Authors: Tage T Burnett, Jakob G Bates, Christopher R Dillon, Matthew R Jones
Mentors: Christopher R Dillon
Insitution: Brigham Young University
In recent years, modeling and simulation have become more prominent in solving heat transfer problems. The accuracy and predictive power of heat transfer simulations is limited by the quality of the thermal properties used within the model. Thus, one method for improving computational accuracy is measuring thermal properties more precisely. Additionally, increased precision of thermal properties benefits other aspects of engineering including design and analysis. This research focuses on quantifying approximation errors in the widely adopted flash method for measuring thermal diffusivity. The flash method leverages several approximations to make it simple and easy to use; however, these approximations do not reflect reality and introduce measurement errors. Understanding these errors is critical for developing high-precision thermal diffusivity measurement techniques.
In the flash method, the top surface of a small, cylindrical disc of material is subjected to a short pulse from a laser or flash lamp and the time-dependent temperature at the opposite surface is recorded. The thermal diffusivity is calculated using those temperature measurements in combination with a mathematical model. The accuracy of the flash method depends upon the accuracy of the mathematical model. One common mathematical model is the Parker Model. This model assumes that all of the energy from the pulse is deposited in an infinitesimally thin layer at the surface of the material and negligible heat is lost to the environment. These assumptions simplify the model, making it easy to use, but introduce errors into the measured thermal diffusivity.
Computational methods can quantify these inaccuracies. Factors including heat lost to the environment, the temporal profile of the laser pulse, and the spatial distribution of the deposited energy can be incorporated into heat transfer simulations. Higher fidelity mathematical models can also be developed to account for these complexities. This project includes these and other factors to make simulations as realistic as possible. Various mathematical models, such as the Parker Model and higher fidelity models, are then used to calculate the thermal diffusivity from the resulting time-dependent temperature profiles and their measurements are compared to the simulated material’s true thermal diffusivity. Repeating this process for several material types will allow the precision of the models to be analyzed for each case. This analysis will be summarized at the conclusion of this project, providing a framework for developing more precise thermal diffusivity measurement techniques.