Simplified estimation method for the determination of the thermal effusivity and thermal conductivity using a low cost hot strip

This paper presents the study of a hot strip made of thin rectangular electrical resistance with a thermocouple placed on its centre. The purpose was to simultaneously estimate thermal effusivity and conductivity in a limited time (t(2) < 180 s) using a low cost probe. Heat transfer has been modelled with the quadrupole formalism to simulate the evolution of the temperature at the centre of a hot strip set between two samples of material to be characterized when a heat flux step is applied. Simulation is used to fix the optimal dimensions of a hot strip that behaves as a hot plate (1D transfer) during a minimal time t(1) (>20 s) and that has higher sensitivity to the thermal conductivity between t(1) and t(2) (2D transfer). The thermal effusivity is estimated between 0 and t(1) by minimization of the quadratic errors between the experimental curve and the curve calculated by the classical hot plate model. The thermal conductivity is estimated between t(1) and t2 but using the complete 2D model. To validate the model and the estimation process, experimental tests were realized on three materials with low diffusivities (a < 2 x 10(-7) m(2) s(-1)) and having typical area of 6 cm x 4 cm and typical thickness of 1.5 cm.