Contactless thermal parameters characterization based on infrared image methods: Uncertainly improvement of flash method for thin samples

摘要

Infrared (IR) active thermography has been successfully used for non-invasive thermal parameters determination and is fostering significant industrial outcomes in new materials development, quality control, safety, manufacturing processes efficiency, etc. A new approach for thermal parameters characterization, adapted from the standard flash method, is presented for thin samples. The flash method is a classical methodology to obtain the thermal parameters of materials without any contact with analysed sample. Briefly, the front face of an opaque sample is heated by means of a short-duration light pulse and then the temperature evolution at the rear surface of the sample is analysed. The time evolution of the temperature at one point is related to the thermal parameters of the sample, it leads to obtain them. The minimum thickness of the sample is determined by the requirement that the flash duration must be short compared to the time the temperature begins to rise at the back surface. A sample that is too thin results in the recording of a low value of thermal diffusivity and consequentially an erroneous estimation of the other thermal parameters. The adaptation presented here consists of an infrared camera measurement in the rear face temperature synchronize with a flash lamp. The procedure is based on experimental-theory adjustment to obtain the thermal parameters: thermal diffusivity, thermal conductivity and volumetric heat capacity. The procedure has required the flash lamp optical energy and time modulation characterization; it was performed through an infrared image based non-destructive method. Finally, the results have been validated by comparison between the experimental data and those provided by a heat transfer model.