Study on Calculation of Minimum Thickness of Sample in Thermal Conductivity Measurement

Abstract

It is found that the true thermal conductivity can be measured only when material reaches a certain minimum thickness, within which the thermal conductivity varies with thickness. Based on the derivative of Fourier's law, it is pointed out that the phenomenon of thermal conductivity varying with thickness is caused by the existence of second derivative of temperature. Both of the FTC (function of thermal conductivity) and the calculation formula of MMT (minimum measured thickness) are established. For materials of GFRP (glass fiber reinforced plastic), neoprene and silicone, their R-squared of FTC are respectively 0.9995, 0.9668 and 0.9976, and their MMTs are 5.2287 mm, 4.7034 mm and 12.7532 mm, respectively. What’s more, their interfacial thermal conductivities are different, which reveals that thermal conductivity of material is a numerical field.