Estimation of thermal properties of composite materials without instrumentation inside the samples

Abstract

Recent contributions of parameter estimation in the measurement of thermal properties are of great importance. In comparison with other techniques such as steady state (hot guarded plate, etc.) or transient (line source method, flash method, etc.), the use of parameter estimation provides more information and, in most cases, produces faster results. With this technique the thermal conductivity and the volumetric specific heat are estimated simultaneously and as a function of time, temperature, or position. This method requires experimental data, such as transient temperature and heat flux measurements. Previously, the temperature measurements came from thermocouples embedded in the sample. These thermocouples are introduced in the sample either by drilling holes or by molding the material around a series of thermocouples. Both operations are time-consuming and costly and are needed for each sample. In this study, temperature measurements are made only on the two sides of the samples with thin resistance thermometers. Since the sensors are not inside the material, the effect of the thermal contact conductance between sensor and sample was first investigated. The value of this thermal contact conductance was estimated by using samples of high-conductivity material. Using these values, the estimated thermal properties obtained with surface temperature measurements are compared with values provided by other methods for several low-thermal conductivity materials; agreement has been very good.