Improved Transient Method Measures Thermal Conductivity of Insulating Materials

Thermal conductivity is typically measured using steady state techniques, such as the guarded hot plate. Such measurements are impractical, time consuming, and can't be used in situ, or on moist materials, where water migrates under a thermal gradient. Transient methods, such as the heated needle, overcome such limitations. Measurements in insulations, however, remain a challenge, due to the large mismatch between specific heat of the probe and the sample. We revisited the traditional algorithm, based on a simplified model of the conduction process, and analyzed the actual response in a multilayered system, where the thermal properties of the probe are accounted for. A newly devised inversion scheme allowed us to estimate both conductivity and diffusivity. Preliminary tests in Styrofoam and goose down material confirmed the validity of the method.