Non-destructive Thermal Diagnostics of Porous Materials

Abstract

Developed mathematical models of apparent thermal conductivity of porous materials are applied to non-destructive methods of thermal diagnostics. The non-destructive thermal diagnostics of porous materials can be used to estimate the size of pores and cracks in the range 10 −9 to 10 −3 m. A fractal model of porous structure and dependences of thermal conductivity/diffusivity on (experimental) gas pressure are used as a basis for structure parameter calculations. The measuring element (sensor) in this method is the mean free path of gas molecules in pores and cracks (Knudsen number) that is very sensitive to changes in gas pressure. Possible applications of the developed methods include non-destructive thermal diagnostics (NDTD) of nano-and micro-crack sizes; opening, closing and size changes of the cracks at high temperatures in a wide temperature range; evaluation of interfacial and contact heat barrier resistance for coatings; remote laser thermal diagnostics of the cracks; as well as obtaining data on strength, thermal shock behavior, failure and fatigue behavior of coatings and other structures. Examples of several applications of the NDTD method are presented.

Simultaneous reconstruction of thermal degradation properties for anisotropic scattering fibrous insulation after high temperature thermal exposures

“…The fibrous materials are semitransparent, strongly anisotropic scattering, and of high porosity [8]. The heat conduction and radiation transportation within the material are strongly coupled together depending on the microstructural parameters of particles and application conditions [9]. The conjugate nature and complex scattering mechanisms make the thermal properties measurement be a difficult task.…”