Discussão sobre os efeitos de perda de calor e efeitos de pulso finito na determinação da difusividade térmica por meio do método Flash

Abstract

The thermal diffusivity relates the material's ability to transport heat energy to its ability to store it. This property can be determined using the Flash method experiment, where a heat pulse of radiant energy is applied to the front-surface of the sample and the temperature increase on the rear-surface is measured. In 1961, Parker et al. introduce a new method to estimate the thermal diffusivity of the material by analyzing the half time required for the rear-surface of the sample to reach its maximum temperature value. In this work, we evaluated and discussed in what the heat loss and finite pulse effects imply for the thermal diffusivity obtained by the method proposed by Parker et al. The analyzes for the effects of heat loss showed that the boundary conditions don’t let the temperature to reach the maximum value given by the Parker model, reaching a lower maximum value in a shorter time, which implies a higher value for the diffusivity thermal. For the finite pulse effect, it was verified that the energy is delivered more slowly to the sample, depending on the shape and width of the pulse, resulting in a longer time and in a lower value for the thermal diffusivity consequently. Analyzes were also carried out for combined effects of heat loss and finite pulse using the Gaussian profile, a profile that is used in the Photonic Nanometry Laboratory at Federal University of Espírito Santo, and it was concluded that the effects can be evaluated separately.