Investigation Of Heat Transfer Properties Of C/SiC Lattice Core Sandwich Composites

The interest for ultra-lightweight,integration and multi-functional integration has a rapid improvement in aerospace field over recent years.As the functional configuration material with careful consideration of material,structure and function,C/Si C lattice core sandwich composites have not only excellent mechanical properties but also the potential advantages of realizing the multifunction integration of heat dissipation,energy absorption,impact resistance,vibration and noise reduction so on.Therefore,they have become one of the most promising new structural materials candidates in aerospace field.So far,many investigations have been performed on the configuration optimization,preparation method and mechanical property of the C/Si C lattice core sandwich composites.However,few studies focused on the heat transfer properties of C/Si C lattice core sandwich composites.In this paper,based on theoretical analysis and numerical simulation,the heat transfer performance of C/Si C lattice core sandwich composites are sysemtically studied.The main contents are as follows:Based on the net heat flux method and Monte Carlo method,an analytical model is presented to predict the equivalent thermal conductivity of the C/Si C pyramidal lattice core sandwich composites by considering geometric configuration of lattice core.The equivalent thermal conductivity of C/Si C pyramidal lattice core sandwich composites is calculated.The effects of the geometrical parameters(such as the core height,the strut diameter,inclination angle and cross-section shape),solid surface emissivity and temperature on the equivalent thermal conductivity of the pyramidal lattice core sandwich structures are well discussed.The heat transfer mechanism of C/Si C pyramidal lattice core sandwich composite is revealed.The results show that the equivalent thermal conductivity increases with the increasing of solid emissivity and top facesheet temperature.When the temperature of the top facesheet increases from 373 K to1473 K,the equivalent thermal conductivity increases 8.7 times.Moreover,in order to reduce weight,the geometric configuration of the strut of pyramidal lattice sandwich structure is improved.Compared with the original structure,the mechanical properties and thermal insulation performance of the improved pyramid lattice core sandwich composite are significantly promoted,which can provide the solid foundation for the achievement of the load/heat integration of the C/Si C pyramidal lattice core sandwich composite.Based on the net heat flux method,an analytical model for predicting the equivalent thermal conductivity of C/Si C pyramidal lattice core sandwich composite by considering the radiation emitted from the struts is established.The equivalent thermal conductivity of C/Si C pyramidal lattice core sandwich composite is calculated.The effects of geometric parameters,temperature and solid surface emissivity on the equivalent thermal conductivity of C/Si C pyramidal lattice core sandwich composite are discussed.The results show that when the temperature is higher than 1273 K,the contribution of the radiation emitted from the struts of the lattice core to the overall heat transfer of the lattice sandwich structures is more than 10%,which therefore cannot be neglected.The effect of the solid emissivity on the radiative conductivity is more significant at higher temperatures.In order to optimize the structure and improve the heat insulation efficiency,C/Si C composite sandwich structure with thickness-direction graded lattice core is designed.A heat transfer analytical model of C/Si C composite sandwich structure with thickness-direction graded lattice core without considering the thermal resistance of the panel is established.The equivalent thermal conductivity of C/Si C composite sandwich structure with thickness-direction graded lattice core is calculated,and the effects of graded parameter and geometric parameters on the equivalent thermal conductivity of thickness-direction graded lattice core sandwich structures are discussed.Based on the analysis of the actual heat transfer process,an analytical model of heat transfer in C/Si C thickness-direction graded lattice core sandwich composite which considers the thermal resistance of the panel is established.The equivalent thermal conductivity of C/Si C thicknessdirection graded lattice core sandwich composite is predicted.The effects of graded parameter and geometric parameters on the equivalent thermal conductivity of thickness-direction graded lattice core sandwich structures are discussed.Based on the theory of radiation energy conservation,the heat transfer models of C/Si C pyramidal lattice core sandwich composite and C/Si C axially graded lattice core sandwich composite with under non-uniform thermal load are established.The radiative transfer coefficient is calculated by the improved Monte Carlo method.The temperature field of two kinds of lattice core sandwich structure is predicted by variational method.The finite element heat transfer models of these two kinds of lattice core sandwich structures are established.The effects of gradient distribution and geometric parameters on the temperature response of the bottom surface of the lattice core sandwich structures are studied.The results show that the thermal insulation performance of the sandwich structures can be improved by adjusting the gradient of the struts without increasing the additional structural mass.Under the same non-uniform thermal load,the average temperature of the bottom surface decreases by increasing the core height as well as decreasing the strut’s inclination angle.Based on the equivalent theory,the thickness-direction graded lattice core sandwich composite is equivalent to the functional graded(FG)sandwich panel.The heat transfer model of FG sandwich panel is established.The temperature field distribution of FG sandwich panel with convective-radiative boundary conditions is predicted by the Ferrari’s method,and the equivalent thermal conductivity of the FG sandwich panel is obtained by thermal network method.The effects of geometrical and physical parameters on the temperature field and equivalent thermal conductivity of the FG sandwich panels are studied.The studies show that the change of the thickness of the graded core changes the distribution of the temperature field of FG sandwich panels when the thickness of the FG sandwich panel is fixed.It is a suitable way to improve the thermal insulation performance of the FG sandwich panel by decreasing the thickness of the graded core.