considered in the formulation of the model. The governing differential equations are derived, and its implicit finite difference formulations are programmed in MATLAB. Examples are given to demonstrate the effectiveness and accuracy of this model. The thermal response of Charring material with antioxidants is also predicted under actual service conditions.

Qi Wang - One of the best experts on this subject based on the ideXlab platform.

  • the investigation of intumescent flame retardant polypropylene using a new macromolecular Charring agent polyamide 11
    Polymer Composites, 2009
    Co-Authors: Zhiqiang Feng, Qi Wang
    Abstract:

    This article deals with a new macromolecular Charring agent, polyamide 11 (PA11), which is in combination with a small Charring agent, pentaerythritol (PER) and a flame retardant, ammonium polyethylene to flame-retardant polypropylene (PP). When compared with polyamide 6 (PA6), an existing macromolecular Charring agent extensively reported, PA11 has longer alkyl segment in its chain unit and shows better compatibility with PP; additionally, with a relatively lower melt point close to that of PP, PA11 can be more effectively compounded with PP in the melt state and better dispersed in PP matrix, thus enhancing the flame retardancy and mechanical properties. Moreover, with certain synergistic effects between PA11 and PER, the system using PA11/PER as composite Charring agents showed better Charring performance in comparison with the system only using PER. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

  • flame retarded poly propylene with melamine phosphate and pentaerythritol polyurethane composite Charring agent
    Macromolecular Materials and Engineering, 2007
    Co-Authors: Qi Wang
    Abstract:

    In this paper, a novel intumescent system including MP as well as PER/TPU which acts as composite Charring agent, is adopted to flame-retarded PP. The encapsulation of Charring agent PER by TPU effectively avoids the reaction of PER with MP during the compounding with PP at high temperature and also prevents the leaching out of polar PER from nonpolar PP matrix, thus remarkably enhancing the stability and water-resistance of the intumescent system. PER and TPU have different but complementary Charring mechanisms. So flame-retarded PP with MP/composite Charring agent shows a much better Charring performance and flame-retardancy than MP/ PER flame-retarded PP. The experimental results show that the former can reach UL-94 V-0 rating at 1.6 mm thickness at 25 wt.-% flame retardant loading.