Thermal conductivity estimation of high solid loading particulate composites: A numerical approach

The problem addressed here is the determination of thermal conductivity of high solid loading particulate composites through computational techniques. The primary material of study is a composite solid propellant which is used extensively in the launch vehicle industry and also has application in missiles for the defence sector. Composite propellants generally have a very high solid loading of reinforced particles as compared to the conventional composite materials (particulate composites). Thermal diffusivity is one of the important properties of a propellant which plays a role in determining the thermal profile inside the solid phase of the propellant during its combustion. The thermal profile dictates the energy stored in the condensed phase. The specific heat capacity of the solid and density of the solid depend on the volume, while surface area along with volume could be the controlling parameters in determining thermal conductivity. This study evaluates the thermal conductivity of wide range of composite solid propellants using a numerically developed finite volume model. For this, a simulated propellant pack is constructed using a random packing method, assuming particles as spheres. The results of few of the packs are compared with experiments. The simulations predict a slightly lower value compared to the experimental results probably due to the spherical nature of the particles assumed here. The contact between two particles (spheres) is a point while AP and Al particles are not exactly spherical in nature. As a consequence, the contact surface area is reduced and this reduces the paths of least resistance that could be available for heat flow. The paper brings out the pitfalls of using homogenization of fine sized particles with the matrix.