Reflection Of Thermal Radiation Research Articles

Multiphase hybrid model and thermal insulation simulation of elytra-mimetic ceramic fiber aerogel

In our previous work, the coaxial electrostatic spinning method was applied to construct nanofiber/SiBCN ceramic aerogel with an elytra-mimetic structure. The material presented excellent mechanical, insulation, oxidation resistance, and other properties. Based on preliminary experiments and literature reports, the integrated heat transfer behavior of nanofiber/SiBCN composite ceramic aerogels in high-temperature environments was affected by several factors, such as coaxial fiber size properties, fiber particle content, interactions, and spatial distribution. Moreover, the above factors overlapped and interacted with each other, and it was hard to generalize a clear law of action through traditional experiments and characterization. Therefore, the paper constructed a representative volume unit (RVE) model based on the complex spatial distribution characteristics of composite aerogels, using fractal theory, Rosseland equation theory, and multiphase model theory. This paper investigated the fiber and particle content, the size characteristics of the coaxial fibers, and the overall heat transfer process in high-temperature environments using the finite element method. The finite element simulated the effective thermal conductivity of multiphase aerogel composites under multiple parameters, such as fiber occupancy, fiber core-shell diameter ratio, temperature, and heat transfer mode. We obtained the property parameters of the complex composition of the material through fractal theory. The model was combined with finite elements to study the fiber particle content, the size characteristics of coaxial fibers, and the integrated heat transfer process in high-temperature environments. The fibers improved the absorption and reflection of thermal radiation with increasing fiber mass fraction, leading to improved ability of ceramic fiber aerogel to extinguish light. The fibers had a larger area to absorb and reflect thermal radiation. Based on the excellent extinction ability of SiC fibers, the composite ceramic aerogel had improved thermal performance at a specifically fiber-to-shell diameter ratio through a comprehensive multifactor simulation analysis.

Glassy carbon cladding structure with elongated SiCnw reinforced carbon foam insert

In this study, glassy carbon cladding structure with elongated SiCnw reinforced carbon foam insert (GC-CF/SiCnw) is prepared by slow Polymer Infiltration Pyrolysis (PIP) method. It is tested that the density of the structure reaches 0.6362 g cm−3 while the open porosity reaches 0.8% and total porosity reaches 52.6%. The SEM images show the obvious boundary between the inner and outer parts. In addition, the structure exhibits excellent mechanical properties, its compressive strength reaches 6.6 MPa, and the specific strength reaches 10.3877 MPa g−1 cm−3. Considering the fracture mechanism, the four-stage different force composition in the fracture process is significantly different from the traditional material, reflecting the influence of the excellent structural design of the material on the mechanical properties. Moreover, the structure exhibits excellent high temperature insulation properties. As the temperature increases from 293 K to 1273 K, the effective thermal conductivity increases from 0.215 W m−1K−1 to 0.587 W m−1K−1. Considering the thermal insulation mechanism, the reflection of thermal radiation from the dense and smooth GC shell and the scattering of thermal radiation from the SiC nanowires greatly reduces the transmission of thermal radiation. Besides, the temperature field index diagram under steady-state heat conduction as a heat-source temperature of 1200 K is obtained by thermal resistance network method.

Compare of Experimental and Numerical Evaluation of Structure with Application of Reflective Insulation

Thermal insulation effect of reflective insulation is based on the reflection of thermal radiation. Reflective insulations are mainly used in combination with the non-ventilated air cavity. Proposed paper deals with experimental measurements of the thermal insulation properties of the air cavity surrounded by low-emissivity surfaces and comparison of measured values with calculated values according to the standardized procedures. The beginning for determination of the thermal resistance of air cavity was to conduct several experimental measurements by Hot Box method using heat flow meter. The results show good agreement between measured and calculated data.

Evaluation of the Thermal Resistance of Structure with Reflective Insulation: Measurement under Non-Stationary Boundary Conditions

Some manufacturers of reflective insulation products claim that their relatively thin products have the same thermal insulation properties as common insulation with much times higher thickness. This paper deals with experimental measurements of the thermal insulation properties of real structures with reflective insulation. Several experimental sequences were conducted to determine the thermal resistance of the structure. The evaluation was conducted according to the procedures specified in the international standard (ISO 9869 - 1994). Effect of products (based on the reflection of thermal radiation) on the thermal insulation properties of the structure will be determined by evaluation. This effect will be compared with the effects of common insulation (with the intention of reduce of the heat transfer by the conduction).