Modified Angström’s method for measurement of thermal diffusivity of materials with low conductivity

Semiconducting Peltier devices are used as heat sources and sinks to apply sinusoidally varying temperature versus time profiles through square sheets of material. The thermal diffusivity may be determined by recording the temperature as a function of time at the interfaces of a stack of two or three sample sheets. The design of the experimental rig is described and its use is illustrated. The thermal diffusivity of a variety of poorly conducting materials such as ceramics and polymers, having a wide range of values of thermal diffusivity, may be measured using this approach by merely selecting the frequency and amplitude to allow for the thickness and material so as to be able to resolve the temperature phase differences and amplitudes at the junctions of the sheets. In this case, the technique is applied to the determination of thermal diffusivity of polyethylene by way of illustration of the method. Reproducibility and precision achieved throughout the temperature range 4–46 °C used was found to be no better than ±5%, but precision could be improved by interfacing the equipment with a computer. Good agreement was obtained with published values of thermal diffusivity.