Determination of Thermal Diffusivity of Fibrous Insulating Materials

The problem of determining thermal diffusivity from transient temperature measurements is analysed, and some simulated and experimental results concerning fibrous insulators are reported and discussed. The thermal diffusivity is reconstructed in the form of a polynomial approximation by solving the nonlinear inverse heat-conduction equation, in which the temperature-dependent thermal diffusivity is the unknown function and the time-temperature histories on the boundary and inside the specimen (at known positions) are the measured variables. The estimator algorithm is based on the minimisation of the squared-error function by means of the gradient method. From a single 1 h test, the estimator is able to provide a quadratic approximation (three unknown coefficients) of the thermal diffusivity valid in a temperature interval of about 250 K.