Abstract
A mathematical model based on minimal thermal resistance and equal law of specific equivalent thermal conductivity is developed to discuss the heat transfer characteristics of ablative thermal insulating material from the mesoscopic scale. Based on the statistical results of mesoscopic parameters, the microstructure unit cell model was established to analyze the influence rule of mesoscopic parameterization which includes the size, distribution, and positional relation of microsphere and fiber. The results show that the equivalent thermal conductivity decreases with the density, size, distribution area, and distance of microsphere and the space distance and volume fraction of fiber decreasing. Besides, the equivalent thermal conductivity will become larger when more quality of heat transfers along the fiber direction. Exploring the relationship between the macroscopic heat transfer process and the microstructure is meaningful for exploring the heat transfer behavior of thermal insulating material and improvement of the processing technology.
Highlights
With the acceleration of the flight speed of an aircraft, and the strong aerodynamic heating of a reentry aircraft, to ensure that the internal instruments are not burnt out, it is necessary to take effective measures of heat insulation
The heat transfer characteristics of ablative thermal insulating materials at room temperature are analyzed, and the influence of various parameters on the thermal conductivity is discussed from two scales by establishing a kind of theoretical model
The conclusions are as follows: (1) The mathematical model established in this article which is based on the law of minimal thermal resistance and the equal law of the specific equivalent thermal conductivity can get relatively accurate thermal conductivity prediction results
Summary
With the acceleration of the flight speed of an aircraft, and the strong aerodynamic heating of a reentry aircraft, to ensure that the internal instruments are not burnt out, it is necessary to take effective measures of heat insulation. The Hashin-Shtrikman bounding model is based on the variational principle; the Mori-Tanaka model and Benveniste’s model are based on mean field approximation They focus on one factor and are suitable for some specific material. By analyzing the heat transfer mechanism, the series-parallel thermal resistance model is established; the equivalent thermal conductivity can be gotten. The challenge of this method is how to establish the unit cell model and the series-parallel thermal resistance model This method is convenient to consider the influence of microstructure on heat transfer characteristics. This paper discusses the heat transfer characteristics of thermal insulation materials with the establishment of a theoretical model, especially to explore the influence law of mesoscopic parameters from different scales. The purpose is to explore the relationship between material macroscopic heat transfer mechanism and material mesoscopic parameters and to provide reference for process design of ablative thermal insulating material
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