An improved transient plane source technique and methodology for measuring the thermal properties of anisotropic materials

Abstract

The transient plane source (TPS) technique has recently garnered attention due to its ability to measure thermal properties of an extensive range of isotropic materials such as solids, liquids and powder. It also can be employed to measure thermal properties of anisotropic materials at a low cost and reduced time scale; however, it requires that thermal capacity be determined a priori in a separate experiment. In this study, a new methodology has been theoretically established to characterize the transport coefficients of anisotropic materials in both directions without requiring the measurement of heat capacity. We propose a new experimental configuration of the TPS setup which allows for measurement of the conductivity ratio of anisotropic materials and is coupled with the conventional TPS technique for anisotropic material to measure all transport coefficients, including thermal capacity. This is accomplished by measuring the samples in two different orientations and deriving a relation between the conductivity ratio and the time ratio through a specific time window during the measurement time, which depends on the sample size. The viability of this method was verified numerically by simulating the proposed approach for an ABS polymer composite material. The numerical model is further used to examine the proposed approach for different anisotropic thermal conductivity ratios ranging from 1.225 to 4. The effect of other factors—such as the influence of sensor thermal capacity and heater power—were explored. The results show that the error in predicting the thermal conductivity ratio ranges from 0.26% at an anisotropic ratio of 1.225–1.5% at an anisotropic ratio of 4. The numerical model was revised to represent a realistic embodiment of an experimental apparatus. The revised model shows that the predicted error in testing this approach experimentally will be approximately less than 8%, which demonstrates the viability of the experimental implementation of this technique.